Heterobimetallic Re=Pd complexes bridged by Î·1:Î·5

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Heterobimetallic Re=Pd complexes bridged by g1 :g5 -Ph2 PC5 H4 ligand. Synthesis, electronic and crystal structure of (CO)2 (PR3 )(g5 -C5 H4 PPh2 )Re–PdCl2 , R = Me and OMe† Diego Sierra,a A. Hugo Klahn,*a Rodrigo Ramirez-Tagle,b Ramiro Arratia-Perez,*b Fernando Godoy,c Maria Teresa Garlandd and Mauricio Fuentealbab,d Received 5th January 2010, Accepted 6th May 2010 First published as an Advance Article on the web 3rd June 2010 DOI: 10.1039/b927265h The new rhenium complexes (h5 -C5 H4 PPh2 )Re(CO)2 (PR3 ) (R = Me (1) and OMe (2)) were prepared photochemically from (h5 -C5 H4 PPh2 )Re(CO)3 in the presence of PMe3 or P(OMe)3 . Further reaction of these ligands with PdCl2 (NCPh)2 in chloroform, produces the heterobimetallic complexes (CO)2 (PMe3 )(h5 -C5 H4 PPh2 )Re–PdCl2 (3) and (CO)2 (P(OMe)3 )(h5 -C5 H4 PPh2 )Re–PdCl2 (4). IR spectroscopy reveals that both complexes possess a Re–Pd interaction which was confirmed by X-ray ˚ in 3 and 2.774 A ˚ in 4). Relativistic functional density crystallography (Re–Pd bond distance = 2.762 A theory calculations have also been carried out in order to probe the bonding in these compounds.

Introduction Diphenylphosphinocyclopentadienyl groups h5 -coordinated to metal fragments have proven to be versatile unsymmetrical mono- or bidentate ligands to form homo- and heterobimetallic complexes.1–3 The most common complexes of this class include those which have two metal centers held together through a simple bridging (monodentate) ligand.4,5 A large number of bimetallic complexes containing ligands of the type (h5 C5 H4 PPh2 )MLn , M = Fe, Ti, Zr, Co, Mo, Rh, etc., with interesting chemical, electrochemical and catalytic properties have been prepared.1,2,6 Nevertheless, bimetallic complexes containing group 7 ligands remain relatively unexplored. As far as we are aware, only a few examples of these types of complexes have been reported. For instance, Rausch and co-workers7 reported the homobimetallic complex [m-(h5 -C5 H4 PPh2 )Mn(CO)2 ]2 , whereas Gladysz and co-workers described the formation of Pd(II)8 and Rh(I)9 adducts by using the related chelating diphosphine ligands (h5 -C5 H4 PPh2 )Re(NO)(PPh3 )((CH2 )n PPh2 ) (n = 0, 1). Very recently, we reported the coordination capability to Pd(II), Au(I) and Cu(I) of the ligand (h5 -C5 H4 PPh2 )Re(CO)3 supported by crystallographic information.10 With regard to bidentate ligands, most of the literature reports deal with the anionic derivatives having diphenylphosphinocyclopentadienyl bound to the tricarbonyl moiety of group 6 transition metals, especially molybdenum and tungsten [(h5 C5 H4 PPh2 )M(CO)3 ]- , (M = Mo, W).11 These anions can be viewed as difunctional chelated ligands, with phosphine and metal anion a Instituto de Qu´ımica, Pontificia Universidad Católica de Valpara´ıso, Valpara´ıso, Chile. E-mail: [email protected]; Tel: (56)-(32)-2274922 b Universidad Andres Bello, Departamento de Ciencias Qu´ımicas, Santiago, Chile c Departamento de Qu´ımica de los Materiales Facultad de Qu´ımica y Biolog´ıa, Universidad de Santiago de Chile, Santiago, Chile d CIMAT, Facultad de Ciencias F´ısicas y Matemáticas, Universidad de Chile, Santiago, Chile † CCDC reference numbers 756945 and 756946. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b927265h

This journal is © The Royal Society of Chemistry 2010

donor groups. Casey and Rheingold12 described for the first time the synthesis and characterization of manganese and rhenium complexes (CO)3 (h5 -C5 H4 PR2 )MoM(CO)4 (M = Re, Mn; R = Ph, p-tolyl). Since then, a large number of homo- and heterobimetallic complexes have been published. Some other examples are: MoI[h5 C5 H4 (CO)3 [h5 -C5 H4 P(Ph)(h5 C5 H4 )](CO)3 MoPd(PPh3 )I,13 P(Ph)(Bu)](CO)3 MoPd(PPh3 )I,14 Me[m-(h5 -C5 H2 (PR2 )]2 ZrRh(CO)(L), R = Ph, iso-Pr, Cy; L = CO, PPh3 ,15 (CO)3 (h5 -C5 H2 (Ph2 )PPh2 )MPd(PPh3 )I, M = Mo, W,16 [m-(h5 -C5 H4 PPh2 )M(CO)2 ]2 (M = Cr, Mo, W),17 and (CO)3 (h5 -C5 H4 PR2 )MPd(PPh3 )I (M = Mo, W)18 [m-(h5 -C5 H4 PPh2 )Rh(CO)]2 2+ .19 In this paper we would like to report the synthesis and characterization of the new ligands based on rhenium (h5 C5 H4 PPh2 )Re(CO)2 (PR3 ) (R = Me and OMe) and their reactions with PdCl2 (NCPh)2 leading to the bimetallic complexes (CO)2 (PR3 )(h5 -C5 H4 PPh2 )RePdCl2 in which the palladium moiety is chelated by the phosphine and rhenium atoms.

Results and discussion 1. Synthesis of the ligands (g5 -C5 H4 PPh2 )Re(CO)2 (PR3 ) and their palladium complexes The ligands (h5 -C5 H4 PPh2 )Re(CO)2 (PR3 ) R = Me (1) and R = OMe (2) were prepared following the same procedure described for the preparation of Cp or Cp*Re(CO)2 (PR3 ),20,21 (see Scheme 1) that is, by UV-irradiation (l = 300 nm) of the tricarbonyl complex (h5 -C5 H4 PPh2 )Re(CO)3 in the presence of the corresponding phosphorous ligand.

Scheme 1

After work up the compounds were isolated as white solids in about 51% yield. It is important to note that we have no evidence Dalton Trans., 2010, 39, 6295–6301 | 6295

for the formation of a dimeric species [m-(h5 -C5 H4 PPh2 )Re(CO)2 ]2 , which could be formed in the photochemical reactions, as was previously observed by Rausch in the photolysis of (h5 C5 H4 PPh2 )Mn(CO)3 in THF.7 The spectroscopic data for these derivatives resemble those reported for the analogous cyclopentadienyl carbonyl rhenium complex containing phosphine20 or phosphite21 and the precursor (h5 -C5 H4 PPh2 )Re(CO)3 .7 For example, the IR spectra for 1 and 2 showed two n(CO) absorption bands at 1923, 1852 and 1947, 1877 cm-1 respectively, which are almost identical to the ones measured for CpRe(CO)2 (PR3 ).20 Similarly in the 31 P NMR spectra, the phosphorus (bound to Re) chemical shifts are comparable to the above complexes. Also, the 1 H and 31 P NMR spectra showed similar chemical shifts for both hydrogen and phosphorus nuclei of the (h5 -C5 H4 PPh2 ) group to the ones reported for the precursor (h5 -C5 H4 PPh2 )Re(CO)3 .7,10,22 Compounds 1 and 2 react with PdCl2 (NCPh)2 in CHCl3 to yield the unexpected bimetallic derivatives (CO)2 (PR3 )(h5 C5 H4 PPh2 )RePdCl2 R = Me, (3); R = OMe, (4), (see Scheme 2).

Drawings of the molecular structures of complexes 3 and 4 with their respective labelling scheme are shown in Figs. 1 and 2, the hydrogen atoms and the solvent molecules have been omitted for clarity.

Fig. 1 Molecular structure of (CO)2 (PMe3 )(h5 -C5 H4 PPh2 )RePdCl2 (3) drawn with 30% probability displacement ellipsoids. Hydrogen atoms and solvent molecules are omitted.

Scheme 2

Neither the coordination product (CO)2 (R3 P)Re(h5 C5 H4 PPh2 )PdCl2 (NCMe) (similar to (CO)3 Re(h5 -C5 H4 PPh2 )PdCl2 (NCMe)10 ) nor any other intermediates were observed. Both complexes were isolated as pure samples, based on the elemental analyses which are in good agreement with the proposed formula. Our first suspicion about the unusual structure of these new compounds was obtained from IR spectroscopy. The IR spectra of 3 and 4 (in MeCN) showed two n(CO) absorptions (expected for a dicarbonyl-phosphine or phosphite) shifted to a higher wavenumber compared to their precursor, with a typical pattern of a four-legged piano-stool type of structure with the two carbonyl groups with a trans arrangement (the higher wavenumber absorption being the less intense of the pair). By considering our IR values and those reported for trans-CpRe(CO)2 X2 23 and trans-CpMeRe(CO)2 X2 24 we considered that these new compounds also possess a trans stereochemistry at the rhenium center. This finding means that the rhenium atom is involved in a bonding interaction with the palladium(II) center. The 1 H and 31 P NMR of the (h5 -C5 H4 PPh2 ) group did not show any unusual features when compared with the data measured for the same group in (CO)3 Re(h5 -C5 H4 PPh2 )PdCl2 (NCMe).10 With the aim to obtain more insight into the proposed rhenium-palladium bond we undertook a crystallographic study of complexes 3 and 4 (see below). 2.

X-Ray structure of 3·2CH3 CN and 4·CH2 Cl2

The bimetallic complexes 3 and 4 crystallise with two acetonitrile molecules and one dichloromethane molecule, respectively. 6296 | Dalton Trans., 2010, 39, 6295–6301

Table 1 contains a summary of the crystallographic information, while selected measured and calculated bond lengths and angles are included in Table 2. Table 1 Summary of crystallographic data and structure refinement for 3 and 4

Empirical Formula Formula mass/g mol-1 Collection T/K Crystal system Space group ˚ a/A ˚ b/A ˚ c/A ˚3 V /A Z Dc /g cm-3 Crystal size/mm F(000) m/mm-1 q range (◦ ) Range h,k,l No. total refl. No. unique refl. Data/restrains/ parameters Final R [I > 2s(I)] R indices (all data) Goodness of fit/F2 Largest diff. peak and ˚ -3 hole/e A

3·2CH3 CN

4·CH2 Cl2

C26 H29 Cl2 N2 O2 P2 PdRe 826.95 298(2) Orthorhombic Pna21 16.853 (2) 17.329(2) 10.1789(13) 2972.8(7) 4 1.848 0.36 ¥ 0.24 ¥ 0.19 1600 4.986 2.32 to 28.02 -20/21, -22/19, -13/12 14883 6413 [R(int) = 0.0656] 6413/1/330

C23 H25 Cl4 O5 P2 PdRe 877.77 150(2) Orthorhombic Pbca 19.1773 (6) 13.3897(4) 22.1610(7) 5690.5(3) 8 2.049 0.38 ¥ 0.28 ¥ 0.08 3376 5.403 1.84 to 27.89 -25/25, -17/17, -29/28 72639 6555 [R(int) =0.0733] 6555/0/328

R1 = 0.0692 wR2 = 0.1255 R1 = 0.0969 wR2 = 0.1358 1.059 3.111 and -1.867

R1 = 0.0327 wR2 = 0.0826 R1 = 0.0398 wR2 = 0.0858 1.052 3.535 and -1.065


˚ ) and angles (◦ ) for 3 and 4 Table 2 Selected experimental and calculated bond lengths (A Distances

3

4

Angles

3

4

Re–Pd Re–Cpb Re–C(6) Re–C(7) Re–P(2) P(1)–C(1) O(1)–C(6) Pd–P(1) Pd–Cl(1) Pd–Cl(2)

2.763(1) 2.798a 1.943(6) 1.970a 1.949(16) 1.926a 1.951(18) 1.943a 2.367(4) 2.374a 1.820(20) 1.819a 1.108(16) 1.168a 2.190(4) 2.230a 2.394(4) 2.364a 2.351(3) 2.349a

2.774(1) 2.800a 1.938(2) 1.972a 1.936(4) 1.926a 1.933(4) 1.954a 2.315(1) 2.324a 1.796(4) 1.813a 1.143(5) 1.168a 2.194(1) 2.251a 2.388(1) 2.350a 2.361(1) 2.365a

Re–Pd–P(1) Re–Pd–Cl(1) P(1)–Pd–Cl(2) P(1)–Pd–Cl(1) Cl(1)–Pd–Cl(2) P(2)–Re–Pd C(6)–Re–C(7) C(1)–P(1)–Pd C(11)–P(1)–C(17) O(1)–C(6)–Re O(2)–C(7)–Re Cpb –Re–Pd Cpb –Re–P(2) Cpb –Re–C(6) Cpb –Re–C(7)

77.87(9) 79.9a 98.86(11) 98.6a 91.61(13) 87.4a 175.39(16) 175.6a 91.47(14) 93.7a 131.79(10) 129.2a 102.3(7) 102.3a 106.0(4) 101.9a 110.7(6) 103.4a 173.3 (14) 170.7a 170.4(17) 165.4a 109.63(19) 107.0a 118.5(2) 123.2a 124.8(4) 124.8a 128.8(5) 125.3a

77.67(3) 78.9a 99.51(3) 100.0a 89.39(4) 88.2a 177.06(4) 173.8a 93.37(4) 92.2a 133.43(3) 129.3a 102.80(17) 103.8a 104.84(13) 103.8a 109.16(18) 109.0a 173.2(4) 171.7a 172.5(4) 164.4a 109.13(5) 108.2a 117.09(6) 121.8a 125.71(13) 124.3a 126.72(14) 124.0a

a

Gas phase optimization with the ADF+ZORA method. b Centroid (C5 H4 PPh2 ).

Fig. 2 Molecular structure of (CO)2 (P(OMe)3 )(h5 -C5 H4 PPh2 )RePdCl2 (4) drawn with 30% probability displacement ellipsoids. Hydrogen atoms and solvent molecules are omitted.

The most important features of the structure of 3 and 4, are the presence of a four membered bimetallic ring Cp–Re–Pd–P (assuming the whole Cp participates as a single unit of the ring). In this ring there is a strong bimetallic interaction between the ˚ rhenium and palladium atoms with a bond distance of 2.763(1) A ˚ for 4. Both distances are significantly shorter for 3 and 2.774(1) A ˚ )25 and the Re– than the sum of the respective covalent radii (2.85 A ˚ ) found in the complex Pd2 Re2 (CO)8 (mPd single bond (2.8580(5) A SnPh2 )2 (PBut )2 .26 On this criterion, as well as the correlation between the Re–Pd bond length found in 3 and 4 and that reported for the complex (PCy2 )(PMe3 )2 Re(m-PCy2 )2 Pd(PMe3 ) ˚ ),27 we consider that our products also have a Re=Pd (2.7575(9) A double bond. In order to probe the bonding in these complexes This journal is © The Royal Society of Chemistry 2010

Relativistic Density Functional Theory Calculations have also been carried out (see below). The existence of a Re=Pd bond represents the key feature determining the overall arrangement of the entire molecule. For example, in complex 3 the phosphorus atom attached ˚ below the least squares to the Cp ring is deviated 0.670 A (l.s.) plane formed by the ring, very similar to the deviation ˚ ), whereas a deviation of obtained for the complex 4 (0.655 A ˚ above the l.s. plane was found in the closely related 0.234 A complex (CO)3 Re(h5 -C5 H4 PPh2 )PdCl2 (NCMe), which does not have a bonding interaction between the rhenium and palladium atoms.10 The short distance between the metal centers also ˚ in 3 and exerts a shortening of the Pd–P bond (2.190(4) A Dalton Trans., 2010, 39, 6295–6301 | 6297

˚ in 4) when compared to the similar distances mea2.194(1) A ˚ ),10 sured in (CO)3 Re(h5 -C5 H4 PPh2 )PdCl2 (NCMe) (2.2217(13) A 5 ˚ )8 (NO)(PPh3 )(h -C5 H4 PPh2 )Re(m-CH2 )PPh2 PdCl2 (2.248(3) A and in the related phosphinoferrocene complex trans˚ ).28 [PdMeCl(PPh2 Fc)2 ], (2.3328(10) A Significant variations from the ideal square-planar geometry are also observed around the Pd center. The Re–Pd–P(1) and Re–Pd– Cl(1) angles deviate to about 77.7◦ and 99.0◦ respectively, far from the 90◦ expected for a normal square planar coordination around Pd. The rhenium environment is also affected by the presence of the intermetallic bond, for example the Cp–Re–Pd angle is close to 109◦ , and differs strongly from the values of the other bond angles measured for the Cp–Re axis and the two Re–CO and Re–P(2) (~126◦ and 117.5◦ , respectively). Similar deformations have been previously reported for related angles in complexes having a four member bimetallic ring Cp–M–Pd–P (M = Mo, W).14,29 Despite the variations already mentioned, the Re–CO distances and OC– Re–CO interbond angles are comparable to those measured in other trans dicarbonyl cyclopentadienyl rhenium complexes, possessing a four legged piano stool type of structure.30,31

3. Theoretical calculations The geometry optimization of the complexes was performed using the ADF code.32 All the calculated bond distances and bond angles, included in Table 2, are in reasonable agreement with the measured experimental values, indicating that this method, which includes scalar relativistic effects, is quite efficient for optimizing geometries of complexes containing heavy metals. The calculations clearly show the existence of a double bond ˚ between the rhenium and palladium atoms (Re=Pd) of 2.798 A ˚ (3) and 2.800 A (4) which compares well with the distance of ˚ (3) and 2.774(1) A ˚ (4) determined by X-ray diffraction 2.763(1) A ˚ measured in a binuclear and with the distance of 2.7575(9) A Re=Pd complex reported by Baker et al.27 In order to clarify the s and p character of the Re=Pd double bond, we carried out a fragment analysis in compounds 3 and 4, which is graphically depicted in Fig. 3. The interaction between the Re(5dz2 ) and the Pd(4dz2 ) orbitals gives rise to the ds bond, while the interaction between the Re(5dxz) and the Pd(4dxz) orbitals gives rise to the dp bond. In Fig. 4, we show the principal levels involved in a Re=Pd p bond. The orbital percent composition shown in Table 3 indicates those MO’s with major Re and Pd content which are involved in bonding interactions.

Fig. 3 Density surface picture of the s and p bonds in the Re–Pd fragment of the complex (CO)2 (PMe3 )(h5 -C5 H4 PPh2 )RePdCl2 (3).

To further explain the existence of the Re=Pd bond, we plotted in Fig. 5 and 6 the Mulliken charge distribution over the Re and Pd centers in compounds 3 and 4. Calculations demonstrate that the charge on the Pd atom is almost the same in both compounds while the Re atom is more negatively charged in compound 4. The Re=Pd bond can be interpreted as electron donation from the more electron rich Re(I) to the high valent and less electron rich Pd(II). The charge difference between the rhenium centers in 3 and 4 can be explained by considering the large s donor capability of the trimethylphosphine compared to the trimethylphosphite ligand, accordingly the more positive charge calculated for the phosphorous atom of P(OMe)3 is indicative of its weakest s donor and strongest p acceptor abilities. These quantum chemical results are also experimentally supported by the 31 P chemical shifts (115.7 and 27.0 ppm for P(OMe)3 in 4 and PMe3 in 3, respectively) and by the shift to a higher energy of the n(CO) frequencies observed in the IR spectra of 4 compared to 3 (1986, 1934 cm-1 for 4 vs. 1972, 1916 cm-1 for 3).

Conclusion Herein we have shown that the new electron-rich complexes (h5 C5 H4 PPh2 )Re(CO)2 PR3 (1 and 2) behave as neutral chelating ligands and coordinate to the Pd(II) center through the phosphine side arm of the cyclopentadienyl group and the rhenium atom. This coordination mode resembles the one observed in binuclear complexes containing the anionic ligand [(h5 -C5 H4 PPh2 )M(CO)3 ](M = Mo, W), but contrasts with the coordination capability of the analogous (h5 -C5 H4 PPh2 )Re(CO)3 which acts only as monodentate ligand. The X-ray structure of the two binuclear complexes clearly reveals a strong bonding interaction between the rhenium and palladium atoms. Relativistic Density Functional Theory Calculations proved useful in supporting the existence of a double bond between the two transition metals.

Table 3 Percent (%) contributions of selected molecular orbitals of compounds 3 and 4 HOMO-3

HOMO-2

HOMO-1

HOMO

LUMO

LUMO+1

LUMO+2

LUMO+3

3

74.2% Cl 14.7% Pd 2.7% P 1.9% Re

41.5% Cl 36.9% Pd 12.5% Re

72.9% Cl 20.1% Pd 1.1% Re

73.4% Cl 16.1% Pd 2.9% Re

85.7% C 9.6% P

73.3% C 5.4% P 2.2% O

53.7% C 16.3% O 10.7% Re 1.9% Pd

4

77.5% Cl 11.5% Pd 2.5% P 1.9% Re

41.6% Cl 37.4% Pd 11.3% Re

72.5% Cl 18.2 Pd

71.8% Cl 16.7% Pd 2.4% Re

31.3% Pd 22.3% Cl 15.4% P 10.0% Re 5.8% C 31.2% Pd 23.8% Cl 15.2% P 10.1% Re 7.2% C

77.7% C 10.3% P

61.6% C 8.7% O 3.7% Re 2.3% P 1.3% Pd

68.4% C 7.3% Re 5.9% O 2.4% Pd

6298 | Dalton Trans., 2010, 39, 6295–6301


Fig. 4 Calculated MO’s scheme for 3, showing the principal levels involved in p Re–Pd bonding.

Fig. 5 Mulliken charge distribution over Re, Pd and P centers for 3. Fig. 6

Mulliken charge distribution over Re, Pd and P centers for 4.

Experimental All experiments were carried out under a nitrogen atmosphere using standard Schlenck techniques. Solvents were purified as follows: hexane and tetrahydrofuran by distillation from sodium/benzophenone ketyl; dichloromethane, chloroform and acetonitrile by distillation from P2 O5 . The compounds PMe3 , P(OMe)3 and PdCl2 (NCPh)2 (Aldrich) were use as received. The organometallic ligand (h5 -C5 H4 PPh2 )Re(CO)3 was prepared according to the procedure reported by Gladysz.22 NMR spectra were recorded on a Bruker AVANCE 400 MHz spectrometer; 1 H and 13 C were referenced to a residual solvent signal and 31 P{1 H}NMR chemical shifts were referenced to 85% H3 PO4 as an external standard. IR spectra were recorded on a PerkinThis journal is © The Royal Society of Chemistry 2010

Elmer FT-IR Spectrum One spectrophotometer in a KBr solution cell. Photochemical reactions were carried out at 300 nm with a Rayonet RPR 100 photoreactor in Pyrex tubes. Elemental analyses ´ were obtained at the Centro de Instrumentacion, Pontificia ´ Universidad Catolica de Chile, Santiago, Chile. Synthesis of (g5 -C5 H4 PPh2 )Re(CO)2 PR3 (1 and 2) A Pyrex tube was charged with (h5 -C5 H4 PPh2 )Re(CO)3 (90 mg, 0.173 mmol), dissolved in 20 mL of dry THF and sealed with a rubber septum. This solution was purged with N2 for 5 min, after which the PR3 was added (0.30 mmol). The colorless reaction mixture was irradiated at 300 nm and monitored by IR Dalton Trans., 2010, 39, 6295–6301 | 6299

spectroscopy until the n(CO) absorption bands of the precursor almost disappeared (about 2 h). The resulting yellow solution was evaporated to dryness and the dark-brown oil obtained was purified through a silica gel column and eluted with a hexane/dichlorometane 3 : 1 mixture. The first fraction moved the unreacted precursor (about 10%) and the second fraction moved the organometallic ligand (h5 -C5 H4 PPh2 )Re(CO)2 PR3 . (g5 -C5 H4 PPh2 )Re(CO)2 PMe3 (1). Yield based on (h5 C5 H4 PPh2 )Re(CO)3 : 46 mg, (0.081 mmol), 52%. IR [CH2 Cl2 , n(CO), cm-1 ]: 1923 (s), 1852 (s). 1 H-NMR (CDCl3 ) d: 1.68 (d, 2 J PH = 9.8 Hz, 9H, PMe3 ), 5.06 (m, 2H, C5 H 4 ), 5.13 (m, 2H, C5 H 4 ), 7.35 (m, 10H, C6 H 5 ). 13 C{1 H} NMR (CDCl3 ) d: 24.1 (d, 1 J PC = 36.6 Hz, PMe3 ), 83.4 (d, 3 J PC = 2.7 Hz, C 5 H4 ), 89.9 (d, 2 J PC = 13.9 Hz, C 5 H4 ), 91.4 (d, 1 J PC = 14.8 Hz, Cipso C 5 H4 ), 128.4 (d, 3 J PC = 6.8 Hz, C 6 H5 ), 128.7 (s, C 6 H5 ), 133.4 (d, 1 J PC = 19.4 Hz, Cipso C 6 H5 ), 138.0 (d, 2 J PC = 10.2 Hz, C 6 H5 ) 201.6 (d, 2 J PC = 8.4 Hz, CO). 31 P{1 H}-NMR (CDCl3 ) d: -27.3 (s, PMe3 ), -16.7 (s, PPh2 ). Anal. Calcd. for C22 H25 O2 P2 Re: C 46.39, H 4.42. Found: C 46.22, H 4.70. (g5 -C5 H4 PPh2 )Re(CO)2 P(OMe)3 (2). Yield based on (h5 C5 H4 PPh2 )Re(CO)3 : 49 mg, (0.080 mmol) 51%. IR [CH2 Cl2 , n(CO), cm-1 ]: 1947 (s), 1877 (s). 1 H-NMR (CDCl3 ) d: 3.51 (d, 3 J PH = 12.3 Hz, 9H, P(OMe3 ), 5.13 (m, 2H, C5 H 4 ), 5.21 (m, 2H, C5 H 4 ), 7.38 (m, 10H, C6 H 5 ). 13 C{1 H}- NMR (CDCl3 ) d: 52.2 (d, 2 J PC = 3.0 Hz, P(OMe)3 ), 84.9 (d, br., 2 J PC = 2.2 Hz, C 5 H4 ), 89.1 (dd, 2 J PC = 2.2 Hz, 2 J PC = 13.3 Hz, C 5 H4 ), 94.4 (dd, 2 J PC = 2.2 Hz, 1 J PC = 16.9 Hz, Cipso C 5 H4 ), 128.4 (d, 3 J PC = 6.8 Hz, C 6 H5 ), 128.9 (s, C 6 H5 ), 133.5 (d, 1 J PC = 19.6 Hz, Cipso C 6 H5 ), 137.7 (d, 2 J PC = 10.5 Hz, C 6 H5 ), 198.9 (d, J PC = 13.8 Hz, CO). 31 P{1 H}NMR (CDCl3 ) d: -16,3 (s, PPh2 ), 138.9 (s, PMe3 ). Anal. Calcd. for C22 H25 O5 P2 Re: C 42.79, H 4.08. Found: C 42.51, H 4.33. Synthesis of (CO)2 (PR3 )(g5 -C5 H4 PPh2 )RePdCl2 (3 and 4) (0.10 mmol) of the organometallic ligands (h5 -C5 H4 PPh2 )Re(CO)2 PR3 (1 or 2), was poured into a 50 mL round bottom flask equipped with a magnetic stirrer bar, and dissolved in 15 mL of dry chloroform at room temperature. To this solution 38.4 mg (0.100 mmol) of solid PdCl2 (NCPh)2 was added. The resulting orange mixture was stirred and refluxed under a N2 atmosphere for 6 h. After this period an orange solid was formed. The solvent was evaporated to dryness and the residual orange solid dissolved in acetonitrile and allowed to crystallize at low temperature. In both cases the bimetallic complexes were isolated as orange crystals suitable for X-ray diffraction. (CO)2 (PMe3 )(g5 -C5 H4 PPh2 )RePdCl2 (3). Yield: 65 mg, (0.087 mmol) 87%. IR (n CO ) (CH3 CN) (cm-1 ): 1972 (m); 1916 (s); 1 H-NMR (CD3 SOCD3 ) d: 1.92 (d, 2 J PH = 11.3 Hz, 9H, PMe3 ); 4.86 (m, 2H, C5 H 4 ); 5.90 (m, 2H, C5 H 4 ); 7.50–8.50 (m, 10H, C6 H 5 ). 31 P{1 H}-NMR (CD3 CN) d: -26.3 (s, PMe3 ); 27.0 (d, 3 J PP = 4.8 Hz, PPh2 ). Anal. Calcd. for C26 H29 Cl2 N2 O2 P2 PdRe: C 37.76, H 3.53; found: C 37.92, H 3.70. (CO)2 (P(OMe)3 )(g5 -C5 H4 PPh2 )RePdCl2 (4). Yield: 66 mg, (0.083 mmol) 83%. IR (n CO ) (CH3 CN) (cm-1 ): 1986 (m); 1934 (s). 1 H-NMR (CD3 CN) d: 3.78 (d, 3 J PH = 12.3 Hz; 9H; P(OMe)3 ), 4.84 (m, 2H, C5 H 4 ), 5.63 (m, 2H, C5 H 4 ), 7.58 (m, 7H, C6 H 5 ), 8.32 (m, 3H, C6 H 5 ). 31 P{1 H}-NMR (CD3 CN) d: 27.2 (d, 3 J PP = 5.2 Hz, 6300 | Dalton Trans., 2010, 39, 6295–6301

PPh2 ); 115,7 (s, P(OMe)3 ). Anal. Calcd. for C23 H25 Cl4 O5 P2 PdRe: C 31.47, H 2.87; found: C 31.18, H 2.66.

Computational details Calculations for (CO)2 (PMe3 )(h5 -C5 H4 PPh2 )Re–PdCl2 3 and (CO)2 (P(OMe)3 )(h5 -C5 H4 PPh2 )Re–PdCl2 4 were carried out by using the Amsterdam Density Functional (ADF) code.32 The scalar relativistic effects were incorporated by using the zero order regular approximation (ZORA).33,34 All the molecular structures were fully optimized via the analytical energy gradient method implemented by Verluis and Ziegler employing the local density approximation (LDA) within the Vosko-WilkNusair parametrization for local exchange correlations.35,36 We also used the GGA (Generalized Gradient Approximation) PW91 function.34 The cluster geometry optimization and the excitation energies were calculated using standard Slater-type-orbital (STO) basis sets with triple-zeta quality plus double polarization functions (TZ2P) for all the atoms. X-ray crystal structure determinations Suitable X-ray single crystals of compounds 3 and 4 were obtained as described above and were mounted on top of glass fibers in a random orientation. Crystal data, data collection, and refinement parameters are given in Table 1. Compounds 3 and 4 were studied at 298(2) and 150(2) K, respectively, on a Bruker Smart Apex diffractometer equipped with bidimensional CCD detector employing graphite-monochromated Mo-Ka radiation ˚ ). The diffraction frames were integrated using the (l = 0.71073 A SAINT package,37 and corrected for absorption with SADABS.38 The structures were solved using XS in SHELXTL-PC,39 by Patterson and completed (non-H atoms) by difference Fourier techniques. The complete structure was then refined by the fullmatrix least-squares procedures on reflection intensities (F2 ).40 The non-hydrogen atoms were refined with anisotropic displacement coefficients, and all hydrogen atoms were placed in idealized locations.

Acknowledgements This work has been supported by Fondecyt No. 1060487 and 1070345. D. S. and R. R.-T. are grateful to CONICYT-fellowship. A. K. acknowledges DI-Pontificia Universidad Catolica de Valparaiso. R. A.-P. thanks MECESUP2-FSM0605 and UNAB-DI42-06/R, UNAB-DI-05-06/I.

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