Journal of Organometallic Chemistry 577 (1999) 197 – 204
Synthesis and structural characterization of new weakly coordinating
anions. Crystal structure of Ag(1-CH
3
–CB
11
H
5
X
6
) (X = H, Cl, Br, I)
Zuowei Xie *, Chi-Wing Tsang, Feng Xue, Thomas C.W. Mak
Department of Chemistry, The Chinese Uniersity of Hong Kong, Shatin NT, Hong Kong, China
Received 15 July 1998; received in revised form 9 October 1998
Abstract
New weakly coordinating anions 1-CH
3
–CB
11
H
5
X
6
-
(X =Cl, Br, I) have been prepared in high yield by either C -methylation
of hexahalocarborane anions CB
11
H
6
X
6
-
or direct halogenation of 1-CH
3
–CB
11
H
11
-
. The lithiation of CB
11
H
6
X
6
-
works just as
well as that of the parent anion CB
11
H
12
-
, which offers a convenient method for the preparation of C -alkylated carborane anions
of the type 1-R–CB
11
H
5
X
6
-
. The useful silver(I) reagents of these new anions not only showed increased solubility in various
organic solvents but also demonstrated the subtlety and diversity of their solid state structures. They are all one-dimensional
coordination polymers in the solid state. The coordination details are, however, unique to each structure. © 1999 Elsevier Science
S.A. All rights reserved.
Keywords: Hexahalocarborane; Lithiation; Weakly coordinating anions
1. Introduction
As a new class of weakly coordinating anions [1],
monocarborane anions CB
11
H
6
X
6
-
(X =Cl, Br, I) have
played a very important role in stabilizing coordina-
tively unsaturated cations such as the silylium ion
(R
3
Si
+
) [2–4], the four-coordinate tetraphenylpor-
phyrinatoiron(III) ion (Fe(tpp)
+
) [5], fullerene cation
(C
76
+
) [6], hydronium ion (H
9
O
4
+
) [7], and in enhancing
the reactivity of organolanthanide cations [8]. However,
due to the poor solubility of these anions in less polar
organic solvents such as benzene and toluene, they have
limited applications. With the ultimate goal of making
more bulkier, more soluble and less coordinating an-
ions, we have explored the C -derivatization of
CB
11
H
6
X
6
-
. On the other hand, silver(I) salts of carbo-
rane anions are very useful halide metathesis reagents
for introducing weakly coordinating anions into vari-
ous kinds of compounds [1–9]. They are also of struc-
tural interest in their own right because they illustrate
the subtlety and diversity of coordination chemistry
when anions have comparable donor ability to solvent
molecules [10]. As part of our attempt to prepare new
weakly coordinating anions and to understand the sys-
tematics of silver – carborane structural chemistry, we
now report the syntheses and structures of new weakly
coordinating anions 1-CH
3
-7,8,9,10,11,12-CB
11
H
5
X
6
-
(X =Cl, Br, I) as well as their silver(I) salt reagents.
2. Results and discussion
2.1. Synthesis
2.1.1. C -Deriatization of CB
11
H
6
X
6
-
Reaction of Li[CB
11
H
6
X
6
] (X =Cl, Br, I) with excess
n
BuLi in THF gave Li
2
[CB
11
H
5
X
6
], after addition of
hexane, as a white precipitate in a quantitative yield
according to
11
B-NMR. This dilithium salt is a very
important intermediate for the preparation of C -substi-
* Corresponding author. Tel.: +852-2609-6269; fax: +852-2603-
5057.
E-mail address: zxie@cuhk.edu.hk (Z. Xie)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII:S0022-328X(98)01040-7