Tritopic NHC Precursors: Unusual Nickel Reactivity and Ethylene Insertion into a C(sp3)–H Bond

Abstract

AbstractThe imidazolium chloride [C3H3N(C3H6NMe2)N{C(Me)(=NDipp)}]Cl (1; Dipp=2,6‐diisopropyl phenyl), a potential precursor to a tritopic NimineCNHCNamine pincer‐type ligand, reacted with [Ni(cod)2] to give the NiI‐NiI complex 2, which contains a rare cod‐derived η3‐allyl‐type bridging ligand. The implied intermediate formation of a nickel hydride through oxidative addition of the imidazolium C−H bond did not occur with the symmetrical imidazolium chloride [C3H3N2{C(Me)(=NDipp)}2]Cl (3). Instead, a Ni−C(sp3) bond was formed, leading to the neutral NimineCHNimine pincer‐type complex Ni[C3H3N2{C(Me)(=NDipp)}2]Cl (4). Theoretical studies showed that this highly unusual feature in nickel NHC chemistry is due to steric constraints induced by the N substituents, which prevent Ni−H bond formation. Remarkably, ethylene inserted into the C(sp3)−H bond of 4 without nickel hydride formation, thus suggesting new pathways for the alkylation of non‐activated C−H bonds.