Platinum–alkyl–B(C6F5)3 (or BF3) ‘in situ’ systems as tin(II) halide-free enantioselective hydroformylation catalysts

The dialkyl/diaryl-platinum complexes (Pt(CH3)2(bdpp); PtPh2(bdpp) and Pt(2-Thioph)2(bdpp), where bdpp stands for (2S,4S)-2,4-bis(diphenylphosphino)pentane) were reacted either with B(C6F5)3, BPh3 or BF3. In the presence of PPh3 or carbon monoxide cationic species with a general formulae [PtR(L)(bdpp)]+ (L = PPh3, CO) were formed exclusively. The ability of boron additives to provide vacant coordination site at the platinum made these systems suitable as hydroformylation catalysts. Enantioselective hydroformylation of styrene was carried out in the presence of in situ catalysts formed from Pt(alkyl/aryl)2(bdpp) and B(C6F5)3 or BF3. Moderate e.e-s depending strongly on the structure of the catalytic precursor have been obtained. DFT/PCM calculations reveal an SN2-type reaction mechanism for the alkyl/aryl ligand abstraction with a notably lower activation barrier for BF3.

The dialkyl/diaryl-platinum complexes (Pt(CH3)2(P-P); PtPh2(P-P) and Pt(2-Thioph)2(P-P), where P-P stands for 2,4-bis(diphenylphosphino)pentane) proved to be active hydroformylation catalysts in the presence of a boron additive (B(C6F5)3, PPh3 or BF3). The alkyl/aryl ligand abstraction by the boron additives has been proved by NMR studies and DFT/PCM calculations.Figure optionsDownload as PowerPoint slide