INDENYLMETHYL-MOLYBDENUM AND INDENYLMETHYL-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 i someric 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)]. Co mpared to such transformations in cyclopentadienyl-or methyl-substitut ed cyclopentadienyl-containing analogues investigated previously, a si gnificantly greater proportion of the dihapto-iminoacyl products are g enerated. Solution NMR studies of the products demonstrated that both types of complex are fluxional at room temperature; for the eta(2)-imi noacyls 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 pr oducts the temporary attainment of a planar metallaazacyclobutenyl str ucture 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}(C O)(2)] have been characterized in the solid state by single-crystal X- ray diffraction.