Synthesis, structure, and bonding properties of 5-carbaphosphatranes: A new class of main group atrane

Article abstract of DOI:10.1021/ja011458j

1-Hydro-5-carbaphosphatrane (1) and 1-methyl-5-carbaphosphatrane (2), the first 5-carbon analogues of phosphatranes, were synthesized by a demethylation reaction of cyclic phosphinate 3. X-ray analysis revealed that 1 has a typical trigonal bipyramidal st

Full text of DOI:10.1021/ja011458j

Published on Web 03/14/2002
Synthesis, Structure, and Bonding Properties of
5-Carbaphosphatranes: A New Class of Main Group Atrane
Junji Kobayashi,† Kei Goto,† Takayuki Kawashima,*,† Michael W. Schmidt,*,‡ and
Shigeru Nagase§,|
Contribution from the Department of Chemistry, Graduate School of Science, The UniVersity of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan, and Department of Chemistry,
Graduate School of Science, Tokyo Metropolitan UniVersity, Hachioji, Tokyo 192-0397, Japan
Received June 14, 2001
Abstract: 1-Hydro-5-carbaphosphatrane (1) and 1-methyl-5-carbaphosphatrane (2), the first 5-carbon
analogues of phosphatranes, were synthesized by a demethylation reaction of cyclic phosphinate 3. X-ray
analysis revealed that 1 has a typical trigonal bipyramidal structure with hydrogen and carbon atoms at the
apical position and three oxygen atoms at the equatorial positions, indicating that 1 is a phosphorane in
the perfectly “anti-apicophilic” arrangement. Apical P-C and P-H bond lengths were 1.921(2) and 1.38(2)
1
1
Å, respectively. The JPH value of 1 and the JPC(P-CH3) value of 2 were 852 and 215 Hz, respectively,
which are extraordinarily large for the apical coupling constants of phosphoranes, but close to those of the
reported phosphatranes with a 5-nitrogen atom. IR and Raman spectra are also reported. Force constant
calculations indicate the transannular bond in carbaphosphatrane is 3 times stronger than in silatrane, due
to its covalent character.
Introduction
There have been extensive studies on a wide variety of main
group atranes, generally depicted as A.1,2 A number of their
derivatives bearing different ring sizes, and other building
elements have also been reported so far. A silatrane (I) was
first reported by Frye and co-workers3 and has been widely
investigated. Voronkov reported the chemical properties of
silatranes as well as their biological activities.2a Verkade
investigated phosphorus-centered atranes, phosphatranes (II),
and revealed that they have unique structure, physical properties,
and reactivities.1a Pro-phosphatranes, that is, the conjugated
bases of phosphatranes, are known as very strong neutral bases
and have been utilized as catalysts in organic synthesis.4a These
unique features of phosphatranes are considered to be caused
by the NfP dative bond. From such a viewpoint, it is
† The University of Tokyo.
‡ Present address: 201 Spedding Hall, Iowa State University Ames, IA
50011
§ Tokyo Metropolitan University.
| Present address: Department of Theoretical Studies, Institute for
Molecular Science, Myodaiji, Okazaki 444-8585, Japan.
(1) For reviews, see: (a) Verkade, J. G. Acc. Chem. Res. 1993, 26, 483-489.
(b) Verkade, J. G. Coord. Chem. ReV. 1994, 137, 233-295. (c) Alder, R.
W.; Read, D. Coord. Chem. ReV. 1998, 176, 113-133.
(2) For silatranes, see: (a) Voronkov, M. G. Pure Appl. Chem. 1966, 13, 35-
59. (b) Voronkov, M. G.; D’yakov, V. M.; Kirpichenko, S. V. J. Organomet.
Chem. 1982, 233, 1-147. (c) Voronkov, M. G.; Baryshok, V. P.; Petukhov,
L. P.; Rakhlin, V. I.; Mirskov, R. G.; Pestunovich, V. A. J. Organomet.
Chem. 1988, 358, 39-55. (d) Corriu, R. J. P. J. Organomet. Chem. 1990,
400, 81-106. (e) Hencsei, P. Struct. Chem. 1991, 2, 21-26. (f) Chuit, C.;
Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. ReV. 1993, 93, 1371-1448.
(3) Frye, C. L.; Vogel, G. E.; Hall, J. A. J. Am. Chem. Soc. 1961, 83, 996-
997.
particularly intriguing how their properties will change when
the ΝfP dative bond is replaced by a covalent bond with group
14 elements such as carbon (III). Very recent work has shown
that the protonated atrane containing PfP has a short P-P
(4) (a) Kisanga, P. B.; Verkade, J. G.; Schwesinger, R. J. Org. Chem. 2000,
65, 5431-5432 and references therein. (b) Alder, R. W.; Butts, C. P.; Orpen,
A. G.; Read, D.; Oliva, J. M. J. Chem. Soc., Perkin Trans. 2 2001, 282-
287. (c) Alder, R. W.; Butts, C. P.; Orpen, A. G.; Read, D. J. Chem. Soc.,
Perkin Trans. 2 2001, 288-295.
9
10.1021/ja011458j CCC: $22.00 © 2002 American Chemical Society
J. AM. CHEM. SOC. 2002, 124, 3703-3712
3703

A R T I C L E S
Kobayashi et al.
distance and is highly resistant to deprotonation.4b,c 5-Carba-
phosphatranes are expected to have structural properties similar
to reported phosphatranes since they have an isoelectronic
structure. On the other hand, they are expected to have
reactivities different from those of phosphatranes, reflecting the
difference in their bonding properties. Such comparisons
between 5-carbaphosphatranes and phosphatranes will give
important information about the relationship between bonding
properties and reactivities of hypervalent compounds. Here we
report the synthesis of the first carbon analogues of a phospha-
trane, 5-carbaphosphatranes (IV), and the elucidation of their
structural and spectroscopic properties by both experimental data
and theoretical calculations. Parts of this work have been
communicated.5
Preparation of 5,5′,5′′-Tri-tert-butyl-2,2′,2′′-trimethoxytriphenyl-
methane (5). To a solution of 4 (8.92 g, 17.2 mmol) in acetic acid
(100 mL) was added triethylsilane (40 mL, 26 mmol), and the mixture
was stirred at 80 °C overnight. The mixture was neutralized with
aqueous NaOH and extracted with CHCl3. The extracts were dried over
anhydrous MgSO4. After removal of the solvent, the residue was
reprecipitated from CHCl3/EtOH to give 5 as colorless crystals (7.24
g, 84% yield). 5: colorless crystals; mp 122-125 °C;1H NMR (270
MHz, CDCl3) δ 1.15 (s, 27H), 3.67 (s, 9H), 6.50 (s, 1H), 6.75 (d, 3H,
J ) 8.5 Hz), 6.84 (d, 3H, J ) 2.4 Hz), 7.14 (dd, 3H, J ) 8.5, 2.4
Hz);13C{1H} NMR (125 MHz, CDCl3, 27 °C) δ 31.41 (s), 33.96 (s),
36.78 (s), 56.08 (s), 110.43 (s), 122.94 (s), 127.48 (s), 132.07 (s), 142.16
(s), 155.23 (s). Anal. Calcd for C34H46O3: C, 81.23; H, 9.22. Found:
C, 80.56; H, 9.21.
Preparation of Phosphinic Acid 6. To a solution of 5 (1.05 g, 2.09
mmol) in benzene (50 mL) was added n-BuLi (1.60 M hexane solution,
9.9 mmol) at 50 °C. The mixture was stirred at 50 °C for 24 h. To this
solution was added PCl3 (2.0 mL, 23 mmol), and the mixture was stirred
at room temperature for 5 days. After removal of the solvent, the residue
was subjected to wet column chromatography (WCC) (SiO2/CHCl3)
and dry column chromatography (DCC) (SiO2/CHCl3) to give a fraction
containing 6, which was further purified by HPLC to give 6 (116.4
mg, 12% yield). 6: colorless solids; mp 276-278 °C;1H NMR (500
MHz, CDCl3, 27 °C) δ 1.02 (s, 27H), 3.66 (s, 9H), 6.29 (brs, 3H),
6.82 (d, 3H, J ) 8.3 Hz), 7.22 (br d, 3H, J ) 8.3 Hz), 7.34 (d, 1H, JPH
) 610 Hz); 13C{1H} NMR (125 MHz, CDCl3, 27 °C) δ 31.15 (s), 33.87
(s), 55.15 (s), 62.00 (d, JPC ) 86 Hz), 110.36 (s), 124.32 (s), 128.19
(s), 128.69 (br s), 142.67 (s), 155.55 (s); 31P NMR (109 MHz, CDCl3,
27 °C) δ 44.5; LRMS (EI 70 eV) m/z 567, calcd for C34H47O5P 567.
Anal. Calcd for C34H47O5P‚0.5H2O: C, 70.93; H, 8.40. Found: C,
70.72; H, 8.19.
The present compound is being described as an atrane since
it is a substituted tricyclo[3.3.3.0]undecane with a highly
coordinated bridgehead atom. The superficially related systems
with N substituted for P6 are typically formulated as salts
C[-(CH2)3-]3N+X-, X- ) Br-,6a Cl-,6b I3- 6c BPh4- 6d,e Since
, .
the available structural data for these do not indicate the presence
of an NX bond, these compounds are named azoniapropellanes
and are not generally regarded as atranes.
Experimental Section
General Information. 2-Bromo-4-tert-butylanisole was synthesized
by a reported procedure in two steps.7 Solvents were purified according
to standard procedures. All the reactions were carried out in a dry argon
atmosphere. 1H and 13C NMR spectra were recorded on a Bruker
DRX500 FT-NMR spectrometer, and 31P NMR spectra were recorded
Preparation of Cyclic Phosphinate 3. To a solution of 5 (5.06 g,
11.0 mmol) in benzene (250 mL) was added n-BuLi (1.67 M hexane
solution, 50 mmol) at 50 °C. The mixture was stirred at 50 °C for 24
h. To the mixture was added PCl3 (10 mL, 0.11 mmol), and the mixture
was stirred at 50 °C for 2 days and 80 °C for 5 days. After removal of
the solvent, the residue was subjected to WCC (SiO2/CHCl3) and DCC
(SiO2/CHCl3) to give a fraction containing 3, which was further purified
by HPLC to give 3 (1.22 g, 21% yield). 3: colorless solids; mp 218-
219 °C;1H NMR (500 MHz, CDCl3, 27 °C) δ 1.12 (s, 9H), 1.19 (s,
9H), 1.23 (s, 9H), 3.42, (s, 3H), 3.77 (s, 3H), 6.60 (br s, 1H), 6.77 (d,
1H, J ) 8.5 Hz), 6.86 (d, 1H, J ) 1.9 Hz), 6.93 (d, 1H, J ) 8.5 Hz),
7.00 (d, 1H, J ) 8.5 Hz), 7.14 (br s, 1H), 7.21 (br d, 1H, J ) 8.4 Hz),
7.27 (dd, 1H, J ) 8.4, 2.2 Hz), 7.27 (d, 1H, JPH ) 624 Hz), 7.40 (d,
1H, J ) 8.4 Hz); 13C{1H} NMR (125 MHz, CDCl3, 27 °C) δ 31.35
(s), 31.41 (s), 31.56 (s), 34.02 (s), 34.35 (s), 34.39 (s), 55.19 (s), 56.04
(s), 56.77 (d, JPC ) 77 Hz), 110.44 (s), 111.92 (d, JPC ) 9.0 Hz), 112.28
(s), 125.08 (s), 125.13 (s), 125.17 (s), 125.38 (s), 125.80 (d, JPC ) 5.1
1
on a JEOL EXcalibur270 spectrometer. All H and 31P NMR spectra
were recorded in CDCl3 unless otherwise mentioned. Chemical shifts
are reported in parts per million, downfield positive, and relative to
tetramethylsilane for 1H NMR or 85% H3PO4 for 31P NMR. High-
pressure liquid chromatography (HPLC) was performed by LC-918 and
LC-908 C60 with JAIGEL 1H+2H columns (Japan Analytical Industry)
with chloroform as solvent. Elemental analyses were performed by the
Microanalytical Laboratory of Department of Chemistry, Faculty of
Science, the University of Tokyo.
Preparation of 5,5′,5′′-Tri-tert-butyl-2,2′,2′′-trimethoxytriphenyl-
methanol (4). To Mg turnings (1.01 g, 41.5 mmol) was added a solution
of 2-bromo-4-tert-butylanisole (10.1 g, 41.5 mmol) in THF (10 mL),
and the mixture was refluxed for 4 h. To the mixture was added a
solution of diethyl carbonate (1.5 mL, 13 mmol) in THF (5 mL), and
the mixture was refluxed overnight. The mixture was treated with H2O
and extracted with CHCl3. The extracts were dried over anhydrous
MgSO4. After removal of the solvent, the residue was recrystallized
from hexane to give 4 (6.44 g, 99% yield). 4: colorless crystals; mp
113-115 °C;1H NMR (270 MHz, CDCl3) δ 1.20 (s, 27H), 3.45 (s,
9H), 5.49 (s, 1H), 6.76 (d, 3H, J ) 8.4 Hz), 7.18-7.23 (m, 6H);13C-
{1H} NMR (125 MHz, CDCl3, 27 °C) δ 31.28 (s), 34.10 (s), 55.44 (s),
81.19 (s), 111.22 (s), 124.19 (s), 127.49 (s), 132.64 (s), 142.06 (s),
155.17 (s). Anal. Calcd for C34H46O4: C, 78.72; H, 8.94. Found: C,
78.43; H, 8.92.
Hz), 126.17 (s), 126.54 (s), 127.51 (d, JPC ) 8.3 Hz), 129.39 (d, JPC
)
6.6 Hz), 142.49 (s), 144.18 (s), 145.00(s), 152.57 (d, JPC ) 5.6 Hz),
154.55 (d, JPC ) 6.4 Hz), 155.41 (d, JPC ) 3.6 Hz); 31P NMR (109
MHz, CDCl3, 27 °C) δ 58.1; HRMS (EI 70 eV) m/z 534.2930, calcd
for C33H43O4P 534.2899. Anal. Calcd for C33H43O4P: C, 74.13; H, 8.11.
Found: C, 74.05; H, 8.04.
Reaction of Cyclic Phosphinate 3 with Iodotrimethylsilane. To
a solution of cyclic phosphinate 3 (34.9 mg, 0.0653 mmol) in CDCl3
(0.5 mL) in a 5-mm-diameter Pyrex glass tube was added iodotrim-
ethylsilane (0.02 mL, 0.16 mmol). The solution was allowed to stand
at room temperature, and the reaction was monitored by 31P NMR.
After 22 h, a signal was observed at δ ) 190 by 31P NMR and elemental
sulfur (17.2 mg, 0.536 mmol) was added to the reaction mixture. After
removal of the solvent under reduced pressure, the crude products were
subjected to HPLC to give phosphonothioate 13 (8.9 mg, 26%). 13:
1H NMR (270 MHz, CDCl3, 27 °C) δ 1.25 (s, 18H), 1.26 (s, 9H), 3.44
(s, 3H),6.85 (d, 1H, J ) 8.4 Hz), 6.96 (d, 2H, J ) 8.4 Hz), 7.18-7.40
(5) Kobayashi, J.; Goto, K.; Kawashima, T. J. Am. Chem. Soc. 2001, 123,
3387-3388.
(6) (a) Sorm, F.; Bera´nek, J. Collect. Czech. Chem. Commun. 1954, 19, 298-
303. (b) Newkome, G. R.; Moorefield, C. N.; Theriot, K. J. J. Org. Chem.
1988, 53, 5552-5554. (c) Bakshi, P. K.; James, M. A.; Cameron, T. S.;
Knop, O. Can. J. Chem. 1996, 74, 559-573. (d) Bakshi, P. K.; Linden,
A.; Vincent, B. R.; Roe, S. P.; Adhikesavalu, D.; Cameron, T. S.; Knop,
O. Can. J. Chem. 1994, 72, 1273-1293. (e) Knop, O.; Cameron, T. S.;
Bakshi, P. K.; Linden, A.; Roe, S. P. Can. J. Chem. 1994, 72, 1870-
1881.
(7) Kursanov, D. N.; Parnes, Z. N.; Loim, N. M. Synthesis 1974, 633-651.
9
3704 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002

5-Carbaphosphatranes
A R T I C L E S
(m, 6H);31P NMR (109 MHz, CDCl3, 27 °C) δ 126.9; LRMS (FAB 70
eV) m/z 535, calcd for C32H40O3PS 535.
Table 1. Crystallographic Data for 1
formula
temperature (K)
crystal system
space group
a (Å)
C34H37O3P
123
monoclinic
P21/c
15.9630(10)
11.2780(10)
15.2690(10)
93.842(4)
2742.7(3)
4
1.183
16 713
5236
0.021
1048.00
1.059
R1 ) 0.0571
wR2 ) 0.1453
Synthesis of 1-Hydro-5-carbaphosphatrane 1 (Method A). To a
solution of phosphinic acid 6 (55.1 mg, 0.0971 mmol) in CDCl3 (0.5
mL) in a 5-mm-diameter Pyrex glass tube was added iodotrimethylsilane
(0.07 mL, 0.50 mmol). The solution was allowed to stand at room
temperature for 1 week. After removal of the solvent under reduced
pressure, the crude products were subjected to HPLC to afford 1 (17.9
mg, 38%), which was further purified by recrystallization from CHCl3/
b (Å)
c (Å)
â (deg)
V (Å3)
Z
1
calculated density (g cm-3
reflection collected
unique
)
EtOH. 1: colorless crystals; mp 272-274 °C; H NMR (500 MHz,
CDCl3, 27 °C) δ 1.32 (s, 27H), 6.76 (d, 1H, JPH ) 852 Hz), 6.95 (d,
3H, J ) 8.4 Hz), 7.14 (dd, 3H, J ) 8.4, 2.1 Hz), 7.88 (br d, 3H, J )
0.8 Hz); 13C{1H} NMR (125 MHz, CDCl3, 27 °C) δ 31.52 (s), 34.47
(s), 39.21 (d, JPC ) 125 Hz), 112.41 (d, JPC ) 10.3 Hz), 122.20 (d, JPC
) 22.3 Hz), 124.59 (s), 131.95 (d, JPC ) 13.3 Hz), 146.39 (s), 149.71-
(s); 31P NMR (109 MHz, CDCl3, 27 °C) δ 2.7; HRMS (EI 70 eV) m/z
488.2491, calcd for C31H37O3P 488.2480. Anal. Calcd for C31H37O3P:
C, 76.20; H, 7.63. Found: C, 76.48; H, 7.61.
Rint
F000
goodness of fit (F)
R indices (I > 2σ(I))
tional.11 Most structural optimizations were performed with the 6-
31G(d) basis set.12 For the study of transannular bonding, improved
structures were obtained using a basis set containing triple-ú quality
sets and two sets of d orbitals on the hypervalent center but only one
d on the other heavy atoms, which is termed 6-311G(2d,d).13 All
calculations used Cartesian Gaussians rather than spherical harmonics.
Bond orders were computed using Mayer’s RHF formula14 with the
MP2 density matrix. MP2 Raman intensities were computed by a finite
difference technique.15 A vibrational decomposition due to Boatz and
Gordon16 was used for normal-mode analysis and force constant
extraction, using Pulay’s natural internal coordinates,17 which include
the transannular bond as an individual symmetry-adapted coordinate.
Additional bonding comparisons were made using RHF localized
orbitals18 and Mulliken population analysis.19 Most calculations were
performed using the parallel computing procedures20 contained in the
GAMESS program,21 except the B3LYP computations which were
made using GAUSSIAN98.22
Synthesis of 1-Hydro-5-carbaphosphatrane 1 (Method B). To a
solution of cyclic phosphinate 3 (1.18 g, 2.21 mmol) in CHCl3 (50
mL) was added a solution of boron tribromide (1.0 M in CH2Cl2, 10
mL, 10 mmol). The solution was stirred at room temperature for 60 h,
treated with aqueous NaHCO3, and extracted with CHCl3. The extracts
were dried over anhydrous MgSO4. After removal of the solvent under
reduced pressure, the crude products were subjected to HPLC to afford
1, which was further purified by reprecipitation from CHCl3/EtOH and
obtained as colorless crystals (0.58 g, 54%).
Synthesis of 1-Methyl-5-carbaphosphatrane (2). To a solution of
cyclic phosphinate 3 (31.2 mg, 0.0584 mmol) in CDCl3 (0.5 mL) in a
5-mm-diameter Pyrex glass tube was added iodotrimethylsilane (0.05
mL, 0.35 mmol). After a few freeze-pump-thaw cycles, the tube was
sealed in vacuo and the solution was heated at 80 °C for 63 h. After
confirmation of disappearance of 3 by 31P NMR, the sealed tube was
opened and the solvent was removed under reduced pressure. The crude
products were separated by HPLC to afford 2 (8.5 mg, 29%). 2:
colorless crystals; mp 187-190 °C; 1H NMR (500 MHz, CDCl3, TMS,
27 °C) δ 1.32 (s, 27H), 1.66 (d, 3H, JPH ) 18.3 Hz), 6.89 (d, 3H, J )
8.4 Hz), 7.11 (dd, 3H, J ) 8.4, 2.2 Hz), 7.86 (br s, 3H); 13C{1H} NMR
(125 MHz, CDCl3, 27 °C) δ 20.26 (d, JPC ) 215 Hz), 31.54 (s), 34.43
(s), 40.08 (d, JPC ) 133 Hz), 111.92 (d, JPC ) 9.9 Hz), 121.96 (d, JPC
) 22.1 Hz), 124.38 (s), 132.54 (d, JPC ) 12.5 Hz), 145.78 (s), 149.49
(d, JPC ) 4.1 Hz); 31P NMR (109 MHz, CDCl3, 27 °C) δ 21.1; HRMS
(EI 70 eV) m/z 502.2637, calcd for C32H39O3P 502.2606.
(11) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. ReV. 1988, B37, 785-789.
(12) (a) For H, C, N, O, and F: Hariharan, P. C.; Pople, J. A. Theor. Chim.
Acta 1973, 28, 213-222. (b) For Si: Gordon, M. S. Chem. Phys. Lett.
1980, 76, 163-168. (c) For P and S: Francl, M. M.; Pietro, W. J.; Hehre,
W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem.
Phys. 1982, 77, 3654-3665.
(13) (a) For H, C, N, O, and F: Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople,
J. A. J. Chem. Phys. 1980, 72, 650-654. (b) For Si, P, and S: neutral
atom sets of McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72,
5639-5648. (c) Multiple polarization sets follow: Frisch, M. J.; Pople, J.
A.; Binkley, J. S. J. Chem. Phys. 1984, 80, 3265-3269. The 2d exponents
are Si ) 0.225 and 0.90 and P ) 0.275 and 1.00.
X-ray Studies. Single crystals of 1 were grown from their benzene
solution. The intensity data were collected at 123 K on a MAC Science
DIP-2030 imaging plate area detector with Mo KR radiation (λ )
0.710 69 Å). Reflection data were corrected for Lorentz and polarization
factors and for absorption using the multiscan method. Crystallographic
and experimental data are listed in Table 1. The structures were solved
by the direct method (SIR97) and refined by full-matrix least squares
on F2 (SHELXL-97).8 The non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms without the hydrogen directly bonding to
phosphorus atom were idealized by using the riding model.
(14) Mayer, I. Chem. Phys. Lett. 1983, 97, 270-274.
(15) Komornicki, A.; McIver, J. W., Jr. J. Chem. Phys. 1979, 70, 2014-2016.
(16) Boatz, J. A.; Gordon, M. S. J. Phys. Chem. 1989, 93, 1819-1826.
(17) Fogarasi, G.; Zhou, X.; Taylor, P. W.; Pulay, P. J. Am. Chem. Soc. 1992,
114, 8191-8201.
(18) Edminston, C.; Ruedenberg, K. ReV. Mod. Phys. 1963, 35, 457-465.
(19) Mulliken, R. S. J. Chem. Phys. 1955, 23, 1833-1840.
(20) Fletcher, G. D.; Schmidt, M. W.; Bode, B. M.; Gordon, M. S. Comput.
Phys. Commun. 2000, 128, 190-200.
(21) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M.
S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S.; Windus,
T. L.; Dupuis, M.; Montgomery, J. A. J. Comput. Chem. 1993, 14, 1347-
1363.
Calculational Method. To understand bonding and assist in the
identification of structures, a variety of calculational methods were
used: closed-shell SCF (RHF),9 second-order Møller-Plesset perturba-
tion (MP2),10 and density functional theory using the B3LYP func-
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.;
Cammmi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski,
J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. Gaussian98; Gaussian, Inc.; Pittsburgh, PA,
1998.
(8) Sheldrick, G. M. SHELXL 97. Program for crystal structure refinement,
University of Go¨ttingen 1997.
(9) Roothaan, C. C. J. ReV. Mod. Phys. 1951, 23, 69-89.
(10) (a) Pople, J. A.; Binkley, J. S.; Seeger, R. Int. J. Quantum Chem. 1976,
S10, 1-19. (b) Fletcher, G. D.; Schmidt, M. W.; Gordon, M. S. AdV. Chem.
Phys. 1999, 110, 267-294.
9
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A R T I C L E S
Kobayashi et al.
Scheme 1 a
compound was converted to phosphonothioate 13 (δP 126) by
addition of elemental sulfur. A possible mechanism for the
formation of 5-carbaphosphatranes is shown in Scheme 2. The
reaction of iodotrimethylsilane with cyclic phosphonite 8, which
is a tautomer of cyclic phosphinate 3, affords silyl phosphonite
9 with generation of hydrogen iodide. However, these species
were not observed by 31P NMR. This is probably because
phosphonium salt 10 is formed by the protonation of silyl
phosphonite 9 with hydrogen iodide. The demethylation process
proceeds via the attack of iodide anion on the methyl group of
phosphonium salt 10. The intermediate 12, which was observed
by 31P NMR (δP 190) during the reaction, is formed by the
reductive elimination of trimethylsilanol from phosphorane 11.
The phosphonium salts 14a and 14b were formed by the reaction
of cyclic phosphonite 12 with hydrogen iodide or methyl iodide
in a way similar to the phosphonium salt 10. In the case of
phosphonium salts 14a and 14b, the demethylation reaction is
considered to proceed similarly to afford 5-carbaphosphatranes
1 and 2, respectively.
a Conditions: (a) n-BuLi; (b) PCl3, room temperature, then H2O, 11%
(two steps); (c) PCl3, 50 °C, then H2O, 38% (two steps); (d) TMSI, room
temperature, 38%; (e) TMSI, room temperature, 39%; (f) BBr3, room
temperature, then aqueous NaHCO3, 54%; (g) TMSI, 80 °C, in a sealed
tube, 29%.
Results and Discussion
Synthesis. Scheme 1 outlines the synthetic pathways for
5-carbaphosphatranes. A triarylmethyl group was employed for
the synthesis of 5-carbaphosphatranes for the following rea-
sons: (a) it can be easily synthesized from an aryl halide and
diethyl carbonate; (b) it has a rigid structure and so is suitable
for the multidentate ligand which suppresses pseudorotation.
Triarylmethane 5 was prepared according to the typical proce-
dure. Lithiation of 5 followed by reaction with phosphorus
trichloride at room temperature afforded phosphinic acid 6 after
hydrolysis. When the reaction was effected at 50 °C, the cyclic
phosphinate 3 was obtained as a result of intramolecular
cyclization with loss of chloromethane and hydrolysis.23 1-Hy-
dro-5-carbaphosphatrane (1) was synthesized by treatment of 3
or 6 with iodotrimethylsilane at room temperature in CDCl3.24
On the other hand, when the reaction of 3 with iodotrimethyl-
silane was carried out at 80 °C in a sealed tube, 1-methyl-5-
carbaphosphatrane (2) was obtained instead of 1. Compound 1
was also obtained by the reaction of 3 with boron tribromide in
CHCl3. It was reported that the tribenzophosphatrane 7 bearing
Structure. The structure of 1 was definitively determined
by X-ray crystallographic analysis. Single crystals of 1 were
grown by the slow evaporation of a saturated benzene solution
at room temperature. The side and top views of 1 are shown in
Figure 1. It is clearly shown that 1 has a nearly ideal trigonal
bipyramidal structure around the central phosphorus atom. The
apical positions are occupied by hydrogen and carbon atoms
while three oxygen atoms are located at the equatorial positions,
indicating that 1 is a 10-P-5 phosphorane in the perfectly “anti-
apicophilic” arrangement.27 Selected bond lengths and angles
are summarized in Table 2. The sum of bond angles between
equatorial bonds is 359.7°, while the bond angle between apical
bonds and those between apical and equatorial bonds are 178.7-
(9)° and 87.2(9)-91.99(9)°, respectively. These parameters
indicate the trigonal bipyramidal geometry around the central
phosphorus atom. The P-H and P-O bond lengths are 1.38(2)
and 1.648(2)-1.649(2) Å, respectively, which are typical lengths
for P-H and P-O bonds. On the other hand, the P-C bond
length is 1.921(2) Å, slightly longer than the typical value for
the apical P-C bond of a phosphorane.28 Such an elongation is
attributable to the rigidity of the tetradentate ligand based on
a 5-nitrogen atom is observable by NMR spectroscopy in
solution but too fragile to be isolated.25 In contrast, 1 was
obtained as stable crystals, showing the difference between a
phosphatrane with an NfP dative bond and that with a C-P
covalent bond.
(23) For a similar reaction, see: Yoshifuji, M.; Nakazawa, M.; Sato, T.; Toyota,
K. Tetrahedron 2000, 56, 43-55.
(24) For a demethylation reaction of anisole derivatives with iodotrimethylsilane,
see: Jung, M. E.; Lyster, M. A. J. Org. Chem. 1977, 42, 3761-3764.
(25) Mu¨ller, E.; Bu¨rgi, H.-B. HelV. Chim. Acta 1987, 70, 1063-1069.
(26) Gorenstein, D. S. Prog. NMR Spectrosc. 1983, 16, 1-98.
(27) Holmes, R. R. Pentacoordinated Phosphorus: Structure and Spectroscopy;
ACS Monographs 175 and 176; American Chemical Society: Washington,
DC, 1980; Vols. I, II.
Reaction Mechanism. When the reaction of 3 with iodo-
trimethylsilane was carried out in CDCl3 and the reaction was
monitored by 31P NMR, a compound giving a signal at 190
ppm was observed as an intermediate. This compound is
considered to be the cyclic phosphonite 12, because the chemical
shift is a reasonable value for a cyclic phosphonite26 and this
(28) (a) Timosheva, N. V.; Chandrasekaran, A.; Prakasha, T. K.; Day, R. O.;
Holmes, R. R. Inorg. Chem. 1996, 35, 6552-6560. (b) Timosheva, N. V.;
Prakasha, T. K.; Chandrasekaran, A.; Day, R. O.; Holmes, R. R. Inorg.
Chem. 1995, 34, 4525-4526.
9
3706 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002

5-Carbaphosphatranes
A R T I C L E S
Scheme 2. Possible Mechanism for the Formation of 5-Carbaphosphatranes 1 and 2
the triarylmethyl unit, as discussed in the literature for triben-
zosilatranes.29
NMR Spectra. In the 31P NMR spectra, 5-carbaphosphatranes
1 and 2 showed signals at 2.7 and 21.1 ppm, respectively. The
13C NMR signals for the central carbon of the triarylmethyl
ligand of 1 and 2 were observed at 39.2 and 40.8 ppm,
respectively, which are high-field shifted by ∼20 ppm from
phosphinic acid 6 (62.0 ppm). These observations can be
explained by assuming that the carbon atom located at the apical
position is shielded due to the electronic property of the three-
center four-electron apical bond.30 In the 1H NMR spectrum of
1, the aromatic protons at positions ortho to the central carbon
atom (δ 7.88) showed a low-field shift by ∼1.5 ppm from the
usual position. Such a low-field shift of the ortho protons was
also reported for tribenzo-1-hydrophosphatrane 7 (δ 8.49) and
boratrane 15 (δ 8.10-7.80),31 suggesting a structural similarity
between 5-carbaphosphatrane 1 and the usual phosphatrane 7
and boratrane 15. The rest of the aromatic protons of 1 were
observed in the usual region (6.95, 7.14 ppm).
The 1JPH value of 1 and the 1JPC(P-CH3) value of 2 are 852
and 215 Hz, respectively, which are extraordinarily large for
(29) Boer, F. P.; Turley, J. W.; Flynn, J. J. J. Am. Chem. Soc. 1968, 90, 5102-
5105.
(30) Cahill, P. A.; Dykstra, C. E.; Martin, J. C. J. Am. Chem. Soc. 1985, 107,
6359-6362.
Figure 1. Ortep drawings of 1 with thermal ellipsoid plot (50% probability).
(31) Paz-Sandoval, M. A.; Ferna´ndez-Vincent, C.; Uribe, G.; Contreras, R.;
Klae´be´, A. Polyhedron 1988, 7, 679-684.
(A) Side view; (B) top view.
9
J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002 3707

A R T I C L E S
Kobayashi et al.
7 (1JPH ) 853 Hz) and 16 (1JPH ) 791 Hz).36 Although there is
a difference that 1 is a neutral compound and 7 and 16 are ionic,
these results indicate that the spectroscopic properties of 1 are
more similar to those of the usual phosphatranes than to those
of known neutral phosphoranes. It was reported that, in some
phosphoranes such as 20 and 21, where all the equatorial
positions are occupied by oxygen and nitrogen atoms, the apical
P-C coupling constants are as large as 117-128 Hz.37 These
reports associated with the results given in Table 3 suggest that
anomalously large apical coupling constants are one of the
characteristics of pentacoordinate phosphorus compounds where
all the equatorial positions are occupied by electronegative
atoms.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1
P(1)-H(1)
P(1)-C(1)
P(1)-O(1)
P(1)-O(2)
P(1)-O(3)
1.38(2)
H(1)-P(1)-O(1)
H(1)-P(1)-O(2)
H(1)-P(1)-O(3)
O(1)-P(1)-O(2)
O(1)-P(1)-O(3)
O(2)-P(1)-O(3)
87.2(9)
88.0(9)
89.4(9)
118.14(9)
121.96(9)
119.62(9)
1.921(2)
1.649(2)
1.649(2)
1.648(2)
H(1)-P(1)-C(1)
O(1)-P(1)-C(1)
O(2)-P(1)-C(1)
O(3)-P(1)-C(1)
178.7(9)
91.65(9)
91.99(9)
91.69(9)
1
1
Table 3. Coupling Constants (Hz), JPH and JPC of
Carbaphosphatranes 1 and 2, Phosphatranes 16 and 7, and
Related Compounds 17-21
1
16
7
17
18
2
19
20
21
Vibrational Spectrum. IR and Raman spectra of 5-carba-
phosphatrane 1 are shown in Figures 2 and 3, respectively.
Although the infrared P-H stretching frequencies for hydro-
1JPH 852 791 853 266 733
1JPC 125
215
116
125 122
(P-CH3) (P-CH2)
133
phosphoranes usually fall in the range 2360-2430 cm-1 38
, lower
P-H stretching frequencies were reported for the phosphoranes
bearing an apical P-H bond (2240 and 2286 cm-1 for 16, 2250
cm-1 for 17). However, the P-H frequency of 1 was observed
at 2377 cm-1, falling in the usual range and higher than those
of the P-H apical phosphoranes.
(P-CAr3)
the apical P-H and P-C coupling constants of phosphoranes
(Table 3). It is well known that the coupling constants are
dominated by the s character of each bond, increasing as the s
character increases.32 It is widely recognized that the coupling
constant of an apical bond of a phosphorane is smaller than
that of an equatorial bond since the apical bond is a three-center
four-electron bond formed from the p orbital of a phosphorus
Matching a RHF/6-31G(d) theoretical vibrational spectrum
of a model compound of 1, where tert-butyl groups are replaced
by hydrogens, to the observed IR and Raman spectra of 1
permits an assignment of the 888-cm-1 band to the PC stretch.
The observed intense IR bands at 888, 820, and 787 cm-1
(which has a distinct shoulder) can be matched to intense
computed IR modes at 980 (a1) and 932 (e) cm-1, and two close
values 871 and 855 cm-1 (both e). The ratio of experimental to
RHF values is close to 0.89 in all cases, the recommended value
for the scaling factor for RHF frequencies. Examination of the
computed 980-cm-1 normal mode shows it is a PC stretch with
some PO3 umbrella motion. A very strong calculated Raman
intensity for an a1 mode at 746 cm-1 corresponds to the observed
691-cm-1 Raman line.
atom.33 Indeed, the JPH value of phosphorane 17 bearing an
1
Comparison of Bonding to Other Atranes. Since 5-carba-
phosphatranes are isoelectronic to phosphatranes and silatranes
bearing a 5-nitrogen atom, it is of interest to compare the
transannular bonding in these species. Ideally one would like
to know the energy associated with formation of each transan-
nular bond. However, a direct computation of this bond energy
is impossible, as separation of the base atom from the central
atom also requires breaking bonds in the three side chains.
apical hydrogen is much smaller than that of phosphorane 18
bearing an equatorial hydrogen.34 Similarly the apical 1JPC value
of a usual phosphorane is also smaller than that for an equatorial
Thus, the force constant for the transannular stretch would
seem to be the most accessible measure of these bond strengths.
These values can be readily extracted from theoretical force
fields, provided a level of computation of sufficient accuracy
can be reached. This means the method chosen must be capable
of reproducing not just the bond’s distance but also its potential
energy surface for stretching. Experimental structural and
vibrational information is available for silatranes, and this can
be used to calibrate the theoretical methods used. The calcula-
tions reported below use alkyl side groups, rather than benzene
rings, for C3 symmetry atranes.
1
P-C bond. However, the JPH value of 1, where the hydrogen
atom is located at the apical position, is much larger than that
of the equatorial P-H bond of phosphorane 18 (1JPH ) 733
1
Hz). The JPC(P-CH3) value of 2 is also larger than that of
phosphorane 19 (1JPC(P-CH2) ) 116 Hz) bearing an equatorial
1
P-C bond.35 The JPC(P-CAr3) values of 1 (125 Hz) and 2
(133 Hz) are smaller than the 1JPC(P-CH3) value of 2, but still
larger than the usual apical P-C coupling constants. On the
other hand, the 1JPH value of 1 is similar to those of phosphatrane
(32) Jameson, C. J. In Multinuclear NMR; Mason, J., Ed.; Plenum: New York,
1987; Chapter 4.
(36) Clardy, J. C.; Milbrath, D. S.; Springer, J. P.; Verkade, J. G. J. Am. Chem.
Soc. 1976, 98, 623-624.
(33) Akiba, K.-y. In Chemistry of HyperValent Compounds; Akiba, K.-y., Ed.;
John Wiley & Sons: New York, 1999; Chapter 1.
(37) Francke, R.; Sheldrick, W. S.; Ro¨schenthaler, G.-V. Chem. Ber. 1989, 122,
301-306.
(34) Ross, M. R.; Martin, J. C. J. Am. Chem. Soc. 1981, 103, 1234-1235.
(35) Kojima, S.; Kajiyama, K.; Nakamoto, M.; Akiba, K.-y. J. Am. Chem. Soc.
1996, 118, 12866-12867.
(38) Brazier, J. F.; Houalla, D.; Loenig, M.; Wolf, R. Top. Phosphorus Chem.
1976, 8, 99-192.
9
3708 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002

5-Carbaphosphatranes
A R T I C L E S
Figure 2. IR spectrum of 1-hydro-5-carbaphosphatrane (1).
Figure 3. Raman spectrum of 1-hydro-5-carbaphosphatrane (1).
Theoretical Calculation of Transannular Bond Distance
of Alkyl Atranes. An early surprise in silatrane chemistry was
the recognition that the Si-N bond distance was not only
capable of varying over the range 2.02-2.18 Å for halogen,
OR, or R substituents in X-ray studies,2e it also changes
according to the state of the compound. Thus, the X-ray distance
for methylsilatrane of 2.18 Å39 is considerably shorter than the
gas-phase value of 2.45 Å.40 Later experiments showed the same
behavior for fluorosilatrane, with an X-ray structure of 2.04 Å41
compared to 2.32 Å in the gas phase.42 An NMR and IR study
suggested that Si-N distances take on intermediate values in
solution.43 Recent X-ray experiments have further broadened
the range of known Si-N distances: two very short values are
2.01 Å for SCN substitution,44 2.01 Å for an OR ligand
containing cobalt,45 and an extremely long 3.00 Å for an osmium
substituent.46 This wide range is indicative of only a weak Si-N
bond, with a low force constant.
Of course, a number of theoretical studies have attempted to
reproduce and therefore understand this wide range of silatrane
distances. A large number of substituted silatranes and phos-
phatranes were previously considered by us at the RHF/6-31G-
(d) level, but no comparisons between these two families of
atrane were made.47 However, this level of computation gave
silatrane bond distances ∼0.25 Å longer than the two available
gas-phase structures. Probe calculations were reported indicating
that the structures were sensitive both to the basis set and to
the inclusion of electron correlation. Our earlier study included
pertinent references to prior calculations, but new theoretical
(39) Parkanyi, L.; Bihatsi, L.; Hencsei, P. Cryst. Struct. Commun. 1978, 7, 435-
440.
(44) Narula, S. P.; Shankar, R.; Kumar, M.; Chadha, R. K.; Janaik, C. Inorg.
Chem. 1997, 36, 1268-1273.
(40) Shen, Q.; Hilderbrandt, R. L. J. Mol. Struct. 1980, 64, 257-262.
(41) Parkanyi, L.; Hencsei, P.; Bihatsi, L.; Mu¨ller, T. J. Organomet. Chem. 1984,
269, 1-9.
(45) Kim, M. W.; Uh, D. S.; Kim, S.; Do, Y. Inorg. Chem. 1993, 32, 5883-
5885.
(46) Attar-Bashi, M. T.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J.;
Woodgate, S. D. Organometallics 1998, 17, 504-506.
(47) (a) Schmidt, M. W.; Windus, T. L.; Gordon, M. S. J. Am. Chem. Soc.
1995, 117, 7480-7486. (b) Windus, T. L.; Schmidt, M. W.; Gordon, M.
S. J. Am. Chem. Soc. 1994, 116, 11449-11455.
(42) Forgacs, G.; Kolonits, M.; Hargittai, I. Struct. Chem. 1990, 1, 245-250.
(43) Pestunovich, V. A.; Shterenberg, B. Z.; Lippmaa, E. T.; Magi, M. Ya.;
Alla, M.; Tandura, S.; Baryshok, V. P.; Petukhov, L. P.; Voronkov, M. G.
Doklady Phys. Chem. (Engl. Transl.) 1981, 258, 587-590.
9
J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002 3709

A R T I C L E S
Kobayashi et al.
Table 4. Computed Atrane Structures (in Å)a
I
II
III
IV
R ) F
R) Me
R ) H
R) H
R) H
R) R′ ) H
1.940
RHF/6-31G(d)
RHF/6-311G(2d,d)
MP2/6-31G(d)
MP2/6-311G(2d,d)
B3LYP/6-31G(d)
B3LYP/6-311G(2d,d)
ED experiment
2.534
2.572
2.269
2.300
2.424
2.484
2.324d
2.042d
2.734
2.771
2.384
2.443
2.642
2.719
2.45c
2.648
2.690
2.302
2.327
2.475
2.576
2.444
2.463
2.110
2.122
2.188
2.219
1.902
1.900
1.907
1.902
1.928
1.927
1.951
1.958
X-ray experiment
2.175e
2.146f
1.986g
1.921h
a Computed values with the 6-31G(d) basis differ slightly from ref 46e due to use of a different 6-31G(d) basis set for Si. b Reference 42. c Reference 40.
d Reference 41. e Reference 39. f Reference 52. g Reference 36. h Present work; the experiment is for R′ ) t-Bu.
reports have appeared since.48 One of these48c contains a first
attempt to provide a theoretical force field for four silatranes,
but the results given focus on zero point energies and skeleton
modes. Most importantly, Anglada and co-workers demonstrated
that full MP2/6-31G(d) geometry optimization on methylsila-
trane gave a Si-N distance of 2.40 Å,48e in good agreement
with the gas-phase value 2.45 ( 0.05 Å, although B3LYP/6-
31G(d) does not (2.69 Å). The present work will show that MP2
computations also give a similar good result for the gas-phase
geometry of fluorosilatrane and, furthermore, that this level of
theory is in good agreement with the available vibrational
experiments on the parent silatrane.
Table 4 compares computed transannular distances for various
theoretical methods using two basis sets. As Anglada and co-
workers showed, MP2/6-31G(d) gives good results for meth-
ylsilatrane, and the present calculation for fluorosilatrane is
similar. Both MP2/6-31G(d) results are ∼0.06 Å shorter than
the gas-phase structures, which is a marked improvement over
the 0.25-Å elongation from RHF/6-31G(d). Improvements in
the basis set lead to MP2/6-311G(2d,d) values that are in
essentially perfect agreement with experiment. Note that B3LYP,
which is the only DFT functional that was considered, gives
results shorter than RHF but deteriorates considerably with basis
set improvement.
Unfortunately, there is no experimental data regarding the
gas-phase structure of the phosphatrane cation II (R ) H), but
the MP2 results indicate some fraction of the difference between
solid and gas phase observed in silatrane persists in this
compound. Again, the RHF and B3LYP values seem too long.
For 5-carbaphosphatrane, all methods give very similar bond
distances, and improving the basis does not change the result.
Furthermore, the computations for IV (R ) R′ ) H) are in good
agreement with the present solid-state experimental PC bond
distance of 1, hinting that the transannular bond in 5-carba-
phosphatrane possesses a steeper potential well than silatrane
or phosphatrane.
From Table 4, it is clear that MP2/6-31G(d) is the minimal
level of theory needed to obtain reasonable structures for the
simple atranes I-III. Accordingly, this method is used to obtain
vibrational frequencies for these simple atranes, to allow
comparison of their transannular stretching force constants. For
subsequent calculations on 5-carbaphosphatranes and related
species, which include the three benzene rings, it appears that
the RHF/6-31G(d) method will give acceptable results in much
shorter computer time.
Vibrational Analysis. Several experimental studies of the
vibrational spectroscopy of parent and substituted silatranes have
been conducted.49 Early experiments often used samples in KBr
pellets (which absorb below ∼400 cm-1), which complicated
their assignments, but modes in the range 540-590 cm-1 are
now considered to be skeletal breathing rather than transannular
stretches.2b Lukevits and co-workers assigned a mode in the
range 320-390 cm-1 to the transannular stretch in various
organic silatranes.49c Two experiments have been carried out
on the polycrystalline parent I (R ) H). A Raman spectrum
and its associated force field calculation missed the transannular
stretch due to its low Raman intensity.49e An IR and Raman
study observed an intense IR transition (with low Raman
intensity) at 313 cm-1 but did not assign this or any other band
to the transannular stretch.49g
Table 5 compares the theoretical MP2/6-31G(d) spectrum
with the experimental data.49g After reordering the three
computed bands near 610 cm-1, there is a clear match in the
intensity patterns for all bands shown. The calculated 267-cm-1
mode corresponds to the strong IR absorption observed at 313
cm-1. A vibrational decomposition analysis shows that the Si-N
stretch coordinate is 62% of this mode. A large IR intensity is
to be expected, as the dipole moment of silatranes is known to
undergo a large change with the Si-N distance, which is
responsible for the shortening of the Si-N distance in the solid
state.47a Bearing in mind that the experiment is carried out on
a solid sample, where the Si-N bond should be slightly
stronger,49g there is good agreement between the computed
Si-N stretching frequency and experiment.
Comparisons of Bonding Characteristics. Because of the
reasonable match between the experimental and computed MP2/
(49) (a) Egorov, Yu. P.; Voronkov, M. G.; Lutsenko, T. B.; Zelchan, G. Chem.
Heterocycl. Compd. (Engl. Transl.) 1966, 2, 17-24. (b) Voronkov, M. G.;
Brodskaya, E. I.; Reich, P.; Shevchenko, S. G.; Baryshok, V. P.; Frolov,
Yu. L. Doklady Phys. Chem. (Engl. Transl.) 1979, 241, 723-726. (c)
Birgele, I. S.; Mazeika, I.; Liepin’s, E.; Lukevics, E. J. General Chem.
USSR (Engl. Transl.) 1980, 50, 711-714. (d) Voronkov, M. G.; Shevchen-
ko, S. G.; Brodksaya, E. I.; Baryshok, V. P.; Reich, P. Kunath, D.; Frolov,
Yu. L. IzV. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk 1981, 135-143.
(e) Imbenotte, M.; Palavit, G.; Legrand, P. J. Raman Spectrosc. 1983, 14,
135-137. (f) Imbenotte, M.; Palavit, G.; Legrand, P.; Huvenne, J. P.; Fleury,
G. J. Mol. Spectrosc. 1983, 102, 40-55. (g) Ignat’ev, I. S.; Lazarev, A.
N.; Shevchenko, S. G.; Baryshok, V. P. Bull. Acad. Sci. USSR, Chem. Sci.
(Engl. Transl.) 1987, 1375-1381. (h) Wen, Z.; Jia, L.; Lu, K.; Wu, G.
Guangpuxue Yu Guangpu Fenxi 1988, 8, 15-19. (i) Hencsei, P.; Ambrus,
L.; Farkas, R.; Morvai, L.; Szakacs, L.; Gal, M. Acta Chim. Hung. 1989,
126, 145-148. (j) Voronkov, M. G.; Brodskaya, E. I.; Udodov, Yu. N.;
Sapozhnikov, Yu. M.; Baryshok, V. P. Doklady Phys. Chem. (Engl. Transl.)
1990, 313, 649-651.
(48) (a) Boggs, J. E.; Peng, C.; Pestunovich, V. A.; Sidorkin, V. F. J. Mol.
Struct. (THEOCHEM) 1995, 357, 67-73. (b) Csonka, G. I.; Hencsei, P. J.
Mol. Struct. (THEOCHEM) 1996, 362, 199-208. (c) Csonka, G. I.; Hencsei,
P. J. Comput. Chem. 1996, 17, 767-780. (d) Dahl, T.; Skancke, P. N. Int.
J. Quantum Chem. 1996, 60, 567-578. (e) Anglada, J. M.; Bo, C.; Bofill,
J. M.; Crehuet, R.; Poblet, J. M. Organometallics 1999, 18, 5584-5593.
9
3710 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002

5-Carbaphosphatranes
A R T I C L E S
Table 5. Vibrational Frequencies of Silatrane (I)a
experimentb
MP2/6-31G(d)
c
e
f
mode
IR
Raman
sym
ωd
IR
Raman
1
2
3
4
5
6
7
8
9
10
11
12
13
a
e
e
a
a
e
e
a
a
e
a
e
a
80.0
0.205
0.116
0.402
1.375
0.017
0.178
0.019
0.060
0.153
0.073
2.179
3.452
0.006
0.013
1.181
0.522
0.611
0.269
1.840
0.671
2.825
14.527
1.642
1.068
6.440
2.571
184 w
250 s
313 s
249 w
249 w
316 w
176.4
260.5
266.6
321.4
365.2
449.7
495.7
620.0
610.5
603.0
777.4
785.4
345 w
465 vw
491 vw
589 s
347 m
468 m
492 m
596 vs
625 sh
634 s
629 vs
755 vs
755 sh
764 s
a Only modes up to 800 cm-1 are given. Silatrane is a C3 molecule with
44 vibrational modes, 22 of a, and 22 of e symmetry. b Reference 49g, with
their characterization of intensities. c Symmetry of the mode. d Frequency
in cm-1 e IR intensity in D/amu Å2. f Raman intensity in Å4/amu.
.
Table 6. Atrane Bonding Characteristicsa
b
R
ωc
kd
boie
µf
Silatrane (I)
267 (62)
226 (61)
R ) H
R ) CH3
R ) F
2.302
2.384
2.269
0.83
0.72
0.91
0.225
0.179
0.254
6.68
250 (63)
Phosphatrane (II)
R ) H
2.110
354 (67)
1.34
0.367
5.82g
4.61
5-Carbaphosphatrane (III)
R ) H
1.907
1.922
1.915
1.903
1.905
626 (37)
580 (26)
564 (21)
603 (25)
627 (40)
2.89
2.77
3.39
3.04
2.98
0.731
0.709
0.732
0.754
0.732
R ) CH3
R ) OH
R ) F
R ) Cl
a This table contains computational results obtained at the MP2/6-31G(d)
level. b Transannular distance, in Å. c Transannular vibrational frequency,
in cm-1. For carbaphosphatrane, the normal modes are more mixed than in
the other atranes, so the frequency shown is the one with the greatest
contribution of P-C stretch. Values in parentheses, percent. d Transannular
force constant, in mdyn/Å. e Mayer’s bond order index for the transannular
bond. f Dipole moment, in D. g This ion’s dipole moment is computed with
respect to its center of mass.
6-31G(d) frequencies in silatrane, the force constant matrix can
be assumed to be fairly accurate at this level of theory.
Accordingly, MP2/6-31G(d) force fields were obtained for the
isoelectronic atrane series I-III (R ) H) and for a number of
substituted compounds. Their stretching force constants are
given in Table 6, along with bond orders. The parent R ) H
force constants for silatrane I, phosphatrane II, and 5-carba-
phosphatrane III are 0.83, 1.34, and 2.89 mdyn/Å respectively,
in the ratio 0.62:1:2.16. The bond order formula does not
correspond to an experimental, which the force constant is in
principle, but the bond orders are remarkably similar in their
ratios, namely, 0.61:1:1.99. The force constant values indicate
that the transannular bond in 5-carbaphosphatrane is more than
3 times stronger than in silatrane.50
Figure 4. Transannular RHF/6-31G(d) localized orbital at the MP2/6-31G-
(d) structures. Each contour represents 0.05 b-3/2. Numerical values are
the Mulliken population analysis of each pair, which sum to more than 2
because of small negative populations on the other atoms.
upon substitution, but 5-carbaphosphatrane’s larger force con-
stants mean its bond is not sensitive to substitution. The dipole
moments given in Table 6 decrease from silatrane to 5-carba-
phosphatrane, indicating less ionic character in the transannular
bonds. This is born out in Figure 4, which shows the localized
RHF/6-31G(d) orbitals, at MP2/6-31G(d) geometries. The
contour lines indicate 5-carbaphosphatrane possesses much more
covalent character, as does the partitioning of these electrons
pairs by population analysis. A comparison of the sum of the
van der Waals radii, the computed transannular distances, and
the sum of the covalent radii, respectively, confirms the same
point.51 For the parents, these three values are as follows:
Supporting evidence for increased carbaphosphatrane tran-
sannular bonding is as follows. Silatrane shows matching
variations in its bond lengths, force constants, and bond orders
(50) All three atranes actually have very similar first-order wave functions: of
the 64 valence electrons, the weakly occupied MP2/6-311G(2d,d) natural
orbitals contain a total of 0.99, 1.00, and 1.02 e- for silatrane, phosphatrane,
and 5-carbaphosphatrane, and the occupancy of the highest of the principal
natural orbitals is 1.950, 1.947, and 1.946 e-, respectively. Thus, it is simply
the smaller force constant in silatrane that makes accurate computation of
its true length more difficult, not a lack of single reference character.
(51) Emsley, J. The Elements; Clarendon Press: Oxford, U.K., 1991.
9
J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002 3711

A R T I C L E S
Kobayashi et al.
silatrane, 3.54, 2.33, and 1.87; phosphatrane, 3.44, 2.12, and
1.80; and 5-carbaphosphatrane, 3.75, 1.90, and 1.87. In 5-car-
baphosphatrane, the transannular distance is not much larger
than the P-C covalent radii sum, while the weaker silatrane
bond is longer than this sum.
The frequency attributed to the 5-carbaphosphatrane stretch
in Table 6 is around 600 cm-1, considerably lower than the
888-cm-1 observed band attributed above to the PC stretch. The
alkyl side group in the small model III is less rigid than the
benzene side groups present in IV, which must be a large factor
in this difference.
large for those of apical bonds of phosphoranes but quite similar
to those of phosphatranes. Such similarities between 5-carba-
phophatranes and phosphatranes are due to the isoelectronic
structure of both compounds. Theoretical calculations indicated
that the transannular bond in 5-carbaphosphatrane is twice as
strong as that of phosphatrane and more than 3 times stronger
than that of silatrane, reflecting the difference between a
substantially covalent C-P bond and the more ionic NfP or
NfSi dative bonds.
Acknowledgment. This work was partly supported by Grants-
in-Aid for Scientific Research (A) 12304037 (T.K.) 11166254
(S.N.) from the Ministry of Education, Culture, Sports, Science
and Technology, Japan. We also thank Shin-etsu Chemical Co.,
Ltd. and Tosoh Finechem Corp. for the generous gifts of
iodosilanes and alkyllithiums, respectively. We are grateful to
Professor Y. Furukawa, Waseda University, for the measurement
of FT-Raman spectrum. M.W.S. acknowledges additional sup-
port by the U.S. Air Force Office of Scientific Research.
Conclusion
5-Carbaphosphatranes, a new class of main group atranes,
were synthesized. X-ray crystallographic analysis revealed a
nearly ideal trigonal bipyramidal structure of 1-hydro-5-carba-
phosphatrane that positions the most electronegative oxygens
at equatorial sites. The structural parameters of 1 are quite
similar to usual phosphatranes. The coupling constants for the
transannular bonds of 5-carbaphosphatranes are extraordinarily
Supporting Information Available: X-ray crystallographic
files (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
(52) Demidov, M. P.; Aleksandrov, G. G.; Struchkov, Yu. T.; Baryshok, V. P.;
D’yakov, V. M.; Frolov, Yu. L.; Voronkov, M. G. Koord. Khim. 1981, 7,
1262-1267.
JA011458J
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