Low-Cost Phosphite Ligands Improve Metathesis Catalysts

A class of olefin metathesis catalysts that contains phosphite ligands has advantages over current catalysts for some challenging reactions, such as ring-closing metatheses of hindered dienes, according to chemists in Scotland. Inexpensive phosphites have not been extensively investigated as metathesis catalyst ligands. But Catherine S. J. Cazin and coworkers at the University of St. Andrews modified an existing ruthenium indenylidene metathesis catalyst with tri­iso­propyl­phos­phite groups to form cis and trans phosphite complexes that represent a new type of metathesis catalyst (Chem. Commun. 2010, 46, 7115). The catalysts, which they call cis- and trans-Caz-1, promote a difficult tosylamine ring-closing with 100% conversion, compared with about 60% achieved by existing catalysts. And a considerably smaller amount of Caz-1 is needed to promote ring-closing metathesis of hindered dienes than is required for current catalysts. The Caz-1 catalysts also show unusually good stability and longevity in reactions, and the cis form has a unique configuration that “hasn’t been observed before” in a metathesis catalyst, Cazin says. cis-Caz-1, which has been commercialized by Strem Chemicals and Umicore, went “from discovery to market in less than six months,” she notes.