A Reduced β-Diketiminato-Ligated Ni₃H₄ Unit Catalyzing H/D Exchange

Abstract

An investigation concerning the stepwise reduction of the β-diketiminato nickel(II) hydride dimer [LNi(μ-H)(2)NiL], 1 (L = [HC(CMeNC(6)H(3)(iPr)(2))(2)](-)), has been carried out. While the reaction with one equivalent of potassium graphite, KC(8), led to the mixed valent Ni(I)/Ni(II) complex K[LNi(μ-H)(2)NiL], 3, treatment of 1 with two equivalents of KC(8) surprisingly yielded in the trinuclear complex K(2)[LNi(μ-H)(2)Ni(μ-H)(2)NiL], 4, in good yields. The Ni(3)H(4) core contains one Ni(II) and two Ni(I) centers, which are antiferromagnetically coupled so that a singlet ground state results. 4 represents the first structurally characterized molecular compound with three nickel atoms bridged by hydride ligands, and it shows a very interesting chemical behavior: Single-electron oxidation yields in the Ni(II)(2)Ni(I) compound K[LNi(μ-H)(2)Ni(μ-H)(2)NiL], 5, and treatment with CO leads to the elimination of H(2) with formation of the carbonyl complex K(2)[LNi(CO)](2), 6. Beyond that, it could be shown that 4 undergoes H/D exchange with deuterated solvents and the deuteride-compound 4-D(4) reacts with H(2) to give back 4. The crystal structures of the novel compounds 3-6 have been determined, and their electronic structures have been investigated by EPR and NMR spectroscopy, magnetic measurements, and DFT calculations.

Catalytic Hydrogen/Deuterium Exchange of Unactivated Carbon–Hydrogen Bonds by a Pentanuclear Electron‐Deficient Nickel Hydride Cluster

“…The 1 H NMR hydride chemical shift is only modestly affected by temperature, which suggests a smaller contact shift for the hydride nuclei relative to the 31 P nuclei, consistent with related reports of a temperature dependence of hydride resonances in a Ni I -Ni II -Ni I trinuclear hydride. [10] Full details for the model are provided in the Supporting Information.…”

Synthesis, Spectroscopy, and Hydrogen/Deuterium Exchange in High-Spin Iron(II) Hydride Complexes

“…11 The relaxation of 1 H nuclei directly bonded to the paramagnetic metal is particularly rapid, and to our knowledge no metal-bound 1 H nuclei have been detected in NMR spectra of hydride complexes with a paramagnetic ground state. 12,13 Another challenge is that the paramagnetic hydride complexes in Chart 1 are highly reactive: for example, they cleave B–C bonds 14 and reductively eliminate H 2 with light or with added ligands 3 including N 2 . 8,15 Though the high reactivity of the hydrides makes them difficult to handle, their reactivity is also an opportunity to form new C–H bonds, because the M–H bonds undergo rapid [1,2]-addition to practically all multiple bonds in organic molecules.…”

High‐Frequency Fe–H Vibrations in a Bridging Hydride Complex Characterized by NRVS and DFT

“…[13] Murray has prepared Fe 3 H 3 species with a related ligand environment and high-spin iron(II) ions, but no direct spectroscopic detection of hydrides was reported. [14] Limberg and Yang have studied related nickel hydride complexes, [15],[16] but neither report assigned hydride bands in the IR spectra. In a recent paper, Ohki has described IR stretching bands for iron-hydride clusters.…”