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 abso lute alcohols in the presence of LiCl (electroconductive additive). Ta (OPri)(5) (5) was isolated by distillation in the course of thermolysi s 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 isostructu ral with the corresponding [Nb(OR)(5)](2) (R = Me,Pr-i); their molecul es involve two [MO(6)] octrahedra sharing a common edge. Recrystalliza tion of 1 from MeOH at < 20 degrees C resulted in the isolation of a m onosolvate 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. Th e dinuclear molecule 4 has one mu-O(oxo) and one mu-OR group, ROH is i n an axial position. Compound 4 is the first example of a stable oxoal koxide (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 nuclear ity. Crystalline Ta7O9(OPri)(17) (7) was obtained by the uncontrolled hydrolysis of 4 and 5. Its molecule is a heptanuclear metal oxoalkoxid e 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 for med as a result of elimination of R(2)O from Ta(OR)(5). Copyright (C) 1996 Elsevier Science Ltd