Nucleophilic T-Shaped (LXL)Au(I)-Pincer Complexes: Protonation and Alkylation

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Carbene Chemistry

Background:

• Gold(I) complexes typically show limited reactivity towards electrophiles.
• Pincer ligands offer unique coordination environments and influence metal center reactivity.
• Mesoionic carbenes (MICs) are versatile ligands in organometallic chemistry.

Purpose of the Study:

• To synthesize and characterize novel T-shaped (LXL)Au(I)-pincer complexes incorporating a carbazole framework and two MIC ligands.
• To investigate the reactivity of these Au(I) complexes with electrophiles, particularly protonation and alkylation.
• To explore the formation and properties of unusual cationic gold species.

Main Methods:

• Synthesis of carbazole-based pincer ligands.
• Coordination of ligands to Au(I) precursors.
• Reaction of Au(I) complexes with electrophiles (e.g., protons, alkylating agents).
• Characterization using NMR spectroscopy (including 1H NMR) and potentially X-ray crystallography.

Main Results:

• Successful synthesis of T-shaped (LXL)Au(I)-pincer complexes featuring a carbazole core and MIC ligands.
• Demonstration of electrophilic attack (protonation, alkylation) at either the gold metal center or the ligand, influenced by steric factors.
• Formation of a unique cationic Au(III) hydride species upon protonation at gold, characterized by a distinct 1H NMR signal at δ -8.34 ppm.
• Observation that the reactivity of the Au(III) hydride species is protic rather than hydridic.

Conclusions:

• The synthesized T-shaped (LXL)Au(I)-pincer complexes display unexpected reactivity towards electrophiles, diverging from typical Au(I) behavior.
• Protonation can lead to the formation of a novel cationic Au(III) hydride, expanding the known organometallic chemistry of gold.
• The observed reactivity highlights the significant influence of ligand design (carbazole framework, MICs) on the electronic and steric properties of gold complexes.