Electronic communication in dinuclear C-4-bridged tungsten complexes

Abstract

The dinuclear tungsten carbyne X(CO)(2)(dppe)WC4W(dppe)(CO)(2)X] (dppe = 1,2-bis(diphenylphosphino)ethane; X = 1 (3), Cl (7)) complexes were prepared from the bisacetylide precursor Li-2(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)(2)X] 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)(2)I] (11) allows reversible one-electron oxidation which results in the monocationic species I(CO)(2)(dppe)WC4W(dppe)(2)I]PF6] (11PF6]). The ``all-dppe substituted'' complex I(dppe)(2)WC4W(dppe)(2)I] (10) possesses two reversible redox states leading to the stable monocationic I(dppe)(2)WC4W(dppe)(2)I]PF6] (10PF6]) and the dicationic I(dppe)(2)WC4W(dppe)(2)I]PF6](2) (10PF6](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)(2)X] (X = 1 (5), Cl (6)), 7, 8, 10, 11 and 11PF6] were characterized by single crystal X-ray diffraction. The electronic properties of complexes 10, 10PF6], 10PF6](2), as well as of compounds 11 and 11PF6], 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 10PF6] (comproportionation constant K-c 7.5 x 10(4)) and to the strong antiferromagnetic coupling in the dicationic complex 10PF6](2) (exchange integral J = -167 cm(-1)). In addition, the rate for electron transfer between the tungsten centers in 10PF6] was evaluated by near-IR and IR studies.