Metal alkoxides: models for metal oxides. 7. Trinuclear and tetranuclear alkylidyne clusters of tungsten supported by alkoxide ligands

Abstract

The ethylidyne capped triangulo compound W/sub 3/(..mu../sub 3/-CMe)(..mu../sub 2/-O-i-Pr)/sub 3/(O-i-Pr)/sub 6/ is formed in the reaction between W/sub 2/(O-i-Pr)/sub 6/(py)/sub 2/ and 1 equiv of MeC identical with CMe. Similarly, (t-BuO)/sub 3/ W identical with CMe and Mo/sub 2/(O-i-Pr)/sub 6/ react in hexane/i-PrOH to give Mo/sub 2/ W(CMe)(O-i-Pr)/sub 9/ which is isomorphous with the tritungsten compound. The W/sub 3/(CMe)(O-i-Pr)/sub 9/ molecule has virtual C/sub 3v/ symmetry. Variable-temperature /sup 1/H NMR studies on the W/sub 3/ and Mo/sub 2/W compounds indicate that a similar structure is maintained in solution and that site exchange between the terminal O-i-Pr ligands involves a pseudorotation mechanism. The reaction between (Me/sub 3/SiCH/sub 2/)/sub 4/ W/sub 2/(..mu..-CSiMe/sub 3/)/sub 2/ and excess EtOH in hexane yields W/sub 4/-(CSiMe/sub 3/)/sub 2/(OEt)/sub 14/ and Me/sub 4/Si. The molecule may be viewed as a dimer (W/sub 2/(..mu..-CSiMe/sub 3/)(OEt)/sub 7/)/sub 2/ with the two halves joined by a pair of alkoxy bridges. Each tungsten is in a distorted octahedral geometry, and the W/sub 4/C/sub 2/O/sub 14/ core represents the fusing together of two confacial bioctahedra along a common edge. The ..mu..-CSiMe/sub 3/ ligand occupies one site of the face shared by two tungsten atoms. These are the first trinuclear and tetranuclear alkylidynemore » clusters of tungsten supported exclusively by alkoxide ligands. 22 references, 5 figures, 7 tables.« less