A team of scientists from Boston College and MIT have discovered a new class of highly efficient and enantioselective chemical catalysts that promote the olefin metathesis reaction with an “unprecedented” level of control, opening up a new platform to researchers in medicine, biology and materials. The new catalysts can be easily prepared and possess unique features never before utilized by chemists, according to findings from a team led by professors Amir Hoveyda of BC and Richard Schrock of MIT. A report on the team’s findings was published 16 November in the online edition of the journal Nature.
Richard R. Schrock shared the 2005 Nobel Prize in Chemistry with Yves Chauvin and Robert H. Grubbs for the development of the metathesis method in organic synthesis.
|“We expect this highly flexible palette of catalysts to be useful for a wide variety of catalytic reactions that are catalyzed by a high oxidation state alkylidene species, and to be able to design catalytic metathesis reactions with a control that has rarely if ever been observed before.”|
Olefin metathesis, which swaps molecular fragments on either side of a carbon-carbon double bond, has become an efficient and widely-used chemical process in petroleum refining and other industries. Its advantages include the creation of fewer sideproducts and hazardous wastes.
However, a chief challenge has been developing catalysts to this organic chemical reaction that are practical and offer exceptional selectivity for a significantly broader range of reactions. Schrock, the Frederick G. Keyes Professor of Chemistry at MIT, said the unprecedented level of control the new class of catalysts provides will advance research across multiple fields.
Highly versatile molecules that contain carbon—carbon double bonds, alkenes, or olefins—are ubiquitous in medicinally relevant and biologically active molecules. Tetrahedral in constitution, the new catalysts are the first to exploit a metal with four different ligands—molecules that bond to the central metal—which in turn dictate the catalysts’ high level of reactivity and selectivity.
For the first time these catalysts take advantage of the configuration of a metal with four different ligands attached to it, an untested situation that has long been predicted to be a strong director of asymmetric catalytic reactions that take place at the metal center.—Richard Schrock
A novel aspect at the center of the catalyst is that the metal molybdenum is a source of chirality, also known as handedness. Like the mirror image of left hand and right, molecules can come in two variations, one a reflection of the other. But these two variations often function in entirely different ways—sometimes one proves harmful, while the other is benign.
With molybdenum at its core, the new catalyst gives chemists a simple, unique and efficient way to produce one form of the molecule or the other in order to yield the desired reactions.
The new catalysts are also structurally flexible, a relatively unconventional attribute that lends them exceptional chemical activity. The discovery of catalysts with stable configurations and flexible structures is expected to allow chemists to design, prepare and develop new chemical transformations that furnish unprecedented levels of reactivity and selectivity, according to the co-authors, which include BC researchers Steven J. Malcolmson, Simon J. Meek, and Elizabeth S. Sattely.
The findings mark the latest discovery from the long-standing collaboration between the Hoveyda and Schrock labs, work that has been supported by more than $3.5 million in funding from the National Institutes of Health for nearly a decade.
Steven J. Malcolmson, Simon J. Meek, Elizabeth S. Sattely, Richard R. Schrock & Amir H. Hoveyda (2008) Highly efficient molybdenum-based catalysts for enantioselective alkene metathesis. Nature doi: 10.1038/nature07594
Schrock Nobel Lecture “Multiple Metal-Carbon Bonds for Catalytic Metathesis Reactions”