Mechanism for Site-Selective Hydroboration of C 70 Fullerene with Borane by DFT-D3 Study

We studied the hydroboration of the C fullerene using both B3LYP-D3(BJ)/6-311G(d,p) and M06-2X-D3/6-311G(d,p) levels of theory, incorporating the empirical dispersion interaction, and Fukui index calculations. Potential energy surfaces (PESs) and Gibbs free energy surfaces (GFESs) were calculated for the pathways from four BH adducts (located at the , , , and sites) on the C to eight products formed by the 1,2-addition of BH across the four [6,6]-ring fused bonds ( , , , and ) and across the two [5,6]-ring fused bonds ( and ). These pathways are two-step consecutive reactions. We denoted the positions on the fullerene cage as through , from the pole to the equator, based on the D symmetry of the C fullerene. In the first step reaction, the product ratios for the four adduct intermediates should be as the primary intermediate BH ( ), the secondary intermediate BH ( ), the tertiary intermediate BH ( ), and the minor intermediate BH ( ), based on the Fukui indices. In addition, in the second step reaction, transition states (TSs) from four adduct intermediates to eight product isomers, namely, BH ( )H ( ) to BH ( )H ( ), were obtained using the QST2 method. The calculated reaction coordinates showed exothermic reactions for all bonds except the bond. We also confirmed the transition states by frequency calculations and intrinsic reaction coordinate (IRC) analyses. The PESs and GFESs suggest spontaneous processes for the four isomers, of which the primary products are BH ( )H ( ) and its isomer BH ( )H ( ), the secondary product is BH ( )H ( ), and the tertiary product is BH ( )H ( ), all formed through adduct intermediates. Therefore, through the hydroboration reaction of C , we could predict and design the site selectivity of C by controlling the energy barrier of the transition state in the second step of the reaction. This implies that we could selectively synthesize mainly BH ( )H ( ) isomers across the AB-[6,6]-ring fused bond and also design BH ( )H( ) isomers across the DD-[5,6]-ring fused bond. Also, the calculations of formation rate constants can well simulate the experimental ratio of two C H isomers by the hydrolysis of BH ( )H( ), BH ( )H( ), and BH ( )H( ) products at room temperature.