P‐C Bond Cleavage in Platinum Complexes Containing bis (Diphenylphosphino) Methane Promoted with a Phase‐Transfer Catalyst

With a phase-transfer catalyst, Pt-dppm (dppm = Ph2PCH2PPh2) complexes undergo basic hydrolysis, in which a dppm ligand is hydrolyzed to produce PPh2Me and PPh2OH (or PPh2O). The ease of this hydrolysis reaction depends partly on the molecular charges of the metal complexes. Hydrolysis of neutral [Pt(dppm)(L-L)] (L-L = S2CO2, S2P(O)(OEt)2− and mnt = S2C2(CN)22−) is slower than that of monocationic [Pt(dppm)(L′-L′)]Cl (L′-V = S2CNEt2-, (CH2)2S(O)Me and acetylacetonate) compounds. Among the neutral compounds, hydrolysis of [Pt(dppm)(mnt)] is more rapid than that of the other two. These results are rationalized according to the ease with which partial positive charges are induced on the dppm phosphorus atoms. The steric effect due to ligands trans to dppm also influences the rate of hydrolysis of Pt-dppm compounds. When trans ligands are Ph2P(CH)2PPh2, Ph2P(CH2)3PPh2 and (Ph2PO2)H, no hydrolysis of dppm occurs. Hydrolysis of Pt-dppm compounds depends further on the concentrations of both the phase-transfer catalyst and OH− ions. All these results are consistent with nucleophilic attack of OH− on dppm phosphorus atoms to release strain in the Pt-dppm ring.

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