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GATE 2025 CY – Question 39

Inorganic Chemistry · Organometallics: 18-Electron rule; metal-alkyl, metal-carbonyl, metal-olefin and metal-carbene complexes and metallocenes. Fluxionality in organometallic complexes. Types of organometallic reactions. Homogeneous catalysis – Hydrogenation, hydroformylation, methanol to acetic acid process, olefin metathesis and Wacker oxidation. Heterogeneous catalysis – Fischer-Tropsch reaction, Ziegler-Natta polymerization. · 2 marks · Multiple choice

The 1H NMR spectrum of the given iridium complex at room temperature gave a single signal at 2.6 ppm, and its 31P NMR spectrum gave a single signal at 23.0 ppm. When the spectra were recorded at lower temperatures, both these signals split into a complex pattern. The intra-molecular dynamic processes shown by this molecule are

Five-coordinate iridium complex with a chelating diphosphine and two ethylene ligands.
  1. Berry pseudo-rotation and rotation of the ethylene units along the C=C axis
  2. Berry pseudo-rotation and propeller type rotation of the ethylene units along the Ir-alkene axis
  3. Ray-Dutt twist and rotation of the ethylene units along the C=C axis
  4. Ray-Dutt twist and propeller type rotation of the ethylene units along the Ir-alkene axis

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Correct answer: (B) Berry pseudo-rotation and propeller type rotation of the ethylene units along the Ir-alkene axis

Explanation

The five-coordinate complex undergoes Berry pseudorotation, exchanging ligand positions. Propeller-like ethylene rotation about the metal–alkene axis exchanges its proton environments; rotation about C=C would break its pi bond.