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 0
  • [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 10/2013; · 5.93 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: After the lithiation of PYR-H(2) (PYR(2-) =[{NC(Me)C(H)C(Me)NC(6) H(3) (iPr)(2) }(2) (C(5) H(3) N)](2-) ), which is the precursor of an expanded β-diketiminato ligand system with two binding pockets, its reaction with [NiBr(2) (dme)] led to a dinuclear nickel(II)-bromide complex, [(PYR)Ni(μ-Br)NiBr] (1). The bridging bromide ligand could be selectively exchanged for a thiolate ligand to yield [(PYR)Ni(μ-SEt)NiBr] (3). In an attempt to introduce hydride ligands, both compounds were treated with KHBEt(3) . This treatment afforded [(PYR)Ni(μ-H)Ni] (2), which is a mixed valent Ni(I) μ-HNi(II) complex, and [(PYR-H)Ni(μ-SEt)Ni] (4), in which two tricoordinated Ni(I) moieties are strongly antiferromagnetically coupled. Compound 4 is the product of an initial salt metathesis, followed by an intramolecular redox process that separates the original hydride ligand into two electrons, which reduce the metal centres, and a proton, which is trapped by one of the binding pockets, thereby converting it into an olefin ligand on one of the Ni(I) centres. The addition of a mild acid to complex 4 leads to the elimination of H(2) and the formation of a Ni(II) Ni(II) compound, [(PYR)Ni(μ-SEt)NiOTf] (5), so that the original Ni(II) (μ-SEt)Ni(II) X core of compound 3 is restored. All of these compounds were fully characterized, including by X-ray diffraction, and their molecular structures, as well as their formation processes, are discussed.
    Chemistry 01/2013; · 5.93 Impact Factor
  • [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; · 3.81 Impact Factor