Modifications of substituents on the chelating oxygen atom in stereoretentive Hoveyda-Grubbs-type complexes and their influence on catalytic properties

One of the main drawbacks of stereoretentive ruthenium catalysts that allow the synthesis of olefins with defined double bond geometry is their limited stability in the presence of oxygen. To remove the bottleneck that inhibits its widespread use, we prepared a series of Hoveyda-Grubbs-type complexes with a modified ether moiety in the benzylidene substituent. Although the yields obtained in air are still lower than in reactions carried out in an inert gas atmosphere, the Ru21 complex typically led to better yields with high selectivities compared to the benchmark catalyst Ru5. DFT calculations con-firmed that the formation of the four-coordinate Ru(IV)-oxo product postulated by Fogg is a result of oxygen attack on the Ru-C bond and its cleavage through a dioxetane-like transition state.