Titanium amine bis(phenolate) complexes of general formulas [Ti(L)Cl(THF)], [Ti(L)X₂] and [{Ti(L)Cl}₂-μ-O] (X = Cl, OⁱPr) were assessed as catalysts of PhCHO pinacol coupling. In optimal conditions (7.5 mol% catalyst load, 55 °C and 16 h of reaction time in THF) and TMSCl as additive, [Ti(L3)Cl₂] (11) is the most efficient catalyst giving 100% conversion and 95% yield in diol with a ratio DL:meso = 57:43 and 27% ee. Using acidic additives, lower diol yields but higher diasteriomeric ratios are obtained. No significant improvements are observed when p-substituted benzaldehydes are used. The reduction of the Ti(IV) complexes to Ti(III) species is identified by EPR and a stoichiometric reaction between a [Ti^III(L1)Cl(THF)] (6) and benzaldehyde shows that the pinacol coupling occurs with a conversion in diol of 72%. Different D,L ratios obtained in the absence or in the presence of reducing metals indicate that different Ti(III) catalysts may form, namely mono- and trinuclear species.

中文翻译：

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钛配合物介导的苯甲醛的Pinacol偶联显示胺双（酚盐）配体

通式[Ti（L）Cl（THF）]，[Ti（L）X ₂ ]和[{Ti（L）Cl} ₂ -μ-O]的钛胺双（酚盐）配合物（X = Cl，O ^（ Pr）被评估为PhCHO频哪醇偶联的催化剂。在最佳条件下（催化剂负载量为7.5 mol％，在THF中为55°C，反应时间为16 h），以TMSCl作为添加剂，[Ti（L3）Cl ₂ ]（11）是效率最高的催化剂，转化率100％，95％比率为DL：中观 = 57:43的二元醇收率和ee的27％。使用酸性添加剂，可获得较低的二醇收率，但可获得较高的非对映异构体比率。当p时，没有观察到明显的改善使用取代的苯甲醛。Ti（IV）配合物还原为Ti（III）的物种通过EPR进行了鉴定，[Ti ^III（L1）Cl（THF）]（6）与苯甲醛之间的化学计量反应表明，频哪醇偶联发生了转化在二醇中为72％。在不存在或存在还原金属的情况下获得的不同的D，L比表明，可能形成不同的Ti（III）催化剂，即单核和三核物种。