Organometallic Compounds – NEB Class 12 Chemistry

Chapter 17: Organometallic Compounds

NEB Class 12 Chemistry Chapter 17 – Organometallic Compounds Notes, Exercise, Question Answer for Academic Year 2081-2082.

Organometallic Compound Syllabus

• 17.1 Introduction, general formula, and examples of organolithium, organocopper, and organocadmium compounds
• 17.2 Nature of Metal-Carbon bond
• 17.3 Grignard reagent
• 17.3.1 Preparation (using haloalkane and haloarene)
• 17.3.2 Reaction of the Grignard reagent with water, aldehydes, and ketones ( preparation of primary, secondary, and tertiary alcohols), carbon dioxide, HCN, RCN, ester, and acid chloride

Organometallic Compounds – NEB Class 12 Chemistry

Those compounds which consist of metal to carbon bonds are called organometallic compounds.

General Formula:

The general formula of organometallic compounds is R-M, where R is the carbon chain.

Some Examples of Organometallic Compounds:

1. CH3​Li – Methyl lithium
2. C6​H5​Li – Phenyl lithium
3. R2​CuLi – Lithium di-alkyl cuprate
4. (C2​H5​)2​Cd – Diethyl cadmium

Properties:

• Organolithiums possess the general formula RLi.
• Because of the small size and high polarization power of lithium, organolithium compounds possess more ionic character than the Grignard reagent.

Preparation:

Organolithium compounds can be prepared as:

Organolithium compounds can be prepared as: $$\text{R-X} + 2\text{Li} \xrightarrow{\text{dry ether}} \text{R-Li} + \text{LiX} $$

Applications:

• Organolithiums are used in making lithium diorganocopper compounds R2​CuLi, called Gilman reagent. $$ 2\text{RLi} + \text{CuI} \xrightarrow{\text{dry ether}} \text{R}_2\text{CuLi} + \text{LiI}$$

Nature of Metal-Carbon Bond

Based on the nature of metal to carbon bonds, organometallic compounds are classified into the following types:

1. Ionic Organometallic Compounds:
   • They are mainly formed by more electro-positive metals such as Na, K, where metals are present in the form of the cation.
   • In such compounds, the negative charge on the hydrocarbon anion is delocalized over several carbon atoms.
   For example:
   1. KC5H5 – Cyclopentadienyl potassium
   2. Mg(C5H5)2 – Bis(cyclopentadienyl) magnesium
2. Covalent Organometallic Compounds:
   • Covalent organometallic compounds are mainly formed by less electropositive metals such as Pb, Cd, Zn, and so on.
   • In such compounds, metal is bonded with carbon atom by a single covalent bond.
   For example:
   1. (C6H5)4Pb – Tetraethyl lead
   2. (C6H5)2Zn – Diphenyl zinc

Organometallic Compounds PDF – Class 12 Chemistry

Organometallic-Compound