Catalytic H/D exchange between organic compounds and D2O with TpRu(PPh3)(CH3CN)H (Tp = hydro(trispyrazolyl)borate). Reaction of TpRu(PPh3)(CH3CN)H with water to form acetamido complex TpRu(PPh3)(H2O)(NHC(O)CH3)

摘要

Deuteration of organic molecules using D2O as the deuterium source is affected with catalytic systems based on the ruthenium solvente hydride complex TpRu(PPh3)(CH3CN)H. The deuteration reactions can be performed under Ar or H2. In the former case, the hydride ligand is rapidly deuterated by D2O, and in the course of the catalysis, D2O converts TpRu(PPh3)(CH3CN)D into the acetamido complex TpRu-(PPh3)(D2O)(NDC(O)CH 3), which at the later stage of the reaction generates two additional minor species, one of which is the partially deuterated carbonyl hydride species TpRu(PPh3)(CO)H(or D). All of these complexes are, however, found to be inactive for the H/D exchange reactions between the organic molecules and D2O. In the exchange reactions under H2, a mixture of the HD isotopomers, TpRu(PPh3)H3-xD x, of the dihydrogen hydride complex TpRu(PPh3)(H 2)H are the active species. On the basis of our previous work on the TpRu(PPh3)(CH3CN)H-catalyzed H/D exchange reactions between deuterated organic molecules and CH4, it is proposed that TpRu(PPh3)(CH3CN)D and TpRu(PPh3)(H 3-x)Dx exchange their deuteride ligands Ru-D with R-H via the intermediacies of the η2-R-H(or D) and η2-H- H(or D) σ-complexes; the Ru-H bonds thus formed after the exchange are deuterated by D2O to regenerate the metal deuterides. The solvento complex TpRu(PPhs)(CH3CN)D under Ar is suggested to be more active than TpRu(PPh3H3-Dx under H2 for the H/D exchange reactions because the former reacts more readily with the organic molecule R-H to generate the η2-R-H σ-complex due to higher lability of the CH3CN ligand in comparison with the dihydrogen or hydrogen-deuterium ligand of TpRu(PPh3)(H3-x)D x. The acetamido complex TpRu(PPh3)(H2O)(NHC(O) CH3) was independently prepared by refluxing a THF solution of TpRu(PPh3)(CH3CN)H containing excess water for 24 h, and its molecular structure was determined by X-ray crystallography. Theoretical calculations at the Becke3LYP level of DFT theory have been performed to study the reaction of TpRu(PPh3)(CH3CN)H with H2O that leads to the formation TpRu(PPh3)(H2O)(NHC(O)CH 3). It is shown that the hydration reaction is promoted by a Ru-H⋯H-OH dihydrogen-bonding interaction between the hydride ligand and the attacking water molecule. An explanation for the failure of the chloro analogue TpRu(PPh3)(CH3CN)Cl to react with water to form the acetamido complex is also provided.