Identification of Cyclohexadienyl Hydrides as Intermediates in Molybdenum‐Catalyzed Arene Hydrogenation
Gabriele Hierlmeier, Paolo Tosatti, Kurt Puentener, Paul J. Chirik
Abstract
Abstract Treatment of phosphino(imino)pyridine (PIP) molybdenum cyclooctadiene (COD) complexes [(PIP)Mo(COD)] with dihydrogen in the presence of benzene selectively furnished the molybdenum cyclohexadienyl hydrides [(PIP)MoH( η 5 ‐C 6 H 7 )], which are precatalysts for the hydrogenation of benzene to cyclohexane. [(PIP)MoH( η 5 ‐C 6 H 7 )] arises from a rarely observed insertion of benzene into a molybdenum‐hydride bond, a key step in the molybdenum‐catalyzed homogeneous hydrogenation of arenes. The reaction with toluene afforded a single isomer of the corresponding molybdenum cyclohexadienyl hydride while para ‐xylene predominantly formed the molybdenum η 6 ‐arene complex with the insertion product being a minor component. Addition of carbon monoxide to a cyclohexane‐ d 12 solution of [(PIP)MoH( η 5 ‐C 6 H 7 )] liberated cyclohexadiene, providing experimental support for a higher kinetic barrier for the subsequent steps en route to cycloalkanes.