Remarkable Influence of X and R on the Charge Transfer Character(MLCT or XLCT) of the Complexes [Ru(X)(R)(CO)2(L)] (X = Halide, Triflate; R = Alkyl; L = .alpha.-Diimine): an UV-Vis Absorption and Resonance Raman Study

Abstract

Complexes of the type [Ru(X)(R)(CO)2(L)] (X = halide, CF3S03; R = alkyl; L = N,N '-diisopropyl-1,4-diaza-1,3-butadiene, pyridine-2-carbaldehyde TV-isopropylimine, 2,2,-bipyridine) experience significant influences of X and R on the energies and relative intensities of their lowest-energy electronic transitions. The halide complexes show two absorption bands in the visible region, which are assigned to two sets of charge transfer transitions from mixed metal-halide orbitals. Variation of the halide from Cl to I gives rise to a change in character of the lowestenergy band from MLCT to XLCT, as evidenced by resonance Raman spectra. These spectra show enhancement of Raman intensity for both ys(CN) and vs(CO) in the case of the Cl complex, but only for vs(CN) for the corresponding I complex. Variation of the alkyl ligand from Me to iPr leads to a shift of both absorption bands to lower energy with a concomitant change of their relative intensities. The latter effect is again ascribed to a change of charge transfer character of the electronic transitions.

FT-EPR study of alkyl radicals formed in the photochemical reaction of Re(alkyl)(α-diimine) and Ru(alkyl)(α-diimine) complexes

“…In the optical spectra of these complexes there is no evidence of a a -i' band over the wavelength region from 300 to 550 nm. The interpretation of the optical spectra of the [Ru(I)(R)(CO) 2 (adiimine)] complexes is less straightforward because of the effect of admixture of Ru(d.) and I(pn) orbitals [23]. However, here again is no evidence of an optically allowed a -in' transition in the 300-550 nm range.…”

Synthesis and spectroscopic properties of Re(R)(CO)3(α-diimine) (R  alkyl; α-diimine  R′-pyCa, R′-DAB) complexes. Crystal structure of Re(Me) (CO)3 (iPr-DAB)

“…Resonance Raman spectroscopy has proved to be very useful in characterizing allowed electronic transitions [12,33], since only those vibrations that are vibronically coupled to these transitions will be resonance-enhanced.…”

“…The spectroscopic, photophysical and photochemical properties of the first set of complexes have been described elsewhere [12][13][14], while the synthesis, structural and spectroscopic properties of the second set are reported here. A preliminary account of the photochemistry of these Re complexes has appeared [15].…”

Synthesis, structure and spectroscopic properties of novel metal-metal bonded manganese-ruthenium complexes with α-diimine ligands. X-ray structure of [(CO)5MnRu(Me)(CO)2(σ(N′)-iPr-PyCa)] (iPr-PyCa = pyridine-2-carbaldehyde-N-isopropylimine)

“…The frequencies of these bands are high compared to the values obtained for related complexes. Thus, the highest vs(CO) frequency of [Ru(C1)(Me)(CO)2(iPr-DAB)] is at 2033 cm -1 (CH2C12) [28]. As shown before, replacement of C1 by Mn(CO)5 increases the electron density at Ru and the zr-backbonding to the iPr-DAB ligand.…”

“…This means that the electronic transition is indeed accompanied by transfer of negative charge to this ligand. The value of 1485 cm -~ is much lower than that measured for a mononuclear halide complex such as [Ru(CI)(Me)(CO)2(iPr-DAB)] (us(CN)=1568 cm-1) [28]. This effect is caused by the stronger electrondonating properties of the Mn(CO)5 group with respect to C1, which is reflected in an increase of-rr-backdonation to the iPr-DAB ligand.…”