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Herbert C. Brown (1912Ц2004) Organoboranes

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Obituary
Herbert C. Brown (1912–2004):
Organoboranes
Herbert C. Brown, R. B. Wetherill
Research Professor Emeritus at Purdue
University, passed away on December 19, 2004 at the age of 92.
Born in London, Professor Brown came to the USA
at the age of two. He
attended Wright Junior College prior to enrolling at the
University
of
Chicago,
where he completed his BS
in 1936 and his PhD in
1938. His graduate studies
under the guidance of H. I.
Schlesinger were focused
on the reaction of diborane
with carbonyl compounds. After studying free-radical reactions in Chicago in
1939 with M. S. Karasch, he became
Schlesingers assistant with the rank of
instructor.
Brown started his independent
career in 1943 at Wayne University,
first as assistant professor and later as
associate professor. In 1947 he moved
as professor to Purdue University,
where he was appointed R. B. Wetherill
Professor in 1959 and R. B. Wetherill
Research Professor in 1960. Emeritus
professor since 1978, Brown remained
actively involved in research until his
death. During his career, he supervised
163 PhD students and 190 postdoctoral
fellows. He also authored 8 books and
nearly 1300 scientific publications.
Brown received numerous prestigious awards, including the 1979 Nobel
Prize in Chemistry, the 1969 National
Medal of Science, and the 1981 Priestley
Medal. He was also awarded the Nichols
Medal, the ACS Award for Creative
Research in Synthetic Organic Chemistry, the Linus Pauling Medal, the
Roger Adams Medal, the Perkin
Medal, and the National Academy of
Sciences Award in Chemical Sciences.
He was a member of the National Academy of Sciences as well as a number of
other international scientific societies.
Throughout his scientific career,
Brown examined a variety of topics in
physical, inorganic, and organic chemistry. At the University of Chicago, while
working with Schlesinger, he codiscovered sodium borohydride. At Wayne
1438
University, his investigation of molecular addition compounds contributed to
the reacceptance of steric effects as a
major factor in chemical behavior. His
studies on aromatic substitution led to
a quantitative theory based on the new
Brown d+ constants.[1a] His physical
organic research continued at Purdue,
where he played an active role in the
“nonclassical carbonium ion” debate
that polarized the physical organic community in the 1970s. Brown believed
that many proposals of the existence of
nonclassical carbocations at that time
were not based on firm experimental
foundations, and that a more traditional
interpretation involving the interconversion of classical carbocations was sufficient to explain the experimental
results.[1b] In his view, the nonclassical
bridged carbocation would exist as a
transition state rather than as an intermediate. This viewpoint led to lively,
sometimes heated, debates at scientific
meetings and in the literature. In the
ensuing years, NMR spectroscopic
investigations at ultralow temperatures
in non-nucleophilic superacid solvents
provided evidence to support the existence of s-bridged norbornyl cations.
Whether or not such cations exist
under solvolysis conditions remains a
matter for debate.
Browns greatest contributions, for
which he won the Nobel Prize, were in
the application of boron reagents in
organic chemistry. The simple observation in 1956 that the reduction of ethyl
oleate by sodium borohydride in the
presence of aluminum chloride consumed more hydride than expected
formed the basis of an entirely new
area of organometallic chemistry.[1c] Further studies established that the addition
of diborane to alkenes was catalyzed by
ethers and led Brown to explore the
preparation and use of organoborane
reagents. Indeed, his powers of observation and deductive reasoning provided
the driving force for the fledgling field
of organoboron chemistry. Standardized
procedures for hydroboration were soon
developed, exciting new hydroborating
agents that generated regio- and stereochemically defined intermediates were
designed, and a plethora of important
new organic transformations were created.[1d,e] Browns development of the
asymmetric hydroboration of olefins
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/anie.200500286
may well have ushered in the modern
era of reagent control in asymmetric
synthesis.[1f] It is nearly impossible to
read a current issue of any journal
devoted to organic chemistry and not
encounter a boron reagent that doesnt
have at least a historical tie to Brown.
Brown was a caring, calm, and optimistic man. He was not known to
speak harshly of any colleague; he
always endeavored to keep lines of communication open. It has been almost 40
years since I met Professor Brown and
was introduced to boron chemistry.
Like all his students, I benefited from
his keen intellect as we learned to
design and perform chemical experiments. His patience and optimism were
legendary. However poor our initial
chemical yields, he would encourage us
by pointing out that the first one percent
was the most important; he felt that it
was all downhill from that point and
that quantitative yields were surely on
the horizon.
Brown was thankful for the love and
support of his wife Sarah, a fellow student at the University of Chicago,
whom he married in 1937. Later in life,
he enjoyed collaborating with his son
Charles, who was born in 1944. Sarah
watched over everything in their lives
so that her husband could focus on
chemistry. Brown was especially appreciative that Sarah presented him with
Alfred Stocks “Hydrides of Boron and
Silicon” upon completion of their undergraduate studies at the University of
Chicago. It played a role in his choice
of Professor Schlesinger as his research
advisor. The rest is history!
George W. Kabalka
The University of Tennessee (USA)
[1] a) H. C. Brown, Boranes in Organic
Chemistry, Cornell University Press,
Ithaca, 1972; b) H. C. Brown, P. von
Ragu Schleyer, The Nonclassical Ion
Problem, Plenum Press, New York,
1977; c) H. C. Brown, Hydroboration,
W. A. Benjamin, Inc., New York, 1962;
d) H. C. Brown, Organic Syntheses via
Boranes, Wiley, New York, 1975;
e) H. C. Brown, M. Zaidlewicz, Organic
Syntheses via Boranes Vol. 2: Recent
Developments, Aldrich Chemical Company, Milwaukee, 2001; f) H. C. Brown,
G. Zweifel, J. Am. Chem. Soc. 1961, 83,
486 – 487.
Angew. Chem. Int. Ed. 2005, 44, 1438
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