Aerobic Epoxidation of Olefins Catalyzed by Electronegative Vanadyl Salen Complexes.
Vanadyl salen complexes bearing electron-withdrawing substituents have been prepared and characterized. Systematic substitutions on the ancillary ligand have allowed V(5+)/V(4+) reduction potentials to be tuned over a range of approximately 500 mV. The complexes are catalysts for the aerobic epoxidation of cyclohexene; catalytic activity roughly increases with increasing V(5+)/V(4+) reduction potential. The mechanism likely involves oxygen transfer from intermediate hydroperoxides that are formed by radical-chain autoxidation.
Chang
Christopher J.
CJ
Arthur Amos Noyes Laboratory and Beckman Institute, California Institute of Technology, Pasadena, California 91125.
Labinger
Jay A.
JA
Gray
Harry B.
HB