Syntheses, structures, and spectroscopic properties of cis,cis- and trans,cis-[Ru(I)(Me)(CO)2(α-diimine)] complexes

The syntheses, structures, and spectroscopic properties are reported for trans,cis and cis, cis isomers of [Ru(I)(Me)(CO)(2)(alpha-diimine)] [alpha-diimine = N,N'-diisopropyl-1,4-diazabutadiene (iPr-DAB), pyridine-2-carbaldehyde N-isopropylimine (iPr-PyCa), 4,4'-dimethyl-2,2'-bipyridine (dmb)] which differ in their photochemical behaviour. The structures of trans,cis- and cis,cis-[Ru(I)(Me)(CO)(2)(iPr-DAB)] have been determined by a single-crystal X-ray diffraction study. The crystals of both isomers are monoclinic and belong to the same P2(1)/n space group with Z = 4. Refinement converged to R = 0.043 for the trans,cis isomer and to R = 0.065 for the cis,cis isomer. Both complexes have a distorted octahedral geometry, in the cis,cis isomer the methyl ligand is located in an equatorial, the iodide in an axial position. According to the H-1- and C-13-NMR and resonance Raman spectra the imine groups of the iPr-DAB ligand are inequivalent in the cis,cis isomer. The absorption spectra vary with the alpha-diimine, not so much with the isomeric structure of the complex. Both isomers possess two visible absorption bands, which, according to the resonance Raman spectra, belong to charge transfer transitions from mixed metal-halide orbitals to the alpha-diimine. The resonance Raman spectra show that this charge transfer excitation is accompanied, for both isomers, with an angular distortion of the methyl Ligand. These spectral data show that the difference in photochemical behaviour of the two isomers is not due to a change in the excited state character.