A Reduced β-Diketiminato-Ligated Ni_3H_4 Unit Catalyzing H/D Exchange

摘要

An investigation concerning the stepwise reduction of the β-diketiminato nickel(Ⅱ) hydride dimer [LNi(μ-H)_2NiL], 1 (L = [HC(CMeNC_6H_3(/Pr)_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)_2NiL], 3, treatment of 1 with two equivalents of KC_8 surprisingly yielded in the trinuclear complex K_2[LNi(μ-H)_2Ni(μ-H)_2NiL], 4, in good yields. The Ni_3H_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_2Ni~Ⅰ compound K[LNi(μ-H)_2Ni(μ-H)_2NiL], 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.