Science
S a m a r i u m complex is Uniquely reactive Chemists at the University of California, Irvine, have discovered a way to insert two carbon monoxide molecules into a carbon-carbon double bond by the use of an organosamarium complex. The net reaction R H C = C H R + 2CO + 2 e _ —
Organosamarium complex inserts two CO molecules into carbon-carbon double bond >• [C5(CH3)5]2Sm(THF)2 + /
[C5(CH3)5l2Sm
0"
O-
I
I
J—O Hcf
j3m[C5(CH3)5]2
that of ferrocene—in which two parallel cyclopentadienyl groups sandwich an iron cation—in that the aromatic pentamethylcyclopentadienyl groups sandwich the samarium cation. In the samarium complex, however, the pentameth-
C-CH3
O.. *C-CH,
2-Hydroxyacetophenone (2-HAP)
4-Hydroxyacetophenone (4-HAP)
Large volumes of both 4-HAP and 2-HAP will be available from our multi-million pound acetaminophen plant in mid-1989. For more information, contact:
Hoechst Celanese Advanced Technology Group, 1250 West Mockingbird Lane, Dallas, TX 75356, Attention: Dr. W. D. Alley. 1-214689-8018
Hoechst Celanese
Hoechst M
CIRCLE 11 ON READER SERVICE CARD May 2, 1988 C&EN
THF
=0
C5(CH3)$ = Pentamethylcyclopentadienyl
Commercial quantities of superior quality 4-HAP & 2-HAP are currently available.
34
+ 2 CO — -
£H
Building Blocks Q>
\
O-t
RHC=C—C=CHR
converts an alkene to a bis-enolate. William J. Evans, a chemistry professor at Irvine, and Donald K. Drummond, a graduate student, worked with the divalent organosamarium complex bis(pentamethylcyclopentadienyl) samarium(II) bis(tetrahydrofuranate) or [C5(CH3)5]2Sm(THF) 2 [/. Am. Chem. Soc, 110, 2772 (1988)]. The structure of this complex is somewhat analogous to
\—CH=CH—/
ylcyclopentadienyl groups are not parallel to each other. Rather, they are tilted, allowing the samarium to bind to the oxygen atoms on two tetrahydrofuran groups. Evans and coworkers have shown that this samarium complex possesses a remarkable reductive chemistry with unsaturated substrates such as carbon monoxide, alkynes, and azo compounds. According to Evans, the samarium reagent induces facile multiple-bond cleavage and reorganization leading to unusual transformations of multiply bonded species. In the current work, which was supported by the National Science Foundation, Evans and Drummond react l,2-di-2-pyridylethene with [C5(CH3)5]2Sm(THF)2 to form a red complex that then reacts with carbon monoxide to form the bisenolate compound complexed to two [C5(CH3)5]2Sm groups in 90% yield. The chemists obtained crystals of the product suitable for x-ray crystallography and d e t e r m i n e d its structure. "To my knowledge, this is an unprecedented reaction in organic chemistry," Evans says. "The reaction may prove to be a new way to derivatize alkenes." Evans has yet to establish mechanisms for the reactions of [C5(CH3)5]2Sm(THF)2. Efforts in his laboratory are under way to develop such an understanding through mechanistic studies and characterization of other reactions of the complex. Rudy Baum, San Francisco
