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, Bu^t3, 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, Bu^t7, 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.