Organonitrogen groups in metal carbonyl complexes. Part V. Fluxional behaviour of aza-allyl/allene †; complexes

Abstract

Variable-temperature ¹H n.m.r. studies of the complexes [(π-C₅H₅)M(CO)₂{(p-tolyl)₂CNC(p-tolyl)₂}](M = Mo or W), showed the molecules to be fluxional, the observed temperature dependance being consistent with the occurrence of two distinct averaging processes within the aza-allyl/allene ligand. Further structural information was obtained from the ¹H n.m.r. spectra of the compounds [(π-C₅H₅)Mo(CO)₂{(R′C₆H₄)(R″C₆H₄)CNC(R′C₆H₄)-(R″C₆H₄)}](R′=p-Me, R″=p-OMe or H) which showed that at low temperatures, certain orientations of the CR₂ groups with respect to the rest of the ligand are preferred. Kinetic measurements made from the ¹⁹F n.m.r. spectra of the compounds [(π-C₅H₅)M(CO)₂{(p-CF₃C₆H₄)₂CNC(p-CF₃C₆H₄)₂}](M = Mo or W) gave values for E_a of 11·6 and 6·8 kcal/mol respectively.