| Research Abstract |
Higher (than four)-coordinated complexes of silicon (IV) are not very familiar as compared to four-coordinated tetrahedral compounds.
We already reported the complete optical resolution and the properties of [Si (phen)_3]^<4+>. The resoluion of [Si (phen)_3]^<4+> was performed by a liquid column chromatographic method using SP-Sephadex C-25 as an adsorbent and a 0.08 M potassium bis ((+)-tartrato) diantimonate (III) as an eluent. Each enantiomer is so stable in an aqueous that solution the absorption spectrum and optical rotation were unchanged after a month at room temperature. This is the first example of stable (in water) enanntiomers of six-coordinated octahedral silicon (IV) complexes.
Successively the ion-association contants between the optically-active complex cations (LAMBDA- or DELTA-[Si (phen)_3]^<4+>) and the aforementioned resolving agent anions ([Sb_2{(+)-tart}_2]^<2->, tart=tartrate(4-) ion) were determined spectrophotometrically. The ion association between the complex ca
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tion and the resolving agent anions occurred in two steps and the stereoselective interaction was observed in the second step. The second-step association constant for the LAMBDA-enantiomer (KAPPA_2=1.41*10^3) is larger than that for the DELTA-one (KAPPA_2=1.07*10^3). The second-step association plays a dominant role in determining the elution order in column-chromatographic resolution.
The molecular mechanics calculations for the ion-associated species were performed to obtain the information about the microscopic interaction between the ions. The total strain energy for the species containing the LAMBDA-enantiomer is smaller than that containing the DELTA-one and this result can explain the experimental finding that the LAMBDA-enantiomer is eluted faster than the DELTA-one.
In the present study, the optical resolution of [Si (bpy)_3]^<4+> was also attempted by a chromatographic method using an SP-Sephadex C-25 column and various resolving-agent solutions, sodium (+)-bitartrate (NaHtart), sodium (+)-tartrate (Na_2tart), potassium bis ((+)-tartrato) diantimonate (III)(K_2[Sb_2{(+)-tart}_2), and sodium (2R,3R)-O,O'-dibenzoyltartrate (Na_2(benz)_2tart) as eluents. This faster-moving enantiomer was LAMBDA except the DELTA moved faster for K_2[Sb_2{(+)-tart}_2]. However, the complete resolution (i.e.the complete separation of the elution band) was attained only by the use of an aqueous solution (0.16 M) of sodium (2R,3R)-O,O'-dibenzoyltartrate as the elunt.
We carried out the force-field calculations of the above ion-pair systems and elucidated the chromatographic elution mechanism.
This study was developed to syntheses and stereochemistry of the other higher-coordinated silicon (IV) compounds containing Schiff Bases and Hinokitiolate.
At present the stereoselective formation is being investigated about the silatrane derivatives having L-alaninol and L-valinol skeletons. Less
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