Synthesis and structural characterization of an 11-vertex nido-diphosphaborane, 7,9-Ph2-nido-7, 9-P2B9H9

Article abstract of DOI:10.1016/S0022-328X(03)00165-7

The new 11-vertex nido-diphosphaborane, 7,9-Ph₂-nido-7, 9-P₂B₉H₉, has been synthesized by the reaction of Me₄N⁺[nido -B₉ H₁₂^-] with PhPCl₂ in the presence of NaH. A single crystal X-ray diffraction determination and DFT/GIAO/NMR methods have both established that the compound has an open cage structure containing the phosphorus atoms in non-adjacent positions on the open face.

Full text of DOI:10.1016/S0022-328X(03)00165-7

Journal of Organometallic Chemistry 680 (2003) 61ꢃ65
/
www.elsevier.com/locate/jorganchem
Synthesis and structural characterization of an 11-vertex nido-
diphosphaborane, 7,9-Ph2-nido-7,9-P2B9H9
Daewon Hong, Patrick J. Carroll, Larry G. Sneddon *
Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, PA 19104-6323, USA
Received 14 February 2003; received in revised form 11 March 2003; accepted 11 March 2003
Dedicated to Professor M. Fred Hawthorne on the occasion of his 75th birthday.
Abstract
The new 11-vertex nido-diphosphaborane, 7,9-Ph2-nido-7,9-P2B9H9, has been synthesized by the reaction of Me4Nꢀ[nido-B9H1ꢁ2
with PhPCl2 in the presence of NaH. A single crystal X-ray diffraction determination and DFT/GIAO/NMR methods have both
]
established that the compound has an open cage structure containing the phosphorus atoms in non-adjacent positions on the open
face.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Diphosphaborane; Heteroborane; DFT/GIAO; Boron
1. Introduction
ization of the first neutral 11-vertex nido-
diphosphaborane 7,9-Ph2-nido-7,9-P2B9H9 that is also
Although there are now a variety of monophospha-
the first diphosphaborane to have exo-substituents at
the phosphorus cage atoms.
boranes and monophospha-carbaboranes, [1] it has been
only relatively recently that methods have become
available for the syntheses of diphosphadicarbaboranes
[2], including nido-7,8,9,11-P2C2B7H9, 3-Cl-nido-7,8,9,-
11-P2C2B7H8, nido-7,9,8,10-P2C2B7H9, nido-7,8,9,10-
P2C2B7H9, and 11-Cl-nido-7,8,9,10-P2C2B7H8; triphos-
phamonocarbaboranes [3], 4-Me-nido-7,8,9,10-P3C-
B7H7 and 4-Me-11-Cl-nido-7,8,9,10-P3CB7H6; and a
small number of diphosphaboranes, 2,3,4-(iPr2N)3-1,5-
P2B3 [4], closo-1,2-P2B10H10, [5,6] closo-1,7-P2B10H10
2. Results and discussion
We have previously prepared a wide variety of
monophosphacarbaboranes and monophosphaboranes
via in situ dehydrohalogenation/phosphorus-insertion
reactions of RPCl2 reagents with polyboranes in the
presence of Proton Sponge [11]. During our attempt to
employ similar methods to produce the previously
unknown 10-vertex R-nido-PB9H11 compound, we sur-
prisingly found that the reaction of Me4Nꢀ[nido-B9H1ꢁ2]
[12] with PhPCl2 in the presence of NaH (instead of
Proton Sponge, where no reaction was observed) does
not produce the monophosphaborane Ph-nido-PB9H11,
but instead yields the diphosphaborane 7,9-Ph2-nido-
7,9-P2B9H9 (1). Better yields were obtained when two
equivalent of PhPCl2 were used (Eq. (1)), but even in
reactions employing 1.0 equivalent of PhPCl2, only the
formation of 1 was observed.
[5], nido-7,8-P2B9H1ꢁ0 [7], closo-1,2-P2B4X4 (Xꢂ
Cl [8]
/
or Br [9]) and closo-1,7-P2B10Cl10 [10]. In all of the
diphospha- and triphosphapolyboranes that have been
reported to date, the phosphorous cage atoms do not
have an exo-substituent, but rather have an exo-
polyhedral lone pair of electrons. In this communica-
tion, we report the synthesis and structural character-
* Corresponding author. Tel.: ꢀ
6743.
E-mail address: lsneddon@sas.upenn.edu (L.G. Sneddon).
/
1-215-898-8632; fax: ꢀ1-215-573-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00165-7

62
D. Hong et al. / Journal of Organometallic Chemistry 680 (2003) 61ꢃ
/65
3NaH
Me4Nꢀ[B9H1ꢁ2]ꢀ2PhPCl2
ꢁ3NaCl; 3H2; Me4NCl
7; 9-Ph2-nido-7; 9-P2B9H91
(1)
The composition of 1 was confirmed by elemental
analysis and mass spectroscopy. If each RꢀP unit
/
donates four skeletal-electrons, then a compound of
composition 7,9-Ph2-nido-7,9-P2B9H9 would contain a
total of 26 skeletal electrons, and be expected to adopt
the normal 11-vertex nido-deltahedral structure, an
icosahedron missing one vertex, that has been observed
for such systems [13]. Consistent with this prediction, a
single crystal X-ray diffraction study of 1 established the
structure shown in Fig. 1.
To our knowledge, 1 is the first crystallographically
characterized nido-class diphosphaborane. In 1, the
phosphorus atoms are located in non-adjacent positions,
separated by boron atoms in the open pentagonal face.
There is a crystallographic mirror plane coincident with
the B8ꢀ
structure. Unlike in the isoelectronic 7-Me-nido-7-
PB10H12 phosphaborane, where all the PꢀB distances
2.001(6) A) regardless of
/
B5ꢀ
/
B1 plane that equates the two halves of the
Fig. 2. 11B-NMR spectra of 7,9-Ph2-nido-7,9-P2B9H9 (1), (a) 1H-
/
coupled (b) 1H-decoupled.
˚
have similar values (1.978(6)ꢃ
/
˚
B8 (1.917(2) A)
˚
B10 (1.923(3) A) distances in the open face of 1
their locations in the cluster [14], the P9ꢀ
/
chemical shifts (B3LYP/6-311G*) [15], based on the Cs
symmetric optimized geometry (B3LYP/6-311G*) of 1
(I) shown in Fig. 3, are congruous with the experimental
data (Table 1). As expected based on its DFT/GIAO
assignment to the B8 boron situated between the P7 and
and P9ꢀ
/
are significantly shorter than distances between the
phosphorus atoms and the borons in the lower ring,
˚
˚
B4 (2.028(3) A). The
P9ꢀ
phosphorus atoms are also puckered (0.2160(5) A)
above the B8ꢀB10ꢀB10? plane. As a result, the B8ꢀ
P9ꢀB10 and B3ꢀB4ꢀB5 planes are not parallel, but
/
B3 (2.061(3) A) and P9ꢀ
/
˚
P9 atoms, the resonance at ꢁ
mental NMR spectrum shows a broad triplet structure
arising from boronꢃ
phosphorus coupling. In the 1H-
/28.6 ppm in the experi-
/
/
/
/
/
/
/
have an 11.8(4)8 dihedral angle. This is probably a
consequence of the fact that both of the large phospho-
rus atoms are located on the open face.
Consistent with its crystallographically established
structure, the 11B-NMR spectrum obtained for 1 shows
a six-resonance pattern in 1:2:2:2:1:1 ratios, indicating
Cs symmetry (Fig. 2). The DFT/GIAO calculated 11B
Fig. 1. ORTEP drawing of the structure of 7,9-Ph2-nido-7,9-P2B9H9 (1).
˚
Selected bond distances (A): P9ꢀ
/
B8, 1.917(2); P9ꢀ
B3, 2.061 (3); B1ꢀ
B5, 1.785(5); B3ꢀB3?, 1.748(5); B3ꢀ
B8, 1.875(4); B4ꢀB5, 1.753(3); B4ꢀB10, 1.860(4); B5ꢀ
1.778(4); B10ꢀB10?, 1.740(5).
/
B10, 1.923(3); P9ꢀ
B3, 1.758(4);
B4, 1.843(4);
B10,
/
C12, 1.796(2); P9ꢀ
B1ꢀB4, 1.770(3); B1ꢀ
B3ꢀ
/
B4, 2.028(3); P9ꢀ
/
/
/
/
/
/
/
/
/
/
Fig. 3. Optimized geometries (B3LYP/6-311G*) of 7,9-Ph2-nido-7,9-
P2B9H9 (I) and 7,8-Ph2-nido-7,8-P2B9H9 (II).
/

D. Hong et al. / Journal of Organometallic Chemistry 680 (2003) 61ꢃ
/65
63
Table 1
NMR Data for 7,9-Ph2-nido-7,9-P2B9H9 (1) a,b,c
Nucleus
11B
d (multiplicity, assignment, J (Hz))
ꢁ
/
11.4 (d, B5; JBH
14.4 (d, B2,3; JBH
16.6 (d, B10,11; JBH
17.5 (d, B4,6; JBH
28.6 (B8; JBH 159, JBP
39.4 (d, B1; JBH 154)
12.3 (B5), ꢁ14.5 (B2,3),
16.9 (B10,11), ꢁ17.6 (B4,6),
30.3 (B8), ꢁ41.3 (B1)
7.37ꢃ6.78 (m, 5, phenyl),
3.06 (t, 1, P2BH; JPH 25),
ꢂ
ꢂ
/
148),
159),
150),
150),
ꢁ
/
/
ꢁ
/
Â
/
/
ꢁ/
Â
ꢁ/
ꢂ/
Â/70),
ꢁ/
ꢂ/
11B (Calc.) d
1H{11B}
ꢁ/
/
ꢁ/
/
ꢁ/
/
/
ꢂ/
2.92 (2, BH), 2.84 (2, BH),
2.50 (1, BH), 2.39 (2, BH),
2.13 (1, BH)
13C{1H}
13C(Calc.)
31P
132.6ꢃ/129.4 (phenyl)
137.2ꢃ/133.1 (phenyl)
ꢁ
/
69.2 (P7,9)
31P(Calc.) d
ꢁ
/
59.9 (P7,9)
a
NMR shifts in ppm.
1H-NMR (500.4 MHz), 11B-NMR (160.5 MHz), 13C-NMR (125.8
b
MHz), 31P-NMR (145.8 MHz).
c
C6D6.
DFT/GIAO/NMR method (B3LYP/6-311G*//B3LYP/6-311G*).
d
Fig. 4. HOMO (top) and LUMO (bottom) density surfaces (B3LYP/6-
311G*) for 7,9-Ph2-nido-7,9-P2B9H9 (I).
NMR spectrum, 1 exhibited terminal BH hydrogen
resonances in the predicted 1:2:2:1:2:1 intensity-ratios
along with the phenyl ring resonances. Consistent with
its assignment to the terminal BH hydrogen at B8, the
calculated as ꢁ
tively, which corresponds to a DEꢂ
for the HOMOꢃLUMO gap. Although the fluorescence
/
0.23955 and ꢁ
/
0.06513 hartrees, respec-
/4.7 eV (or 262 nm)
/
resonance at 3.06 ppm showed a triplet structure (JPH
25 Hz) arising from coupling to the two phosphorus
ꢂ
/
emission of 1 was completely quenched, 1 did show
strong absorption at 262 nm in a dichloromethane
atoms. The 31P-NMR spectrum showed a single phos-
solution (o262
ꢂ
/
1.45ꢄ
104 l molꢁ1 cmꢁ1) in agreement
/
phorus resonance at ꢁ
large 31P-NMR chemical shift range, is again close to
the DFT/GIAO calculated value of ꢁ59.9 ppm.
/
69.2 ppm, which, considering the
with the calculated HOMOꢃ/LUMO transition.
As shown in Fig. 4 [16], the HOMO of I is mainly
derived from the diphosphaborane cage orbitals, with
very little contribution from the two phenyl rings, and is
largely localized on the five-membered open face of the
structure. These results suggest that 1 should show
strong donor properties facilitating the formation of ‘p-
arene’-type metal complexes where 1 functions as a
neutral six-electron donor to a transition metal h5-
coordinated to the open face of the cluster. For the
LUMO in I, the phenyl ring orbitals participate as much
/
In principle, phosphorus atom insertions into the
starting nido-B9H1ꢁ2 anion could have produced either
the observed 7,9-Ph2-nido-P2B9H9 product or its adja-
cent-phosphorus isomer 7,8-Ph2-nido-P2B9H9. However,
electron-rich cage atoms, such as phosphorus, are
known to favor both low-coordinate positions on an
open face and positions in which maximum separation
between heteroatoms can be attained [13c]. Indeed,
although it has not been crystallographically character-
ized, the isoelectronic 9-Ph-nido-7,9-SPB9H9 [11a] clus-
ter is proposed to adopt a structure similar to that
established for 1, in which the heteroatoms adopt non-
adjacent positions on the open face. In agreement with
this trend, the DFT calculations (B3LYP/6-311G*)
showed that the adjacent-phosphorus isomer 7,8-Ph2-
nido-P2B9H9 (I) is 35.7 kcal molꢁ1 higher in energy than
the phosphorus non-adjacent isomer 7,9-Ph2-nido-
P2B9H9 (II) (Fig. 3).
as the cage cluster orbitals. Thus, the HOMOꢃLUMO
/
transition qualitatively corresponds to an electron
excitation from cage to phenyl centered orbitals. Mono-
borane and polyborane compounds containing conju-
gated p systems have recently become of great interest
because of the potential that HOMOꢃLUMO charge
/
transfer transitions in these compounds could yield
important photochemical [17], liquid crystalline [18],
and/or nonlinear optical properties [19]. The HOMO/
LUMO excitation observed for 1 suggests that com-
pounds having p systems linked by diphosphaboranes
might also have uses in these areas. Further investiga-
The HOMO and LUMO energy levels of the DFT
optimized 7,9-Ph2-nido-7,9-P2B9H9 (I) geometry were

64
D. Hong et al. / Journal of Organometallic Chemistry 680 (2003) 61ꢃ65
/
tions of the properties of 1, as well as the syntheses and
properties of related compounds are in progress.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: ꢀ44-1223-336033; e-
/
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
3. Experimental
3.1. Preparation of 7,9-Ph2-nido-7,9-P2B9H9 (1)
A sample of 0.916 g (5.0 mmol) of Me4Nꢀ[nido-
B9H1ꢁ2] [12] was dissolved in 30 ml of 1,2-dimethox-
yethane with 0.268 g (11.2 mmol) of NaH and 1.37 ml
(10.1 mmol) of PhPCl2. The reaction mixture was heated
at 80 8C for 39 h under an inert atmosphere. The
Acknowledgements
We thank the National Science Foundation for the
support of this work.
product
(hexanes:dichloromethaneꢂ
was
purified
by
preparative
TLC
4:1, v/v) to yield 0.320 g
/
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19
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/
0.15ꢄ
/
0.08 mm, Mꢂ322.50, monoclinic (P21/
/
˚
˚
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/
2; aꢂ
/
7.5068(2) A; bꢂ
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imaginary frequencies).
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Crystallographic data for the structural analysis of
compound 1 has been deposited with the Cambridge
Crystallographic Data Center, CCDC no. 203302.

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