Transition metal-alkenyl complexes [M–(CH2)nCHCH2, n ≥ 2]: Synthesis, structure, reactivity and applications

A historical perspective is followed by an overview of methods used to synthesize transition metal-alkenyl complexes of the type LmM(CH2)n–CHCH2 (where Lm = other ligands, M = transition metal and n ≥ 2). Both mono- and bis(alkenyl) compounds are discussed. X-ray structures show that the alkenyl groups can coordinate either in an η1- or an η1,η2-fashion. We have shown that reactivity patterns for these metal-alkenyl complexes can be different to those shown by metal-alkyl complexes and these differences are highlighted. For example bis(alkenyl) complexes can undergo ring closing metathesis (RCM) reactions to give metallacycloalkenes, as demonstrated recently by our research group. The intermediacy of transition metal-alkenyl species in ethylene oligomerization and other catalytic reactions is also discussed.