Effective catalysts for optical purity
The catalysts required to induce the formation of optically pure compounds must themselves be asymmetric. Appropriate chiral catalysts are being investigated by an international team spanning Bangor (Wales), Rostock, Paris, Oxford and Moscow. Derivatives of paracyclophane structurally related to ferrocene from which many catalysts have already been developed can produce highly active catalysts for the asymmetric addition of cyanide to aldehydes. This process is significant for preparing agrochemicals based on pyrethroids, for example. The most effective catalyst so far discovered is a titanium complex with one of the (R,R)-cyclohexanediamine derivatives. At room temperature and in remarkably low concentration it induces the asymmetric addition of trimethylsilyl cyanide to aldehydes with 90% enantiomeric excess. Water is an ingredient of success, it combines with the initial complex to create a more reactive form.