Article

A reduced β-diketiminato-ligated Ni3H4 unit catalyzing H/D exchange.

Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Strasse 2, 12489 Berlin, Germany.
Journal of the American Chemical Society (Impact Factor: 10.68). 10/2010; 132(39):13684-91. DOI: 10.1021/ja106266v
Source: PubMed

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.

0 Bookmarks
 · 
139 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Two dimeric boron complexes of potentially tetradentate and trianionic β-diketiminate ligands bearing phenol substituents were prepared and characterized. The synthetic routes employed were designed to circumvent the undesirable formation of β-ketimines and 2-methylbenzoxazoles observed when traditional synthetic routes toward the target β-diketiminate ligands were attempted. The title complexes were isolated via demethylation of β-diketimine ligands and boron difluoride complexes bearing 2-anisole N-aryl substituents using boron tribromide. The resulting complexes were found to contain a unique hydrogen-bond-supported boron-oxygen-boron bridge, as confirmed by X-ray crystallography. The stability of the resulting dimeric structures relative to the corresponding monomeric, tetradentate boron complexes was studied computationally, and theory confirmed that the dimeric structures were strongly favored. The absorption spectra of the dimers were red-shifted relative to the parent β-diketimine ligands. The complexes were irreversibly oxidized and reduced electrochemically and were weakly emissive at low concentrations (Stokes shifts between 23 and 31 nm), showing little solvent dependence.
    Dalton Transactions 10/2013; · 4.10 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The catalytic system Ni(COD)2/BF3·OEt2 is highly active in the addition polymerization of nor-bornene (NB). Its activity, which is up to 1930 (kg NB) (mol Ni)−1 h−1, is higher than the activity of the other known nickel complex catalysts. Another advantage of this system over the latter is that it contains a smaller proportion of a Lewis acid (5 molar parts or below) and no conventional stabilizing organoelement ligands. The activity of this system in NB polymerization has been investigated by Fourier-transform IR spectroscopy. According to EPR data, NB polymerization is accompanied by the formation of low-spin complexes of trivalent nickel, which result from the oxidative addition of the monomer to univalent nickel complexes. A metallacyclic mechanism involving Ni(I) and Ni(III) complexes is suggested for NB polymerization.
    Kinetics and Catalysis 53(4). · 0.54 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A nickelnickel-bonded complex, [{Ni(μ-L(.-) )}2 ] (1; L=[(2,6-iPr2 C6 H3 )NC(Me)]2 ), was synthesized from reduction of the LNiBr2 precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)3 ]⋅[{Ni(μ-L(.-) )}2 ] (2; DME=1,2-dimethoxyethane), [Na(Et2 O)]Na[(L(.-) )NiNiL(2-) ] (3), and [Na(Et2 O)]2 Na[L(2-) NiNiL(2-) ] (4). Here L represents the neutral ligand, L(.-) denotes its radical monoanion, and L(2-) is the dianion. All of the four compounds feature a short NiNi bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular (1 and 2) and the coaxial (3 and 4) structure, in which the metalmetal bond axis is perpendicular to or collinear with the axes of the α-diimine ligands, respectively. The electronic structures, NiNi bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations.
    Chemistry - A European Journal 10/2013; · 5.93 Impact Factor