Experimental Gas-Phase Thermochemistry for Alkane Reductive Elimination from Pt(IV)

Abstract

The gas-phase reactivity of the [(NN)(PtMe3)-Me-IV](+) (NN = alpha-diimine) complex 1 and its acetonitrile adduct has been investigated by tandem mass spectrometry. The only observed reaction from the octahedral d(6) complex 1 center dot MeCN is the simple dissociation of the coordinated solvent molecule with a binding energy of 24.5(6) kcal mol(-1) measured by energy-resolved collision-induced dissociation experiments. Further reactions of 1 are observed. In addition to the expected reductive elimination of ethane from 1, competitive loss of methane occurs. Methane is generated from the initially formed ethane agostic complex via either C-H activation/bond formation or sigma-bond metathesis with the third methyl group. Energy-resolved collision-induced dissociation experiments indicate that the initial reductive C-C coupling step is rate limiting for both ethane and methane elimination, and afford a gas-phase barrier of 22.6(7) kcal mol(-1) for this process. Density functional theory calculations confirm the reaction mechanisms, and a variety of functionals are benchmarked. The results at the M06-L/SDB-cc-pVTZ//mPW1K/SDD(d,p) level of theory agree well with the experiments and suggest that the generation of [(NN)PtH](+) at higher collision energy proceeds through sequential loss of methane and ethylene.