In-Situ Vibrational Spectroscopies, BTEM Analysis and DFT Calculations

Abstract

Reactions of $\mathrm{{Rh}}_{2}(\mathrm{{CO}})_{4}\mathrm{{Cl}}_{2}$ with two conjugated dienes, namely, 2,3-dimethyl-1,3-butadiene (DMBD) and isoprene, were performed in anhydrous hexane under argon atmosphere with multiple perturbations of reagents. These reactions were monitored by in-situ FTIR (FIR and MIR) and/or Raman spectroscopies and the collected spectra were further analyzed with BTEM family of algorithms. The combined spectroscopic data seems to suggest that one organo-rhodium product $\mathrm{{Rh}}_{2}(\mathrm{{CO}})_{4}\mathrm{{Cl}}_{2}(\eta ^{4}$-diene) ($\mathrm{{diene}} = \mathrm{{DMBD}}$, isoprene) was the main product during the reactions. DFT calculations further confirm that three carbonyls are bonded to one rhodium atom while the 4th carbonyl and a chelating diene ligand are bonded to the other rhodium atom. The possible coordination geometry was obtained with (1) the consideration of the coordination chemistry and (2) the consistence between the DFT predicted spectra in FTIR and Raman regions with the corresponding BTEM estimates. The present contribution shows that BTEM can be meaningfully applied to the reaction of $\mathrm{{Rh}}_{2}(\mathrm{{CO}})_{4}\mathrm{{Cl}}_{2}$ and DMBD/isoprene in order to provide enhanced spectroscopic analysis, especially in the FIR and Raman regions. Furthermore, the present results provide a better understanding of the coordination chemistry of $\mathrm{{Rh}}_{2}(\mathrm{{CO}})_{4}\mathrm{{Cl}}_{2}$ with conjugated dienes.