Niobium pinacolate complexes: synthesis and molecular structures of Nb-3(mu-O)(2)(mu, eta(2)-OCMe2CMe2O)(2)(eta(2)-OCMe2CMe2O)(4)H and of Nb-4(mu-O)(2)(mu(3)-O)(2)(mu, eta(2)-OCMe2CMe2O)(2)(OPri)(8)

The reactions between niobium alkoxides [Nb(OR)(5)](2) (R = Pr-1, Et) and p inacol HOCMe2CMe2OH (pinH(2)) were investigated in different stoichiometrie s in toluene at room temperature. Nb4O4(pin)(2)(OPr1)(8) (1), [Nb2O(pin)(4) H-2(OPr1)(2)](m) (2) and Nb3O3(pin)(6)H (3) were isolated. The various prod ucts were characterized by elemental analyses, FT-IR and H-1 NMR spectrosco py and by X-ray diffraction for 1 and 3. The niobium atoms are all six-coor dinated. The Nb-O bond lengths vary according to Nb-OPr1<Nb-mu O<Nb mu(3)-O similar to Nb-O(pin). The structure of [Nb-3(mu-O)(2)(mu,eta(2)-pin)(2)( e ta(2)-pin)(4)H] is based on a bent open-shell framework with a short intram olecular O...O contact of 2.48 A suggesting hydrogen bonding. The structure of [Nb-4(mu-O)(2)(mu(3)-O)(2)(mu, eta(2))-pin)(2)(OPr1)(8)] corresponds to a rhombus. (C) 1999 Elsevier Science Ltd. All rights reserved.