Comparing Isomeric Tridentate Carbazole-Based Click Ligands: Metal Complexes and Redox Chemistry.

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• Carbazole derivatives are versatile ligands in coordination chemistry.
• Triazole moieties offer tunable electronic properties through regioselective synthesis.
• Metal complexes with carbazole-triazole ligands are of interest for their photophysical and redox behavior.

Purpose of the Study:

• To synthesize novel bis(triazolyl)carbazole ligands with different triazole regiochemistry.
• To prepare and characterize metal complexes (M=Ru, Zn, Ni) of these ligands.
• To investigate the redox properties of the resulting metal complexes and correlate them with ligand structure.

Main Methods:

• Synthesis of bis(triazolyl)carbazole ligands (Hbtc1, Hbtc2) via copper-catalyzed azide-alkyne cycloaddition ('click chemistry').
• Formation of M(btc)2 complexes through metalation with Ru, Zn, and Ni precursors.
• Electrochemical and spectroscopic characterization, including cyclic voltammetry (CV), UV/Vis spectroscopy, and spectroelectrochemistry.

Main Results:

• Two ligands, Hbtc1 and Hbtc2, differing in triazole attachment regiochemistry, were successfully synthesized.
• Octahedral M(btc)2 complexes were formed, featuring two deprotonated ligands coordinating in a tridentate fashion.
• Ruthenium complexes exhibited three quasi-reversible oxidation waves (RuII/III and two ligand-based).
• Zinc and Nickel complexes showed two ligand-based oxidation waves.
• Complexes from Hbtc1 ligands displayed 300-400 mV lower oxidation potentials compared to Hbtc2 analogs, indicating enhanced electron donation.

Conclusions:

• The regiochemistry of triazole attachment significantly impacts the electronic properties of bis(triazolyl)carbazole ligands and their metal complexes.
• The N(2) attachment in Hbtc1 facilitates greater electron donation compared to N(3) attachment in Hbtc2.
• These findings provide insights into the design of novel organometallic materials with tunable redox potentials.