MECHANISM OF AN OXYGEN-ATOM TRANSFER-REACTION INVOLVING AN OXO-BRIDGED MO(V) COMPLEX

The kinetics of the oxygen atom transfer reaction Mo2O3I2(dtc)(2)(THF)(2) (1) + pyridine-N-oxide = 2MoO(2)I(dtc) + pyridine was investigated in methylene chloride solution using a variety of substituted pyridine-N-oxides. This is the first kinetics study of the reaction of an oxo-bridged Mo(V) complex participating in an ore-transfer reaction. Reactions were studied using pseudo-first-order conditions of excess N-oxide. These reactions were characterized by saturation kinetics in which 1 reversibly forms a Mo2O34+-N-oxide precursor complex that generates products via irreversible breaking of an Mo-O-b bond to give two equivalents of MoO22+ complex and the appropriate pyridine derivative. A considerable group effect was observed (two orders of magnitude) when substituents on the pyridine-N-oxides were varied, with electron releasing substituents slowing the rate of reaction. This observation is used to support a proposed mechanism by which the rate of Mo-O-b bond breaking in the precursor complex is determined by the N-O bond strength of the substrate N-oxide.