Observation of the Oxidative Addition Reaction

Three years after Green discovered the tetramethyl silane CH bond activation (reaction 5) [14], Bergman et al. [19] and Graham et al. [20] found independently, in 1982, the first examples of oxidative addition reaction of alkane CH bonds with formation of hydrido alkyl complexes (reactions 6 and 7). 

In the Graham system, irradiation of the carbonyl iridium complex 1 extrudes a CO molecule and leads presumably to the coordinatively unsaturated intermediate 2 which then inserts into the CH bonds of cyclohexane or neopentane giving the compounds 3. Similarly, Bergman found that the iridium dihydride 4 loses H2 upon irradiation when the reaction takes place in cyclohexane or neopentane, the hydrido alkyl compounds 6 are formed, resulting from the oxidative addition of a CH bond to the intermediate 5. 

Free or solvent-caged radicals are not involved in the formation of compounds 6 this was demonstrated by crossover experiments and by relative reactivity studies [21]. Thus, the products of irradiation of 4 in a mixture of neopentane and cyclohexane- /i2 were the hydrido neopentyl and the deuterio (perdeuteriocyclohexyl) iridium complexes, with very small quantities of the cross products. Moreover, it was found that irradiation of 4 in liquid cyclopropane leads only to the CH insertion product (reaction 8). 

These unprecedented results were tentatively explained by steric factors the CH bonds in the smaller rings should be more accessible, because the two carbon atoms adjacent to the reacting carbon are more tightly tied back . 

Bergman also studied competition reactions between the different CH bonds located in the same alkane molecule, and found, here again, an anti 

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