Unified Synthesis Platform for 1,2,3-Trisubstituted Cyclopentadienyl Ligands Decouples Sterics from Electronics

Area of Science:

• Organometallic Chemistry
• Catalysis
• Synthetic Chemistry

Background:

• Cyclopentadienyl (Cp) ligands are crucial in coordination chemistry and transition-metal catalysis, influencing reactivity, selectivity, and stability.
• Existing Cp ligands have limited chemical space due to constraints on substituent nature, pattern, and number.
• A unified strategy for diverse, partially substituted Cp ligands is needed to expand their utility.

Purpose of the Study:

• To develop a streamlined, general synthetic strategy for preparing 1,2,3-trisubstituted cyclopentadienes (1,2,3-Cps).
• To enable access to underexplored Cp substitution patterns with diverse functionalities.
• To demonstrate the tunability and catalytic performance of novel Cp ligands.

Main Methods:

• A general strategy using an inexpensive precursor for synthesizing 1,2,3-Cps.
• Operationally straightforward reactions and purifications for scalable sequences.
• Complexation studies with early and late transition metals and stereoelectronic parametrization.

Main Results:

• A robust platform for synthesizing 1,2,3-Cps with diverse alkyls, aryls, halogens, chalcogens, and alkynes.
• Demonstrated ligand tunability, decoupling sterics from electronics.
• Cobalt and rhodium complexes with novel Cps outperformed classical Cp ligands in benchmark catalytic reactions, showing improved reactivity, regioselectivity, and lower catalyst loading.

Conclusions:

• The developed strategy provides access to a broad range of novel Cp ligands, significantly expanding the accessible chemical space.
• Novel 1,2,3-Cp metal complexes exhibit superior catalytic performance compared to traditional Cp ligands.
• A 1,2,3-Cp cobalt complex achieved a turnover number (TON) of 180 in C-H annulation, highlighting practical catalytic utility.