Alkene Epoxidation Catalysts [Ru(pdc)(tpy)] and [Ru(pdc)(pybox)] Revisited: Revealing a Unique RuIV═O Structure from a Dimethyl Sulfoxide Coordinating Complex
摘要:
The X-ray crystal structure of a dimethyl sulfoxide (DMSO) coordinating complex [Ru-II(kappa(2)-pdc)(tpy)(DMSO)] (H(2)pdc = 2,6-pyridyl dicarboxylic acid and tpy = 2,2':6',2 ''-terpyridine) led to the discovery of a unique Ru-IV=O configuration for the Ru-pybox (pybox = pyridine-bis(oxazoline) ligands) epoxidation catalyst by theoretical calculations. On the basis of this structure, a detailed theoretical study was conducted on the alkene epoxidation reaction using ruthenium-based epoxidation catalysts. It was found that the process of H2O2 coordination proceeded via an associative path in which one carboxylate detached. The following H2O-elimination step was found to be facilitated by the detached carboxylate group. The resulting Ru-IV=O rearranges to the species trans-2a-oxo, in which one carboxylate group is situated over the tpy ring; the trans-2a-oxo was found to have the lowest activation free energies toward alkene epoxidation. These results demonstrated the importance of the hemilabile properties of the pdc(2-) ligand for the Ru-pdc alkene epoxidation catalysts.
Novel ruthenium–pyridinedicarboxylate complexes of terpyridine and chiral bis(oxazolinyl)pyridine: a new catalytic system for alkene epoxidation with [bis(acetoxy)iodo]benzene as an oxygen donor
作者:Hisao Nishiyama、Yukihiro Motoyama
DOI:10.1039/a705109c
日期:——
Rutheniumâpyridine-2,6-dicarboxylate (pydic) complexes 1â3 of terpyridine and chiral bis(oxazolinyl)pyridines (pybox-ip and pybox-ph), which can be synthesized from [Ru(p-cymene)Cl2]2 and the corresponding ligands, exhibit catalytic activity for epoxidation of trans-stilbene in combination with [bis(acetoxy)iodo]benzene: asymmetric induction with 2 was observed in 74% ee for trans-stilbene.