Unusual
Bonds
UGA chemists make the
unimaginable real, defying the
theories (and gaining the praise)
of their colleagues elsewhere,
all while creating the potential
for whole new industries.
By Helen Fosgate
Photos by Peter Frey
C
hemists have been transforming the earth’s resources for centuries.
Early chemists learned to make glass, render animal fats into soap,
extract metal from ores, and derive chemicals from plants to make
medicines and perfumes. Modern chemists continue to synthesize new
chemical compounds. Whether to develop lifesaving drugs, industrial
coatings, or new semiconductors, among other applications, chemists
remain essentially the only scientists to produce new forms of matter.
Within this class of groundbreaking researchers, two UGA faculty
members stand out. Gregory H. Robinson (in blue shirt), Franklin
Professor and Distinguished Research Professor in the Franklin College
of Arts and Sciences, and Yuzhong Wang (far left, in lab coat), associate
research scientist, are renowned for synthesizing new compounds that many
conventional thinkers believed weren’t even possible.
“The chemistry emanating from the Robinson laboratory is some of
the most innovative worldwide occurring at this time,” says Jerry Atwood,
Curators’ Professor of Chemistry and chair of the department of chemistry
at the University of Missouri-Columbia.
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New Forms of
Boron and Silicon
Associate research scientist Yuzhong Wang (above)
prepares an air-sensitive
crystal for an x-ray diffraction experiment.
The Un-Carbons
In 1995, Robinson’s research group made an
important discovery using gallium, the volatile
metal that resides just below aluminum on the
periodic table. They synthesized a compound
containing the first reported gallium threemember ring. More important, the compound
displayed metalloaromatic properties, meaning it
was unusually stable and possessed a collection of
mobile electrons around the gallium-ring system.
Two years later, Robinson’s team installed
a triple bond between two gallium atoms in a
most unusual chemical compound. While triple
bonding is quite common for carbon, the new
Robinson compound was significant because
it demonstrated for the first time that a metal
from the periodic table’s “main group” (whose
elements are among the most abundant on
earth) could form a triple bond. Their discovery
generated both accolades and skepticism in the
scientific community. Today, more than a decade
later, the consensus is that this compound was
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one of the most important inorganic molecules
to be synthesized in the past 20 years.
“Whenever a chemist synthesizes a new
molecule or discovers a new mode of bonding
for an element, it is often provocative because
most of our long-standing theories of structure
and bonding are largely based on carbon,” says
Robinson. “However, these theories frequently
do not adequately characterize the bonding
behavior of heavier main-group elements.”
Subsequently, other chemists showed that
aluminum, too, behaves like gallium (and not
like carbon) in similar bonding processes. “We
discovered that with heavier elements, the rules
governing carbon—that iconic main-group
element—do not always apply,” says Robinson.
“Essentially, our work led to a more nuanced
definition of multiple bonding among maingroup elements.” While this expanded definition
is now widely accepted, Robinson continues to
push the boundaries of tradition in other ways.
The next big discovery came in 2007, when Robinson’s lab
synthesized the first compound containing a double bond between
two boron atoms—the first diborene. Boron, a main group
element often used in refractory materials and in reagents to effect
chemical transformation of organic compounds, frequently forms
compounds that are electron-deficient. This “makes the boronboron double bond particularly reactive,” Robinson explains.
“So we asked ourselves, ‘Might there be a simple way to quench
boron’s thirst for electrons while, at the same time, stabilizing the
boron-boron double bond?’”
After some trial and error, the scientists decided to try
carbenes, a class of organic compounds in which one of the carbon
atoms has a lone pair of electrons that can be “donated” to another
atom in a different compound. As recently as two decades ago,
carbenes themselves were considered so unstable and temporary
as to be unsuitable for routine laboratory study, but the team’s idea
worked: the carbenes stabilized the boron-boron double bond—
and at room temperature. “It was like Jedi mind control at the
molecular level,” says Robinson, laughing. “The carbenes fooled
the boron atoms into behaving as if they were carbon atoms.”
The scientists now plan to explore whether they can make a
boron-based polymer, which also has never been done. Robinson
said it would have different properties than traditional polymers
and perhaps certain advantages over them as well. Meanwhile, the
team’s boron success led it to another, even bigger, discovery.
In 2008, Robinson and Wang stunned the scientific community
by creating a new form of elemental silicon, again using carbenes to
stabilize this highly reactive disilicon molecule. In this compound,
two silicon atoms—each bonding to one carbene—are connected
by a silicon-silicon double bond.
The achievement was hailed in top journals, including Science,
the Journal of the American Chemical Society, Nature, and Chemical
and Engineering News. Reviewing scientists called it “a major
advance in low-valent, low-coordinate, main-group chemistry” and
one that “opens new, unprecedented possibilities in organometallic
chemistry.
Daniel Nocera, Henry Dreyfus Professor of Energy and
Chemistry at MIT, wrote: “Silicon was discovered in 1823; I am
overwhelmed that a new allotrope [a structurally different form]
of a long-known element can be discovered almost 200 years
later, though I admit I am not surprised. My community looks
to Professor Robinson for the unimaginable, and he continues to
deliver, time and time again.”
In addition to research, Robinson also loves to teach,
especially introductory chemistry for non-chemistry
majors. “Three years later, I’ll see these students
somewhere on North Campus, and they’ll say ‘I had
you for chemistry, and I learned so much.’ I enjoy that
because these are students I’d otherwise have never
met,” he says.
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Seminal
Contributions
Robinson and Wang have now used carbenes to stabilize
highly reactive allotropes of the main-group elements boron,
silicon, phosphorous, and arsenic. Their technique of employing
such bases as stabilizing influences for otherwise fleeting molecules
is now considered a seminal scientific discovery—and one of
potentially great practical importance. Not only does their work
challenge traditional theories of structure and bonding, it is also
“pushes the boundaries of current understanding and paves the way
for unthinkable applications and insight into chemical processes,”
according to Jonathan Steed, professor of inorganic chemistry at
Durham University, United Kingdom. “But what I like most about
Robinson’s contribution to science is not just that he does new,
exciting chemistry in a painstaking and rigorous way, but that he
communicates the results…in meaningful terms.”
Marcetta Darensbourg, professor of chemistry at Texas A&M
University agrees. “I always enjoy reading Greg’s papers. He makes
interesting connections between significant chemical events in the
past and in current research. He has a perspective that frequently
opens my eyes.”
In 2010, Robinson was named a Creative Research Award
recipient by the University of Georgia Research Foundation—
its highest honor—to recognize his contributions to chemistry.
Robinson and Wang have since filed a patent application on their
new form of silicon and are now exploring its characteristics and
potential uses. Some have suggested it may have application in the
solar energy industry as a base layer that could increase the energy
efficiency of individual panels, but the possibilities are wide open.
“It’s often the case,” says Robinson, “that we don’t have a specific
application in mind when new discoveries come our way.”
Yuzhong Wang (above), who Robinson calls “his partner and right-hand man,”
coordinates the work of undergraduates, graduate students, and postdocs in the
Robinson lab.
Contact Greg Robinson: [email protected]
(Helen Fosgate is editor of ugaresearch; Peter Frey is a UGA photographer.)
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