Carbaborane-substituted 1,2,3-triphospholanes and 1-aza-2,5-diphospholane: New synthetic approaches

Article abstract of DOI:10.1002/chem.201302878

New phosphorus-containing, five-membered P,P,P and P,N,P heterocycles were synthesized and fully characterized. The P,P,P heterocycles, 1,2,3-triphospholanes, can be synthesized by two different facile pathways, whereas the P,N,P compound, a 1-aza-2,5-diphospholane, can only be obtained with silylamine.

Full text of DOI:10.1002/chem.201302878

DOI: 10.1002/chem.201302878
Full Paper
&
Heterocycles
Carbaborane-Substituted 1,2,3-Triphospholanes and 1-Aza-2,5-
diphospholane: New Synthetic Approaches
Anika Kreienbrink, Sarah Heinicke, Thi Thuy Duong Pham, Renꢀ Frank, Peter Lçnnecke, and
Evamarie Hey-Hawkins*[a]
Abstract: New phosphorus-containing, five-membered P,P,P
and P,N,P heterocycles were synthesized and fully character-
ized. The P,P,P heterocycles, 1,2,3-triphospholanes, can be
synthesized by two different facile pathways, whereas the
P,N,P compound, a 1-aza-2,5-diphospholane, can only be ob-
tained with silylamine.
Introduction
1976, Heinicke et al. described the synthesis of different CÀE1À
E2ÀE3ÀC heterocycles (E1=NR; E2=BR, SiR2, PR, AsR, SnR2;
E3=AsR; R=alkyl, aryl).[10]
Strained phosphorus-containing heterocycles have attracted
considerable interest due to their unusual reactivity and struc-
tures,[1] and also as ligands for transition metals.[2] However,
the synthesis of stable four- and five-membered phosphorus-
containing heterocycles with endocyclic PÀP bonds remains
a challenge.[3,7] The first triphospholane, namely, 1,2,3-triphen-
yl-1,2,3-triphosphaindane, was obtained by Mann and Pragnell
in 1966[4] from the reduction of dichlorophenylphosphane with
lithium followed by reaction with 1-bromo-2-iodobenzene;
5,10-dihydro-5,10-diphenylphosphanthrene was obtained as
a byproduct.
1,2-Dicarba-closo-dodecaborane(12) [ortho-carbaborane][11] is
an interesting electron-poor C2-symmetrical backbone for bis-
phosphanes.[12] Most research is focused on disubstituted de-
rivatives, in which the ortho-carbaborane imitates an ethylene
or phenylene system, but acts more like a rigid backbone.[13]
When combined with the electron-withdrawing and -delocaliz-
ing ability of the carbaborane moiety the properties of
phosphorus(III) compounds change dramatically. Furthermore,
when the carbaborane backbone was employed, cyclic 1,2-di-
phosphetanes could be obtained.[14] In this work, we extend
this synthetic approach to carbaborane-based five-membered
heterocycles, namely, 1,2,3-triphospholanes and 1-aza-2,5-di-
phospholane.
X-ray structure analysis showed a trans arrangement of the
three phenyl groups.[5] Further studies by Mann and Mercer ac-
cessed new synthetic routes and illustrated the chemistry of
these interesting compounds.[6] In 1985, Sheldrick and co-work-
ers prepared 1,2,3-triphospholane-2-ide from o-phenylene-bis-
(lithiumphenylphosphanide) and white phosphorus in good
yield.[7] This anionic species can then be treated with different
halogenated substrates to give the corresponding 1,2,3-tri-
phospholanes.[7]
Results and Discussion
Synthesis of 4,5-dicarba-closo-dodecaboranyl-1,2,3-triphos-
pholanes
Besides 1,2,3-triphospholanes, several two-element 1,3-di-
phospholanes have been reported. One of the first P,As,P het-
erocycles was synthesized by the reaction of a dilithiodiphos-
phanide species with different arsenic dichlorides.[8] Extensive
studies of o-phenylenebisphosphanes by Issleib et al. revealed
that these are versatile reagents that allow easy access to a va-
riety of five-membered CÀPÀEÀPÀC heterocycles (E=BR, AlR,
CR2, SiR2, SnR2, NR, AsR, S; R=alkyl, aryl, N(alkyl)2, N(aryl)2).[9] In
4,5-Dicarba-closo-dodecaboranyl-1,2,3-triphospholanes can be
obtained by two different routes.
Synthesis from carbaborane-based 1,2-diphosphetanes
Carbaborane-based 1,2-diphosphetanes,[14] which can be pre-
pared in a facile way and with excellent yield, have proved to
be highly versatile starting materials for a variety of P-substi-
tuted carbaboranes.[15] Alkali metals,[16] lithium alkyls,[17] and
platinum(0) complexes[18] were reported to cleave the PÀP
bond of phosphorus heterocycles. Thus, the tert-butyl-substi-
tuted 1,2-diphosphetane 1a (Scheme 1) reacts with elemental
lithium in THF with cleavage of the PÀP bond to give a deep-
red solution of the dianionic lithium salt, which offers access to
novel open-chain or cyclic derivatives.[19] Treatment with one
equivalent of dichlorophenylphosphane gave the first five-
[a] Dr. A. Kreienbrink, S. Heinicke, T. T. Duong Pham, Dr. R. Frank,
Dr. P. Lçnnecke, Prof. Dr. E. Hey-Hawkins
Fakultꢀt fꢁr Chemie und Mineralogie, Institut fꢁr Anorganische Chemie
Universitꢀt Leipzig, Johannisallee 29, 04103 Leipzig (Germany)
Fax: (+49)341-9739319
E-mail: hey@rz.uni-leipzig.de
Homepage: http://www.uni-leipzig.de/chemie/hh/
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201302878.
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Scheme 1. Synthetic routes to trans,trans-4,5-dicarba-closo-dodecaboranyl-1,2,3-triphospholanes 2a–d.
membered 4,5-dicarba-closo-dodecaboranyl-1,3-di-tert-butyl-2-
Table 1. Chemical shifts (d) and coupling constants (J) of the C2P3 system
in 2a–d.
phenyl-1,2,3-triphospholane (2a) in moderate yield (Scheme 1).
31P{1H} NMR
(162 MHz, CDCl3)
d [ppm]
13C{1H} NMR
(100 MHz, CDCl3)
d (ABX spin system)
[ppm]
1J(P,P)
[Hz]
1J(C,P)+2J(C,P)
[Hz]
Synthesis from 1,2-bis(halophosphanyl)-1,2-dicarba-closo-do-
decaborane(12)s
2a À21.0 (t), 50.8 (d) 172.8
2b À7.3 (t), 28.1 (d) 184.0
80.4 (m)
83.7 (m)
88.8 (m)
85.3 (m)
89.5
79.2
78.1
75.7
2c
5.5 (t), 34.0 (d) 225.0
2.4 (t), 23.0 (d) 201.0
An alternative synthetic route is the reaction of 1,2-bis(halo-
phosphanyl)-1,2-dicarba-closo-dodecaborane(12)s[12a,13c,l,m,20]
with dichlorophosphanes and a reducing agent (Scheme 1).
The starting materials 1,2-bis(chlorophenylphosphanyl)-1,2-di-
carba-closo-dodecaborane(12) (1b)[12a] and 1,2-bis(chlorocyclo-
hexylphosphanyl)-1,2-dicarba-closo-dodecaborane(12) (1c) (see
the Supporting Information for X-ray structures) are easily ac-
cessible by reaction of the dilithiated carbaborane with dichlor-
ophenylphosphane or dichlorocyclohexylphosphane. Reduc-
tion of the diastereomeric mixture of 1b or 1c with zinc fol-
lowed by addition of dichlorophenyl- or dichlorocyclohexyl-
phosphane exclusively gave the all-trans isomers of the 1,2,3-
triphospholanes 2b–d (Scheme 1), shown by 31P{1H} NMR spec-
troscopy of the reaction solutions. Apparently, the electron-
withdrawing and -delocalizing ability of the cluster and the
long CÀC bond stabilize the five-membered heterocycles 2a–
d.[12b] Compounds 2a–d were obtained in good to moderate
yield as colorless crystals. They are highly soluble in nonpolar
solvents, water stable, and moderately air stable due to the re-
duced electron density at phosphorus.[21]
2d
Molecular structures of 2a–d
X-ray structure analyses[22] were carried out for 2a–d. The five-
membered rings of the unsymmetrically substituted com-
pounds 2a and 2d (Figure 1) have an envelope conformation,
illustrated by the large torsion angles (Table 2), in contrast to
2b and 2c, which show almost planar rings (Figure 2). The en-
docyclic PÀC bond lengths (185.6(2)–188.1(4) pm) of 2a–d are
larger than those found in cyclic phosphanes, for example,
1,2,3-triphenyl-1,2,3-triphospholane (average PÀC bond
length=182.5 pm),[5,23] whereas the PÀP bonds (220.4(1)–
222.0(1) pm) compare well with the standard value (222 pm)
for PÀP bonds.[24] The C1ÀC2 bond lengths (167.4(2)–
169.9(2) pm) of the five-membered heterocycles are in the
same range as those of the parent four-membered 1,2-diphos-
phetane 1a (164.5(4) pm), but shorter than in the parent 1,2-
bis(halophosphanyl)-1,2-dicarba-closo-dodecaborane(12)s 1b
Spectroscopic properties of 2a–d
The 31P NMR spectra of 2a–d in CDCl3 exhibit a doublet and
a triplet signal for the A2B spin system with 1J(P,P) coupling
constants that range from 170 to 225 Hz. The 13C{1H} NMR
spectra of 2a–d show a complex coupling pattern for the ABX
spin system of the PCCP moiety (1J(C,P)+2J(C,P)ꢀ80 Hz
(Table 1)), which is generally observed for 1,2-bisphosphanyl-
substituted carbaboranes.[12] The dynamic cyclohexyl substitu-
Figure 1. Molecular structures of the unsymmetrically substituted 1,2,3-tri-
phospholanes 2a (left) and 2d (right) with thermal ellipsoids at the 50%
probability level. Hydrogen atoms have been omitted for clarity.
1
ents in 2c and 2d appear as broad multiplets in the H NMR
spectra, thus, no assignment is possible.
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An attempt to synthesize five-membered P,N,P heterocycles
from 1b and primary amines (RNH2; R=tBu, Cy, Ph) failed. The
formation of the disubstituted aminobisphosphane derivatives
was always preferred,[27] and the strong base leads to decapp-
ing of the boron cluster. Compound 3 was previously prepared
from 1b and gaseous ammonia but the product was only char-
acterized by elemental analysis.[12a] However, in a facile alterna-
tive method,[28] elimination of SiMe3Cl in the reaction of chloro-
phosphanes and bis(trimethylsilyl)amine gave the desired P,N,P
heterocycle, 4,5-dicarba-closo-dodecaboranyl-1-aza-2,5-diphos-
pholane (3; Scheme 2), as a white powder in moderate yield.
Diphospholane 3 was fully characterized, is air stable in the
solid state, and highly soluble in nonpolar solvents.
Table 2. Selected bond lengths [pm], angles [8], and torsion angles [8]
for 2a–d.
2a[a]
2b
2c
2d
C1ÀC2
C1ÀP1
C2ÀP3
P1ÀP2
P2ÀP3
P1ÀCSub
P2ÀCSub
P3ÀCSub
168.4(7)
187.1(3)
188.1(4)
220.4(1)
220.4(1)
188.1(4)
183.2(4)
188.1(4)
97.0(1)
96.14(7)
97.0(1)
115.2(1)
115.2(1)
38.8(1)
167.5(4)
186.2(3)
186.5(3)
221.0(1)
222.0(1)
182.5(3)
185.4(3)
182.5(3)
100.4(1)
101.83(4)
100.4(1)
118.5(2)
117.9(2)
9.0(1)
169.9(2)
186.6(2)
185.6(2)
220.68(6)
220.45(6)
187.3(2)
186.9(2)
187.3(2)
99.40(5)
102.91(2)
99.80(5)
118.0(1)
118.1(1)
12.0(5)
167.4(2)
187.0(2)
186.2(2)
220.76(8)
221.66(8)
182.8(3)
186.6(3)
182.8(3)
98.53(7)
99.70(2)
98.53(7)
117.3(2)
117.3(2)
26.29(7)
18.5(1)
[b]
C1-P1-P2
P1-P2-P3
P2-P3-C2
P3-C2-C1
C2-C1-P1
P1-P2-P3-C2
P2-P1-C1-C2
P1-C1-C2-P3
27.6(1)
0.09(3)
6.2(1)
0.5(2)
8.5(1)
0.0(1)
0.6(2)
[a] C2 and P3 are C1’ and P1’ in the case of 2a. [b] Sub=substituent.
Scheme 2. Synthesis of 4,5-dicarba-closo-dodecaboranyl-1-aza-2,5-diphenyl-
diphospholane (3).
The 31P{1H} NMR spectrum of 3 exhibits one singlet signal at
d=87.6 ppm (cf. d=80.9 ppm in 1b),[12a] which indicates the
formation of only one isomer. A triplet signal at d=2.21 ppm
(2J(H,P)=18.5 Hz) was observed for the NÀH proton in the
1H NMR spectrum. The N–H stretching mode was detected at
n˜ =3368 cmÀ1 in the IR spectrum. In the 13C{1H} NMR spectrum,
a complex coupling pattern was observed for the ABX spin
system of the PCCarbCCarbP group (Carb=carbaborane) at d=
84.2 ppm. The 11B{1H} NMR spectrum showed three broad sig-
nals at d=À3.0, À5.1, and À11.1 ppm (2:2:6).
Figure 2. Molecular structures of 2b (left) and 2c (right) with thermal ellip-
soids at the 50% probability level. Hydrogen atoms have been omitted for
clarity.
and 1c (170.2(3) and 173.7(2) pm, respectively). In contrast to
the CÀC bond length in 1,2,3-triphenyl-1,2,3-triphospholane
(141.6(8) pm),[5] the CÀC bond lengths in 4,5-dicarba-closo-do-
decaboranyl-1,2,3-triphospholanes are significantly longer,
which may explain the higher stability of these compounds.[12b]
The endocyclic bond angles at the phosphorus atoms vary,
with the smallest value of 96.14(7)8 for 2a and largest of
102.91(2)8 for 2c. Nevertheless they compare well with the
average angles found in (PPh)5 (101.38)[25] and 1,2,3-triphenyl-
1,2,3-triphospholane (100.28).[5] In summary, the geometries of
all 1,2,3-triphospholanes are similar: they occur as trans,trans
isomers and have similar bond lengths and angles.
Colorless crystals of 3 were obtained from n-hexane. An X-
ray structure analysis showed the expected five-membered
C2PNP heterocycle, however, one phosphorus atom is partially
oxidized (ca. 16%, P(2)/P(2)O(1)=0.84(1):0.16(1), see the Sup-
porting Information). Partial oxidation of compound 3 (ca. 5%)
was also observed in the 31P{1H} NMR spectrum of the obtained
crystals.
Conclusions
Two versatile routes to 4,5-dicarba-closo-dodecaboranyl-1,2,3-
triphospholanes were developed: 1) reductive PÀP bond cleav-
age of 1,2-diphosphetanes with lithium and subsequent reac-
tion with dichlorophosphane; 2) reduction of bis(halophos-
phanyl)-1,2-dicarba-closo-dodecaborane(12)s with zinc in the
presence of dichlorophosphanes. Furthermore, less basic silyl-
amines seem to be suitable precursors to P,N,P heterocycles.
Thus, diphospholane 3 could be obtained by reaction of bis-
(chlorophenylphosphanyl)-1,2-dicarba-closo-dodecaborane(12)
with bis(trimethylsilyl)amine.
Synthetic approach to P,N,P heterocycles
Among the routes to generate PÀN bonds, the most frequently
used method is aminolysis of halophosphanes because halo-
phosphanes are readily accessible from commercial sources.[26]
The liberated HCl forms an insoluble salt with an added base
(the amine reagent, triethylamine, or 1,8-diazabicyclo-
[5.4.0]undec-7-ene [DBU]), which leads to facile separation and
purification of the desired products.
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Compared to the corresponding benzene analogues,[4–6] the
carbaboranyl backbone offers several possibilities for further
functionalization.[11a] These include selective substitution of the
hydrogen atom of boron atom B9[29] or deboronation of the
closo cluster to give nido derivatives.[30] Preliminary NMR spec-
troscopic studies have shown that 2b reacts with tetra-n-butyl-
ammonium fluoride (TBAF) in THF at room temperature to
form the corresponding nido species without PÀP bond cleav-
age. The resulting nido cluster should be an interesting ligand
in transition metal chemistry because it combines the features
of a nido-carbaborane ligand with those of an oligophosphane.
These studies are now underway.
Table 3. Crystal data for compounds 2a–d.
Compound
2a
2b
2c
2d
empirical
formula
C16H33B10P3
C20H25B10P3 C20H43B10P3 C20H31B10P3
formula weight 426.43
466.41
130(2)
484.55
130(2)
472.46
130(2)
T [K]
130(2)
crystal system
space group
a [pm]
b [pm]
c [pm]
orthorhombic monoclinic monoclinic monoclinic
Pnma
1373.65(7)
1347.57(7)
1328.61(6)
90
P21/n
P21/n
P21/c
954.69(4)
1926.30(6)
1329.07(4)
90
1060.03(3)
1242.48(3)
2068.12(5)
90
95.562(2)
90
2.7110(1)
4
1.187
1399.91(8)
1005.04(4)
1911.6(1)
90
111.436(7)
90
2.5035(2)
4
1.254
a [8]
b [8]
g [8]
90
90
93.392(3)
90
2.4399(2)
4
1.270
26.37
V [nm3]
Z
1calcd
2.4594(2)
4
1.152
25.35
896
Experimental Section
qmax
30.51
1032
30.51
984
General
F(000)
960
All reactions were carried out under dry high-purity nitrogen by
standard Schlenk techniques. Solvents were purified and degassed
with an MBraun SPS-800 solvent purification system. NMR spectra
were recorded at 258C with a Bruker Avance DRX 400 MHz spec-
trometer (1H NMR: 400.13 MHz, 11B NMR: 128.38 MHz, 13C NMR:
100.63 MHz, 31P NMR: 161.98 MHz). TMS was used as an internal
reflns collected
independent
reflns
R1/wR2 [I>2s(I)] 0.0591/
0.1360
16043
2350
21584
4971
29887
8275
35939
7833
0.0563/
0.1138
0.0854/
0.1244
0.0524/
0.0936
0.0797/
0.1024
0.0432/
0.0807
0.0603/
0.0875
R1/wR2 (all data) 0.0608/
0.1368
1
standard in the H NMR spectra and all other nuclei spectra were
referenced to TMS by using the X scale.[31] 13C{1H} NMR spectra
were obtained as APT (attached proton test) spectra, mass spectra
(EI) with a VG12–250 apparatus, and FTIR spectra with a Perkin
Elmer Spectrum 2000 FTIR spectrometer in the range of n˜ =400–
4000 cmÀ1 with samples dispersed in KBr. Elemental analyses were
performed with a Heraeus VARIO EL CHN-O-S Analyzer. Melting
points were determined in glass capillaries that were sealed under
nitrogen on a Gallenkamp apparatus and are uncorrected. Carba-
borane derivatives 1a[14] and 1b,[12a] and dichlorocyclohexylphos-
phane[32] were prepared by literature methods. PPhCl2, 1,2-dicarba-
closo-dodecaborane(12), lithium in mineral oil, hexamethyldisila-
zane, and zinc are commercially available.
C(CH3)3), 1.20–3.60 (m, 10H; B10H10), 7.26–7.80 ppm (m, 5H; C6H5);
11B{1H} NMR (128 MHz, CDCl3): d=À10.8 (brs, 2B), À7.9 (brs, 2B),
À6.2 (brs, 2B), À3.3 (brs, 1B), À2.5 ppm (brs, 3B); 13C{1H} NMR
(100 MHz, CDCl3): d=27.4 (dd, J(C,P)=9.2, 21.1 Hz, C(CH3)3), 35.2
(dd, J(C,P)=45.5, 16.4 Hz; C(CH3)3), 80.4 (m, 1J(C,P)+2J(C,P)=
89.5 Hz; C2B10H10), 128.8 (d, J(C,P)=8.2 Hz; m-C, C6H5), 130.1 (s; p-C,
C6H5), 133.2 (dt, J(C,P)=25.6, 16.3 Hz; ipso-C, C6H5), 136.3 ppm (dt,
J(C,P)=7.6, 21.3 Hz; o-C, C6H5); 31P{1H} NMR (162 MHz, CDCl3): d=
À21.0 (t, J(P,P)=172.8 Hz; P2), 50.8 ppm (d, J(P,P)=172.8 Hz; P1,
P3); IR (KBr): n˜ =3070 (w; CH), 2991 (m; CH), 2976 (w; CH), 2934 (s;
CH), 2922 (s; CH), 2862 (s), 2620 (s; BH), 2579 (s; BH), 1656 (w; C=
C), 1572 (w; C=C), 1469 (s), 1459 (s), 1436 (s), 1392 (s), 1365 (s),
1262 (w), 1175 (s), 1070 (s), 1026 (w), 932 (w), 800 (s), 745 (s), 694
(s), 626 (w), 578 (w), 503 (w), 456 (m), 410 cmÀ1 (m); MS (EI+,
70 eV): m/z (%): 426 [M]+ (25), 370 [M-tBu]+ (30), 314 [M-2ꢂtBu]+
(45), 57 [tBu]+ (100); elemental analysis calcd (%) for C16H33B10P3: C
45.06, H 7.80; found: C 43.76, H 7.65.
X-ray crystallographic analysis
The data were collected on an Agilent Technologies CCD Xcalibur-
S diffractometer. Data collection and data reduction were per-
formed with the CrysAlis Pro software package, and the pro-
gramme SCALE3 ABSPACK was used for empirical absorption cor-
rection.[33] The structures were solved by direct methods with
SHELXS-97 or SIR-92 programmes and the anisotropic refinement
of all non-hydrogen atoms was performed with the SHELXL-97 pro-
gramme.[34] Hydrogen atoms of all structures were located on dif-
ference Fourier maps calculated at the final stage of the structure
refinement. Structure figures were generated with ORTEP.[35] The
data are collected in Table 3.
Synthesis of compound 1c
Synthesis of compound 2a
Compound 1a (2.0 g, 6.3 mmol) was added to lithium powder
(0.1 g in mineral oil, 14.5 mmol) suspended in THF (40 mL). The re-
action mixture was stirred for 12 h and dichlorophenylphosphane
(1.1 g, 6.3 mmol) was slowly added. The reaction mixture was
stirred for 24 h and LiCl was filtered off. The solvent was removed
under vacuum and the yellow residue extracted with toluene (3ꢂ
20 mL). The solution was concentrated, cooled to À208C, and crys-
tals of compound 2a (1.3 g, 50%) were obtained. M.p. 208–2108C;
1H NMR (400 MHz, CDCl3): d=1.14 (d, J(P,H)=14.0 Hz, 18H;
1,2-Dicarba-closo-dodecaborane(12) (2.5 g, 17.3 mmol) was dis-
solved in Et2O (40 mL) and dilithiated by addition of n-butyllithium
(20.4 mL, 1.7m) at 08C. The reaction mixture was warmed to rt,
stirred for 2 h and then added, over a period of 1 h, to a solution
of dichlorocyclohexylphosphane (6.4 g, 34.6 mmol) in Et2O (30 mL).
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After stirring for 24 h, LiCl was filtered off and the solvent removed
under vacuum. Compound 1c (5.7 g, 75%) crystallized at À208C
from n-hexane (see the Supporting Information for X-ray structure).
M.p. 143–1448C; 1H NMR (400 MHz, CDCl3): d=1.09–2.14 (brm,
22H; C6H11), 1.65–3.30 ppm (m, 10H; B10H10); 11B{1H} NMR (128 MHz,
CDCl3): d=À9.7 (brs, 6B), À6.3 (brs, 2B), 0.51 ppm (brs, 2B);
13C{1H} NMR (100 MHz, CDCl3): d=26.4 (m), 27.1 (s), 30.1 (m), 41.9
(m; C1 [rac]), 42.3 (m; C1 [meso]), 84.1 ppm (m, 1J(C,P)+2J(C,P)=
91.3 Hz; C2B10H10); 31P{1H} NMR (162 MHz, CDCl3): d=106.9 (s; rac),
107.6 ppm (s; meso); IR (KBr): n˜ =2931 (s; CH), 2850 (s; CH), 2617
(s; BH), 2571 (s; BH), 1448 (s; CH), 1345 (w), 1289 (w), 1269 (w),
1175 (m), 1072 (s), 1043 (m), 996 (s), 890 (w), 845 (w), 802 (w), 728
(m), 624 (w), 510 (s), 500 cmÀ1 (s); MS (EI+, 70 eV): m/z (%): 441.3
[M]+ (30), 358.3 [M-C6H11]+ (40), 83.2 [C6H11]+ (100); elemental anal-
ysis calcd (%) for C14H32B10Cl2P2: C 38.10, H 7.43; found: C 38.45, H
7.43.
13C{1H} NMR (100 MHz, CDCl3): d=25.8 (brs; C6H11), 26.3 (brm;
C6H11), 27.2 (brm; C6H11), 30.9 (m; C2, C6H11), 33.0 (m; C6, C6H11),
36.8 (m; C5, C6H11), 38.2 (dd, J(C,P)=25.0, 13.9 Hz; C1, C6H11),
88.8 ppm (m, 1J(C,P)+2J(C,P)=78.1 Hz; C2B10H10); 31P{1H} NMR
(162 MHz, CDCl3): d=5.5 (t, J(P,P)=225.0 Hz; P2), 34.0 ppm (d,
J(P,P)=225.0 Hz; P1, P3); IR (KBr): n˜ =2923 (s; CH), 2851 (s; CH),
2601 (s; BH), 2573 (s; BH), 1447 (s), 1340 (w), 1294 (w), 1264 (m),
1188 (w), 1172 (w), 1075 (m), 998 (m), 885 (w), 849 (w), 801 (w),
739 cmÀ1 (w); MS (EI+, 70 eV): m/z (%): 484.4 [M]+ (60), 402.3
[MÀC6H11]+ (20), 320.2 [MÀ2ꢂC6H11]+ (100); elemental analysis
calcd (%) for C20H43B10P3: C 49.57, H 8.94; found: C 49.30, H 8.83.
General procedure for the synthesis of 2b–d
Zinc dust was activated with 1,2-dibromoethane and suspended in
toluene (50 mL). 1,2-Bis(halophosphanyl)-1,2-dicarba-closo-dodeca-
borane(12) (1 equiv) and dichlorophosphane (excess) were added
and the reaction mixture was heated at reflux until the 31P NMR
spectrum of the solution showed full conversion of the starting
material. The zinc dust was filtered off and the solvent was evapo-
rated under vacuum. The product was dissolved in n-hexane/tolu-
ene. Residual LiCl was removed by filtration. The solution was con-
centrated and cooled to À208C to give 2b–d as colorless crystals.
Compound 2d: Compound 1b (1.0 g (2.3 mmol), dichlorocyclo-
hexylphosphane (0.55 g, 3.0 mmol), zinc dust (3.3 g, 50 mmol).
Yield: 0.33 g (30%); m.p. 198.08C; 1H NMR (400 MHz, CDCl3): d=
1.00–2.51 (m, 11H; C6H11), 1.10–3.50 (m, 10H; B10H10), 7.47–
8.31 ppm (m, 10H; C6H5); 11B{1H} NMR (128 MHz, CDCl3): d=À10.1
(brs, 4B), À5.8 (brs, 2B), À3.9 (brs, 2B), À3.0 ppm (brs, 2B);
13C{1H} NMR (100 MHz, CDCl3): d=25.6 (s; C4), 26.5 (d, J(C,P)=
Compound 2b: Compound 1b (1.0 g, 2.3 mmol), dichlorophenyl-
phosphane (1.0 g, 5.6 mmol), zinc dust (3.3 g, 50 mmol). Yield:
1
0.64 g (60%); m.p. 1988C; H NMR (400 MHz, CDCl3): d=1.00–3.20
(m, 10H; B10H10), 7.24–8.00 ppm (m, 15H; C6H5); 11B{1H} NMR
(128 MHz, CDCl3): d=À10.3 (brs, 2B), À9.0 (brs, 2B), À6.0 (brs,
2B), À3.6 ppm (brs, 4B); 13C{1H} NMR (100 MHz, CDCl3): d=83.7
(m, 1J(C,P)+2J(C,P)=79.2 Hz; C2B10H10), 129.1 (m; C6H5), 130.2 (s;
C6H5), 131.3 (m; ipso-C, C6H5), 131.7 (s; C6H5), 143.8 ppm (m; C6H5);
31P{1H} NMR (162 MHz, CDCl3): d=À7.3 (t, J(P,P)=184.0 Hz; P2),
28.1 ppm (d, J(P,P)=184.0 Hz; P1, P3); IR (KBr): n˜ =3070 (w; CH),
3056 (w), 2598 (s; CH), 2571 (s; CH), 1948 (w; BH), 1880 (w; BH),
1583 (m), 1482 (s; C=C), 1434 (s; C=C), 1304 (C=C), 1262 (w; C=C),
1188 (m), 1161 (w), 1076 (s), 1025 (s), 998 (s), 801 (w), 737 (s), 692
(s), 488 (s), 419 (s), 690 cmÀ1 (s); MS (EI+, 70 eV): m/z (%): 466.5
[M]+ (100), 389.3 [M-C6H5]+ (20); elemental analysis calcd (%) for
C20H25B10P3: C 51.50, H 5.40; found: C 51.43, H 5.10.
1
10.9 Hz; C3), 32.8 (m; C2), 36.6 (m; C1), 85.3 (m, J(C,P)+2J(C,P)=
75.7 Hz; C2B10H10), 128.8 (s; p-C, C6H5), 131.3 (s; m-C, C6H5), 132.0
(dd, J(C,P)=30.0, 12.3 Hz; ipso-C, C6H5), 134.6 ppm (dd, J(C,P)=
12.9, 22.4 Hz; o-C, C6H5); 31P{1H} NMR (162 MHz, CDCl3): d=2.4 (t,
J(P,P)=201.0 Hz; P2), 23.0 ppm (d, J(P,P)=201.0 Hz; P1, P3); IR
(KBr): n˜ =3055 (w; CH), 2928 (s; CH), 2852 (w; CH), 2576 (s; BH),
1628 (w; C=C), 1435 (s; C=C), 1263 (s), 1077 (s), 803 (s), 742 (s), 693
(s), 489 cmÀ1 (w); MS (EI+, 70 eV): m/z (%): 472 [M]+ (40), 390 [M-
C6H11]+ (100); elemental analysis calcd (%) for C20H31B10P3: C 50.84,
H 6.61; found: C 50.03, H 6.44.
Synthesis of compound 3
Hexamethyldisilazane (0.20 g, 1.21 mmol) was added at rt to a solu-
tion of 1b (0.52 g, 1.21 mmol) in THF (30 mL). The reaction mixture
was heated at 608C for 12 h. The solvent was evaporated under
vacuum and the residue extracted with n-hexane (3ꢂ10 mL). The
n-hexane fractions were cooled at À208C to give 3 (0.25 g, 55%)
1
as a white powder. M.p. 1898C; H NMR (400 MHz, CDCl3): d=1.15–
3.13 (m, 10H; B10H10), 2.21 (t, J(P,H)=18.5 Hz, 1H; NH), 7.39–
7.59 ppm (m, 10H; C6H5); 11B{1H} NMR (128 MHz, CDCl3): d=À11.1
(brs, 6B), À5.1 (brs, 2B), À3.0 ppm (brs, 2B); 13C{1H} NMR
(100 MHz, CDCl3): d=84.2 (m, 1J(C,P)+2J(C,P)=70.6 Hz; C2B10H10),
128.6 (m; o-C, C6H5), 130.2 (d, J(C,P)=12.9 Hz; m-C, C6H5), 131.3 (s;
p-C, C6H5), 136.9 ppm (d, J(C,P)=30.2 Hz; ipso-C, C6H5); 31P{1H} NMR
(162 MHz, CDCl3): d=87.6 ppm (s); IR (KBr): n˜ =3368 (s; NH), 3074
(m; CH), 3056 (m; CH), 3005 (w; CH), 2552 (s; BH), 1958 (w), 1587
(w), 1572 (w; C=C), 1482 (s; C=C), 1425 (s; C=C), 1308 (m), 1246 (s),
1231 (s), 1080 (s), 998 (m), 969 (m), 850 (s), 806 (s), 740 (s), 707 (s),
692 (s), 629 (s), 561 (m), 490 (s), 476 (s), 426 cmÀ1 (s); MS (EI+,
70 eV): m/z (%): 373 [M]+ (100); elemental analysis calcd (%) for
Compound 2c: Compound 1c (0.8 g, 1.7 mmol), dichlorocyclohex-
ylphosphane (0.50 g, 2.7 mmol), zinc dust (3.1 g, 47 mmol). Yield:
1
0.35 g (43%); m.p. 2378C; H NMR (400 MHz, CDCl3): d=0.99–2.02
(brm, 33H; C6H11), 1.50–3.35 ppm (m, 10H; B10H10); 11B{1H} NMR
(128 MHz, CDCl3): d=À9.5 (brs, 6B), À3.6 ppm (brs, 4B);
Chem. Eur. J. 2014, 20, 1434 – 1439
www.chemeurj.org
1438
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Received: July 22, 2013
Published online on December 16, 2013
Chem. Eur. J. 2014, 20, 1434 – 1439
www.chemeurj.org
1439
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim