Porphyrin-Based Metal-Organic Frameworks as Heterogeneous

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Oct 12, 2016 - mini-review the application of these materials as catalysts in ... assembled using the same basic principles, but which are non-porous [3].
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Porphyrin-Based Metal-Organic Frameworks as Heterogeneous Catalysts in Oxidation Reactions Carla F. Pereira 1,2 , Mário M. Q. Simões 2, *, João P. C. Tomé 2,3 and Filipe A. Almeida Paz 1, * 1 2 3

*

Department of Chemistry & CICECO–Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal; [email protected] Department of Chemistry & QOPNA, University of Aveiro, 3810-193 Aveiro, Portugal; [email protected] CQE, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal Correspondence: [email protected] (M.M.Q.S.); [email protected] (F.A.A.P.); Tel.: +351-234370713 (M.M.Q.S.); +351-234401418 (F.A.A.P.)

Academic Editors: Diego A. Alonso and Isidro M. Pastor Received: 27 July 2016; Accepted: 22 September 2016; Published: 12 October 2016

Abstract: Porphyrin-based Metal-Organic Frameworks (Por-MOFs) constitute a special branch of the wide MOF family that has proven its own value and high potential in different applications. In this mini-review the application of these materials as catalysts in oxidation reactions is highlighted. Keywords: metal-organic frameworks; porphyrins; oxidation; heterogeneous catalysis

1. Introduction Heterogeneous catalysis constituted one of the earliest purposed applications for crystalline Metal-Organic Frameworks (MOFs) [1]. The MOF concept was introduced in the literature by Yaghi’s research group [2], being these materials, in the most elementary sense, obtained by connecting together metal ions with organic linkers, often resulting in fascinating structural architectures. We note that the term coordination polymer (CP) is more general, also including crystalline materials, assembled using the same basic principles, but which are non-porous [3]. Porphyrin-based MOFs (Por-MOFs) are composed by (metallo)porphyrin-based linkers interconnected by metal ions or metal cluster secondary building units (SBUs) [4]. These materials constitute a highly interesting branch of MOFs, which despite being in its infancy has, nevertheless, received much attention in the past decade. On the one hand, because porphyrins are structurally functional robust molecules with terminal pendant functional groups that can be easily tuned, while exhibiting a relatively rigid geometry and high thermal stability [5], resulting materials can thus be characterized by peculiar properties and architectures. On the other hand, the well-known role of metalloporphyrins in Nature in diverse biological functions as cofactors for many enzyme/protein families, including peroxidases, cytochromes, hemoglobins, and myoglobins [6,7], brings special importance for their use in a novel class of functional materials. For example, cytochrome P-450 (CP-450) features an iron porphyrin core and is well known in Nature for its performance in catalytic oxidations. In this sense, iron(III) porphyrins are typically used as models to mimic CP-450 in the catalytic oxidation of organic substrates [8–11]. The enzymatic pocket in CP-450 protects the porphyrin core preventing its decomposition and nonselective oxidation. Nevertheless, in a laboratory setting, because of the absence of the protective protein shell, metalloporphyrins can undergo catalytic deactivation via suicidal self-oxidation, lowering their catalytic activity and sustainability relatively to their counterparts in Nature [12–14]. It is, thus, easy to understand how the immobilization of (metallo)porphyrin moieties, by its utilization as linkers for the preparation of Por-MOFs materials, not only can retain but also enhance the functionalities of the individual building blocks. The main goal behind the immobilization of (metallo)porphyrin moieties in MOFs (or CPs) is thus very clear, Molecules 2016, 21, 1348; doi:10.3390/molecules21101348

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(or CPs) isinthus very clear, of consisting in the which stabilization of these structures which recognition ultimately consisting the stabilization these structures ultimately facilitates the molecular facilitates the and molecular recognition of efficient substrates and the design of highly efficient catalysts. of substrates the design of highly catalysts. In this sense, the preparation of MOFs using In this sense, the preparation of MOFs using (metallo)porphyrins (metallo)porphyrinsisis currently currentlyhighly highlyattractive attractive because it mimics diverse biological functionalities [15–17]. However, the preparation of because it mimics diverse biological functionalities [15–17]. However, the preparation of catalytically catalytically activestill Por-MOFs still constitutes a great challenge because often these have materials have active Por-MOFs constitutes a great challenge because these materials large often open pores, large open pores, being thus more susceptible to structural collapse upon removal of the confined being thus more susceptible to structural collapse upon removal of the confined solvent molecules. It solvent molecules.difficult It is also difficult to incorporate free-base porphyrins as linkers because is also extremely toextremely incorporate free-base porphyrins as linkers because of their great tendency of their great tendency to scavenge and coordinate the metal ions present in the reaction media [18–21]. to scavenge and coordinate the metal ions present in the reaction media [18–21]. The The first first porphyrin-based porphyrin-based CP CP was was reported reported by by Robson Robson and and co-workers co-workers back back in in 1991, 1991, aa three-dimensional three-dimensionalmaterial materialcomposed composedof of[tetrakis(p-pyridyl)porphyrinato] [tetrakis(p-pyridyl)porphyrinato]Pd(II) Pd(II)connected connectedby byCd(II), Cd(II), which suffered an irreversible decomposition upon the removal of solvent because of its which suffered an irreversible decomposition upon the removal of solvent because of its large large cavities note that thisthis is anisiconic paperpaper in theinrealm of MOFs a veryinsimple cavities[22]. [22].We We note that an iconic the realm of since, MOFsinsince, a veryfashion, simple the authors clearly describe many advantages and disadvantages of the chemistry using a fashion, the authors clearly describe many advantages and disadvantages of MOF the MOF chemistry using Por-MOF compound, which remained true to our days. The first catalytic study performed over a a Por-MOF compound, which remained true to our days. The first catalytic study performed over a Por-MOF Por-MOFwas wasreported reported14 14years yearslater laterby by Suslick Suslicket et al. al. (details (detailsin inthe thesections sectionsof of alkanes alkanesand andalkenes alkenes oxidation) for a three-dimensional net of [tetrakis(p-carboxyphenyl)porphyrinato] Mn(III) connected oxidation) for a three-dimensional net of [tetrakis(p-carboxyphenyl)porphyrinato] Mn(III) connected by by trinuclear trinuclear manganese manganese clusters clusters [23]. [23]. Besides Besidesthe theutilization utilizationof ofPor-MOFs Por-MOFsas as catalysts, catalysts, namely namely as as oxidative oxidativecatalysts, catalysts,the themain mainsubject subjectexplored exploredand andreviewed reviewedin inthe thepresent presentdocument, document,these thesematerials materials also alsorevealed revealedaahigh highpotential potentialwhen whenused usedas asphotocatalysts photocatalystsand andin inthe thefield fieldof ofgas gasseparation, separation,storage storage and light harvesting [19,21]. and light harvesting [19,21]. 2.2.Por-MOFs Por-MOFsasasHeterogeneous HeterogeneousCatalysts CatalystsininOxidation OxidationReactions Reactions Figure structure of ofthe theporphyrins porphyrinstypically typicallyused used linkers preparation of Figure 11 depicts the structure asas linkers in in thethe preparation of the the catalytically active Por-MOFs herein reviewed.Table Table11lists listsknown knowncatalytic catalytic Por-MOFs in oxidation catalytically active Por-MOFs herein reviewed. oxidation reactions. reactions.AAdescription descriptionof ofthe thesubstrates substratesand andinformal informalmnemonic mnemonicnames names(used (usedin inthe the description descriptionof of the thestudies studiesin inthe thesections sectionsbelow) below) are are also also provided. provided.

Figure 1. Cont. Figure 1. Cont.

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Figure 1. 1. Porphyrins Porphyrinsused usedin inthe thepreparation preparationofofPor-MOFs Por-MOFsreported reportedasascatalysts catalystsininoxidation oxidation reactions. Figure reactions. Table1.1.Por-MOFs Por-MOFsreported reportedasascatalysts catalystsininoxidation oxidationreactions. reactions. Table MOF a MOF a

[(Mn(TpCPP)Mn 1.5)(C3H7NO)]· [(Mn(TpCPP)Mn1.5 )(C3 H7 NO)]· 5C 5C3H NO (PIZA-3) (PIZA-3) 3 H77NO

Catalyzed Reaction (s) Catalyzed Reaction (s) Oxidation of linear Oxidation of linear and cyclic alkanes and cyclic alkanes

Epoxidation of olefins Epoxidation of olefins

ZnMn-RPM (Zn designates the metal in TpCPP ZnMn-RPM (Zn designates the metal in TpCPP while Mn while Mn designates the metal in F10DPyP) designates the metal in F DPyP) 10

Fe-MMOF Fe-MMOF

[Mn5 Cl2 (MnCl-OCPP)(DMF)4 (H2 O)4 ]· 2DMF ·8CH3 COOH·14H2 O (ZJU-18) [Mn 5Cl2(MnCl-OCPP)(DMF) 4(H2O)4]· 2O (ZJU-18) 2DMF·8CH [Mn5 Cl3COOH·14H 2 (Ni-OCPP)(H 2 O) 8 ]· 7DMF ·6CH COOH·11H2 O 2(ZJU-19) [Mn 5Cl23(Ni-OCPP)(H O)8]· [Cd Cl (MnCl-OCPP)(H (ZJU-19) 7DMF·6CH 5 2 3COOH·11H2O2 O) 6 ]· 13DMF·2CH3 COOH·9H2 O (ZJU-20) [Cd5Cl2(MnCl-OCPP)(H2O)6]· II MnIII (F5 CPP)–Mn 3COOH·9H 2O (ZJU-20) 13DMF·2CH III II MnIII(F (F55CPP)–Mn CPP)–Co II Mn III(F Mn MnIII (F55CPP)–Co CPP)–NiIIII III III Mn (F (F105CPP)–Ni Mn CPP)–MnII III II Mn MnIII(F (F1010CPP)–Mn CPP)-CoII III(F10CPP)-CoII Mn MnIII (F10 CPP)-NiII MnIII(F10CPP)-NiII [Cd1.25 (Pd−H1.5 TpCPP)-(H2 O)]·2DMF [Cd1.25(Pd−H1.5TpCPP)-(H2O)]·2DMF [Co2(μ2-H2O)(H2O)4](Co-DCDBP) (MMPF-3) [Cd8(Cd-OCPP)3][(H3O)8] (MMPF-5) [(CH3)2NH2][Zn2(HCOO)2(MnIII-TpCPP)]·5DM

Oxidation of

Oxidation of cyclic alkanes cyclic alkanes

Substrate (s) Ref. Substrate (s) cyclohexane, cycloheptane, hexane Ref. cyclohexane, andcycloheptane, heptane [23] hexane and heptane [23] cyclopentene, cyclohexene, cyclopentene, cyclohexene, cyclooctene and limonene cyclooctene and limonene

cyclohexane

cyclohexane

Epoxidation of olefins Epoxidation of olefins Oxidation of alkanes

styrene styrene cyclohexane Oxidation of alkanes cyclohexane cyclooctene,cyclohexene, styrene, cyclooctene,cyclohexene, styrene, hex-1-ene, hex-1-ene, oct-1-ene, dodec-1-ene, Epoxidation ofof olefins oct-1-ene, dodec-1-ene, 1H-indene, Epoxidation olefins 1H-indene, acetate, vinyl acetate,vinyl methyl acrylatemethyl acrylate cyclohexanol, benzyl alcohol, Oxidation of alcohols cyclohexanol, benzyl alcohol, octan-2-ol, pentan-1-ol Oxidation of alcohols octan-2-ol, pentan-1-ol ethylbenzene, diphenylmethane, 4-phenyl-ethylbenzene Oxidation of ethylbenzene, diphenylmethane, aromatic alkanes 4-phenyl-ethylbenzene ethylbenzene Oxidation of aromatic alkanes ethylbenzene

Oxidation of aromatic alkanes

Oxidation of aromatic alkanes

Oxidation of alkenes

Oxidation of alkenes Epoxidation of olefins Epoxidation of olefins Epoxidation of olefins

ethylbenzene

ethylbenzene

styrene

styrene trans-stilbene trans-stilbene styrene, cyclopentene, cyclohexene,

[24]

[24]

[25]

[25]

[26]

[26]

[27]

[27]

[28]

[28] [29] [30] [31]

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Table 1. Cont. MOF a

Catalyzed Reaction (s)

Substrate (s)

Ref.

[Co2 (µ2 -H2 O)(H2 O)4 ](Co-DCDBP) (MMPF-3)

Epoxidation of olefins

trans-stilbene

[29]

[Cd8 (Cd-OCPP)3 ][(H3 O)8 ] (MMPF-5)

Epoxidation of olefins

trans-stilbene

[30]

styrene, cyclopentene, cyclohexene, cyclooctene, terminal linear alkenes (hex-1-ene, oct-1-ene, dodec-1-ene), stilbene, and some modified stilbenes and styrenes

[31]

[(CH3 )2 NH2 ][Zn2 (HCOO)2 (MnIII -TpCPP)]·5DMF·2H2 O [(CH3 )2 NH2 ][Cd2 (HCOO)2 (MnIII -TpCPP)]·5DMF·3H2 O

Epoxidation of olefins

[Zn2 (HCOO)(FeIII (H2 O)-TpCPP)]·3DMF·H2 O

styrene

[Cd3 (H2 O)6 (µ2 -O)(FeIII -HTpCPP)2 ]·5DMF

styrene

[Zn2 (MnOH-TpCPP)(DPNI)]· 0.5DMF·EtOH·5.5H2 O (CZJ-1)

Epoxidation of olefins

styrene

[32]

MMPF

Epoxidation of olefins

cyclohexene, cyclooctene, hex-1-ene, oct-1-ene, dodec-1-ene, styrene, trans-stilbene

[33]

MnTNPP@MOF

Oxidation of alcohols

3,5-di-tert-butylcathecol

[34]

Zr6 O8 (CO2 )8 (H2 O)8 -[FeCl(TpCPP)] (MMPF-6)

Oxidation of alcohols

1,2,3-trihydroxybenzene

[35]

Oxidation of alcohols

1,2,3-trihydroxybenzene, 3,30 ,5,50 -tetramethylbenzidine, o-phenylenediamine

[36]

Zr6 (OH)8 -FeTpCPP (PCN-222 (Fe))

a TpCPP—5,10,15,20-tetrakis(p-carboxyphenyl)porphyrin; F10 DPyP—5,15-bis(pentafluorophenyl)-10,20-di (pyridyl)porphyrin; H8 OCPP—5,10,15,20-tetrakis(3,5-dicarboxyphenyl)porphyrin; F5 CPP—5,10,15-tris(pcarboxyphenyl)-20-(pentafluorophenyl)porphyrin; F10 CPP—5,15-bis(p-carboxyphenyl)-10,20-bis (pentafluorophenyl)porphyrin; DCDBP—5,15-bis(3,5-dicarboxyphenyl)-10,20-bis(2,6-dibromophenyl)porphyrin; DPNI—N,N 0 -di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide; TNPP—5,10,15,20-tetrakis[p(nicotinoyloxy)phenyl]porphyrin.

2.1. Oxidation of Alkanes The first report of a catalytically active Por-MOF dates back to 2005 and concerns the PIZA-3 material (Porphyrinic Illinois Zeolite Analogue—PIZA, Figure 2). This compound consists of a three-dimensional net of [5,10,15,20-tetrakis(p-carboxyphenyl)porphyrinato] Mn(III) connected by trinuclear manganese clusters [23]. The compound is stable upon the removal of the solvent molecules, and catalytically active in the oxidation of linear and cyclic alkanes at ambient temperature using iodosylbenzene as oxidant. The small channels in these materials restricted the catalysis of larger substrates, being concluded by the researchers that the catalysis is dominated by the reactivity on the exterior surface of the crystallites. The oxidation of alkanes is selective for the alcohol in the case of cyclic substrates, with an alcohol/ketone ratio of 8.9 and 8.0, achieved for the cyclic substrates cyclohexane (43% yield of alcohol) and cycloheptane (47% yield of alcohol), respectively. On the other hand, the hydroxylation of the linear alkanes such as hexane (17% total alcohols: 2-ol; 3-ol; 4-ol) and heptane (23% total alcohols: 2-ol; 3-ol; 4-ol) catalyzed by PIZA-3 gives similar yields for alcohols at positions 2 and 3 [23]. Hupp, Farha and coworkers employed Zn paddlewheel nodes to build three-dimensional MOFs with open channels. Although paddlewheel clusters are known to be less stable in humid conditions, they succeeded in building a catalytically active MOF based on this node by employing a mixed-ligand strategy [24]. ZnMn-RPM (Robust Porphyrinic Material—RPM), catalytically competent for the oxidation of alkanes and alkenes, was prepared using a [5,10,15,20-tetrakis(pcarboxyphenyl)porphyrinato] Zn(II) as a spacer and the redox metalloligand [5,15-bis (pentafluoro-phenyl)-10,20-di(pyridyl)-porphyrinato] Mn(III) structured by paddlewheel dinuclear zinc(II) clusters [24]. The choice of these porphyrins had a clear purpose: the dipyridyl porphyrin was chosen because of the ability of electron-withdrawing groups, such as fluorine, to greatly increase the activity of metalloporphyrins for oxidative catalysis. On the other hand, the choice of tetracarboxylated porphyrin was because of the design principles of MOFs, so to lead to the formation of the intended paddlewheel clusters and avoid the formation of interpenetrated networks. The structure of ZnMn-RPM is depicted in Figure 3.

substrates, being concluded by the researchers that the catalysis is dominated by the reactivity on the exterior surface of the crystallites. The oxidation of alkanes is selective for the alcohol in the case of cyclic substrates, with an alcohol/ketone ratio of 8.9 and 8.0, achieved for the cyclic substrates cyclohexane (43% yield of alcohol) and cycloheptane (47% yield of alcohol), respectively. On the other hand, the hydroxylation of the linear alkanes such as hexane (17% total alcohols: 2-ol; 3-ol; Molecules 2016, 1348 4-ol) and21,heptane (23% total alcohols: 2-ol; 3-ol; 4-ol) catalyzed by PIZA-3 gives similar yields for5 of 19 alcohols at positions 2 and 3 [23].

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Hupp, Farha and coworkers employed Zn paddlewheel nodes to build three-dimensional MOFs with open channels. Although paddlewheel clusters are known to be less stable in humid conditions, they succeeded in building a catalytically active MOF based on this node by employing a mixed-ligand strategy [24]. ZnMn-RPM (Robust Material—RPM), Figure 2. Schematic representation of the PIZA-3 Por-MOFPorphyrinic viewed along the [1,0,0] direction of catalytically the competent for the oxidation of alkanes and alkenes, was prepared using a [5,10,15,20-tetrakis unit cell. Solvent and coordinated N,Nʹ-dimethylformamide molecules have been removed for clarity. (p-carboxyphenyl)porphyrinato] Zn(II) as Copyright a spacer(2005) andAmerican the redox metalloligand [5,15-bis Reprinted (adapted) with permission from [23]. Chemical Society. (pentafluoro-phenyl)-10,20-di(pyridyl)-porphyrinato] Mn(III) structured by paddlewheel dinuclear Hupp, Farha[24]. and coworkers employed Zn paddlewheel nodes to build three-dimensional MOFs zinc(II) clusters with open channels. Although paddlewheel clusters are known to be lessporphyrin stable in humid conditions, The choice of these porphyrins had a clear purpose: the dipyridyl was chosen because of they building a catalytically activesuch MOFasbased on this by employing a mixedthe succeeded ability of in electron-withdrawing groups, fluorine, to node greatly increase the activity of ligand strategy [24].for ZnMn-RPM (Robust Porphyrinic competent for metalloporphyrins oxidative catalysis. On the otherMaterial—RPM), hand, the choicecatalytically of tetracarboxylated porphyrin Figure 2. Schematic representation of the PIZA-3 Por-MOF viewed along the [1,0,0] direction of the Figure 2. Schematic representation of the PIZA-3 Por-MOF viewed along the [1,0,0] direction of the the of alkanes and alkenes, was prepared using aof the [5,10,15,20-tetrakis(pwas oxidation because design MOFs, so to lead to the formation intended paddlewheel unit of cell.the Solvent andprinciples coordinatedof N,N′-dimethylformamide have been removed for clarity. 0 -dimethylformamidemolecules unit and cell. Solvent and coordinated N,N molecules havestructure been removed for clarity. is carboxyphenyl)porphyrinato] Zn(II) as a spacer and the redox metalloligand [5,15-bis(pentafluoroclusters avoid the formation of interpenetrated networks. The of ZnMn-RPM Reprinted (adapted) with permission from [23]. Copyright (2005) American Chemical Society. Reprinted (adapted) with permission from [23]. Copyright Chemical Society. zinc(II) phenyl)-10,20-di(pyridyl)-porphyrinato] Mn(III) structured(2005) by American paddlewheel dinuclear depicted in Figure 3. clusters [24].

Figure 3. (a) Optical photograph of of ZnMn-RPMcrystals; crystals.(b–d) (b–d)Schematic Schematicrepresentations representations Figure of of thethe crystal Figure 3.3. (a) (a)Optical Opticalphotograph photograph ZnMn-RPM of ZnMn-RPM crystals; (b–d) Schematic representations of the crystal structure features of ZnMn-RPM showing channels inthree the three crystallographic directions structure features of ZnMn-RPM showing channels in the crystallographic directions (Colour crystal structure features of ZnMn-RPM showing channels in the three crystallographic directions (Colour scheme: = Zn, redgreen = O, green = F, blue = N, gray = C, white = H, purple = Mn). scheme: yellowyellow =yellow Zn, red O, blue == N, Mn). Disordered (Colour scheme: ==Zn, red = =O,F,green F, gray blue == C, N,white gray = = H, C, purple white ==H, purple = Mn). Disordered solvent molecules have been omitted for clarity. Reprinted (adapted) with permission solvent molecules been omitted for omitted clarity. for Reprinted permission from [24]. Disordered solventhave molecules have been clarity. (adapted) Reprinted with (adapted) with permission from [24]. Copyright (2011) American Chemical Society. Copyright (2011) American from [24]. Copyright (2011) Chemical AmericanSociety. Chemical Society.

In the oxidation C using oxidation of of cyclohexane cyclohexane at at 25 25 ◦°C using 2-(tert-butylsulfonyl)iodosylbenzene 2-(tert-butylsulfonyl)iodosylbenzene as oxidant oxidant (Scheme yield of of 20%, with 83% andand 17%17% selectivity for cyclohexanol and (Scheme 1), 1),ZnMn-RPM ZnMn-RPMled ledtotoa atotal total yield 20%, with 83% selectivity for cyclohexanol cyclohexanone, respectively. The poor yield yield was, nevertheless, attributed to diffusion difficulties of the and cyclohexanone, respectively. The poor was, nevertheless, attributed to diffusion difficulties substrate into the solid [24]. [24]. of the substrate into thecatalyst solid catalyst

Scheme 1. General scheme of cyclohexane oxidation. Scheme 1. General scheme of cyclohexane oxidation.

Jiang and collaborators reported in 2014 [25] a new porphyrin-based MOF composed of manganese 5,10,15,20-tetrakis(p-carboxyphenyl)porphyrin as a bridging ligand bound to Fe(II) ions (Fe-MMOF). The material revealed to be an efficient catalyst in the selective oxidation of versatile natural substrates, acting as an effective peroxidase mimic. This compound is an efficient catalyst in the oxidation of different substrates, namely cyclohexane, different alkenes, cyclohexanol (please note:

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Jiang and collaborators reported in 2014 [25] a new porphyrin-based MOF composed of manganese 5,10,15,20-tetrakis(p-carboxyphenyl)porphyrin as a bridging ligand bound to Fe(II) ions (Fe-MMOF). The material revealed to be an efficient catalyst in the selective oxidation of versatile natural substrates, acting as an effective peroxidase mimic. This compound is an efficient catalyst in the oxidation of different substrates, namely cyclohexane, different alkenes, cyclohexanol (please note: pertinent results for the oxidation of alkenes and alcohols will be presented and discussed in the sections below). Using this material as catalyst in the oxidation of cyclohexane led to a conversion up to 70%, and about 100% selectivity toward cyclohexanone. To date there are, to the best of our knowledge, only a couple of reports focused on the oxidation of aromatic alkanes using Por-MOFs as catalysts [26,27]. The research groups of Chen and Wu described the utilization of 5,10,15,20-tetrakis(3,5-dicarboxylphenyl)porphyrin with different metals in the core as a powerful linker to the preparation of isotypical Por-MOFs with high porosity: ZJU-18, ZJU-19 and ZJU-20 (ZJU—Zheijang University). The incorporation of functional groups into the porphyrin synthons and its 3D configuration within the porous frameworks exhibited a synergistic effect for highly efficient oxidation of alkylbenzenes [26]. ZJU-18 is built up from a manganese porphyrin and manganese individual clusters (Figure 4), while ZJU-19 has nickel(II) porphyrin as building block and manganese SBUs; finally ZJU-20 consists of manganese porphyrins connected by cadmium clusters (see Table 1 for the individual empirical formulae). In the oxidation of ethylbenzene to acetophenone at 65 ◦ C by tert-butyl hydroperoxide, the homometallic ZJU-18 was found to be efficient with quantitative conversion values. On the other hand, in the case of ZJU-19, a negligible catalytic activity was obtained with only 9% of acetophenone being formed. The significant difference in the catalytic transformation of ethylbenzene to acetophenone clearly showed that the manganese porphyrin sites in the material ZJU-18 are the efficient catalytic sites. On the other hand, the manganese sites on the SBU nodes might also be partially responsible and work collaboratively with the manganese porphyrin, improving the overall catalytic activity. Indeed, conversion values obtained for ZJU-20 are much higher (conversion of 69%) than those registered for ZJU-19. The homogeneous catalysis with manganese (III) and nickel (II) porphyrins typically affords conversions to ketone of 16% or traces, respectively. In this way, these results showed that the building blocks of the manganese porphyrin clearly are the catalytically active species in the ZJU family, and that the Mn-SBU clusters contribute only slightly to oxidative reactions. In the specific case of ZJU-18, the material showed to be better than the catalyst in homogeneous phase because the MOF architecture avoids self-oxidation and dimerization of the metalloporphyrin. The good performance of ZJU-18 prompted the researchers to study its activity in the oxidation of longer-chain alkylbenzenes. The compound with a larger alkyl chain presents the worst catalytic performance of this metalloporphyrinic MOF, suggesting that catalysis also depends on the accessibility to the channels of the material. The oxidation of diphenylmethane, for which ZJU-18 gives lower conversion when compared with the same reaction in homogeneous medium (18% and 26% conversion, respectively), confirms this assumption. This catalytic pattern is also true for the oxidation of 4-phenyl-ethylbenzene by ZJU-18 (conversion of 16% and 28% in heterogeneous and homogeneous medium, respectively), but not for smaller substrates. All these observations prompted the authors to conclude that catalysis occurs only at the external surface of the MOF for larger substrates, whilst it takes place inside the pores for smaller hydrocarbons. Therefore, ZJU-18 is size- and shape-selective [26]. Li and co-workers described six MnIII (porphyrin)-based porous CPs in which 5,10,15tris(p-carboxyphenyl)-20-(pentafluorophenyl)porphyrin manganese(III) [MnIII (F5 CPP)] or 5,15-bis (p-carboxyphenyl)-10,20-bis(pentafluorophenyl)porphyrin manganese(III) [MnIII (F10 CPP)] molecules were interlinked via coordination to the peripheral carboxylate groups of several transition metal centers: MnIII (F5 CPP)–MnII , MnIII (F5 CPP)–CoII , MnIII (F5 CPP)–NiII , MnIII (F10 CPP)–MnII , MnIII (F10 CPP)-CoII and MnIII (F10 CPP)-NiII . The catalytic performance of these CPs was studied in the oxidation of ethylbenzene at 65 ◦ C using tert-butyl hydroperoxide as oxidant (Scheme 2). All six

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materials revealed to be efficient as catalysts with acetophenone being obtained with yields between 71 and 82% and with selectivity over 99%. Authors justified the higher catalytic activity of the CPs over the homogeneous counterparts to the combined effect of the immobilization of the catalytic active units Mn(F5 CPP)/Mn(F10 CPP), thus preventing their self-dimerization and oxidative degradation, and to the fact that both of the Mn(F5 CPP)/Mn(F10 CPP) units and metal ions nodes were involved Molecules 2016, 21, 1348 7 of 18 in the catalytic reaction, probably via a synergistic effect. Authors also reported the utilization of the Molecules 2016, 21, 1348 7 of 18 CPs as catalysts for three consecutive times with only a slight decrease thecatalytic catalyticactivities activitiesand and as catalysts for three consecutive times with only a slight decrease ofofthe without any any detectable leaching leaching of of the the catalysts catalysts [27]. [27]. without as catalysts detectable for three consecutive times with only a slight decrease of the catalytic activities and without any detectable leaching of the catalysts [27].

IIIN4Cl; (b) trinuclear [Mn3(COO)4(μ-H2O)2(H2O)6]; and (c) Figure Figure 4. 4. Mn-containing Mn-containingSBUs SBUs(a) (a)Mn MnIII N4 Cl; (b) trinuclear [Mn3 (COO)4 (µ-H2 O)2 (H2 O)6 ]; and II 2(COO) binuclear [MnSBUs 4Cl2] III their linkage to the 3-coordinated nodeO)to6];form (e) II (a) Figure 4.paddlewheel Mn-containing Mn4and N24Cl; (b) [Mn 3(COO) 4(μ-H2O)2(H2node and (c) (c) binuclear paddlewheel [Mn Cl ] (d) and (d)trinuclear their linkage to the 3-coordinated to form 2 (COO) the net from four nodes in the actual crystal structure of ZJU-18. Yellow and blue balls are centered (e) the net from four nodes inIIthe actual crystal ZJU-18. and blue balls are to centered in 2(COO) binuclear paddlewheel [Mn 4Cl 2] and structure (d) their of linkage to Yellow the 3-coordinated node form (e) in small cavities instructure. thecrystal structure. Reprinted (adapted) with from [26]. thethe large andand small cavities Reprinted (adapted) with permission from [26]. Copyright netlarge from four nodes in in thethe actual structure of ZJU-18. Yellow and permission blue balls are centered Copyright (2012) American Chemical Society. (2012) Society. in the American large andChemical small cavities in the structure. Reprinted (adapted) with permission from [26].

Copyright (2012) American Chemical Society.

Scheme 2. General scheme of ethylbenzene oxidation.

2.2. Oxidation of Alkenes

Scheme 2. 2. General scheme of of ethylbenzene ethylbenzene oxidation. oxidation. Scheme General scheme

2.2. Oxidation of Alkenes The catalytically active Por-MOF (PIZA-3) mentioned in the previous subsections also proved to be The active in the epoxidation of alkenes usingmentioned iodosylbenzene oxidant.subsections This MOFalso selectively catalytically active Por-MOF (PIZA-3) in the as previous proved oxidizes cyclopentene (23% epoxide), cyclohexene (23% epoxide), cyclooctene (74% epoxide), and to be active in the epoxidation of alkenes using iodosylbenzene as oxidant. This MOF selectively limonene (20% 1,2-epoxide), with no allylic products being detected after the performed reactions oxidizes cyclopentene (23% epoxide), cyclohexene (23% epoxide), cyclooctene (74% epoxide), and

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2.2. Oxidation of Alkenes The catalytically active Por-MOF (PIZA-3) mentioned in the previous subsections also proved to be active in the epoxidation of alkenes using iodosylbenzene as oxidant. This MOF selectively oxidizes cyclopentene (23% epoxide), cyclohexene (23% epoxide), cyclooctene (74% epoxide), and limonene (20% 1,2-epoxide), with no allylic products being detected after the performed reactions [23]. ZnMn-RPM also proved to be active in the epoxidation of styrene at 25 ◦ C using Molecules 2016, 21, 1348 8 of 18 2-(tert-butylsulfonyl)iodosylbenzene as oxidant (Scheme 3) [24]. This Por-MOF is more stable when Molecules 2016, 21, 1348 8 of 18 compared with the homogeneous counterpart [5,10,15,20-tetrakis-(pentafluorophenyl)-porphyrinato] Mn(III) chloride, second-generation catalyst In this Mn(III) chloride, catalyst [37].[37]. In fact, whilewhile this second-generation catalystcatalyst affords chloride,a aasecond-generation second-generation catalyst [37]. In fact, fact, while this second-generation second-generation catalyst affords a turnover number (TON) of 780 in homogeneous catalysis, because of total catalyst a turnover number (TON) 780 in homogeneous catalysis, because of total catalyst deactivation, affords a turnover numberof (TON) of 780 in homogeneous catalysis, because of total catalyst deactivation, ZnMn-RPM TON of after oxidant consumption. The ZnMn-RPM affords a TONaffords of 2150 a complete consumption. The catalysis is heterogeneous deactivation, ZnMn-RPM affords aafter TON of 2150 2150oxidant after complete complete oxidant consumption. The catalysis catalysis is heterogeneous because removal the itself catalytic reaction stops. no because after removal of theafter MOF itself theof reaction stops. Moreover, no manganese porphyrin is heterogeneous because after removal ofcatalytic the MOF MOF itself the the catalytic reaction stops. Moreover, Moreover, no manganese porphyrin was leached during the reaction [24]. was leachedporphyrin during thewas reaction [24]. manganese leached during the reaction [24]. O O Catalyst, Catalyst, oxidant oxidant

Scheme 3. General scheme of styrene epoxidation. Scheme Scheme 3. 3. General General scheme scheme of of styrene styrene epoxidation. epoxidation.

Also (Pd−H1.5TpCPP) Also in in 2011 2011 Wu Wu and and coworkers coworkers reported reported the the porous porous coordination coordination network network [Cd [Cd1.25 1.25(Pd−H1.5TpCPP) Also in 2011 Wu and coworkers reported the porous coordination network [Cd (Pd −H1.5 TpCPP) 1.25 (H (H22O)]·2DMF, O)]·2DMF, which which comprises comprises [5,10,15,20-tetrakis(p-carboxyphenyl)[5,10,15,20-tetrakis(p-carboxyphenyl)- porphyrinato] porphyrinato] Pd(II) Pd(II) and and (H O)] · 2DMF, which comprises [5,10,15,20-tetrakis(p-carboxyphenyl)porphyrinato] Pd(II) and Cd(II) 2 Cd(II) connecting nodes (Figure 5). This material was studied as catalyst in styrene oxidation Cd(II) connecting nodes (Figure 5). This material was studied as catalyst in styrene oxidation [28]. [28]. connecting nodes (Figure 5). This material was studied as catalyst in styrene oxidation [28]. Results Results Results suggested suggested that that the the square-coordinated square-coordinated Pd(II) Pd(II) ions ions in in TpCPP TpCPP are are highly highly active active in in oxidation oxidation suggested that the square-coordinated Pd(II) ions in TpCPP are highly active in oxidation reactions by reactions reactions by by forming forming high high valent valent Pd Pd intermediates. intermediates. In In this this sense, sense, authors authors reported reported aa complete complete forming highstyrene valent Pd intermediates. In this sense, authors reported a complete at oxidation of styrene oxidation benzaldehyde oxidation of of styrene into into aa mixture mixture of of 91% 91% acetophenone acetophenone and and 9% 9% at 55 55 °C °C using using H H22O O22 ◦ Cbenzaldehyde into a mixture of 91% acetophenone and 9% benzaldehyde at 55 using H O as oxidant (Scheme 4). 2 2 as as oxidant oxidant (Scheme (Scheme 4). 4).

Figure Crystal packing of [Cd (Pd−H 1.5TpCPP)-(H 2O)]·2DMF viewed thealong [1,1,0] direction, Figure 5. 5. (a) Crystal packing of 1.25 [Cd −H1.5 TpCPP)-(H ·2DMF along viewed [1,1,0] 1.25 (Pd 2 O)]viewed Figure 5. (a)(a) Crystal packing of [Cd 1.25 (Pd−H 1.5TpCPP)-(H 2O)]·2DMF along the [1,1,0]the direction, depicting the arrangement of the palladium-porphyrins; (b) Schematic representation of the crystal direction, the depicting the arrangement of the palladium-porphyrins; (b) representation Schematic representation of depicting arrangement of the palladium-porphyrins; (b) Schematic of the crystal structure ofstructure the material viewed down thedown [1,0,0]the crystallographic direction, emphasizing the 1D the crystal of the material viewed [1,0,0] crystallographic direction, emphasizing structure of the material viewed down the [1,0,0] crystallographic direction, emphasizing the 1D opening channelschannels and the accessible PdIIII sites;Pd (c)IISide view of theview 1D channel present in this porous the 1D opening and the accessible sites; (c) Side of the 1D channel present in opening channels and the accessible Pd sites; (c) Side view of the 1D channel present in this porous framework. Reprinted (“Adapted” or(“Adapted” “in part”) from [28]part”) with permission of thepermission PCCP Owner Societies. this porous framework. Reprinted or “in from [28] with of the PCCP framework. Reprinted (“Adapted” or “in part”) from [28] with permission of the PCCP Owner Societies. Owner Societies.

O O

Catalyst, Catalyst, oxidant oxidant

O O

+ +

Scheme 4. General scheme of styrene oxidation. Scheme 4. General scheme of styrene oxidation.

H H

Figure 5. (a) Crystal packing of [Cd1.25(Pd−H1.5TpCPP)-(H2O)]·2DMF viewed along the [1,1,0] direction, depicting the arrangement of the palladium-porphyrins; (b) Schematic representation of the crystal structure of the material viewed down the [1,0,0] crystallographic direction, emphasizing the 1D opening channels and the accessible PdII sites; (c) Side view of the 1D channel present in this porous9 of 19 Molecules 2016, 21, 1348 framework. Reprinted (“Adapted” or “in part”) from [28] with permission of the PCCP Owner Societies.

O Catalyst, oxidant

O

H

+

Scheme 4. 4. General General scheme scheme of of styrene styrene oxidation. oxidation. Scheme

It was further demonstrated that the catalytic reaction occurs inside the pores of the material. It was further demonstrated that the catalytic reaction occurs inside the pores of the material. Remarkably this MOF exhibits better results than those obtained with the metalloporphyrin in Remarkably this MOF exhibits better results than those obtained with the metalloporphyrin in homogeneous medium (90% conversion and 78% selectivity for acetophenone) [28]. homogeneous medium (90% conversion and 78% selectivity for acetophenone) [28]. Molecules 21, 1348 18 In 2016, the evaluation of the influence of different acids in the oxidation of styrene (Scheme 4), 9itofwas In the evaluation of the influence of different acids in the oxidation of styrene (Scheme 4), observed that acetic acid did not boost the catalytic transformation, while hydrochloric acid it was observed that acetic acid did not boost the catalytic transformation, whilevalues hydrochloric acid prompted the transformation less efficient. Despite the acetophenone selectivity with nitric prompted the transformation less efficient. Despite the acetophenone selectivity values with nitric acid (86% for acetophenone and 14% for benzaldehyde) and sulfuric acid (95% for acetophenone and acidfor (86% for acetophenone and 14% for andacid sulfuric for acetophenone 5% benzaldehyde) are comparable tobenzaldehyde) that of perchloric (91%acid for(95% acetophenone and 9% and for 5% for benzaldehyde) are comparable to that of perchloric acid (91% for acetophenone and 9% for benzaldehyde), the styrene substrate cannot be oxidized completely. This Por-MOF system proved benzaldehyde), the styrene be oxidized completely. This Por-MOF system to be heterogeneous with thesubstrate catalyst cannot being recovered and reused in subsequent cycles [28].proved to be heterogeneous with the catalyst being frameworks recovered and reusedhas in subsequent cycles [28]. A family of metal-metalloporphyrin (MMPF) been explored since 2011 by Ma´s A family metal-metalloporphyrin (MMPF) has(see been explored since 2011 details). by Ma´s research groupof[29,30,35,38], herein coinedframeworks MMPF-2, -3, -5 and -6 Table 1 for additional research group [29,30,35,38], herein coined MMPF-2,metalloporphyrins -3, -5 and -6 (see Table 1 for additional details). These MOFs consist of carboxyphenyl-substituted linked through SBUs with These MOFs consist of carboxyphenyl-substituted metalloporphyrins linked through SBUs with different metals (Cu, Co, Zn, Cd, Zr, Fe) and do not contain any additional linkers or spacers. different metals (Cu, Co, Zn, Cd, Zr, Fe) and do not contain any additional linkers or spacers. Noteworthy, different porphyrins were used for their construction: while for MMPF-2 and MMPF-5 Noteworthy, different porphyrins were used for their construction: while and [5,10,15,20-tetrakis(3,5-dicarboxyphenyl)porphyrinato] Co(III) was employed [30],fortheMMPF-2 preparation MMPF-5 [5,10,15,20-tetrakis(3,5-dicarboxyphenyl)porphyrinato] Co(III) was employed [30], the of MMPF-3 and MMPF-6 involved, respectively, [5,15-bis(2,6-dibromophenyl)-10,20-bis(3,5preparation of MMPF-3 and MMPF-6 involved, [5,15-bis(2,6-dibromophenyl)-10,20-bis(3,5dicarboxyphenyl)porphyrinato] Co(III) [29] andrespectively, [5,10,15,20-tetrakis(p-carboxyphenyl)-porphyrinato] dicarboxyphenyl)porphyrinato] Co(III) [29] and [5,10,15,20-tetrakis(p-carboxyphenyl)-porphyrinato] Fe(III) [35]. Compound MMPF-3 exhibits different types of polyhedral cages – cubohemioctahedron, Fe(III) [35]. Compoundand MMPF-3 exhibits differentbeing typesthe of polyhedral cages – cubohemioctahedron, truncated tetrahedron truncated octahedron, last one represented in Figure 6. When truncated tetrahedron and octahedron, being the one represented Figure 6. When this this material was used astruncated catalyst in the epoxidation oflast trans-stilbene at 60in°C using tert-butyl ◦ C using tert-butyl hydroperoxide material was used as catalyst in the epoxidation of trans-stilbene at 60 hydroperoxide as oxidant (Scheme 5), a conversion and epoxide yield of ca. 96% and 87% were as oxidantrespectively. (Scheme 5), a conversion and epoxide yield of ca. 96% and 87% were afforded, respectively. afforded,

Figure 6. Schematic representation of the truncated octahedron polyhedral cages present in MMPF-3. Figure 6. Schematic representation of the truncated octahedron polyhedral cages present in MMPF-3. Adapted Adaptedfrom from http://sqma.myweb.usf.edu/pages/publications.html#anchor2012. http://sqma.myweb.usf.edu/pages/publications.html#anchor2012.

Scheme 5. General scheme of of trans-stilbene epoxidation.

Results were compared with the following control reactions: (i) homogeneous catalysis using only the cobalt porphyrin used as the MOF building block of MMPF-3, for which a conversion of

Figure Schematic representation of the truncated octahedron polyhedral cages present in MMPF-3. Molecules 2016,6.21, 1348 10 of 19 Adapted from http://sqma.myweb.usf.edu/pages/publications.html#anchor2012.

Scheme 5. 5. General trans-stilbene epoxidation. epoxidation. Scheme General scheme scheme of of of of trans-stilbene

Results were compared with the following control reactions: (i) homogeneous catalysis using Results were compared with the following control reactions: (i) homogeneous catalysis using only the cobalt porphyrin used as the MOF building block of MMPF-3, for which a conversion of only the cobalt porphyrin used as the MOF building block of MMPF-3, for which a conversion of 60% 60% and a selectivity of 67% were obtained; (ii) reaction using another MOF with the same topology and a selectivity of 67% were obtained; (ii) reaction using another MOF with the same topology as as MMPF-3, namely fcu-MOF-1, which contains the tetracarboxylic acid porphyrin as building MMPF-3, namely fcu-MOF-1, which contains the tetracarboxylic acid porphyrin as building block, for block, for which a conversion of ca. 47% and a yield of ca. 77% were obtained; and (iii) a blank which a conversion of ca. 47% and a yield of ca. 77% were obtained; and (iii) a blank reaction with reaction with no catalyst, for which a low conversion of ca. 9% was registered. These results permit no catalyst, for which a low conversion of ca. 9% was registered. These results permit to conclude to conclude that the cobalt porphyrins account for the major catalytic activity of MMPF-3, but there that the cobalt porphyrins account for the major catalytic activity of MMPF-3, but there is also some is also 2016, some contribution from cobalt paddlewheel clusters because the topological analogous Molecules 21, 1348 cobalt paddlewheel 18 contribution from clusters because the topological analogous fcu-MOF-1 10 is of also fcu-MOF-1 is also active in the same reaction [29]. active in the same reaction [29]. The activity asas catalyst in in thethe epoxidation of The other othermember memberof ofthis thisfamily familythat thatalso alsoshowed showedgood good activity catalyst epoxidation trans-stilbene was MMPF-5(Co). This material was prepared using post-synthetic modification by of trans-stilbene was MMPF-5(Co). This material was prepared using post-synthetic modification linker exchange from MMPF-5, which [5,10,15,20-tetrakis by linker exchange from MMPF-5, whichis isa acadmium(II)-based cadmium(II)-based MOF MOF with with [5,10,15,20-tetrakis (3,5-dicarboxyphenyl)porphyrinato] Cd(II) connected by cadmium(II) clusters (Figure 7). In this (3,5-dicarboxyphenyl)porphyrinato] Cd(II) connected by cadmium(II) clusters (Figure 7). In this process, the cadmium porphyrins are exchanged for cobalt ones with the resulting MMPF-5(Co) process, the cadmium porphyrins are exchanged for cobalt ones with the resulting MMPF-5(Co) framework retaining the crystal features of the parent MMPF-5 one. framework retaining the crystal features of the parent MMPF-5 one.

Figure 7. Schematic representation of MMPF-5(Co) preparation by post-synthetic modification, Figure 7. Schematic representation of MMPF-5(Co) preparation by post-synthetic modification, catalytically competent in trans-stilbene epoxidation. Adapted from http://sqma.myweb.usf.edu/ catalytically competent in trans-stilbene epoxidation. Adapted from http://sqma.myweb.usf.edu/ pages/publications.html#anchor2013. pages/publications.html#anchor2013.

MMPF-5(Co) catalyzes catalyzes the the oxidation oxidationof of trans-stilbene trans-stilbeneinto intothe theepoxide epoxidewith withaaconversion conversionof ofca. ca. MMPF-5(Co) 87%, with being obtained in ca. It is important to emphasize that the cadmium 87%, with the theepoxide epoxide being obtained in 82% ca. yield. 82% yield. It is important to emphasize that the building units did not show any catalytic activity: control tests performed with MMPF-5 andMMPF-5 without cadmium building units did not show any catalytic activity: control tests performed with any catalyst typically led to very low conversions (both values of ca. 9%) [30]. and without any catalyst typically led to very low conversions (both values of ca. 9%) [30]. Iron porphyrins porphyrins are are expected expected to to be be attractive attractive building building blocks blocks for for the the design design of of catalytically catalytically Iron active MOFs. Indeed, these could provide a solid basis to induce biomimetic catalysis. An identical active MOFs. Indeed, these could provide a solid basis to induce biomimetic catalysis. An identical rationale could could be be applied applied to to manganese manganese porphyrins, porphyrins, which which are are the the basis basis of of the the heme heme cofactor cofactor rationale analogues of CP-P450 enzymes that can efficiently oxidize a variety of organic molecules. Wu and analogues of CP-P450 enzymes that can efficiently oxidize a variety of organic molecules. Wu and coworkers reported four isotypical Por-MOFs based on tetrakis(p-carboxyphenyl)porphyrin which coworkers reported four isotypical Por-MOFs based on tetrakis(p-carboxyphenyl)porphyrin which III (H O)were used used as as catalysts were catalysts in in the the epoxidation epoxidation of of olefins. olefins. The The crystal crystal structure structure of of [Zn [Zn22(HCOO)(Fe (HCOO)(FeIII(H 22O)III TpCPP)] · 3DMF · H O is composed of a layered network of Fe -TpCPP connected with binuclear 2 is composed of a layered network of FeIII-TpCPP connected with binuclear TpCPP)]·3DMF·H2O Zn (COO) paddle-wheel SBUs, which which are are further further linked linked by by formate formate pillars pillars to to interconnect interconnect 2 4 Zn2(COO)4 paddle-wheel SBUs, Zn22(COO) (COO)44SBUs. SBUs. Zn When Cd2+ ions are used as connecting nodes, two FeIII−HTpCPP ligands are coupled by one μ2-oxo group to form a dimer leading to the 3D microporous framework [Cd3(H2O)6(μ2-O) (FeIII-HTpCPP)2]·5DMF. These materials revealed to be inefficient catalysts in the epoxidation of styrene at ambient temperature using iodosylbenzene as oxidant, being obtained 17.9% and 8.4% yields of epoxide for [Zn2(HCOO)(FeIII(H2O)-TpCPP)]·3DMF·H2O and [Cd3(H2O)6(μ2-O)

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When Cd2+ ions are used as connecting nodes, two FeIII −HTpCPP ligands are coupled by one µ2 -oxo group to form a dimer leading to the 3D microporous framework [Cd3 (H2 O)6 (µ2 -O) (FeIII -HTpCPP)2 ]·5DMF. These materials revealed to be inefficient catalysts in the epoxidation of styrene at ambient temperature using iodosylbenzene as oxidant, being obtained 17.9% and 8.4% yields of epoxide for [Zn2 (HCOO)(FeIII (H2 O)-TpCPP)]·3DMF·H2 O and [Cd3 (H2 O)6 (µ2 -O) (FeIII -HTpCPP)2 ]·5DMF, respectively. This lack of efficiency was attributed to the self-oxidation of the individual pyrrolic rings. This fact was evident from bleaching studies [31]. When manganese porphyrins were used as synthons for the preparation of the materials, researchers observed that the axial coordination sites of the octahedrally coordinated MnIII ions could be easily replaced by additional ligands, a feature that could obstruct the catalytic ability. The active MnIII sites in the isotypical Por-MOFs [(CH3 )2 NH2 ][Zn2 (HCOO)2 (MnIII -TpCPP)]·5DMF·2H2 O and [(CH3 )2 NH2 ][Cd2 (HCOO)2 -(MnIII -TpCPP)]·5DMF·3H2 O were blocked by formate ligands, leading to inaccessibility of the active sites to the substrate. In this way, catalysis occurred on the external surface of the Por-MOF crystals, being afforded 100% product yield during styrene epoxidation. Other substrates were also tested as described in Table 1, being observed that these materials are efficient in the epoxidation of olefins at ambient temperature using iodosylbenzene as oxidant [31]. The research groups of Chen and Wu described a porous Por-MOF coined as CZJ-1 (CZJChemistry Department of Zhejiang University) based on a carboxylate Mn(III) porphyrin, N,N 0 -di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide, and Zn(II) (Figure 8) which was highly efficient as catalyst in styrene epoxidation at ambient temperature using iodosylbenzene as oxidant (> 99% conversion and 98% selectivity). Authors proved that the reaction takes place inside the pores T based on single-crystal X-ray diffraction studies of CZJ-1-Mn⊃ 2styrene (Figure 8b), and attributed the high catalytic efficiency of CZJ-1-Mn to a combination of factors: neighboring MnIII -porphyrins, flexibility of the structure and specific electronic environments around the catalytic MnIII sites [32]. The efficient Fe-MMOF material reported by Jiang and coworkers in 2014 [25] also exhibited a high catalytic activity in the epoxidation of different alkenes at ambient temperature using hydrogen peroxide as oxidant and NaHCO3 as co-catalyst. Under these conditions, cyclooctene was almost fully oxidized into the epoxide with 99% selectivity, registering a very high conversion (>99%) and selectivity (>99%) until the third cycle. For the epoxidation of cyclohexene a conversion of 87% and a selectivity of >99% were afforded instead. The authors further described a conversion of 99% for the epoxidation of styrene. The low electron density of styrene and methyl acrylate usually reduces their nucleophilicity toward electrophilic oxygen of porphyrin-MnV = O. Based on the comparison of the catalytic performance of Fe-MMOF with their primary building blocks (MnCl2 , FeCl2 and Mn-TpCPP), as well as with that of the physical mixtures obtained under identical reaction conditions, authors postulated that the active catalytic sites should be the Mn-porphyrin moieties lining the pores of the Fe-MMOF network. The µ-oxo dimerization of Mn-porphyrin was prevented by its immobilization in the Fe-MMOF. Unlike the homogeneous porphyrin catalysts, Fe-MMOF could be easily recovered and reused [25]. Jiang and collaborators reported a novel Por-MOF containing a Mn(III) tetrakis(pcarboxyphenyl)porphyrin as bridging ligand and Fe(III) as the metal source. This material, coined as MMPF (MMPF denotes iron-based Metalloporphyrinic Metal-Organic Framework) was successfully obtained as a 3D MOF (Figure 9). Authors described that MMPF is structurally robust in boiling water and when in contact with basic aqueous solutions with pH ranging from ca. 7 to 12. In acidic conditions MMPF decomposes into the metalloporphyrinic monomers. The solvent-induced breathing effect of MMPF was also demonstrated with the immersion of the material in different solvents [33]. The catalytic activity of MMPF was tested for the selective epoxidation of a variety of alkenes, as summarized in Table 1, using iodosylbenzene as oxidant at ambient temperature. It was observed that for cyclohexene, a conversion of 100% was obtained, while for cyclooctene a conversion of 93% was registered instead, both with a selectivity >99%. Based on these results, the authors postulated

(CZJ-Chemistry Department of Zhejiang University) based on a carboxylate Mn(III) porphyrin, N,N′-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide, and Zn(II) (Figure 8) which was highly efficient as catalyst in styrene epoxidation at ambient temperature using iodosylbenzene as oxidant (> 99% conversion and 98% selectivity). Authors proved that the reaction takes place inside the pores based on single-crystal X-ray diffraction studies of CZJ-1-Mn⊃2styrene (Figure 8b), and attributed Molecules 2016, 21, 1348 12 of 19 the high catalytic efficiency of CZJ-1-Mn to a combination of factors: neighboring MnIII-porphyrins, flexibility of the structure and specific electronic environments around the catalytic MnIII sites [32]. The efficient Fe-MMOF reported by Jiang and in 2014 [25]greatly also exhibited a that MMPF contains channelsmaterial with accessible catalytic sites forcoworkers the substrates, which facilitates high activity in the epoxidation of different alkenes at ambientalkenes temperature using hydrogen their catalytic diffusion. In addition, the low electron density of conjugated usually reduces their V = O. The peroxide as oxidant andthe NaHCO 3 as co-catalyst. these conditions, cyclooctene almost nucleophilicity towards electrophilic oxygen ofUnder porphyrin-Mn conversionwas of styrene fully oxidized intoisthe epoxide withonly 99%50% selectivity, registering a very high and trans-stilbene thus low, with selectivity for the epoxide beingconversion registered(>99%) duringand the selectivity untilthe thekinetic third cycle. Forcyclohexene the epoxidation of cyclohexene a conversion of 87% and a oxidation. (>99%) Concerning profiles, prompted a faster reaction, with the registered selectivity >99% were afforded Theorder: authors further described a conversion of 99% for the> conversionof being accordingly to theinstead. following cyclohexene > cyclooctene > hex-1-ene> styrene epoxidation trans-stilbeneof>styrene. oct-1-ene > dodec-1-ene [33].

Figure of of compounds (a) (a) CZJ-1 viewed along [0,1,0] direction; (b) Figure 8. 8. Crystal Crystalpacking packingfeatures features compounds CZJ-1 viewed along [0,1,0] direction; T CZJ-1⊃2 styrene viewed along [0,0,1] direction; and (c) CZJ-1-Ti viewed along [0,1,0] direction. (b) CZJ-1⊃ 2 styrene viewed along [0,0,1] direction; and (c) CZJ-1-Ti viewed along [0,1,0] direction. (Colour scheme: bright green = = Zn, yellow = = Mn, = Ti, gray = = H, = C, (Colour scheme: bright green Zn, dark dark yellow Mn, dark dark green green = Ti, gray H, dark dark gray gray = C, light light blue = N, red = O). blue = N, red = O).

The low electron density of styrene and methyl acrylate usually reduces their nucleophilicity In a similar fashion to that previously described for Fe-MMOF, based on a direct comparison of toward electrophilic oxygen of porphyrin-MnV = O. Based on the comparison of the catalytic the catalytic activity of MMPF with its primary building blocks, as well as with the obtained physical performance of Fe-MMOF with their primary building blocks (MnCl2, FeCl2 and Mn-TpCPP), as well mixtures prepared using identical reaction conditions, authors also concluded that for this system the Mn(II) porphyrins are the active catalytic sites. This catalytic process is heterogeneous in nature with MMPF being used in successive catalytic runs. Data show a constant high catalytic activity with a small decrease in the initial reaction rate for the oxidation of cyclooctene.

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Figure 9. Schematic representationof ofthe the (a) (a) asymmetric asymmetric unit Figure 9. Schematic representation unit and and(b) (b)the thecrystal crystalpacking packingofofMMPF MMPF viewed along [1,0,0] direction. (Colour scheme: bright green = Fe, dark yellow = Mn, dark viewed along [1,0,0] direction. (Colour scheme: bright green = Fe, dark yellow = Mn,gray gray= =H,H, dark gray = C, light blue = N, red = O). gray = C, light blue = N, red = O).

2.3. Oxidation of Phenols The Fe-MMOF material reported by Jiang and coworkers in 2014 [25] is also active in the oxidation of phenols (Table 1). Among the tested substrates, benzyl alcohol reacted easier (99% conversion) in comparison with the other primary or secondary alcohols containing electron donating groups. Authors attributed the great versatility of this catalyst to the high-quality of the crystals, the stability of Scheme 6. General scheme of 3,5-di-tert-butylcathecol oxidation. the framework and the pore structure having suitable pore sizes and catalytic metal sites with desirable electronic environments [25]. Authors observed that CuTNPP@MOF exhibited the highest catalytic activity with a high Polyphenolic compounds are commonly selected as substrates to perform the evaluation of the conversion of 3,5-di-tert-butylcathecol to the corresponding o-quinone (around 60%). In this case, the peroxidase activity of porphyrin catalysts. Three reports on Por-MOFs as catalysts in the oxidation co-catalytic contribution of the nicotinoyl groups in CuTNPP was studied by performing the of this type of compounds can be found in the literature, one using 3,5-di-tert-butylcathecol as oxidation of 3,5-di-tert-butylcathecol in the presence of meso-tetrakis[4-methoxyphenyl]porphyrin. substrate [34] while the other two employ 1,2,3-trihydroxybenzene instead [35,36]. Because the transformation of the substrate was similar when using these compounds as catalysts, Incatalytic the oxidation of CuTNPP 3,5-di-tert-butylcathecol bycopper hydrogen peroxide at ambient the activity of was assigned to the ion and not to any nicotinoyltemperature functional (Scheme two new microporous materials used as catalysts: theCuTNPP@MOF and groups 6), in the periphery of the porphyrinic ring. Inwere the recycling experiments, catalytic activity of MnTNPP@MOF. These materials were prepared by the reaction of the flexible linker 1,1-bis-[3,5-bis CuTNPP@MOF was maintained during four cycles. The oxidation of 3,5-di-tert-butylcathecol in the (carboxy)phenoxy]methane and in the presence of 5,10,15,20-tetrakis[p-(nicotinoyloxy)-phenyl] presence of MnTNPP@MOF ledCuCl to a 2conversion not higher than 50%. In this case, conversion was not porphyrin to afford CuTNPP@MOF or, ininthe of the complex enhanced(TNPP) by the incorporation of MnTNPP, which fact presence typically leads to manganese a low conversion, veryof TNPP(MnTNPP), to afford MnTNPP@MOF. In Figure 10 is represented the structure of these much similar to that obtained for the blank experiment [34]. porphyrin@MOFs type-catalysts.

Figure 9. Schematic representation of the (a) asymmetric unit and (b) the crystal packing of MMPF Molecules 2016, 21, 1348 viewed along [1,0,0] direction. (Colour scheme: bright green = Fe, dark yellow = Mn, gray = H, dark gray = C, light blue = N, red = O).

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Scheme 6. General scheme of 3,5-di-tert-butylcathecol oxidation.

Scheme 6. General scheme of 3,5-di-tert-butylcathecol oxidation.

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Authors observed that CuTNPP@MOF exhibited the highest catalytic activity with a high conversion of 3,5-di-tert-butylcathecol to the corresponding o-quinone (around 60%). In this case, the co-catalytic contribution of the nicotinoyl groups in CuTNPP was studied by performing the oxidation of 3,5-di-tert-butylcathecol in the presence of meso-tetrakis[4-methoxyphenyl]porphyrin. Because the transformation of the substrate was similar when using these compounds as catalysts, the catalytic activity of CuTNPP was assigned to the copper ion and not to any nicotinoyl functional groups in the periphery of the porphyrinic ring. In the recycling experiments, the catalytic activity of CuTNPP@MOF was maintained during four cycles. The oxidation of 3,5-di-tert-butylcathecol in the presence of MnTNPP@MOF led to a conversion not higher than 50%. In this case, conversion was not enhanced by the incorporation of MnTNPP, which in fact typically leads to a low conversion, very much similar to that obtained for the blank experiment [34].

Figure 10. Schematic representation of porphyrin@MOFs type-catalysts. (Colour scheme: bright Figure 10. Schematic representation of porphyrin@MOFs type-catalysts. (Colour scheme: bright green = Cu, gray = H, dark gray = C, light blue = N, red = O, sky blue = metal in the porphyrin core, green = Cu, gray = H, dark gray = C, light blue = N, red = O, sky blue = metal in the porphyrin core, purple = porphyrin representation). purple = porphyrin representation).

MMPF-6 previously mentioned in the Section 2.2, constructed via the self-assembly of the [tetrakis(p-carboxyphenyl)porphyrinato] iron(III)exhibited chloride ligand with in catalytic situ generated Zr6Owith 8(COO) Authors observed that CuTNPP@MOF the highest activity a8 high (H 2 O) 6 SBUs (Figure 11), was further examined as catalyst in the peroxidase activity experiments conversion of 3,5-di-tert-butylcathecol to the corresponding o-quinone (around 60%). In this case, commonly used to assess the activity of synthetic biocatalysts. reactions involve the the the co-catalytic contribution ofbiomimetic the nicotinoyl groups in CuTNPP wasBoth studied by performing oxidation of a substrate: for the first, the oxidation of 1,2,3-trihydroxybenzene (Scheme 7) specifically oxidation of 3,5-di-tert-butylcathecol in the presence of meso-tetrakis[4-methoxyphenyl]porphyrin. examines the catalyst’s capability to transfer oxygen; in the second reaction, the oxidation of Because the transformation of the substrate was similar when using these compounds as catalysts, 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate examines the efficiency of the catalyst in electronic the catalytic activity of CuTNPP was to peroxidase-like the copper ion activity and not of to MMPF-6, any nicotinoyl functional transference. Authors reported an assigned interesting very much groups in the periphery of the porphyrinic ring. In the recycling experiments, the catalytic activity comparable to that of the heme protein myoglobin with respect to the initial reaction rates in buffer of CuTNPP@MOF solution [35]. was maintained during four cycles. The oxidation of 3,5-di-tert-butylcathecol in

the presence of MnTNPP@MOF led to a conversion not higher than 50%. In this case, conversion was not enhanced by the incorporation of MnTNPP, which in fact typically leads to a low conversion, very much similar to that obtained for the blank experiment [34]. MMPF-6 previously mentioned in the Section 2.2, constructed via the self-assembly of the [tetrakis(p-carboxyphenyl)porphyrinato] iron(III) chloride ligand with in situ generated Zr6 O8 (COO)8 (H2 O)6 SBUs (Figure 11), was further examined as catalyst in the peroxidase activity experiments commonly used to assess the biomimetic activity of synthetic biocatalysts. Both reactions involve the oxidation of a substrate: for the first, the oxidation of 1,2,3-trihydroxybenzene (Scheme 7) specifically examines the catalyst’s capability to transfer oxygen; in the second reaction, the oxidation of 2,20 -azino-bis(3-ethylbenzothiazoline)-6-sulfonate examines the efficiency of the catalyst in electronic transference. Authors reported an interesting peroxidase-like activity of MMPF-6, very much comparable to that of the heme protein myoglobin with respect to the initial reaction rates in buffer solution [35].

Figure 11. Schematic representations of the (a) iron(III) TpCPP chloride ligand, the (b) Zr6O8(CO2)8(H2O)8 SBUs and the (c) hexagonal and triangular one-dimensional channels of the crystal structure of MMPF-6. Color scheme: C, gray; O, red; Cl, green; Zr, turquoise. Reprinted (adapted) with permission from [35]. Copyright (2012) American Chemical Society.

oxidation of a substrate: for the first, the oxidation of 1,2,3-trihydroxybenzene (Scheme 7) specifically examines the catalyst’s capability to transfer oxygen; in the second reaction, the oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate examines the efficiency of the catalyst in electronic transference. Authors reported an interesting peroxidase-like activity of MMPF-6, very much comparable to that Molecules 2016, 21, 1348 of the heme protein myoglobin with respect to the initial reaction rates in buffer 15 of 19 solution [35].

Figure 11. Schematic representations of the (a) iron(III) TpCPP chloride ligand, the (b) Figure 11. Schematic representations of the (a) iron(III) TpCPP chloride ligand, the (b) Zr6 O8 (CO2 )8 Zr6O8(CO2)8(H2O)8 SBUs and the (c) hexagonal and triangular one-dimensional channels of the (H2 O)8 SBUs and the (c) hexagonal and triangular one-dimensional channels of the crystal structure of crystal structure of MMPF-6. Color scheme: C, gray; O, red; Cl, green; Zr, turquoise. Reprinted MMPF-6. Color scheme: C, gray; O, red; Cl, green; Zr, turquoise. Reprinted (adapted) with permission (adapted) with permission from [35]. Copyright (2012) American Chemical Society. from [35]. (2012) American Chemical Society. Molecules 2016, 21,Copyright 1348 15 of 18

Scheme 7. General oxidation. Scheme 7. General scheme scheme of of 1,2,3-trihydroxybenzene 1,2,3-trihydroxybenzene oxidation.

Simultaneously, Zhou and co-workers reported a stable Por-MOF, coined as PCN-222(Fe), Simultaneously, Zhou and co-workers reported a stable Por-MOF, coined as PCN-222(Fe), prepared from ZrCl4 and Fe-TpCPP in the presence of benzoic acid (Figure 12). The zirconium(IV) prepared from ZrCl4 and Fe-TpCPP in the presence of benzoic acid (Figure 12). The zirconium(IV) cation is responsible for the high stability of the network. Indeed, due to its high charge density, the cation is responsible for the high stability of the network. Indeed, due to its high charge density, this cation polarizes the oxygen atoms of the carboxylate groups to form strong Zr—O bonds with a the this cation polarizes the oxygen atoms of the carboxylate groups to form strong Zr—O bonds significant covalent character. The resulting PCN-222(Fe), also having iron centers, exhibited with a significant covalent character. The resulting PCN-222(Fe), also having iron centers, exhibited excellent peroxidase-like catalytic activity, whereas other MOFs did not show significant properties excellent peroxidase-like catalytic activity, whereas other MOFs did not show significant properties under identical conditions, which proves the stability of PCN-222 as an efficient, accessible under identical conditions, which proves the stability of PCN-222 as an efficient, accessible biomimetic biomimetic catalyst. The authors further reported an enzymatic kinetic study for PCN-222(Fe), being catalyst. The authors further reported an enzymatic kinetic study for PCN-222(Fe), being observed observed that the ĸcat value of the PCN-222(Fe) catalyst is 16.1 min−1, which is approximately seven − 1 that the kcat value of the PCN-222(Fe) catalyst is 16.1 min , which is approximately seven times times higher than the value for free hemin (2.4 min−1) (please note: ĸcat gives the maximum number of higher than the value for free hemin (2.4 min−1 ) (please note: kcat gives the maximum number of substrate molecules catalyzed per molecule of catalyst per unit of time). On the other hand, the Km substrate molecules catalyzed per molecule of catalyst per unit of time). On the other hand, the Km value (≈0.33 mm) is lower than that of the natural enzyme HRP (horseradish peroxidase, 0.81 mm), value (≈0.33 mm) is lower than that of the natural enzyme HRP (horseradish peroxidase, 0.81 mm), which indicates a better affinity of the substrate to PCN-222(Fe) (please note: Km is the Michaelis which indicates a better affinity of the substrate to PCN-222(Fe) (please note: Km is the Michaelis constant and indicates the affinity of the catalyst molecules for the substrate). Other substrates such constant and indicates the affinity of the catalyst molecules for the substrate). Other substrates such as as 3,3′,5,5′-tetramethylbenzidine and o-phenylenediamine were also tested for peroxidase-like 3,30 ,5,50 -tetramethylbenzidine and o-phenylenediamine were also tested for peroxidase-like oxidations oxidations to demonstrate the general applicability of PCN-222(Fe) as an enzyme mimic. PCN-222(Fe) to demonstrate the general applicability of PCN-222(Fe) as an enzyme mimic. PCN-222(Fe) showed showed superior catalytic activity over free hemin as its KCat value was nearly ten times higher than superior catalytic activity over free hemin as its KCat value was nearly ten times higher than that of that of free hemin [36]. free hemin [36].

value (≈0.33 mm) is lower than that of the natural enzyme HRP (horseradish peroxidase, 0.81 mm), which indicates a better affinity of the substrate to PCN-222(Fe) (please note: Km is the Michaelis constant and indicates the affinity of the catalyst molecules for the substrate). Other substrates such as 3,3′,5,5′-tetramethylbenzidine and o-phenylenediamine were also tested for peroxidase-like oxidations to demonstrate the general applicability of PCN-222(Fe) as an enzyme mimic. PCN-222(Fe) showed superior Molecules 2016, 21, 1348 catalytic activity over free hemin as its KCat value was nearly ten times higher than 16 of 19 that of free hemin [36].

Figure 12. Schematic representation of the 3D network in Kagome-like topology of PCN-222(Fe) Figure 12. Schematic representation of the 3D network in Kagome-like topology of PCN-222(Fe) viewed along [0,0,1] direction. (Colour scheme: bright green = Zr, dark yellow = Fe, green = Cl, gray = viewed along [0,0,1] direction. (Colour scheme: bright green = Zr, dark yellow = Fe, green = Cl, gray = H, dark gray = C, light blue = N, red = O,). H, dark gray = C, light blue = N, red = O,).

3. Outlook

3. Outlook

The unique physicochemical properties and the large diversity of porphyrin derivatives make

themunique an ideal class of linkers properties for the design preparation of new crystallinederivatives frameworks.make The physicochemical and and the large diversity of porphyrin Nevertheless, despite the intensive individual research over the years on both porphyrins and them an ideal class of linkers for the design and preparation of new crystalline frameworks. MOFs, the combination of both research worlds to produce novel materials (coined in this review Nevertheless, despite the intensive individual research over the years on both porphyrins and as MOFs, Por-MOFs) is still in an early stage. The delay of 14 years between the first report of a Por-MOF and the combination of both research worlds to produce novel materials (coined in this review as Por-MOFs) the study of the potential of this branch of materials as catalysts clearly demonstrates the difficult is still in an early stage. The delay of 14 years between the first report of a Por-MOF and the study of the potential of this branch of materials as catalysts clearly demonstrates the difficult challenges found by researchers concerning their preparation. It is possible to conclude by the scrutiny of the construction units employed that the porphyrins bearing carboxylic/pyridyl moieties and the transition metals used in the first reports still dominate the niche of Por-MOFs. Because of the high potential of this novel class of compounds, clearly demonstrated in the present short literature review, combined with new high-yield synthetic methodologies for both MOFs and porphyrins, it is expected that a more profound research will be carried out in the near future in the use of porous heterogeneous Por-MOFs as catalysts. In the addition the use of modern and more advanced X-ray laboratory equipment able to provide a faster response in the characterization of these materials, has significantly contributed to the characterization of these “giant” and new materials. The inclusion of porphyrins as linkers in Por-MOFs, as well as its incorporation into porous MOFs, presents many advantages in the catalytic performance of these materials due to several reasons: (i) isolation of the catalytic centers that usually suffer degradation in solution through undesirable reactions; (ii) Por-MOFs usually exhibit large pores that lead to the fast diffusion of molecules; (iii) good interaction between open metal sites and substrates and (iv) the catalytic activity of the porphyrinic linkers can be adjusted with the study of different metals coordinated to the porphyrinic core. Throughout this review it was possible to infer that in the last years there is a clear concern to perform adequate control experiments instead of just report that a certain Por-MOF is catalytically competent. Even in this way, the lack of mechanistic studies in this branch of materials is very clear. In addition to this lacuna, and because the nature of the oxidant is an important factor in an oxidation reaction, an appropriate screening of the most effective oxidants in each case remains pertinent. The knowledge gathered to date in the research of porphyrins as oxidative catalysts, under homogeneous and heterogeneous conditions, has undoubtedly a very high value, but the screening for the more adequate conditions to use in oxidation reactions with Por-MOFs as catalysts needs to be performed.

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We are firm believers that this is an exciting new research area which will see a fast growth in coming years. We envision the preparation of ultra-stable Por-MOFs isolated from porphyrins with increased stability in comparison with the porphyrins nowadays used as building blocks. We believe that the future of this niche will lie in their study mainly as artificial enzymes in order to overcome the main problems, mostly related to stability, found over many years in the research on porphyrins as biomimetic catalysts. Acknowledgments: Authors wish to thank Ricardo F. Mendes for his help in the production of some images for this paper. Funding Agencies and Projects: We wish to thank Fundação para a Ciência e a Tecnologia (FCT, Portugal), the European Union, QREN, FEDER through Programa Operacional Factores de Competitividade (COMPETE), CICECO—Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), QOPNA (FCT UID/QUI/00062/2013) and CQE (FCT UID/QUI/0100/2013) research units, financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. We also thank FCT for funding the R&D project FCOMP-01-0124-FEDER-041282 (Ref. FCT EXPL/CTM-NAN/0013/2013). Individual Grants and Scholarships: FCT is also gratefully acknowledged for the Ph.D. grant No. SFRH/BD/86303/2012 (to CP). Conflicts of Interest: The authors declare no conflict of interest.

Abbreviations The following abbreviations are used in this manuscript: CP CP-450 CZJ DCDBP DPNI F10 DPyP F5 CPP F10 CPP H8 OCPP MMPF MOFs PIZA Por-MOFs RPMs SBUs TNPP TpCPP TON ZJU

Coordination Polymer Cytochrome P-450 Chemistry Department of Zhejiang University 5,15-bis(2,6-dibromophenyl)-10,20-bis(3,5-dicarboxyphenyl)porphyrin N,N 0 -di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide 5,15-bis(pentafluorophenyl)-10,20-di(pyridyl)porphyrin 5,10,15-tris(p-carboxyphenyl)-20-(pentafluorophenyl)porphyrin 5,15- bis(p-carboxyphenyl)-10,20-bis(pentafluorophenyl)porphyrin 5,10,15,20-tetrakis(3,5-dicarboxylphenyl)porphyrin Metal-Metalloporphyrin Frameworks Metal-Organic Frameworks Porphyrinic Illinois Zeolite Analogue Porphyrin-based MOFs Robust Porphyrinic Materials Secondary Building Units 5,10,15,20-tetrakis[p-(nicotinoyloxy)phenyl]porphyrin 5,10,15,20-tetrakis(p-carboxyphenyl)porphyrin Turnover Number Zheijang University

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