Inverse Isotope Effects in Single-Crystal to Single-Crystal Reactivity and the Isolation of a Rhodium Cyclooctane...

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Organometallic Chemistry

Background:

• Single-crystal to single-crystal reactions offer precise mechanistic insights.
• Rhodium complexes with chelating phosphines are key catalysts in hydrogenation.
• Understanding reaction pathways in the solid state is crucial for catalyst design.

Purpose of the Study:

• To investigate the sequential solid/gas reaction of a rhodium complex with H2/D2.
• To elucidate the mechanism and kinetics of the hydrogenation reaction in the solid state.
• To determine the structural features of the resulting sigma-alkane complex.

Main Methods:

• In situ monitoring using solid-state 31P{1H} NMR spectroscopy (SSNMR).
• Ex situ analysis via solution quenching and Gas Chromatography-Mass Spectrometry (GC-MS).
• Kinetic modeling using a two-step Johnson-Mehl-Avrami-Kologoromov (JMAK) model.
• Structural determination aided by Density Functional Theory (DFT) calculations.

Main Results:

• Observed a sequential single-crystal to single-crystal reaction pathway.
• Quantified reaction kinetics using the JMAK model, revealing an inverse isotope effect for the second H2 addition.
• Determined the structure of the sigma-alkane complex, showing an eta2,eta2-binding mode to the Rh(I) center.
• Documented extensive H/D exchange during D2 addition, influenced by the solid-state environment.

Conclusions:

• The solid-state microenvironment significantly influences rhodium-catalyzed hydrogenation reactions.
• An inverse isotope effect was identified, providing mechanistic details for the reaction.
• The study successfully determined the structure of a transient sigma-alkane complex formed in situ.