Theoretical study of the dissociation of a single carbonyl from chromium hexacarbonyl
- Additional Document Info
- View All
Extended-basis-set Hartree-Fock-Roothaan calculations are reported for the dissociation of a single carbonyl ligand from chromium hexacarbonyl. As expected, the theoretical dissociation energy for the process Cr(CO)6 → Cr(CO)5 + CO (49.8 kcal mol-1) is larger than the average dissociation energy (29.5 kcal mol-1). The theoretical dissociation energy for the ion, Cr(CO)6+ → Cr(CO)5+ + CO (30.8 kcal mol-1), agrees well with the recent mass spectral value (33.0 kcal mol-1) of Michels, Flesch, and Svec (Inorg. Chem. 1980,19, 479). Energy partitioning and analysis suggests that π bonding accounts for about 25% of the dissociation energy. Plots of the change in electron density as the carbonyl dissociates are reported. Comparison of these plots with those produced from various population analyses suggest that the σ bond involves primarily a rehybridization of the CO with little net transfer of electron density to the metal. The π bond, however, does involve a net transfer of charge from the metal to the carbonyl. Thus, the chromium is found to bear a net positive charge in agreement with the recent X-ray diffraction study of Rees and Mitschler (J. Am. Chem. Soc. 1976, 98, 7918). At very long chromium-carbon distances the carbonyl moiety may act like a “σ-only” ligand. Calculations of the change in the force between the C and the O of a free carbonyl as it approaches the Cr(CO)5 fragment show that at moderately long Cr-C distances the force is such that the C-O bond distance should be shorter than that of free CO. A well-documented example of this is provided by the low-temperature X-ray structure of Rh2(O2CCH3)4(CO)2 by Koh and Christoph (J. Am. Chem. Soc. 1979, 101, 1422). This molecule has a long Rh-C distance of 2.092 (4) Å and a remarkably short C-0 distance of 1.120 (4) Å. Recently, Gagné et al. (Inorg. Chem. 1982, 21, 254) reported the structure of a Cu dimer that had C-0 distances of 1.10 (1) and 1.11 (1) Å. © 1983, American Chemical Society. All rights reserved.
author list (cited authors)
Sherwood, D. E., & Hall, M. B.