A surfactant based oxodiperoxo molybdenum complex, which could activate molecular oxygen, has been employed as a catalyst for controlled oxidation of benzylic alcohols to corresponding carbonyls. The oxidation reactions were carried out under aqueous environment, however, in the absence of any extraneous base or co-catalyst. Sensitive/oxidizable functional groups like cyano, sulfide, hydroxyl, aryl-hydroxyl
Ancillary ligands switch the activity of Ru–NHC-based oxidation precatalysts
作者:Suraj K. Gupta、Tanmoy Mandal、Tejaswinee Gangber、Vivek Singh、Joyanta Choudhury
DOI:10.1016/j.ica.2019.119195
日期:2020.1
Herein we demonstrate how the inner-sphere coordinating ligands switch the activity of Ru-NHC-based oxidation precatalysts in the oxidative conversion of olefins to carbonyl compounds, with the help of a series of systematically varied imidazolydene-NHC (Im-NHC) and triazolydene-NHC (Tz-NHC)-based ruthenium(II)-complexes. It is shown that the catalytic activity of the para-cymene-containing precatalysts varies in the order of [(Tz-NHC)Ru(para-cymene)Cl](+) > [(Im-NHC)Ru(para-cymene)Cl](+), while the order of activity of the MeCN-containing precatalysts is found to be reversed, i.e., [(Im-NHC)Ru(MeCN)(4)](2+) > [(Tz-NHC)Ru(MeCN)(4)](2+). Along with the electronic influence of the NHC ligands, the effect of the lability of the para-cymene and MeCN ligands, and the overall charge of the complexes might be attributed toward such a switching of catalytic activity. This finding led to develop a new precatalyst with improved activity which was further utilized in selective oxidation of a series of styrene substrates containing other oxidation-sensitive functionalities.