Nepali young scientist's (Dr. Raghu Dhital-Oasis) work has recently been featured as Editors's choice in reputed journal Science. Here is the text.
"In the
classic Ullmann coupling reaction reported more than a century ago, iodine substituted
aromatic rings were coupled at high temperatures by using copper as a reducing
agent to form a carbon-carbon bond. Further work extended this coupling
reaction to more conventional chloroarenes by using coreductants and
precious-metal catalysts, but reaction temperatures still tended to be high.
Dhital et al. now show that a wide variety of chloroarenes can be coupled at
ambient temperatures (25° to 45°C). The reactions proceeded under basic
conditions (in a mixed organic-aqueous solvent) in the presence of
gold-palladium nanocluster catalysts. Neither pure gold nor pure palladium clusters
could catalyze the reaction, indicating that alloying of the metals was
critical for reactivity. Density functional theory calculations indicated that the
critical difference for the alloy clusters is that they favor activation of the
carbon-chlorine bond through the dissociative adsorption of the arene
chlorides."
Dr. Dhital's work has also been featured in JACS's spotlight. See below.
TWO METALS ARE
BETTER THAN ONE
Heterogeneous
catalysis using nanoclusters consisting of more than one metal is seeing more
widespread application in chemistry, because these types of catalysts can be
highly efficient or may have unusual properties. Particularly attractive are
the gold/palladium bimetallic cluster alloys, due to their high catalytic
turnover. Masahiro Ehara, Hidehiro Sakurai, and co-workers have used this
bimetallic alloy to activate the high-energy carbon−chlorine bond (DOI:
10.1021/ja309606k). They discover that the Au/ Pd nanocluster can catalyze
Ullmann coupling of chloroarenes at room temperature, a reaction that otherwise
requires harsh conditions. The reaction does not progress with either gold or
palladium single-metal nanoclusters alone, nor with a macroscopic mixture of
the two metals. Through computational analysis, the researchers find that the
high activity of the bimetallic nanocluster is due to the substrate being
adsorbed onto the alloy surface, which is unlikely to occur with single metal
catalysts. In addition, the nanocluster is found to have higher activity toward
chloroarenes than their bromo equivalents. This straightforward method to
activate the robust C−Cl bond may enable the design and synthesis of new
multimetallic catalyst for similar activation energy. (JACS spotlight, J. Am. Chem. Soc. 2013, 135, 949)
Dr. Dhital completed his PhD last year from Institute for Molecular Science, The
Graduate University for Advanced Studies (SOKENDAI) with Prof Hidehiro Sakurai. He is now working as post-doctoral fellow. He has MSc degree from CDC, Tribhuvan university, Nepal.
Following are some of his recent publications.
1. R. N. Dhital, A. Murugadoss and H.
Sakurai, “Dual Roles of Polyhydroxy Matrices in the Homocoupling of Arylboronic
Acids Catalyzed by Gold Nanoclusters under Acidic Conditions”, Chem. Asian J. 2012, 7, 55. (Inside
cover picture)
2. R. N. Dhital and H. Sakurai, “Anomalous Efficacy
of Bimetallic Au/Pd Nanoclusters in C-Cl Bond Activation and Formal
Metathesis-type C-B Bond Activation at Room Temperature”, Chem. Lett. 2012, 41,
630. (Editor’s choice)
3.
R. N. Dhital, C. Kamonsatikul, E.
Somsook, K. Bobuatong, M. Ehara, S. Karanjit and H. Sakurai, “Low-temperature
Carbon–Chlorine Bond Activation by Bimetallic Gold/Palladium Alloy
Nanoclusters: An Application to Ullmann Coupling”, J. Am. Chem. Soc. 2012, 134, 20250. (Highlight in Science, 2013, 339, January 4 and
Highlight in JACS spotlight, J. Am. Chem.
Soc. 2013,135, 949).
4.
R. N. Dhital, C. Kamonsatikul, E.
Somsook Y. Sato and H. Sakurai, “Aryl Iodide as a Strong Inhibitor for the Gold
and Gold-based Bimetallic quasi-Homogeneous Catalysis”, Chem.Comm. DOI: 10.1039/C3CC39019E, in press.
