Iron May Be Cheaper, Greener Catalyst

May substitute for more expensive, toxic metals

The use of iron as a catalyst may avoid the need for more expensive, more toxic metals in the chemical processes used to make pharmaceuticals, according to researchers in Toronto.

Ruthenium compounds are widely used as catalysts in the production of the enantiopure alcohols that are used in the manufacture of many drugs, including fluoxetine hydrochloride (Prozac), as well as in perfume and flavor additives, said Robert H. Morris, PhD, a professor of chemistry at the University of Toronto, in an e-mail to PFQ.

Iron is very abundant, and iron compounds cost much less than those of ruthenium.

Robert H. Morris, PhD, University of Toronto

"The ruthenium complexes are very expensive because of the cost of the metal and the ligands (that must be purely in one enantiomeric form) that make the metal soluble in its ionic form," Dr. Morris said. "… Ruthenium is toxic, and so when it is used as part of a catalyst system, it must be completely removed from the product alcohol. Iron, on the other hand, is very abundant, and iron compounds cost much less than those of ruthenium."

Dr. Morris and colleagues recently published two papers describing the use of iron as a catalyst. (Meyer N, Lough AJ, Morris RH. Iron(II) complexes for the efficient catalytic asymmetric transfer hydrogenation of ketones [published online ahead of print April 9, 2009]. Chemistry. Mikhailine A, Lough AJ, Morris RH. Efficient asymmetric transfer hydrogenation of ketones catalyzed by an iron complex containing a P-N-N-P tetradentate ligand formed by template synthesis. J Am Chem Soc. 2009;131(4):1394-1395.)

The Chemistry paper showed that the catalysts are able to produce alcohols from a wide range of simple ketones with enantioselectivity of up to 96%. The synthesis of these novel iron catalysts is "very practical and actually much simpler than that of ruthenium catalysts," Dr. Morris said. "All of the steps can be performed in a few reaction vessels."