A new class of homoleptic 12-electron molybdenum and tungsten alkoxide clusters of formula [M4(OR)12

Abstract

The authors are interested in developing efficient synthetic routes to alkoxide-supported molybdenum and tungsten clusters that may prove to be excellent models for fragments of reduced oxides of the same metals. These clusters should include both coordinative unsaturation and redox flexibility at the metal centers to initiate organometallic chemistry upon substrate reduction. Complementary metal oxide model systems such as polyoxoanions may prove effective for oxidation catalysis. They have recently demonstrated that W/sub 2/(O-i-Pr)/sub 6/ (I) exists in reversible equilibrium with its 12-electron cluster W/sub 4/(O-i-Pr)/sub 12/ (II) in solution at room temperature, eq 1, whereas Mo/sub 2/(O-i-Pr)/sub 6/ is indefinitely stable with respect to cluster formation. Even by reducing the steric demands at the molybdenum center they were unable to induce the formation of new metal-metal bonds in (Mo/sub 2/(O-i-Pr)/sub 5/(OMe))/sub 2/ (III), which instead retains isolated, unbridged Mo-Mo triple bonds. The authors report here the isolation and characterization of members of a new class of 12-electron tetranuclear alkoxide clusters, IV-XI, which are spectroscopically isostructural for both molybdenum and tungsten together with the single-crystal X-ray diffraction structure of one derivative, (Mo/sub 4/(O-CH/sub 2/-c-Bu)/sub 12/(HO-CH/sub 2/-c-Bu)) (XI) (where c-Bu = cyclobutyl). This represents the first group of structurally related homoleptic alkoxidemore » clusters for molybdenum and tungsten in oxidation state (3+).« less