| In this thesis, our major purpose is to investigate the molecular structures, bonding, and mechanisms of the reactions in the two different projects in which most of the species are involved in ruthenium and tungsten organometallic compounds, using B3LYP level of density functional theory (DFT) calculations.1,On the basis of L.D.Field experimental observations, the mechanisms on the reaction of the 18e complex trans-Ru(CH3)2(dmpe)2, cis-Ru(CH3)2(dmpe)2 respectively with C2H2 are investigated by using density functional theory (DFT). Our calculated results show that trans-Ru(CH3)2(dmpe)2 is much more favorable kinetically than cis-Ru(CH3)2(dmpe)2 under the heated condition, which are consistent with the experimental observations. However, compared with trans-Ru(CH3)2(dmpe)2, cis-Ru(CH3)2(dmpe)2 is more stable thermodynamically. It is predicted that the rate-determining step is the migration of hydrogen from acetylene to methyl carbon atom, and there is no difference in steps and in rate-determining step on the reaction of trans-Ru(CH3)2(dmpe)2 and cis-Ru(CH3)2(dmpe)2 respectively with C2H2.2,In 2007 the first [2+4] cycloaddition reactions were developed, where the neutral hydrido(hydrosilylene) tungsten complexes Cp'(CO)2(H)W=Si(H)- [C(SiMe3)3] (la, Cp'=Cp*; 1b, Cp' =η5-C5Me4Et) react withα,β-unsaturated carbonyl compounds reported by T.Watanabeet al. At the same time, the reaction mechanism is proposed qualitatively depending on the experimental observations. On the basis of experiments and theoretical hypothesis, the mechanisms for selective formation of (η3-siloxyallyl)tungsten complexes by reaction of hydrido(hydrosilylene)tungsten complexes with a,p- unsaturated carbonyl compounds are re-investigated with the aid of the density functional calculations at the b31yp level of theory. It is theoretically predicted that route 2, where the 18e Cp*(CO)2(H)W=Si(H)[C(SiMe3)3] hydride completely moves to the silicon atom to give a 16e species, is inaccessible, because our theoretical calculations show that the model reactant Cp(CO)2(H)W=Si(H)[C(SiH3)3] (R) derived from the initial experimental reactant Cp*(CO)2(H)W=Si(H)[C(SiMe3)3] is always obtained instead of giving the intermediate Cp(CO)2W-SiH2[C(SiH3)3]. Two possible pathways in route 1 (PathⅠand PathⅡ) are put forward. The results of theoretical calculations confirm the following reaction mechanism: the first step starts with the attack of the oxygen in methyl vinyl ketone from the different sides of Si-H1 bond, giving the first kind of intermediates; the second step is a process of [2 + 4] cycloaddition in which the W-Si moiety in the first intermediate couples with methyl vinyl ketone, giving the six-membered ring; the last step is the transformation from a six-membered metallacycle to aη3-substituted allyl tungsten complex where the H atom of metal center transfers to Si atom connected with oxygen. PathⅠ(starting with the attack of the oxygen in methyl vinyl ketone from the Si-H1 side) is found to be preferred over PathⅡ(starting with the attack of the oxygen in methyl vinyl ketone from the opposite side of Si-H1) kinetically. Furthermore, nearly only the exo-anti isomers were obtained, which was also elucidated theoretically in this work. The high regioselectivity for formation of the exo-anti isomeric product is believed to be kinetic-controlled but not thermodynamic-controlled. |
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