Wilkinson catalyst is:

🧠 Wilkinson's Catalyst — Three Triphenylphosphines and One Rhodium

Wilkinson's catalyst is chlorotris(triphenylphosphine)rhodium(I): $[(\mathrm{Ph_3P})_3\mathrm{RhCl}]$.

Used for: homogeneous catalytic hydrogenation of alkenes (especially terminal C=C double bonds) under mild conditions.

Two structural cues:

• Rh (not Ir): Rh(I) is the active centre.
• PPh₃ (not PEt₃): aryl phosphine, not alkyl.

🗺️ Eliminate Wrong Choices

• (1) Et₃P + Ir → wrong on both counts.
• (2) Ph₃P + Rh → Wilkinson's. ✓
• (3) Ph₃P + Ir → close, but iridium analogue is Vaska's, not Wilkinson's.
• (4) Et₃P + Rh → wrong phosphine.

⚡ The Three Famous Catalysts

| Catalyst | Formula | Use | |---|---|---| | Wilkinson | $[(\mathrm{PPh_3})_3\mathrm{RhCl}]$ | hydrogenation | | Vaska | $[(\mathrm{PPh_3})_2\mathrm{Ir(CO)Cl}]$ | $\mathrm{O_2}$ binding studies | | Ziegler-Natta | $\mathrm{TiCl_4 + Et_3Al}$ | polyolefin polymerisation | | Grubbs | Ru-carbene + PCy₃ | olefin metathesis |

⚠️ Wilkinson Uses Ph, Vaska Uses Ph — Don't Confuse the Metals

Both use triphenylphosphine. The metal differentiates: Rh = Wilkinson, Ir = Vaska. Memorise the metals, not just the phosphine.

$\boxed{\text{Answer: (2) } [(\mathrm{Ph_3P})_3\mathrm{RhCl}]}$