Introducing the Perfluorinated Cp* Ligand into Coordination Chemistry

Area of Science:

• Organometallic Chemistry
• Fluorine Chemistry
• Coordination Chemistry

Background:

• The perfluorinated pentamethylcyclopentadienyl ([C5(CF3)5]-) ligand, synthesized in 1980, has been challenging to coordinate due to its weak basicity.
• Understanding ligand interactions is crucial for designing novel catalysts and materials.

Purpose of the Study:

• To synthesize and characterize a novel rhodium complex featuring the [C5(CF3)5]- ligand.
• To investigate the bonding properties and stability of this complex.
• To compare the interaction of [C5(CF3)5]- with rhodium against the traditional [C5(CH3)5]- ligand.

Main Methods:

• Salt metathesis reaction between AgBF4, [Rh(COD)Cl]2, and [NEt4][C5(CF3)5].
• Isolation and full characterization of the resulting complex [Rh(COD)(C5(CF3)5)] and byproduct [Rh(COD)(C5(CF3)4H)].
• Density Functional Theory (DFT) calculations to determine interaction energies.
• Experimental substitution studies with toluene.

Main Results:

• Successful synthesis of the fluorocarbon-soluble complex [Rh(COD)(C5(CF3)5)].
• DFT studies revealed a significantly lower interaction energy (≈70 kcal/mol) for [C5(CF3)5]- compared to [C5(CH3)5]- with the [Rh(COD)]+ fragment.
• Experimental evidence confirmed the weak bonding interaction through reversible substitution by toluene, indicating the ligand's ability to act as a weakly coordinating anion.

Conclusions:

• The [C5(CF3)5]- ligand can be successfully coordinated to rhodium, forming a stable complex.
• The perfluorinated nature of the ligand drastically reduces its electrostatic interactions and π-donor properties, leading to exceptionally weak bonding.
• This weak interaction opens possibilities for using [C5(CF3)5]- as a weakly coordinating anion in catalysis and materials science.