Cj. Kleverlaan et al., FT-EPR study of alkyl radicals formed in the photochemical reaction of Re(alkyl)(alpha-diimine) and Ru(alkyl)(alpha-diimine) complexes, APPL MAGN R, 15(2), 1998, pp. 203-214
A Fourier transform EPR (FT-EPR) study was made of the photochemistry of [R
e(R)(CO)(3) (alpha-diimine)] and [Ru(E)(R)(CO)(2)(alpha-diimine)] complexes
, where R = alkyl or benzyl, E = I or SnPh3, and a-diimine = 4,4'-dimethyl-
2,2' -bipyridine (DMB) or N,N'-diisopropyl-1,4-diazabutadiene (iPr-DAB). Ph
otoexcitation of these complexes leads to homolysis of the metal-alkyl (ben
zyl) bonds as evident from the detection of the spectra of the alkyl (benzy
l) radicals. FT-EPR spectra display strong spin polarization effects attrib
uted to Triplet Mechanism (TM) and Radical Pair Mechanism (RPM) Chemically
Induced Dynamic Electron Polarization (CIDEP). CIDEP patterns point to bond
dissociation via a triplet state precursor For a number of complexes, spin
polarization was found to exhibit unusually large solvent effects, whereas
for one complex the CIDEP pattern proved to be sensitive to the wavelength
of laser light used to initiate bond dissociation. These effects reflect t
he strong dependence of CIDEP on the character of the excited states involv
ed in the photochemical reactions and contribute to the understanding of th
e reaction mechanism.