E. Negishi, Principle of activation of electrophiles by electrophiles through dimeric association - Two are better than one, CHEM-EUR J, 5(2), 1999, pp. 411-420
Electron-deficient metal compounds can be significantly activated as electr
ophiles through dimeric (or polymeric) association with either the same or
different electrophiles. Although this phenomenon has played an important r
ole in many reactions, such as the Friedel - Crafts reaction and the Ziegle
r-Natta polymerization, it has apparently only recently been fully recogniz
ed. Its widespread exploitation promises to lead to many new synthetically
useful reactions as well as ready and accurate interpretations of mechanist
ic and structural phenomena in acid-catalyzed and -promoted reactions.