New discoveries at the interface of boron and
carbon chemistries*
M. Frederick Hawthorne
Department of Chemistry and Biochemistry, University
of California, Los Angeles, CA 90024, USA
Abstract: The continued growth of polyhedral borane chemistry
is illustrated by the successful synthesis of [closo-B12(OH)12]2
–by the H2O2 oxidation of [closo-B12H12,]2. The hydroxylated species
reacts with common organic reagents to produce 12-fold degenerately
substituted carboxylate esters, ethers, and carbamate esters. The ether
derivatives undergo facile and reversible redox reactions in which the
B12 scaffold serves as a one-or two-elec-
tron donor giving stable oxidation states described by [closo
-or hypercloso-B12OR)12]n with
n = –2,–1,and 0. The loss of polyhedral electrons is compensated
by back-bonding from the attached ether oxygen substituents. Structural
comparisons are presented along with representative reaction chemistry.
Derivatives that bear functional groups on the termini of the 12-fold
set of substituents provide a vast array of potential applications.
To distinguish these new polyfunctional icosahedral species from dendrimers,they
have been designated as closomers.
*Lecture presented at the XIth International Meeting
on Boron Chemistry (IMEBORON XI), Moscow, Russia, 28 July - 2 August
2002. Other presentations are published in this issue,
pp. 1157-1355.
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