Copper and Silver Carbene Complexes without Heteroatom-Stabilization: Structure, Spectroscopy, and Relativistic...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Coordination Chemistry

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.
• Carbenoid species are implicated as intermediates in various catalytic transformations.
• Understanding the electronic and structural properties of metal-carbene bonds is crucial for catalyst design.

Purpose of the Study:

• To synthesize and characterize novel silver and copper carbene complexes stabilized by a bulky NHC ligand (IPr**).
• To investigate the carbenoid character of these complexes using spectroscopic and crystallographic methods.
• To compare the properties of these Group 11 metal carbene complexes and elucidate the role of relativistic effects.

Main Methods:

• Synthesis of dimesityl diazomethane.
• Preparation of silver and copper carbene complexes using the IPr** ligand.
• Single-crystal X-ray diffraction analysis.
• Spectroscopic characterization (UV-Vis, NMR).

Main Results:

• Isolation and characterization of the first silver carbene complex, [IPr**Ag=CMes2 ](+) [NTf2 ](-), exhibiting predominant carbenoid character.
• Synthesis of the corresponding copper carbene complex, [IPr**Cu=CMes2 ](+) [NTf2 ](-).
• Spectroscopic data for the copper complex fall between those of the silver and previously reported gold analogues.
• Single-crystal X-ray diffraction confirms the carbenoid nature of the silver complex.

Conclusions:

• The steric bulk of the IPr** ligand enables the isolation of unprecedented silver carbene complexes.
• The characterized silver carbene complex provides strong evidence for carbenoid intermediates in silver-catalyzed C-H activation.
• Relativistic effects significantly influence the bonding in gold carbene moieties within the Group 11 series.