Mono and dinuclear hydrotris(3,5-dimethylpyrazolyl)borato tantalum complexes

Abstract

In an effort to obtain suitable starting materials, the synthesis and crystal structure of hydrotris(3,5-dimethylpyrazolyl)borato (Tp Me2) tantalum(III) complexes are reported. Reaction of KTp Me2 with [TaCl 2(tht)] 2(μ-Cl) 2(μ-tht) ( 1) (tht=tetrahydrothiophene) gives the X-ray characterized unsymmetrical (Tp Me2Ta)(TaCl 3)(μ-Cl 2)(μ-tht) ( 2) in fair yield. This doubly bonded TaTa complex [2.6791(5) Å, diamagnetic, 18e per Ta] is a rare example of an unsymmetrical Ta 2X 6L 3 complex. The X-ray structure of Tp Me2TaCl 2(PhCCMe) ( 3) is also reported. It has the (4e)-alkyne in the symmetry plane of the molecule. The trans effects of tht and phenylpropyne are discussed. 1 is inert towards the reaction with a second equivalent of KTp Me2.