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

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.