Structure and Dynamics of [Nb(η5-C5H4SiMe3)2(η2-H2BR2)] (R2 = O2C6H4, C8H14, H2) Complexes. A Combined Experimental and Theoretical Study

Abstract

Dihydrogen elimination from the reaction of the niobocene trihydride Cp‘2NbH3 (Cp‘ = η5-C5H4SiMe3) and the appropriate borane provides a synthetic route to the new borate-containing niobocene complexes [Nb(η5-C5H4SiMe3)2(η2-H2BR2)] (R2 = O2C6H4 (1), C8H14 (2), H2 (3)). The reaction with H2BO2C6H4 or H2BC8H14 proceeds at mild temperature, and the BH3·THF adduct reacts even at low temperature. Complexes 2 and 3 show dynamic behavior in solution. Spectroscopic and theoretical studies were carried out in order to clarify these dynamic processes. In addition, X-ray diffraction studies of 2 were carried out and the results correlated with the theoretical data. Finally, reactions of Cp‘2Nb(H)(L) (L = CO, CN(2,6-Me2C6H3), tBuOOCHCHCOOtBu) with BH3·THF give rise to the complex 3, with the elimination of the appropriate ancillary ligand L.