The stereochemical course of electrophilic cleavage of metal–carbon bonds at a chiral ruthenium centre. X-Ray crystal structure of [(S)Ru-RuBr(CO)PPh3{η-C5H4(neomenthyl)}]

Abstract

The stereochemical course of the cleavage of the metal–methyl bond in [RuMe(CO)PPh₃{η-C₅H₄(neomenthyl)}] by electrophiles has been investigated. Cleavage by hydrogen halides occurs predominantly with retention of configuration at the ruthenium whereas cleavage by halogens shows little stereoselectivity. These results have been rationalised by proposing that the reactions proceed via an oxidative addition mechanism involving a configurationally labile seven co-ordinate ruthenium(IV) intermediate. In the case of hydrogen halides, rapid reductive elimination of methane from the ruthenium(IV) intermediate does not allow significant epimerisation of the ruthenium centre whereas with halogens a slower reductive elimination of methyl halide results in significant epimerisation. The crystal structure of [(S)_Ru-RuBr(CO)PPh₃{η-C₅H₄(neomenthyl)}] is also reported.