誘導式自組裝生成 C4-對稱釩酸鹽為中心之四聚簇狀體，作為增效式金屬離子之篩選傳送及不對稱催化劑

Abstract

我們經由手性氧釩甲氧化物與金屬的偏釩酸鹽增效式自組裝，或以鋰離子及鈉離子鉗合的四聚簇狀體與其他陽離子的交換反應來合成一系列的 C4-對稱釩酸鹽為中心之四聚簇狀體。此人為的誘導性自組裝策略，可以作為鹼金屬離子 (K+ > Cs+ > Na+ > Li+)、鹼土金屬離子 (Ba2+ > Sr2+ >> Ca2+ > Mg2+)、重金屬離子 (Hg2+ > Pb2+ > Cd2+ >> Zn2+) 及非金屬銨鹽離子 (MeNH3+ > NH4+ > Me2NH2+ >> Me3NH+ and Me4N+) 的特殊篩選傳送與回收，並可歸納出此四大種類之間的增效式篩選強度為 K+ ≈ MeNH3+ > Hg2+ > Ba2+。由 X-ray 單晶繞射結構發現，正一價陽離子鉗合之四聚簇狀體結構 (1-K, 1-Cs, 1-Ag, 1-MeNH3, 1-NH4)，其陽離子與帶負一價的釩酸鹽是以一比一的比例形成錯合物，且陽離子會與外圍四個單體上羰基的氧原子形成配位鍵或氫鍵；而在正二價鋇離子鉗合的錯合物 (1-Ba 和 2-Ba) 中，陽離子與帶負一價的釩酸鹽是以二比一的比例形成似三明治的八聚簇狀體結構；然而在 2-Pb 和 3-Hg 結構中，正二價金屬離子會與負一價的釩酸鹽及硝酸根離子形成一電中性且以鉛離子或汞離子為配位中心之扭曲三菱鏡幾何結構的四聚簇狀體。另外 1-Li 和1-Na 亦可應用至 a-羫基芐基扁桃酸硫酯之增效式不對稱氧化反應，當溫度降為 0 oC 時，其鏡像超越值可高達 98% 以上。

We have developed directed encapsulation of metal metavandate (MVO3-2H2O) by tailor-made, chiral oxidovanadium(V) methoxides with concomitant formation of C4-symmetric vanadate-centered clusters. This artificial, directed evolution process in chiral vanadyl(V) complex allows for highly efficient K+-, Ba2+-, Hg2+- and MeNH3+-specific transport from aqueous phase containing other alkali metal cations, alkaline-earth matal cations, heavy metal cations and ammonium cations respectively, into organic solvents. The X-ray crystal structures of 1-K, 1-Cs, and 1-Ag revealed distorted square planar geometry around the binding site which are in close similarity to the K+ transport mode exerted by four homochiral glycine residues of the opening site in KcsA. For the +2 cation cases, the X-ray crystal structures of 1-Ba and 2-Ba existed as a unique 2:1 sandwich like complexes between the C4-vanadate in order to fulfill the ionic charge interaction and charge balance between Ba2+ and the central vanadate. On the other hand, 2-Pb and 3-Hg displayed a square planar binding mode topped with a nitrate ligand to form a trigonal prism cage. Beside the synergistic metal ion-specific transport, we also found that the Li+ and Na+ encapsulated clusters can effect a highly enantioselective aerobic oxidation of racemic S-benzyl-thiomandelate with complete kinetic resolution in a synergistic mode.