Novel photo-induced deracemization of [Co(acac)(3)] (acac=acetylacetonate)with a chiral ruthenium(II) complex, Delta-[Ru(menbpy)(3)](2+) (menbpy=4,4'-bis{(1R,2S,5R)-(-)-menthoxycarbonyl}-2,2 '-bipyridine). Reaction mechanism and significant effects of solvent and anion
T. Hamada et al., Novel photo-induced deracemization of [Co(acac)(3)] (acac=acetylacetonate)with a chiral ruthenium(II) complex, Delta-[Ru(menbpy)(3)](2+) (menbpy=4,4'-bis{(1R,2S,5R)-(-)-menthoxycarbonyl}-2,2 '-bipyridine). Reaction mechanism and significant effects of solvent and anion, J CHEM S DA, (6), 2001, pp. 928-934
Citations number
26
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
Deracemization of a racemic mixture of Delta- and Lambda-[Co(acac)(3)] (aca
c=acetylacetonate) took place with a chiral ruthenium(II) complex, Delta-[R
u(menbpy)(3)](2+) (menbpy=4,4'-bis{(1R,2S,5R)-(-)-menthoxycarbonyl}-2,2'-bi
pyridine), under visible light (420 < lambda < 470 nm) irradiation in the p
resence of either triethylamine or NaOH. The enantiomeric excess (e.e.) of
Lambda-[Co(acac)(3)] was 28% in acetonitrile-water (7:3 v/v; ionic strength
(I)=0.1 mol dm(-3) (KCl)) without acetylacetone and 38% with acetylacetone
(50 mmol dm(-3)) added to the solution. Quenching experiments on Delta-*[R
u(menbpy)(3)](2+) led to the conclusion that this deracemization occurs thr
ough combination of the preferential photo-reduction of Delta-[Co(acac)(3)]
by Delta-*[Ru(menbpy)(3)](2+) to afford [Co(acac)(2)] and the thermal oxid
ation of [Co(acac)(2)] by Delta-[Ru(menbpy)(3)](3+) to afford preferentiall
y Lambda-[Co(acac)(3)]. The selectivity of deracemization remarkably depend
s on the solvent; the e.e. value is 51% in acetone-water (7:3 v/v), 38% in
ethanol-water (7:3 v/v), and 37% in DMF-water (7:3 v/v). The e.e. value sig
nificantly decreases to 33% from 51% in acetone-water (7:3 v/v) when the KC
l concentration is increased to 0.3 mol dm(-3) from 0.1 mol dm(-3). When ei
ther KF or CH3CO2K is added to acetone-water (7:3 v/v) instead of KCl the d
eracemization proceeds much more rapidly without decrease of the e.e. value
(approximate to 50%). These counter anion effects are interpreted in terms
that the reduction potential of [Co(acac)(3)] becomes more negative by add
ition of either F- or CH3CO2-.