Organometallic Compounds - Practice Questions & MCQ

Compounds that contain at least one carbon-metal bond are called organometallic compounds. Zeise, in 1830, prepared the first organometallic compound by the action of ethylene on a solution of potassium chloroplatinate(II). In the last four decades, enormous work has been done in this field and many fascinating compounds have been synthesized and investigated. Grignard reagent, RMgX is a familiar example of organometallic compounds where R is an alkyl group. Diethyl zinc [Zn(C₂H₅)₂], lead tetraethyl [Pb(C₂H₅)₄], ferrocene [Fe(C₅H₅)₂], dibenzene chromium[Cr(C₆H₆)₂], metal carbonyls are other examples of organometallic compounds. The compounds of metalloids such as germanium and antimony and mon-metallic elements such as boron and silicon are also included under this classification.

Organometallic compounds may be classified in three classes:

Sigma(σ) bonded complexes: These complexes contain a metal and carbon atom attached with a sigma bond e.g. Tetramethyl Tin, Trimethyl aluminium etc.

Bonding in Trimethyl aluminium is shown below

Pi(π) bonded complexes:  These complexes contain a metal and carbon atom attached with a Pi bond. e.g. Ferrocene, Dibenzene Chromium etc. Bonding in Ferrocene and Dibenzene Chromium is shown below:

Complexes containing both  and  bonding characteristics: These complexes contain both  as well as  bonding characteristics. e.g. Metal Carbonyls. The  bond is formed by the donation of the lone pair of electrons of carbonyl group into the vacant d orbital of metal while the  bond is formed by back donation of lone pair of electrons from the metal into vacant antibonding  molecular orbital of CO. This synergic bonding leads to the formation of stronger bonds and stable metal carbonyl complexes. The bonding in metal carbonyls is shown below: