Before You Begin

Question #44605

Difficulty: 8/10 | 🟢 Free

The Question

Consider the reaction of solid pentacarbonylchloromanganese(I), $\ce{[Mn(CO)5Cl]}$ , with a solution of methylmagnesium bromide ( $\ce{CH3MgBr}$ ) in THF at 298 K to form an intermediate organometallic complex $\mathbf{X}$ . Subsequent heating of $\mathbf{X}$ with one equivalent of triphenylphosphine ( $\ce{PPh3}$ ) in a non-polar solvent yields complex $\mathbf{Y}$ . Assuming all major complexes obey the 18-electron rule, identify the structures of $\mathbf{X}$ and $\mathbf{Y}$ .

Options

A.
$\mathbf{X} = \ce{[Mn(CH3)(CO)5]}$ , $\mathbf{Y} = \ce{[Mn(COCH3)(CO)4(PPh3)]}$
B.
$\mathbf{X} = \ce{[Mn(COCH3)(CO)4Cl]-}$ , $\mathbf{Y} = \ce{[Mn(COCH3)(CO)3(PPh3)Cl]-}$
C.
$\mathbf{X} = \ce{[Mn(CH3)(CO)5]}$ , $\mathbf{Y} = \ce{[Mn(CH3)(CO)4(PPh3)]}$
D.
$\mathbf{X} = \ce{[Mn(CO)4(CH3)Cl]-}$ , $\mathbf{Y} = \ce{[Mn(CH3)(CO)3(PPh3)Cl]-}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Synergic Bonding in Carbonyls|Grignard Reagent Sensitivity|Nucleophilic Acyl Substitution

Why This Question Is Tricky

Common Mistakes

The trap exploits the student's organic chemistry bias.

When presented with a Grignard reagent and a carbonyl-containing compound, students instinctively predict nucleophilic acyl substitution at the carbonyl carbon (Option B).

However, in transition metal carbonyls, synergic $\pi$ -backbonding increases electron density on the CO carbon, rendering it less electrophilic.

The metal center, bearing a leaving group ( $\ce{Cl-}$ ), is the actual electrophilic site.

Furthermore, students must recognize that ligand substitution in alkyl carbonyl complexes typically proceeds via migratory insertion rather than direct CO displacement (Option C).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Coordination Compounds - Class 12
Concept	Synergic Bonding in Carbonyls
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free