DFT Study on the Co-Xe Bond in the HCo(CO) Xe Adduct

The metal-xenon interaction has been studied in hydrido-cobalt-carbonyl complexes by means of density functional methods. The method of choice has been selected after testing various functionals including dispersion correction on the bond dissociation enthalpy of Xe in the Cr(CO)5Xe adduct. In general, the long range corrected versions of popular gradient-corrected functionals performed well. In particular, LC-mPWPW91 resulted in a perfect match with available experimental data; therefore this functional was selected for the computation of HCo(CO)3Xe adducts. For HCo(CO)3Xe two isomers have been located; the structure with CS symmetry has proved to be more stable by 5.3？kcal/mol than the C3V adduct in terms of free energy. The formation of HCo(CO)3Xe is, however, endergonic by 3.5？kcal/mol for the CS isomer. 1. Introduction Hydroformylation of olefins is one of the most important applications of homogeneous catalysis in industry. The first precatalyst system containing Co2(CO)8 and HCo(CO)4 was applied originally by Roelen [1]. This catalytic system is still in application predominantly for hydroformylation of higher olefins. According to Heck and Breslow [2] the initial step of the reaction is the dissociation of one of the CO ligands from HCo(CO)4 resulting in HCo(CO)3 as the active catalyst. It is known that the rate of cobalt-catalyzed hydroformylation of olefins can be significantly reduced by the addition of a seemingly inert gas component such as N2, Ar, or Xe to the reaction mixture [3–5]. The retarding effect can be explained by competitive coordination of the inert gas component, for example, the xenon to the catalytically active coordinatively unsaturated HCo(CO)3 complex: Among the few examples of transition metal, noble gas adducts and the M(CO)5-Ng complexes (M = Group 6 metals; Ng = noble gas, such as argon, krypton, or xenon) are best examined. The experimental studies provided information about bond energies and infrared spectra [6, 7]; however, no structural information was obtained. The most comprehensive theoretical study on these types of complexes was completed by Ehlers et al. Optimized geometries and M-Ng bond energies were reported, which corresponded well with the experimental results [8]. Ono and Taketsugu investigated the binding of noble gas atoms to the coordinative highly unsaturated NiCO and CoCO species with density functional, multireference, and coupled-cluster methods [9, 10]. It was also shown that two Ng atoms can bind with Pt atom in linear geometry [11]. The aim of this work is to shed some light to the molecular