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Electronic Communication in Dinuclear C4-Bridged Tungsten Complexes

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posted on 2010-03-10, 00:00 authored by Sergey N. Semenov, Olivier Blacque, Thomas Fox, Koushik Venkatesan, Heinz Berke
The dinuclear tungsten carbyne [X(CO)2(dppe)WC4W(dppe)(CO)2X] (dppe = 1,2-bis(diphenylphosphino)ethane; X = I (3), Cl (7)) complexes were prepared from the bisacetylide precursor Li2[(CO)3(dppe)WC4W(CO)3(dppe)] (2) via oxidative replacement of one CO group at each tungsten center with a halide substituent. The iodide ligand in 3 could be substituted with isothiocyanate or triflate resulting in [X(CO)2(dppe)WC4W(dppe)(CO)2X] complexes (X = NCS (8), OTf (9)). Substitution of two and all four CO ligands in 3 was achieved via subsequent photolytic or thermal activation with dppe. The “half-substituted” complex [I(CO)2(dppe)WC4W(dppe)2I] (11) allows reversible one-electron oxidation which results in the monocationic species [I(CO)2(dppe)WC4W(dppe)2I][PF6] (11[PF6]). The “all-dppe substituted” complex [I(dppe)2WC4W(dppe)2I] (10) possesses two reversible redox states leading to the stable monocationic [I(dppe)2WC4W(dppe)2I][PF6] (10[PF6]) and the dicationic [I(dppe)2WC4W(dppe)2I][PF6]2 (10[PF6]2) compounds. The complexes 2, 3, [W(CO)3(dppe)(CCPh)(I)] (4), [X(CO)2(dppe)WC−C(Me)C(Me)−CW(dppe)(CO)2X] (X = I (5), Cl (6)), 7, 8, 10, 11 and 11[PF6] were characterized by single crystal X-ray diffraction. The electronic properties of complexes 10, 10[PF6], 10[PF6]2, as well as of compounds 11 and 11[PF6], were investigated using cyclic voltammetry (CV), EPR, IR, near-IR spectroscopy, and magnetization measurements. These studies showed that the [W]C−CC−C[W] canonical form of the bridged system with strong tungsten−carbon interaction contributes significantly to the electronic coupling in the mixed-valent species 10[PF6] (comproportionation constant Kc = 7.5 × 104) and to the strong antiferromagnetic coupling in the dicationic complex 10[PF6]2 (exchange integral J = −167 cm−1). In addition, the rate for electron transfer between the tungsten centers in 10[PF6] was evaluated by near-IR and IR studies.