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

Pincer protic N-heterocyclic carbene (PNHC) complexes were synthesized by direct metalation, the formation of a metal carbon bond from an unfunctionalized CH 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 1H, 13C, and 15N 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 OH bonds to alkynes, including catalyzed alkyne hydration, were demonstrated on the Pt triflate analog.