Synthesis and reactivity of ortfto-carbaborane-containing chiral aminohalophosphines

Article abstract of DOI:10.1021/ic900443c

The synthesis of chiral ortho-earbaboranyl bis(aminohalophosphines) is presented, and spectroscopic and crystal-lographic data of these compounds are discussed. Furthermore, their reactivity toward alcoholysis was investigated. Quantum chemical calculatio

Full text of DOI:10.1021/ic900443c

6072 Inorg. Chem. 2009, 48, 6072–6082
DOI: 10.1021/ic900443c
Synthesis and Reactivity of ortho-Carbaborane-Containing Chiral
Aminohalophosphines
::
†
‡
Sven Stadlbauer, Rene Frank, Ilham Maulana,†,§ Peter Lonnecke,† Barbara Kirchner,‡ and Evamarie Hey-Hawkins*,†
ꢀ
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†Institut fur Anorganische Chemie, Universitat Leipzig, Johannisallee 29, 04103 Leipzig, Germany, and
::
::
::
‡
ꢀ
Wilhelm-Ostwald-Institut fur Physikalische und Theoretische Chemie, Universitat Leipzig, Linnestrasse 2,
04103 Leipzig, Germany. § New address: Department of Chemistry, Faculty of Mathematics and Natural Science
Syiah Kuala University, Banda Aceh, 23111, Indonesia
Received March 5, 2009
The synthesis of chiral ortho-carbaboranyl bis(aminohalophosphines) is presented, and spectroscopic and crystal-
lographic data of these compounds are discussed. Furthermore, their reactivity toward alcoholysis was investigated.
Quantum chemical calculations showed that the inhibition of methanolysis is of kinetic and not of thermodynamic
origin. The disubstitution of the carbaboranes leads to P P interactions as strong as a hydrogen bond that extremely
3 3 3
lower the rate of the methanolysis.
Introduction
decomposition product of a fluorination process.7 However,
the chemistry of PCl-functionalized dicarba-closo-dodeca-
borane(12) derivatives containing NR2 groups has hardly
been explored. Moreover, sterically hindered tertiary phos-
phine ligands play a major role in catalysis8 by generating
unique coordination spheres and promoting reactions
that do not occur efficiently with less hindered ligands.9
The steric properties of bisphosphines are determined by
the substituents at the two phosphorus atoms and the length
of the spacer between them.10 The majority of conventional
sterically hindered phosphine ligands, such as PtBu3, undergo
oxidation in the air. To prevent unwanted conversion to
PV, the phosphines must be handled under special condi-
tions.11
Therefore, the design of sterically encumbered tertiary
phosphine ligands that are resistant to oxidation is desira-
ble. Dicarba-closo-dodecaboranes are thus attractive back-
bones from which to construct bulky phosphines. The
derivatives of bidentate bisphosphinodicarba-closo-dodeca-
borane(12) form stable chelate complexes.12 Lately, several
Bidentate chiral phosphines have received increasing atten-
tion due to their important role as ligands in the development
of asymmetric catalytic applications of metal complexes.1 The
steric and electronic properties of the substituents at the
two phosphorus atoms play a crucial role,2 for example, in
determining the relative donor/acceptor ability of the phos-
phines.3 Dicarba-closo-dodecaborane(12) is a particularly
interesting potential substituent due to its electron-withdrawing
character, electron-delocalizing ability, and bulk.4,5
In the early 1970s, Zakharkin et al. reported the synthesis
of monosubstituted ortho-carbaboranes with aminochloro-
and diaminophosphino substituents.6 Hill and Silva-Trivino
described the formation of 1,2-bis(N,N-dimethylamino-
fluorophosphino)-1,2-dicarba-closo-dodecaborane(12) as a
*To whom correspondence should be addressed. E-mail: hey@uni-leipzig.de.
(1) Barbaro, P.; Bianchini, C.; Giambastiani, G.; Parisel, S. L. Coord.
Chem. Rev. 2004, 248, 2131–2150.
(2) (a) Suresh, C. H.; Koga, N. Inorg. Chem. 2002, 41, 1573–1578.
(b) Van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.; Dierkes,
P. Chem. Rev. 2000, 100, 2741–2769. (c) Marchenko, A. V.; Huffmann, J. C.;
Valerga, P.; Tenorio, M. J.; Puerta, M. C.; Caulton, K. G. Inorg. Chem. 2001,
40, 6444–6450.
(3) (a) Bowen, R. J.; Garner, A. C.; Berner-Price, S. J.; Jenkins, I. D.; Sue,
R. E. J. Organomet. Chem. 1998, 554, 181–184. (b) Magee, M. P.; Luo, W.;
Hersh, W. H. Organometallics 2002, 21, 362–372.
(4) (a) Grimes, R. N. Carboranes; Academic Press: New York, 1970.
(b) Bregadze, I. Chem. Rev. 1992, 92, 209–223.
(7) Hill, W. E.; Silva-Trivino, L. M. Inorg. Chem. 1978, 17, 2495–2498.
(8) (a) Beare, N. A.; Hartwig, J. F. J. Org. Chem. 2002, 67, 541–555.
(b) Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi, J. P.;
Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 4369–4378.
(9) Tsuji, J. Palladium Reagents and Catalysts, New Perspective for the
21st Century, 2nd ed.; John Wiley & Sons Ltd.: West Sussex, U. K., 2004.
(10) Tolman, C. A. Chem. Rev. 1977, 77, 313–348.
(11) Netherton, M. R.; Fu, G. C. Org. Lett. 2001, 3, 4295–4298.
(12) (a) Calhorda, M. J.; Crespo, O.; Gimeno, M. C.; Jones, P. G.;
Laguna, A.; Lopez-de-Luzuriaga, J. M.; Perez, J. L.; Veiros, L. F. Inorg.
Chem. 2000, 39, 4280–4285. (b) Balema, V. P.; Somoza, F. Jr.; Hey-Hawkins,
E. Eur. J. Inorg. Chem. 1998, 651–656. (c) Crespo, O.; Gimeno, M. C.; Jones,
P. G.; Laguna, A.; Villacampa, M. D. Angew. Chem., Int. Ed. 1997, 36, 993–
995.
(5) Beal, H. In Boron Hydride Chemistry; Muetterties, E., Ed.; Academic
Press: New York, 1975.
(6) (a) Zakharkin, L. I.; Kazantsev, A. V.; Zhubekova, M. N. Izv. Akad.
Nauk SSSR, Ser. Khim. 1969, 9, 2056–2057. (b) Zakharkin, L. I.; Zhubekova,
M. N.; Kazantsev, A. V. Zh. Obsh. Khim. 1971, 41, 588–592. (c) Kazantsev,
A. V.; Zhubekova, M. N.; Zakharkin, L. I. Zh. Obsh. Khim. 1971, 41, 2027–
2033. (d) Zakharkin, L. I.; Zhubekova, M. N.; Kazantsev, A. V. Zh. Obsh.
Khim. 1972, 42, 1024–1028.
r
2009 American Chemical Society
pubs.acs.org/IC
Published on Web 06/01/2009

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6073
metal complexes with five-membered chelate rings were
reported to exhibit high catalytic activity.13
accelerated resolution of identity24 were used. The TZVPP basis
set25 was applied to all atoms. The convergence criterion for the
SCF calculations was fulfilled at 10-8 au, and the length of the
gradient vector and geometry optimizations was set to 10-4 au.
The calculations were carried out with and without the con-
ductor-like screening model (COSMO).26 The COSMO para-
meters were chosen as follows: ε = 30 (for methanol as a solvent)
and solvation shell rsolv = 130 pm. The transition states were
counterpoise-corrected.27
While nonchiral bisphosphines of dicarba-closo-dodeca-
borane(12) were largely explored,14 only limited studies on
chiral bidentate tertiary phosphine derivatives, in particular,
chlorophosphino-substituted compounds,15 have been re-
ported. Moreover, chiral derivatives with highly electro-
negative groups or NR2 groups at phosphorus were
hardly explored.7,16
X-Ray Crystallographic Analysis. The data were collected on
a Siemens CCD diffractometer (SMART,28 data reduction with
SAINT29 including the program SADABS30 for empirical ab-
sorption correction) or an Oxford Diffraction CCD Xcalibur-S
diffractometer (data reduction with CrysAlis Pro31 including
the program SCALE3 ABSPACK32 for empirical absorption
correction) using Mo KR radiation (λ = 71.073 pm) and ω-scan
rotation. The structures were solved by direct methods, and the
refinement of all non-hydrogen atoms was performed with
SHELXL97.33 H atoms were located on difference Fourier
maps calculated at the final stage of the structure refinement.
For disordered solvent molecules in 5a or the completely
disordered molecule 8a/b, H atoms were calculated on idealized
positions. Structure figures were generated with ORTEP34 and
DIAMOND-3.35 CCDC 722657, 2a; 722658, 2b; 722659, 3b;
722660, 5a; 722661, 6a; 722662, 7b; and 722663, 8a/b contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or deposit@ccdc.cam.uk). Crystal data for 2a,
2b, 3b, 5a, 6a, 7b, and 8a/b can be found in Table 1.
Here, we describe the synthesis and reactivity of bidentate
chiral tertiary aminophosphine ligands containing ortho-
carbaborane(12) as a backbone. An amino group at the
phosphorus atom can result in significant changes in the
electronic donor/acceptor properties of the phosphines as
well as their steric demand.
Experimental Section
All of the reactions were carried out in an atmosphere
ofdry nitrogen. The solvents were purified and distilledunder
nitrogen.17 The infrared spectra were recorded on a Perkin-
Elmer System 2000 FT-IR spectrometer scanning between
400 and 4000 cm-1 using KBr disks. The 1H, 13C, 31P, and 11
B
NMR spectra were recorded on an AVANCE DRX 400
spectrometer (Bruker). The chemical shifts for the 1H
and 13C NMR spectra are reported in parts per million at
400.13 and 100.63 MHz with tetramethylsilane as a standard.
The chemical shifts for the 31P NMR spectra are reported in
parts per million at 161.97 MHz (with an 85% H3PO4
external standard) and chemical shifts for 11B NMR spectra
in parts per million at 128.38 MHz with BF3 OEt2 as an
Synthesis of N,N-Diisopropylaminodichlorophosphine. Phos-
phorus trichloride (25 mL, 286 mmol) was dissolved in diethyl
ether (600 mL), and the solution was cooled to 0 °C. N,N-
Diisopropylamine (80 mL, 569 mmol) was added dropwise over
2 h. After complete addition, the reaction mixture was warmed
to room temperature and stirred overnight. The ammonium salt
was filtered off and then washed with two portions of diethyl
ether (2 ꢀ 200 mL). Then, the solvent was evaporated and the
resulting yellow oil distilled in a vacuum at 2.4 mbar and 54 °C to
3
external standard. The mass spectra were recorded on an VG
Analytics ZAB HSQ spectrometer (FAB) or on a Finnigan
MAT MAT8200 spectrometer (EI). The elemental analyses
wererecordedonaVARIOEL(Heraeus). Themeltingpoints
were determined in sealed capillaries and are uncorrected.
1,2-Dicarba-closo-dodecaborane and 1,7-dicarba-closo-
dodecaborane are commercially available. PCl2NMe2 was
18
purchasedfromAldrichanddistilledpriortouse. PCl2NEt2
and PCl2NPh219 were prepared according to the literature.
Computational Details. All electronic structure calcula-
tions were carried out with the Turbomole20 program suite.
The geometry-optimized structures were obtained by DFT
calculations with the BP86 density functional,21,22 in which the
resolution of identity approximation23 and the multipole
1
give 41.3 g (71%) of the product. H NMR (CDCl3): δ 3.59
3
(s, br, 2H, CH), 0.87 (d, JHH = 6.4 Hz, 12H, CH3). 31P{1H}
NMR (CDCl3): δ 168.1 (s).
Synthesis of N,N-Diisopropylaminodibromophosphine. Phos-
phorus tribromide (28.2 mL, 300 mmol) was dissolved in diethyl
ether (800 mL), and the solution was cooled to 0 °C. N,N-
Diisopropylamine (84.3 mL, 600 mmol) was added dropwise
over 2 h. After complete addition, the reaction mixture was
warmed to room temperature and stirred overnight. The am-
monium salt was filtered off and then washed with diethyl ether
(2 ꢀ 200 mL). Then, the solvent was evaporated and the
(13) (a) Cornils, B. In Applied Homogeneous Catalysis with Organome-
tallic Compounds; Herrmann, W.A., Ed.; Wiley-VCH: Weinheim, Germany,
2002; Vol. 2. (b) Kumada, M.; Sumitani, K.; Kiso, Y.; Tamao, K.
J. Organomet. Chem. 1973, 50, 319–326.
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(14) (a) Paavola, S.; Teixidor, F.; Vinas, C.; Kivekas, R. J. Organomet.
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Chem. 2002, 657, 187–93. (b) Vinas, C.; Benakki, R.; Teixidor, F.; Casabo, J.
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Inorg. Chem. 1995, 34, 3844–3845. (c) Teixidor, F.; Vinas, C.; Abad, M. M.;
(24) Sierka, M.; Hogekamp, A.; Ahlrichs, R. J. Chem. Phys. 2003, 118,
9136–9148.
(25) EMSL Basis Set Exchange. https://bse.pnl.gov/bse/portal (accessed
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Nunez, R.; Kivekas, R.; Sillanpaa, R. J. Organomet. Chem. 1995, 503, 193–
203. (d) Contreras, J. G.; Silva-Trivino, L. M.; Solis, M. E. Inorg. Chim. Acta
1988, 142, 51–54.
(15) (a) Alexander, R. P.; Schroeder, H. J. Inorg. Chem. 1963, 2, 1107–
1110. (b) Balema, V. P.; Blaurock, S.; Hey-Hawkins, E. Polyhedron 1999, 18,
545–552. (c) Sterzik, A.; Rys, E.; Blaurock, S.; Hey-Hawkins, E. Polyhedron
2001, 20, 3007–3014. (d) Smith, T. A.; Knowles, H. S. Inorg. Chem. 1965, 4,
107–111.
(16) Hill, W. E.; Silva-Trivino, L. M. Inorg. Chem. 1979, 18, 361–364.
(17) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press, Oxford, U. K., 1988.
(18) Perich, J. W.; Johns, R. B. Synthesis 1988, 2, 142–144.
May 2009).
:: ::
(26) Klamt, A.; Schuurmann, G. J. Chem. Soc., Perkin Trans.2 1993, 5,
799–805.
(27) Boys, S. F.; Bernardi, F. Mol. Phys. 1970, 19, 553–556.
(28) SMART; Siemens Industrial Automation, Inc.: Madison, WI, 1993.
(29) SAINT, version 6.01; Siemens Industrial Automation, Inc.:
Madison, WI, 1999.
::
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(30) Sheldrick, G. M. SADABS; University of Gottingen: Gottingen,
Germany, 1997.
(31) CrysAlis Pro; Oxford Diffraction Ltd.: Oxfordshire, U. K.
(32) SCALE3 ABSPACK; Oxford Diffraction Ltd.: Oxfordshire, U. K.
(19) Fabius, H.; Babin, M. Z. Anorg. Allg. Chem. 1976, 420, 65–73.
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(33) Sheldrick, G. M. SHELX97, release 97-2; University of Gottingen:
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(20) Ahlrichs, R. Turbomole, V5.9; Lehrstuhl fur Theoretische Chemie,
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Gottingen, Germany, 1997; includes SHELXS97 and SHELXL97.
Universitat Karlsruhe: Karlsruhe, Germany, 2006.
(34) ORTEP3 for Windows: Farrugia, L. J. J. Appl. Crystallogr. 1997, 30,
(21) Becke, A. D. Phys. Rev. A 1988, 38, 3098–3100.
(22) Perdew, J. P. Phys. Rev. B 1986, 33, 8822–8824.
(23) Eichkorn, K.; Treutler, O.; Ohm, H.; Haser, M.; Ahlrichs, R. Chem.
565.
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(35) Brandenburg, K. DIAMOND 3; Crystal Impact GbR: Bonn,
Phys. Lett. 1995, 242, 652–660.
Germany.

6074 Inorganic Chemistry, Vol. 48, No. 13, 2009
Stadlbauer et al.
Table 1. Crystal Data for Compounds 2a, 2b, 3b, 5a, 6a, 7b, and 8a/b
compound
2a
2b
3b
5a
6a
7b
8a/b
empirical formula
C
10H30B10
Cl2N2P2
-
C10H30B10
Cl2N2P2
419.30
210(2)
triclinic
P1
757.2(1)
866.8(1)
1864.6(3)
95.524(3)
91.078(3)
115.643(2)
1.0956(3)
2
1.271
0.441
436
6805
-
C14H38B10
Cl2N2P2
475.40
213(2)
monoclinic
P21/c
1782.3(1)
983.72(7)
1511.4(1)
90
101.368(1)
90
2.5979(3)
4
1.215
-
C26H30B10-
Cl2N2P2 C7H8
703.59
210(2)
orthorhombic
P21212
752.7(1)
1949.0(4)
1228.3(2)
90
90
90
1.8018(6)
2
1.297
C12H36B10
N2O2P2
410.47
210(2)
monoclinic
C2/c
1433.9(2)
1029.0(2)
1778.8(3)
90
112.890(4)
90
2.4179(7)
4
1.128
0.190
872
9892
-
C16H44B10
N2O2P2
466.57
-
C14H38B10
Br2N2P2
564.32
180(2)
monoclinic
P21
773.7(1)
1476.1(3)
1202.5(2)
90
103.96(1)
90
1.3327(4)
2
1.406
3.168
572
45801
-
3
fw
T/K
cryst syst
space group
a/pm
419.30
213(2)
monoclinic
P21/n
715.7(1)
1668.0(3)
1915.4(3)
90
92.301(3)
90
2.2847(6)
4
1.219
213(2)
orthorhombic
P212121
1034.8(2)
1495.0(3)
1832.4(4)
90
90
90
2.835(1)
4
1.093
b/pm
c/pm
R/deg
β/deg
γ/deg
V/nm3
Z
F
calcd/Mg m-3
Mo-KR/mm-1
F(000)
μ
0.423
872
0.380
1000
0.298
728
0.170
1000
26739
no. of reflns collected 14558
R1/wR2 (I > 2σ(I))
R1/wR2 (all data)
18423 18095
0.0383/ 0.0879 0.0370/ 0.0889 0.0339/0.0806 0.0333/ 0.0790
0.0583/ 0.0947 0.0455/ 0.0929 0.0449/ 0.0863 0.0376/ 0.0806
0.0334/ 0.0893 0.0375/ 0.0918 0.0475/ 0.1086
0.0415/ 0.0942 0.0464/ 0.0971 0.0833/ 0.1267
resulting yellow oil distilled in a vacuum at 1.0 mbar and 67-
2936 (s), 2870 (s) (CH); 2621 (s), 2573 (s) (BH); 2006 (w), 1627 (s),
1462 (s), 1441 (m), 1380 (s), 1344 (w), 1291 (m), 1262 (w), 1201 (s),
1165 (s), 1104 (s), 1066 (s), 1023 (s), 971 (w), 947 (s), 918 (w),
831 (m), 795 (s), 744 (m), 730 (m), 668 (m), 621 (m), 564 (m), 502 (s),
489 (s), 448 (m), 417 (m). MS (FAB+, 3-nitrobenzyl alcohol
matrix) m/z: 419 (24%, M+), 383 (42%, M+ - Cl), 347 (100%,
M+ - 2Cl), 317 (76%, M+ - 2Cl - C2H5). Anal. calcd for
C10H30B10Cl2N2P2 (M = 419.30): C, 28.64; H, 7.21; N, 6.68.
Found: C, 29.00; H, 7.23; N, 6.46%.
68 °C to give 61 g (71%) of the product. Mp: 72-73 °C.
=
3
1H NMR (C6D6): δ 3.59 (s, br, 2H, CH), 0.87 (d, JHH
6.40 Hz, 12H, CH3). 31P{1H} NMR (C6D6): δ 170.8 (s).
Synthesis of rac-/meso-1,2-Bis(N,N-dimethylaminochlorophos-
phino)-1,2-dicarba-closo-dodecaborane(12) (1a/1b). ortho-Car-
baborane (1.0 g, 57.2 mmol) was dissolved in diethyl ether
(30 mL). After cooling to 0 °C, a solution of n-BuLi in n-hexane
(5.90 mL, 13.8 mmol) was added dropwise to the solution. The
mixture was warmed to room temperature and stirred for 2 h,
during which 1,2-dilithiodicarba-closo-dodecaborane(12) was
formed as a white solid. The resulting mixture was then added
slowly through a cannula to a cooled solution of N,N-dimethyl-
aminodichlorophosphine (1.90 mL, 16.5 mmol) in diethyl ether
(20 mL). The mixture was stirred overnight at room temperature
and then filtered through silica gel. The filtrate was concen-
trated in a vacuum, and the resulting residue was dissolved in
n-pentane. Cooling to 4 °C yielded colorless microcrystals of
1a/b. Yield: 1.09 g (43%). Mp: 110-111 °C. 1H NMR (C6D6):
δ 3.80-1.80 (m, vbr, 10H, C2B10H10), 2.24 (d, 3JHP = 6.0 Hz,
Data for 2b. Mp:106°C. 1HNMR(CDCl3): δ3.50-1.35 (m, vbr,
3
10H, C2B10H10), 3.19 (m, 8H, CH2), 1.08 (t, JHH = 7 Hz, 12H,
CH3). 13C{1H} NMR (CDCl3): δ 87.2 (m, 1JPC + 2JPC = 111.0 Hz,
C2B10H10), 42.1 (m, vbr, CH2), 13.4 (s, CH3). 31P{1H} NMR
=
1
(CDCl3): δ 117.1 (s). 11B NMR (CDCl3): δ -0.4 (d, JBH
1
147.0 Hz, 2B, C2B10H10), -6.3 (d, JBH = 138.2 Hz, 1B,
1
C2B110H10), -7.3 (d, JBH = 140.9 Hz, 1B, C2B10H10), -9.5 (m,
1
vbr, JBH n.d., 2B, C2B10H10), -10.4 (d, JBH = 142.0 Hz, 2B,
C2B10H10), -11.9 (m, vbr, 2B, C2B10H10). IR (KBr, cm-1): 2974 (s),
2936 (s), 2869 (s) (CH); 2619 (s), 2572 (s) (BH); 1461 (s), 1439 (s),
1379 (s), 1342 (m), 1290 (m), 1201 (s), 1164 (s), 1103 (m), 1065 (s),
1022 (s), 971 (m), 947 (s), 830 (m), 793 (m), 728 (m), 667 (m), 619 (m),
561 (w), 500 (s), 448 (m), 423 (w). MS (FAB+, 3-nitrobenzyl alcohol
matrix) m/z: 419 (24%, M+), 383 (42%, M+ - Cl), 347 (100%,
M+ - 2Cl), 317 (76%, M+ - 2Cl - C2H5). Anal. calcd for
C10H30B10Cl2N2P2 (M = 419.30): C, 28.64; H, 7.21; N, 6.68. Found:
C, 28.70; H, 7.23; N, 6.61%.
12H, CH3). 13C{1H} NMR (C6D6): δ 87.2 (m, 1JCP + 2JCP
=
80.9 Hz, C2B10H10), 39.6 (m, vbr, CH3). 31P{1H} NMR (C6D6);
δ 119.5 (s) and 118.4 (s) (diastereomers). 11B{1H} NMR (C6D6):
δ -0.4 (s, 3B, C2B10H10), -6.5 (s, 3B, C2B10H10), -9.6 (s, 4B,
C2B10H10). IR (KBr, cm-1): 2963 (m), 2848 (m), 2802 (w) (CH);
2618 (s), 2574 (s) (BH); 1659 (w), 1474 (s), 1447 (w), 1410 (w),
1262 (s), 1171 (m), 1097 (s), 1066 (s), 1023 (s), 981 (s), 901 (w),
864 (w), 801 (s), 733 (w), 688 (m), 621 (w), 560 (w), 472 (m),
445 (w), 410 (m). MS (FAB+, 3-nitrobenzyl alcohol matrix) m/z:
362.2 (11%, M+), 328.2 (100%, M+-Cl). Anal. calcd for
C6H22B10Cl2N2P2 (M = 363.19): C, 19.84; H, 6.10; N, 7.71.
Found: C, 19.99; H, 6.04; N, 7.59%.
Synthesis of rac-/meso-1,2-Bis(N,N-diisopropylaminochloro-
phosphino)-1,2-dicarba-closo-dodecaborane(12) (3a/3b). Using
the same experimental procedure with N,N-diisopropylamino-
dichlorophosphine yielded 3a/b as a mixture of both diastereo-
mers. From a concentrated n-hexane solution at room
temperature, 3b could be crystallized. Yield: 1.5 g (40%) of 3b.
Data for 3b. Mp: 183-184 °C. 1H NMR (C6D6): δ 4.0-2.0
(m, 10H, C2B10H10), 3.92 (s, br, 2H, N{CH(CH3)2}), 2.99 (s, br,
2H, N{CH(CH3)2}), 1.08 (s, vbr, 12H, N{CH(CH3)2}), 0.92
Synthesis of rac-/meso-1,2-Bis(N,N-diethylaminochlorophos-
phino)-1,2-dicarba-closo-dodecaborane(12) (2a/2b). Using the
same experimental procedure with N,N-diethylaminodichloro-
phosphine yielded 2 from a concentrated n-hexane solution.
Yield: 12.7 g (62%). Fractional crystallization gave first 6.8 g
(33%) of 2b and then 4.3 g (21%) of 2a.
(s, vbr, 12H, N{CH(CH3)2}). 13C{1H} NMR (C6D6): δ 89.8
1
(m, JCP
+
2JCP = 110.4 Hz, C2B10H10), 51.2 (s, N{CH-
(CH3)2}), 46.5 (pseudo t, 2JCP = 18.9 Hz, N{CH(CH3)2}), 26.2
(s, N{CH(CH3)2}), 23.9 (s, N{CH(CH3)2}), 21.2 (d, 3JCP = 46.3 Hz,
N{CH(CH3)2}). 31P{1H} NMR (C6D6): δ 113.5 (s). 11B NMR
Data for 2a:Mp:92°C. 1HNMR(CDCl3): δ3.52-1.43 (m, vbr,
10H, C2B10H10), 3.23 and 3.13 (m, 8H, CH2), 1.08 (t, 3JHH = 4 Hz,
1
12H, CH3). 13C{1H} NMR (CDCl3): δ 87.2 (m, 1JCP + 2JCP
=
106.6 Hz, C2B10H10), 42.0 (m, vbr, CH2), 13.4 (s, CH3). 31P{1H}
=
(C6D6): δ 0.2 (d, br, JBH = 142.5 Hz, 3B, C2B10H10,), -4.0
(s, 1JBH n.d., 1B, C2B10H10), -5.5 (d, br, 1JBH = 67.3 Hz, 1B,
1
NMR (CDCl3): δ 117.2 (s). 11B NMR (CDCl3): δ -0.5 (d, 1JBH
C2B10H10), -7.1 (s, br, JBH n.d., 1B, C2B10H10), -9.3 (s, br,
147.0 Hz, 2B, C2B10H110), -6.8 (d, JBH = 151.0 Hz, 2B,
C2B10H10), -10.0 (d, JBH = 155.1 Hz, 4B, C2B10H10),
1JBH n.d., 3B, C2B10H10), -10.6 (s, br, 1JBH n.d., 1B, C2B10H10).
IR (KBr, cm-1): 2975 (s), 2937 (m), 2871 (w) (C-H); 2660 (w),
2624 (s), 2605 (s), 2585 (s), 2560 (s) (BH); 1631 (w), 1461 (m),
1
1
-11.2 (m, JBH n.d., 2B, C2B10H10). IR (KBr, cm-1): 2973 (s),

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6075
1392 (s), 1368 (s), 1307 (w), 1245 (m), 1197 (m), 1168 (w),
1149 (w), 1121 (m), 1065 (m), 1021 (m), 963 (m), 878 (w),
852 (w), 831 (w), 798 (w), 734 (w), 663 (w), 640 (w), 620 (w),
531 (m), 501 (w), 462 (s), 433 (w). MS (FAB+, 3-nitrobenzyl
alcohol matrix) m/z: 475.3 (13, M+); 439.3 (30, M+ - Cl); 375.2
(35, M+ - NiPr2); 340.2 (9, M+ - Cl - NiPr2). Anal. calcd for
C14H38N2P2B10Cl2 (M = 475.43): C, 35.37; H, 8.06; N, 5.89.
Found: C, 35.26; H, 8.19; N, 5.72%.
2628 (s), 2580 (s), 2552 (s) (BH); 1948 (w), 1868 (w), 1796 (w),
1736 (w), 1662 (w) (Ph); 1591 (s), 1487 (s), 1450 (m), 1393 (w),
1328 (w), 1310 (w), 1279 (w), 1232 (s), 1190 (w), 1108 (w),
1067 (s), 1030 (s), 1011 (m), 978 (s), 914 (w), 905 (w), 878 (m),
837 (m), 800 (w), 756 (s), 694 (s), 623 (w), 603 (w), 536 (s), 577 (s),
448 (m), 427 (m). MS (FAB+, 3-nitrobenzyl alcohol matrix)
m/z: 611 (7%, M+), 575 (8%, M+ - Cl). Anal. calcd for
C26H30B10Cl2N2P2 (M = 611.49): C, 51.07; H, 4.94; N, 4.47;
Found: C, 51.46; H, 5.10; N, 4.47%.
Synthesis of rac-/meso-1,2-Bis(N,N-diisopropylaminobromo-
phosphino)-1,2-dicarba-closo-dodecaborane(12) (4a/4b). Using
the same experimental procedure with N,N-diisopropylamino-
dibromophosphine yielded 4 from a concentrated n-hexane
solution at room temperature. Yield: 0.8 g (40%) of one
Synthesis of rac-/meso-1,7-Bis(N,N-diisopropylaminobromo-
phosphino)-1,7-dicarba-closo-dodecaborane(12) (8a/b). meta-
Carbaborane (0.53 g, 3.67 mmol) was dissolved in diethyl ether
(15 mL). After cooling to 0 °C, a solution of n-BuLi in n-hexane
(3.0 mL, 7.1 mmol) was added dropwise to the solution. The
mixture was warmed to room temperature and stirred for 2 h,
during which 1,7-dilithiodicarba-closo-dodecaborane(12) formed
as a white solid. The resulting mixture was then added slowly
through a cannula to a cooled solution of N,N-diisopropylami-
nodibromophosphine (2.21 g, 7.59 mmol) in diethyl ether (15 mL).
The mixture was stirred overnight at room temperature. LiBr
was filtered off. The solvent was evaporated in a vacuum to
dryness, and the resulting residue was extracted with n-hexane.
The n-hexane fraction was concentrated to give crystals of the
diastereomeric mixture of 8. Yield: 0.93 g (45%). Mp: 122-
124 °C. 1H NMR (C6D6): δ 4.0-1.8 (m, 10H, C2B10H10), 3.81
(m, br, 2H, N{CH(CH3)2}), 2.87 (m, br, 2H, N{CH(CH3)2}),
1
diastereomer. Data for 4. Mp: 196-197 °C. H NMR (C6D6):
δ 4.0-1.8 (m, 10H, C2B10H10), 3.89 (m, br, 2H, N{CH(CH3)2}),
2.93 (m, br, 2H, N{CH(CH3)2}), 1.06 (dd, 3JHH = 8.0 Hz, 12H,
N{CH(CH3)2}), 0.89 (pseudo t, 12H, N{CH(CH3)2}). 13C{1H}
NMR (C6D6): δ 88.5 (m, 1JCP + 2JCP = 116.7 Hz, C2B10H10),
53.4 (s, N{CH(CH3)2}), 46.8 (pseudo t, 2JCP = 18.9 Hz, N{CH-
(CH3)2}), 25.9 (s, N{CH(CH3)2}), 22.9 (pseudo t, 3JCP = 12.1 Hz,
N{CH(CH3)2}), 21.0 (s, N{CH(CH3)2}), 20.0 (s, N{CH-
(CH3)2}). 31P{1H} NMR (C6D6): δ 112.8 (s) (one of the two
diastereomers). 11B{1H} NMR (C6D6): δ 0.3 (s, br, 3B, C2B10H10),
-4.1 (s, 1B, C2B10H10), -6.2 (d, br, 1B, C2B10H10), -8.1 (s, br,
1B, C2B10H10), -9.3 (s, br, 3B, C2B10H10), -11.7 (s, br, 1B,
C2B10H10). IR (KBr, cm-1): 2974 (s), 2868 (w) (CH); 2657 (w),
2648 (w), 2627 (w), 2604 (m), 2576 (s), 2563 (m), 2552 (w) (BH);
1459 (m), 1393 (s), 1368 (s), 1308 (w), 1261 (w), 1197 (m),
1167 (m), 1148 (m), 1121 (s), 1062 (m), 1018 (s), 963 (s),
903 (w), 877 (w), 851 (w), 830 (w), 796 (w), 733 (w), 663 (w),
638 (w), 618 (w), 556 (w), 526 (m), 494 (w), 437 (w). MS (EI+,
3
1.06 (d, JHP = 6.4 Hz, 12H, N{CH(CH3)2}), 0.93 (s, 12H,
N{CH(CH3)2}). 31P{1H} NMR (C6D6): δ 127.2 (s). 13C{1H}
NMR (C6D6): δ 78.5 (d, 1JCP = 105.2 Hz, C2B10H10), 52.4 (s,
N{CH(CH3)2}), 46.3 (d, 2JCP = 34.4 Hz, N{CH(CH3)2}), 26.0
3
(s, N{CH(CH3)2}), 22.5 (d, JCP = 25.6 Hz, N{CH(CH3)2}),
70 eV) m/z: 564.2 (1, M+); 484.2 (26, M+ - Br); 385.2 (6, M+
-
21.2 (s, N{CH(CH3)2}), 19.9 (s, N{CH(CH3)2}). 11B NMR
Br - NiPr2); 209.9 (11, BrPNiPr2+); 100 (21, NiPr2+); 43 (100,
iPr+). Anal. calcd for C14H38B10Br2N2P2 (M = 564.33): C,
29.78; H, 6.79; N, 4.96. Found: C, 30.05; H, 6.88; N, 4.66%.
Synthesis of rac-/meso-1,2-Bis(N,N-diphenylaminochlorophos-
phino)-1,2-dicarba-closo-dodecaborane(12) (5a/5b). Using the
same experimental procedure with N,N-diphenylaminodichloro-
1
(C6D6): δ -2.8 (d, br, JBH = 139.3 Hz, 2B, C2B10H10), -8.4
(d, 1JBH = 139.9 Hz, 3B, C2B10H10), -9.5 (d, br, 1JBH = 131.8 Hz,
3B, C2B10H10), -12.3 (d, br, 1JBH = 168.2 Hz, 2B, C2B10H10).
IR (KBr, cm-1): 2971 (s), 2931 (w), 2870 (w) (CH); 2654 (w),
2592 (s) (BH); 1636 (w), 1459 (m), 1393 (s), 1367 (s), 1309 (w),
1262 (w), 1198 (s), 1166 (m), 1150 (m), 1121 (s), 1078 (m),
1023 (m), 963 (s), 877 (w), 852 (w), 830 (w), 734 (w), 692 (w),
641 (w), 580 (w), 529 (m), 480 (w), 419 (w). MS (EI+, 70 eV)
m/z: 564.3 (3, M+); 484.3 (35, M+ - Br); 210 (23, BrPNiPr2+);
phosphine yielded 5b as the first and the rac isomer 5a CH3C6H5
3
as the second crystal fraction.
Data for 5a. Yield: 11.2 g (32%). Mp: 140 °C. 1H NMR
(CDCl3): δ 7.33-7.19 (m, 20H, C6H5, + C6H5 of toluene),
3.52 - 1.33 (m, vbr, 10H, C2B10H10), 2.34 (s, CH3 in toluene).
31P{1H} NMR (CDCl3): δ 104.3 (s). 13C{1H} NMR (CDCl3):
δ 146.0 (s, ipso-C, Ph), 137.8 (s, ipso-C, C7H8), 129.2 (s, m-C, Ph),
129.0 (s, o-C, C7H8), 128.2 (s, m-C, C7H8), 127.2 (s, o-C, Ph),
i
42.9 (100, Pr+). Anal. calcd for C14H38B10Br2N2P2 (M =
564.33): C, 29.78; H, 6.79; N, 4.96. Found: C, 30.09; H, 6.97;
N, 4.97%.
Methanolysis of 2b. Compound 2b (1.0 g, 57.15 mmol) was
heated to reflux in triethylamine (1 mL) and methanol (150 mL)
for 4 h. The solvent was evaporated and the resulting residue
extracted with two portions of n-hexane (30 mL). The solution
was concentrated and cooled to -8 °C to give colorless crystals
of rac-1,2-bis(N,N-diethylamidomethylphosphonito)-1,2-dicarba-
closo-dodecaborane(12) (6a).
126.5 (s, p-C, Ph), 125.3 (s, p-C, C7H8) 86.9 (m, 1JPC + 2JPC
=
104.0 Hz, C2B10H10), 21.4 (s, CH3 in C7H8). 11B NMR (CDCl3):
δ 0.6 (d, 1JBH =128.0Hz,2B,C2B110H10), -5.8 (d, 1JBH = 144.1 Hz,
4B, C2B10H10), -10.0 (m, vbr, JBH n.d., 4B, C2B10H10). IR
(KBr, cm-1): 3086 (w), 3065 (m), 3031 (m) (CH); 2630 (s),
2577 (s) (BH); 1945 (w), 1875 (w), 1859 (w), 1798 (w) (Ph);
1594 (s), 1584 (s), 1488 (s), 1450 (m), 1309 (w), 1277 (w), 1235 (s),
1187 (s), 1173 (s), 1157 (m), 1075 (s), 1065 (s), 1029 (s), 1009 (m),
978 (s), 931 (w), 918 (m), 878 (s), 834 (m), 801 (w), 751 (s), 731 (s),
691 (s), 621 (w), 602 (m), 555 (w), 533 (s), 523 (s), 472 (s), 451 (m),
429 (s), 405 (w). MS (FAB+, 3-nitrobenzyl alcohol matrix)
m/z: 611 (1%, M+), 575 (2%, M+ - Cl). Anal. calcd for
1
Data for 6a. Yield: 0.38 g (39%). Mp: 87-88 °C. H NMR
(CDCl3): δ 3.55 (pseudo t, 3JHP = 8.0 Hz, 6H, OCH3), 3.21 and
3.08 (m, 8H, NCH2CH3), 3.00 - 1.50 (m, vbr, 10H, C2B10H10),
3
1.09 (t, JHH = 8.0 Hz, 12H, NCH2CH3). 31P{1H} NMR
(CDCl3): δ 132.4 (s). 13C{1H} NMR (CDCl3): δ 85.5 (m, 1JCP
+
2
2JCP = 85.0 Hz, C2B10H10), 55.2 (pseudo t, JCP = 12.9 Hz,
OCH3), 40.5 (s, vbr, NCH2CH3), 14.5 (s, NCH2CH3). 11B NMR
1
(CDCl3): δ -1.2 (d, JBH = 142.9 Hz, 2B, C2B10H10), -7.8
C26H30B10Cl2N2P2 CH3C6H5 (M = 703.63): C, 56.33; H,
3
(d, 1JBH = 148.1 Hz, 2B, C2B10H10), -10.7 (d, 1JBH = 141.2 Hz,
5.44; N, 3.98. Found: C, 56.70; H, 5.19; N, 4.01%.
1
Data for 5b. Yield: 11.9 g (34%). Mp: 191 °C. 1H NMR
(CDCl3): δ 7.32-7.20 (m, 20H, Ph), 3.51-1.30 (m, vbr, 10H,
C2B10H10). 31P NMR (CDCl3): δ 103.0 (s). 13C{1H} NMR
(CDCl3): δ 146.2 (s, ipso-C, Ph), 129.3 (s, m-C, Ph), 127.2
(s, o-C, Ph), 126.4 (s, p-C, Ph), 87.1 (m, 1JCP + 2JCP = 104.0 Hz,
C2B10H10). 11B NMR (CDCl3): δ 0.4 (d, 1JBH = 130.0 Hz, 2B,
4B, C2B10H10), -11.9 (m, vbr, JBH n.d., 2B, C2B10H10). IR
(KBr, cm-1): 2981 (s), 2930 (s), 2882 (s), 2829 (s) (CH); 2617 (s),
2593 (s), 2558 (s) (BH); 2033 (w), 1871 (w), 1773 (w), 1687 (w),
1608 (w), 1508 (w), 1461 (s), 1440 (s), 1380 (s), 1345 (m),
1296 (m), 1205 (s), 1181 (s), 1105 (s), 1063 (s), 1023 (s),
972 (m), 938 (s), 832 (m), 796 (s), 756 (s), 664 (s), 624 (w),
564 (w), 528 (w), 487 (s), 440 (w), 409 (m). MS (FAB+,
3-nitrobenzyl alcohol matrix) m/z: 410 (3%, M+),
379 (4%, M+-OCH3). Anal. calcd for C12H36B10N2O2P2
1
C2B10H10), -5.6 (m, vbr, JBH n.d., 2B, C2B10H10), -6.2
1
1
(m, vbr, JBH n.d., 2B, C2B10H10), -10.3 (m, vbr, JBH n.d.,
4B, C2B10H10). IR (KBr, cm-1): 3064 (m), 3036 (m) (CH);

6076 Inorganic Chemistry, Vol. 48, No. 13, 2009
Stadlbauer et al.
(M = 410.47): C, 35.11; H, 8.84; N, 6.82. Found: C, 35.10; H,
8.69; N, 6.81%.
Table 2. 31P{1H} NMR Data for Compounds 1-5
1a/b 2a 2b 3a 3b
4a/b
5a
5b
Methanolysis of 8a/b. Compounds 8a/b (0.45 g, 0.8 mmol)
was heated to reflux in triethylamine (1 mL) and methanol
(10 mL) for 4 h. The solvent was evaporated and the residue kept
under full vacuum conditions at 70 °C for 2 h to obtain 0.35 g
δ(31P) 119.5; 118.4 117.2 117.1 112.4 113.5 114.6; 112.8 104.3 103.0
(ppm)
1
(94%) of 9a/b as a pale yellow oil. Data for 9a/b. H NMR
(CDCl3): δ 4.0-1.8 (m, 10H, B10H10), 3.26 (m, 4H, N{CH-
(CH3)2} + 6H, OCH3), 1.08 (m, 24H, N{CH(CH3)2}). 13C{1H}
Scheme 1. Synthesis of Chiral ortho-Carbaboranylbis(halophos-
phines)
1
NMR (CDCl3): δ 80.6 (d, JCP = 73.2 Hz, C2B10H10), 55.4
(d, JCP = 28.8 Hz, OCH3,), 45.0 (m, N{CH(CH3)2}), 24.5
2
(m, N{CH(CH3)2}). 31P{1H} NMR (CDCl3): δ 135.6 (s, br, rac +
meso isomer). 11B NMR (CDCl3): δ -3.8 (s, br, 1JBH n.d., 2B,
1
C2B10H10), -8.4 (s, br, JBH n.d., 2B, C2B10H10), -9.6 (s, br,
1JBH n.d., 4B, C2B10H10), -13.0 (s, br, 1JBH n.d., 2B, C2B10H10).
IR (KBr, cm-1): 2970 (s), 2933 (s), 2829 (m) (CH); 2600 (s) (BH);
2347 (w), 2172 (w), 2055 (w), 1846 (w), 1766 (w), 1656 (w),
1606 (w), 1460 (m), 1393 (m), 1365 (m), 1310 (w), 1260 (w),
1197 (m), 1175 (m), 1155 (w), 1124 (w), 1085 (w), 1038 (m),
970 (m), 913 (w), 875 (w), 850 (w), 824 (w), 795 (w), 735 (m),
695 (w), 640 (w), 589 (w), 521 (m), 440 (w). MS (EI+, 70 eV) m/z:
466.4 (100, M+); 423.3 (65, M+ - iPr); 409.3 (18, M+ - iPr -
CH2); 366.3 (30%, M+ - NiPr2); 324.2 (34%, M+ + H - NiPr2 -
iPr). Anal. calcd for C16H44B10N2O2P2 (M = 466.57): C, 41.19;
H, 9.50; N, 6.00. Found: C, 40.95; H, 9.74; N, 5.96%.
alcohol matrix) m/z: 466.4 (2%, M+); 435.3 (2%, M+ - OCH3);
367.3 (17%, M+ + H - NiPr2); 304.3 (2%, M+ - PNiPr2OCH3);
162.1 (100%, PNiPr2OCH3+). Anal. calcd for C16H44N2O2P2B10
(M = 466.59): C, 41.19; H, 9.50; N, 6.00; Found: C, 41.05;
H, 9.86; N, 5.87%.
Synthesis of N,N-Diisopropylamidomethylchlorophosphite.
Methyldichlorophosphite (10 mL, 106 mmol) was dissolved in
diethyl ether (600 mL), and the solution was cooled to 0 °C.
Then, N,N-diisopropylamine (29.7 mL, 211 mmol) was added
dropwise over 2 h. After complete addition, the reaction mixture
was warmed to room temperature and stirred overnight. The
ammonium salt was filtered off and then washed with diethyl
ether (2 ꢀ 200 mL). Then, the solvent was evaporated and the
resulting yellow oil distilled in a vacuum at 10 mbar and 76-
78 °C to yield the product as a colorless liquid. Yield: 16.5 g
(78%). 1H NMR (CDCl3): δ 3.66 (m, 2H, N{CH(CH3)2}), 3.38
Results and Discussion
rac-/meso-1,2-Bis(N,N-dialkylaminohalophosphino)-1,2-di-
carba-closo-dodecaborane(12)s 1-5 were obtained from
dilithiated ortho-carbaborane and N,N-dialkylaminodichloro-
or -dibromophosphines in diethyl ether at 0 °C (Scheme 1).
The yields range from about 60 to 70%. In the case of the
N,N-diethyl-substituted compound, a side product was
obtained in 20% yield (according to the 31P{1H} NMR
spectrum, 53.0 ppm), which is probably the 2:2 product.
Compounds 1-5 were obtained as mixtures of rac and meso
isomers (ratio 1:1) because of the two chiral phosphorus
atoms. Separation of the diastereomers by fractional crystal-
lization from n-hexane solutions was possible for 2, 3, 4, and
5, whereas separation of N,N-dimethylamino-substituted
compound 1 failed. All compounds were obtained as air-
and water-stable colorless solids which are soluble in organic
solvents.
3
3
(d, JHP = 14.4 Hz, 3H, OCH3), 1.19 (d, JHP = 6.8 Hz, 6H,
N{CH(CH3)2}), 0.89 (d, JHP = 6.0 Hz, 6H, N{CH(CH3)2}).
3
31P{1H} NMR (CDCl3): δ 181.4 (s).
Direct Synthesis of rac-/meso-1,2-Bis(N,N-diisopropylamido-
methylphosphonito)-1,2-dicarba-closo-dodecaborane(12) (7a/b).
ortho-Carbaborane (1.0 g, 6.9 mmol) was dissolved in diethyl
ether (30 mL). After cooling to 0 °C, a solution of n-BuLi in
n-hexane (5.90 mL, 13.8 mmol) was added dropwise to the
solution. The mixture was warmed to room temperature and
stirred for 2 h, during which 1,2-dilithiodicarba-closo-dodeca-
borane(12) formed as a white solid. The resulting mixture was
then added slowly through a cannula to a cooled solution of N,
N-dimethylamidomethylchlorophosphite (2.80 mL, 15.6 mmol)
in diethyl ether (20 mL). The mixture was stirred overnight at
room temperature. LiCl was filtered off, and the solvent was
then evaporated to dryness under vacuum conditions. The
resulting residue was extracted with n-hexane. The combined
n-hexane fractions were concentrated, and fractional crystal-
lization yielded colorless crystals of the meso form 7b. Yield:
1.4 g (43%), meso isomer. Data for 7b. Mp: 150-151 °C.
1H NMR (CDCl3): δ 4.2-1.9 (m, br, 10H, B10H10), 3.26
(m, 4H, N{CH(CH3)2}, 6H, OCH3), 1.08 (m, br, 24H, N{CH-
Spectroscopic Properties. The 31P{1H} NMR spectra of
1-5 exhibit two signals due to the two diastereomers,
while the proton coupled spectra show only broadening
of the signals and, therefore, sometimes only one signal
due to overlap (Table 2 gives 31P{1H} NMR data). Where
X-ray crystallography could be employed, the signals
could be assigned to the respective diastereomers. The
chemical shifts range from about 119 ppm for 1a/b to
103.0 ppm for 5b. They show a significant linear trend:
with increasing steric demand of the amino group,
a marked high-field shift is observed, for example, ca.
119 ppm for dimethylamino-substituted compound 1a/b
and 103.0 ppm for the diphenylamino-substituted com-
pound 5b. The exchange of chlorine by a bromine atom
obviously did not have a significant influence on the
chemical shift, as can be seen by comparing 3a/b with
4a/b. In general, the signals are shifted by about 45 to
1
2
(CH3)2}). 13C{1H} NMR (CDCl3): δ 87.2 (m, JCP + JCP
=
80.9 Hz, C2B10H10), 54.6 (m, OCH3), 45.6 (m, br, N{CH-
(CH3)2}), 24.3 (m, br, N{CH(CH3)2}). 31P{1H} NMR (CDCl3):
δ 126.1 (s, meso isomer). 11B NMR (CDCl3): δ -0.3 (s, br,
1
1JBH = 143.3 Hz, 2B, C2B10H10), -5.3 (s, JBH n.d., 1B,
1
C2B10H10), -7.1 (d, br, JBH = 150.8 Hz, 2B, C2B10H10,),
1
-10.5 (s, br, JBH n.d., 5B, C2B10H10). IR (KBr, cm-1):
2972 (s), 2930 (m), 2827 (w) (CH); 2625 (s), 2564 (s) (BH);
1456 (m), 1394 (m), 1366 (s), 1198 (s), 1174 (s), 1153 (m), 1121 (s),
1036 (s), 970 (s), 877 (m), 853 (w), 831 (w), 808 (m), 746 (s),
639 (m), 519 (m), 456 (w), 431 (w). MS (FAB+, 3-nitrobenzyl

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6077
55 ppm to a high field compared to those of the corre-
sponding starting materials, while similar values were
observed for the corresponding rac-/meso-1,2-bis(tert-
butylchlorophosphino)-1,2-dicarba-closo-dodecaborane
(12) (rac, 116.7 and meso, 116.4 ppm).15c
The diastereomeric mixture of 1 exhibits two doublets
for the NMe2 groups (3JPH 6.0 Hz). Due to the chirality of
the phosphino groups, compound 2a shows two multi-
1
plets in the H NMR spectrum for the diastereotopic
protons of the CH2 fragment. This phenomenon is,
however, not observed for the CH2 groups of 2b, which
give rise to only one multiplet. Interestingly, in 3b the CH3
groups exhibit not one signal, as expected, but two broad
singlets. Probably, the isopropyl groups are inequivalent
due to hindered rotation. The four CH groups are also
different and exhibit two broad singlets, one at 2.99 and
one at 3.92 ppm. Similar observations were made in the
13C{1H} NMR spectrum. Due to the mirror plane in
the molecule, four signals for the eight methyl groups
are observed. One of the four signals occurs as a pseudo-
triplet, which became a singlet in the phosphorus-
decoupled mode. This observation can be explained by
the assumption that two methyl groups have a dihedral
angle which allows coupling to phosphorus. Bromo ana-
logue 4 exhibits similar behavior in the NMR spectrum.
As no suitable crystals for X-ray crystallography could
be obtained of the diastereomers of 4, we assume that the
diastereomer which crystallizes is the meso isomer be-
cause it exhibits similar NMR spectra to those of the meso
isomer of 3.
Figure 1. Molecular structure of 2a (ORTEP with atom labeling
scheme; thermal ellipsoids are drawn at the 50% probability level;
hydrogen atoms are omitted for clarity; only the S,S enantiomer is
shown).
Figure 2. Molecular structure of 2b (ORTEP with atom labeling
scheme; thermal ellipsoids are drawn at the 50% probability level;
hydrogen atoms are omitted for clarity).
All compounds show a pseudotriplet for the carbon
atoms of the carbaborane cluster in the 13C{1H} NMR
spectrum. For long measuring times, two small satellites
can additionally be observed. As reported elsewhere,36
these satellites occur because of the presence of strong
P-P coupling. Due to the low natural abundance of 13C
(1.1%), the majority of molecules which are detected by
13C{1H} NMR only contain one 13C atom at this special
position. Therefore, these molecules are asymmetric, and
the 13C nucleus couples with both phosphorus nuclei
Table 3. Selected Bond Lengths (pm) and Angles (deg) of 2a, 2b, 3b, and 5a
2a
2b
3b
5a
P(1)-C(1)
190.0(2)
190.8(2)
208.2(8)
207.9(7)
164.6(2)
164.3(1)
170.6(2)
104.7(7)
103.9(6)
97.5(6)
104.0(7)
103.5(5)
96.9(5)
116.7(2)
126.9(2)
115.8(1)
191.1(2)
190.6(2)
207.6(7)
207.5(7)
164.4(2)
164.6(1)
170.4(2)
106.1(7)
104.1(6)
96.9(5)
104.3(7)
103.6(6)
97.4(5)
116.9(2)
126.4(1)
115.7(1)
190.3(2)
189.7 (2)
208.87(5)
208.47(6)
165.4(1)
164.4(1)
172.6(2)
105.30(7)
103.65(5)
98.32(5)
106.81(6)
104.61(5)
97.80(5)
116.7(1)
126.2(1)
114.5(1)
188.9(1)
209.1(6)
166.7(1)
P(2)-C(2)
P(1)-Cl(1)
P(2)-Cl(2)
P(1)-N(1)
P(2)-N(2)
C(1)-C(2)
174.7(3)
104.9(6)
106.0(5)
98.3(5)
N(1)-P(1)-C(1)
N(1)-P(1)-Cl(1)
C(1)-P(1)-Cl(1)
N(2)-P(2)-C(2)
N(2)-P(2)-Cl(2)
C(2)-P(2)-Cl(2)
C(3)-N(1)-C(5)
C(3)-N(1)-P(1)
C(5)-N(1)-P(1)
2
(1JCP and JCP). This scenario causes a spin system of
higher order. By simulating an ABX spin system with
SpinWorks,37 the coupling constants JPP 1JCP, and
,
2JCP could be determined for 3b, and JPP was found to
be 280.0 Hz. The reason for the occurrence of strong P-P
coupling will be explained below. The distance between
the two external signals of the triplets corresponds to the
sum of 1JCP and 2JCP. For 3b, the sum amounts to 110 Hz.
The correct values of the coupling constants can only be
determined by simulation with SpinWorks. Subse-
quently, 1JCP was found to be 90 Hz and 2JCP 20 Hz.
Molecular Structures of 2a, 2b, 3b, and 5a. While
compound 2a (Figure 1) crystallizes in the centrosym-
metric monoclinic space group P21/n with four molecules
in the unit cell, compound 2b (Figure 2) crystallizes in the
triclinic space group P1 with two molecules in the unit
cell. In the racemic isomer 2a, the molecule has a non-
crystallographic C2 axis, which bisects the C(1)-C(2) and
116.2(1)
127.7(1)
114.1(1)
B(4)-B(7) bonds; in the meso isomer 2b, the molecule has
a noncrystallographic pseudomirror plane on which the
atoms B(2), B(3), B(8), and B(9) are located. Due to the
presence of an inversion center in the space group, both
enantiomeric forms of 2a (R,R and S,S) are present in the
unit cell. Selected bond lengths and angles are listed in
Table 3.
Single crystals of the meso isomer of 3 were obtained by
recrystallization from n-hexane at room temperature.
Compound 3b (Figure 3) crystallizes in the monoclinic
space group P21/n with four molecules in the unit cell. The
molecule has a noncrystallographic mirror plane, which
bisects the C-C bond of the cluster. Compound 5a
crystallizes in the orthorhombic space group P21212
with two formula units and two molecules of toluene
in the unit cell. The molecule of 5a (Figure 4) has a
::
(36) Bauer, S.; Tschirschwitz, S.; Lonnecke, P.; Frank, R.; Kirchner, B.;
Clarke, M. L.; Hey-Hawkins, E. Eur. J. Inorg. Chem., in press.
(37) Marat, K. SpinWorks, version 2.3; University of Manitoba:
Winnipeg, Canada, 2004.

6078 Inorganic Chemistry, Vol. 48, No. 13, 2009
Stadlbauer et al.
Scheme 2. Methanolysis of Carbaboranylbis(aminohalophosphines)
Figure 3. Molecularstructure of3b (ORTEP withatomlabeling scheme;
thermal ellipsoids are drawn at the 50% probability level; hydrogen
atoms are omitted for clarity; only the R,R enantiomer is shown).
large excess of 120 equiv of methanol was added to the
reaction mixture. After a further 24 h, 62% of 3b was still
left and about 20% of the product was observed, besides a
significant amount of decomposition products. To accel-
erate the conversion, 2 equiv of 1H-1,2,4-triazole
were added to the reaction mixture. After a further
5 days at room temperature, about 10% of 3b was still
unconverted. The reaction mixture contained about 60%
product and nearly 30% decomposition products. In-
stead of solely one signal for the meso product, a mixture
of rac and meso isomers in a ratio of 1:6 was detected. The
occurrence of the rac isomer shows that methanolysis
surprisingly proceeds with retention at some phosphorus
atoms. The reaction with 3b was also conducted under
reflux conditions in methanol as a solvent and triethyla-
mine or pyridine as a base. In both cases, decomposition
was observed to a large extent, and only minor formation
of 7 was observed. Surprisingly, the reaction with the
more reactive bis(bromophosphine) derivative 4a/b led
under reflux for 3 h to very similar results. The same
problems were observed when 2a, 2b, and a bis(tert-
butylchlorophosphine) derivative38 were treated with
methanol.
These findings are in contrast to the observation that
carbaboranylmonochlorophosphines smoothly under-
went alcoholysis with different alcohols by stirring over-
night at room temperature to yield the expected
products.39 The extended reaction time and the formation
of byproducts indicate that methanolysis in the 1,2-di-
substituted derivatives is prevented to a certain extent.
Theoretical investigations of the bisphosphines were
therefore carried out to account for the inhibited metha-
nolysis.
Figure 4. Molecular structure of5a (ORTEPwith atomlabeling scheme;
thermal ellipsoids are drawn at the 50% probability level; hydrogen
atoms are omitted for clarity; only the R,R enantiomer is shown).
crystallographic C2 axis, which bisects the C(1)-C(1a)
and B(4)-B(4a) bonds. Selected bond lengths and angles
are collected in Table 3.
In 2a, 2b, 3b, and 5a, each phosphorus atom has
pyramidal coordination by one nitrogen atom, one car-
bon atom of the carbaborane cluster, one chlorine atom,
and the lone pair of electrons. The C-C bond length of
the cluster ranges from 170.6 (2a) to 174.7 pm (5a) and is
therefore in the same range as in similar compounds.12b,14
In general, the bond lengths and angles of 2a/b, 3b, and 5a
show no remarkable deviations from comparable struc-
tures. Nevertheless, the P-Cl bond lengths in 2a/b, 3b,
and 5a are longer by approximately 4 pm than those
observed in rac-1,2-(PPhCl)2(C2B10H10) (205.1(1) pm)15b
and rac- and meso-1,2-(PtBuCl)2(C2B10H10) (207.4(9)/
207.0(8) and 207.0(9)/205.8(9) pm).15c The comparison
shows the influence of the NR2 groups on the electronic
properties of the phosphorus atoms, which are reflected
in changes in the P-Cl bond lengths.
Methanolysis of the Halophosphines. The methanolysis
of carbaboranylchlorophosphines 2-5 (Scheme 2)
was studied for further functionalization of the phos-
phorus atom. Due to the P-Cl bond, the compounds
were expected to undergo rapid reactions with O or N
nucleophiles. This was attempted by treating the meso
isomer 3b with an excess of 4.7 equiv of methanol and
pyridine at room temperature. Unexpectedly, the reac-
tion proceeds very slowly. After 18 h, only about 10% of
the desired product and 90% of the starting material were
observed in the 31P{1H} NMR spectrum. Therefore, a
Computational Approach to Inhibited Methanolysis. In
general, incomplete conversion of the reactants can be
traced back to either thermodynamics or kinetics, both of
which are to be considered apart from each other. The
thermodynamic discussion focuses on the calculation of
the Gibbs energy of the reaction ΔRG°. A kinetic inves-
tigation encompasses a transition-state (TS) search of the
most likely reaction path and includes the calculation of
the activation barrier ΔRG‡. Herein, the computational
studies are based on numerous simplifications which are
presented in detail in the Supporting Information.
We employed the known reactions of monosubstituted
ortho-carbaboranes as a benchmark, because they are
::
(38) Maulana, I. Ph.D. thesis, Universitat Leipzig, Leipzig, Germany,
2005.
::
(39) Tschirschwitz, S.; Lonnecke, P.; Hey-Hawkins, E. Organometallics
2007, 26, 4715–4724.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6079
Figure 5. Investigated monosubstituted derivatives of benzene and ortho-carbaborane (top) and their disubstituted analogues (bottom). The illustration
shows the attack of methanol at phosphorus. Boron (tan), carbon (gray), chlorine (green), hydrogen (white), nitrogen (blue), oxygen (red), phosphorus
(orange). Note the distinct geometry for the nitrogen-substituted TS5 and TS6.
Table 4. Differences in the Free Activation Enthalpies for the Transition States
and the Resulting Relative Rate Constants, Obtained from Eyring’s Equation and
Calculated for Standard Conditions
TS2/TS1
TS4/TS3
TS6/TS5
Δ(ΔG‡) [kJ/mol] 3.8
krel krel
10.0
krel
13.8
krel
kTS2
kTS1
kTS4
kTS3
kTS6
kTS5
1
4:6
1
56:5
1
261:7
¼
¼
¼
¼
¼
¼
Figure 6. Numbering of the atoms in disubstituted phenyl and carba-
borane derivatives.
certainly known to proceed with respect to thermody-
namics and kinetics. The thermodynamics and kinetics of
the disubstituted derivatives were calculated and com-
pared to the monosubstituted ones.
Thermodynamics. The values of ΔRG° for the metha-
nolysis of the mono- and disubstituted ortho-carbaborane
derivatives were found to be of similar magnitude. Be-
cause ΔRG° < 0, thermodynamic hindrance could be
excluded for the disubstituted derivatives, and a kinetic
investigation was carried out.
Kinetics. The transition states (Figure 5) were found to
be solvent-supported, because methanol is a solvent and a
nucleophile at the same time. We only obtained reason-
able transition states when a dimer of methanol was
simulated to attack, whereas attempts with a single
molecule of methanol failed. Table 4 gives differences in
the free activation enthalpies for the transition states and
the resulting relative rate constants.
The entries suggest that the alcoholysis of the disub-
stituted derivatives proceed at rates which are lower than
those of the monosubstituted compounds. These findings
are in accordance with the experiment. The alcoholysis of
the disubstituted ortho-carbaborane bearing P(Cl)(Me)
substituents is 57 times slower than its monosubstituted
analogue (TS4 and TS3). This effect is even more pro-
nounced in case of P(Cl)(NMe2) substituted compounds.
Here, the alcoholysis of the disubstituted compound is
262 times slower compared to the monosubstituted deri-
vative (TS6 and TS5). It was clearly demonstrated that
the problems in alcoholysis are of kinetic origin and arise
from the 1,2-disubstitution pattern. The kinetic inhibition
is especially distinct in the case of the carbaborane
derivatives and, in turn, even more pronounced in the
case of the amino derivatives. We assume that inhibition
occurs for two reasons: the steric demand of the carba-
borane moiety and interactions between the two phos-
phorus atoms.
P
P Interactions. For further investigation, we
3 3 3
inspected the geometrically optimized structures and
compared them to the unsubstituted scaffolds (Figure 7).
All disubstituted structures exhibit distances between the
phosphorus atoms shorter than the sum of the van der
Waals radii (2 ꢀ 190 pm)40 and attraction of the
phosphorus moieties to each other, indicated by compres-
sion of the covalent angles (Table 5).
The numbering of the atoms is in accordance with
Figure 6.
These findings clearly show that attractive interactions
between the phosphorus moieties occur. Further indica-
tions for the interactions was obtained by means of
the shared electron number (SEN) values. The SEN
values between the phosphorus atoms (Figure 7) range
from 0.026 to 0.059 and are therefore on the same order of
magnitude as a hydrogen bond in a simulated water dimer
(0.040). Visualization of the canonical molecular orbitals
for Ia-III shows significant overlap of orbital fragments
with the same sign and therefore rationalizes attraction
between the phosphorus moieties (Figure 7).
(40) (a) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 260. (b) Batsanov, S. S. Russ. J. Inorg.
Chem. 1991, 36, 1694–1708.

6080 Inorganic Chemistry, Vol. 48, No. 13, 2009
Stadlbauer et al.
Figure 7. Geometrically optimized disubstituted compounds. P(Cl)(Me) derivatives occur in two conformations, denoted by a and b, respectively.
Canonical molecular orbitals visualized with a spatial probability of 95%. The red and blue areas symbolize a positive or negative sign of the wave function,
respectively. Ia (HOMO-1), Ib (HOMO-1), IIa (HOMO-2), IIb (HOMO-2), and III (HOMO-3); boron (tan), carbon (gray), chlorine (green), hydrogen
(white), and phosphorus (orange).
Table 5. Calculated Distances and Angles
distance H1-H2
(P1-P2) [pm]
bond angle H-C-C
(P-C-C) [deg]
o-C6H4
o-(-CB10H10C-)
248.9
258.7
301.2
307.3
317.5
324.7
308.5
120.0
116.3
115.4
111.0
118.2
113.5
110.6
Ia
IIa
Ib
IIb
III
The quantum chemical considerations are consistent
with a couple of experimental observations. The geome-
try is demonstrated for 3bas a selected example (Figure 3).
Figure 8. Molecular structure of 8a/b (ORTEP with atom labeling
scheme; thermal ellipsoids are drawn at the 50% probability level;
hydrogen atoms are omitted for clarity; only the R,R enantiomer is
shown).
The respective distance P1 P2 amounts to 314.6 pm.
3 3 3
The P1-C1-C2 angle is 113.65(9)°, and the P2-C2-C1
angle is 109.75(9)°. The extraordinarily high P-P
coupling constant described above is in accordance with
the orbital and population analysis. In accordance with
this theory, a meta-carbaborane derivative should react
without any problems. Therefore, the meta-carbaborane
analogue of 4 was synthesized according to the procedure
described for the ortho-carbaborane. The resulting com-
pound, 8, was formed as a mixture of rac and meso
isomers.
Table 6. Selected Bond Lengths (pm) and Bond Angles (deg) of 8a/b
bond lengths [pm]
bond angles [deg]
Br(1)-P(1)
227.3(1)
164.5(3)
188.2(4)
227.5(2)
164.9(9)
188(1)
N(1)-P(1)-C(1)
106.8(2)
104.2(1)
99.2(1)
107.3(6)
105.7(5)
98.4(3)
116.7(3)
126.2(2)
115.2(2)
P(1)-N(1)
P(1)-C(1)
Br(2)-P(2)
P(2)-N(2)
C(1)-C(2)
N(1)-P(1)-Br(1)
C(1)-P(1)-Br(1)
N(2)-P(2)-C(2)
N(2)-P(2)-Br(2)
C(2)-P(2)-Br(2)
C(3)-N(1)-C(6)
C(3)-N(1)-P(1)
C(6)-N(1)-P(1)
Molecular Structure of 8a/b. The compound crystal-
lizes in the monoclinic space group P21 with two mole-
cules in the unit cell. The crystal contains about 80% rac
isomer and 20% meso isomer. The molecular structure
(without disorder, only the R,R enantiomer is shown)
is presented in Figure 8; selected bond lengths and
angles are listed in Table 6. The molecule exhibits a
noncrystallographic C2 axis, which bisects the center of
the B(2)-B(3) bond and the center of the B(9)-B(10)
bond.
The P-C bond length shows no difference in comparison
with the corresponding ortho-carbaborane derivates 2a/b, 3b,
and 5a. The P-Br bonds are slightly shorter (ca. 227 pm) than
the P-Br bonds in dibromotetraphosphatetracyclononane
derivatives (228.6(2) and 231.2(2) pm41 or 228.7(1) and
231.3(1) pm42). On the other hand, they are in good
accordance with the P-Br bond lengths found for 1,8-bis-
(dibromophosphanyl)naphthalene (between 222.53(9) and
227.37(9) pm).43
::
(41) Asmus, S. M. F.; Bergstrassler, U.; Regitz, M. Synthesis 1999, 9,
1642–1650.
::
(42) Dietz, J.; Schmidt, T.; Renner, J.; Bergstrassler, U.; Tabellion, F.;
Preuss, F.; Binger, P.; Heydt, H.; Regitz, M. Eur. J. Org. Chem. 2002, 1664–
1676.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6081
Spectroscopic Properties of 8a/b. Due to the larger
distance between the two chiral phosphorus atoms
(573.2 pm), only one signal is observed for the mix-
ture of diastereomers in the 31P{1H} NMR spectrum at
127.2 ppm. The proton NMR spectrum is not different
from that for the ortho-carbaborane analogue 4. The 11B-
{1H} NMR spectrum shows four signals in a ratio of
2:3:3:2, which can be assigned according to the literature,
where boron atoms closest to carbon atoms are observed
at the lowest chemical shift and boron atoms furthest
from carbon atoms at the highest.44
Methanolysis of 8a/b. The diastereomeric mixture 8a/b
was then heated under reflux for 4 h according to the
protocol for the ortho-carbaborane derivatives 2-5 with
methanol as a solvent and triethylamine as a base
(Scheme 3). A 31P{1H} NMR spectrum of the reaction
mixture showed exclusive formation of methoxy-substi-
tuted compound 9a/b. This result is in excellent agree-
Figure 9. Molecular structure of6a (ORTEPwith atomlabeling scheme;
thermal ellipsoids are drawn at the 50% probability level; hydrogen
atoms are omitted for clarity; only the R,R enantiomer is shown).
ment with the theory of missing P P interactions.
Separation of the diastereomers of 9, which is a pale
yellow oil, was unsuccessful.
3 3 3
An alternative approach for alkoxy-substituted ortho-
carbaboranylbisphosphines is the reaction of the ortho-
dilithiocarbaborane, with an alkoxy-substituted amido-
chlorophosphine having only one chlorine atom for
substitution. This reaction pathway is more favored,
because it has only one step instead of two, and therefore
the total yield is higher than in the two-step synthesis
discussed above.
Figure 10. Molecular structure of 7b (ORTEP with atom labeling
scheme; thermal ellipsoids are drawn at the 50% probability level;
hydrogen atoms are omitted for clarity).
The 31P{1H} NMR spectra of these compounds exhibit
signals at 132.8 ppm (6a) and 126.1 ppm (7b), which is a
markedly low-field shift in comparison to the halophos-
phine derivatives 2 and 3. For the carbon atoms of the
cluster, a triplet similar to compounds 1-5 is observed at
85.5 ppm (6a) and 87.7 ppm (7b). The sum of the direct
and geminal C-P coupling constants amounts to 85.0 Hz
(6a) and 80.9 Hz (7b).
Molecular Structures of 6a and 7b. Compound 7b
crystallizes in the orthorhombic space group P212121 with
four molecules in the unit cell and 6a in the monoclinic
space group C2/c with four molecules in the unit cell. The
structure of 6a is shown in Figure 9, and 7b is shown in
Figure 10. Selected bond lengths and angles are listed in
Table 7. The rac isomer 6a has a crystallographic C2 axis
which bisects the C(1)-C(1a) and B(4)-B(4a) bonds.
Due to the presence of an inversion center in this
space group, both enantiomeric forms of 6a (R,R and
S,S) are present in the unit cell. The meso isomer 7b
has a mirror plane, which bisects the C(1)-C(2) bond.
Table 7. Selected Bond Lengths (pm) and Bond Angles (deg) of 6a and 7b
6a
7b
P(1)-O(1)
162.9(1)
165.4(1)
190.3(1)
164.0(1)
166.5(2)
191.1(2)
164.7(1)
166.4(2)
191.3(2)
171.8(2)
104.87(7)
93.39(7)
106.47(7)
103.59(7)
94.46(7)
105.68(7)
116.9(2)
115.8(2)
P(1)-N(1)
P(1)-C(1)
P(2)-O(2)
P(2)-N(2)
P(2)-C(2)
C(1)-C(2)
169.2(2)
103.8(6)
94.2(5)
O(1)-P(1)-N(1)
O(1)-P(1)-C(1)
N(1)-P(1)-C(1)
O(2)-P(2)-N(2)
O(2)-P(2)-C(2)
N(2)-P(2)-C(2)
C(9)-O(1)-P(1)
C(16)-O(2)-P(2)
104.8(5)
116.4(1)
Scheme 3. Methanolysis of the meta-Carbaboranylbis(aminobromophosphine) 8a/b

6082 Inorganic Chemistry, Vol. 48, No. 13, 2009
Stadlbauer et al.
The bond lengths are, overall, in the same range as
those of the carbaboranylbis(halophosphines) presented
above.
are, on the one hand, the steric demand of the carbaborane
core and, on the other hand, possible P P interactions.
3 3 3
SEN analysis gives values ranging from 0.026 to 0.059
between P1 and P2, on the same order of magnitude as a
hydrogen bond in a water dimer. Visualization of the cano-
nical molecular orbitals shows significant overlap of orbital
fragments with the same sign and therefore supports the
picture of a possible attraction between the phosphorus
moieties. In accordance with this theory, a meta-carba-
boranylbis(aminobromophosphine) was found to undergo
smooth alcoholysis. An alternative approach for alkoxy-
substituted ortho-carbaboranylbisphosphines is the reaction
of the ortho-dilithiocarbaborane with an alkyl-substituted
amidochlorophosphite. This reaction yields the desired pro-
duct in one step and is therefore favored for the synthesis of
ortho-carbaboranylbis(N,N-dialkylamidoalkylphosphonites).
Conclusions
Novel amidohalophosphine derivatives of ortho-carbabor-
ane were synthesized and fully characterized. The separation
of the rac and meso diastereomers was successful in most
cases, and therefore the configuration of the phosphorus
atoms could be determined. Further functionalization of the
phosphorus atom was studied for carbaboranylbis(amino-
halophosphines) 2-5. Due to the P-Cl bond, the com-
pounds were expected to undergo rapid reactions with O or
N nucleophiles, but instead it was found that alcoholysis is
hindered. Quantum chemicalcalculationsusing DFT showed
that inhibition of the alcoholysis is of kinetic and not of
thermodynamic origin. The rate of the methanolysis of
the disubstituted ortho-carbaborane derivatives is about
57-262 times lower than that of the corresponding mono-
substituted derivatives. The reasons for these observations
Acknowledgment. We gratefully acknowledge support
from the Deutscher Akademischer Austausch Dienst
(DAAD doctoral grant for I.M.).
Supporting Information Available: Computational details for
theoretical calculations. This material is available free of charge
via the Internet at http://pubs.acs.org.
(43) Kilian, P.; Slawin, A. M. Z.; Woollins, J. D. Chem.;Eur. J. 2003, 9,
215–222.
(44) Hermanek, S. Inorg. Chim. Acta 1999, 289, 20–44.