A series of new cobalt(III) octahedral complexes of the general formula Na[Co(ohb-aa)2] (ohb-aa = N-(o-hydroxybenzyl)amino acid anion); amino acid = glycine, (S)-α-alanine, α-aminoisobutyric acid, (S)-valine, (S)-norvaline and (S)-leucine) were prepared by the charcoal catalyzed reaction of the appropriate ligand with [Co(NH3)6]3+ in alkaline aqueous solution. Complexes obtained have, regardless of the amino acid used, the same facial all-trans symmetry (CoN2O4 chromophore) with the vicinal effects as the entire source of the optical activity. 13C NMR spectra reveal that the leucine derivative has, due to the steric reasons, a different ground state structure. Absorption maxima reflect a positive inductive effect from the amino acid side chain carbon atoms. Complexes of the ligands bearing electrophobic alkyl groups exhibit more negative E1/2 in comparison with the glycine derivative, reduction of which occurs at a more positive potential. Reduction potentials do not correlate with cobalt(III) Lewis acidity modulated by ligands.
一系列新的
钴(III)八面体配合物的通式为Na[Co(ohb-aa)
2](ohb-aa = N-(o-羟基苯甲基)
氨基酸根离子);
氨基酸=甘
氨酸,(S)-α-丙
氨酸,α-
氨基
异丁酸,(S)-缬
氨酸,(S)-正缬
氨酸和( S)-亮
氨酸),通过适当
配体在碱性
水溶液中与[Co(NH
3)
6]
3+在木
炭催化下反应制备。无论使用哪种
氨基酸,所得到的配合物具有相同的facial all-trans对称性(CoN
2O
4色团),邻位效应是光学活性的全部来源。
13C NMR光谱显示,由于立体位阻,亮
氨酸衍
生物具有不同的基态结构。吸收峰反映了
氨基酸侧链碳原子的正电感应效应。具有亲电性烷基基团的
配体配合物与甘
氨酸衍
生物相比,表现出更负的E
1/2,其还原发生在更正的电位。还原电位与由
配体调节的
钴(III)
路易斯酸性不相关。