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Synthesis and Reactivity of (N2P2)Ni Complexes Stabilized by a Novel Diphosphonite Pyridinophane Ligand
preprintsubmitted on 02.01.2021, 21:54 and posted on 04.01.2021, 13:22 by Kei Fuchigami, Michael B. Watson, Giang N. Tran, Nigam P. Rath, Liviu M. Mirica
A series of (N2P2)NiII 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 NiI oxidation state at moderate redox potentials for these NiII complexes. In situ EPR, low-temperature UV-vis, and electrochemical studies were employed to detect the formation of NiI species during the reduction of NiII precursors. Furthermore, the [(N2P2)NiI(CNtBu)](SbF6) complex was isolated upon reduction of the NiII precursor with 1 equiv of CoCp2, and was characterized by EPR and X-ray photoelectron spectroscopy (XPS). Finally, the (N2P2)NiIIBr2 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.