Organometallic Compound | NEB Class 12 Chemistry | NEPALI EDUCATE

Unit 17: Organometallic Compound

The compound which is formed by a covalent bond between one or more metals with carbon atoms of organic moiety are called organometallic compounds.

Examples:

• Grignard reagent
• Alkyl lithium
• Dimethyl Cadmium
• Ferrocene (FeC₅H₅)₂

Nature of bond between metal and carbon:

Metal is electropositive, i.e., less electronegative (0.8-1.8) than carbon, which is more electronegative. Therefore, carbon acquires a partial negative charge while the metal acquires a partial positive charge, making the metal-carbon bond a partial polar covalent bond.

Characteristics:

1. Organometallic compounds contain polar covalent bonds between metal and carbon.
2. Some organometallic compounds are toxic in nature, especially volatile compounds.
3. They have reducing properties.
4. They are insoluble in water but soluble in dry ether.
5. They have lower melting points.
6. Some organometallic compounds have catalytic properties.

Preparation of Organometallic Compounds:

By direct reaction method:

If the electronegative difference between metal and carbon is greater than one, then organometallic compounds can be prepared directly by reacting organic compounds.

Examples:

1. Preparation of alkyl Lithium:

Alkyl lithium is prepared by treating lithium metal with alkyl halides in the presence of dry ether and an inert atmosphere.

CH₃-CH₂-Cl + 2Li → CH₃-CH₂-Li + LiCl

2. Preparation of Grignard Reagent:

Grignard reagent is prepared by treating magnesium metal with haloalkane in the presence of dry ether and an inert atmosphere.

CH₃-CH₂-Cl + Mg → CH₃-CH₂-MgCl

Use of Grignard reagent:

1. Preparation of Alcohol:

CH₃-CH₂-MgCl + HCOH → CH₃-CH₂-OH + MgCl

2. Preparation of Carboxylic Acid:

CH₃ - MgCl + CO₂ → CH₃COOH + Mg(OH)Cl

3. Preparation of Alkane:

CH₃ - MgCl + H-OH → CH₃-H + Mg(OH)Cl

4. Preparation Of Aldehyde and Ketone:

CH₃ - MgCl + H-CN → CH₃-CH=NMgBr → (H₂O/H+) CH₃CHO + Mg(NH₂)Br

Classification of Organometallic Compounds:

Sigma Bonded Organometallic Compound:

The organometallic compounds containing sigma bonds between carbon and metal are called sigma bonded organometallic compounds.

Examples:

• Alkyl lithium
• Grignard reagent
• Di alkyl zincs

Pi-Bonded Organometallic Compound:

The organometallic compounds containing pi-bonds are called pi-bonded organometallic compounds.

Examples:

• Cobaltocene
• Ferrocene
• Ruthenocene

Applications:

1. Organometallic compounds are used to synthesize polymers like polythene.
2. Some organometallic compounds are used as reducing agents.
3. Some organometallic compounds are used as homogeneous and heterogeneous catalysts.
4. Some organometallic compounds, like Grignard reagents, are used to prepare alcohols, alkanes, carboxylic acids, etc.
5. Organometallic compounds play a vital role in organic synthesis.
6. They are used for the synthesis of compounds with large carbon chains.