Question

Which of the following is $\pi -$ complex?
A) Trimethylaluminum
B) Ferrocene
C) Diethyl Zinc
D) Nickel Carbonyl

Answer 1

Hint : $\pi$ -effects or $\pi$ -interactions are a form of non-covalent interaction involving systems in chemistry. The electron-rich system will interact with a metal (cationic or neutral), an anion, another molecule, and even another system, much as in an electrostatic interaction where a region of negative charge interacts with a positive charge.

Complete Step By Step Answer:
The following are the most common -interactions:
Metal– $\pi$ interactions: involves the contact of a metal with the face of a $\pi -$ system. The metal may be a cation (known as cation– $\pi$ interactions) or neutral (neutral– $\pi$ interactions).
Polar– $\pi$ interactions: a polar molecule and a $\pi -$ system's quadrupole moment interact.
Aromatic–aromatic interactions ( $\pi$ stacking): involves aromatic molecules interacting with one another.
 $\pi$ - Donor: Interactions between a low-energy empty orbital (acceptor) and a high-energy filled orbital (donor) are known as donor–acceptor interactions (donor).
Anion- $\pi$ system interaction: Interactions between anion and other $\pi$ system.
Cation- $\pi$ system Interaction: Interactions of a cation with a $\pi$ -system are called cation– $\pi$ interactions.
Ferrocene has the formula $$Fe(C_5{H}_5{)}_2$$ and is an organometallic compound. Two cyclopentadienyl rings are connected on opposite sides of a central iron atom in the molecule. It's a camphor-like orange solid that sublimes above room temperature and dissolves in most organic solvents.
According to Hückel's law, the number of -electrons on each ring is then six, making it aromatic. Covalent bonding is used to share the twelve -electrons with the metal. The complex achieves an $18$ -electron configuration, which accounts for its stability, since $F{e}^{2+}$ has six d-electrons.
The correct option is B.

Note :
Pi ligands are a type of organometallic ligand that includes linear molecules like ethylene and allyl, as well as cyclic molecules like cyclopentadienyl, and have extended pi systems. These molecules have a direct effect on the reactivity of the organometallic complex as a dative L-type ligand.