Catalyzing the Synthesis - Pharmaceutical Technology

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Catalyzing the Synthesis
Researchers develop various catalytic approaches for improving yield, purity, stereoselectivity, and process conditions.


Pharmaceutical Technology
pp. 44-50

Making acids behave like bases

A research team lead by Guy Bertrand, a distinguished professor of chemistry at the University of California at Riverside, recently reported on the use of boron-based compounds to build Lewis bases.

The researchers reported on the synthesis and characterization of a neutral tricoordinate organoboron isoelectronic with amines. The neutral tricoordinate boron derivative acted as a Lewis base and underwent one-electron oxidation into the corresponding radical cation. These compounds were the parent borylene and borinylium, respectively, stabilized by two cyclic (alkyl)(amino) carbenes. Ab initio calculations showed that the highest occupied molecular orbital of the borane and the singly occupied molecular orbital of the radical cation were essentially a pair and a single electron, respectively, in the p(p) orbital of boron (7).

"The result is totally counterintuitive," said Bertrand, in an July 28, 2011, University of California at Riverside press release. "...But we have achieved it. We have transformed boron compounds into nitrogen-like compounds. In other words, we have made acids behave like bases."

Nitrogen- or phosphorus-based compounds are commonly used as ligands in catalysts. "The trouble with using phosphorus-based catalysts is that phosphorus is toxic and it can contaminate the end products," Bertrand said. "Our work shows that it is now possible to replace phosphorus ligands in catalysts with boron ligands. And boron is not toxic," he added. Researchers at Philipps–Universitat in Marburg, Germany, also contributed to the study.

References

1. J.N.H. Reek et. al., J. Am. Chem. Soc., online DOI: 10.1021/ja208589, Sept. 30, 2011.

2. S. Ritter, Chem. & Eng. News 89 (42), 13 (2011).

3. J.M. John and S.H. Bergens, Angew. Chem. Int. Ed. 50 (44), 10377–10380 (2011).

4. K.C. Harper and M.S. Singer, Science 333 (6051), 1875–1878 (2011).

5. F. Meyer nd C. Limber, eds., "Preface" in Organometallic Oxidation Catalysis (Springer, New York, 2007).

6. J.T. Yates, Jr., et al., Science 333 (6043), 736–739 (2011).

7. G. Bertrand, Science 333 (6042), 610–613 (2011).


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