Utility of hydridotributyltin as both reductant and hydride transfer reagent in organotransition metal chemistry: I. A convenient synthesis of the organoditantalum(IV) hydrides ( η-C 5Me 4R) 2Ta 2( μ-H) 2Cl 4 (R=Me, Et) from ( η-C 5Me 4R)TaCl 4, and probes of the possible reaction pathways

Abstract

The reaction of ( η-C 5Me 4R)TaCl 4 (R=Me, Cp *; Et) with two equivalents of Bu 3SnH in toluene at 25°C yields ( η-C 5Me 4R) 2Ta 2( μ-H) 2Cl 4 in 92% yield (R=Me) or 63% (R=Et) along with Bu 3SnCl and H 2. The μ-H group is derived from the tin reagent, as shown by a deuterium labelling study. UV/vis spectra of the reaction mixture exhibit several isosbestic points during the reaction which are consistent with the absence of significant concentrations of intermediate(s). The ditantalum(IV) halide ( η-C 5Me 4R) 2Ta 2Cl 6 is not a major species on the pathway from ( η-C 5Me 4R)TaCl 4 to ( η-C 5Me 4R) 2Ta 2( μ-H) 2Cl 4, since the reaction of ( η-C 5Me 4R) 2Ta 2Cl 6 with two equivalents of Bu 3SnH to form ( η-C 5Me 4R) 2Ta 2( μ-H) 2Cl 4 is significantly slower. Possible pathways for the formation of ( η-C 5Me 4R) 2Ta 2( μ-H) 2Cl 4 from ( η-C 5Me 4R)TaCl 4 are discussed.