Synthesis and crystal structure of 9,12-bis-(4-acetylphenyl)-1,2- dicarbadodecaborane(12): Self-assembly involving intermolecular carboranyl C- H hydrogen bonding [3]

Full text of DOI:10.1021/ja9803411

J. Am. Chem. Soc. 1998, 120, 6405-6406
6405
Synthesis and Crystal Structure of
9,12-Bis-(4-acetylphenyl)-1,2-dicarbadodecaborane(12):
Self-Assembly Involving Intermolecular Carboranyl
C-H Hydrogen Bonding
George Harakas, Tuan Vu, Carolyn B. Knobler, and
M. F. Hawthorne*
Department of Chemistry and Biochemistry
UniVersity of California, Los Angeles
Los Angeles, California 90095
ReceiVed January 30, 1998
The rigid three-dimensional nature of the isomeric icosahedral
carborane (C2B10H12) cages, 1,2 (ortho), 1,7 (meta), and 1,12
(para), accompanied by the versatile chemistry observed at both
the carborane C-H and B-H vertices1-3 makes their derivatives
attractive candidates for crystal engineering.4 The syntheses of
molecules containing modular carborane subunits, which may
prove useful in this quest, have been reported by this laboratory
as well as others.5-8 It has been demonstrated that ortho-
carborane forms host-guest complexes with cyclodextrins9 and
cyclotriveratrylene.10 Furthermore, Wade has recently demon-
strated that ortho-carborane forms a well-ordered 1:1 adduct with
hexamethylphosphoramide (HMPA).11 Similarly, the deca-B-
chloro-ortho-carborane dimethyl sulfoxide (DMSO) adduct has
been shown to exhibit strong hydrogen bond interactions in the
solid state.12 The characteristic common to these host-guest
complexes and solvent adducts is the pivotal role of hydrogen
bonding provided via the carborane’s C-H vertices, which
defines the organization of the complex in the solid state. We
now report the synthesis and solid-state structure of a novel ortho-
carborane derivative, 9,12-bis-(4-acetylphenyl)-1,2-carborane) (1,
see Figure 1)13 which provides the first example of a carborane
system involving intermolecular hydrogen bonding in which the
functional group interacting with the carborane C-H is connected
to the carborane cage.
Functionalization of ortho-carborane at the 9- and 12-boron
can be readily achieved by iodination at the 9,12-vertices followed
by reaction with the appropriate Grignard reagent,14,15 in the
present instance the Grignard derived from 4-bromoacetophenone
ethylene ketal. Colorless crystals of 1 were grown from acetone
solution by slow evaporation of the solvent. The structure of 1
was confirmed by an X-ray crystal analysis, which also revealed
an interesting intermolecular phenomenon.16 Each carboranyl
C-H is within close proximity of a carbonyl oxygen atom
extended from another molecule. However, it is apparent from
the differing C-H-O bond distances C(1)‚‚‚O(11) 3.015(7) Å
Figure 1. Crystal packing diagram of 1. Selected distances (Å) and angles
(°): C(1)‚‚‚H(1) ) 0.98(4), H(1)‚‚‚(O11) ) 2.17(4), C(2)‚‚‚H(2) )
1.02(4), H(2)‚‚‚O(5) ) 2.36(4); C(1)-H(1)‚‚‚O(11) ) 146(3), C(2)-
H(2)‚‚‚O(5) ) 160(3). The remaining phenyl and carborane hydrogen
atoms are not shown for clarity.
and C(2)‚‚‚O(5) 3.335(8) Å that only the hydrogen at C(1) is
significantly interacting with a carbonyl oxygen attached to
another molecule. Atom O(5) is the carbonyl oxygen of a
molecule related by a center of symmetry at x ) 1/2, y ) 0, z )
1/2, and O(11) is the carbonyl oxygen of a molecule related by
a translation along the a axis (see Figure 1). This distance of
3.015(7) for C(1)‚‚‚O(11) is significantly shorter than the corre-
sponding values of 3.130(5) and 3.179(6) in the HMPA-ortho-
carborane dimer reported by Wade.11 The solid-state infrared
spectrum of 1 exhibits two stretching frequencies for carborane
C-H (3070 and 3044 cm-1; 1,2 carborane 3071 cm-1). This
observation of two stretching modes and the shift to lower
(13) All manipulations were carried out under anaerobic and anhydrous
conditions unless otherwise stated. The 4-bromoacetophenone was purchased
from the Aldrich Chemical Co. and converted to the ethylene ketal using
azeotropic distillation with ethylene glycol/benzene in a Dean-Stark apparatus.
A solution of the Grignard was prepared by adding the bromoketal (15.7 g,
64.6 mmol) to Mg (2.20 g, 90.5 mmol) in THF (300 mL) over the course of
2 h. The solution was then stirred overnight at 25 °C. The acidic carborane
CH vertexes react with Grignard reagents. To prevent the unnecessary loss
of the Grignard reagent derived from the 4-bromoacetophenone ketal, they
were removed prior to the coupling reaction with CH3MgBr. To a THF (200
mL) solution of 9,12-I2-1,2-C2B10H10 (8.50, 21.5 mmol) was added 13.5 mL
of CH3MgBr (3.0 M, in diethyl ether). The evolution of methane ceased after
∼15 min, and the solution was stirred overnight at 25 °C. The bromoketal-
derived Grignard solution and trans-PdCl2(PPh3)2 (50 mg, 0.071 mmol) were
added to the carborane solution via cannula. The resulting reaction mixture
was refluxed under nitrogen for 3 days. The reaction mixture was quenched
with HCl(aq) 10% (100 mL), the organic phase was separated, and the aqueous
layer was extracted with diethyl ether (2 × 100 mL). The organic phases
were combined and dried over anhydrous MgSO4. The MgSO4 was separated,
and the solvent was removed under reduced pressure to yield 1 as a red solid.
The crude product was recrystallized from acetone to yield a white solid (4.43
g, 54%) mp 252 °C (sealed capillary). 1H NMR (400 MHz, CDCl3): δ )
7.87 and 7.29 (d 4H, C6H4), δ ) 3.50 (br s, 2 CH carborane), δ ) 2.58 (s
3H, CH3); 13C{1H} NMR (100 MHz, CDCl3): δ ) 190.5 (C6H4COCH3), δ
) 135.9, 133.0 and 127.0 (C6H4COCH3), δ ) 50.1 (CHcarborane), δ ) 26.6
(C6H4COCH3); 11B{1H} NMR (160 MHz, (CH3)2CO): δ ) 8.24 (s, 2B,
BC6H4COCH3), δ ) -8.83 (d, 2B, BH), δ ) -13.58 (d, 4B, BH), δ ) -15.86
(d, 2B, BH); MS (EI): For C18B10H24O2 calcd 380.2779, found 380.2781; IR
(KBr pellet, ν cm-1): νCH(carborane) 3070, 3044; νBH 2601, 2592, 2560, νCdO
1660.
(1) Grimes, R. N. Carboranes; Academic Press: New York, 1970.
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(16) Crystal data for 1 at 25 °C: C18B10H24O2, colorless crystal, monoclinic,
P21/c, a ) 11.749(10) Å, b ) 13.204(12) Å, c ) 13.815(11) Å, b ) 101.71-
(3)°, V ) 2098 Å3, Z ) 4, R1 ) 8.1, Rw ) 10.1, GOF ) 2.88 for 1792
reflections (I > 3 σ (I)).
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S0002-7863(98)00341-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/12/1998

6406 J. Am. Chem. Soc., Vol. 120, No. 25, 1998
Communications to the Editor
energy17 is consistent with the X-ray structure and the conclusion
that only the one C-H of C(1) is significantly involved in
hydrogen bonding.
and carboracycles24 with novel solution and solid-state properties.
Acknowledgment. We are grateful to the National Science Foundation
(Grant No. CHE-93-14037) for their support of the research. G.H.
acknowledges the National Institutes of Health (Grant No. T32-NS-07356)
for their support.
In the present example of a carborane species involved in
intermolecular hydrogen bonding via the carborane C-H, the use
of a chelating ligand or a donor solvent molecule to orient the
solid-state structure was not required. The highly ordered
structure of 1 strongly suggests the participation of the isomeric
carborane moieties in self-assembly processes involving more
complex molecules which result in applications to catalysis and
biological systems.18 We are currently continuing our investiga-
tion of boron-substituted carborane derivatives using an array of
other functional groups which will provide a route to highly
functionalized carboranes,19 mercuracarborands,20-22 carborods,23
Supporting Information Available: Tables of position and thermal
parameters, bond lengths, and crystallographic data and an ORTEP view
of (1) (8 pages, print/PDF). See any current masthead page for ordering
and Web access instructions.
JA9803411
(21) Zheng, Z.; Knobler, C. B.; Mortimer, M. D.; Kong, G.; Hawthorne,
M. F. Inorg. Chem. 1996, 35, 1235-1243.
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Chem. Soc. 1996, 118, 70-74.
(23) Jiang, W.; Harwell, D. E.; Mortimer, M. D.; Knobler, C. B.;
Hawthorne, M. F. Inorg. Chem. 1996, 35, 4355-4359.
(24) Jiang, W.; Chizhevsky, I. T.; Mortimer, M. D.; Chen W. L.; Knobler,
C. B.; Johnson, S. E.; Gomez, F. A.; Hawthorne, M. F. Inorg. Chem. 1996,
35, 5417-5426.
(17) Leites, L. A. Chem. ReV. 1992, 92, 279-323.
(18) Conn, M. M.; Rebek, J. J. Chem. ReV. 1997, 97, 1647-1668.
(19) Jiang, W.; Knobler, C. B.; Hawthorne, M. F. Angew. Chem., Int. Ed.
Engl. 1996, 35, 2536-2537.
(20) Zheng, Z.; Yang, X.; Knobler, C. B.; Hawthorne, M. F. J. Am. Chem.
Soc. 1993, 115, 5320-5321.