Mechanistic insights into the reaction Cp2Nb(CO)H (Cp = η5-C5H5) with acetylenedicarboxylic acid (ADCA): DFT studies

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The insertions of unsaturated molecules into metal-hydride bonds are very common steps in industrial catalytic reactions such as olefinic isomerization, hydrogenation and hydroformylation. In this paper, the reaction mechanism of Cp2Nb(CO)H (Cp = η5-C5H5) with acetylenedicarboxylic (ADCA) has been investigated based on density functional theory calculations. Kinetic calculation and topological analyses of electron density have been conducted. The calculated results show that the reaction can proceed easily even at very low temperature. (Z)-pro Cp2Nb(CO)(η1-(Z)–HOOCC = CHCOOH) and the isomer (E)-pro can be got via two parallel steps. The yield rate of (E)-pro is larger than that of (Z)-pro because of its lower energy barrier. In addition, the carboxylato-containing niobocene compound Cp2Nb(CO)(k1-OOCC(H)= CHCOOH) can also be got as the most stable product through a proton transfer process. Along the reaction pathway, there is a η2-(C, C)-Nb agostic structure. The results provide useful informations and theoretical predictions on much more insertion reactions.