Reactions of Alkanes by Oxidative Addition

A long controversy also grew up over the work of Shilov et al [28]. In 1969 these authors published the first example of homogeneous CH bond activation in alkanes the hydrogen—deuterium exchange reaction catalyzed by platinum(II) complexes (reaction 13). 

These reactions also lead to the formation of alkyl chlorides and acetates. Cycloalkanes are more reactive than acyclic alkanes primary CH bonds were found to react faster than secondary CH bonds. Because of the presence of platinum metal, which sometimes precipitates, these reactions were suspected to be heterogeneous. Shilov demonstrated that Pt(TV) and Pt(0) are inactive in these exchanges it is now accepted that these reactions may involve an oxidative addition step. 

Crabtree et al. discovered the first system which reacted with saturated hydrocarbons to give stable and isolated organometallic products with a hgand coming from the alkane molecule [29]. The cationic iridium complex 10a reacts in dichloroethane in the presence of 3,3-dimethylbutene with cyclopentane, cycloheptane and cyclooctane to give the compounds 11a—13a, respectively (reaction 14). Other alkanes did not react. 3,3-Dimethylbutene, which acts as a hydrogen acceptor, must be present to observe the reactions. Convincing evidence that these reactions are homo- 

In a subsequent report [30], the related complex 10b was used instead of 10a. The reactions with 10b were performed in pure alkanes thus, the yields were greatly improved and a variety of previously unreactive hydrocarbons were found to react under these new conditions. Methyl and ethylcyclopentane gave [L2lr(R—C5H4)H][SbF6](R == Me, Et L = (p-F— 6114)3 ). Activation of cyclohexane is exemplified by reaction 15. Methylcyclohexane gave only a cyclohexadienyl complex. 

Baudry, Ephritikhine and Felkin found the first soluble organometallic system capable of functionalizing alkanes selectively and catalytically under mild conditions. The bis(phosphine)rhenium heptahydrides L2ReH7 14 react with cycloalkanes C H2 n = 6, 7, 8) in the presence of dimethylbutene to give the corresponding cycloolefins (reaction 16) [32, 33] these are not further dehydrogenated to dienes or benzene. The 

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