Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556-5670, USA.
Dalton Trans. 2010 Nov 14;39(42):10105-15. doi: 10.1039/c0dt00828a. Epub 2010 Sep 7.
The 2,2'-bis(methylene)biphenyl bridged bis(diketonate) (Tol(2)Bob)Ti(IV) fragment is resolved by reaction of the isopropoxide complex with (R)-1,1'-bi-2-naphthol, which selectively forms (S,Δ)-(Tol(2)Bob)Ti(R-BINOL). The binaphtholate ligand can be cleaved from titanium by careful treatment with trifluoromethanesulfonic acid to give (S,Δ)-(Tol(2)Bob)Ti(OTf)(2), which has a half-life toward racemization of at least 34 h at 51 °C. Racemization of the (Tol(2)Bob)Ti(IV) fragment is strongly accelerated under protic conditions, probably due to protonolysis of one of the diketonate ligands. Analogous optically active titanium bis(diketonates) can also be prepared by using an optically active 2,2'-bis(methylene)-1,1'-binaphthyl bridged bis(diketonate) ligand, Tol(2)Bobbinap, prepared from (R)-BINOLH2. Complexation of (R)-Tol(2)BobbinapH(2) with Ti(OiPr)(4) gives only a single diastereomer with the Λ configuration at titanium. The bis(diketonate)titanium(IV) fragment gives rise to characteristic signals in circular dichroism spectra which can be used to identify the configuration at the metal centre.
2,2'-亚甲基双（联苯）桥联双（二酮）（Tol(2)Bob）Ti(IV)片段通过异丙氧基配合物与（R）-1,1'-联-2-萘酚反应拆分，该反应选择性地形成（S,Δ）-（Tol(2)Bob）Ti（R-BINOL）。通过小心地用三氟甲磺酸处理，可以从钛上裂解联萘酚配体，得到（S,Δ）-（Tol(2)Bob）Ti（OTf）（2），其在 51°C 下至少有 34 小时的外消旋半衰期。在质子条件下，（Tol(2)Bob）Ti(IV)片段的外消旋化被强烈加速，可能是由于其中一个二酮配体的质子解。通过使用由（R）-BINOLH2制备的光学活性 2,2'-亚甲基-1,1'-联萘基桥联双（二酮）配体 Tol(2)Bobbinap，也可以制备类似的光学活性钛双（二酮）。（R）-Tol(2)BobbinapH（2）与 Ti（OiPr）（4）络合仅得到具有钛的 Λ构型的单一非对映异构体。双（二酮）钛（IV）片段在圆二色光谱中产生特征信号，可用于鉴定金属中心的构型。
