An Unsaturated Nickel(0) NHC Catalyst: Facile Preparation and Structure of Ni(0)(NHC)2, Featuring a Reduction Process from Ni(II)(NHC)(acac)2

A facile synthetic route to Ni(0)(NHC)(2) from stable Ni(II)(acac)(2) was established without common but labile Ni(0) precursors. The intermediate is a divalent mono-NHC adduct of Ni(acac)(2), Ni(NHC)(acac)(2). Reduction of Ni(NHC)(acac)(2) in both the presence and absence of an NHC ligand gave Ni(NHC)(2) in ca. 90% and 40% conversions, respectively. Ni(NHC)(2), especially with bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, has strong Ni-C(carbene) bonds and remarkable anagostic Ni-H(methyl) interactions, stabilizing its 14e unsaturated structure.