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(η⁵-C₉H₇)Me(CO)₂ (CNBu^t)] (M = Mo or W) cleanly afforded mixtures of isomeric dihapto-iminoacyls [M(η⁵-C₉H₇){η² -C(=NBu^t)Me}(CO)₂] and trihapto-azaallyls [M(η⁵-C₉H₇){η³ -H₂CC(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 η²-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(η⁵-C₉H₇)Me(CO)₂ (CNBu^t)] and [W(η⁵-C₉H₇){η² -C(=NBu^t)Me}(CO)₂] have been characterized in the solid state by single-crystal X-ray diffraction.

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