1-Phenyl-1,2-dicarba-closo-dodecaborane, 1-Ph-1,2-closo-C2B10H11. Synthesis, Characterization, and Structure As Determined in the Gas Phase by Electron Diffraction, in the Crystalline Phase at 199 K by X-ray Diffraction, and by ab Initio Computations

Article abstract of DOI:10.1021/ic9511128

The compound 1-phenyl-1,2-dicarba-closo-dodecaborane(12), 1-C₆H₅-1,2-closo-C₂B₁₀H₁₁ (1), has been synthesized and characterized by a complete assignment of its ¹¹B NMR spectrum via ¹¹B{¹H}/¹¹B{¹H} (COSY), ¹H{¹¹B_selective} and ¹H{¹¹B}/¹H{¹¹B} (COSY) spectroscopy. An electron- and X-ray diffraction investigation of 1, complemented by ab initio calculations, has been undertaken. The gas-phase electron-diffraction (GED) data can be fitted by several models describing conformations which differ in the position of the phenyl ring with respect to the carborane cage. Local symmetries of C_2v and D_6h for the 1,2-C₂B₁₀ and C₆ moieties, respectively, were adopted in the GED model in order to simplify the problem. In addition, constraints among the close-lying C-C and B-B bonds were employed. However, even though such simplifications led to satisfactory refinements (R_G = 0.069- 0.071), a unique, definitive solution could not be gained. The (C-C)_mean, (C-B)_mean and (B-B)_mean bond lengths, r_a, are ca. 1.44, 1.72, and 1.78 ?, respectively. The C₆ hexagon, with r_a(C-C) = ca. 1.394 ?, either eclipses the C(1)-C(2) vector (overall C_s symmetry) or more or less eclipses the C(1)-B(4) cluster bond (overall C₁ symmetry). In contrast, in the solid at 199 K, the ring lies at a position intermediate between the two GED positions, as determined by X-ray crystallography [C₈H₁₆B₁₀, monoclinic P2₁/a: a = 12.047(3) ?, b = 18.627(4) ?, c = 12.332(5) ?, β = 110.09(4)°, Z = 8]. The C-B distances span the range 1.681(6)-1.743(5) ?, and B-B lengths lie between 1.756(6) and 1.795(6) ?. A similar conformation was found for the theoretical (RHF/6-31G* level) structure which was fully optimized in C₁ symmetry. The r_e distances are consistent with the dimensions derived in the experimental studies. IGLO calculations of the ¹¹B chemical shifts, in addition to SCF single-point energies of the GED structures, further support these observations.

Full text of DOI:10.1021/ic9511128

Inorg. Chem. 1996, 35, 1701-1708
1701
1
-Phenyl-1,2-dicarba-closo-dodecaborane, 1-Ph-1,2-closo-C2B10H11. Synthesis,
Characterization, and Structure As Determined in the Gas Phase by Electron Diffraction,
in the Crystalline Phase at 199 K by X-ray Diffraction, and by ab Initio Computations
†
Paul T. Brain, Jill Cowie, David J. Donohoe, Drahom ´ı r Hnyk, David W. H. Rankin,
David Reed, Bruce D. Reid, Heather E. Robertson, and Alan J. Welch*
Department of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, U.K.
Matthias Hofmann and Paul von Ragu e´ Schleyer
Computer-Chemie-Centrum des Instituts f u¨ r Organische Chemie, Universit a¨ t Erlangen-N u¨ rnberg,
N a¨ gelbachstrasse 25, D-91052 Erlangen, Germany
X
ReceiVed August 24, 1995
The compound 1-phenyl-1,2-dicarba-closo-dodecaborane(12), 1-C6H5-1,2-closo-C2B10H11 (1), has been synthesized
1
1
11
1
11
1
1
11
and characterized by a complete assignment of its B NMR spectrum Via B{ H}/ B{ H} (COSY), H{ Bselective}
1
11
1
11
and H{ B}/ H{ B} (COSY) spectroscopy. An electron- and X-ray diffraction investigation of 1, complemented
by ab initio calculations, has been undertaken. The gas-phase electron-diffraction (GED) data can be fitted by
several models describing conformations which differ in the position of the phenyl ring with respect to the carborane
cage. Local symmetries of C2V and D6h for the 1,2-C2B10 and C6 moieties, respectively, were adopted in the
GED model in order to simplify the problem. In addition, constraints among the close-lying C-C and B-B
bonds were employed. However, even though such simplifications led to satisfactory refinements (RG ) 0.069-
0
.071), a unique, definitive solution could not be gained. The (C-C)mean, (C-B)mean and (B-B)mean bond lengths,
ra, are ca. 1.44, 1.72, and 1.78 Å, respectively. The C6 hexagon, with ra(C-C) ) ca. 1.394 Å, either eclipses the
C(1)-C(2) vector (overall Cs symmetry) or more or less eclipses the C(1)-B(4) cluster bond (overall C1 symmetry).
In contrast, in the solid at 199 K, the ring lies at a position intermediate between the two GED positions, as
determined by X-ray crystallography [C8H16B10, monoclinic P21/a: a ) 12.047(3) Å, b ) 18.627(4) Å, c )
1
2.332(5) Å, â ) 110.09(4)°, Z ) 8]. The C-B distances span the range 1.681(6)-1.743(5) Å, and B-B lengths
lie between 1.756(6) and 1.795(6) Å. A similar conformation was found for the theoretical (RHF/6-31G* level)
structure which was fully optimized in C1 symmetry. The re distances are consistent with the dimensions derived
11
in the experimental studies. IGLO calculations of the B chemical shifts, in addition to SCF single-point energies
of the GED structures, further support these observations.
-
Introduction
-Ph-1,2-closo-C2B10H11 (henceforth referred to as monophen-
C2B9H10]2 which can function as an η-ligand to a variety of
5
metal-based fragments.
In considering the structural chemistry of monophenylcar-
borane and its various derivatives, one important feature is the
orientation of the phenyl ring relative to the C(1)-C(2) vector.
This is described in terms of the angle θ′, where θ′ ) 90° -
C(2)-C(1)-C(11)-C(16)], such that (a) when θ′ ) 90°, C(2)
lies in the plane of the phenyl ring (Figure 1a), and (b) when θ′
1
ylcarborane, 1) was one of the first carbon-substituted analogues
1
of 1,2-closo-C2B10H12 to be reported, more than 30 years ago.
Surprisingly, however, even though it can be regarded as the
fusion of two fragments (phenyl and closo-carborane) each of
which has an extensive chemistry, relatively little work on it or
its derivatives has since been published. There are a few reports
of derivatives of 1-Ph-2-X-1,2-closo-C2B10H10, where X is an
organic group, an inorganic group,3 or a transition metal
[
(
3) (a) Zakharkin, L. I.; Podvistotskaya, L. S. IzV. Akad. Nauk SSSR, Ser.
Khim. 1965, 8, 1464. (b) Zakharkin, L. I.; Bregadze, V. I.; Okhlobytsin,
O. Yu. J. Organomet. Chem. 1965, 4, 211. (c) McGrath, T. D.; Welch,
A. J. Acta Crystallogr. 1995, C51, 649. (d) McGrath, T. D.; Welch,
A. J. Acta Crystallogr. 1995, C51, 651. (e) McGrath, T. D.; Welch,
A. J. Acta Crystallogr. 1995, C51, 654.
2
4
fragment; also, monophenylcarborane is readily deboronated
[losing B(3) or B(6)] to afford the anion [7-Ph-7,8-nido-
(
4) (a) Garrett, P. M.; Hawthorne, M. F.; Owen, D. A.; Smart, J. C. J.
Am. Chem. Soc. 1971, 93, 1362. (b) Bresadola, S.; Frigo, A.; Longato,
B.; Rigatti, G. Inorg. Chem. 1973, 12, 2788. (c) Reid, B. D.; Welch,
A. J. J. Organomet. Chem. 1992, 438, 371.
*
Author to whom correspondence should be addressed.
On leave from the Institute of Inorganic Chemistry of the Academy of
†
Sciences of the Czech Republic, 250 68 Rˇ e zˇ near Prague, Czech Republic.
X
Abstract published in AdVance ACS Abstracts, February 15, 1996.
(5) (a) Doi, J. A.; Mizusawa, E. A.; Knobler, C. B.; Hawthorne, M. F.
Inorg. Chem. 1984, 23, 1482. (b) Knobler, C. B.; Marder, T. B.;
Mizusawa, E. A.; Teller, R. G.; Long, J. A.; Behnken, P. E.;
Hawthorne, M. F. J. Am. Chem. Soc. 1984, 106, 2990. (c) Lewis, Z.
G.; Reed, D.; Welch, A. J. J. Chem. Soc., Dalton Trans. 1992, 731.
(d) Lewis, Z. G.; Welch, A. J. J. Organomet. Chem. 1992, 438, 353.
(e) Baghurst, D. R.; Copley, R. C. B.; Fleischer, H.; Mingos, D. M.
P.; Kyd, G. O.; Yellowlees, L. J.; Welch, A. J.; Spalding, T. R.;
O’Connell, D. J. Organomet. Chem. 1993, C14, 447. (f) Cowie, J.;
Reid, B. D.; Watmough, J. M. S.; Welch, A. J. J. Organomet. Chem.
1994, 481, 283. (g) Kyd, G. O.; Yellowlees, L. J.; Welch, A. J. J.
Chem. Soc., Dalton Trans. 1994, 3129.
(
1) Heying, T. L.; Ager, J. W.; Clark, S. L.; Mangold, D. J.; Goldstein,
H. L.; Hillman, M.; Polak, R. J.; Szymanski, J. W. Inorg. Chem. 1963,
2, 1089.
(
2) (a) Lewis, Z. G.; Welch, A. J. Acta Crystallogr. 1993, C49, 705. (b)
Murphy, D. M.; Mingos, D. M. P.; Forward, J. M. J. Mater. Chem.
1993, 3, 67. (c) Murphy, D. M.; Mingos, D. M. P.; Haggitt, J. L.;
Powell, H. R.; Westcott, S. A.; Marder, T. B.; Taylor, N. J.; Kanis,
D. R. J. Mater. Chem. 1993, 3, 139. (d) Clegg, W.; Coult, R.; Fox,
M. A.; Gill, W. R.; MacBride, J. A. H.; Wade, K. Polyhedron 1993,
1
2, 2711. (e) McGrath, T. D.; Welch, A. J. Acta Cryst. 1995, C51,
646.
0
020-1669/96/1335-1701$12.00/0 © 1996 American Chemical Society

1
702 Inorganic Chemistry, Vol. 35, No. 6, 1996
Brain et al.
Table 1. Nozzle-to-Plate Distances, Weighting Functions,
Correlation Parameters, Scale Factors, and Electron Wavelengths
Used in the Electron-Diffraction Study of 1
weighting
functions/nm
Nozzle-
to-plate
electron
wavelength /
pm
-
1
b
corrln
scale
dist/mm ∆s smin sw
1
sw
2
s
max param factor, ka
2
58.7
2
4
30 50 140 164 0.489 0.655(8)
92 112 232 272 0.131 0.538(11)
5.701
5.698
9
3.8
a
Figures in parentheses are the estimated standard deviations.
b
Determined by reference to the scattering pattern of benzene vapor.
1
1
1
11
1
results of an B{ H}/ B{ H} (TOCSY; total correlation
spectroscopy) experiment on 1-Ph-1,2-closo-C2B10H11 reported
recently.
Figure 1. (a) When θ′ ) 90°, C(2) lies in the plane of the phenyl
ring. (b) When θ′ ) 0°, the ring is twisted about C(1)-C(11) such
that C(2) lies in a plane perpendicular to it.
1
1
Experimental Section
)
0°, the ring is twisted about C(1)-C(11) such that C(2) lies
6
in a plane perpendicular to it (Figure 1b).
2 10
General Procedures. The synthesis of 1-Ph-1,2-closo-C B H11 was
Recently, extended H u¨ ckel molecular orbital (EHMO) cal-
culations on an idealized model of monophenylcarborane have
been reported.2 These suggested that the conformation with
θ′ ) 90° occurred at the minimum on the potential energy
surface, ca. 22 kJ mol lower in energy than the conformation
with θ′ ) 0°. Interestingly, these calculations further suggested
that both the C(1)-C(2) and C(1)-C(11) interactions should
be strongest at θ′ ) 90°, with, moreover, C(1)-C(2) stronger
in this conformation (and weaker at θ′ ) 0°) than in the parent
compound C2B10H12. However, as far as we are aware, the
optimum conformation of monophenylcarborane, and the strength
of preference for that conformation, have been explored neither
experimentally nor by ab initio MO calculations.
performed using standard Schlenk techniques with subsequent manipu-
lation in the open atmosphere. Benzene, chloroform and pentane were
dried over sodium wire prior to use. Acetonitrile, N,N-dimethylaniline,
(a)
and CDCl
3
were predried over 4 Å molecular sieves. B10H14 (Callery)
-
1
was recrystallized from Et O before use. PhCCH (Aldrich) was used
2
as supplied. The IR spectrum was recorded from a CHCl
3
solution on
cells. NMR
spectra ( H at 600 MHz, B at 192.5 MHz) were recorded from CDCl
solutions at 291 K on a Varian VXR600S spectrometer. Chemical shifts
a Perkin-Elmer 598 spectrophotometer using matched CaF
2
1
11
3
1
11
are referenced to external SiMe
4
( H) or BF
3
2
‚OEt ( B) with positive
11
1
11
1
12
shifts to high frequency. Techniques for recording B{ H}/ B{ H}
1
11
1
11
13
and H{ B}/ H{ B} spectra have been reported previously.
Improved Synthesis of 1-Ph-1,2-closo-C 14 (3.91 g,
32.1 mmol), PhCCH (3.47 g, 34.0 mmol), and MeCN (2.78 g, 67.8
mmol) were stirred for 1 h at room temperature in 45 mL of C , and
2
10
B H11. B10H
The molecular structures of other large heteroboranes, e.g.
6 6
H
7,8
the reaction mixture heated subsequently to reflux for 72 h. After
cooling, volatiles were removed in Vacuo, leaving a yellow oil. The
product was extracted into n-pentane (5 × 20 mL) and filtered, and
the pentane was removed in Vacuo to afford the crude product as a
1
,7-Cl2-1,7-closo-C2B10H10 and 1,2-closo-C2B8H10, have been
determined recently in the gas-phase. In these studies, electron-
diffraction data and ab initio geometry optimizations (MP2/6-
1
1
3
1G* level) have been combined with B IGLO (individual
white, waxy solid. Crystallization from MeOH/H
temperature produced 3.65 g (52% yield) of colorless needles of 1-Ph-
,2-closo-C 11 which were analytically pure. Using N,N-dimethyl-
aniline instead of MeCN afforded yields at least as high (60-65%).
2
O (1:6) at room
9
gauge for localized orbitals) chemical-shift calculations in the
so-called ab initio/IGLO/NMR/GED approach.10 In such stud-
ies, constraints derived from geometries optimized ab initio are
used in the GED refinements for parameters describing the boron
cage. Such parameters, defining small differences in interatomic
B-B and B-C distances, generally cannot be refined due to the
effects of correlation between parameters.
1
2 10
B H
1
11
H{ B} NMR: δ 7.58-7.33 (5H, m, C H ), 3.97 (1H, s, CcageH), 2.62
6
5
(2H, s, BH), 2.53 (2H, s, BH), 2.46 (1H, s, BH), 2.35 (3H [2 + 1
coincidence], s, BH), 2.30 ppm (2H, s, BH). 11B{ H} NMR: δ -1.19
1
(
-
C
1B, s), -3.49 (1B, s), -8.06 (2B, s), -9.88 (2B, s), -10.32 (2B, s),
-
1
11.85 ppm (2B, s). IR: 2595 cm (broad, νB-H). Anal. Calcd for
10: C, 43.6; H, 7.32. Found: C, 43.6; H, 7.44.
Electron Diffraction. Electron-scattering intensities were recorded
In this paper, we report the results of studies of the molecular
structure and the conformation of monophenylcarborane in both
the gas phase (by electron diffraction) and the solid phase (by
X-ray crystallography). In addition, the results of a theoretical
study of the structure by ab initio and 11B IGLO NMR
calculations are presented. Finally, we report the experimental
8
H
16
B
on Kodak electron image plates using the Edinburgh gas-diffraction
14
apparatus operating at ca. 44.5 kV (electron wavelength ca. 5.7 pm).
9
Nozzle-to-plate distances for the stainless steel inlet nozzle employed
-1
were ca. 94 and 259 mm, yielding data in the s range 30-272 nm
.
1
1
B NMR spectrum of monophenylcarborane and its complete
The sample and nozzle were held at ca. 468 and 488 K respectively
during the exposures.
11
1
11
1
1
11
assignment Via B{ H}/ B{ H} (COSY), H{ Bselective} and
1
11
1
11
H{ B}/ H{ B} (COSY) spectroscopy. These complement
The scattering patterns of benzene were also recorded for the purpose
of calibration; these were analyzed in exactly the same way as those
of the carborane so as to minimize systematic errors in the wavelengths
and camera distances. Nozzle-to-plate distances, weighting functions
used to set up the off-diagonal weight matrix, correlation parameters,
final scale factors, and electron wavelengths for the measurements are
collected together in Table 1.
(
6) This is slightly different from the definition θ ) the modulus of the
average Ccage-Ccage-Cring-Cring used previously. See: Cowie, J.; Reid,
B. D.; Watmough, J. M. S.; Welch, A. J. J. Organomet. Chem. 1994,
4
81, 283.
(
7) Hnyk, D.; Brain, P. T.; Robertson, H. E.; Rankin, D. W. H.; Hofmann,
M.; Schleyer, P.v.R.; B u¨ hl, M. J. Chem. Soc., Dalton Trans. 1994,
2
885.
(
8) Hnyk, D.; Rankin D. W. H.; Robertson, H. E.; Hofmann, M.; Schleyer,
P.v.R.; B u¨ hl, M. Inorg. Chem. 1994, 33, 4781.
9) (a) Kutzelnigg, W. Isr. J. Chem. 1980, 19, 193. (b) Schindler, M.;
Kutzelnigg, W. J. Chem. Phys. 1982, 76, 1919. (c) Kutzelnigg, W.;
Schindler, M.; Fleischer, U. NMR, Basic Principles and Progress;
Springer Verlag: Berlin, New York, 1990; Vol. 23, p 165. (d) Meier,
U.; van W u¨ llen Ch.; Schindler, M. J. Comput. Chem. 1992, 13, 551.
(11) Donohoe, D. J.; Reed, D.; Welch, A. J. Polyhedron 1995, 14, 961.
(12) (a) Venable, T. L.; Hutton, W. C.; Grimes, R. N. J. Am. Chem. Soc.
1984, 106, 29. (b) Jacobsen, G. B.; Meina, D. G.; Morris, J. H.;
Thomson, C.; Andrews, S. J.; Reed, D.; Welch, A. J.; Gaines, D. F.
J. Chem. Soc., Dalton Trans. 1985, 1645.
(13) Fontaine, X. L. R.; Kennedy, J. D. J. Chem. Soc., Chem. Commun.
1986, 779.
(
(
10) See, for example: Hnyk, D.; B u¨ hl, M.; Volden, H. V.; Gundersen,
(14) Huntley, C. M.; Laurenson, G. S.; Rankin, D. W. H. J. Chem. Soc.,
Dalton Trans. 1980, 954.
S.; M u¨ ller, J.; Paetzold, P. Inorg. Chem. 1993, 32, 2442.

1
-Phenyl-1,2-dicarba-closo-dodecaborane
Inorganic Chemistry, Vol. 35, No. 6, 1996 1703
Table 2. Crystallographic Data for 1-Ph-1,2-closo-C
2
10 11
B H
C
8
H
16
B
10
fw ) 220.23
space group: P2
T ) 199 K
a ) 12.047(3) Å
b ) 18.627(4) Å
c ) 12.332(5) Å
â ) 110.09(4)°
V ) 2595.3(14) Å
Z ) 8
1
/a (monoclinic)
λ
bar ) 0.71069 Å
-
3
D
calc ) 1.128 g cm
3
-1
R
µ(Mo K ) ) 0.49 cm
a
R ) 0.0831
b
S ) 1.073
a
. b S ) (∑w(|F
2
)]1/2
.
o
R ) ∑||F | - |F
c
||/∑F
o
o
| - |F
c
|) /(n
o
- n
v
Figure 3. Perspective view of molecule B refined from the X-ray data
(30% ellipsoids except for H atoms which have an artificial radius of
0
.1 Å for clarity).
Figure 2. Perspective view of molecule A refined from the X-ray data
30% ellipsoids except for H atoms which have an artificial radius of
(
0
.1 Å for clarity).
The electron-scattering patterns were converted into digital form
using a computer-controlled Joyce-Loebl MDM6 microdensitometer
1
5
with a scanning program described elsewhere. The programs used
15
16
for data reduction and least-squares refinement have been described
previously; the complex scattering factors employed were those listed
by Ross et al.
1
7
X-ray Diffraction. Crystals suitable for X-ray diffraction were
grown by very slow cooling (to room temperature) of a warm,
concentrated, ethanolic solution. Crystallographic data were collected
on an Enraf-Nonius CAD4 diffractometer operating with Mo-K
R
X-radiation (λbar ) 0.71069 Å), with the glass capillary containing the
crystal held in a stream of nitrogen gas at 199 K. The unit cell was
determined by the least-squares refinement of the setting angles of 25
reflections in the range 16 < 2θ < 22°. Intensity data in the range 2
<
2θ < 50° were collected by the ω-2θ scan technique; ω-scan width
-
1
(
0.8 + 0.34 tan θ), ω-scan speeds in the range 0.235 to 0.782° min
The intensities of 4572 unique reflections were measured (h, -14 to
14; k, 0 to 22; l, 0 to 14); of these, 2592 reflections had F > 4σ(F).
There was no decay or crystal movement during the 158 h of data
.
+
1
8
collection (CADABS ). Crystallographic data are summarized in
Table 2.
The structure was solved using direct methods (SHELXS86)19 and
developed by iterative full matrix least-squares refinement and differ-
2
0
ence Fourier syntheses (SHELXTL). In molecule A (Figure 2), the
cage carbon not carrying the phenyl substituent could not be unambigu-
(
(
(
15) Cradock, S.; Koprowski, J.; Rankin, D. W. H. J. Mol. Struct. 1981,
7, 113.
16) Boyd, A. S. F.; Laurenson, G. S.; Rankin, D. W. H. J. Mol. Struct.
981, 71, 217.
17) Ross, A. W.; Fink, M.; Hilderbrandt, R. In International Tables for
Crystallography; Wilson, A. J. C., Ed.; Kluwer Academic Publish-
ers: Dordrecht, The Netherlands, Boston, MA, and London, 1992;
Vol. C, p 245.
Figure 4. Views of 1 along C(11)-C(1): (a) molecule B from the
X-ray study, with θ′ ) ca. 68°; (b) GED refinement B, with θ′ ) 54°.
Parts of the phenyl ring and carborane cage are omitted for clarity.
7
1
ously identified and consequently a disordered model was adopted in
which all five boron atoms adjacent to C(1A) were given an occupancy
of 1.04. In contrast, molecule B (Figures 3 and 4) was fully ordered
and the position of C(2B) was clear. Phenyl rings were treated as planar
hexagons (C-C ) 1.390 Å) with phenyl-H atoms set in idealized
positions (C-H ) 0.93 Å). In the final stages of refinement, all non-H
atoms were refined with anisotropic thermal parameters. Cage-H atoms
were set 1.10 Å from C or B on a radial extension. All H atoms were
(
(
(
18) Gould, R. O.; Smith, D. E. CADABS. Program for data reduction.
University of Edinburgh, U.K., 1986.
19) Sheldrick, G. M. SHELXS86. Program for crystal structure solution.
University of G o¨ ttingen, Germany, 1986.
20) SHELXTL PC version 5.0. Siemens Analytical Intruments Inc.,
Madison, WI, 1994.

1
704 Inorganic Chemistry, Vol. 35, No. 6, 1996
Brain et al.
4
a
Table 3. Fractional Coordinates (×10 ) and Equivalent Isotropic
Table 4. Molecular Parameters (r
of 1
a
/Å or ∠ /deg) for the GED Study
a
2
3
Displacement Parameters (Å × 10 ) in 1-Ph-1,2-closo-C
2
B
10
H
11
refinementc
x
y
z
U
eq
parameterb
A
B
C(12A)
C(13A)
C(14A)
C(15A)
C(16A)
C(11A)
C(1A)
B(2A)
B(3A)
B(4A)
B(5A)
B(6A)
B(8A)
B(9A)
B(10A)
B(11A)
B(7A)
B(12A)
C(12B)
C(13B)
C(14B)
C(15B)
C(16B)
C(11B)
C(1B)
462(2)
1091(2)
1758(2)
1795(2)
1166(2)
499(2)
-197(3)
-160(3)
560(4)
-45(1)
-401(1)
-13(2)
732(2)
1089(1)
700(1)
1083(2)
1985(2)
1458(2)
712(2)
6913(2)
6321(2)
5803(2)
5877(2)
6468(2)
6986(2)
7610(3)
7745(3)
8944(3)
8787(3)
7511(4)
6846(4)
9734(4)
8846(4)
7623(4)
7752(4)
9059(4)
9001(4)
2294(2)
1825(3)
1252(3)
1148(2)
1617(2)
2190(2)
2669(3)
2949(3)
4102(3)
3650(3)
2199(3)
1757(3)
2210(4)
3377(4)
4553(4)
4094(4)
2662(4)
3651(4)
43(1)
58(1)
62(1)
59(1)
43(1)
31(1)
30(1)
48(1)
53(1)
51(1)
53(1)
56(1)
46(1)
49(1)
51(1)
50(1)
47(1)
51(1)
60(1)
85(2)
86(2)
79(2)
59(1)
41(1)
32(1)
42(1)
42(1)
37(1)
34(1)
38(1)
42(1)
41(1)
46(1)
50(1)
53(1)
47(1)
1
p
1
r(C-C)av, /
8
2
[(1-2) + 6(C-C)ring
[(1-3) + (1-4)]
+
1.440(2)
1.436(2)
(1-11)]
1
p
p
2
r(C-B)av, /
1.711(5)
1.788(4)
1.720(6)
1.784(5)
1
3
r(B-B)av, /15[4(3-4) + 4(4-8) +
2
(7-11) + (9-12) + 4(8-12)]
p
p
p
p
p
p
p
4
r(C-H)
r(B-H)
1.113(10)
1.179(8)
111.1(4)
126.3(7)
120.0(f)
117.0(f)
90.0(f)
0.238(7)
0.121(8)
-0.006(9)
-0.004(8)
0.005(8)
1.120(12)
1.176(13)
110.6(4)
119.6(17)
120.0(f)
5
6
C(2)C(1)B(4)
C(2)C(1)C(11)
BBH
C(1)C(2)H(2)
θ′ [90° - C(2)C(1)C(11)C(16)]
∆ [C(1)-C(2)]-[(C-C)ring
∆ [C(1)-C(2)]-[C(1)-C(11)]
∆ [C(1)-B(3)]-[C(1)-B(4)]
∆ [B(3)-B(4)]-[B(4)-B(8)]
∆ [B(3)-B(4)]-[B(7)-B(11)]
∆ [B(3)-B(4)]-[B(9)-B(12)]
∆ [B(3)-B(4)]-[B(8)-B(12)]
7
-348(4)
-1557(3)
-1437(4)
-422(4)
-1720(4)
-2412(4)
-1524(4)
-298(4)
-1713(4)
-63(2)
8
754(2)
9
117.0(f)
54.0(f)
1566(2)
1390(3)
947(3)
10
p11
p12
]
0.233(7)
0.126(8)
-0.004(9)
-0.001(9)
0.002(8)
1492(3)
2279(2)
2209(2)
1893(3)
5150(1)
5680(1)
5493(2)
4775(2)
4244(1)
4431(1)
3872(2)
3067(2)
3605(2)
4069(2)
3813(2)
3177(2)
2872(2)
3431(2)
3305(3)
2678(3)
2415(3)
2567(2)
p
13
p
14
p
15
p
16
p
17
-0.007(10) -0.008(10)
-0.047(7) -0.045(7)
445(3)
a
Figures in parentheses are the estimated standard deviations of the
1213(3)
1473(2)
965(2)
197(2)
-406(3)
175(3)
b
last digits: f ) fixed.c For definitions, see text; for atom numbering
see Figures 3 and 4. For method of refinement, see text.
contracted to [21] for H. Computations employing the DZ basis were
obtained with an IGLO lobe version, while for the II′′ basis the direct
IGLO program (DIGLO)9d was used.
C(2B)
B(3B)
B(4B)
B(5B)
B(6B)
B(10B)
B(9B)
B(8B)
B(7B)
274(4)
-1081(3)
-1911(3)
-1073(4)
-2225(4)
-2234(4)
-879(4)
-36(4)
Molecular Model for the GED Refinement. Since 1-phenyl-1,2-
dicarba-closo-dodecaborane(12), 1-Ph-1,2-closo-C
or, at most, C symmetry and a large number of different interatomic
distances, it is a difficult system for investigation by electron-diffraction.
Thus, in order to reduce the problem to a manageable dimension, local
symmetries of C2V and D6h for the 1,2-C
ring, respectively, were assumed. Such assumptions were based on
the theoretically optimized geometry (HF/6-31G* level) in C symmetry
which predicted only small deviations from the idealized symmetries
for these moieties (see below). However, even for this simplified
2 10 1
B H11, has either C
s
2 6
B10 cage and the C hexagonal
B(11B)
B(12B)
-852(5)
-1586(4)
1
a
Ueq ) ∑
i
∑
j
U
ij
a
i
*a
j
*a
i
j
‚a .
model, in which only the weighted mean values of the C-C (p
1
), C-B
given isotropic displacement parameters riding at 1.2 times the
equivalent isotropic parameter of their attached atom. Data were
(p ), and B-B (p ) bonds were considered (see Table 4), seven
2
3
parameters (p -p ) defining differences between the close-lying C-B,
11
17
-
1
2
2
2
weighted such that w ) [σ (F
o
) + (0.1189P) + 1.05P] where P )
B-B and C-C distances were also necessary. The initial values of
such differences were derived from the HF/6-31G* optimization in C1
symmetry. To complete the description of the C B framework, the
2
2
[
max.(F
o
or 0) + 2F
c
]/3. Using 2592 observed data, R ) 0.0831
and S ) 1.073 for 301 variable parameters. The maximum residue
and minimum trough in a final Fourier synthesis were +0.34 and -0.26
2
10
C(2)C(1)B(4) bond angle (p ) was used. The position of the phenyl
6
-
3
e Å , respectively. Atomic scattering factors were those inlaid in
SHELXTL. The atomic fractional coordinates and equivalent isotropic
thermal parameters for non-hydrogen atoms are listed in Table 3.
Hydrogen atom fractional coordinates, non-hydrogen anisotropic
thermal parameters, and a full listing of bond lengths and bond angles
are available as Supporting Information.
ring with respect to the cage was defined by both the C(2)-C(1)-
C(11) bond angle (p ) and by the torsion angle, θ′ ) 90° - [C(2)-
7
C(1)-C(11)-C(16)],(p ). The B-H bonds were assumed to be all
10
of equal length (p ), as were the six C-H bonds [five (C-H) and
5
ring
C(2)-H(2)] (p ). For the angle parameters, the cluster hydrogens were
4
located assuming a single value for the BBH angles (p ) and the angle
8
Ab Initio Calculations. The geometry was fully optimized in C
s
C(1)C(2)H(2) (p ). Thus, the structure was defined by 17 refinable
parameters in this model as listed in Table 4.
9
2
1
and C
1
symmetry by standard ab initio methods at the RHF/6-31G*
2
2
level using the Gaussian 92 program package. Computations at a
correlated level (e.g. MP2) were not possible due to the demands on
CPU time and disk space for such a large, low symmetry molecule.
Results
1
1
B chemical shieldings were computed with the IGLO (individual
Electron Diffraction. Electron-diffraction refinements for
structures with a range of fixed θ′ values were undertaken. The
fit of data for the Cs structure with θ′ ) 0° was poorer (RG >
9
23
gauge for localized orbitals) program using Huzinaga basis sets: DZ;
7s3p) contracted to [4111, 21] for C,B and (3s) contracted to [21] for
(
H; II′′, (9s5p1d) contracted to [51111, 2111, 1] for C,B (cage atoms
and C(11)), (7s3p) contracted to [4111, 21] for C(12-16) and (3s)
0
.09) than for either the Cs structure with θ′ ) 90° (refinement
A, RG ) 0.069) or the optimum refinement in C1 symmetry
with θ′ ) 54°, i.e. B(4)-C(1)-C(11)-C(12) ) ca. 1° (refine-
ment B, RG ) 0.071). In the original refinements, it was
possible to refine five of the geometrical parameters (Table 4),
Viz. p1-p4 and p7. Attempts to refine other parameters led to
either unreasonable values or an unstable refinement. Conse-
quently, the esd’s for some of the independent and dependent
parameters were likely to be underestimated, e.g. r[C(1)-C(2)]
(
21) See: (a) Hehre, W.; Radom, L.; Schleyer, P. v.R.; Pople, J. A. Ab
Initio Molecular Orbital Theory; Wiley: New York, 1986. (b)
Foresman, J. B.; Frisch, Æ. Exploring Chemistry with Electronic
Structure Methods; Gaussian Inc.: Pittsburgh PA, 1993.
(
22) Frisch, M. J.; Trucks, G. W.; Head-Gordon, M.; Gill, P. M. W.; Wong,
M. W.; Foresman, J. B.; Schlegal, H. B.; Raghavachari, K.; Robb, M.
A.; Replogle, E. S.; Gomperts, R.; Andres, J. L.; Binkley, J. S.;
Gonzalez, C.; Martin, R.; Fox, D. J.; DeFrees, D. J.; Baker, J.; Stewart,
J. J. P.; Pople, J. A. Gaussian Inc., Pittsburgh, PA, 1992.
)
1.629(2) Å. Subsequent refinements were therefore under-
(
23) Huzinaga, S. Approximate Atomic WaVefunctions; University of
24
Alberta: Edmonton, Canada, 1971.
taken using the method of flexible parameter constraints.

1
-Phenyl-1,2-dicarba-closo-dodecaborane
Inorganic Chemistry, Vol. 35, No. 6, 1996 1705
Table 5. Final Interatomic Distances (r
/Å)a-c and Mean
Flexible parameter constraints may allow the refinement of
a
Amplitudes of Vibration (u/Å) from the GED Refinement B of 1
parameters which would usually have to be fixed. Estimates
of the values of these parameters and their uncertainties are used
as additional observations in a combined analysis similar to those
routinely carried out for electron-diffraction data combined with
rotation constants and/or dipolar coupling constants. The
starting values and uncertainties for the extra observations are
derived from another method such as X-ray diffraction or
theoretical computations. All parameters are then included in
the refinements. Upon refinement, if the intensity pattern
contains useful information concerning one of these parameters,
it will refine with an esd less than the uncertainty in the
corresponding additional observation. However, if there is little
or no relevant information, the parameter will refine with an
esd equal to the uncertainty of the extra observation. In this
case, the parameter can simply be fixed, in the knowledge that
doing this does not influence either the magnitudes or the esd’s
of other parameters. In some cases, increasing the number of
refining parameters allows all effects of correlation to be
considered, and so some esd’s may actually increase. Overall,
this approach utilizes all available data as fully as possible and
returns more realistic esd’s for parameters, e.g. r[C(1)-C(2)]
distance
C(1)-C(2)
ra
u
r
r
r
r
r
r
r
r
1
2
3
4
5
6
7
8
1.627(8)
1.718(8)
1.722(7)
1.771(6)
1.770(9)
1.816(5)
1.772(9)
1.779(12)
1.806(14)
1.788(18)
1.500(8)
0.045(f)
0.054(f)
0.054(f)
C(1)-B(3)
C(1)-B(4)
B(3)-B(4)
B(4)-B(5)
B(8)-B(12)
B(4)-B(8)
B(9)-B(12)
B(7)-B(12)
B(3)-B(8)
C(1)-C(11)
(C-C)ring
0.062(4)
}
}
r9
r
r
r
r
r
10
11
12
13
14
0.042(f)
0.042(f)
0.108(f)
0.078(f)
0.085(f)
1.394(2)
B-H
(C-H)ring
1.176(13)
1.120(12)
1.120(12)
2.752-2.831
2.837-2.925
3.302(18)
3.343-3.418
2.414(3)
r15
C(2)-H(2)
(C‚‚‚B) [two bond]
(B‚‚‚B) [two bond]
r
16
r
17
r
18
r
19
r
20
r
21
r
22
r
23
0.075(5)
d
(C‚‚‚B)
0.084(f)
0.093(f)
0.067(4)
0.068(7)
0.152(30)
0.185(26)
(B‚‚‚B)d
C(12)‚‚‚C(16)
C(11)‚‚‚C(14)
2.788(3)
4.470-5.071
4.678-5.370
(Cring‚‚‚B) [four/five bond]
(Cring‚‚‚B) [four/five bond]
)
1.627(8) Å.
Using the method of flexible constraints, it was possible to
a
Values in parentheses are the estimated standard deviations of the
b
refine simultaneously 14 geometrical parameters (Table 4).
Heavy-atom distance differences (p11-p17) were constrained
with an uncertainty of 0.01 Å and r(B-H) with 0.02 Å.
Additionally, eight amplitudes of vibration were refined simul-
taneously in the final refinements while the dependence of the
final structure on other fixed amplitudes was also explored.
The parameters for refinements A and B are summarized in
Table 4. Interatomic distances, vibrational amplitudes and
angles as obtained in refinement B are listed in Table 5 and the
most important elements of the least-squares correlation matrix
are given in Table 6. Atomic coordinates of the HF/6-31G*
and GED (refinement B) C1 geometries are included as part of
the Supporting Information. The radial-distribution curves and
molecular-scattering intensities are shown in Figures 5 and 6,
respectively.
final digits: f ) fixed. For atom numbering scheme, see Figures 3
and 4. c All C(x)‚‚‚C(1,2) and C(x)‚‚‚B(N) distances (x ) 11, 14, 15,
1
6; N ) 3, ..., 12) with multiplicity 1 were included in the refinement
but most are not shown here. Similarly, all the B‚‚‚H, C‚‚‚H, and H‚‚‚H
distances (cage and ring), with amplitudes fixed in the range 0.090-
.180 Å, were also included. d Cage body diagonals.
0
Table 6. Least Squares Correlation Matrix (×100) for GED
Refinement Ba
Ab Initio and IGLO Computations. IGLO 11B chemical-
shift calculations, performed for various HF/6-31G* optimized
structures differing mainly in the phenyl ring position, indicated
11
that the δ( B) values are sensitive to the phenyl-ring orientation,
if only to a small degree. The HF/6-31G* level energy
computations favor the structures in which the ring eclipses the
C(1)-C(2) bond (Cs symmetry, θ′ ) 90°), or more or less
eclipses the C(1)-B(4) bond (C1 symmetry, θ′ ) 65°, B(4)-
C(1)-C(11)-C(12) ) ca. 14°), the latter being found as the
minimum on the potential energy (p.e.) hypersurface, relative
to the structure with the phenyl ring “perpendicular” to the
C(1)-C(2) bond (Cs symmetry, θ′ ) 0°). Selected geometrical
parameters from the ab initio study are given in Table 7, and
the results of the IGLO computations are shown in Table 8.
X-ray. There are two crystallographically-independent mol-
ecules of 1-Ph-1,2-closo-C2B10H11 (molecules A and B) in the
asymmetric fraction of the unit cell, and these are drawn in
Figures 2 and 3, respectively. There are no significant contacts
between molecules. Interatomic distances and selected inter-
bond angles are given in Table 8; a full listing of geometrical
parameters is included in the Supporting Information. In
molecule A, the cage carbon atom not carrying the phenyl
substituent, C(2), could not be distinguished with a sufficient
a
Only elements with absolute values g 50 are shown.
degree of certainty [C(1A)-cage atom distances ) 1.674(5)-
.728(5) Å], whereas in molecule B its location (based on a
1
combination of interatomic distances and refined [as B] isotropic
thermal parameters) was unambiguously established. Since the
key feature of the structure of monophenylcarborane is the twist
angle θ′ which describes the conformation of the phenyl ring
with respect to C(1)-C(2), only parameters for molecule B will
be discussed.
NMR. The 11B{1H} NMR spectrum of monophenylcarbo-
rane (Figure 7) reveals 6 resonances of relative integral 1:1:2:
2
:2:2 at -1.19, -3.49, -8.06, -9.88, -10.32, and -11.85 ppm
1
respectively, all of which appear as doublets ( JBH ) 148-170
Hz) in the proton-coupled spectrum.
In the 11B{ H}/ B{ H} COSY spectrum (Figure 8) the only
1
11
1
11
integral-2 peak which couples to all other B resonances is that
at -8.06 ppm and is therefore assigned to B(8,10). The two
highest frequency resonances (each integral-1) must be due to
B(9) and B(12). They show, as expected, coupling to each other
and to B(8,10). In addition, each couples to one other integral-2
resonance. The integral-2 resonance that does not couple to
(
24) Blake, A. J.; Brain, P. T.; McNab, H.; Miller, J.; Morrison, C. A.;
Parsons, S.; Rankin, D. W. H.; Robertson, H. E.; Smart, B. A. J. Phys.
Chem., in press.

1
706 Inorganic Chemistry, Vol. 35, No. 6, 1996
Brain et al.
Table 7. Comparison of Theoretical and Experimental Geometrical
a-c
Parameters for 1
theoreticald
GEDe
X-rayf
distance/angle
θ′ ) 65°
θ′ ) 54°(f)
θ′ ) 67.7(3)°
C(1)-C(2)
1.626
1.627(8)
1.640(5)
C(1)-B(3)
C(1)-B(6)
C(2)-B(3)
C(2)-B(6)
1.733
1.739
1.713
1.708
1.743(5)
1.719(5)
1.709(6)
1.711(6)
1.718(8)
C(1)-B(4)
C(1)-B(5)
C(2)-B(7)
C(2)-B(11)
1.720
1.722
1.701
1.702
1.716(5)
1.705(5)
1.683(5)
1.681(6)
1.722(7)
1.771(6)
B(3)-B(4)
B(6)-B(5)
B(3)-B(7)
B(6)-B(11)
1.780
1.779
1.782
1.785
1.758(6)
1.761(6)
1.766(7)
1.768(6)
Figure 5. Observed and final weighted difference radial-distribution
curves for the GED study of 1. Before Fourier inversion the data were
2
multiplied by s exp[(-0.00002s )/(Z
B
- f
)(Z
B C
- f
C
)].
B(4)-B(8)
B(5)-B(10)
B(7)-B(8)
B(10)-B(11)
1.792
1.785
1.787
1.782
1.771(6)
1.795(6)
1.764(7)
1.770(7)
1.772(9)
1.770(9)
1.816(5)
B(4)-B(5)
B(7)-B(11)
1.785
1.785
1.784(5)
1.767(7)
B(8)-B(12)
B(10)-B(12)
B(8)-B(9)
1.803
1.803
1.799
1.802
1.787(7)
1.767(6)
1.783(6)
1.780(6)
B(9)-B(10)
B(9)-B(12)
1.791
1.779(12)
1.806(14)
1.769(6)
B(7)-B(12)
B(11)-B(12)
B(4)-B(9)
B(5)-B(9)
1.784
1.783
1.785
1.781
1.766(6)
1.761(7)
1.769(6)
1.778(6)
B(3)-B(8)
B(6)-B(10)
1.766
1.770
1.788(18)
1.756(6)
1.761(6)
C(1)-C(11)
1.516
1.386g
1.500(8)
1.394(2)
1.503(4)
1.39(f)
Figure 6. Observed and final weighted difference combined molecular-
scattering intensity curves for the GED study of 1. Theoretical data
are shown for the regions 0-30 and 272-360 nm for which no
experimental data are available.
(C-C)ring
-
1
C(2)C(1)C(11)
C(2)C(1)B(4)
C(1)C(2)B(7)
118.3
109.9
113.5
119.6(17)
110.6(4)
110.6(4)
119.2(3)
108.6(3)
113.1(3)
either B(9) or B(12) is that at -10.32 ppm, which must therefore
a
For atom numbering scheme, see Figures 3 and 4. b θ′ ) 90° -
arise from B(3,6).
1
11
[C(2)C(1)C(11)C(16)]. c Figures in parentheses are the estimated
In the H{ B} spectrum (Figure 9) there are five peaks in
the BH region, of relative integral 2:2:1:3:2 (high frequency to
low frequency) the underlined resonance representing a 2 + 1
coincidence. In addition, the C(2)H proton (integral-1) resonates
d
standard deviations of the last digits: f ) fixed. HF/6-31G* level.
Model B, C2V cage geometry. Molecule B. A mean value is given.
e
f
g
Refinements of the electron-diffraction data, assuming local
1
at a much higher frequency, 3.97 ppm. A series of H-
C2V symmetry for the C2B10 cage and D6h symmetry for the
phenyl ring, are consistent equally with conformations in which
θ′ ) 90° (refinement A) or θ′ ) 54° (refinement B). Both
conformations exhibit geometrical parameters similar to those
found in the ab initio optimization in C1 symmetry (Table 7)
with the exception of the bond angle C(2)C(1)C(11), which is
considerably larger in refinement A [126.3(7)°] than in B
1
1
11
{
Bselective} experiments, following the order of the
resonances, revealed enhancement of the proton signals at 2.46,
.35, 2.35, 2.53, 2.62 and 2.30 ppm, respectively. Clearly
H(8,10) resonates at 2.35 ppm and H(3,6) at 2.62 ppm.
B
2
11
1
The ambiguities in the B and H assignments were resolved
1
11
1
11
by a H{ B}/ H{ B} COSY spectrum (Figure 10). C(2)H
showed two couplings, to the highest (2.62 ppm) and lowest
[
119.6(17)°], cf. HF/6-31G* 118.3°. Theoretical single-point
(2.30 ppm) frequency BH resonances, and the last must therefore
SCF energies are computed lower for refinement B than for A,
both with the DZ and II′′ basis sets. Thus, considered in
conjunction with the ab initio study, GED refinement B, with
θ′ ) 54°, is favored over refinement A.
be due to H(7,11). Therefore B(7,11) resonates at -11.85 ppm.
1
1
1
11
1
From the B{ H}/ B{ H} COSY spectrum the resonance at
-
3.49 ppm is now assigned to B(12), that at -1.19 ppm to
B(9), and that at -9.88 ppm to B(4,5); from these, the remaining
At 488 K, the temperature of the vapor in the GED
1
H assignments were easily made.
-
1
experiment, RT ) 4.1 kJ mol . The potential-energy barrier
to rotation of the phenyl ring about C(1-C(11), assuming that
the conformation with θ′ ) 90° lies at the maximum on the
Discussion
At the HF/6-31G* level, a conformation with the phenyl twist
-1
p.e. hypersurface (Table 8), is predicted to be 2.1 kJ mol at
(θ′) of ca. 65° is computed to be a minimum on the potential-
the HF/6-31G* level. It thus seems likely that the gas-phase
geometry of 1 is defined by almost unrestricted rotation of the
phenyl ring, although the complexity of the GED analysis of
such a dynamic motion precludes the possibility of confirming
this experimentally.
energy hypersurface (Table 8). However, a conformation with
Cs symmetry in which the phenyl ring eclipses the C-C cluster
-
1
bond (θ′ ) 90°) is predicted to lie only 0.3 kJ mol higher in
energy.

1
-Phenyl-1,2-dicarba-closo-dodecaborane
Inorganic Chemistry, Vol. 35, No. 6, 1996 1707
2 10 11
Table 8. IGLO results for 1-Ph-1,2-C B H
1
1
a
δ( B)
relative
energy
b
level of theory//geometry
B(3,6)
B(4,5)
B(7,11)
B(8,10)
B(9)
B(12)
DZ//HF/6-31G* (C
DZ//HF/6-31G* (C
DZ//HF/6-31G* (C
1
, θ′ ) 65°)
-11.9
-11.8
-14.5
-12.2
-12.4
-12.2
-14.9
-14.5
-13.7
-15.6
-11.4
-13.9
-16.9
-17.3
-16.4
-16.7
-15.0
-14.1
-16.2
-16.0
-17.1
-15.9
-12.6
-13.1
-3.8
-3.9
-2.1
-2.9
4.7
-3.6
-3.7
-3.5
-2.9
2.1
0.0
0.3
2.1
5.8
60.7
53.1
s
, θ′ ) 90°)
, θ′ ) 0°)
s
c
DZ//HF/6-31G* (“C2V”, θ′ ) 65°)
d
DZ//GED (C
DZ//GED (C
s
, θ′ ) 90°)
, θ′ ) 54°)
d
1
3.8
1.8
II′′//HF/6-31G* (C
1
, θ′ ) 65°)
, θ′ ) 90°)
, θ′ ) 54°)
-11.4
-11.8
-11.6
-12.5
-8.8
-11.4
-15.0
-13.2
-12.0
-12.0
-7.9
-8.4
-2.2
6.7
5.7
-2.7
3.6
3.3
0.0
57.7
50.6
e
II′′//GED (C
II′′//GED (C
s
e
1
experimentalf
-10.3
-9.9
-11.9
-8.1
-1.2
-3.5
a
symmetry. b Energy (kJ mol-1) of the structure relative to the HF/6-31G* fully
Relative to BF
optimized C structure (θ′ ) 65°, potential energy minimum).
respect to the HF/6-31G* fully optimized C
3
‚OEt
2
(ppm); average values for effective C
s
c
d
1
C
2V symmetry for the C
2
B
10 cage is used. HF/6-31G* single-point energy with
e
f
1
structure. Relative energies at the HF/II′′ level. This work.
1
1
1
1
11
Figure 7. B{ H} NMR spectrum of 1.
Figure 9. H{ B} NMR spectrum of 1.
1
11
1
11
Figure 10. H{ B}/ H{ B} NMR COSY spectrum of 1.
1
1
1
11
1
Figure 8. B{ H}/ B{ H} NMR COSY spectrum of 1.
shifts of B(9,8,10,7,11), and (c) a marked shift to low frequency
1
11
(∆δ ) ca. 2.7 ppm) of the resonance due to the antipodal atom
The fully assigned H and B chemical shifts for monophen-
ylcarborane are listed in Table 9. Comparing the 11B chemical
1
1
B(12). Overall the pattern and values of B resonances in
monophenylcarborane are very similar to those recently re-
shifts with those of the ubiquitous parent species 1,2-closo-
C2B10H12, we note (a) a significant shift to high frequency of
2
5
2
5
2 3
ported for the ether-substituted species 1-(CH OCH )-1,2-
closo-C2B10H11.
the resonances due to B(3,6) (∆δ ) ca. 4 ppm) and B(4,5) (∆δ
The experimental 11B chemical shifts are reproduced well by
the IGLO calculations, (see Table 8), with the exception of the
)
(
ca. 3 ppm), atoms adjacent to C(1), the site of substitution,
b) relatively little difference (∆δ ) 0-1 ppm) in the chemical
11
δ( B) IGLO values of B(9) and B(12), antipodally coupled with
(
25) Shaw, K. F.; Welch, A. J. Polyhedron 1992, 11, 157.
C(2) and C(1), which are slightly overestimated (with both the

1
708 Inorganic Chemistry, Vol. 35, No. 6, 1996
Brain et al.
Table 9. Assignment of the Experimental 11B and H NMR
1
2 10 11
Chemical Shifts in 1-Ph-1,2-closo-C B H
1
11
11
2 10
δ( B, 1,2-C B H
12)25
position
9
δ( H)
δ( B)
2.46
2.35
2.35
2.53
2.62
2.30
-1.19
-3.49
-8.06
-9.88
-10.32
-11.85
-1.78
-1.78
-8.59
-12.99
-14.10
-12.99
1
8
4
3
7
2
, 10
, 5
, 6
, 11
DZ and II′′ basis sets) when employing the GED structures.
For refinement B, the final experimental geometry of 1 is
-
1
computed to lie 53.1 kJ mol (6-31G* basis set) and 50.6 kJ
-
1
mol (II′′ basis set) above the theoretical C1 fully optimized
structure. Such values are somewhat larger than usually
observed for “excess energies” of GED structures.7
,8,10
How-
ever, considering the large number of relatively poorly defined
geometrical parameters (including 16 hydrogen atoms), these
values are not unreasonable.
Figure 11. Space-filling plot of molecule B from the X-ray study.
Sphere radii are proportional to the respective van der Waals’ radii.
Figure 4 shows a view of the molecule from above (top half
of the phenyl ring omitted for clarity), showing that the
H(16B)‚‚‚H(2B) repulsion would be more pronounced if the θ′
In the solid-phase molecular structure, the angle θ′ in
molecule B is 67.7(3)°. The distance C(1B)-C(2B) is 1.640(5)
Å (cf. GED 1.627(8) Å, ab initio 1.626 Å), significantly shorter
than any other connectivity on the surface of the pseudoicosa-
hedral carborane polyhedron including others to C(2B), 1.681(6)-
)
90° conformation were adopted. Figure 11, a side view of
the molecule, confirms that there are touching van der Waals’
spheres on H(16B) and H(2B).
2
6
2a
1
.711(6) Å. We have already noted that a contribution to
the short C(1)-C(2) connectivity derives from the orientation
of the phenyl substituent. Thus, in derivatives 1-Ph-2-X-1,2-
closo-C2B10H10 (X ) Me, Br), the 2-substituent is sufficiently
bulky to ensure a conformation near θ′ ) 0° (experimentally
Acknowledgment. We acknowledge the Science and En-
gineering Research Council (now EPSRC) for support of the
Edinburgh Electron-Diffraction Service (Grant No. GR/J59258),
including provision of microdensitometer facilities at the
Daresbury laboratory, the award of research fellowships to D.H.,
P.T.B., and H.E.R, and the award of research studentships to
D.J.D. and B.D.R. We also thank the University of Edinburgh
for the award of a studentship to J.C. D.H. thanks the Academy
of Sciences of the Czech Republic (Grant No. 432402) and the
Grant Agency of the Czech Republic (Grant No. 203/94/0984)
for financial support. We thank Dr. M. B u¨ hl for performing
the IGLO calculations employing the II′′ basis set. The
calculations in Erlangen were performed on a Convex C220S
computer and were supported by the Deutsche Forschungsge-
meinschaft and the Fonds der Chemischen Industrie. Computer
time was granted on a Cray YMP-8 of the H o¨ chstleistungsre-
chenzentrum J u¨ lich. We thank Professor W. Kutzelnigg, Dr.
M. Schindler, Dr. U. Fleischer, and Dr. Ch. van W u¨ llen for the
IGLO and DIGLO programs. A.J.W. acknowledges the Callery
Chemical Co. for a generous gift of B10H14.
1
6.7 and 2.2°, respectively)2e,3c and results in C(1)-C(2) distances
2
a
of 1.695(5) Å and 1.692(8) Å. Bulkier X groups, such as Ph,
CCCPh,2 SiMe3, and SiMe2 Bu maintain or extend C(1)-
C(2) and can additionally result in bending back of substituents
and/or deformation of the cage.
e
3d
t
3e
In molecule B of 1-Ph-1,2-closo-C2B10H11, C-B distances
span the range 1.681(6)-1.743(5) Å, and B-B lengths lie
between 1.756(6) and 1.795(6) Å. Inspection of the C(11B)-
C(1B)-C/B angles reveals that the phenyl substituent is slightly
tilted away from B(4B) and B(5B); however, there is a
compensatory asymmetry in C(1B)-C(11B)-C angles, with
that to C(12B) being measureably narrower than that to C(16B).
The conformation of molecule B is in excellent agreement
with that determined by ab initio MO calculations (Table 7),
as discussed above. We believe that this conformation is
measureably different from that (θ′ ) 90°) predicted by the
2a
earlier EHMO calculations because of steric crowding between
cage- and ortho-phenyl-H atoms, poorly modeled in the former,
low-level, calculation. In molecule B determined crystallo-
graphically, H(16B)‚‚‚H(2B) ) 2.21 Å, H(16B)‚‚‚H(6B) ) 2.81
Å, H(12B)‚‚‚H(4B) ) 2.30 Å and H(12B)‚‚‚H(5B) ) 3.03 Å.
Supporting Information Available: Listings of (a) data pertinent
to the crystal structure analysis, including (i) all bond distances and
angles, (ii) fractional atomic coordinates and isotropic displacement
parameters for the hydrogen atoms, and (iii) fractional atomic coordi-
nates and anisotropic displacement parameters for the non-hydrogen
atoms, and (b) atomic coordinates for the GED and theoretically
optimized geometries is available (9 pages). Ordering information is
given on any current masthead page.
(
26) Since submission of this manuscript, the crystal structure of a second
polymorph of monophenylcarborane has been determined. In this new
modification, θ′ ) 71.2(2)° and r[C(1)-C(2)] ) 1.649(2) Å. See:
Thomas, R. Ll.; Rosair, G. M.; Welch, A. J. Acta Crystallogr., C, in
press.
IC9511128