Synthesis and structural characterisation of new isocyanate and imido niobocene complexes. Crystal structures of [{Nb(η-C₅H₄SiMe₃)₂Cl}₂] and [Nb(η-C₅H₄SiMe₃)₂(=NPh)Cl]

Abstract

The isocyanate complexes [Nb(η-C5H4SiMe3)2(RNCO)Cl](R = Ph 2, But3, Prn4, Pri5) have been prepared from the reaction of [Nb(η-C5H4SiMe3)2Cl]1 with the appropriate ligands. Treatment of 1 with the corresponding amines NH2R afforded the imido complexes [Nb(η-C5H4SiMe3)2(=NR)Cl](R = Ph 6, But7, Prn8 or Pri9) which can also be prepared by thermal treatment of the corresponding isocyanate complexes 2–5. All complexes have been characterised in solution by both 1H and 13C NMR spectroscopy. Complex 1 crystallises in the monoclinic space group P21/c showing two crystallographic in dependent molecules with Z= 8, a= 12.968(4), b= 23.988(7), c= 25.546(7)Å and β= 103.22(3)°. It has a binuclear structure with two almost symmetrical chloride bridges, giving a closed-shell, 18-electron configuration. Complex 6 crystallises in the monoclinic space group P21/n with Z= 4, a= 7.343(2), b= 16.880(3), c= 20.227(4)Å and β= 96.41(2)°. The structure shows a value of 165.1(2)° for the Nb–N–C angle and an Nb–N bond distance of 1.792(2)Å, intermediate between that expected for double and triple bonds.