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

A series of (N2P2) Ni-II complexes (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-I oxidation state at moderate redox potentials for these Ni-II complexes. In situ EPR, low-temperature UV-vis, and electrochemical studies were employed to detect the formation of Ni-I species during the reduction of Ni-II precursors. Furthermore, the [(N2P2)Ni-I(CNt-Bu)](SbF6) complex was isolated upon reduction of the Ni-II precursor with 1 equiv of CoCp2 and was characterized by EPR and X-ray photoelectron spectroscopy (XPS). Finally, the (N2P2)(NiBr2)-Br-II complex 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.

Automated summary

A series of (N2P2) Ni-II complexes stabilized by a modified tetradentate pyridinophane ligand containing two phosphonite groups were synthesized and characterized. The Ni-I oxidation state was found to be accessible at moderate redox potentials for these Ni-II complexes, and the N2P2 ligand was able to support various Ni species involved in catalytic C-C bond formation reactions.