Question

The molecular formula of Wilkinson catalyst, used in hydrogenation of alkenes is:
A. ${\text{Co}}{\left( {{\text{CO}}} \right)_{\text{8}}}$
B. ${\left( {{\text{P}}{{\text{h}}_{\text{3}}}{\text{P}}} \right)_{\text{3}}}{\text{RhCl}}$
C. $\left[ {{\text{Pt}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}} \right]$
D. ${\text{K}}\left[ {{\text{Ag}}{{\left( {{\text{CN}}} \right)}_{\text{2}}}} \right]$

Answer 1

Hint: Wilkinson catalyst is a coordination compound. The centre of coordination of Wilkinson catalyst is rhodium. Wilkinson catalyst is named after Sir Geoffrey Wilkinson. The Wilkinson catalyst is reddish-brown coloured solid substance at ambient temperatures.

Complete step by step solution:
We are given that Wilkinson catalyst is used in hydrogenation of alkenes to alkanes. Wilkinson catalyst mainly catalyses hydrogenation of hydrocarbons along with many other reactions like hydroacylation, hydroboration and hydrosilylation of alkenes, it is effective in the selective reduction of olefins.
Wilkinson catalyst is produced by the reaction of rhodium (III) chloride hydrate with excess triphenylphosphine in ethanol. Triphenylphosphine acts as a reducing agent and ethanol acts as a refluxing agent.
The reaction is as follows:
${\text{RhC}}{{\text{l}}_{\text{3}}}{\left( {{{\text{H}}_{\text{2}}}{\text{O}}} \right)_{\text{3}}} + {\text{4PP}}{{\text{h}}_{\text{3}}} \to {\left( {{\text{P}}{{\text{h}}_{\text{3}}}{\text{P}}} \right)_{\text{3}}}{\text{RhCl}} + {\text{OPP}}{{\text{h}}_{\text{3}}} + {\text{2HCl}} + {\text{2}}{{\text{H}}_{\text{2}}}{\text{O}}$
The IUPAC name of Wilkinson catalyst is chlorotris (triphenylphosphine) rhodium (I). Its molecular formula is ${\left( {{\text{P}}{{\text{h}}_{\text{3}}}{\text{P}}} \right)_{\text{3}}}{\text{RhCl}}$. The structure of Wilkinson catalyst is as follows:

From the structure, we can conclude that the rhodium centre is bound to total four ligands. One chloride ligand and three triphenylphosphine ligands. Thus, the coordination number of the rhodium centre is four.
Thus, the molecular formula of Wilkinson catalyst, used in hydrogenation of alkenes is ${\left( {{\text{P}}{{\text{h}}_{\text{3}}}{\text{P}}} \right)_{\text{3}}}{\text{RhCl}}$.

Thus, the correct option id (B) ${\left( {{\text{P}}{{\text{h}}_{\text{3}}}{\text{P}}} \right)_{\text{3}}}{\text{RhCl}}$.

Note:
Wilkinson catalyst is insoluble in water but it is soluble in many hydrocarbon-based solvents like benzene, tetrahydrofuran, etc. The geometry of Wilkinson catalyst is a slightly distorted square planar having hybridisation $ds{p^2}$. It is diamagnetic in nature. Wilkinson catalyst undergoes dimerization when it is stirred in benzene solution. The formula of the dimer is ${\left[ {{{\left( {{\text{P}}{{\text{h}}_{\text{3}}}{\text{P}}} \right)}_{\text{3}}}{\text{RhCl}}} \right]_2}$.