Which of the following is a `pi` – complex

Options

A. Trimethyl aluminum
B. Ferrocene
C. Diethyl zinc
D. Nickel carbonyl

Answer

To determine which of the given compounds is a π-complex, we need to analyze each option based on the nature of the bonding involved. A π-complex typically involves a metal center that interacts with a ligand through π-bonds, as opposed to just σ-bonds.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question presents four compounds: Trimethyl Aluminum, Ferrocene, a Carbon-Zinc compound, and Nickel Carbonyl.

2. **Analyze Trimethyl Aluminum**:
- **Structure**: Trimethyl Aluminum (Al(CH₃)₃) consists of aluminum bonded to three methyl groups.
- **Bonding**: The bond between aluminum and carbon in this compound is a σ-bond.
- **Conclusion**: This is not a π-complex.

3. **Analyze Ferrocene**:
- **Structure**: Ferrocene consists of an iron atom sandwiched between two cyclopentadienyl (Cp) ligands.
- **Bonding**: The bonding involves the iron atom interacting with the π-electrons of the cyclopentadienyl rings.
- **Conclusion**: This is a π-complex because the interaction is through π-bonds.

4. **Analyze the Carbon-Zinc Compound**:
- **Structure**: This compound typically involves a carbon atom bonded to zinc.
- **Bonding**: The bond between carbon and zinc is a σ-bond.
- **Conclusion**: This is not a π-complex.

5. **Analyze Nickel Carbonyl**:
- **Structure**: Nickel Carbonyl (Ni(CO)₄) consists of nickel bonded to four carbon monoxide ligands.
- **Bonding**: The bonding involves both σ-bonds and π-backbonding. The carbon monoxide donates electron density to the nickel, and the nickel can back-donate into the empty π* orbitals of CO.
- **Conclusion**: While it has π-bonding character, it is primarily a σ and π organometallic compound, not strictly a π-complex.

### Final Answer:
The only compound that qualifies as a π-complex is **Ferrocene**.

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