Lithium bridged cyclosiloxy-niobium(v) and -tantalum(v) complexes: thermal decomposition, solid-state and solution structural studies

Treatment of MCl5 (M = Nb or Ta) with 3 equivalents of dilithium tetraphenyldisiloxanediolate, [(Ph2SiOLi)(2)O], gave the lithium-bridged metallasiloxane complex, [M{O(SiPh2O)(2)}(3)]-mu-[Li(L)(2)] (M = Nb 1 or M = Ta 2; L = pyridine). The solid-state structure of compound 2 determined by single crystal X-ray diffraction is reported. Variable-temperature Li-7 NMR of 2 revealed two separate exchange processes which may account for the equilibration of non-equivalent silicon environments in 1 and 2. Preparative scale thermal decomposition of the solid samples with L = tetrahydrofuran (thf) gave crystalline LiNbO3 and LiTaO3.