M. Bashirpoor et al., MODELS FOR VANADATE-DEPENDENT HALOPEROXIDASES - VANADIUM COMPLEXES WITH O4N-DONOR SETS, Chemische Berichte, 130(5), 1997, pp. 651-657
Reaction of vanadyl sulfate with the Schiff base H2L1 derived from o-v
anillin and glycine leads to [(VO)-O-IV(H2O)L-1] (1), treatment of whi
ch with acetyl chloride affords cis-[(VCl2L1)-Cl-IV] (2). Reaction of
[VO(acac)(2)] with the Schiff base H2L2 derived from o-hydroxynaphthal
dehyde and o-hydroxyaniline under aerobic conditions yields [{(VO)-O-V
(L-2)}(2) mu-O] (3), which undergoes methanolysis in excess methanol t
o form [(VO)-O-V(MeOH)(OMe)L-2] (5a). Complex 5a is also obtained via
[(VOCl)-O-V(L-2)] (4) and MeOH. On treatment of 3 with an equimolar am
ount of ethanol, [(VO)-O-V(OEt)L-2] (5b) is obtained. With the chiral
tertiary bis(ethanol)amine (S)- or (R)(HOCH2CH2)(2)NCH(Ph)Me, H2L3, [V
O(acac)(2)] loses only one acetylacetonate(1-) ligand, and the complex
es (S)- and (R)[(VO)-O-V(acac)L-3] (6a) are formed. As is evident for
the corresponding reaction with (HOCH2CH2)(2)NPh, H2L4, which affords
[(VO)-O-V(acac)L-4] (6b), the substitution is a second-order process (
rate constant 0.013 M-1 h(-1)). 5a . MeOH, 5b, (R)- 6a, and (S)-6a hav
e been structurally characterized by single crystal X-ray diffraction
analysis. The molecular connectivities have also been established for
1 . H2O. All of the structurally characterized complexes contain an O
O3N donor set (O denotes a doubly-bonded oxo group) and thus model th
e coordination environment of the active site in vanadate-dependent ha
loperoxidases. This model character is particularly pronounced in 5b,
the coordination geometry of which is half-way to trigonal-bipyramidal
. 5a and 6a contain, in addition to the OO3N set, a labile V-O or V-N
bond, respectively, which may mimic substrate binding to the active c
entre. 6a is also of relevance to the enantioselective peroxide oxidat
ion of sulfides to sulfoxides by catalyst systems containing vanadium
and H2L3.