Organometallic Compounds

What are Organometallic Compounds?

Those compounds which have at least one metal – carbon bond, are called organometallic compounds. Most common example of an organometallic compound is Grignard reagent – RMgX. Few other examples of organometallic compounds are given below –

  • Gilman reagent – R2CuLi 

  • Dimethylmagnesium – Me2Mg

  • Triethylborane – Et3B

  • Ferrocene –  Image will be uploaded soon

  • Cobaltocene – Image will be uploaded soon

Wilkinson Catalyst - [Rh(PPh3)3Cl] is also an organometallic compound. Although it does not possess direct metal – carbon bond. But it forms a metal carbon bond during hydrogenation. 

Exceptions - Cyanides such as NaCN and carbides such as CaC2 are not organometallic compounds. We count them as inorganic compounds. While carbonyl compounds such as Ni(CO)4 are counted as organometallic compounds. 

Thus, in organometallic compounds metal – carbon bond can either be direct carbon to metal bond means sigma bond or a metal complex bond means pi bond. The branch of chemistry which includes study of organometallic compounds is called organometallic chemistry. It is also called organometallics. 

Presently organometallic compounds are a huge subject of research due to their various pharmaceutical applications. Many journals are published on the subject such as American Chemical Society publishes biweekly journals on organometallic compounds called organometallics. 

Structure and Properties of Organometallic Compound

Metal carbonyl organometallic compounds generally follow the 18-electron rule which is helpful in predicting the stability of metal carbonyls. Although other organometallic compounds do not follow the 18-electron rule. In this rule it is assumed that metal atoms gain electrons from the ligands and attain nearest noble gas configuration. The total of d-electrons (outermost electrons of transition elements) and number of electrons supplied by ligands should be 18. It is assumed that the valence shell of the metal will contain 18 electrons. 

Generally, organosodium and organopotassium compounds are ionic in nature while most of the other organometallic compounds form polar covalent bonds. 

Properties of Organometallic Compounds – 

  • They have relatively low melting points. 

  • They are insoluble in water.

  • They are soluble in ether.

  • They are highly reactive. That is why they are kept in organic solvents. 

  • In organometallic compounds carbon has an electronegativity of 2.5 while most metals have electronegativities less than 2.0. 

Classification of Organometallic Compounds 

Organometallic compounds can be classified into following three types –

  • Main group organometallic compounds 

  • Transition metal organometallic compounds 

  • Lanthanide and actinide organometallic compounds 

Main Group Organometallic Compounds – These organometallic compounds have s or p – block elements (metals) in them. Most common example of a main group organometallic compound is Grignard reagent – RMgX. Cacodyl oxide [(CH3)2As]2O was the first main group organometallic compound which was isolated by Louis Claude Cadet de Gassicourt in 1760. Other examples include organoborane, AlEt3 etc. 

Structures of few of them are given below –

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Cacodyl Oxide

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Triethylaluminium (AlEt3)

Transition Metal Organometallic Compounds – In these organometallic compounds d-block metals are present. Following are the main examples of transition metal organometallic compounds –

  • Gillmann’s reagent – R2CuLi 

  • Collmann’s reagent – [Fe(CO)4]2-

  • Wilkinson’s catalyst - [Rh(PPh3)3Cl]

  • Palladium catalyst – Pd(PPh3)4 for coupling reaction is also an example of transition metal organometallic compound. 

  • Vaska’s complex – [Ir(PPh3)(CO)Cl]

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Lanthanide and Actinide Organometallic Compounds - In these organometallic compounds f-block metal/s are present. Following are the main examples of lanthanide and actinide metal organometallic compounds –

  • Uranocene – 

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  • Cyclopentadienides (C5H5-) Compounds –

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Applications of Organometallic Compounds 

Organometallic compounds are very useful in various fields. Few of them are listed below –

  • Organometallic compounds are used as reagents. 

  • Wilkinson’s catalyst is used in hydrogenation of alkenes.

  • Ziegler – Natta catalyst [(C2H5)3AlTiCl4] is used for polymerization of alkenes. 

  • Organoarsenic compounds are used for treatment of syphilis. 

  • Palladium catalysts are used in coupling reactions. 

  • Grignard reagent is used in the synthesis of many compounds such as secondary alcohols, aldehydes etc. 

  • Organometallic compounds have a wide range of industrial applications. Such an organolithium is highly basic and reducing so useful in many polymerization reactions stoichiometrically.

  • Cp2TiCl2 (Cp is cyclopentadienyl anion) organometallic compound is used as a drug.

  • Cis-Platin is used as anticancer drug. 

  • Organometallic compounds are used as additives. Such as TEL (Tertaethyl lead) is used as an anti-knocking agent in fuels. 

Organometallic compounds are a vast topic of chemistry. This was a brief on organometallic compounds, if you are looking for detailed study notes on this topic or various other topics of chemistry class XII then log on to Vedantu website or download Vedantu Learning app. By doing so you will get access to NCERT Solutions of chemistry class XII, study notes, revision notes, mock tests and much more.