Allyi Metal Complexes

Abstract

This chapter reviews various allyl metal complexes. There are two main preparative routes to σ-allyl complexes, both of which involve standard methods for preparing metal–carbon σ bonds. Reaction of sodium metal carbonyls with allyl halides and addition of metal hydride complexes to conjugated dienes are also explained. A list of known σ–allyl complexes of transition metals has been provided. All the known compounds are yellow oils, which are insoluble in water, but very soluble in nonpolar solvents, such as petroleum ethers or benzene. Both the pure complexes and, especially, their solutions are oxidized by atmospheric oxygen, as are the closely related σ-alkyl metal complexes. The field of both σ- and π-allyl complexes was brought into focus following studies by Jonassen and coworkers on the complex C 4 H 7 Co(CO) 3. There are several general methods available for preparing π-allyl or the more simply substituted π-allylic complexes; these methods are explained along with examples. Allyl complexes form a part of the series of π organometallic complexes classified by the number of electrons the ligand formally contributes to the ligand–metal bond. Using these examples, and in the light of the rare gas formalism and consideration of other known organometallic complexes, possible complexes of the first-row transition metals, which are not known but which might be expected to exist, are formulated.