@article {2627, title = {Noninnocent Behavior of Ancillary Ligands: Apparent Trans Coupling of a Saturated N-Heterocyclic Carbene Unit with an Ethyl Ligand Mediated by Nickel}, journal = {Journal of the American Chemical Society}, volume = {131}, number = {30}, year = {2009}, note = {ISI Document Delivery No.: 479FFTimes Cited: 6Cited Reference Count: 26Steinke, Tobias Shaw, Bryan K. Jong, Howard Patrick, Brian O. Fryzuk, Michael D. Green, Jennifer C.}, month = {Aug}, pages = {10461-10466}, type = {Article}, abstract = {Oxidative addition of the tridentate N-heterocyclic carbene (NHC) diphosphine ligand precursor ([PCP]H)PF6 (1) {[PCP] = o-(Pr2PC6H4)-Pr-i(NC3H4N)o-(C6H4PPr2)-Pr-i} to Ni(COD)(2) results in the formation of the nickel(II) hydride complex ([PCP]NiH)PF6 (2). This hydride undergoes a rapid reaction with ethylene to generate a nickel(O) complex in which an ethyl group has been transferred to the carbene carbon of the original NHC-diphosphine ligand. If the first intermediate is the anticipated square-planar nickel(II) ethyl species, then the formation of the product would require a process that involves a trans C-C coupling of the NHC carbon and a presumed Ni-ethyl intermediate. Deuterium-labeling studies provide evidence for migratory insertion of the added ethylene into the Ni-H bond rather than into the Ni-catene linkage; this is based on the observed deuterium scrambling, which requires reversible P-elimination, alkene rotation, and hydride readdition. However, density functional theory studies suggest that a key intermediate is an agostic ethyl species that has the Ni-C bond cis to the NHC unit. A possible transition state containing two cis-disposed carbon moieties was also identified. Such a process represents a new pathway for catalyst deactivation involving NHC-based metal complexes.}, keywords = {ACTIVATION, CHEMISTRY, COMPLEXES, MECHANISM, MIGRATORY INSERTION, NHC, ORGANOMETALLIC CATALYSIS, palladium, REDUCTIVE ELIMINATION, ruthenium}, isbn = {0002-7863}, url = {://000268644400040}, author = {Steinke, T. and Shaw, B. K. and Jong, H. and Patrick, B. O. and Fryzuk,Michael D. and Green, J. C.} }