Oxidatively Induced Reductive N Binding: A Dinickel-Bridging Bent N Radical Anion and Its Redox-Triggered N Release.

Nitrogenase accumulates reducing equivalents in hydrides and couples H elimination to the reductive binding of N at a di-iron edge of its FeMo cofactor (FeMoco). Here, we describe that oxidation of a pyrazolato-based dinickel(II) dihydride complex K[L(Ni-H)] (), either electrochemically or chemically using H or ferrocenium, triggers H elimination and binding of N in a constrained and extremely bent bridging mode in [LNi(μ-N)] (). Spectroscopic and computational evidence indicate that the electronic structure of is best described as Ni-(N)-Ni, with a rare 1e reduced and significantly activated N substrate ( = 1894 cm).

Reductive O Binding at a Dihydride Complex Leading to Redox Interconvertible μ-1,2-Peroxo and μ-1,2-Superoxo Dinickel(II) Intermediates.

Dioxygen activation at nickel complexes is much less studied than for the biologically more relevant iron or copper systems but promises new reactivity patterns because of the distinct coordination chemistry of nickel. Here we report that a pyrazolate-based dinickel(II) dihydride complex [KL(Ni-H)] (1a) smoothly reacts with O via reductive H elimination to give the μ-1,2-peroxo dinickel(II) complex [KLNi(O)] (2a) and, after treatment with dibenzo[18]-crown-6, the separated ion pair [K(DB18C6)][LNi(O)] (2b); these are the first μ-1,2-peroxo dinickel intermediates to be characterized by X-ray diffraction. In 2a, the K is found side-on associated with the peroxo unit, revealing a pronounced weaking of the O-O bond: d(O-O) = 1.

Pairwise H/D Exchange and H Substitution at a Bimetallic Dinickel(II) Complex Featuring Two Terminal Hydrides.

A compartmental ligand scaffold HL with two β-diketiminato binding sites spanned by a pyrazolate bridge gave a series of dinuclear nickel(II) dihydride complexes M[LNi(H)], M = Na (Na·2) and K (K·2), which were isolated after reacting the precursor complex [LNi(μ-Br)] (1) with MHBEt (M = Na and K). Crystallographic characterization showed the two hydride ligands to be directed into the bimetallic pocket, closely interacting with the alkali metal cation. Treatment of K·2 with dibenzo(18-crown-6) led to the separated ion pair [LNi(H)][K(DB18C6)] (2[K(DB18C6)]).