Cycloaddition reactions of 16-electron d4 metallocene complexes with C60: a theoretical study

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Cycloaddition reactions involving fullerenes are crucial for synthesizing novel carbon-based materials.
• Bis(cyclopentadienyl)metal complexes (Cp(2)M) are versatile organometallic compounds with potential applications in catalysis and materials science.

Purpose of the Study:

• To investigate the potential-energy surfaces and reaction pathways for the cycloaddition of Cp(2)M (M=Cr, Mo, W) to C60.
• To elucidate the factors governing the reactivity and selectivity of these cycloaddition reactions.

Main Methods:

• Density functional theory (DFT) calculations using the B3LYP functional and LANL2DZ basis set were employed.
• Analysis of two competing reaction pathways: [6,5] attack and [6,6] attack on the C60 cage.

Main Results:

• The [6,6]-attack pathway was found to be kinetically and thermodynamically more favorable than the [6,5]-attack pathway for all studied Cp(2)M complexes.
• A qualitative model correlating singlet-triplet splitting (ΔE_st) of the reactants with reaction barrier heights was developed.
• The propensity for cycloaddition to C60 increases in the order Cp(2)Cr < Cp(2)Mo < Cp(2)W.

Conclusions:

• The [6,6]-attack pathway is the preferred mechanism for Cp(2)M cycloaddition to C60.
• Singlet-triplet splitting serves as a reliable predictor of reactivity in these cycloaddition reactions.
• Both electronic and geometric factors significantly influence the energy barriers and reaction enthalpies, dictating the cycloaddition outcome.