Theoretical studies on transition metal mediated reactions

Computational studies have been widely applied in understanding the nature of bonding in transition-metal complexes and mechanistic study on reactions of transition-metal complexes. With the aid of quantum chemical calculation, we are able to study the complicated electronic structures of these complexes and provide insights into the nature of metal-ligand bonding.; To obtain a better understanding of the interesting chemistry that treatment of [OsCl(H2)(PPh3){lcub}Ph2P(CH 2)2CH = CH(CH2)2PPh2{rcub}]OTf with H2 produced the (hydrido)dihydrogen complex [OsH(H2){lcub}Ph 2P(CH2)2CH = CH(CH2)2PPh 2{rcub}]OTf rather than the hydrogenated products, we calculated the structures of complexes involved in the above process. It has been found that the hydrogenation of [OsCl(H2)(PPh3){lcub}Ph2P(CH2) 2CH = CH(CH2)2PPh2{rcub}]OTf was thermodynamically fessibie but kinetically unfavorable.; The reactions of H2 with NBD in the model complexes [CpRu(H 2)(NBD)]+ were found to proceed through a stepwise mechanism. Theoretical calculations support the proposal that [CpRu(H2)(NBD)] + is the active species in the observed reaction. The energy profile shows that the reaction of H2 with NBD is energetically very favorable. The [2+2] hydrogenation of NBD ligand is kinetically unfavorable.; The hydration reaction of CH3CN can be catalyzed by some Ru-complexes. Experiments show that (eta5-C9H7)Ru(dppm)H can catalyze the hydration reaction, but (eta5-C9H 7)Ru(dppm)Cl cannot. In addition, a remarkable rate acceleration in the [(eta5-C9H6CH2CH 2NMe2)Ru(dppm)H]-catalyzed nitrile hydration reactions was observed. In order to understand these phenomena, theoretical calculations based on the B3LYP density functional theory have been carried out to examine the structural and energetic aspects related to the possible reaction pathways. The calculations have indicated that in the catalytic process the dissociation of one arm in the bidentate ligand from the metal center followed by the coordination of CH3CN is the initial event.; Density functional theory calculations at the B3LYP level have been performed to study the reaction mechanism of the Ru-catalyzed cycloaddition of 1,5-cyclooctadiene (COD) with alkynes. Our calculations point towards the proposed mechanism that the cycloaddition reaction occurs via an intermediate formed by the active species [CpRu(COD)]+.; In addition, theoretical calculations have been carried out to examine the structural and energetic aspects of beta-hydrogen elimination in several metallocycle complexes of ruthenium and platinum.(Abstract shortened by UMI.)...