Organometallic Compounds with n Bonding

The bonding in n complexes of alkenes is the result of two major contributions. The filled n orbital acts as an electron donor to empty d orbitals of the metal ion. There is also a contribution to bonding, called back-bonding, from a filled metal orbital interacting with the alkene n orbital. These two types of bonding are represented in Fig. 8.1. 

These same general bonding concepts apply to all the other n organometallics. The details of structure and reactivity of the individual compound depend on such factors as (a) the number of electrons that can be accommodated by the metal orbitals, (b) the oxidation level of the metal, and (c) the electronic character of other ligands on the metal. 

Alkene-metal complexes are usually prepared by a process in which some other ligand is dissociated from the metal. Both thermal and photochemical reactions are used. 

7r-Allyl complexes of nickel can be prepared either by oxidative addition on Ni(0) or by transmetalation of a Ni(II) salt. 

Organic ligands with a cyclic array of four carbon atoms have been of particular interest in connection with the chemistry of cyclobutadiene. Organometallic compounds containing cyclobutadiene as a ligand were first prepared in 1965.183 184 185 186 187 The carbocyclic ring 

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