Hujun Xie

Dehydrogenation of benzyl alcohol with N2O as the hydrogen acceptor catalyzed by the rhodium(I) carbene complex: insights from quantum chemistry calculations

The detailed mechanisms of the dehydrogenation of benzyl alcohol with N2O as the hydrogen acceptor catalyzed by the rhodium(i) carbene complex for the formation of the corresponding carboxylic acid or ester have been investigated via density functional theory (DFT) calculations at the M06 level of theory. Three cycles were considered for the formation of benzaldehyde, benzyl benzoate and benzoic acid. On the basis of the calculations, the rate-determining step for these three cycles is involved in N2O activation by the rhodium ammine hydride complex with an activation barrier of only 22.6 kcal mol-1, which is different from the previous mechanism proposed by Gianetti and co-workers, where the hydride is transferred from the Rh atom to the oxygen atom of N2O with a barrier of 30.5 kcal mol-1. In addition, the calculations also demonstrated that one more N2O is necessary to give benzoic acid, and the reaction can only take place under anhydrous conditions. Present calculations are in good agreement with the experimental observations and provide new insights into the dehydrogenation of benzyl alcohol with N2O as the hydrogen acceptor.

Oxidation of phenyl and hydride ligands of bis(pentamethylcyclopentadienyl)hafnium derivatives by nitrous oxide via selective oxygen atom transfer reactions: insights from quantum chemistry calculations.

The mechanisms for the oxidation of phenyl and hydride ligands of bis(pentamethylcyclopentadienyl)hafnium derivatives (Cp* = η(5)-C5Me5) by nitrous oxide via selective oxygen atom transfer reactions have been systematically studied by means of density functional theory (DFT) calculations. On the basis of the calculations, we investigated the original mechanism proposed by Hillhouse and co-workers for the activation of N2O. The calculations showed that the complex with an initial O-coordination of N2O to the coordinatively unsaturated Hf center is not a local minimum. Then we proposed a new reaction mechanism to investigate how N2O is activated and why N2O selectively oxidize phenyl and hydride ligands of . Frontier molecular orbital theory analysis indicates that N2O is activated by nucleophilic attack by the phenyl or hydride ligand. Present calculations provide new insights into the activation of N2O involving the direct oxygen atom transfer from nitrous oxide to metal-ligand bonds instead of the generally observed oxygen abstraction reaction to generate metal-oxo species.

A substrate-dependent mechanism for the reactions of a hydrido(hydrosilylene)ruthenium complex with carbonyl compounds: insights from quantum chemical calculations

The detailed mechanisms for the reactions of a neutral silylene ruthenium complex with ketones and aldehydes have been investigated with the aid of density functional theory calculations. Through the investigation, the difference in reactivity between ketones and aldehydes towards the ruthenium silylene hydride complex has been explained and discussed. The calculations showed that the reaction mechanisms are dependent on the substituents of the carbonyl substrates. The present calculations are consistent with the experimental observations.

N-Insertion reaction mechanisms of phenyl azides with a hafnium hydride complex: a quantum chemistry calculation

Density functional theory (DFT) calculations were performed to investigate the detailed mechanisms for the N-insertion reaction of phenyl azides with a hafnium hydride complex. This reaction involves an intermolecular hydride transfer from the hafnium center of complex 1 Cp2*HfH2 to the terminal nitrogen atom of a phenyl azide. Subsequently, a 1,3 hydrogen shift from the N1 atom to the N3 atom takes place, accompanied by cleavage of the N2–N3 bond to provide amido complex 3 Cp2*HfH(NHPh) and dinitrogen. A further reaction is related to the intermolecular hydride transfer from the hafnium center to the N1′ atom of a second phenyl azide, followed by the formation of the final product, bis(amido) complex 9 Cp2*HfH(NHPh)2via the liberation of the second dinitrogen, which is the rate-determining step with an overall barrier of 29.8 kcal mol−1. Frontier molecular orbital theory analysis shows that phenyl azides are activated by nucleophilic attack by the hydride ligand, which is consistent with our previous studies of N2O activation by other transition-metal hydride complexes.