Photoinduced deracemization

However, very efficient deracemization was reported in tris(4,4 -dimethyl-2,2 -bipyridine)iron(II), [Fe(4,4 -Me2bpy)3]2+, with tris(trichlorobenzenedi-olato)phosphate (trisphat), where trisphat is shown in Scheme 16 [42]. Though this is not a photoreaction but a thermal reaction, we briefly discuss this result because this deracemization is very interesting and provides an interesting idea of photoinduced deracemization. 

This idea was realized in recent photoinduced deracemization of Co(acac)3 with A-[Ru(( —)-menbpy)3]2+ in the absence of oxygen [44]. When the solution of rac-Co(acac)3 and A-[Ru(( —)-menbpy)3]2+ was irradiated with visible light corresponding to the MLCT absorption of this ruthenium(II) complex, Co(acac)3 was little consumed, but the CD spectrum exhibited a positive peak at 580 nm and a negative one at 660 nm. This CD spectrum is the same as that of A-Co(acac)3. This result clearly shows that rac-Co(acac)3 converts to A-Co(acac)3 with A-[Ru(menbpy)3]2 +. ... 

Photoderacemizations of Cr(acac)3 with circular polarized light gave very small ee values . Later, photoinduced deracemization of a racemic mixture of A- and A-Co(acac)3 was successfully carried out and was followed by CD measurements. With a chiral ruthe-nium(II) complex, A-[Ru(menbpy)3] + (menbpy = 4,4 -bis (l/f,25, 5/f)-(-)-menthoxy-carbonyl -2,2 -bipyridine), in acetonitrile-HiO (7 3 v/v), in the presence of either triethylamine or NaOH, under visible light irradiation (420 < X < 470 nm), the A-isomer was obtained preferentially with 38% ee . The selectivity of deracemization remarkably depends on the solvent and anion concentration. These counter anion effects were interpreted in terms that the reduction potential of Co(acac)3 becomes more negative by addition of or AcO . ... 

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