Investigation of the Exchange Mechanism in Some Rhodium Complexes using Density Functional Theory and comparison with Experimental Results

Abstract

This work focus on theoretical studies by DFT/B3LYP that is in order to determine the mechanism of transition between two isomers of Rh (III) CpRh (SiR₂R^') (H) (C₂H₄) (R₂R^'= H3, Me₃) and then compared with experimental results. The structure and the infrared spectrum of the intermediate state between two isomers were identified. Results of structure of intermediate state obtained indicate to the existence of bond of type η²-Si–H, and the length of the Si-H bond was about 1.6 Å. Spectroscopic study insist that the intermediate state is transition state due to the presence of imaginary frequency . It was found as well the following values of ΔS = 7.6 kJ / mol ,  ΔH = 65.4 kJ / mol, ΔG = 62.9 kJ/mol which were obtained by calculating the parameters of activation transitional state of the complex CpRh (SiMe₃) (H) (C₂H₄). These values were in a very good agreement with the following experimental values of the complex CpRh (SiMe₃) (H) (C₂H₃CO₂^tBu), ΔS = 12 ± 9 kJ / mol, ΔH = 61.9 ± 3 kJ / mol, ΔG = 58.9 ± 0.1 kJ / mol. Based on the results of the theoretical study it can be concluded that the transition between two isomers are made through forming a complex transitional contain the bond type η²-Si-H followed by a rotation around the Si –H bond.