Evidence for the Existence of Terminal Scandium Imidos: Mechanistic Studies Involving Imido–Scandium Bond Formation and C–H Activation Reactions

Arene C-H amination at nickel in terphenyl-diphosphine complexes with labile metal-arene interactions

The meta-terphenyl diphosphine, m-P2, 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-P2)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=CH3CN, CO, Ph2CN2), Ni(I)X complexes (3-X: X=Cl, BF4, N3, N3B(C6F5)3), and [(m-P2)Ni(II)Cl2] (4). Complex 2 reacts with substrates, such as diphenyldiazoalkane, sulfur ylides (Ph2 S=CH2 ), organoazides (RN3: R=para-C6H4OMe, para-C6H4CF3, 1-adamantyl), and N2O 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-Ph2CN2), 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.