Molecular Recognition in Electron and Oxygen Transfer Reactions of Metal Complexes in Solid and in Solution

我们看到，光学活性的基氧烷（V）物种催化了氧化物（V）物种的变性对之间的异构化。氧化物（IV）和氧化物（V）复合体之间的电转移反应已建议在异构化中发挥重要作用。Chiral Schiff base-Oxovanadium （IV）复合体如[VO {Sal-（RR）-chxn}] （1）已经发现了用于硫氧化物的不对称氧化物的有效催化剂。确切地说，我们研究了[VO {萨尔-（RR）-chxn}]Cl （2）和[VO{3-MeOsal-（RR）或（SS）-chxn}] （3-a或3-b）给1和[VO {3-MeOsal-（RR）或（SS）-chxn}] Cl （4-a或4-b）在equilibrium。反应取决于温度。例如，3-b反应比3-a快2.0次，在25个C时1.6次，激活参数是DELTAH<thermodynamics>_&lt;RR-RR&gt;=15.2（]SY.+-.]）0.6 kJ mol^&lt;-1&gt;， DELTAS（] SY. thermod. [)_< ... More RR-RR\=-70.2（]SY.+-.]）1.9 J mol^\-1&gt; K^\-1&gt;， DELTAH（] SY. thermod. [）_&lt;SS-RR&gt;=21.4（]SY.+-.]）2.4 kJ mol^&lt;-1&gt;， and DELTAS（] SY. thermod. [）_&lt;SS-RR&gt;=-43.7（]SY.+-.]）8.1 J mol^&lt;-1&gt; K^&lt;-1&gt;.Although我们没有任何综合性证据来确定当前的反应过程是由内部机制决定的，两个反应的Vanadium原子必须在电子转移的情况下足够接近。这应该是合理的，因为氧化物配体（IV）在位置变压器与氧化物配体（V）复合体的位置相互作用，因为较晚的复合体优先考虑六坐标结构。据报道，[（salen）V^<IV>OV^VO （salen）]I_5·CH_3CN （H_2salen=N，N'-非碱性-idene-1，2-乙二胺）的核结构有V^<IV>=O... V^V=O键。一种类似的核结构可能被期望用于电子转移反应的中间体。“手性识别必须要对两个中间结构中的非绑定静态交互之间的差异作出反应。”Less（低）

We have shown that the isomerization between the diastereomeric pair of an optically active Schiff base-oxovanadium (IV) complex is catalyzed by the oxidized oxovanadium (V) species. The electron-transfer reaction between the oxovanadium (IV) and oxovanadium (V) complexes was suggested to have an important role in the isomerization. Chiral Schiff base-oxovanadium (IV) complexes such as [VO {sal-(RR)-chxn}] (1) have been found to be enantioselective catalysts for the asymmetric oxidation of sulfides to sulfoxides. Accordingly, we studied the electron-transfer reaction between [VO {sal-(RR)-chxn}]Cl (2) and [VO{3-MeOsal-(RR) or (SS)-chxn}] (3-a or 3-b) which gives 1 and [VO {3-MeOsal-(RR) or (SS)-chxn}] Cl (4-a or 4-b) at equilibrium.The stereoselectivity of the reaction depends on temperature. For example, 3-b reacts 2.0 times faster than 3-a at 25ﾟC,while 1.6 times at 5ﾟC.The activation parameters were DELTAH<thermodynamics>_<RR-RR>=15.2(]SY.+-.])0.6kJ mol^<-1>, DELTAS(]SY.thermod.[)_< … More RR-RR>=-70.2(]SY.+-.])1.9 J mol^<-1> K^<-1>, DELTAH(]SY.thermod.[)_<SS-RR>=21.4(]SY.+-.])2.4kJ mol^<-1>, and DELTAS(]SY.thermod.[)_<SS-RR>=-43.7(]SY.+-.])8.1 J mol^<-1> K^<-1>.Although we do not have any conclusive evidence which determines that the present reaction proceeds by the inner-sphere mechanism, the two reacting vanadium atoms must be brought sufficiently close together when the electron-transfer occurs. It should be reasonable that the oxo ligand of oxovanadium (IV) complex interacts at the position trans to the oxo ligand of the oxovanadium (V) complex because the latter prefers a six-coordinate structure. The dinuclear structure of [(salen)V^<IV>OV^VO (salen)]I_5・CH_3CN (H_2salen=N,N'-disalicyl-idene-1,2-ethanediamine) was reported, which has a V^<IV>=O・・・V^V=O bond. A similar dinuclear structure may be expected for the intermediate of the electron-transfer reaction. The chiral recognition must be due to the difference in the non-bonding steric interaction between the ligands in the two intermediate structures. Less