Hydrogen-Bonding Pincer Complexes with Two Protic N-Heterocyclic Carbenes from Direct Metalation of a 1,8-Bis(imidazol-1-yl)carbazole by Platinum, Palladium, and Nickel

摘要

Pincer protic N-heterocyclic carbene (PNHC) complexes were synthesized by direct metalation, the formation of a metal carbon bond from an unfunctionalized C-H bond in a single synthetic step. Significantly, direct metalation succeeded even for a first-row metal, nickel. The chloride complexes were isolated and then converted to the acetate, triflate, or in the platinum case, a hydride analogue. Crystal structures and H-1, C-13, and N-15 NMR data, as well as IR spectra, document the effects of intramolecular hydrogen bonding and the planar but flexible pincer framework. Anti-Markovnikov addition of O-H bonds to alkynes, including catalyzed alkyne hydration, were demonstrated on the Pt triflate analog.