Conversion of Pd(I) off-cycle species into highly efficient cross-coupling catalysts.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Palladium complexes like [Pd2(μ-Cl)(μ-η3-R-allyl)(NHC)2] are often considered inactive off-cycle species in cross-coupling reactions.
• Understanding the transformation of these species is crucial for optimizing catalytic processes.

Purpose of the Study:

• To report a facile method for converting undesirable palladium complexes into active pre-catalysts.
• To elucidate the mechanism of this transformation using DFT calculations.
• To identify factors that promote or inhibit the formation of palladium(I) dimers.

Main Methods:

• Conversion of [Pd2(μ-Cl)(μ-η3-R-allyl)(NHC)2] complexes to [PdCl(μ-Cl)(NHC)]2 pre-catalysts.
• Mild reaction conditions: 40 °C, 1-2 hours in acetone.
• Use of hydrochloric acid (HCl) as an oxidant and chloride source.
• Density Functional Theory (DFT) calculations to investigate reaction pathways.

Main Results:

• Successful and facile conversion of off-cycle palladium species into active pre-catalysts.
• Reactions occur under mild, energy-efficient conditions.
• DFT calculations suggest a mechanism involving two distinct pathways.
• Insights gained into the formation of undesired palladium(I) dimers.

Conclusions:

• A practical method for activating dormant palladium complexes has been developed.
• The study provides a mechanistic understanding of the conversion process.
• This work contributes to controlling palladium speciation and improving cross-coupling catalysis.