Electronic Supplementary Material (ESI) for Chemical Science. This journal is © The Royal Society of Chemistry 2015
SUPPORTING INFORMATION FOR Metal-Free Dehydrogenation of Formic Acid to H2 and CO2 Using Boron-Based Catalysts Clément Chauvier, Anis Tlili, Christophe Das Neves Gomes, Pierre Thuéry and Thibault Cantat* CNRS, UMR n° 3685 CEA – CNRS, F-91191 Gif-sur-Yvette France. E-mail:
[email protected]
S1
1.
Experimental details ........................................................................................................................ 3 1.1.
General considerations ............................................................................................................ 3
1.2.
Crystallography ....................................................................................................................... 3
2.
Outcome of the catalytic experiments ............................................................................................. 5
3.
Procedures for the catalytic dehydrogenation of formic acid. ......................................................... 8
4.
Synthetic procedures. .................................................................................................................... 12 a)
Synthesis of [2+, I–]. ............................................................................................................... 12
b)
Synthesis of [TBDH+, 5]. ..................................................................................................... 13
c)
Synthesis of [Et3NH+, 5 ]. ..................................................................................................... 14
d)
Synthesis of [Et3NH+, 6–]. ..................................................................................................... 16
5.
Gases Analysis .............................................................................................................................. 18
6.
Computational details and structures............................................................................................. 19
7.
6.1.
Computed pathways for the dehydrogenation of formic acid ............................................... 19
6.2.
HCOOH, HCOO–, H2 and CO2 ............................................................................................. 21
6.3.
9-BBN derivatives ................................................................................................................. 21
6.4.
Cy2B derivatives .................................................................................................................... 24
3.1.
CatB derivatives .................................................................................................................... 28
References ..................................................................................................................................... 31
S2
1. Experimental details 1.1.
General considerations
All reactions and manipulations were performed at 20 ºC in a recirculating mBraun LabMaster DP inert atmosphere (Ar) drybox and vacuum Schlenk lines. Glassware was dried overnight at 120ºC or flame-dried before use. 1H, 13C and 11B NMR spectra were obtained using a Bruker DPX 200 MHz spectrometer. Chemical shifts for 1H and 13C{1H} NMR spectra were referenced to solvent impurities. 11B NMR spectra were externally referenced using BF3•Et2O. Unless otherwise noted, reagents were purchased from commercial suppliers and dried over 4 Å molecular sieves prior to use. 4 Å molecular sieves (Aldrich) were dried under dynamic vacuum at 250 °C for 48 h prior to use. Tetrahydrofuran (THF), d8tetrahydrofuran (d8-THF), toluene, pentane and d6-benzene were dried over a sodium(0)/benzophenone mixture and vacuum-distilled before use. CD3CN and CD2Cl2 were dried over CaH2 and vacuum-distilled before use. Boranes (B-I-9-BBN, B-Cl-9-BBN, BOMe-9-BBN, B-OTf-9-BBN, 9-BBN dimer, BCy2I and BCy2Cl, PinBOMe, CatBCl, CatBBr, BCl3, BH3•SMe2, PhBCl2, BMes2F) and H13CO2H were obtained from Aldrich and used as received. HCO2H (99 %) was obtained from Acros and degassed prior to use. Triethylamine was purchased from Carlo Erba and degassed prior to use. Cyclohexene was purchased from Aldrich, passed through a column of alumina, dried over CaH2 and vacuum-distilled before use.
1.2.
Crystallography
The data were collected at 150(2) K on a Nonius Kappa-CCD area detector diffractometer[1] using graphite-monochromated Mo K radiation ( = 0.71073 Å). The crystals were introduced into glass capillaries with a protective coating of Paratone-N oil (Hampton Research). The unit cell parameters were determined from ten frames, then refined on all data. The data (combinations of - and -scans with a minimum redundancy of 4 for 90% of the reflections) were processed with HKL2000.[2] Absorption effects in [2+, I] were corrected empirically with the program SCALEPACK.[2] The structures were solved by direct methods with SHELXS-97[3] or by intrinsic phasing with SHELXT,[4] expanded by subsequent difference Fourier synthesis and refined by full-matrix least-squares on F2 with SHELXL97.[3] All non-hydrogen atoms were refined with anisotropic displacement parameters. One carbon atom of the TBDH+ cation in [TBDH+, 5] is disordered over two positions which were refined with occupancies constrained to sum to unity. The hydrogen atoms bound to nitrogen atoms in [TBDH+, 5] were found on a difference Fourier map and the carbon-bound hydrogen atoms were introduced at calculated positions in both compounds; all were treated as riding atoms with an isotropic displacement parameter equal to 1.2 times that of the parent atom (1.5 for CH3, with optimized geometry). S3
Crystal data for [2+, I]: C16H29BIN3, M = 401.13, monoclinic, space group C2/c, a = 17.3182(7), b = 19.7092(5), c = 12.0924(5) Å, = 120.773(2)°, V = 3546.3(2) Å3, Z = 8. Refinement of 191 parameters on 5407 independent reflections out of 60769 measured reflections (Rint = 0.027) led to R1 = 0.024, wR2 = 0.060, S = 1.049,min = –0.61,max = 0.60 e Å–3. Crystal data for [TBDH+, 5]: C17H30BN3O4, M = 351.25, orthorhombic, space group P212121, a = 7.1546(4), b = 12.8526(7), c = 20.4294(6) Å, V = 1878.59(16) Å3, Z = 4. Refinement of 237 parameters on 3552 independent reflections out of 42486 measured reflections (Rint = 0.021) led to R1 = 0.038, wR2 = 0.088, S = 1.068,min = –0.13,max = 0.16 e Å–3. The molecular plots were drawn with ORTEP-3.[5] CCDC-1035083 and -1035084 contain the supplementary crystallographic data for compounds [2+, I] and [TBDH+, 5], respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
S4
2. Outcome of the catalytic experiments Definitions: In 1H NMR experiments, conversion of formic acid was determined by integration of the formic acid/formate proton (H-COOH) and the protons of the bis(formyloxy)borate species (R2B(OCHO)− 2 ) versus the internal standard (CAr-H, δ = 6.79 ppm in CD3CN). Qualitatively, H2 (δ = 4.57 ppm in CD3CN, δ = 4.55 ppm in d8-THF) and 13 CO2 (δ = 125.8 ppm in CD3CN, δ = 125.69 ppm in d8-THF) are detected by 1H and 13C NMR spectroscopy. In all experiments, the chemical shift of the formate proton slightly depends on the pH of the solution i.e. on the amount of free base and actual formate concentration. On the contrary the bis(formyloxy)borate protons do not exhibit pH-dependency (Δδ < 0.1 ppm). Turnover number at time t (TON) is: 𝑇𝑂𝑁 =
𝑖 𝑡 𝑛𝐻𝐶𝑂𝑂𝐻 − 𝑛𝐻𝐶𝑂𝑂𝐻
𝑛𝑐𝑎𝑡.
𝜌
=𝑥
𝑖 𝑛𝐻𝐶𝑂𝑂𝐻 is the initial number of moles of formic acid 𝑡 𝑛𝐻𝐶𝑂𝑂𝐻 is the number of moles of formate (including bis(formyloxy)borate) at time t 𝑛𝑐𝑎𝑡. is the initial number of moles of catalyst at time t 𝜌 is the actual measured conversion (%) 𝑥 is the molar percentage (mol%) of catalyst introduced for the reaction.
Turnover frequency number (TOF) after t hours is: 𝑇𝑂𝐹(ℎ−1 ) =
𝑇𝑂𝑁 𝑡
Observation: For the reactions with R2B-X (R2B = Cy2B or BBN, X = I, Cl, OTf, OMe) in CD3CN, FA and the base must be either pre-mixed or added sequentially prior to the borane to ensure that the catalysis takes place. Indeed, when the borane and the base are added prior to formic acid, temporary deactivation of the catalyst was observed that resulted in a lengthy activation period of the catalytic system. Control experiments. a) The heating of the 5 HCOOH / 2 NEt3 mixture in either CD3CN or THF showed no detectable conversion after 48h at 130°C (Entries 1 and 2, Table S1). b) The heating of pure HCOOH with BBN–I (5 mol%), but without external base (NEt3 or MTBD) led to no reaction after 30 h at 130°C in acetonitrile (Entry 11, Table S1).
S5
Table S1. Organocatalytic dehydrogenation of formic acid with triethylamine
Entry
Catalyst [mol%]
– 1 – 2 BBN-I (5.0) 3 BBN-I (5.0) 4 BBN-I (5.0) 5 BBN-I (5.0) 6 BBN-I (5.0) 7 BBN-I (5.0) 8 BBN-I (5.0) 9 BBN-I (5.0) 10 BBN-I (5.0) 11 BBN-OTf (5.0) 12 BBN-OMe (5.0) 13 + [TBDH , 5] (5.0) 14 + 15 [TBDH , 5] (2.0) BBN-H (5.0) 16 Cy2B-I (10.0) 17 Cy2B-I (5.0) 18 Cy2B-I (1.0) 19 Cy2B-Cl (5.0) 20 Cy2B-OTf (5.0) 21 + – [Et3NH , 6 ] (5.0) 22 + – [Et3NH , 6 ] (2.5) 23 + – [Et3NH , 6 ] (1.0) 24 catB-Cl (5.0) 25 catB-Br (5.0) 26 pinB-OMe(5.0) 27 B(C6F5)3 (5.0) 28 PhBCl2 (5.0) 29 Mes2B-F (5.0) 30 BCl3 (5.0) 31 [a] No base added.
Temp [°C]
Solvent
Conversion [%]
TON (time, h)
130 130 130 130 130 130 130 100 110 120 130 130 130 130 130 130 130 130 130 130 130 130 130 130 130 130 130 130 130 130 130
CD3CN TDF TDF C6D6 Tol-d8 CD3OD CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN CD3CN
