Synthesis and Reactivity of (N2P2)Ni Complexes Stabilized by a Diphosphonite Pyridinophane Ligand

A series of (N2P2)Ni^IIcomplexes (N2P2 =P,P′-ditertbutyl-2,11-diphosphonito[3.3](2,6)pyridinophane) stabilized by a modified tetradentate pyridinophane ligand containing two phosphonite groups were synthesized and characterized. Cyclic voltammetry (CV) studies revealed the accessibility of the Ni^Ioxidation state at moderate redox potentials for these Ni^IIcomplexes.In situEPR, low-temperature UV-vis, and electrochemical studies were employed to detect the formation of Ni^Ispecies during the reduction of Ni^IIprecursors. Furthermore, the [(N2P2)Ni^I(CNt-Bu)](SbF₆) complex was isolated upon reduction of the Ni^IIprecursor with 1 equiv of CoCp₂and was characterized by EPR and X-ray photoelectron spectroscopy (XPS). Finally, the (N2P2)Ni^IIBr₂complex acts as an efficient catalyst for the Kumada cross-coupling of an aryl halide with an aryl or alkyl Grignard, suggesting that the N2P2 ligand can support the various Ni species involved in the catalytic C-C bond formation reactivity.