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

The imidazolium chloride [C3 H3 N(C3 H6 NMe2 )N{C(Me)(=NDipp)}]Cl (1; Dipp=2,6-diisopropyl phenyl), a potential precursor to a tritopic Nimine CNHC Namine 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 [C3 H3 N2 {C(Me)(=NDipp)}2 ]Cl (3). Instead, a Ni-C(sp3 ) bond was formed, leading to the neutral Nimine CHNimine pincer-type complex Ni[C3 H3 N2 {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.