Novel complexes cis,cis-[Rh(R)2(I)(CO)(dmb)] (R=Me, iPr; dmb=4,4′-dimethyl-2,2′-bipyridine): synthesis, structure and photoreactivity

The synthesis, structure and photochemistry of the novel rhodium(III) complexes cis,cis-[Rh(R)2(I)(CO)(dmb)] (R=Me (1), iPr (2)) are reported. Although many di- and trimethyl–rhodium(III) complexes are known, cis,cis-[Rh(iPr)2(I)(CO)(dmb)] (2) is the first diisopropyl–rhodium(III) compound. Single-crystal X-ray diffraction studies revealed the structure of 1. Resonance Raman spectra were obtained by excitation into the lowest-energy allowed electronic transition of the complexes. These spectra show that this transition has halide-to-ligand charge transfer (XLCT) character. Upon irradiation in solution, both 1 and 2 give rise to Rh–R bond homolysis as evidenced by IR, UV–vis and spin-trap EPR investigations. The photoreaction is proposed to occur after crossing from the XLCT state to the reactive sigma-bond-to-ligand charge transfer (SBLCT) state. For the iPr-complex homolysis is observed at longer wavelength irradiation than for the methyl derivative, indicating that in the former case the reactive state is lower in energy.