Synthesis and Molecular Structure of a Superbulky Tertiary Phosphine: Bis[2-phenyl-1,2-dicarba-closo-dodecaboran-1-yl(12)]phenylphosphine

Article abstract of DOI:10.1515/znb-1998-1106

Bis[2-phenyl-1,2-dicarba-closo-dodecaboran-1-yl(12)]phenylphosphine (2) was obtained in 91% yield from phenyldichlorophosphine and two equivalents of 1-lithium-2-phenyl-1,2-dicarba-closo-dodecaborane(12) in ether and characterized by spectroscopy (³¹P, ¹¹B, ¹H, ¹³C NMR; IR) and by X-ray structure determination.

Full text of DOI:10.1515/znb-1998-1106

Synthesis and Molecular Structure of a Superbulky Tertiary Phosphine:
Bis[2-phenyl-l,2-dicarba-c/oso-dodecaboran-l-yl(12)]phenylphosphine
Viktor P. Balema, Steffen Blaurock, Evamarie Hey-Hawkins*
Institut für Anorganische Chemie der Universität Leipzig,
Talstrasse 35, D-04103 Leipzig, Germany
Z. Naturforsch. 53 b, 1273-1276 (1998); received May 20, 1998
Synthesis, Molecular Structure, X-Ray Data, NMR Data, Phosphine
Bis[2-phenyl-l,2-dicarba-c/oso-dodecaboran-l-yl(12)]phenylphosphine (2) was obtained in
91% yield from phenyldichlorophosphine and two equivalents of l-lithium-2-phenyl-l ,2-
dicarba-c/o5o-dodecaborane( 12) in ether and characterized by spectroscopy (3IP, 1 B, 'H, l3C
NMR; IR) and by X-ray structure determination.
Introduction
c/ow-dodecaborane(12) [2]. However, besides 1
we also obtained bis[2-phenyl-l,2-dicarba-c/o^o-
dodecaboran-l-yl(12)]phenylphosphine (2) in 18%
yield. When the reaction was carried out with
two equivalents of l-lithium-2-phenyl-l,2-dicarba-
c/o5o-dodecaborane( 12) in diethylether 2 was ob-
tained in 91% yield (eq. (1)).
Information about steric hindrance caused
by substituents at phosphorus atoms is of
great importance in understanding the chemi-
cal reactivity of organophosphorus compounds
and their ability to act as ligands for tran-
sition metals [1]. Among dicarba-c/oso-dode-
caborane(12) derivatives, 1-phenyl-1,2-dicarba-
c/oso-dodecaborane( 12) has been regarded as too
bulky for the preparation of the corresponding
disubstituted tertiary phosphines. The reason for
this conclusion was the report of an unsuccess-
ful attempt to prepare bis[2-phenyl-l,2-dicarba-
c/oso-dodecaboran-1-yl( 12)lphenylphosphine (2)
by reacting l-lithium-2-phenyl-l,2-dicarba-c/oso-
dodecaborane( 12) with 1-chlorophenylphosphino-
2-pheny1-1,2-dicarba-c/oso-dodecaborane( 12) (1)
(1:1) or dichlorophenylphosphine (2:1) [2].
NMR spectra of bis[2-phenyl-l ,2-dicarba-closo-
dodecaboran-l-yl( 1 2 )]phenylphosphine (2 )
The 31P NMR spectrum of 2 exhibits a singlet
at 29.2 ppm. In the n B{‘H} NMR spectrum, three
broad signals are observed for the 2-phenyl-1,2-
dicarba-c/oso-dodecaboran-l-yl(12) clusters at 2.0,
-3.1 and -8.0 ppm. On proton coupling, only the sig-
nals at 2.0 and -3.1 ppm split into doublets ( ' . / b -
h
= 150 and 138 Hz), while the other signal is too
broad to allow observation of B-H coupling. In the
1H NMR spectrum, the signals for the two phenyl
groups overlap in the usual range for aromatic pro-
tons at 7.0 to 6.6 ppm.
The 13C{'H} NMR signals of the phenyl groups
also overlap with each other and with those of the
solvent (CöDö) and were observed at 1 3 8 . 8 , 1 3 8 . 2 ,
1 3 7 . 5 , 1 3 3 . 5 , 1 3 2 . 9 , 1 3 1 . 5 , and 1 3 1 . 2 ppm. The
signals of the carbon atoms of the o-carbaborane
We now report the successful high-yield synthe-
sis of 2 and its characterization by 31P, 11B, l3C and
*H NMR spectroscopy and X-ray structure deter-
mination.
Results and Discussion
In the course of our investigations of dicarba-
c/oso-dodecaborane( 12)-containing
organophos-
cluster appear as two doublets at 9 1 . 5 ppm ( V c -
= 2 9 Hz) and 8 4 . 0 ppm (^ c -p = 7 9 Hz).
p
phorus compounds [3], we prepared 1-chloro-
phenylphosphino-2-phenyl-1,2-dicarba-c/oso-dode-
caborane(12) (1) according to the literature proce-
dure by reaction of dichlorophenylphosphine with
one equivalent of l-lithium-2-phenyl-l,2-dicarba-
X-ray structure analysis o f bis[2-phenyl-1,2-dicar-
ba-closo-dodecaboran-1 -yl(1 2 )]phen\lphosphine
(2)
Crystals of 2 were obtained by recrystallization
from hexane at 0°C. 2 crystallizes in the ortho-
* Reprint requests to Prof. Dr. E. Hey-Hawkins.
0932-0776/98/ 1100-1273 $ 06.00 (c) 1998 Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com
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V. P. Balem a et al. • Synthesis and M olecular Structure o f a Superbulky Tertiary Phosphine
1274
(1)
O
•
=
-
BH
C
CI20I
gles between 103.5 and 107.7° (Table I). The B-B,
C-C (Ph groups) and C(ciuster)-C(Ph) distances lie in
the range observed for other known phosphorus
compounds containing 1-substituted 1,2-dicarba-
closo-dodecaboran-2-yl(12) substituents (Fig. 2,
3-6) [4].
In 2, the C(ciuster)-C(ciuster) bond distance of one
carbaboranyl substituent and the C(ciuster)-P bond
distance in the other cluster unit lie at the higher
end of the range of known C-C and C-P bond dis-
tances in comparable compounds (Table I). The
bond angles at the P atom indicate the steric
demand of the carbaboranyl groups [C(Ciuster)-P-
C(cluster) 107.67(10)°, C(cluster)-P-C(ph) 103.99(11),
103.53(11)°], which is, however, not as large as
was previously assumed [2],
We are presently investigating the potential of 2
as a ligand in transition metal chemistry.
B(9)
Experimental
All experiments were carried out under purified dry
argon. Solvents were dried and freshly distilled under ar-
gon. NMR spectra (in CöDö): Avance DRX 400 (Bruker),
standards: 'H NMR (400 MHz): trace amounts of pro-
tonated solvent, CöDö, l3C NMR (100.6 MHz): internal
solvent,31P NMR (162 MHz): external 85% H3PO4, n B
NMR: external BF_vEt20 . The IR spectrum was recorded
as KBr mull on a Perkin-Elmer FT-IR spectrometer Sys-
tem 2000 in the range 350-4000 cm- 1. The melting point
was determined in a sealed capillary and is uncorrected.
Fig. 1. Molecular structure of 2 showing the atom num-
bering scheme employed (ORTEP plot, 50 % prob-
ability, SHELXTL PLUS; XP [6 ]). H atoms omitted
for clarity. Selected bond distances [A] and angles [°]:
Pl-Cl 1.867(2), PI -C3 1.896(2), PI-C ll 1.825(3), C l-
C2 1.780(3), C3-C4 1.761(3), C2-C5 1.505(3), C4-
C17 1.506(3), C l-B l 1.744(4), C1-B2 1.715(4), C l-
B3 1.708(4), C1-B4 1.724(3), C2-B1 1.733(4), C2-
B4 1.731(3), C2-B5 1.694(4), C2-B6 1.706(4), C3-
B 11 1.744(4), C3-B14 1.733(3), C3-B15 1.713(4), C3-
B16 1.726(4), C4-B11 1.740(4), C4-B12 1.708(4), C4-
B13 1.708(4), C4-B14 1.729(4); Cl 1-P1-C1 103.99(11),
Cl 1-P1-C3 103.53(11),C1-P1-C3 107.67(10), C4-C3-P1
107.50(14), C2-C1-PI 110.37(14), Cl7-C4-C3 119.1(2),
C5-C2-C1 120.4(2).
Preparation of bis[2-phenyl-1,2-dicarba-closo-dode-
caboran-1 -yl(12)]phenylphosphine (2)
At 0 °C, a solution of 0.45 g (2.5 mmol) of PhPCL in 25
cm3 of diethylether was added to a solution of 1 -lithium-
2 -phenyl-1 ,2 -dicarba-c/oso-dodecaborane( 1 2 ) (obtained
from 1.11 g (5.0 mmol) of 1-phenyl-1,2-dicarba-c/oso-
dodecaborane(12) in 25 cm3 of ether and BuLi (1.6 M
solution in hexane, 5.5 mmol)). The solution was kept at
0°C for 1 h and then for 12 h at 20°C. The solvent was
removed, the remaining solid dissolved in hexane/toluene
and the solution filtered. Airstable colourless crystals of 2
rhombic space group P212121 with four formula
units in the unit cell.
The P atom in 2 is coordinated in a slightly dis-
torted pseudo-tetrahedral fashion by two 2-phenyl-
l,2-dicarba-c/oso-dodecaborane(12) cluster frag-
ments and the phenyl group (Fig. 1) with C-P-C an-
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V. P. Balema et al. • Synthesis and M olecular Structure o f a Superbulky Tertiary Phosphine
1275
Table I. Selected bond distances [A ] and angles [°] in compounds 2-6.
2
3
4
5
6
This work
[4c]
[4a]
[4b]
[4d]
1.896(2), 1.867(2)
1.780(3), 1.761(3)
1.694(4) to 1.744(4)
107.67(10)
103.99(11), 103.53(11) 104.4(2), 101.5(2)
104.0(2)
1.854(4), 1.850(4)
1.703(6), 1.722(5) 1.654(4), 1.656(4)
1.710(5) to 1.731(5) 1.698(7) to 1.739(7) 1.692 to 1.736
114.2(2)
1.879(3)
1.769(4)
1.883(5), 1.869(5)
1.755(6), 1.732(6)
1.860(3)
P-Qduster)
C(cluster)~C(ciuster)
C(cluster)"B
C(cluster)‘P"C(c|uster)
C(cluster)-P'C(Ph//_Pr)
C(Ph//-Pr)-P-C(Ph//-Pr)
1.716(4) to 1.736(5)
102.8( 1)
101.3(1), 101.5(1)
102.6(2) to 104.4(2)
105.2(2), 106.5(2)
Fig. 2. Other known phosphorus com-
pounds containing 1 -substituted 1 ,2 -di-
carba-c/os0 -dodecaboran-2 -yl( 1 2 ) sub-
stituents [4].
CI(0)P
were obtained from hexane/toluene at 0°C; recrystalliza-
tion from hexane gave crystals suitable for X-ray analysis.
Yield 1.26 g (91 %), m.p. 273-277°C.
Positions of P, C, and B atoms were located by us-
ing direct methods (SHELXTL PLUS) [6 ]. Subsequent
least-squares refinement and difference electron density
map calculations revealed positions of all H atoms. Final
full-matrix least-squares refinement of 7095 parameters
with a unit weighting scheme (P, C, and B atoms with
anisotropic approximation, H atoms in B-H and Ph-H
groups with isotropic approximation) converged to R\ =
0.0478, wR2 = 0.0998 (for reflections with I > 2cr(I)),
R1 = 0.0865, wR2 = 0.1209 (all data). Further details of
the X-ray structure analysis (thermal parameters, H atom
coordinates, structure factors) have been deposited with
the Fachinformationszentrum Karlsruhe GmbH, D-76344
Eggenstein-Leopoldshafen, Germany. This material may
be requested by quoting the deposition number CSD
380170.
Analysis for C22H35B20P (546.67)
Calcd C 48.35 H6.41 %,
Found C 49.02 H 6.38 %.
IR (selected, cm“ 1): 3062, 2960, 2928, 2870 (i/C-H);
2654, 2578 {uB-H); 1956, 1889, 1800 (uPh).
Data collection and structure refinement of
2
Experimental data (a total of 29167 reflections) were
collected at T = 220 ± 2 K on a Siemens CCD (SMART)
diffractometer between 3.4 and 56° 2 0 with monochro-
mated Mo-Ka (A = 0.71073 A) radiation. This includes
a total of 7096 unique reflections [Rml = 0.0600], All
observed reflections (2(9 range: 3.4-56°) were used for
determination of the unit cell parameters. The studied
specimen was a colourless single crystal of dimensions
0.4 x 0.3 x 0.2 mm. Crystal data for 2: C22H35B20P, M =
546.67, space group P21212 1 (No. 19), orthorhombic, a =
11.521 (2), b = 15.625(3), c = 17.587(4) Ä, V= 3166.0( 11)
A3, at T= 220(2) K, Z = 4, Dc = 1.147 Mg m"3, F(000)
= 1128, ^(Mo-Kq) = 0.103 mm- 1, absorption correction
with SADABS [5],
Acknowledgements
We gratefully acknowledge support from the Fonds der
Chemischen Industrie. Chemetall GmbH has provided a
generous donation of lithium alkyls. V. P. Balema thanks
the Sächsisches Ministerium für Wissenschaft und Kunst
(SMWK) for financial support (Az. 4-7531.50-04-0361-
98/8).
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1276
V. P. Balema et al. • Synthesis and Molecular Structure of a Superbulky Tertiary Phosphine
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