Bis(organoimido)-complexes of tungsten(IV): the crystal and molecular structures of tetrachlorobis(t-butylamine)bis(t-butylimido)bis(µ-p-tolylimido)-ditungsten(VI) and tetrachlorobis(µ-phenylimido)-bis(t-butylamine) bis(t-butylimido)ditungsten(VI)

Abstract

The tungsten(VI) organoimido complexes [{WCl₄(NR)}₂](R = Ph, C₆H₄Me-p, Prⁱ, or Me) were treated with the silylamines Me₃SiNHR″(R″= Ph, Bu^t, Prⁱ, or Et) to form the dimeric complexes [{WCl₂(NR)(NR″)(NH₂R″)}₂], containing terminal and bridging organoimido ligands, cis-oriented chloro ligands, and co-ordinated amine. [{WCl₂(NPh)(NBu^t)(NH₂Bu^t)}₂] was also obtained from the reaction of [{WCl₄(NPh)}₂] with NH₂Bu^t. Spectral studies suggest that these complexes arise from two cis-oriented organoimido groups by an inter-ligand proton-transfer process which proceeds regardless of the size of the group R. The structure of [{WCl₂(NC₆H₄Me-p)(NBu^t)(NH₂Bu^t)}₂] was determined by X-ray crystallography and shown to have distorted edge-shared bioctahedral geometry with terminal t-butylimido groups and bridging unsymmetrical arylimido groups and with the longer W–N bridge bonds trans to the terminal t-butylimido group. The t-butylamine ligands are involved in intramolecular N–H ⋯ Cl bridging within the dimeric unit, which explains some striking features found in the ¹H n.m.r. spectrum. Full details are also given of the crystal structure of [{WCl₂(NPh)(NBu^t)(NH₂Bu^t)}₂].