Polynuclear tantalum oxoalkoxides. Crystal structures of [Ta8O10(OEt)20], [Ta7O9(OPri)17] and [Ta5O7(OBut)11]·C6H5Me

Abstract

By controlled hydrolysis of the parent pentaalkoxides of tantalum [Ta(OR)₅, R = Et, Prⁱ or Bu^t] in mixed alcohol–toluene solutions the following crystalline oxoalkoxides were obtained and their structures determined by single crystal X-ray diffraction: [Ta₈(μ₃-O)₂(μ-O)₈(μ-OEt)₆(OEt)₁₄] 1, [Ta₇(μ₃-O)₃(μ-O)₆(μ-OPrⁱ)₄(OPrⁱ)₁₃] 3 and [Ta₅(μ₃-O)₄(μ-O)₃(μ-OBu^t)(OBu^t)₁₀]·C₆H₅Me 4. Each compound contained all of its tantalum atoms in distorted octahedral co-ordination. Using ¹⁷O-enriched (10 atom%) water these compounds were obtained with ¹⁷O-enriched oxo atoms and their ¹⁷O NMR spectra measured in toluene solution and related to their molecular structures. Structural aspects of these tantalum oxoalkoxides are discussed in terms of the steric effects of the alkoxo ligands and π-electron donation of terminal alkoxo ligands.