Arene C-H Amination at Nickel in Terphenyl–Diphosphine Complexes with Labile Metal–Arene Interactions

Abstract

The meta-terphenyl diphosphine, m-P_2, 1, was utilized to support Ni centers in the oxidation states 0, I, and II. A series of complexes bearing different substituents or ligands at Ni was prepared to investigate the dependence of metal–arene interactions on oxidation state and substitution at the metal center. Complex (m-P_2)Ni (2) shows strong Ni^0–arene interactions involving the central arene ring of the terphenyl ligand both in solution and the solid state. These interactions are significantly less pronounced in Ni^0 complexes bearing L-type ligands (2-L: L=CH_3CN, CO, Ph_2CN_2), Ni^IX complexes (3-X: X=Cl, BF_4, N_3, N_3B(C_6F_5)_3), and [(m-P_2)Ni^(II)Cl_2] (4). Complex 2 reacts with substrates, such as diphenyldiazoalkane, sulfur ylides (Ph_2=CH_2), organoazides (RN_3: R=para-C_6H_4OMe, para-C_6H_4CF_3, 1-adamantyl), and N_2O with the locus of observed reactivity dependent on the nature of the substrate. These reactions led to isolation of an η^1-diphenyldiazoalkane adduct (2-Ph_2CN_2), methylidene insertion into a Ni-P bond followed by rearrangement of a nickel-bound phosphorus ylide (5) to a benzylphosphine (6), Staudinger oxidation of the phosphine arms, and metal-mediated nitrene insertion into an arene C-H bond of 1, all derived from the same compound (2). Hydrogen-atom abstraction from a Ni^I–amide (9) and the resulting nitrene transfer supports the viability of Ni–imide intermediates in the reaction of 1 with 1-azido-arenes.

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