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

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posted on 2010-10-06, 00:00 authored by Stefan Pfirrmann, Christian Limberg, Christian Herwig, Christina Knispel, Beatrice Braun, Eckhard Bill, Reinhard Stösser
An investigation concerning the stepwise reduction of the β-diketiminato nickel(II) hydride dimer [LNi(μ-H)2NiL], 1 (L = [HC(CMeNC6H3(iPr)2)2]), has been carried out. While the reaction with one equivalent of potassium graphite, KC8, led to the mixed valent NiI/NiII complex K[LNi(μ-H)2NiL], 3, treatment of 1 with two equivalents of KC8 surprisingly yielded in the trinuclear complex K2[LNi(μ-H)2Ni(μ-H)2NiL], 4, in good yields. The Ni3H4 core contains one NiII and two NiI 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 NiII2NiI compound K[LNi(μ-H)2Ni(μ-H)2NiL], 5, and treatment with CO leads to the elimination of H2 with formation of the carbonyl complex K2[LNi(CO)]2, 6. Beyond that, it could be shown that 4 undergoes H/D exchange with deuterated solvents and the deuteride-compound 4-D4 reacts with H2 to give back 4. The crystal structures of the novel compounds 36 have been determined, and their electronic structures have been investigated by EPR and NMR spectroscopy, magnetic measurements, and DFT calculations.