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Nippe M, Victor E, Berry JF: Oxidation chemistry of axially protected Mo (2) and W (2) quadruply bonded compounds. Inorg Chem. 2009 Dec 21;48(24):11889-95.
Reported is a facile, high-yielding one-pot synthesis of the quadruply bonded ditungsten (II,II) compound W (2)(dpa)(4) (1) (dpa = 2,2'-dipyridylamide), which was obtained from W (CO)(6) at high temperature in naphthalene. A similar reaction in 1,2-dichlorobenzene furnished a ditungsten (III, III) species as the major product that was crystallized as [W (2)(dpa)(3) Cl (2)][BPh (4)] (3). The [W (2)(dpa)(3) Cl (2)](+) cation is better prepared by oxidation of 1 with SO (2) Cl (2). Compound 1 was characterized by X-ray crystallography and cyclic-voltammetry, and is compared with its earlier reported molybdenum analogue, Mo (2)(dpa)(4) (2). One-electron oxidation products of 1 and 2, [W (2)(dpa)(4)][BPh (4)] (1BPh (4)) and [Mo (2)(dpa)(4)][BPh (4)] (2BPh (4)), respectively, have also been synthesized. The crystallographically determined metal-metal distances of 2.23 A and 2.14 A in 1BPh (4) and 2BPh (4), respectively, are in agreement with metal-metal bond orders of 3.5. Unlike most previously reported Mo (2)(5+) and W (2)(5+) compounds, the primary coordination spheres around the M (2)-units in 1/1BPh (4) and 2/2BPh (4) remain unchanged upon one-electron oxidation, because the tridentate dpa ligand hinders axial coordination of exogenous ligands. |
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