X-Ray Photoelectron Spectroscopy and Reactivity Studies of a Series of Ruthenium Catalysts
Abbreviated Journal Title
ligand effects; metathesis; phosphane ligands; ruthenium; X-ray; photoelectron spectroscopy; OLEFIN-METATHESIS CATALYSTS; IMIDO ALKYLIDENE COMPLEXES; N-HETEROCYCLIC; CARBENE; CROSS-METATHESIS; MOLYBDENUM; LIGANDS; PHOSPHINE; EFFICIENT; POLYMERIZATION; PRECATALYSTS; Chemistry, Physical
X-Ray photoelectron spectroscopy (XPS) was applied to six selected ruthenium precatalysts. The XPS data obtained were compared against reactivity and structural results. The XPS data confirmed some dependencies such as the electron-donor properties of the substituents at the ruthenium center. Additionally, the data combined with structural and reactivity results explain the differences between the character of Grubbs and Hoveyda catalysts. It was found that changing the PCy3 ligand to OiPr (PCy3=tricyclohexylphosphane, OiPr=isopropoxy) has a major influence on relative electron-donating properties of the N-heterocyclic carbene ligand (NHC) and PCy3 groups, which was supported by the relative charges on the Ru center for the examined compounds. Moreover, the turnover frequency (TOF) of a selected example reaction decreased when introducing a NHC group in the case of Grubbs catalysts, but increased in the case of Hoveyda-type catalysts. The XPS data also explained the relative activity values of some catalysts (higher reactivity of nitro-Hoveyda than Hoveyda second-generation catalysts). However, the binding energies do not predict TOFs. Sole examination of the XPS data does not provide a base for reaching unambiguous and binding conclusions as to the relative reactivity of all the investigated systems.
"X-Ray Photoelectron Spectroscopy and Reactivity Studies of a Series of Ruthenium Catalysts" (2009). Faculty Bibliography 2000s. 1666.