Indenylmethyl-molybdenum and -tungsten compounds containing isocyanide ligands. Formation and study of isomeric η2-iminoacyls and η3-1-azaallyls

Abstract

Mild thermolysis of benzene solutions of the methylisocyanides [M(η ⁵ -C ₉ H ₇ )Me(CO) ₂ (CNBu ^t )] (M = Mo or W) cleanly afforded mixtures of isomeric dihapto-iminoacyls [M(η ⁵ -C ₉ H ₇ ){η ² -C(NBu ^t )Me}(CO) ₂ ] and trihapto-azaallyls [M(η ⁵ -C ₉ H ₇ ){η ³ -H ₂ CC(H)NBu ^t }(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 η 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(η ⁵ -C ₉ H ₇ )Me(CO) ₂ (CNBu ^t )] and [W(η ⁵ -C ₉ H ₇ ){η ² -C(NBu ^t )Me}(CO) ₂ ] have been characterized in the solid state by single-crystal X-ray diffraction.