Iron Replaces Ruthenium as Catalyst

Cheaper and less toxic catalysts for producing enantio-enriched alcohols from ketones have been developed by researchers at the University of Toronto, Toronto, Ont. The iron-based complexes promise to replace catalysts containing ruthenium and other platinum-group metals. "Savings will come from the use of a much cheaper catalyst and possibly the simplification of the reduction process, where a ruthenium clean-up step would not be required," explains Robert Morris, a professor in the department of chemistry.

“The catalysts have excellent activity at room temperature but some processes may require the use of higher temperatures.”

- Robert Morris, professor, University of Toronto

The iron carbonyl complexes, which are activated by a strong base, suit asymmetric transfer hydrogenation of aromatic and non-aromatic ketones at room temperature. Catalytic activity rivals that of the best-established ruthenium catalysts, note Nils Meyer, Alan Lough and Morris in a paper in Chemistry — A European Journal. They're the only iron catalysts so far reported that provide high selectivity for left-handed enantiomers at high levels of conversion (enantiomeric excesses of up 96%) — they give turnover frequencies as high as 2,600/hr. with catalyst loadings of only 0.025–0.17%, the researchers add.

"The technical challenges will be to improve the productivity and stability of the catalysts and, if desired, make possible the recovery of catalyst at the end of the reaction. The catalysts have excellent activity at room temperature but some processes may require the use of higher temperatures. We do not know how stable these iron complexes are at temperatures above 50°C," Morris notes.

The researchers also hope to extend applicability to production of enantiomerically pure amines, says Morris.

A company performing asymmetric transfer hydrogenation using a platinum-metal catalyst could run trials now with their materials. "We are seeking a partner in the pharmaceutical or fragrances industry to further the development and commercialization of these promising catalysts," notes Morris.