Molecular complexes of small alkanes with Co+
Résumé
Using ab initio methods, including extensive electron correlation, we studied the molecular complexes of Co+ with H-2 and a number of small alkanes (CH4, C2H6, and C3H8). We found that the bond energies increase with ligand size, ranging from 17.2 (for Co(H2)+) to 29.3 kcal/mol (for Co(C3H8)+), in close agreement with recent experiments. For methane, Co+ coordinates to either two or three C-H bonds, with the eta2 geometry more stable by 1.3 kcal/mol out of 21.4 kcal/mol. For ethane, eta2 and eta3 coordinations of Co+ to the C-H bonds are also favorable, but these bonds can be on either the same carbon center or different centers (strict coordination to the C-C bond was not found). Adding a second CH4 to Co(CH4)+, we found that the second bond is stronger than the first by 1.7 kcal/mol. In addition, with both methanes in the eta2 Configuration, we found that the C-H bonds are eclipsed (8.3 kcal/mol better than the staggered conformation). With both methanes in the eta3 configuration, however, they are staggered.