Density Functional Study on the Electronic and Molecular Structure of the Hydroformylation Catalyst HCo(CO)₃

A theoretical study has been carried out on the electronic and molecular structure of the hydroformylation catalyst HCo(CO)₃ as well as the parent molecule HCo(CO)₄. The study was based on a nonlocal density functional (DF) method. The parent molecule has a trigonalbipyramidal structure with hydrogen in the axial position. The catalyst HCo(CO)₃ adopts a singlet ground state with a geometry of C_s symmetry where one equatorial CO group has been removed from HCo(CO)₄. The other singlet structure of symmetry with an axial CO group removed from HCo(CO)₄ is 35 kJ mol⁻¹ higher in energy. Optimizations have further been carried out on five triplet states of HCo(CO)₃; they are found to be ∼100 kJ mol⁻¹ higher in energy than the C_s singlet structure. Calculations have also been carried out on the IR spectra of HCo(CO)₄ and HCo(CO)₃, in order to interpret the low-temperature vibrational spectra obtained in a krypton matrix after photolysis of HCo(CO)₄. The following bond energies have been obtained for HCo(CO)₄: D_e(Co-CO_ax) = 207 kJ mol⁻¹, De(Co-CO_eq) = 169 kJ mol⁻¹, and D_e-(Co-H) = 288 kJ mol⁻¹.