Experimental and Theoretical Study of the Silicon-Hydrogen Bond Activation by Rhodium Dicarbonyl Complex in Solution

Abstract

The photoreactivity of hydrotris-(3,5-dimethylpyrazolyl)boratedicarbonylrhodium(I) or HB(Pz*)3Rh(CO)2 complex has been studied at room-temperature n-pentane solution in the presence of 0.05 M Et3SiH (Et = C2H5). The IR spectra show that the decline of νCO parent complex at 1980 and 2054 cm-1 is followed by growing bands at 2029 and 2020 cm-1. In light of the photolysis of the parent complex in neat n-pentane solution the feature at 2020 cm-1 is tentatively assigned to the νCO band of the Si-H bond activation product. Upon standing in the dark, the 2020 cm-1 increases slightly in contrast with the 2029 cm-1 peak which decreases over time. These observations raise question whether the intensity increase of the 2020 cm-1 peak occurs unimolecularly resulting from the intramolecular rearrangement of the C-H bond activation of Et3SiH or bimolecularly as a result of the elimination of the C-H bond activation of the solvent and subsequent re-addition of the Si-H bond of the Et3SiH ligand. To gain more insight to reaction dynamics of the Si-H bond activation, the experimental results are compared to the photolysis of the parent complex in neat Et3SiH. The quantum efficiency (ϕSi-H) of this photoreaction yields a low value of 0.16. The results indicate that the Si-H bond activation is facilitated by intramolecular rearrangement mode. In addition, a theoretical study was conducted using density functional study at B3LYP/LanL2DZ level of theory, and the findings implicate that the final complex product was produced by the Si-H bond activation of Et3SiH.