Imidazol-2-ylidene stabilized tetrahedral cobalt carbonyl complexes: A computational and structural database study

A combined crystallographic database and computational chemistry analyses of tetrahedral cobalt (Co) carbonyl (CO) complexes bearing substituted imidazol-2-ylidene (Im) ligands were studied. These group of compounds are potential catalysts in the hydroformylation of alkenes as well as effective precursors for both chemical vapour deposition and atomic layer deposition in integrated circuit manufacture. A substructure search revealed seventeen (17) crystal structures in the Cambridge Structural Database (CSD). Generally, there was a positive correlation between the Im-Co bond length and the Co-CO bond length implying that a strong Im-CO bonding interaction could give rise to a more stable carbonyl complex. The gas phase structures of these complexes were further studied computationally at the BP86 level of the density functional theory. The def2-TZVPP basis set was used for cobalt with 6-31G (d,p) for all other atoms. It was observed that the Co-CO bond length increased with increase in bulkiness of alkyl substituents at the ortho positions of the Im ligands. Subsequent natural bond orbital (NBO) and chemical reactivity parameter analyses revealed that the chemical softness, electronic chemical potential and the ease of ionization also increased with increase in bulkiness of the alkyl substituents. This property has useful applications in catalytic systems and for the design of precursors in integrated circuit manufacture.