Organometallic compounds

Organometallic complexes are complexes formed between organic groups and metal atoms. They can be divided into 2 general classes:

(1) complexes containing metal-carbon σ bonds and
(2) π-bonded metal complexes of unsaturated hydrocarbons-that is, compounds with the multiple bonds between carbon atoms.

Organometallic compounds are becoming increasingly important for the elucidation of reaction mechanisms and as reagents for the synthesis of chiral organic compounds with high stereo selectivity. Chirality can arise in these materials through several mechanisms illustrated by Compounds I-IV. Compound I is chiral by virtue of the presence of four different ligands in a pseudo tetrahedral geometry about the iron atom. In this regard, I is analogous to a classical chiral carbon compound. Compounds II and III contain a chiral group either on the metal or on the ring, respectively.

The metal-carbon bond in organometallic compounds is usually of character intermediate between ionic and covalent. Primarily ionic metal-carbon bonds are encountered either when the metal is very electropositive or when the carbon-containing ligand exists as a stable carbanion. Carbanions can be stabilized by resonance or by the presence of electron-withdrawing substituents. Therefore, the bonding in compounds like sodium acetylide and triphenylmethylpotassium is ionic primarily. The stability and reactivity of organometallic compounds are related with the nature of the organic ligands and the metal to which they are attached. In each of the main groups of the periodic table (groups 1, 2, and 13-15), the thermal stability of a given type of organometallic compound decreases generally from the lightest to the heaviest element in a group. The reactivity of organometallic compounds with water and air vary widely. Organometallic compounds of Li, Mg are amongst some of the very significant organic reagents. Organometallic compounds provide a source of nucleophilic carbon atoms which can react with the electrophilic carbon to form a new carbon-carbon bond. This is significant for the synthesis of complex molecules from simple begning materials.