Niobium pinacolate complexes: synthesis and molecular structures of Nb_3(#mu#-O)_2(#mu#,#eta#~2-OCMe_2CMe_2O)_2(#eta#~2-OCMe_2CMe_2O)_4H and of Nb_4(#mu#-O)_2(#mu#_3-O)_2(#mu#,#eta#~2-OCMe_2CMe_2O)_2(OPr~i)_8

摘要

The reactions between niobium alkoxides [Nb(OR)_5]_2 (R = Pr~i, Et) and pinacol HOCMe_2CMe_2OH (pinH_2) were investigated in different stoichiometries in toluene at room temperature. Nb_4O_4(pin)_2(OPr~i)_8 (1), [Nb_2O(pin)_4H_2(OPr~i)_2]_m (2) and Nb_3O_3(pin)_6H (3) were isolated. The various products were characterized by elemental analyses, FT-IR and ~1H NMR spectroscopy and by X-ray diffraction for 1 and 3. The niobium atoms are all six-coordinated. The Nb-O bond lengths vary according to Nb-OPr~i < Nb-#mu#O < Nb#mu#_3-O approx Nb-O(pin). The structure of [Nb_3(#mu#-O)_2(#mu#,#eta#~2-pin)_2(#eta#~2-pin)_4H] is based on a bent open-shell framework with a short intramolecular O...O contact of 2.48 A suggesting hydrogen bonding. The structure of [Nb_4(#mu#-O)_2(#mu#, #eta#~2)-pin)_2(OPr~i)_8] corresponds to a rhombus.