Conclusion

As we have seen throughout this article, it is now possible to carry out many of the reactions promoted by phosphines, without having to use large quantities of phosphines. This is made possible by the use of a reducing agent, which directly reduces phosphine oxide in situ in the reaction medium to trivalent phosphine. This catalytic process greatly simplifies purification steps, and a life-cycle analysis of the Wittig reaction determined that the catalytic version significantly reduced energy demand and greenhouse gas emissions compared with the stoichiometric version. It remains to be hoped that these catalytic processes can be applied on an industrial scale. Certain parameters can still be improved, such as lowering the catalytic rate to less than 1%mol, notably by designing new catalysts and using "greener" reducing agents than silanes. The preliminary results discussed in the last section...