Synthetic investigations of low-coordinate (N-phosphino-amidinate) nickel chemistry: agostic alkyl complexes and benzene insertion into Ni–H

Abstract

Treatment of (PN)NiX (X = NHdipp or OtBu; PN = N-phosphinoamidinate ligand) with Me₂PhSiH in benzene solvent afforded the crystallographically characterized, antifacial-coordinated, dinuclear species 1, the formation of which corresponds to the hitherto unknown net Ni–H addition of two equivalents of the putative (PN)NiH intermediate across CC units within a single benzene molecule. Computational analysis supports the view of 1 as being comprised of two cationic (PN)Ni^II fragments ligated by a substituted butadiene dianion μ²–η³:η³-C₆H₈²⁻ bridging group. Also described is the formation and characterization of three-coordinate (PN)Ni(alkyl) complexes stabilized by β-agostic (alkyl = Et, 2; n-Bu, 3; n-hexyl, 4) or γ-agostic (alkyl = neopentyl, 5) interactions, and our efforts to employ 2 and 3 as synthons for the generation of (PN)NiHvia β-hydride elimination. Notably, compound 5 represents both the first crystallographically characterized three-coordinate Ni-alkyl complex featuring a heterobidentate ligation, and the first neutral γ-agostic Ni^II-alkyl complex.