Which of the following are `pi`-bonded organometallic compounds ?

Options

A. ferrocene
B. Diethyl zinc
C. Ethylmagnesium iodide
D. Bis(benzene) chromium(0)

Explanation

To determine which of the given compounds are π-bonded organometallic compounds, we will analyze each compound based on its structure and bonding characteristics.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds provided are:
- A) Ferrocene
- B) Diethyl zinc
- C) Ethyl magnesium iodide
- D) Bis(benzene) chromium

2. **Analyze Ferrocene (A)**:
- Structure: Ferrocene consists of two cyclopentadienyl anions (C5H5-) sandwiching a central iron (Fe) atom.
- Bonding: The cyclopentadienyl rings have π-bonds due to the presence of alternating double bonds. The iron atom interacts with these π-electrons.
- Conclusion: Ferrocene is a π-bonded organometallic compound.

3. **Analyze Diethyl Zinc (B)**:
- Structure: Diethyl zinc has the formula Zn(C2H5)2, where zinc is bonded to two ethyl groups.
- Bonding: The bonding between zinc and the ethyl groups is primarily σ-bonding. There are no π-bonds present.
- Conclusion: Diethyl zinc is not a π-bonded organometallic compound.

4. **Analyze Ethyl Magnesium Iodide (C)**:
- Structure: Ethyl magnesium iodide has the formula C2H5MgI.
- Bonding: The bond between magnesium and the ethyl group is a σ-bond. The magnesium is bonded to the ethyl group and iodine through σ-bonds.
- Conclusion: Ethyl magnesium iodide is not a π-bonded organometallic compound.

5. **Analyze Bis(benzene) Chromium (D)**:
- Structure: Bis(benzene) chromium consists of a chromium atom bonded to two benzene rings.
- Bonding: Each benzene ring has π-bonds due to the presence of alternating double bonds. The chromium atom interacts with these π-electrons.
- Conclusion: Bis(benzene) chromium is a π-bonded organometallic compound.

### Final Answer:
The π-bonded organometallic compounds among the options provided are:
- A) Ferrocene
- D) Bis(benzene) chromium