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Quantum mechanical calculations at the MP4(SDQ)//MP2 were carried out to evaluate, a priori, the reactivity of [(η 5 -phospholyl)Rh(CO) 2 ] toward C-H bond activation of methane. The compound [(η 5 -phospholyl)Rh(CO) 2 ] is an analogue of [(Cp)Rh(CO) 2 ], which is well known to activate alkanes of moderate sizes. Our results show that compound [(η 5 -phospholyl)Rh-(CO) 2 ] has a singlet ground state, with the lowest triplet state lying 55.1 kcal/mol above it. The calculation of the electronic spectrum of this compound revealed that the MLCT charge transfer band (M f CO) that leads to CO dissociation occurs at much higher energy (5.28 and 5.54 eV) than the value for the parent Cp compound. The methane substrate interacts with the monocarbonyl compound, generated after CO dissociation, forming a η 2 adduct, which is stabilized by 11.7 kcal/mol. The C-H bond activation of methane proceeds through a three-center transition state with a small activation enthalpy of 6.1 kcal/mol, relative to the η 2 adduct intermediate. Comparisons with the [(Cp)Rh(CO) 2 ] analogue are made and discussed. The results presented in this work suggest that the compound [(η 5 -phospholyl)-Rh(CO) 2 ] can be used to activate the C-H bond of alkanes.

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ABSTRACT:The importance of Sn to improve the performance of noble metal-based catalysts has been extensively discussed in the literature. However, a detailed discussion about the effect of Sn on the electronic structure of the metals has not been reported so far. In this work, density functional theory (DFT) calculations have been performed on the M 2 and MSn (MARu, Rh, Pd, Sn) dimers and their interaction with CH 2 and CF 2 carbenes. The electronic structure, geometry, and harmonic frequencies are reported and compared with the available experimental data and to the previous published high level ab initio and DFT calculations. The calculated values of M 2 are in good agreement with the experimental and theoretical results. The exception is the binding energy of the Sn dimer, which can be different from the experimental estimates as much as 16 kcal ⅐ mol Ϫ1 . It has been stressed that this difficulty is related to the atomic energy reference used to estimate the binding energy. Transition metal elements are still a difficult task for DFT methods. Calculations on MSnOCH 2 and MSnOCF 2 species with different multiplicities and conformations have been performed. Bonding analyses on the MOSn metal dimers showed that carbenes prefer to adsorb in bridge sites favoring a donating/backdonating mechanism of interaction that is enhanced with the presence of the Sn atom. The MSnOCH 2 binding energy is predicted to be 40% smaller than the MSnOCF 2 binding energy, following the same trends observed for the first-row transition-metal MOCH 2 and MOCF 2 complexes.