Kinetics and mechanisms of halogen abstraction reactions of the 17-electron, metal-centered radical CpCr(CO)3 with organic halides

Article abstract of DOI:10.1021/om00002a005

This paper describes detailed kinetics investigations of the reactions of the 17-electron compound CpCr(CO)₃, formed by thermal homolysis of the metal-metal-bonded dimer [CpCr-(CO)₃]₂, with the non-β-hydrogen-containing organic halides BrCH₂CN, BrCH₂CO₂Me CF₃-CH₂I, and p-NO₂C₆H₄CH₂Br, in addition to less detailed kinetics investigations of the reactions of CpCr(CO)₃ with the homologous series of alkyl iodides MeI EtI, i-PrI, and t-BuI, with the benzylic bromides p-XC₆H₄CH₂Br (X = H, NO₂, CN, CF₃, OMe, Me, F, t-Bu , and with the β-hydrogen-containing substrate PhCHMeBr. In most cases, the rate law followed and the observed relative rates are consistent with rate-determining steps involving halogen atom transfer from carbon to chromium. The resulting organic radicals can then in most cases couple with a second molecule of CpCr(CO)₃ to form the corresponding 18-electron, unstable alkylchromium compounds CpCr(CO)₃R; in cases of organic radicals containing β-hydrogen atoms, however, CpCr(CO)₃ can abstract a hydrogen atom to form an olefin plus the metal hydride CpCr(CO)₃H. The latter in turn can transfer the hydridic hydrogen atom to the organic radicals to form the corresponding aliphatic products.