Spectroscopic and theoretical evaluation of the metal-olefin interaction in di-μ-chlorobis (1,5-cyclooctadiene) complexes of Ir and Rh

The complexes of di-μ-chlorobis(1,5-cyclooctadiene) of rhodium(I); [Rh(μ-Cl)(COD)]₂ and iridium(I); [Ir(μ-Cl)(COD)]₂ have shown prominent activities in a number of catalytic reactions. In the solid packing form these two complexes were shown to adopt D_2h and C_2v symmetries for iridium and rhodium, respectively. In this work vibrational spectroscopic techniques assisted with density functional theory (DFT) calculations have been employed to assess the metal-olefin interaction and to provide thorough assignments of the infrared and Raman spectra for both complexes. The wavenumber shifts associated with the CH₂ bending modes have been established as a potential tool to access the σ and π components in the metal-olefin interaction for the two complexes. Examination of the catalytic activity based on calculated reactivity parameters, natural bond orbital (NBO) analysis and coordination energy was also carried out.