Amid Glut of
Superconductivity, Gold Shines
Through
by John Emsley
Chemistry
Top Ten Papers
Rank
Papers
Cites
Sep-Oct 08
Rank
Jul-Aug 08
1
Y. Kamihara, et al.,
"Iron-based layered
superconductor
La[O1-xFx]FeAs
(x = 0.05-0.12) with
Tc = 26 K," J.
Am. Chem. Soc., 130(11):
3296-7, 19 March 2008. [Tokyo
Inst. Technol., Yokohama,
Japan] *273SL 92
92
1
2
C. de la Cruz, et al.,
"Magnetic order close to
superconductivity in the
iron-based layered
LaO1-xFxFeAs
systems," Nature,
453(7197): 899-902, 12 June
2008. [6 U.S. and China
institutions] *311WV
34
†
3
H. Takahashi, et al.,
"Superconductivity at 43 K in
an iron-based layered compound
LaO1-xFxFeAs,"
Nature, 453(7193):
376-8, 15 May 2008. [Nihon U.,
Tokyo, Japan; Tokyo Inst.
Technol., Japan] *301AI
30
†
4
J.E. Green, et al., "A
160-kilobit molecular
electronic memory patterned at
1011 bits per square
centimetre," Nature,
445(7126): 414-7, 25 January
2007. [Caltech, Pasadena; U.
Calif., Los Angeles; Ohio St.
U., Columbus] *128WD
16
9
5
M. Dinca, et al.,
"Hydrogen storage in a
microporous metal-organic
framework with exposed
Mn2+ coordination
sites," J. Am. Chem.
Soc., 128(51): 16876-83,
27 December 2007. [6 U.S.
institutions] *118KQ
16
6
6
J. Peet, et al.,
"Efficiency enhancement in
low-bandgap polymer solar cells
by processing with alkane
dithiols," Nature
Mater., 6(7): 497-500,
July 2007. [U. Calif., Santa
Barbara] *184NH
15
2
7
P.D. Jadzinsky, et
al., "Structure of a thiol
monolayer-protected gold
nanoparticle at 1.1 Å
resolution," Science,
318(5849): 430-3, 19 October
2007. [Stanford U., CA] *221LW
15
†
8
H. Lin, Q.Z. Li, "Using pseudo
amino acid composition to
predict protein structural
class: Approached by
incorporating 400 dipeptide
components," J. Comput.
Chem., 28(9): 1463-6, 15
July 2007. [Inner Mongolia U.,
China] *169EM
15
†
9
T. Watanabe, et al.,
"Nickel-based oxyphosphide
superconductor with a layered
crystal structure, LaNiOP,"
Inorganic Chem.,
46(19): 7719-21, 17 September
2007. [Tokyo Inst. Technol.,
Yokohama, Japan] *209EJ
14
5
10
X.L. Li, et al.,
"Chemically derived,
ultrasmooth
graphene nanoribbon
semiconductors,"
Science, 319(5867):
1229-32, 29 February 2008.
[Stanford U., CA] *267SX
Superconductivity
continues to dominate the Hot Ten of chemistry, occupying five
positions in the list at #1, #2, #3, #9 and #10. Of those
remaining, only #7 and #8 are new to the list. The former reports
the structure of a nanoparticle of gold, while the latter reports a
way of computing and predicting large polypeptide
structures.
Paper #7, from the departments of Structural Biology and Applied
Physics at Stanford University, reports the structure of a
nano-sized agglomerate of 102 gold atoms sheathed in an outer layer
of 44 p-mercaptobenzoic acid molecules. Its structure was
determined by X-ray crystallography. Large thiolate-protected gold
monolayers have been produced by the decomposition of gold(I)
benzenethiolate, but paper #7 is the first time that the structure
of such a nanoparticle of gold has been determined.
The crystals
were grown from a solution in which the gold thiolate had to be
soluble, and this was achieved with 40% methanol, plus small
amounts of sodium chloride and sodium acetate. Fifteen crystals
were prepared by this method and, surprisingly, all were found to
have the same arrangement of 120 gold atoms. According to the
authors of #7, it is electronic forces within the cluster which
explains why Au102 forms and they suggest that such an
arrangement completes a particularly stable 58-electron shell.
The nature of the outer layer of thiolates poses interesting
questions also, and these are addressed by
Robert Whetten and Ryan Price of the Georgia Institute of Technology in the
same issue of Science (318[5849]: 407-8, 19 October
2007). While there are various ways in which thiolate ligands
could bind to gold(I), the most likely one involves the
formation of covalent bonds to two thiolates and these then
arrange themselves like a shell around the positively charged
core of gold atoms.
Gold also features in a paper which only just failed to make the
current list and is at position #12. This reports oxidative
rearrangements catalyzed by gold and is the work of a group led by
Dean Toste of the University of California at Berkeley. It was
published in the Journal of the American Chemical Society
(C.A. Witham, et al., 129[18]: 5838, 2007; 13 citations
this period).
The Berkeley group have demonstrated that oxidative rearrangement
reactions of alkynes with sulfoxides as the oxidizing agents can be
successfully catalyzed by gold(I) compounds to give yields as high
as 94%. The products from such rearrangement reactions contain
carbonyl groups and as such offer routes to other molecules. A
typical catalyst was triphenylphosinegold(I) (Ph3PAuCl)
and it was used in conjunction with silver antimony hexafluoride
(AgSbF6).
So how do gold(I) catalysts effect their magic? In their early
investigations the group focused on intercepting cyclopropane-gold
intermediates which should be present in the formation of ring
compounds from alkynes. These intermediates then reacted further
with dimethylsulfoxide, but yields were disappointing. However, by
a judicious change of reagent to diphenylsulfoxide, and by varying
the ligands on the gold catalyst, the yields of desired products
were boosted to more than 90%. Further research provided further
support for the team's belief that the intermediates which the
catalyst was forming were carbenoid in nature.
Subsequent research by the Berkeley group has focussed on a wider
range of reactions providing additional support for the carbenoid
nature of the gold(I) species in the formation of pyrrolone from an
azide. Toste has also studied the effect of ligands in homogeneous
gold catalysis (D.J. Gorin, et al., Chem. Rev.,
108[8]: 3351, 2008).
In 2008 Toste also showed just how versatile these new catalysts
were. They performed well in a ring-expanding cyclo-isomerization
that was part of the total synthesis of ventircosene (S.G.
Sethofer, et al., Org. Lett., 10[19]: 4315,
2008). They were used in an intermolecular ring formation in the
synthesis of azepines (N.D. Shapiro, et al., J. Am.
Chem. Soc., 130[29]: 9244, 2008), and in the
cyclo-isomerization of 1.5-allenyes (P.H.Y. Cheong, et
al., J. Am. Chem. Soc., 130[13]: 4517, 2008).
Fluorenes and styrenes were produced by a gold(I)-catalyzed
annulation of enynes and alkynes (D.J. Gorin, et al.,
J. Am. Chem. Soc., 130[12]: 3736, 2008).
Gold, once the Cinderella of metals as far as chemical reactivity
was concerned, is now finding itself being wooed and won for all
kinds of synthetic and nanotech applications. For example see
Science Watch January/February 2008 (19[1]: 7), in which
other gold catalyst papers made the Hot Ten, reporting equally
impressive yields.
Dr. John Emsley is based at the Department of Chemistry,
Cambridge University, U.K.
KEYWORDS: GOLD, GOLD NANOPARTICLES, GOLD(I), GOLD CATALYSIS, DEAN
TOSTE, ROBERT WHETTEN, RYAN PRICE.