The correct answer is option 3. \(TiCl_4 + Al(CH_3)_3\).
Ziegler-Natta catalysts are widely used in the polymerization of olefins (alkenes) to produce polyolefins, such as polyethylene and polypropylene. These catalysts are based on a combination of a transition metal compound and an organoaluminum compound. The most common Ziegler-Natta catalyst consists of titanium tetrachloride (\(TiCl_4\)) and trialkyl aluminum (\(Al(CH_3)_3\)).
Here is a detailed explanation of the components and the mechanism:
1. Titanium Tetrachloride (\(TiCl_4\)):
This is a transition metal compound and serves as the active center in the catalyst.
The titanium atom in \(TiCl_4\) can undergo a reduction process with aluminum alkyls.
2. Trialkyl Aluminum (\(Al(CH_3)_3\)):
This is an organoaluminum compound and acts as a cocatalyst.
Trialkyl aluminum, often referred to as an aluminum alkyl, is a compound like \(Al(CH_3)_3\) or \(Al(C_2H_5)_3\).
It reacts with \(TiCl_4\) to form an aluminum alkyl complex with the titanium center.
3. Catalyst Activation:
The aluminum alkyl reacts with titanium tetrachloride to form an aluminum alkyl complex with a reduced titanium center.
This activation step is crucial for the catalytic activity of the system.
\[ \text{TiCl}_4 + \text{AlR}_3 \rightarrow \text{AlR}_3\text{TiCl}_3 + \text{RCl} \]
Here, \(R\) represents alkyl groups.
4. Polymerization:
The activated catalyst now initiates the polymerization of olefins.
The mechanism involves the insertion of olefin monomers into the metal-carbon bond in the activated catalyst.
This process continues, leading to the formation of a polymer chain.
\[ \text{AlR}_3\text{TiCl}_3 + \text{CH}_2=CH_2 \rightarrow \text{AlR}_3\text{Ti(CH}_2\text{CH}_2\text{)Cl}_2 \]
5. Stereochemistry Control:
Ziegler-Natta catalysts have the ability to control the stereochemistry of the polymer produced.
This is essential for achieving the desired properties in the polymer.
Ziegler-Natta catalysts have been crucial in the production of high-density polyethylene (HDPE), isotactic polypropylene, and other polyolefins. The ability to control the polymerization process and stereochemistry makes these catalysts versatile tools in the polymer industry. | 
