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

Abstract

The synthesis, structure and photochemistry of the novel rhodium(III) complexes cis,cis-[Rh(R) 2(I)(CO)(dmb)] (R=Me ( 1), i Pr ( 2)) are reported. Although many di- and trimethyl–rhodium(III) complexes are known, cis,cis-[Rh( i Pr) 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 i Pr-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.