Platinum phosphinothiolato hydride complexes: synthesis, structure and evaluation as tin-free hydroformylation catalysts

Abstract

Ligand 2-diphenylphosphinothiophenol (Hsarp) reacted with Pt(PPh3)4 to yield trans-[PtH(sarp)(PPh3)], which undergoes fast exchange with free PPh3 on the NMR time scale and very slowly and reversibly formed some cis-[PtH(sarp)(PPh3)] over time in solution (11%, 24 h). Reaction of trans-[PtH(sarp)(PPh3)] with Hsarp in boiling toluene gave cis- and trans-[Pt(sarp)2]; the cis isomer being more stable. These complexes were characterized by (1)H and (31)P NMR and also analyzed by XRD in the case of trans-[PtH(sarp)(PPh3)], trans-[Pt(sarp)2], and cis-[Pt(sarp)2]. trans-[PtH(sarp)(PPh3)] was evaluated as a preformed, tin-free hydroformylation catalyst on styrene and found active at 100 °C, at pressures over 75 bar, yielding phenylpropanal (regioselectivities up to 83% in 2-phenylpropanal), with total conversions to aldehydes up to 100% at styrene/platinum ratios from 400/1 to 1000/1 and minimal hydrogenation products.

Tuning diastereoisomerism in platinum(ii) phosphino- and aminothiolato hydrido complexes

“…Equilibrium in solution between cis and trans geometries in Pt(II) (phosphino)thiolato complexes are profusely described, including hydrido(phosphino)thiolato complexes. 5,6 The trans nature of the major isomer agrees with the more thermodynamically stable trans form in [PtH(SAr)(PPh 3 ) 2 ] complexes. 24 The major isomer, trans-8, shows a temperature dependent 1 H NMR.…”

“…The Pt-S distance is also slightly smaller than those found in complexes with bridging m-alkanethiolate trans to a hydride ligand (Table 2, entry 26). 28 The Pt-PPh 3 distance is analogous to that of the hydrido(2-phosphinophenolate)platinum(II) complex 5 but smaller than those observed in neutral and cationic complexes with a PPh 3 ligand trans to a phosphorus of a chelated 1,2-ethanediphosphine ( ligands compared to these diphosphines. However, also the Pt-PPh 2 bond lengths in 2-phosphinothiolate complexes are slightly smaller than those measured for the phosphorous of the chelated ligand in diphosphine complexes (Table 2, entries 16 and 27-29).…”

“…The temperature dependent NMR presented by some 2-phosphinothiolato platinum(II) hydrides was previously assigned to a rapid exchange between coordinated and free PPh 3 , present in excess. 5,6 After several recrystallization processes of product 8, the solution does not contain free PPh 3 , although the presence of traces cannot be ruled out. In fact, a fast dissociation equilibrium of PPh 3 from trans-[PtH(SAr)(PPh 3 ) 2 ] complexes was observed at room temperature, 24 suggesting that similar dissociation equilibrium can be operative in complex trans-8 (up in Scheme 2), being the cause of the temperature dependence of the NMR of this complex.…”

“…4 These complexes show four different donor atoms around metal and become asymmetric for the natural chiral ligands because the symmetry plane of the square-planar coordination is broken by the asymmetric carbon of the aminoacid. A similar synthetic strategy has been used to obtain low symmetry hydrido-(phosphinothiolate) complexes such as the hydrido[2-(diphenylphosphino-kP)thiophenolate-kS] triphenylphosphineplatinum(II) 5 and the hydrido [1-(diphenylphosphino-kP)butane-2-thiolato-kS]triphenylphosphineplatinum(II) 6 complexes. The last one was obtained in a mixture with triphenylphosphine.…”

“…7 As part of a project on the synthesis of new amino-and phosphinothiolato complexes of the group 10 metals and on the analysis of the ligand-based stereoelectronic effects that are determinants in the coordination conformations around the metal, 3,[8][9][10][11][12][13] we now report the preparation of new platinum(II) hydride complexes (8)(9)(10)(11) with 2-phosphinoethanethiolate ligands (2-(diphenylphosphino)ethanethiolate dppet 8, 1-(benzyloxy)-2-(diphenylphosphino)ethanethiolate bdppet 9, and 2-(diphenylphosphino)cyclohexanethiolate dppcyt 10) and a 3-phosphinothiolate ligand (3-(diphenylphosphino)propanethiolate dpppt 11). We also present, for the first time to our knowledge, the crystal structure determined by the X-ray analysis of a platinum(II) hydride complex with 2-phosphinoalkylthiolate ligand (8) and with 2-aminothiolate ligands: cysteamine (5) and natural chiral ligands methyl (cysMe) and ethyl (cysEt) ester-protected natural L-cysteine derivatives (6)(7). Moreover, DFT calculations are carried out to rationalize the diastereoisomerism observed in platinum(II) hydrides with aminoand phosphinothiolate ligands.…”