Investigation on the intramolecular proton transfer mechanism of [Cp2MHn](Cp = C5H5, M = Mo, W, Re; n = 1 ~ 2) with tBuBCl2

Abstract

Transition-metal hydrides play a critical role in catalysis and metal-mediated transformations. Experimental results show that in the reactions of (C5H5)2MHn(M = Mo and W) with tBuBCl2, a zwitterionic trihydride, [CpMH3(η5-C5H4BCl2R)], is formed instead of salt-like compounds. To elucidate the reaction mechanism and the influence factors in this process, the intramolecular hydrogen atom transfer mechanism of metallocene hydrides (C5H5)2MHn (M = Mo, W, Re; n = 1 ~ 2) with tBuBCl2 was studied in detail using density functional theory calculations. The calculated results show that the reaction mechanisms of the Cp2MHn (M = Mo, W, Re; n = 1 ~ 2) with tBuBCl2 are similar. Borane first attacks the Cp-ring and hydrogen migrates from the Cp ring to the M center, converting the dihydride starting material into a trihydride product or the monohydride into a dihydride product and forming the zwitterionic metal-hydride compounds. In n-pentane, Cp2WH2+ tBuBCl2 and Cp2ReH + tBuBCl2 reactions can be occurred easily and no diene intermediate forms in the reaction process. The formation of [CpMoH3 (η5-C5H4BtBuCl2)] in the Cp2MoH2+ tBuBCl2 reaction is difficult due to the low HOMO energy of Cp2MoH2. Due to the d0 electron configuration of Ta, the title reaction cannot occur between CpTaH3 and tBuBCl2.