The DFT study on Rh-C bond dissociation enthalpies of (iminoacyl) rhodium(III)hydride and (iminoacyl)rhodium(III)alkyl

Rhodium transition-metal-organic cooperative catalysis, which has been intensively studied by many chemists, represents a great success in C-H bond activation because of high efficiencies and selectivities. Typically, in the reaction mechanism of aldehyde and alkene catalyzed by Rh(I) complex and 2-amino-3-picoline, two kinds of metala-cyclic transition-metal complexes of (iminoacyl)rhodium(III)hydride and (iminoacyl)rhodium(III) alkyl are generally formed. The two complexes play an important role in the overall reaction, in which the Rh-C bond formations are involved. So it is meaningful to understand the strength of Rh-C bond, which can be measured by the homolytic bond dissociation enthalpies (BDEs). To this end, we first calculated 16 relative Rh-C BDEs of Tp'Rh(CNneopentyl)RH (Tp' = hydridotris-(3,5-dimethylpyrazolyl)borate) by 19 density functional theory (DFT) methods. Furthermore, the 5 absolute Rh-C BDEs of Rh transition-metal complexes were also calculated. The results show that the B97D3 is the most accurate method to predict the relative and absolute Rh-C BDEs and the corresponding RMSE values are the smallest of 2.8 and 3.3 kcal/mol respectively. Therefore, the Rh-C BDEs of (iminoacyl)rhodium(III)hydride and (iminoacyl)rhodium(III)alkyl as well as the substituent effects were investigated by using the B97D3 method. The results indicated that the different substituents exhibit different effects on different types of Rh-C BDEs. In addition, the analysis including the natural bond orbital (NBO) as well as the energies of frontier orbitals were performed in order to further understand the essence of the Rh-C BDE change patterns. (C) 2018 Elsevier Ltd. All rights reserved.