Indenylmethyl-molybdenum and -tungsten compounds containing isocyanide ligands. Formation and study of isomeric eta(2)-iminoacyls and eta(3)-1-azaallyls

Mild thermolysis of benzene solutions of the methylisocyanides [M(eta(5)-C9H7)Me(CO)(2)(CNBut)] (M = Mo or W) cleanly afforded mixtures of isomeric dihapto-iminoacyls [M(eta(5)-C9H7){eta(2)-C(=NBut)Me}(CO)(2)] and trihaptoazaallyls [M(eta(5)-C9H7){eta(3)-H2CC(H)NBut} (CO)(2)]. Compared to such transformations in cyclopentadienyl-or methyl-substituted cyclopentadienyl-containing analogues investigated previously, a significantly greater proportion of the dihapto-iminoacyl products are generated. Solution NMR studies of the products demonstrated that both types of complex are fluxional at room temperature; for the eta(2)-iminoacyls the fluxionality being conveniently envisaged as a rotation of the bound nitrogen-containing fragment about an axis passing through the metal atom and the ligand centroid. In the case of the azaallyl products the temporary attainment of a planar metallaazacyclobutenyl structure is invoked to explain the dynamic behaviour. Two compounds, [W(eta(5)-C9H7)Me(CO)(2)(CNBut)] and [W(eta(5)-C9H7){eta(2)-C(=NBut)Me}(CO)(2)] have been characterized in the solid state by single-crystal X-ray diffraction.