Coffey, Therese Anne; (1998) Structural and reactivity studies of bis(imido) complexes of molybdenum (VI). Doctoral thesis (Ph.D.), University College London.

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Abstract

This thesis concerns the synthesis, structure and reactivity of bis(imido) complexes of molybdenum. Eleven new complexes of the type, [Mo(NR)2(S2CNEt2)2], are synthesised upon reaction of [Mo(NR)2C12(DME)] with sodium diethyldithiocarbamate, differing only by the imido substituent. Crystal structures of [Mo(NtBu)2(S2CNEt2)2] and [Mo(N(2- Me)C6H4)2(S2CNEt2)2] exhibit linear-linear imido ligation. The crystal structure of [Mo(NPh)2(S2CNEt2)2] 1, re-determined at room temperature, shows bent-linear imido ligation. VT solution nmr spectroscopy confirms the fluxionality in all complexes. Structural information is discerned from solid-state 13C nmr spectra; a direct relationship between the difference in imido angles and the difference in ppm of the ipso-carbon peaks has been established. Absolute imido angles are not calculated but comparing the angle difference with known complexes helps predict their potential reactivity. Of the structurally-unknown complexes, only those arylimido complexes without ortho-substituents suggest bending in an imido ligand. MO calculations suggest that, even for 1, there is negligible preference for linear-linear or bent-linear imido ligation. Other molecular interactions, like crystal packing forces, are cited as the dominant structural influence. Bis(imido) complexes with different co-ligands and metal centres are reported. It is suggested that [Mo(NPh)2(S2CNMe2)2] has linear-linear imido ligation, contrasting with 1. Reactivity with other simple molecules is investigated, most notable of which is the reaction with hydrogen sulfide to form disulfide complexes [Mo(NR)(S2)(S2CNEt2)2]- Reaction with acids gave bis(amido), imido-amido and also imidotris(dithiocarbamate) cations. The mechanism of the formation of [Mo(NPh)(S2)(S2CNEt2)2] upon reaction of phenyl isocyanate with [Mo(O2)(S2CNEt2)2] is studied.

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