Kinetic studies of fluorinated aryl molybdenum(ii) tricarbonyl precursors in epoxidation catalysis

Abstract

Benzyl substituted molybdenum tricarbonyl complexes displaying CF₃ groups are synthesized and applied as catalyst precursors in olefin epoxidation reactions. The CF₃ moiety is important for both decarboxylation velocity and active species formation. DFT calculations as well as ¹H, ¹³C, ¹⁹F and ⁹⁵Mo NMR spectroscopy help explain the observed reactivity differences. A variety of olefins can be epoxidized and TOFs of up to ca. 22 000 h⁻¹ are obtained in hexafluoroisopropanol (HFIP). Furthermore, it is possible to recycle the active species at least 10 times without significant activity loss in a two-phase catalytic reaction. ¹⁹F NMR kinetic studies reveal that at least two intermediates are formed during the reaction with excess TBHP, depending on the position of the CF₃ group. The substrate addition mode has also a major influence on the catalyst formation velocity.