Gas-Phase energetics of reductive elimination from a Palladium(II) N-heterocyclic carbene complex

Abstract

Energy-resolved collision-induced dissociation experiments using tandem mass spectrometry are reported for an phenylpalladium N-heterocyclic carbene (NHC) complex. Reductive elimination of an NHC ligand as a phenylimidazolium ion involves a barrier of 30.9(14) kcal mol-1, whereas competitive ligand dissociation requires 47.1(17) kcal mol-1. The resulting threecoordinate palladium complex readily undergoes reductive C-C coupling to give the phenylimidazolium π complex, for which the binding energy was determined to be 38.9(10) kcalmol-1. Density functional calculations at the M06L//BP86/TZP level of theory are in very good agreement with experiment. In combination with RRKM modeling, these results suggest that the rate-determining step for the direct reductive elimination process switches from the C-C coupling step to the fragmentation of the resulting a complex at low activation energy. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.