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 ¹H and ³¹P 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.