Question

An example of a sigma-bonded organometallic compound is:

• A. \( \text{Cobaltocene} \)
• B. \( \text{Ruthenocene} \)
• C. \( \text{Ferrocene} \)
• D. \( \text{Grignard's reagent} \)

Hint:

Grignard's reagents (\( \text{RMgX} \)) are highly reactive compounds in organic synthesis due to their nucleophilic carbon, which makes them excellent for forming carbon-carbon bonds in various reactions.

Answer 1

The Correct Option is D

Organometallic compounds contain a metal atom directly attached to an organic group's carbon atom. Their bonding can be either sigma (\( \sigma \)) bonds, pi (\( \pi \)) bonds, or a combination.

Step 1: Analyze Bonding in Options.

Cobaltocene, Ruthenocene, and Ferrocene: These are sandwich compounds where the metal atom forms \( \pi \)-bonds with cyclopentadienyl ligands, distinct from sigma bonds.

Grignard's Reagent: Conversely, Grignard's reagent (RMgX) features a direct metal-carbon sigma bond. For instance, \( \text{CH}_3\text{MgBr} \) showcases a sigma bond between magnesium and the methyl group's carbon, classifying it as a sigma-bonded organometallic compound.

Step 2: Grignard Reagent Example.

Grignard reagents are typically represented as \( \text{RMgX} \), where:

• \( R \) signifies an alkyl or aryl group (e.g., methyl, ethyl),
• \( Mg \) is magnesium,
• \( X \) is a halogen (commonly bromine or chloride).

The characteristic feature of this organometallic class is the \( \sigma \)-bond between the magnesium and carbon atoms in \( \text{RMgX} \). Methylmagnesium bromide (\( \text{CH}_3\text{MgBr} \)) exemplifies this, with a sigma bond connecting the methyl group's carbon to magnesium.