Protonolysis of Platinum(II) and Palladium(II) Methyl Complexes: A Combined Experimental and Theoretical Investigation

Abstract

The protonolysis of platinum(II) and palladium(II) methyl complexes has been investigated by both experiment and computation. Previously the protonolysis of (COD)PtII(CH3)2 by CF3COOY or (dppe)PdII(CH3)2 by CF3CY2OY (Y = H, D) was found to be accompanied by abnormally large and highly temperature-dependent kinetic isotope effects (KIEs), suggesting the involvement of tunneling. Here we find normal KIEs and no evidence of tunneling for protonolysis of (tmeda)PtII(CH3)Cl by CF3COOY (Y = H, D). Density functional theory (DFT) calculations indicate that protonation at the metal center followed by reductive coupling to the methane σ adduct (stepwise pathway) is favored for Pt complexes with good electron donor ligands, whereas direct protonation of the M−CH3 bond to generate the methane σ adduct (concerted pathway) is favored for Pt with electron-withdrawing ligands as well as for Pd. We suggest that KIE behavior consistent with tunneling may be an experimental indicator of the concerted pathway.