Metal Alkoxides. Models for Metal Oxides. Alkoxide Ligands in Early Transition Metal Organometallic Chemistry. Final Technical Report

摘要

Structural analogies between polynuclear metal alkoxides/metal oxoalkoxides and metal oxides have been noted, with the former providing models for the subunits within the extended networks of the latter. The presence of metal-metal bonds imposes a rigidity to alkoxide clusters in solution and the nuclearity of the cluster is maintained. The ability of alkoxide ligands to act as terminal or bridging ligands ( mu sub 2 and mu sub 3 ) and to respond to electron-deficient metal centers by pi donation, together with their ability to interconvert between these various modes of bonding allows for the uptake and release of substrate molecules. An extensive organometallic chemistry supported by alkoxide ligands is emerging. Key findings during the reporting period have been: (1) the reduction of carbon-monoxide by molybdenum and tungsten alkoxides; (2) the coupling, co-coupling and sometimes metathesis-like reactions between C-C, C-N, and M-M triple bonds supported by alkoxide ligands; (3) unusual beta -hydrogen effects in alkyl ligands bonded to M sub 2 (OR)/sub x/ centers; (4) the isolation of quadruple bonds between Mo atoms supported by RO ligands; (5) the synthesis of new hydrido-tungsten alkoxides of formula NaW sub 2 (H)(OR) sub 8 ; and (6) the synthesis and characterization of the first examples of carbido, nitrido, imido and alkylidyne clusters of tungsten and molybdenum supported by alkoxide ligands. MO calculations employing Extended Huckel or Fenske-Hall methods have been performed on several of these cluster alkoxides and the results compared with observed spectrochemical and electrochemical data. (ERA citation 11:041184)