Tantalum(V) alkoxides: Electrochemical synthesis, mass-spectral investigation and oxoalkoxocomplexes

Ta(OR)(5) (R = Me(1), Et(2), Bu(n)(3)) and Ta2O(OPri)(8) . (PrOH)-O-i (4) were obtained by the anodic oxidation of metallic tantalum in absolute alcohols in the presence of LiCl (electroconductive additive). Ta(OPri)(5) (5) was isolated by distillation in the course of thermolysis of 4 under reduced pressure. Ta(OC(2)H(4)OMe)(5) (6) was obtained by reaction of 5 with 2-methoxyethanol. Compounds 1 and 5 are isostructural with the corresponding [Nb(OR)(5)](2) (R = Me,Pr-i); their molecules involve two [MO(6)] octrahedra sharing a common edge. Recrystallization of 1 from MeOH at < 20 degrees C resulted in the isolation of a monosolvate Ta(OMe)(5) . MeOH. The solubility of Ta(OMe)(5) in MeOH was studied in the temperature range of -80 degrees C to 50 degrees C. The dinuclear molecule 4 has one mu-O(oxo) and one mu-OR group, ROH is in an axial position. Compound 4 is the first example of a stable oxoalkoxide (in solution and gas phase) with as few as two metal nuclei, in contrast to most M(x)O(y)(OR)(2), which are usually of higher nuclearity. Crystalline Ta7O9(OPri)(17) (7) was obtained by the uncontrolled hydrolysis of 4 and 5. Its molecule is a heptanuclear metal oxoalkoxide of a new type containing a metal core consisting of tetrahedral [Ta-4] with a common vertex. In the mass spectra of 1-3 and 5, along with the ions obtained on fragmentation of Ta(OR)(5), fragments of Ta2O(OR)(8) (R = Me, Et, Bu, Pr-i) molecules were recorded; the latter are formed as a result of elimination of R(2)O from Ta(OR)(5). Copyright (C) 1996 Elsevier Science Ltd