The chromium-olefin complex Cr(CO)5(DMB) (DMB = 3,3-dimethyl-1-butene) has been studied in the gas phase using transient infrared spectroscopy. This complex forms by addition of DMB to photogenerated Cr(CO)5 with a rate constant, kL = (7.0 ± 1.5) × 10-11 cm3 molecule-1 s-1. The bond enthalpy for the DMB-Cr(CO)5 bond has been determined from the kinetics for the decay of Cr(CO)5(DMB) to be 20.1 ± 1.7 kcal/mol at 298 K. An energy decomposition analysis has been performed for a series of Cr(CO)5(olefin) complexes (olefin = DMB, ethylene, propene, 1-butene, 1-hexene, cis-2-butene, trans-2-butene, isobutene, and tetramethylethylene (TME)) using density functional theory. These calculations provide insights into trends in the chromium-olefin bond energy. The results reveal that the trend in bond energies in these complexes correlates with the number and the nature of the alkyl groups around the double bond, and that the dominant factor in this trend is the deformation energy of the olefin and Cr(CO)5, where the deformation energy is the energy required to deform the olefin ligand and the unsaturated metal centered moiety from their isolated ground-state geometries to the geometry they adopt in the bound complex.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry