Toward a hexagonal grid polymer: Synthesis, coupling, and chemically reversible surface-pinning of the star connectors, 1,3,5- C6H3(CB10H10CX)3

Article abstract of DOI:10.1021/ja963331d

A synthetic approach to a two-dimensional grid polymer is proposed and the execution of initial steps is described. Pd-catalyzed coupling of (1,12- dicarba-closo-dodecaboran-1-yl)copper (10) with iodobenzene, m-diiodobenzene, and 1,3,5-triiodobenzene yielded the known 1,12-dicarba-closo-dodecaboran-1- ylbenzene (3) and the new m-bis(1,12-dicarba-closo-dodecaboran-1-yl)benzene (4) and 1,3,5-tris(1,12-dicarba-closo-dodecaboran-1-yl)benzene (1), respectively. Each arm of the trigonal connector 1 was provided with one or two sticky tentacles by conversion to 1,3,5-tris[12-((3- (ethylthio)propyl)dimethylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl]benzene (7) and 1,3,5-tris[12-(bis(3-(ethylthio)propyl)methylsilyl)-1,12-dicarba- closo-dodecaboran-1-yl]benzene (8). Linear coupling of carboranyl CH terminals through a mercury atom produced very stable dimeric structures from 3 and 4. The carborane 3, its mercury-linked dimer 13, the 1:1 complex of 13 with 2,2'-bipyridyl, and the 2:1 complex of 13 with 2,2'-bipyrimidyl have been structurally characterized by single-crystal X-ray crystallography, but crystals of 1 showed an intriguing disorder and could not be used for molecular structure determination. Grazing incidence IR spectra show that the tentacled species 7 and 8 adsorb firmly on the surface of gold, apparently without a strong preference for a particular orientation. At room temperature, the tritentacled species 7 can be removed readily and the hexatentacled species 8 more slowly by treatment with a THF solution containing fluoride, which severs the tentacles.

Full text of DOI:10.1021/ja963331d

J. Am. Chem. Soc. 1997, 119, 3907-3917
3907
Toward a Hexagonal Grid Polymer: Synthesis, Coupling, and
Chemically Reversible Surface-Pinning of the Star Connectors,
1,3,5-C6H3(CB10H10CX)3
Ulrich Scho1berl, Thomas F. Magnera, Robin M. Harrison, Frank Fleischer,
Jodi L. Pflug, Peter F. H. Schwab, Xiangsheng Meng, Dariusz Lipiak,
Bruce C. Noll, Viloya S. Allured, Trevor Rudalevige,† Stephen Lee,† and
Josef Michl*,1
Contribution from the Department of Chemistry and Biochemistry, UniVersity of Colorado,
Boulder, Colorado 80309-0215
ReceiVed September 23, 1996X
Abstract: A synthetic approach to a two-dimensional grid polymer is proposed and the execution of initial steps is
described. Pd-catalyzed coupling of (1,12-dicarba-closo-dodecaboran-1-yl)copper (10) with iodobenzene, m-
diiodobenzene, and 1,3,5-triiodobenzene yielded the known 1,12-dicarba-closo-dodecaboran-1-ylbenzene (3) and
the new m-bis(1,12-dicarba-closo-dodecaboran-1-yl)benzene (4) and 1,3,5-tris(1,12-dicarba-closo-dodecaboran-1-
yl)benzene (1), respectively. Each arm of the trigonal connector 1 was provided with one or two sticky tentacles by
conversion to 1,3,5-tris[12-((3-(ethylthio)propyl)dimethylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl]benzene (7) and
1,3,5-tris[12-(bis(3-(ethylthio)propyl)methylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl]benzene (8). Linear coupling
of carboranyl CH terminals through a mercury atom produced very stable dimeric structures from 3 and 4. The
carborane 3, its mercury-linked dimer 13, the 1:1 complex of 13 with 2,2′-bipyridyl, and the 2:1 complex of 13 with
2,2′-bipyrimidyl have been structurally characterized by single-crystal X-ray crystallography, but crystals of 1 showed
an intriguing disorder and could not be used for molecular structure determination. Grazing incidence IR spectra
show that the tentacled species 7 and 8 adsorb firmly on the surface of gold, apparently without a strong preference
for a particular orientation. At room temperature, the tritentacled species 7 can be removed readily and the
hexatentacled species 8 more slowly by treatment with a THF solution containing fluoride, which severs the tentacles.
Introduction
shaped polymers with a trigonal, square, or hexagonal lattice,
with openings of a controlled size.11 Subsequently, we hope
to attach covalently additional regular grid layers on top of the
first, one at a time, to construct ultimately thin layers of materials
whose structure is periodic in two wide dimensions and
controlled in an aperiodic fashion in the third thin dimension.
Desired active groups are to be incorporated into the building
elements.
We are developing a molecular-size construction kit analo-
gous to the children’s Tinkertoy2 play set for use in modular
construction.3-6 Nanotechnology has seen much speculation,7
and great progress in the experimental design of two- and three-
dimensionally networked three-dimensional crystal structures8,9
and in supramolecular architecture10 has been reported.
Our long-range plan5,6 is to use molecular modules for the
construction of firmly connected regular two-dimensional grid-
The elementary modules are inert rods and connectors, chosen
to permit controlled cross-linking polymerization constrained
to two dimensions. The elementary modules are to be combined
into “complex monomeric modules”, in which they are mounted
in a desired orientation on flat molecular pedestals equipped
with detachable tentacles carrying functionalities with affinity
for a liquid surface. Initially, we use the tentacled bottom deck
of a metal sandwich complex as a pedestal and the top deck as
† Department of Chemistry, University of Michigan, Ann Arbor, MI
48109-1055.
X Abstract published in AdVance ACS Abstracts, April 15, 1997.
(1) Presented in part at the 205th ACS National Meeting, Denver, CO,
March 28 to April 2, 1993 (Scho¨berl, U.; Mu¨ller, J.; Basˇe, K.; Ibrahim,
M.; Ibrahim, P. N.; Magnera, T. F.; David, D. E.; Michl, J. Polym. Prepr.
1993, 34, 81) and the 207th ACS National Meeting, San Diego, CA, March
13-17, 1994 (Michl, J.; Meng, X.; Scho¨berl, U.; Lipiak, D. Polym. Prepr.
1994, 35, 397).
(2) Tinkertoy is a trademark of Playskool, Inc., Pawtucket, RI 02862,
and designates a children’s toy construction set consisting of straight wooden
sticks and other simple elements insertable into spool-like connectors.
(3) Kaszynski, P.; Michl, J. J. Am. Chem. Soc. 1988, 110, 5225. Michl,
J.; Kaszynski, P.; Friedli, A. C.; Murthy, G. S.; Yang, H.-C.; Robinson, R.
E.; McMurdie, N. D.; Kim, T. In Strain and Its Implications in Organic
Chemistry; de Meijere, A., Blechert, S., Eds.; NATO ASI Series; Kluwer
Academic Publishers: Dordrecht, The Netherlands, 1989; p 463.
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publication.
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S0002-7863(96)03331-8 CCC: $14.00 © 1997 American Chemical Society

3908 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Scho¨berl et al.
We report the details of the synthesis1 of the trigonal star
connector 123 with three acidic hydrogens at the termini of
1,12-dicarba-closo-dodecaboran-1-yl (2) arms, suitable for
oxidative C-C coupling15,16 similar to the Glaser coupling of
terminal acetylenes. It resembles 1,3,5-tris(ethynyl)benzene, but
is far more stable. The synthesis yields 3 and 4 as byproducts.
(iii) Tentacled Pedestals and Their Reversible Pinning.
We plan to use 1 both as a connector and as a tentacled pedestal.
For the latter, we attached one (5) or two (6) thioether-carrying
aliphatic chains through Si atoms at each arm end, equipping
the tentacled pedestals 7 and 8 for adhesion to a metal surface,
with the benzene ring parallel to the surface if all the tentacles
make contact, and in less well-defined orientations if only some
do. We used a more easily handled gold substrate instead of
mercury, expecting similar adsorption properties for both.
Figure 1. “Point” and “star” connectors (schematic).
a connector. Grid formation is to involve linking of neighboring
modules by sturdy bonds under reversible conditions and
subsequent annealing. Langmuir-Blodgett techniques offer
control over surface concentrations and product transfer to other
substrates. Our initial choice of interface is mercury plus either
a gas or a solvent phase. Hg surface is readily cleaned, has
high affinity for various functional groups, is atomically well
defined, and is favorable for electrochemistry and grazing
incidence reflection spectroscopy.
The synthesis of a two-dimensional regular grid polymer
therefore requires the following: (1) A complex monomeric
module built from (i) rods, (ii) a plain connector, and (iii) a
tentacled connector. (2) Reagent solutions or vapors for (i) two-
dimensional polymerization by coupling of the surface-mounted
complex monomeric modules, (ii) annealing into larger single-
crystal domains by controlled temporary partial reversal of the
coupling process, and (iii) detachment of the tentacles. (3)
Analytical techniques for monitoring the concentration and
orientation of the complex monomeric modules on a surface
and for following their local structural transformations. (4)
Analytical techniques for monitoring long-range order in the
polymer grid. (5) Techniques for transfer of the grid to other
substrates and for its further manipulation.
(iv) Complex Module Assembly. We anticipate three
principal options. The arms on the upper deck can be identical
with the tentacles of the lower deck (e.g., meso pyridine termini
in a double-decker metalloporphyrin6b). The two decks can be
distinct, permitting selective introduction of arms and tentacles
(e.g., derivatives of cyclobutadienecyclopentadienylcobalt4). The
decks can be identical, and the arms and tentacles alone distinct.
Stepwise assembly of triple-decker metallocenes has been
reported24 and inspired the present work, in which the third
option was chosen. This offers access to a two-ply grid by a
second coupling reaction after tentacle removal.
2. Two-Dimensional Polymerization. (i) Arm Coupling.
Oxidative C-C coupling yields strong bonds but is irreversible.
Searching for a reversible linear coupling of the acidic p-
carboranyl termini on the model systems 3 and 4, to avoid the
uncontrolled cross-linking expected for 1, we tried linking
through Hg atoms. Coupling of p-carborane carbons through
mercury25 is sturdy and resembles the long-known26 and recently
much exploited27 mercury coupling of o-carboranes.
(ii) Annealing. For annealing, the coupling, irreversible
under conditions of intended grid use, must be performed
reversibly. We have looked for conditions that sever the
C-Hg-C link.
(iii) Tentacle Detachment. The removal of the pinned
tentacles was tested by treatment with the fluoride anion.28
Without thioether groups, the connectors should desorb from
the surface.
1. Synthesis. (i) Rods. Many classes of axially end-
functionalized straight and relatively rigid rods are now
available,3,5,12-16 permitting the rod length to be controlled to
the nearest Å.17
(ii) Connectors. Few of the connectors used in crystal
engineering8 are suitable for truly sturdy linear coupling. We
envisage two kinds,6 “point” and “star” (Figure 1). In star
connectors, the coupling bonds emanate from the termini of
preattached rigid arms radiating from a common origin, as in
1,3,5-tris(ethynyl)benzene18 and some organometallic com-
3. Analytical Techniques for Local Structure. Grazing-
incidence IR, with which we have had encouraging experience,29
detects the B-H stretch of 1 easily, but the IR signature of the
(19) Bunz, U. H. F.; Enkelmann, V. Organometallics 1994, 13, 3823.
Wiegelmann, J. E. C.; Bunz, U. H. F.; Schiel, P. Organometallics 1994,
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(23) The synthesis of a related structure has been reported recently: Jiang,
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4+
at the connector, as in the well-studied20 complexes of Rh2
,
to which four [n]staffane rods have been attached equatorially21
and two axially.22
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J. Org. Chem. 1980, 45, 3933. Zimmerman, H. E.; King, R. K.; Meinhardt,
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C. B.; Hawthorne, M. F. Inorg. Chem. 1995, 34, 2095.
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Toward a Hexagonal Grid Polymer
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3909
Scheme 1
carborane-Hg-carborane link is indistinct and useless for
monitoring the progress of the coupling reaction. Hoping to
find a spectroscopic marker for these links, we have investigated
the formation of their complexes with 2,2′-bipyridyl and 2,2′-
bipyrimidyl and have characterized two of them structurally.
Requirements 4 and 5 are not addressed presently. Since
issue 1(i) is largely settled, we address issues 1(ii), 1(iii), 2(i),
2(iii), and 3.
n-BuLi in Et2O followed by metal exchange with CuCl in THF,
gave very low yields at best. The Pd-catalyzed reaction with
1,3,5-tribromobenzene yielded mainly the known33 (1,12-
dicarba-closo-dodecaboran-1-yl)benzene (3), 1,3-bis(1,12-di-
carba-closo-dodecaboran-1-yl)benzene (4), and only a small
amount of the desired 1,3,5-tris(1,12-dicarba-closo-dodecaboran-
1-yl)benzene (1). However, a reaction with 1,3,5-triiodobenzene
afforded 1 in 56% yield. The compounds 3 and 4 can be
prepared in a similar way by Pd-catalyzed coupling of 10 with
iodobenzene (68% yield) and 1,3-diiodobenzene (61% yield),
respectively. Coupling reactions of carboranylcopper derivatives
with aryl halides were developed concurrently by others.1,34
The requisite 1,3,5-triiodobenzene can be prepared in 20%
overall yield by the classical multistep procedure from 2,6-
diiodo-4-nitroaniline.35 We find that it can be obtained in 75%
yield in a single step from the commercial 1,3,5-tribromoben-
zene and KI with nickel catalysis, in analogy to the known36
similar reactions of other aryl bromides.
Results and Discussion
Connector Synthesis. A palladium-catalyzed cross-cou-
pling30 of three 1,12-dicarba-closo-dodecaborane (2) units to a
1,3,5-trihalobenzene (Scheme 1) offered the simplest route. The
initial reagent choice,31 l-(trimethylstannyl)-1,12-dicarba-closo-
dodecaborane (9),32 failed to react with aryl bromides and
iodides, despite variation of the solvent (THF, DMF, N-
methylpyrrolidinone), temperature, and catalyst [Pd(CH2Ph)-
Cl(PPh3)2, Pd(PPh3)2Cl2].
In contrast to the reported33 preparation of 1-aryl-1,12-
dicarba-closo-dodecaboranes by uncatalyzed coupling of (1,-
12-dicarba-closo-dodecaboran-l-yl)copper (10) with iodoben-
zene, all uncatalyzed coupling reactions of the organocopper
compound 10, obtained by reaction of the p-carborane 2 with
Connector Structure. We were not able to grow a high-
quality single crystal of 1, and X-ray diffraction data were
collected on disordered twinned crystals. The diffraction data
are compatible with an arrangement of carborane icosahedra
approximately in a cubic closest packed array, with the benzene
rings occupying triangular faces of this array. In a two-
dimensional layer, each icosahedron is a vertex of six different
triangular faces. Only one of these is actually occupied, in a
random fashion. The disorder thus is a result of the closeness
(29) Obeng, Y. S.; Laing, M. E.; Friedli, A. C.; Yang, H. C.; Wang, D.;
Thulstrup, E. W.; Bard, A. J.; Michl, J. J. Am. Chem. Soc. 1992, 114, 9943.
Yang, H. C.; Magnera, T. F.; Lee, C.-M.; Bard, A. J.; Michl, J. Langmuir
1992, 8, 2740.
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(31) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
(32) Stanko, V. I.; Khrapov, V. V.; Klimova, T. V.; Babushkina, T. A.;
Klimova, T. P. Zh. Obshch. Khim. 1978, 48, 368.
(33) Zakharkin, L. I.; Kovredov, A. I. IzV. Akad. Nauk SSSR, Ser. Khim.
1974, 740.
(34) Coult, R.; Fox, M. A.; Gill, W. R.; Herbertson, P. L.; MacBride, J.
A. H.; Wade, K. J. Organomet. Chem. 1993, 462, 19.
(35) Willgerodt, C.; Arnold, E. Chem. Ber. 1901, 34, 3343. Cf., Hirota,
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3910 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Scho¨berl et al.
Scheme 2
this is a perfectly acceptable synthetic procedure, it does not
offer suitable conditions for the two-dimensional coupling that
we ultimately need to perform on a metal surface, as this will
require a one-step treatment with a homogeneous solution.
We find that the coupling of 3 to the mercury-coupled dimer
13 proceeds in 97% yield (79% isolated yield) upon treatment
with t-BuOK, a Hg(II) salt, and excess NaBr, in DMF
(dimethylformamide), TMU (tetramethylurea), or DMPU (“dim-
ethylpropyleneurea”), but not in tert-butyl alcohol or propylene
carbonate. These reaction conditions were inspired by a report38
of mercuration of an o-carborane with a Hg(II) salt and excess
bromide in a basic aqueous medium. While the less forcing
aqueous reaction conditions are sufficient for the more reactive
o-carborane, they are not adequate for the p-carborane derivative
3, reflecting the generally lower acidity of p-carboranes.
In a similar fashion, 4 was converted smoothly into its
mercury-coupled dimer 14 in a homogeneous solution of
t-BuOK, HgBr2, and NaBr in DMF. When the reaction was
stopped before all 4 was consumed, the formation of higher
oligomers did not interfere significantly, and 14 was formed in
61% yield. After correction for recovered 4, the yield was 75%.
Thus, these reaction conditions are likely to be general for the
coupling of p-carboranes under homogeneous conditions.
The mercury coupling link is thermally very stable. No
decomposition occurs when 13 melts at 266 °C, and little occurs
when 14 melts at 354 °C (after cooling it remelts at 330-350
°C).
of the distance between the two carborane icosahedra in 1 to
their van der Waals distance. An example of a molecule in
one of the possible orientations is shown in Figure 2 of the
Supporting Information. It must be emphasized that the R factor
is very poor (24.6%) and the analysis (Supporting Information),
although compatible with the structure 1, cannot be viewed as
an independent structural determination for 1.
A successful X-ray structure analysis was performed for 3
(Figure 3 of the Supporting Information). For our purposes,
the important features are the 1.502 Å C-C bond length
between the phenyl substituent and the carborane ring and the
3.101 Å transannular C-C separation in the 12-vertex p-
carborane cage. Combined with the 1.395 Å distance from the
center of the benzene ring to its carbons, this produces a distance
of 6.0 Å from the benzene ring center to the outer carbon, and
this is our best estimate of the length of the arms of the
connector 1. Their thickness (diameter), obtained from the
estimated positions of the hydrogen atoms in 3 and standard
van der Waals radii for hydrogen (1.2 Å), amounts to 7.3 Å.
Tentacle Attachment and Removal. The (3-(ethylthio)-
propyl)dimethylsilyl and bis(3-(ethylthio)propyl)methylsilyl groups
appeared to offer reasonable adhesive groups and sufficient
mechanical flexibility. The reaction of sodium ethanethiolate
with 1-bromo-3-chloropropane is known to yield 3-(ethylthio)-
propyl chloride37 (11), and we have performed it under phase
transfer conditions. (3-(Ethylthio)propyl)dimethylsilyl chloride
(5) was obtained by a subsequent reaction of the Grignard
compound derived from 11 with Me2SiCl2, and bis(3-(ethylthio)-
propyl)methylsilyl chloride (6) resulted from a similar reaction
of the Grignard compound with MeSiCl3 (Scheme 2).
Reactions of 5 and 6 with the trilithium salt of the trigonal
connector 1 yielded the desired tentacled pedestals, 1,3,5-tris-
[12-((3-(ethylthio)propyl)dimethylsilyl)-1,12-dicarba-closo-dodeca-
boran-1-yl]benzene (7) and 1,3,5-tris[12-(bis(3-(ethylthio)-
propyl)methylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl]-
benzene (8), respectively (Scheme 3). These reactions are
slower than the model reaction, the silylation of 4 with tert-
butyldimethylsilyl chloride to yield 12, and proceed in only
about 25-30% yield. The tentacles are removed with a solution
of Bu4NF in THF.
Under these strongly basic single-step conditions, the coupling
reaction appears to be reversible. In DMF, 14 is not affected
by a 5 h treatment with an 8-fold excess of 0.02 M NaBr, but
about half of it is converted to 4 after a 5-h treatment with a
similar excess of 0.02 M t-BuOK. Unfortunately, the strongly
basic conditions also cause a loss of the silyl substituents from
the carborane cages. Thus, t-BuMe2Si protecting groups are
stable in DMF and DMPU, but when t-BuOK is added, they
are removed rapidly. Also, the action of t-BuOK in DMF on
7 removes its tentacles. Even though the attack of t-BuOK on
the silicon atom may be hindered in the adsorbed state, this
result makes it unlikely that we shall be able to use these reaction
conditions in the surface-confined coupling of complex mon-
omeric modules containing a connector with carborane arms in
the upper deck and the tentacled pedestals 7 and 8 in the lower
deck, since the tentacles would be lost in the process. It is
conceivable that bulkier substituents on the silicon atom would
slow down tentacle removal sufficiently for our purposes, but
the attachment of such modified tentacles to 1 would then
probably be even harder than it is with the present tentacles.
Short of changing the nature of the coupler or the nature of
the attachment of the tentacles to the central unit, there seem
to be two ways out of the dilemma. First, one could reduce
the affinity of the coupling solution for the silicon atom, perhaps
by use of a sterically hindered base. Second, one could enhance
the reactivity of the carborane center toward mercury by
replacing the hydrogen by a suitable leaving group, such as
trimethylstannyl in 15, and by using a strong mercurating
agent, such as mercury(II) triflate in propylene carbonate. These
possibilities are currently under examination.
Structure of Mercury-Linked Connector Arms. An X-ray
structure analysis of 13 revealed a molecule with rotational
disorder in the phenyl rings (Figure 4, Table 1). The C-Hg-C
angle is approximately linear at 174°. The Hg-C bond distance
of 2.075 Å is comparable to that in bis(p-carboran-1-yl)-
mercury25 at 2.084 Å, and this makes the separation of benzene
Connector Arm Linking. In initial tests of linear coupling
(Scheme 4), we used 3 and 4, in which the extent of coupling
can be controlled easier than in 1. Bulk coupling of 3 to yield
13 is accomplished readily by treatment with LDA in THF at
-78 °C followed by metal exchange with HgCl2. Although
(38) Zakharkin, L. I.; Krainova, N. Yu. IzV. Akad. Nauk. SSSR, Ser. Khim.
1984, 1184.
(37) Ba¨hr, G.; Mu¨ller, G. E. Chem. Ber. 1955, 88, 1765.

Toward a Hexagonal Grid Polymer
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3911
Scheme 3
Scheme 4
centroids in the crystal equal to 16.195 Å. This corresponds to
two arms plus a linker and would be the length of the side of
the repeated hexagons that we hope to produce ultimately in
the surface-controlled coupling reaction. If the sides of the
hexagon are linear, the diameter of a circle passing through the
benzene centers would be a little over 32 Å. The smallest
diameter of the resulting hexagonal opening then would be on
the order of 22 ( 2 Å. Since the van der Waals radius of the
rod varies along its length and is smallest at the mercury atom
in the center, it is difficult to provide an exact value. In realistic
situations, the instantaneous value of the diameter will be subject
to modulation by vibrations.
In the crystal, the molecules of 13 are packed in crossed pairs,
with their central mercury atoms 4.904 Å apart. Chloroform
occupies the spaces between the arms of the cross. There is a
3.102 Å contact between the Hg atom of one member of the
pair and the hydrogen atoms H(2), and its 2-fold equivalent,
that belongs to the other member of the pair. The H(2)-Hg-

3912 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Scho¨berl et al.
A
Figure 4. Single-crystal X-ray structure of 13.
Table 1. Selected Bond Lengths (Å) and Angles (deg) in 13 and
Its Complexes
13‚
2(13)‚
3-Hg-Cl‚
bipyridyl
13
bipyridyl bipyrimidyl
B
Hg-C
Hg-N
2.075
2.102
2.631
165
62.2
2.098
2.696
168
60.9
2.088 (2.383)a
2.468
C-Hg-C 174
N-Hg-N
(151)b
66.3
a Hg-Cl bond. b C-Hg-Cl angle.
H(2) angle is 86.3°. This crossed arrangement is similar to that
described below for the 2,2′-bipyridyl and 2,2′-bipyrimidyl
complexes, with the BH hydrogens of one molecule of 13 acting
as “ligands” for the other molecule of 13, except that in the
present case, the long axis of each rod is slightly bent with its
ends toward its partner, not away from it.
Figure 5. Single-crystal X-ray structure of the 1:1 complex of 13 with
2,2′-bipyridyl: (A) the fully coordinated molecule; (B) the half-
coordinated molecule.
Structure of Complexed Connector Arm Links. In order
to permit connector coupling on a metal surface to be followed
by grazing-incidence absorption spectroscopy, we examined
whether the carborane-Hg-carborane link associates in a
structurally well defined way with an intensely absorbing UV
and/or IR chromophore with well-characterized transition mo-
ment directions, which does not by itself strongly adsorb to
mercury in the same geometry. In spite of the less strongly
electron-withdrawing character of p-carborane, we found that
the complexation of 13 with aromatic nitrogen heterocycles
resembles that known39 to occur with bis(o-carboranyl)mercury
derivatives. Complexes of 13 with 2,2′-bipyridyl and 2,2′-
bipyrimidyl form readily upon mixing of the components in
solution and crystallize well.
There were two additional reasons for this investigation. It
may be useful to find a template for the formation of these very
large rings, and complexation to the mercury atoms may provide
the requisite means of attachment to the templating species.
Also, in future attempts to bind constituents of an additional
layer to the polymer grid, heterocycles with two opposed
complexing sites, one of them bound to a mercury atom in the
bottom layer, may provide the necessary sites for epitaxial
attachment of constituents of a top layer. For all three purposes,
it would be best if the complexation did not affect the linear
geometry of the carborane-Hg-carborane link at all.
The complex with 2,2′-bipyridyl has a 1:1 stoichiometry.
There are two crystallographically and chemically distinct
molecules in the asymmetric unit (A and B) shown in Figure 5
(Table 1). In form A, both bipyridyl nitrogens are well
coordinated to the mercury atom, and in form B, only one of
the bipyridyl nitrogens is, while the other is more distant. The
Hg-C bond length is similar in both species, with an average
value of 2.104 Å. In the fully coordinated form A, one of the
Hg-N dative bonds is 2.613(4) Å long and the other 2.656(5)
Å. The corresponding values for the “half-coordinated” form
B are 2.624(4) and 2.726(6) Å. The presence of the bipyridyl
ligand perturbs the geometry of 13 detectably, but not exces-
sively, to give a C-Hg-C bond angle of 165°, with the
carborane rod ends tilted slightly away from the bipyridyl. The
Figure 6. Single-crystal X-ray structure of the 2:1 complex of 13 with
2,2′-bipyrimidyl.
pyridine rings are coplanar in form A and twisted 22° with
respect to each other in form B.
2,2′-Bipyrimidyl binds two molecules of 13 to form a
centrosymmetric 2:1 complex (Figure 6, Table 1). The two
mercury atoms are bound to opposite sides of the bipyrimidyl
molecule and lie in the same plane as the four carbon atoms
bound to them. This plane is nearly perpendicular (86.6°) to
the plane defined by the two pyrimidine rings. The average
Hg-C bond length is 2.098 Å, slightly longer than in free 13.
The rest of the structure of 13 is not perturbed. The average
Hg-N bond length is 2.696 Å, longer than in the bipyridyl
complex. The C-Hg-C bond angle is 168.3°, intermediate
between 13 and its bipyridyl complex. We also analyzed a
complex of (12-phenyl-1,12-dicarba-closo-dodecaboran-1-yl)-
mercury chloride (3-Hg-Cl) with 2,2′-bipyridyl, presumably
formed from an impurity present in initial crude samples of 13
(Table 1 and Supporting Information).
In none of the isolated crystals did we observe a single
mercury with more than one nitrogen heterocycle ligand. The
limitation may be steric but is more likely electronic in nature,
since more electronegative substituents on a divalent mercury
generally promote the formation of stronger complexes. The
p-carborane substituents may withdraw insufficient electron
density to favor the binding of more than one ligand. Using
the C-Hg-C bond angle and the Hg-N bond lengths as a
measure of the strength of the complexes, the complex of
(39) Bregadze, V. I.; Okhlobystin, O. Yu. Dokl. Akad. Nauk SSSR 1967,
177, 347 Usp. Khim. 1968, 37, 353. Zakharkin, L. I.; Podvisotskaya, L. S.
IzV. Akad. Nauk SSSR, Ser. Khim. 1968, 3, 681.

Toward a Hexagonal Grid Polymer
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3913
Supporting Information) contained the characteristic peaks of
the connectors, showing the presence of an adsorbed layer: the
BH stretching vibration, the in-plane benzene ring vibration,
and the deformation vibration of methyl groups on silicon.
Subsequent 1 h boiling of the sample in hexane removed about
half of the adsorbed molecules of 7, as judged by the intensity
of the BH stretching vibration (Figure 8b), whereas 8 appears
not to be removed by this treatment at all (Figure 9b of the
Supporting Information).
The ratio of the peak heights of the ring vibration to the BH
stretching vibration was 1:7 for 7 (1:6 after boiling in hexane,
Figure 8b) and 1:5 for 8 (unchanged after boiling in hexane,
Figure 9b of the Supporting Information), and thus was not
significantly different from the 1:5 value observed in the
isotropic spectrum (Figure 7). Since the ring vibration is
polarized in the plane of the benzene ring, while the sum of the
BH stretching vibrations is likely to be more isotropic, ratios
lower than 1:5 would be expected if the benzene rings of the
adsorbed molecules were oriented parallel to the conducting
surface.40 The observed result suggests that the adsorbed layer
may be quite disordered. Since we ultimately plan to use a
mercury surface, on which surface concentration can be adjusted
easily by use of a Langmuir trough, we did not consider it
important to optimize the conditions for adsorption on the gold
surface and to achieve the proper orientation of the tentacled
pedestal.
Figure 7. IR absorption spectra of 7 (a), 8 (b), and 1 (c) in KBr pellet.
In the spectra of the adsorbed layers, the methyl deformation
peak is doubled. This appears clearly in the spectrum of 7
(Figure 8a) and only vaguely in that of 8, where this peak has
only about half of the relative intensity (Figure 9a of the
Supporting Information). The lower-frequency component
appears very close to the position it has in the spectrum
measured in the KBr pellet, whereas the other component is
Figure 8. Grazing-incidence IR absorption spectrum of a layer of 7
on a gold surface. The B-H stretching (left), benzene ring deformation
(center), and SiCH3 deformation (right) spectral regions are shown.
As adsorbed from hexane (a); after 1 h of reflux in hexane (b); and
after subsequent treatment with Bu4NF in THF (c).
phenylcarboranylmercury chloride with 2,2′-bipyridyl would
appear to be the strongest and that of 13 with 2,2′-bipyrimidyl
the weakest.
shifted by about 5 cm-1 higher to the vicinity of 1260 cm-1
.
After the adsorbed layer is treated with boiling hexane, the
lower-frequency component is significantly reduced in intensity.
The peak shifted to higher frequencies is probably due to methyl
groups perturbed by the proximity of the metal surface, and
the likely effect of the boiling is to reduce the number of
tentacles in the adsorbed layer that are unattached to the surface.
Keeping the samples with an adsorbed layer of 7 or 8 in hexane
over the weekend or in CH2Cl2 for over an hour did not remove
the adsorbate. The effect of refluxing in THF or t-BuOH was
similar to that of refluxing in hexane.
The removal of the tentacles with a solution of fluoride is
facile. Treatment of the gold surface with an adsorbed layer
of 7 with a 10-3 M solution of Bu4NF in tetrahydrofuran at 40
°C for 20 min removed all of it (Figure 8c). A similar treatment
of the adsorbed layer of 8 for 1 h reduced the intensity of the
BH stretching peak by 80%, that of the ring vibration down
into the noise level, and that of the silicon methyl deformation
peak by 25%. At the same time, this last peak lost its doubled
character and was shifted to lower frequencies, appearing at
about 1250 cm-1. Tentatively, we take these results to mean
that most of the tentacles have been severed and 80% of the
trigonal connectors removed, but that the bulk of the detached
tentacles still adhere to the gold surface, albeit in an orientation
different from the one they had while still attached to the
connector. After 36 h of treatment with Bu4NF, none of the
IR signals persist and the gold surface is clean (Figure 9c of
the Supporting Information). Clearly, the hexatentacled mol-
ecule 8 adheres better to the gold surface, but can be removed
if desired.
The results obtained so far are quite encouraging from all
three points of view listed above. The structural modification
induced in 13 by complex formation is minor, the structures of
the complexes are regular and symmetrical, and binding on the
opposite sides of 2,2′-bipyrimidine is possible. The inability
of the mercury atom of 13 to bind to two nitrogen heterocycles
simultaneously imposes some limitations on the concept of using
2,2′-bipyrimidyl as a pillar between hexagonal grid layers, in
that half of the mercury atoms would have to carry such pillars
on one side of the grid plane and the other half on the other
side.
Infrared Spectra of the Connectors. We have chosen IR
spectroscopy for monitoring the adsorption of the tentacled
connectors on metal surfaces. The isotropic IR spectra of 1, 7,
and 8 in a KBr pellet are shown in Figure 7. The assignments
of the three peaks to be used in the surface studies are based
on their positions and on the differences between the spectra of
1, 7, and 8. The intense peaks at 1598 and 2609 cm-1 are
attributed to a benzene ring deformation vibration and an
unresolved sum of all the BH stretching vibrations, respectively.
Their peak intensity ratio is about 1:5. The intense peak at 1254
cm-1 in the spectra of 7 and 8, absent in the spectrum of 1, is
assigned to the deformation vibration of the SiMe2 or SiMe
groups. It is much broader for 7 than for 8. Its integrated
relative intensity is about 2 times higher in 7, which has twice
the number of methyl groups.
Adsorption of the Connectors on a Gold Surface and
Their Removal. A thin layer of gold sputtered on glass was
immersed in a 10-7 M solution of 7 or 8 in hexane for 10 h,
rinsed carefully with hexane, and dried. The grazing-incidence
IR spectra of the surface (Figure 8a, and Figure 9a of the
(40) Michl, J.; Thulstrup, E. W. Spectroscopy with Polarized Light. Solute
Alignment by Photoselection, in Liquid Crystals, Polymers, and Membranes;
VCH Publishers: Deerfield Beach, FL 1986.

3914 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Table 2. Summary of Crystallographic Parameters
Scho¨berl et al.
compound number
empirical formula
formula mass
crystal system
space group
a, Å
1
3
13
13‚bipyridyl
C26H38B20HgN2
795.37
triclinic
P1h
13.4313(2)
16.4607(2)
17.11950(10)
89.5360(10)
89.9270(10)
70.8180(10)
3574.67(7)
4
2(13)‚bipyrimidyl
C23.5H37B20HgN2
764.34
orthorhombic
Pnma
14.7396(3)
27.3694(6)
17.5151(3)
90
90
90
7065.8(2)
8
1.437
3-Hg-Cl‚bipyridyl
C18H23B10ClHgN2
611.52
monoclinic
P21/n
7.1620(14)
21.480(4)
15.318(3)
90
99.39(3)
90
2324.9(8)
4
1.747
6.745
0.48 and 0.24
178(2)
C12H36B30
504.75
rhombohedral
R3h
7.11
7.11
17.42
90
90
120
C8H16B10
220.30
orthorhombic
Pbca
7.6170(10)
15.377(2)
22.715(3)
90
90
90
2660.5(6)
8
1.100
C17H31B20Cl3Hg
758.56
tetragonal
I41/a
15.162(2)
15.162(2)
27.256(6)
90
90
90
6265(2)
8
1.608
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
762.64
1
1.099
F
calcd, mg m-3
1.478
4.330
0.80 and 0.73
156(2)
0.71073
µ, mm-1
0.05
0.047
5.182
4.378
0.90 and 0.68
146(2)
0.71073
35815
trans. coeff.
0.83 and 0.76
ambient
0.71073
7657
71, Rint ) 0.052
71
0.99 and 0.96
ambient
0.71073
6782
0.39 and 0.27
178(2)
0.71073
3701
T (K)
λ, Å
reflections collected
unique reflections
reflections observed
R indicesa [obsd data]
0.71073
7212
10227
3067, Rint ) 0.0343 2755, Rint ) 0.0680 10220, Rint ) 0.0047 6369, Rint ) 0.0692 5335, Rint ) 0.0535
961 (F > 6.0σ(F))
R1 ) 0.0599;
wR ) 0.0766
R ) 0.1652;
wR ) 0.1131
a ) 0.0010b
1660 (I > 2.0σ(I))
R1 ) 0.0561;
wR2 ) 0.1221
R1 ) 0.1045;
9858 (I > 2.0σ(I))
R1 ) 0.0321;
4385 (I > 2.0σ(I))
R1 ) 0.0428;
wR2 ) 0.0653
R1 ) 0.0768;
wR2 ) 0.0797
a ) 0.0074,
b ) 30.3038c
1.136
4043 (I > 2.0σ(I))
R1 ) 0.0435;
wR2 ) 0.0994
R1 ) 0.0617;
wR2 ) 0.1068
a ) 0.0600,
b ) 0c
wR2 ) 0.0837
R1 ) 0.0342;
R indicesa (all data)
weighting coeffs.
R1 ) 0.2459;
wR2 ) 0.5680
wR2 ) 0.1423
wR2 ) 0.0932
a ) 0.0700, b ) 0c a ) 0.0360,
b ) 15.4586c
1.166
goodness-of-fitd on F2
1.71
0.969
0.981
a R1 ) ∑(||Fo| - |Fc||)/∑|Fo|; wR ) {∑(w|Fo| - |Fc| )/∑[w(Fo)2]}1/2; wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
b w-1 ) [σ2(Fo) + aF2]. c w-1
2
2
2
d
) [σ2(Fo2) + (aP)2 + bP], P ) (Fo2 + 2Fc2)/3. Goodness-of-fit ) {∑[w(Fo2 - Fc2)2]/(M - N)}1/2, M ) number of reflections and N ) number
of parameters refined.
metal. Grazing-incidence spectra used a Harrick RGA single-reflection
grazing-incidence attachment. GC MS spectra were measured on an
HP GC/MS 5988A instrument with a fused silica capillary column
(cross linked 5% phenyl methyl silicone). MS spectra were measured
on a VG 7070 EQ-HF Hybrid Tandem Mass spectrometer in EI+ mode.
1,12-Dicarba-closo-dodecaborane was purchased from Katchem, Pra-
gue, Czech Republic. Elemental analyses were performed by Desert
Analytics, Tucson, AZ, and Microanalytical Laboratory, University of
California, Berkeley, CA. Details of X-ray structure determinations
are provided in the Supporting Information and a summary is available
in Table 2.
1,3,5-Triiodobenzene. 1,3,5-Tribromobenzene (2.20 g, 7.0 mmol),
KI (7.00 g, 42 mmol), Ni powder (4.00 g), I2 (10.20 g), and DMF (25
mL) were charged into a 100 mL round-bottomed Schlenk flask. The
flask was evacuated on the vacuum line at 0 °C for 15 min. The mixture
was refluxed under N2 at 185-190 °C for 3 h. After cooling, the
solution was poured into a 500 mL separation funnel. The flask was
washed with 3% aqueous HCl (100 mL) and CH2Cl2 (100 mL) until
all material, except for Ni powder, was transferred into the separation
funnel. The CH2Cl2 layer was separated, and the aqueous layer was
extracted with CH2Cl2 (2 × 20 mL). The combined CH2Cl2 phase
was washed with distilled water (3 × 50 mL) and dried over MgSO4.
The solvent was evaporated, leaving a light-brown crude product (2.8
g). This was further purified by sublimation at 60 °C overnight to
remove most C6H3I2Br (ca. 6%) and other impurities (ca. 6%). The
residue was sublimed at 120 to 140 °C. Yield, 2.38 g (75%), purity
98% by NMR.
Conclusions
We have taken several steps toward the ultimate goal, the
synthesis of two-dimensional grid polymers: (i) a new type of
trigonal connector of the star type has been prepared and
characterized, (ii) it has been converted to a tentacled pedestal
by attachment of three or six tentacles whose affinity for gold
is sufficient for firm pinning to an Au surface, (iii) chemical
removal of the pedestal from the surface has been shown to be
facile under conditions that sever the arms, (iv) two sets of
homogeneous single-step reaction conditions suitable for sym-
metric linear coupling of its arms have been found, one of them
apparently reversible, and (v) complexation of the links with
IR and UV spectroscopic markers has been demonstrated and
structurally characterized.
Three major and several minor steps remain before the crucial
concept, regular grid formation by two-dimensional cross-linking
polymerization, can be tested for connector 1. The major steps
are (i) to find a compatible choice of coupling conditions and
tentacle attachment mode, (ii) to show that the reversible pinning
works on mercury and orients the tentacled pedestal properly,
and if not, to modify the adhesive functionalities in the tentacles
until it does, and (iii) to join the connector and the tentacled
pedestal into an asymmetric metal sandwich complex.
Experimental Section
1-(Trimethylstannyl)-1,12-dicarba-closo-dodecaborane (9). Fur-
ther spectral data obtained for this known32 compound: 1H NMR
(CDC13) δ -0.01 (s, 6 H, CH3), 0.07 (s, 3 H, CH3), 1.20-3.20 (br m,
10 H, BH), 2.72 (s, 1 H, CH); 11B{1H} NMR (CDC13) δ -13.74; IR
All reactions were carried out under nitrogen atmosphere with dry
solvent, freshly distilled under anhydrous conditions unless otherwise
noted. Yields refer to chromatographically and spectroscopically (1H
NMR) homogeneous materials, unless otherwise stated. Melting points
were determined on a Boe¨tius micro heating stage with PHMK 05
viewing device. 1H NMR spectra (299.949 MHz) and 11B NMR spectra
were measured on a Varian VXR-300 S spectrometer and referenced
to external TMS and (MeO)3B, respectively. IR spectra were recorded
on a Nicolet 800 FT-IR Spectrometer. Flat gold surface for adsorption
studies was prepared by sputtering gold on a microscope slide until it
was opaque and was used immediately. Before use, the glass surface
was cleaned with a detergent and absolute alcohol and sputter-etched
with argon ions. The solvents were dried by distillation over sodium
(KBr) 2928 (w), 2603 (s), 1399(s), 1093 (s), 767 cm-1
.
1,3,5-Tris(1,12-dicarba-closo-dodecaboran-1-yl)benzene (1). 1,12-
Dicarba-closo-dodecaborane (2,41 808 mg, 5.6 mmol) and CuCl (554
mg, 5.6 mmol) were charged into a 250 mL three-neck round-bottomed
flask and into a tip tube attached to the flask, respectively. After the
(41) Papetti, S.; Obenland, C.; Heying, T. L. Ind. Eng. Chem. Prod. Res.
DeV. 1966, 5, 334. Our material was purchased from Katchem, Ltd., El.
Kra´snohorske´ 6, 11000 Praha 1, Czech Republic.
(42) International Tables for Crystallography; D. Reidel Publishing
Co.: Boston, 1991, Vol. C.

Toward a Hexagonal Grid Polymer
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3915
flask was evacuated, THF (50 mL) was added under nitrogen. n-BuLi
(3.5 mL, 1.6 M in hexane, 5.6 mmol) was added at -30 °C. After 2
h of stirring at room temperature, the CuCl was added from the tip
tube to the solution at -30 °C and the reaction was allowed to proceed
for 1 h at room temperature (rt) and then for 2 h at reflux. The solvent
was removed under reduced pressure. A clean tip tube was charged
with 1,3,5-triiodobenzene (640 mg, 1.4 mmol) and attached to the flask.
After evacuation, Pd(PPh3)2Cl2 in N-methylpyrrolidinone (30 mL), made
from 100 mg of PPh3 and 40 mg of PdC12, was added through a syringe
needle under nitrogen atmosphere. 1,3,5-Triiodobenzene was added
from the tip tube. The reaction mixture was stirred for 16 h at 100 °C
and then poured into H2O (20 mL) and extracted with toluene (4 × 30
mL). The combined organic phases were washed with brine and dried
with MgSO4. After the solvent was removed, product 1 (342 mg, 56%)
was obtained by crystallization from a hexane-toluene mixture, leaving
mostly p-carboranylbenzene (3) and 1,3-bis(p-carboranyl)benzene (4)
in diethyl ether (25 mL) was added n-BuLi (1.6 M in hexane, 4.10
mL, 6.56 mmol). After 1.5 h of stirring at room temperature, CuCl
(700 mg, 7.08 mmol) and THF (25 mL) were added at -30 °C under
N2. The mixture was stirred at room temperature for 1 h and refluxed
for 0.5 h. After the solvent was removed under reduced pressure,
N-methylpyrrolidinone (20 mL), 1,3-diiodobenzene (1.07 g, 3.24 mmol),
and Pd(PPh3)2Cl2 (190 mg, 0.27 mmol) were added under N2. The
mixture was stirred at 100 °C for 18 h, poured into water (30 mL), and
extracted with methylene chloride (5 × 25 mL). The aqueous layer
was saturated with NaCl, and the combined organic phases were washed
with H2O and dried over MgSO4. After the solvent was removed, the
product was purified by thick-layer chromatography (silica, hexane)
to give a white solid (714 mg, 61%): mp 239-240 °C; 1H NMR
(CDCl3) δ 1.20-3.20 (br m, 20 H, BH), 2.76 (s, 2 H, BCH), 6.95-
7.06 (m, 4 H, aromatic); 13C{1H} NMR (CDCl3) δ 59.94 (CcarboraneH),
85.67 (CcarboraneCar), 126.25 (Car), 126.83 (Car), 127.77 (Car), 136.65
(CarCcarborane); 11B NMR (CDCl3) δ -13.46 (d, J ) 172 Hz), -15.96
(d, J ) 175 Hz); MS m/z (rel intensity) 362 (boron cluster center,
isotope pattern fits the calculated cluster for M, 100), 220 (cluster center,
M -C2B10H11, 20), 177 (20), 143 (cluster center, C2B10H11, 40); IR
(KBr) 3061 (BCH), 2606 (BH), 1604, 1579, 1418, 1091, 1053, 1008,
828, 742, 733 cm-1; HRMS calcd 366.3896, found 366.3900.
m-Bis(12-(tert-butyldimethylsilyl)-1,12-dicarba-closo-dodecabo-
ran-1-yl)benzene (12). To a solution of m-bis(1,12-dicarba-closo-
dodecaboran-1-yl)benzene (4) (31 mg, 0.08 mmol) in THF (5 mL) was
added t-BuLi (0.12 mL, 1.7 M in pentane, 0.2 mmol) at -78 °C under
N2. After 2 min, tert-butyldimethylsilyl chloride (40 mg, 0.27 mmol)
was added (t-BuLi deprotonates much faster than n-BuLi). The reaction
mixture slowly warmed to room temperature. After 16 h of stirring, it
was poured into H2O (20 mL) and extracted with methylene chloride
(3 × 20 mL). After drying the solution with MgSO4, the product was
purified by thick-layer chromatography (silica, hexanes) to give 43 mg
(85%) of a white solid: mp 255 °C; 1H NMR (CDCl3) δ -0.01 (s, 12
H, SiCH3), 0.88 (s, 18 H, t-Bu), 1.20-3.40 (br m, 20 H, BH), 6.95-
7.06 (m, 4 H, aromatic); 13C{1H} NMR (CDCl3) δ -4.39 (SiCH3), 19.18
(SiC(CH)3), 26.88 [SiC(CH)3], 69.43 (CcarboraneSi), 89.74 (CcarboraneCar),
125.99 (Car), 126.59 (Car), 127.62 (Car), 136.84 (CcarboraneCar); 11B NMR
(CDCl3) δ -12.16 (d, J ) 164 Hz, 10 B), -13.53 (d, J ) 166 Hz, 10
B); MS m/z (rel intensity) 591 (boron cluster center, isotope pattern
fits the calculated cluster for M, 5) 535 (cluster center, M - C4H9,
20), 277 (cluster center, M - C8H25B10Si, 100); IR (KBr) 2958, 2933
(CH), 2610 (BH), 1254, 1099, 874, 819, 794, 637 cm-1. Anal. Calcd
for C22H54B20Si2: C, 44.71; H, 9.21. Found: C, 44.79; H, 9.25.
(3-(Ethylthio)propyl)dimethylsilyl Chloride (5). To a mixture of
1-bromo-3-chloropropane (126 g, 0.80 mol), 50% aqueous NaOH (40
g, 0.50 mol), and Bu4NBr (483 mg, 1.5 mmol) was slowly dropped
ethanethiol (24.8 g, 0.40 mol) under vigorous stirring at 0 °C. After 2
h stirring at room temperature, the organic layer was separated, washed
twice with water (50 mL), dried over Na2SO4, and fractionally distilled.
After a fraction of 1-bromo-3-chloropropane (35-60 °C/15 Torr), 36.7
g (264 mmol, 66%) of 3-(ethylthio)propyl chloride (11) (65-75 °C/15
Torr, lit.37 71.5 °C/15 Torr) was collected as a pale yellow oil: lH NMR
(CDCl3) δ 1.24 (t, J ) 7.3 Hz, 3 H, CH3), 2.01 (m, 2 H, CH2), 2.52 (q,
J ) 7.4 Hz, 2 H, SCH2), 2.65 (t, J ) 7.0 Hz, 2 H, SCH2), 3.63 (t, J )
6.4 Hz, 2 H, ClCH2). 3-(Ethylthio)propyl chloride (11, 7.00 g, 50
mmol) was dropped slowly to Mg turnings (1.22 g, 50 mmol) activated
with 2 drops of Br2 in Et2O (70 mL). After 12 h of reflux, the Grignard
reagent was added to Me2SiCl2 (25.8 g, 200 mmol) in diethyl ether
(100 mL). After 18 h of refluxing under mechanical stirring, the Mg
salts were filtered, and washed with Et2O (2 × 25 mL), and the solvent
was evaporated from the combined filtrates. The residue was fraction-
ally distilled to yield 5 (45 °C/0.01 Torr, 4.20 g, 42%): 1H NMR
(CDCl3) δ 0.41 (s, 6 H, SiCH3), 0.91-0.95 (m, 2 H, SiCH2), 1.24 (t,
J ) 3 Hz, 3 H, CH3), 1.64-1.74 (m, 2 H, CH2), 2.49-2.58 (m, 4 H,
CH2SCH2); 13C{1H} NMR (CDCl3) δ 1.87 (SiCH3), 15.07 (SiCH2),
18.58 (CH3), 23.50 (CH2), 26.00 (SCH2CH2), 34.85 (CH3CH2S); MS
m/z (rel intensity) 196 (M, 14), 181 (M - CH3, 20), 93 (M - C5H11S,
100), 75 (C3H7S, 49); IR (neat) 2944 (CH), 1254 (SiMe), 1057 (br),
801, 473. Anal. Calcd for C7H17ClSSi: C, 42.72; H, 8.71. Found:
C, 43.02; H, 8.91.
1
in the mother liquor: mp > 320 °C; H NMR (CDCl3) δ 1.20-3.20
(br m, 30 H, BH), 2.76 (s, 3 H, CH), 6.87 (s, 3 H, aromatic); 13C{1H}
NMR (CDCl3) δ 60.09 (CcarboraneH), 84.91 (CcarboraneCar), 125.83 (Car),
136.44 (CarCcarborane); 11B NMR (CDCl3) δ -13.51 (d, J ) 165 Hz, 15
B), -15.89 (d, J ) 168 Hz, 15 B); MS m/z (rel intensity) 505 (boron
cluster center, isotope pattern fits the calculated cluster for M, 100),
355 (10), 248 (50); IR (KBr) 3100 (CHAr), 3063 (BCH), 2611 (BH),
1599 (CdC), 1447, 1140, 1117, 1059, 1009, 893, 747, 731, 695, 617
cm-l. HRMS calcd 505.5790, found 505.5804. Anal. Calcd for
C12H36B30: C, 28.56; H, 7.19. Found: C, 28.77; H, 7.01.
(1,12-Dicarba-closo-dodecaboran-1-yl)benzene33 (3). To a solution
of 1,12-dicarba-closo-dodecaborane41 (2, 1.0 g, 6.9 mmol) in diethyl
ether (25 mL) was added n-BuLi (1.6 M in hexane, 4.3 mL, 6.9 mmol)
at 0 °C. After 1.5 h of stirring at rt, CuCl (0.69 g, 6.9 mmol) and THF
(20 mL) were added at -30 °C under nitrogen. The mixture was stirred
at room temperature for 1 h and refluxed for 0.5 h. After solvent was
removed under reduced pressure, N-methylpyrrolidinone (25 mL),
iodobenzene (1.59 g, 7.8 mmol), and Pd(PPh3)2Cl2 (276 mg, 0.39 mmol)
were added. The mixture was stirred at 100 °C for 18 h, poured into
water (30 mL), and extracted with diethyl ether (5 × 25 mL). The
combined organic phases were washed with water and dried over
MgSO4. After the solvent was removed, the product was purified by
thick-layer chromatography (silica, hexane) to give a white solid: 1.03
1
g (68%), mp 99.5-100.5 °C (lit.33 99-100 °C); H NMR (CDCl3) δ
1.20-3.40 (br m, 10 H, BH), 2.77 (s, 1 H, CH), 7.12-7.24 (m, 5 H,
aromatic); 13C{1H} NMR (CDCl3) δ 59.74 (CcarboraneH), 86.37 (Ccarbo
-
raneCar), 127.01 (Car), 128.05 (Car), 128.31 (Car), 136.78 (CarCcarborane);
11B NMR (CDCl3) δ -13.38 (d, J ) 167 Hz), -16.02 (d, J ) 168
Hz); MS m/z (rel intensity) 220 (boron cluster center, isotope pattern
fits the calculated cluster for M, 100), 191 (10), 139 (10), 108 (20); IR
(KBr) 3058 (BCH), 2604 (BH), 1583, 1476, 1211, 1147, 1144, 1023,
1007, 831, 583 cm-1; HRMS calcd 222.2183, found 222.2185.
1-Phenyl-12-(trimethylstannyl)-1,12-dicarba-closo-dodecabo-
rane (15). Compound 3 (100 mg, 0.454 mmol) was dissolved in THF
(20 mL) under Ar and cooled to -78 °C. LDA (0.33 mL, 1.5 M in
cyclohexane) was added dropwise, and the solution was allowed to
stir for 2 h at -78 °C. Solid Me3SnCl (120 mg, 0.601 mmol) was
added from a tip tube. The mixture was kept at -78 °C for 5 h and
allowed to warm slowly to room temperature. The reaction mixture
was poured into water (100 mL) and extracted with diethyl ether (3 ×
50 mL). After drying the solution over MgSO4 and removing the
solvent, the product was purified by column chromatography (silica,
hexanes) to yield 126 mg (72%) of a white solid (98% pure by NMR).
An analytical sample was produced by gradient sublimation: mp 88-
91 °C; 1H NMR (CDCl3) δ 7.17 (m, 5 H, aromatic), 1.0-3.5 (br m, 10
H, BH), 0.11 (s, JSnH ) 27 Hz, 9 H, SnCH3); 13C{1H} NMR (CDCl3)
δ -8.49 (CH3), 64.15 (CcarboraneSn), 89.15 (CcarboraneCar), 127.01 (Car),
127.94 (Car), 128.05 (Car), 137.21 (CarCcarborane); 11B NMR (CDCl3) δ
-11.34 (d, J ) 175 Hz), -13.89 (d, J ) 170 Hz); MS m/z (rel intensity)
383 (boron cluster center, isotope pattern fits the calculated cluster for
M, 5), 368 (cluster center, M - CH3, 100), 338 (cluster center, M -
2CH3, 20), 217 (10), 184 (10), 135 (10), 120 (10); IR (KBr) 2924,
2856, 2596, 1459, 1381, 1088, 1023, 777, 691, 539 cm-1. Anal. Calcd
for C11H24B10Sn: C, 34.48; H, 6.31. Found: C, 34.65; H, 6.40.
m-Bis(1,12-dicarba-closo-dodecaboran-1-yl)benzene (4). To a
solution of 1,12-dicarba-closo-dodecaborane41 (2, 935 mg, 6.49 mmol)
1,3,5-Tris[12-((3-(ethylthio)propyl)dimethylsilyl)-1,12-dicarba-
closo-dodecaboran-1-yl]benzene (7). A solution of 1,3,5-tris(1,12-

3916 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Scho¨berl et al.
dicarba-closo-dodecaboran-1-yl)benzene (1, 100 mg, 0.2 mmol) in ether
(40 mL) was cooled to -40 °C. tert-Butyllithium (1.7 M in pentanes,
0.2 mL) was added over 5 min, and the solution was stirred for 1.5 h
while the temperature rose to about -5 °C. It was cooled again to
-25 °C, and 5 (67 mg, 0.34 mmol) was added. The solution was stirred
at -25 °C for 15 min and then heated under reflux for 20 h. The
sequence of cooling, adding tert-butyllithium and 5, and refluxing was
repeated four times. The reaction mixture was then poured into sulfuric
acid (50 mL, 5 M). The organic layer was separated, and the acid
layer was extracted twice with ether (2 × 25 mL). The combined ether
fractions were washed with potassium carbonate solution (10%, 2 ×
50 mL) and dried over sodium sulfate. The solvent was removed,
giving a clear oil, which was chromatographed on silica gel (60-200
mesh, 30 × 1.2 cm) with benzene-hexane (20:80). The product 7
was separated from a siloxane impurity by preparative TLC. Methanol
removed the siloxane and left 7 at the start, and extraction with
dichloromethane gave 54 mg (28%) of a white crystalline solid of
approximately 98% purity. Analytically pure material was obtained
by column chromatography on silica gel (60-200 mesh, hexane-
dichloromethane 1:1): mp 92 °C; lH NMR (CDCl3) δ -0.03 (s, 18 H,
CH3), 0.56 (m, 6 H, SiCH2), 1.23 (t, J ) 7.3 Hz, 9 H, CH3), 1.46 (m,
6 H, CH2), 2.48 (m, 12 H, CH2SCH2), 1.20-3.20 (br m, 30 H, BH),
6.82 (s, 3 H, aromatic); 13C{1H} NMR (CDCl3) δ -3.00 (SiCH3), 14.58
(SiCH2), 14.79 (CH3), 23.89 (CH2), 25.87 (SCH2CH2), 35.01 (CH3CH2S),
69.36 (CcarboraneSi), 87.94 (CcarboraneCar), 125.62 (Car), 136.62 (CarCcarborane);
11B NMR (CDCl3) δ -12.3 (d, J ) 165 Hz, 15 B), -14.1 (d, J ) 165
Hz, 15 B); MS m/z (rel intensity) 986 (boron cluster center, isotope
pattern fits the calculated cluster for M, 5), 971 (cluster center, isotope
pattern fits the calculated cluster for M - CH3, 19), 883 (cluster center,
M - C5H11S, 27), 763 (cluster center, M - C9H22S2Si, 16), 722 (cluster
center, M - C12H26S2Si, 18), 161 (C7H17SSi, 100); IR (KBr) 3140
(CHAr), 2963, 2926 (CH), 2866, 2608 (BH), 1598 (CdC), 1448, 1432,
gel 60-200 mesh, 40 × 2.5 cm column) with benzene-hexane (1:4,
then 1:2, and finally 1:1). The desired product eluted together with a
siloxane impurity, from which it was separated by preparative TLC.
Methanol left 8 at the start and removed the siloxane. Subsequent
elution with dichloromethane gave 262 mg (25%) of a clear viscous
oil of about 98% purity. Analytically pure material was obtained by
column chromatography on silica gel (60-200 mesh) with hexane-
dichloromethane (1:1). For 8: 1H NMR (CDCl3) δ -0.01 (s, 3 H,
SiCH3), 0.59 (m, 4 H, SiCH2), 1.26 (t, J ) 7 Hz, 6H, CH3), 1.5-3.2
(br, 10H, BH), 1.49 (m 4H, CH2CH2CH2,), 2.50 (t, J ) 7 Hz, 4H,
SCH2CH2), 2.52 (q, J ) 8 Hz, 4H, CH3CH2S), 6.83 (s, 1H, aromatic);
13C{1H} NMR (CDCl3) δ -4.63 (SiCH3), 13.26 (SiCH2), 14.74 (CH3),
23.78 (CH2), 25.85 (SCH2CH2), 35.01 (CH3CH2S), 69.01 (CcarboraneSi),
88.24 (CcarboraneCar), 125.55 (Car), 136.55 (CarCcarborane); IR (KBr) 2962,
2925, 2869 (CH), 2607 (BH), 1598 (BH), 1448, 1256 (SiMe), 1115,
1081, 879, 790, 644 cm-1; MS m/z (rel intensity) 1250 (M+, <1%),
1147 (boron cluster center, isotope pattern fits the calculated cluster
for the ion [M - C5H11S]+, 100), 1086 (cluster center, [M - C7H16S2]+,
37), 1026 (cluster center, [M - C9H21S3]+, 20), 899 (cluster center,
62), 651 (cluster center, 21). Anal. Calcd for C45H108B30S6Si3: C,
43.23; H, 8.71. Found: C, 43.19; H, 8.68.
Desilylation of 1,3,5-Tris[12-((3-(ethylthio)propyl)dimethylsilyl)-
1,12-dicarba-closo-dodecaboran-1-yl]benzene (7) with Fluoride
Anion. A solution of 7 (1.8 mg, 0.0018 mmol) and tetra-n-butylam-
monium fluoride (21 mg, 0.065 mmol, 12 equiv) in THF (1 mL) was
stirred at room temperature for 62 h. THF was evaporated, the residue
was extracted with toluene (5 mL), the solvent was evaporated, and
the residue was dissolved in CDCl3. 1H NMR spectrum showed only
the signals of 1,3,5-tris(1,12-dicarba-closo-dodecaboran-1-yl)benzene
(1) and no signals of 7.
Desilylation of 1,3,5-Tris[12-(bis(3-(ethylthio)propyl)methylsilyl)-
1,12-dicarba-closo-dodecaboran-1-yl]benzene (8) with Fluoride
Anion. The above procedure was applied to 8 (2.1 mg, 0.0017 mmol),
using tetra-n-butylammonium fluoride (25 mg, 0.078 mmol, 8 equiv)
in THF (1 mL). At the end, the 1H NMR spectrum again showed only
the presence of 1 and no 8.
1410, 1254 (SiMe), 1117, 1083, 882, 852, 840, 808, 792, 646 cm-1
.
Anal. Calcd for C33H84B30S3Si3: C, 40.21; H, 8.59. Found: C, 40.06;
H, 8.67.
Bis(3-(ethylthio)propyl)methylsilyl Chloride (6). Mg turnings
(10.4 g, 0.433 mol) were placed in a three-neck 500 mL round-bottomed
flask fitted with a pressure equalizing dropping funnel, reflux condenser,
and nitrogen inlet. 3-(Ethylthio)propyl chloride (11, 41.5 g, 0.3 mol)
and THF (250 mL) were charged to the dropping funnel, and several
drops of the solution were added to the main flask. The reaction was
initiated with a few crystals of iodine and gentle heating. The chloride
solution was added slowly over 2 h resulting in a gray solution of the
Grignard reagent. Trichloromethylsilane (22.4 g, 0.15 mol) was then
added to the Grignard reagent, and the mixture was heated under reflux
for 16 h. Mg salts were filtered and washed with THF (3 × 100 mL).
The organic fractions were combined, and the solvent was removed
under reduced pressure to give a light-brown oil. The product was
fractionally distilled at reduced pressure (65 °C/0.1 Torr, 18.8 g, 44%)
to afford 6: 1H NMR (CDCl3) δ 0.39 (s, 3 H, SiCH3), 0.90-0.96 (m,
4 H, SiCH2), 1.25 (t, J ) 6 Hz, 6 H, CH3), 1.64-1.74 (m, 4 H, CH2),
2.49-2.58 (m, 8 H, CH2SCH2); 13C{1H} NMR (CDCl3) δ -0.29
(SiCH3), 14.63 (SiCH2), 16.70 (CH3), 22.97 (CH2), 25.53 (SCH2CH2),
34.41 (CH3CH2S); MS m/z (rel intensity) 284 (M, 2), 249 (M - Cl,
4), 181 (M - C5H11S, 100); IR (neat) 2926 (CH), 1418, 1255 (SiMe),
791, 477 cm-1. Anal. Calcd for C11H25ClS2Si: C, 46.36; H, 8.84.
Found: C, 46.37; H, 8.81.
Stability of m-Bis(12-(tert-butyldimethylsilyl)-1,12-dicarba-closo-
dodecaboran-1-yl)benzene (12) toward DMF and t-BuOK. Com-
pound 12 (5 mg, 0.0085 mmol) was dissolved in dry DMF and stirred
for 1 h at room temperature and then 1 h at 100 °C. No changes were
1
observed by H NMR. Then, t-BuOK (4 mg, 0.035 mmol, 4 equiv)
was added, and the mixture was stirred at room temperature for 1 h.
1H NMR showed complete desilylation of 12. The reaction mixture
was poured into water and extracted with diethyl ether. After the
1
solvent was removed under reduced pressure, the H NMR spectrum
showed only the signals of 4.
Stability of 1,3,5-Tris[12-((3-(ethylthio)propyl)dimethylsilyl)-1,12-
dicarba-closo-dodecaboran-1-yl]benzene (7) toward DMF and t-
BuOK. 7 (2.5 mg, 0.0026 mmol) was dissolved in DMF-d6 and heated
to 100 °C for 1 h. 1H NMR showed no signs of desilylation. t-BuOK
(2 mg, 0.018 mmol, 6 equiv) was added, and the NMR tube was shaken
vigorously. An 1H NMR spectrum taken immediately thereafter showed
no signals of the starting material. The mixture was poured into water
and extracted with diethyl ether. After the solvent was removed under
1
reduced pressure, the H NMR spectrum in CDCl3 was identical with
the spectrum for 1.
Bis(12-phenyl-1,12-dicarba-closo-dodecaboran-1-yl)mercury (13).
Two-Step Procedure. To a solution of p-carboranylbenzene (3) (120
mg, 0.54 mmol) in THF (15 mL) was added lithium diisopropylamide
(2 M, 0.4 mL, 0.8 mmol) at -78 °C. After 1 h of stirring, HgCl2 (70
mg, 0.26 mmol) was added and the reaction mixture was slowly warmed
to room temperature. After 4 h of stirring, the yellow solution was
poured into aqueous NH4Cl and extracted with Et2O (3 × 10 mL).
The combined organic phases were washed with H2O (10 mL) and
dried with MgSO4. After the solvent was removed under reduced
pressure, the beige residue (160 mg) was dissolved in CH2Cl2 and
purified by chromatography (silica, CHCl3) to give a white solid (120
mg, 72%): mp 239-240 °C; lH NMR (CDCl3) δ 1.20-3.40 (br m, 20
H, BH), 7.14-7.17 (m, 10 H, phenyl); 13C{1H} NMR (CDCl3) δ 89.1
(CcarboraneCar), 90.5 (CcarboraneHg), 126.9 (Car), 128.0 (Car), 128.3 (Car),
1,3,5-Tris[12-(bis(3-(ethylthio)propyl)methylsilyl)-1,12-dicarba-
closo-dodecaboran-1-yl]benzene (8). A solution of 1,3,5-tris(1,12-
dicarba-closo-dodecaboran-1-yl)benzene (1, 425 mg, 0.85 mmol) in
ether (100 mL) was cooled to -40 °C. tert-Butyllithium (1.7 M in
pentanes, 0.7 mL) was added over 5 min, and the solution was stirred
for 1.5 h, while it warmed to about -5 °C. It was cooled again to
-25 °C, 6 (340 mg, 1.2 mmol) was added, the stirring was continued
at -25 °C for 15 min, and the solution was then heated under reflux
for 20 h. The sequence of cooling, adding tert-butyllithium and 6,
and heating under reflux was repeated six times. The reaction mixture
was then poured into 5 M sulfuric acid (70 mL). The acidic layer was
extracted twice with ether (2 × 50 mL) and added to the organic layer,
and the combined ether fractions were washed with potassium carbonate
solution (10%, 2 × 50 mL) and dried over sodium sulfate. The solvent
was removed to give a clear oil, which was chromatographed (silica
l
136.3 (CarCcarborane); lB NMR (CDCl3) δ -11.80 (d, J ) 180 Hz, 10
B), -13.98 (d, J ) 175 Hz, 10 B); 199Hg NMR (acetone-d6, against

Toward a Hexagonal Grid Polymer
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3917
Me2Hg; internal standard, PhHgCl in DMSO-d6 δ -1187.00) δ -720.4;
MS m/z (rel intensity) 639 (boron cluster center, isotope pattern fits
the calculated cluster for M, 100), 439 (10), 296 (50), 218 (80); IR
(KBr) 3063 (BCH), 2605 (BH), 1598 (CdC), 1499, 1450, 1400, 1090,
1027, 1006, 915, 844, 780, 738, 690, 625 cm-l; HRMS calcd (rel
intensity) 639.4001 (34.8), 639.4057 (33.1), 639.4097 (32.1), found
639.4055 (unresolved). Anal. Calcd for C16H30B20Hg: C, 30.06; H,
4.73. Found: C, 29.64; H, 4.65.
One-Step Procedure. To a solution of HgBr2 (8.2 mg, 0.023 mmol),
NaBr (4.3 mg, 0.042 mmol), and p-carboranylbenzene (3, 5.0 mg, 0.023
mmol) in DMF (2.5 mL, freshly distilled) was added t-BuOK (10.0
mg, 0.089 mmol) at -10 °C under N2. The reaction mixture was stirred
at rt for 3 h. The mixture was poured into water and extracted with
diethyl ether (3 × 10 mL). The combined organic phases were washed
with brine and dried over MgSO4. The yield was 97% on the basis of
GC. After the solvent was removed, the product was purified by thick-
layer chromatography (silica, CHCl3) and subsequent sublimation (200
°C/10-4 Torr) and isolated in 79% yield. The reaction was performed
in a similar fashion in TMU, DMPU, propylene carbonate, and tert-
butyl alcohol, and followed by NMR. In TMU and DMPU, it
proceeded similarly as in DMF.
mmol) were dissolved in freshly distilled DMF (40 mL) and cooled to
0 °C. Potassium tert-butoxide (35 mg, 0.31 mmol) was then added
from a tip tube, and the mixture was stirred for 2.5 h at 0 °C. The
mixture was poured in water (50 mL) and extracted with ether (3 ×
30 mL). After the solution was dried over Na2SO4 the solvent was
removed under reduced pressure, column chromatography (silica,
hexanes) yielded 11 mg of the starting material and 44 mg (60%, after
correction for recovered 4, 74%) of 14 as a white solid: mp 354 °C;
1H NMR (CDCl3) δ 1.20-3.40 (br m, 40 H, BH), 2.78 (s, 2 H, BCH),
6.88-7.05 (m, 8 H, aromatic); 13C{1H} NMR (CDCl3) δ 59.9
(CcarboraneH), 85.6 (CcarboraneHg), 89.3 (CcarboraneCar), 89.7 (CcarboraneCar),
126.1 (Car), 126.7 (Car), 126.8 (Car), 127.7 (Car), 136.1 (CarCcarborane),
136.6 (CarCcarborane); 11B NMR (CDCl3) δ -11.85 (d, J ) 151 Hz, 10
B), -13.57 (br d, J ) 154 Hz, 20 B), -15.96 (d, J ) 166 Hz, 10 B);
MS m/z (rel intensity) 925 (boron cluster center, isotope pattern fits
the calculated cluster for M, 50), 782 (cluster center, M - C2B10H11,
40), 706 (30), 365 (100); IR (KBr) 3063 (BCH), 3056 (CHAr), 2605
(BH), 1604 (aromatic), 1488, 1097, 1089, 793, 734, 687 cm-1; HRMS
calcd 924.7632, found 924.7623. Anal. Calcd for C20H50B40Hg: C,
26.01; H, 5.46. Found: C, 25.93; H, 5.66.
Acknowledgment. This research was supported by the
National Science Foundation (CHE-9213399 and CHE-9505926)
and the Department of Energy (FG03-94ER12141). U.S. is
grateful to the Alexander von Humboldt Foundation for a Feodor
Lynen Fellowship.
Complex of 13 with 2,2′-Bipyridyl (1:1). 2,2′-Bipyridyl (2.7 mg,
0.017 mmol) and 13 (4.4 mg, 0.007 mmol) were dissolved in chloroform
(0.5 mL). Slow room temperature evaporation of the solvent yielded
small colorless crystals.
Complex of 13 with 2,2′-Bipyrimidyl (2:1). 2,2′-Bipyrimidyl (5.0
mg, 0.032 mmol) and 13 (3.5 mg, 0.0055 mmol) were dissolved in
toluene (1.0 mL). Slow room temperature evaporation of the solvent
yielded small colorless crystals.
Bis{12′-[m-(1′,12′-dicarba-closo-dodecaboran-1′-yl)phenyl]-1,12-
dicarba-closo-dodecaboran-1-yl}mercury (14). Under argon atmo-
sphere, m-bis(1,12-dicarba-closo-dodecaboran-1-yl)benzene (4, 58 mg,
0.16 mmol), NaBr (24 mg, 0.23 mmol), and HgBr2 (28 mg, 0.077
Supporting Information Available: Figures 2, 3, and 9,
discussion of X-ray diffraction, and crystallographic data (81
pages). See any current masthead page for ordering and Internet
access instructions.
JA963331D