Catalysis of Symmetry-disallowed Reactions

Opportunities for applying the principle of the conservation of orbital symmetry to catalytic processes are surveyed. Current views on the role of a transition metal in the catalysis of symmetry-disallowed reactions are reported, and possible mechanisms are discussed. Close attention is paid to the correlation of the catalytic activity of metal-containing catalysts with the electron configuration of the transition metal, the structure of the complex, and the nature of the ligands. Examples of catalytic reactions disallowed by the Woodward–Hoffmann rules – valency isomerisation of hydrocarbons, hydrogenation and disproportionation of alkenes, cyclo-oligomerisation – are considered in the light of ideas on concerted and stepwise mechanisms. A list of 137 references is included.