trans-cis C-Pd-C rearrangement in hemichelates

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Computational Chemistry

Background:

• Heteroleptic palladacycles are known, but their dynamic behavior and isomerization mechanisms are not fully understood.
• Conventional homoleptic palladacycles exhibit distinct isomerization pathways.
• Understanding the kinetic stability and isomerization of metal complexes is crucial for catalysis and materials science.

Purpose of the Study:

• To investigate the kinetic instability and isomerization of heteroleptic trans-bispalladacycles.
• To elucidate the mechanism of trans-to-cis isomerization in these complexes.
• To compare the isomerization pathways of heteroleptic and homoleptic palladacycles.

Main Methods:

• Isolation and characterization of trans and cis isomers using X-ray diffraction analysis.
• Monitoring isomerization via variable temperature Nuclear Magnetic Resonance (NMR) spectroscopy.
• Localization of transition states using Density Functional Theory (DFT) calculations.

Main Results:

• Three trans and five cis isomers of heteroleptic palladacycles were successfully isolated and structurally characterized.
• Variable temperature NMR experiments revealed facile trans-to-cis isomerization in heteroleptic palladacycles.
• DFT investigations identified a low-lying transition state enabling square planar coordination preservation during isomerization, contrasting with homoleptic analogs requiring unfavorable intermediate states.

Conclusions:

• Hemichelation enables kinetically unstable heteroleptic palladacycles to undergo facile trans-to-cis isomerization.
• The isomerization mechanism for heteroleptic palladacycles differs significantly from homoleptic ones due to coordination preferences.
• DFT calculations provide valuable insights into the transition states governing these dynamic processes in organometallic complexes.