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

Abstract

The gas-phase reactivity of the [(NN)PtIVMe3]+ (NN = α-diimine) complex 1 and its acetonitrile adduct has been investigated by tandem mass spectrometry. The only observed reaction from the octahedral d6 complex 1·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 σ-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.