Wikete Cornelia, Wu Pingsong, Zampella Giuseppe, De Gioia Luca, Licini Giulia, Rehder Dieter
Department Chemie, Universität Hamburg, 20146 Hamburg, Germany, Dipartimento di Biotechnologica, Universita di Milano-Bicocca, 20106 Milano, Italy.
Inorg Chem. 2007 Jan 8;46(1):196-207. doi: 10.1021/ic061534p.
Reaction of R-styreneoxide with glycine-tert-butylester yielded amino alcohols of the general formula NR1R2R3, where R1 = CH2COOtBu and R2 = R3 = 2-phenyl-2-hydroxyethyl (H2LA); R2 = 2-phenyl-2-hydroxyethyl and R3 = 1-phenyl-2-hydroxyethyl (H2LB); R2 = H and R3 = 2-phenyl-2-hydroxyethyl (HLC); and R2 = H and R3 = 1-phenyl-2-hydroxyethyl (HLD). The corresponding reaction with sarcosine-tert-butylester and subsequent hydrolysis provided the zwitterion +NH(CH3){CH2CHPh(OH)}(CH2CO2-), HLE* (asterisk refers to unprotected carboxylate). Reaction of these ligands with VO(OiPr)3 in CH2Cl2 gave the oxovanadium(V) complexes [VOL(OiPr)2] and [VOL2(OiPr)] (for LC and LD) or, when reacted in the presence of MeOH, [VOL'(OMe)], where L' represents the methyl ester of LA, LB, and LE. The crystal and molecular structures of R-HLC, S-HLD, R,S-HLE* x H2O, and lambda-[VO(R,S-LB')OMe] have been determined. The complex [VOLB'(OMe)] contains vanadium in a distorted trigonal-bipyramidal array (tau = 0.72), the oxo group in the equatorial plane, and methoxide and N in the apical positions, and thus, it structurally models the active center of vanadate-dependent haloperoxidases. The structure and the bonding parameters, including a particularly long d(V-N) of 2.562 A, are backed up by DFT calculations. The isolated oxovanadium(V) complexes and the in situ systems L + VO(OiPr)3 catalyze the oxidation, by cumylhydroperoxide HO2R', of prochiral sulfides (MeSPh, MeSp-Tol, PhSBn) to chiral sulfoxides plus some sulfone. The best results with respect to enantioselectivity (enantiomeric excess (ee) = 38%) were obtained with the system VO(OiPr)3/LA, and the best selectivity with respect to sulfoxide (100%) was obtained with [VOLA(OiPr)]. The reaction with the hexacoordinated [VO(OMe)(HOMe)LD*] was very slow. Oxidation of PhSBn is faster than that of MeSPh and MeSpTol. Turn-over numbers are up to 60 mol of sulfoxide mol-1 of catalyst h-1 (-20 degrees C). The unspectacular ee apparently is a consequence of flexibility of the active catalyst in solution, as shown by the 51V NMR of the catalysts [VOL(OR)] and the oxo-peroxo intermediates [VOL(O2R')]. As shown by DFT calculations, the peroxo ligand coordinates in the tilted end-on fashion in the axial or equatorial position (energy difference = 17.6 kJ/mol).
R-苯乙烯氧化物与甘氨酸叔丁酯反应生成通式为NR1R2R3的氨基醇，其中R1 = CH2COOtBu且R2 = R3 = 2-苯基-2-羟乙基（H2LA）；R2 = 2-苯基-2-羟乙基且R3 = 1-苯基-2-羟乙基（H2LB）；R2 = H且R3 = 2-苯基-2-羟乙基（HLC）；以及R2 = H且R3 = 1-苯基-2-羟乙基（HLD）。与肌氨酸叔丁酯的相应反应及随后的水解得到两性离子+NH(CH3){CH2CHPh(OH)}(CH2CO2-)，HLE*（星号表示未保护的羧酸盐）。这些配体与VO(OiPr)3在二氯甲烷中反应得到氧钒（V）配合物[VOL(OiPr)2]和[VOL2(OiPr)]（对于LC和LD），或者在甲醇存在下反应时得到[VOL'(OMe)]，其中L'代表LA、LB和LE的甲酯。已测定R-HLC、S-HLD、R,S-HLE*·H2O和λ-[VO(R,S-LB')OMe]的晶体和分子结构。配合物[VOLB'(OMe)]中的钒呈扭曲的三角双锥排列（τ = 0.72），氧原子在赤道平面，甲氧基和氮原子在顶端位置，因此，它在结构上模拟了依赖钒酸盐的卤过氧化物酶的活性中心。结构和键合参数，包括特别长的2.562 Å的d(V-N)，得到了密度泛函理论计算的支持。分离得到的氧钒（V）配合物和原位体系L + VO(OiPr)3通过过氧化异丙苯HO2R'将前手性硫化物（MeSPh、MeSp-Tol、PhSBn）催化氧化为手性亚砜以及一些砜。在对映选择性方面（对映体过量（ee） = 38%），体系VO(OiPr)3/LA给出了最佳结果，而在亚砜选择性方面（100%），[VOLA(OiPr)]给出了最佳结果。与六配位的[VO(OMe)(HOMe)LD*]的反应非常缓慢。PhSBn的氧化比MeSPh和MeSpTol的氧化快。周转数高达每摩尔催化剂每小时60摩尔亚砜（-20℃）。不显著的ee显然是溶液中活性催化剂具有柔韧性的结果，如催化剂[VOL(OR)]和氧过氧中间体[VOL(O2R')]的51V核磁共振所示。如密度泛函理论计算所示，过氧配体以倾斜的端基方式在轴向或赤道位置配位（能量差 = 17.6 kJ/mol）。
