title: Cycloaddition reactions of 16-electron d4 metallocene complexes with C60: a theoretical study.
abstract: The potential-energy surfaces of the cycloaddition reaction Cp(2)M+C60-->Cp(2)M(C60) (Cp=eta5-C(5)H(5); M=Cr, Mo, and W) were studied at the B3LYP/LANL2DZ level of theory. Two competing reaction pathways were found, which can be classified as [6,5] attack (path A) and [6,6] attack (path B). Given the same reaction conditions, the [6,6]-attack pathway for cycloaddition to C60 is more favorable than the [6,5]-attack pathway, both kinetically and thermodynamically. A qualitative model, based on the theory of Pross and Shaik, was used to develop an explanation for the reaction barrier heights. Thus, our theoretical findings suggest that the singlet-triplet splitting DeltaE(st) (=E(triplet)-E(singlet)) of the 16-electron d4 Cp(2)M and C60 species are a guide to predicting their reactivity towards cycloaddition. Our model results demonstrate that the propensity for cycloaddition to C60 increases in the order Cp(2)Cr<Cp(2)Mo<Cp(2)W. We show that both electronic and geometric effects play a decisive role in determining the energy barriers and reaction enthalpies.
authors.affiliation: Department of Applied Chemistry, National Chiayi University, Chiayi 60004, Taiwan.
authors.forename: Jeng-Horng
authors.initials: JH
authors.lastname: Sheu
authors.forename: Ming-Der
authors.initials: MD
authors.lastname: Su
mesh_terms: D004583:Electrons; D037741:Fullerenes / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*
chemical_list: D037741:Fullerenes; D009942:Organometallic Compounds; C013108:metallocene; C069837:fullerene C60