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), Pr-i (2)) are reported. Although many di- and trimethyl-rhodium(III) complexes are known. cis,cis-[Rh(Pr-i),(I)(CO)(dmb)] (2) is the first diisopropyl-rhodium(III) compound. Single-crystal X-ray diffraction studies revealed the structure of I. 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) slate. For the Pr-i-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. (C) 2001 Elsevier Science B.V. All rights reserved.