Experimental and Computational Investigation of the Aerobic Oxidation of a Late Transition Metal-Hydride

The
rational development of homogeneous catalytic systems for selective
aerobic oxidations of organics has been hampered by the limited available
knowledge of how oxygen reacts with important organometallic intermediates.
Recently, several mechanisms for oxygen insertion into late transition
metal-hydride bonds have been described. Contributing to this nascent
understanding of how oxygen reacts with metal-hydrides, a detailed
mechanistic study of the reaction of oxygen with the IrIII hydride complex (dmPhebox)­Ir­(OAc)­(H)
(1) in the presence of acetic acid, which proceeds to
form the IrIII complex (dmPhebox)­Ir­(OAc)2(OH2) (2), is described. The evidence
supports a multifaceted mechanism wherein a small amount of an initially
formed metal hydroperoxide proceeds to generate a metal-oxyl species
that then initiates a radical chain reaction to rapidly convert the
remaining IrIII–H. Insight into the initiation step
was gained through kinetic and mechanistic studies of the radical
chain inhibition by BHT (butylated hydroxytoluene). Computational
studies were employed to contribute to a further understanding of
initiation and propagation in this system.