On the intramolecular interactions of Si/P in 1,2-phenylene frameworks

Article abstract of DOI:10.1002/hc.21044

The synthesis and structure of 1-diphenylphosphino-2-(fluorodiphenylsilyl) benzene 1 and 1-diphenylphosphino-2-(difluorophenylsilyl)- benzene 2 are reported. An X-ray crystal structure analysis of 1 shows a weak interaction between the silicon and phosphorus moieties, producing a hypervalent state at the silicon. The hypervalent state of the silicon is also supported by a natural bond orbital calculation. However, despite having a difluorosilyl group, 2 does not show a hypervalent state for the silicon, based on an X-ray crystal structure analysis.

Full text of DOI:10.1002/hc.21044

Heteroatom Chemistry
Volume 00, Number 0, 2012
On the Intramolecular Interactions of Si/P in
1,2-Phenylene Frameworks
Takanobu Sanji, Keigo Naito, Taigo Kashiwabara, and
Masato Tanaka
Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
Received 7 May 2012; revised 26 June 2012
because of their Lewis acidic or basic nature.
ABSTRACT: The synthesis and structure of
However, there are few examples of hypervalent
1-diphenylphosphino-2-(fluorodiphenylsilyl) benzene
organosilicon compounds with soft phosphine
1 and 1-diphenylphosphino-2-(difluorophenylsilyl)-
donors to date. Tamao et al. reported phosphine-
benzene 2 are reported. An X-ray crystal structure anal-
coordinated fluorodisilanes based on the structurally
ysis of 1 shows a weak interaction between the sili-
rigid 1,8-naphthylene backbone [2]. Walter et al.
con and phosphorus moieties, producing a hyperva-
reported the synthesis of 1-dimethylphosphino-
lent state at the silicon. The hypervalent state of the
2-fluorodimethylsilylbenzene; however, the Si/P
silicon is also supported by a natural bond orbital
interaction in this molecule was not determined [3].
calculation. However, despite having a difluorosilyl
Alternatively, Breit et al. prepared 1-diphenylphos-
group, 2 does not show a hypervalent state for the
phino-2-chlorodi(isopropyl)silylbenzene and found
silicon, based on an X-ray crystal structure analysis.
a Si/P interaction from its X-ray crystal structure
ꢀ
C
2012 Wiley Periodicals, Inc. Heteroatom Chem 00:1–5,
[4]. The degree of hypervalent state of the Si atom
2012; View this article online at wileyonlinelibrary.com.
was quite low, probably because the four-membered
DOI 10.1002/hc.21044
ring structure for the formation of the Si–P bridge
is unfavorable. Very recently, a Sn/P interaction
in a 1,2-phenylene backbone was reported by Lin
INTRODUCTION
et al. [5]. However, when the silicon becomes
more positive by substitution with electronegative
groups on the silicon atom, the silicon center would
be an acceptable hypervalent state [6]. Here, we
report the synthesis of 1-diphenylphosphino-2-
fluorosilylbenzenes 1 and 2 (Chart 1) and discuss
their ability to form Si/P interactions.
The chemistry of hypervalent organosilicon com-
pounds has been extensively explored over the
past two decades [1]. This is because hyperva-
lent derivatives are involved as models for the
intermediate/transition-state structures in SN re-
actions and show unique structural features and
dynamic intramolecular interactions. For example,
organosilicon compounds substituted with hard N-
or O-groups at the adjacent position in the molecule
usually show unique intramolecular interactions
RESULTS AND DISCUSSION
1 - Diphenylphosphino - 2 - (fluorodiphenylsilyl)ben-
zene
1 was synthesized by the reaction of
lithiated triphenylphosphine derived from
3
Correspondence to: Takanobu Sanji; e-mail: sanji.t.aa@m
.titech.ac.jp. Masato Tanaka; e-mail: m.tanaka@res.titech.ac.jp.
Supporting Information is available in the online issue at
and dichlorodiphenylsilane followed by flu-
orination with HF•pyridine (Scheme 1). 1-
Diphenylphosphino-2-(difluorophenylsilyl)benzene
2 was also prepared by the reaction of the lithiated
wileyonlinelibrary.com.
c
ꢀ
2012 Wiley Periodicals, Inc.
1

2
Sanji et al.
160.73◦. When the silicon atom adopts a distorted
trigonal bipyramidal (TBP) geometry, the %TBPa
and %TBPe [7] calculated from the X-ray analysis
are 24 and 40, respectively. The values are quite
small compared with the %TBP when the silicon
atom in the five-coordinated state adopts a distorted
TBP geometry, but larger than those reported for 1-
diphenylphosphino-2-chlorosilylbenzene (%TBPa =
24 and %TBPe = 34) [4]. This is due to the substitu-
tion of the electronegative fluorine group on the Si
atom. These data show that Si(1) in 1 has the abil-
ity to form the weak Si/P interactions to form the
five-coordinated state.
CHART 1
To support the donor–acceptor interaction be-
tween the phosphorus and silicon atoms of the com-
pound, the natural bond orbital (NBO) analysis [8]
was examined. In the calculation, the structure ob-
tained from the X-ray analysis was used as an op-
timized structure (Gaussian 09 program [9] with a
B3LYP/6-31G∗ basis set). The analysis shows that
the hybrid orbital order of Si(1) is sp2.17, and an
n(P)–σ∗(Si) orbital interaction is feasible. Although
the coordination of the lone pair electrons on P1
to the σ∗ orbital of the Si1–F1 bond is not effective
in the structure, the contribution to the stability of
the molecule by the n(P)–σ∗(Si) interaction is calcu-
lated to be 7.7 kcal/mol in 1.
SCHEME 1
In solution, the 29Si chemical shift appeared
1
at −5.7 ppm with JSi−F = 281 Hz, which is
slightly shifted upfield to that observed for triph-
1
enylfluorosilane (–3.3 ppm with JSi−F = 281 Hz)
[10,11]. The Si–P coupling was found in
1
(JSi−P = 7.2 Hz), but not in 1-diphenylphosphino-
2-(chlorodiphenylsilyl)benzene, which is further
smaller than that observed for reported phosphine-
coordinated fluorodisilanes [2]. The NMR study
shows almost no interaction of Si–P atoms in 1 oc-
curred in solution at room temperature, although
further studies are required.
FIGURE 1 An ORTEP drawing of 1 at the 50% probabil-
ity level. All hydrogen atoms are omitted for clarity. Selected
˚
distances (A) and angles (deg): P1· · ·Si1 = 3.243, Si1–F1 =
1.618, F1–Si1· · ·P = 160.73, C2–Si1–F1 = 102.52, C19–
Si1–F1 = 104.31, C25–Si1–F1 = 107.56, C2–Si1–C19 =
114.22, C19–Si1–C25 = 113.69, C25–Si1–C2 = 113.23.
Next, the structure of 2 was determined by
single-crystal X-ray analysis (Fig. 2). However, 2
does not show a hypervalent state for the silicon;
nevertheless, the Si with two F atoms is more posi-
tive than the Si in 1. The distance between P(1) and
triphenylphosphine and trifluorophenylsilane. The
products were fully characterized by spectroscopic
methods.
˚
Si(1) is 3.29(2) A, which is within the sum of the van
˚
The structure of 1 was identified from single-
crystal X-ray analysis (Fig. 1). As expected, the X-
ray crystal structure suggests an electronic interac-
tion between the phosphorus and the silicon atom.
Thus, the distance between P(1) and Si(1) is rather
der Waals radii of the two elements (3.90 A); how-
˚
ever, the Si–F bond distance (1.59 A) is almost the
same as the standard Si(1)–F(1 or 2) bond length.
The P(1)· · ·Si(1)–F(1) angle is 163.55◦. The %TBPs
calculated from the X-ray analysis are rather low
(%TBPa = 17 and %TBPe = 28). The NBO calculation
shows that the hybrid orbital order of the Si(1) atoms
is sp1.44, and the stabilization of the molecule by n(P)–
σ∗(Si) is rather small (ca. 4.5 kcal/mol). Thus, the
coordination of the lone pair electrons on P1 to the
˚
small (3.24(3) A), which is well within the sum of
˚
the van der Waals radii of the two elements (3.90 A).
˚
˚
The Si(1)–F(1) bond distance is 1.61(8) A, where
the standard Si–F bond length is 1.58 A. In the
structure, additionally, the P(1)–Si(1)–F(1) angle is
Heteroatom Chemistry DOI 10.1002/hc

Intramolecular Interactions of Si/P in 1,2-Phenylene Frameworks
3
EXPERIMENTAL
General
1H, 13C, 19F, and 29Si NMR spectra were recorded
using a Bruker BioSpin GmbH (Rheinstetten,
Germany) DPX 300 NMR spectrometer at 300, 75.4,
282, and 60 MHz, respectively. 31P NMR spectra
were recorded on a Bruker BioSpin GmbH Avance
1
400 spectrometer at 162 MHz. H and 13C chemi-
cal shifts were referenced to solvent residues. 19F,
29Si, and 31P NMR chemical shifts were referenced
to external CFCl3, Me4Si, and aq. 85% H3PO4, re-
spectively. High-resolution mass spectra were ob-
tained with a JEOL (Tokyo, Japan) JMS-700 mass
spectrometer. Melting points were measured on
a micromelting point apparatus IA9100 (AsOne,
Tokyo, Japan). All manipulations involving air- and
moisture-sensitive compounds were carried out un-
der an atmosphere of dry nitrogen. 1-Bromo-2-
(diphenylphosphino)benzene [4] and phenyltrifluo-
rosilane [13] were prepared according to the litera-
ture.
FIGURE 2 An ORTEP drawing of 2 at the 50% probability
level. All hydrogen atoms are omitted for clarity. Selected dis-
˚
tances (A) and angles (deg): P1· · ·Si1 = 3.292, Si1–F1 =
1.590, Si1–F2(eq) = 1.588, F1–Si1· · ·P = 163.55, C7–
Si1–C1 = 117.97, C7–Si1–F2(eq) = 111.20, C1–Si1–
F2(eq) = 108.13, F1(ap)–Si1–F2(eq) = 104.44, F1(ap)–
Si1–C7 = 105.17, F1(ap)–Si1–C1 = 109.05.
Synthesis of 1-Diphenylphosphino-2-
(chlorodiphenylsilyl)benzene
σ∗ orbital of the Si1–F1 bond is not effective in the
structure. These data suggest that Si(1) in 2 is not
in the five-coordinated state. This may be due to the
structural stability in the crystal packing of 2, al-
though further study is required. In solution, the 29Si
NMR showed no interactions of the Si and P atoms
(–31.2 ppm with JSi−P = 7.2 Hz and JSi−F = 290.0 Hz).
1.65 M n-butyllithium in hexane (4.2 mL, 5.47 mmol)
was added at room temperature to a solution
of 1-bromo-2-(diphenylphosphino)benzene (1.92 g,
5.63 mmol) in toluene (30 mL) and Et2O (15 mL).
The mixture was stirred at the same temperature for
25 min. Dichlorodiphenylsilane (3.14 g, 12.4 mmol)
was added to the reaction mixture, and then the
reaction mixture was stirred overnight. After filtra-
tion with Celite, the solution was removed under re-
duced pressure. The residue (4.61 g) was recrystal-
lized from a hexane (60 mL)/toluene (13 mL) mixed
solvent at −30◦C to afford the title compound in 87%
yield (2.36 g, 4.92 mmol) as colorless crystals: mp
CONCLUSION
The results reported here show that, even with the
rigidity of the 1,2-phenylene backbone, the phos-
phine and silicon groups of 1 are involved in the
weak intramolecular Si/P interaction, and the silicon
atom has the ability to be is in a hypervalent state.
However, despite having a difluorosilyl group, 2 does
not show a hypervalent state for the silicon, based on
an X-ray crystal structure analysis. This observation
is also supported by the NBO calculations. Although
further studies are required, the Lewis acidity of the
silicon and also the structural motif are important
factors governing the ability to form the hyperva-
lent state on the silicon, even in the same structural
framework. Furthermore, this study may provide a
principle to design main group element containing
molecules with a combination of Lewis acids and
bases, because cooperation between Lewis acids and
Lewis bases in frustrated Lewis pairs has attracted
considerable interest recently and has been shown
to exhibit unique chemical behavior [12]. Further
study is currently in progress.
1
158.9–160.0◦C; H NMR (CDCl3, 300 MHz) δ 6.97–
7.05 (m, 4H), 7.17–7.58 (m, 15H), 7.70–7.80 (m, 4H),
1
7.99–8.07 (m, 1H); 13C{ H} NMR (C6D6, 75 MHz)
δ 127.9, 128.2, 128.3, 129.2, 130.2, 131.3, 133.2 (d,
J = 18.0 Hz), 134.7 (d, J = 18.1 Hz), 135.4 (d, J =
2.8 Hz), 136.1, 137.1 (d, J = 10.6 Hz), 137.6 (d, J =
16.1 Hz), 140.8 (d,
J
= 47.5 Hz), 144.0 (d,
1
J = 11.3 Hz); 29Si{ H} NMR (CDCl3, 60 MHz) δ 6.0;
1
31P{ H} NMR (CDCl3, 162 MHz) δ −11.2; HRMS (EI–
DI, 70 eV) calcd for C24H19F2PSi (value for [M]+) m/z
478.1073, found 478.1069.
Synthesis of 1-Diphenylphosphino-2-
(fluorodiphenylsilyl)benzene 1
70% HF•pyridine complex (57.0 mg, 1.51 mmol)
was added at room temperature to a solution of
Heteroatom Chemistry DOI 10.1002/hc

4
Sanji et al.
(CDCl3, 60 MHz) δ −31.2 (dt, 3 JSi−P = 7.2 Hz, 1 JSi−F
=
1-diphenylphosphino - 2 - ( chlorodiphenylsilyl ) ben-
zene (711 mg, 1.48 mmol) in dichloromethane. The
mixture was stirred at the same temperature for 4 h,
and then the solution was removed under reduced
pressure. Toluene (15 mL) was added to the residue,
and any supernatant liquid was decanted off. The
residual solid was washed with toluene (5 mL × 2).
The combined solution was removed under reduced
pressure (659 mg) followed by recrystallization from
hexane (3 mL) at −30◦C to afford 1 in 60% yield
(415 mg, 0.89 mmol) as colorless crystals: mp 95.0–
1
290.0 Hz); 31P{ H} NMR (CDCl3, 162 MHz) δ −7.10
4
(t, JP−F = 40.5 Hz); 19F NMR (CDCl3, 282 MHz) δ
4
−139.1 (d, JF−P = 40.5 Hz); HRMS (EI–DI, 70 eV)
calcd for C24H19F2PSi (value for [M]+) m/z 404.0962,
found 404.0964.
X-Ray Measurements
The crystallographic measurements were performed
at −160 1◦C using a Rigaku (Tokyo, Japan) Saturn
AFC7R CCD diffractometer with Mo Kα radiation (λ
1
97.9◦C; H NMR (CDCl3, 300 MHz) δ 6.97–7.05 (m,
˚
= 0.7107 A). The structure was solved by direct meth-
4H), 7.15–7.60 (m, 15H), 7.68–7.85 (m (d-like), J =
ods and refined by full-matrix least squares on F2.
Single crystals of 1 were obtained by recrystal-
lization from a toluene/hexane (v/v = 1/12) solution.
A colorless chip crystal (0.30 × 0.30 × 0.30 mm3)
was used. Crystal data for 1: C30H24SiFP, M =
1
6.6 Hz, 4H), 7.92–7.98 (m, 1H); 13C{ H} NMR (C6D6,
75 MHz) δ 127.8, 128.2, 128.3, 129.1, 130.4, 131.1,
133.2 (d, J = 18.0 Hz), 133.8 (dd, J = 17.1 Hz, J =
3.0 Hz), 135.4, 135.5 (dd, J = 3.6 Hz, J = 1.6 Hz),
136.4 (dd, J = 18.2 Hz, J = 4.6 Hz), 137.2 (d,
J = 10.2 Hz), 141.6 (dd, J = 16.7 Hz, J = 50.8 Hz),
˚
3
462.58, orthorhombic,Pbca (#61), a = 17.893(10) A,
˚
˚
˚
1
143.9 (dd, J = 2.5 Hz, J = 10.2 Hz); 29Si{ H} NMR
b = 14.546(8) A, c = 18.660(10) A, V = 4857(5) A ,
Z = 8, D(calc) = 1.265, F000 = 1936.00. Total re-
(CDCl3, 60 MHz) δ −5.7 (dd, 3 JSi−P = 12.9 Hz, 1 JSi−F
=
1
281.2 Hz); 31P{ H} NMR (CDCl3, 162 MHz) δ −9.25
flections collected = 25700 (unique = 5333, R
=
int
4
(d, JP−F = 28.3 Hz); 19F NMR (CDCl3, 282 MHz) δ
0.151), GOF = 1.302, Max S/E = 0.010, R/P ratio =
17.84, R (I > 2.00σ(I)) = 0.1097, Rw (all reflections)
= 0.1117.
4
−163.7 (d, JF−P = 28.2 Hz); HRMS (EI–DI, 70 eV)
calcd for C24H19F2PSi (value for [M]+) m/z 462.1369,
Single crystals of 2 were obtained by recrystal-
lization from a pentane solution. A colorless chip
crystal (0.30 × 0.20 × 0.20 mm3) was used. Crys-
tal data for 2: C24H19PSiF2, M = 404.47, orthorhom-
found 462.1374.
Synthesis of 1-Diphenylphosphino-2-
(difluorophenylsilyl)benzene 2
˚
˚
◦
bic, P−1 (#2), a = 9.663(7) A, b = 11.084(9) A,
◦
˚
c = 11.773(9) A, α = 115.974(10) , β = 91.5949(18) ,
1.65 M n-butyllithium in hexane (5.2 mL, 8.5 mmol)
was added at room temperature to a solution of 1-
bromo-2-(diphenylphosphino)benzene (2.73 g, 8.02
mmol) in Et2O (35 mL). The mixture was stirred
at the same temperature for 15 min. Phenyltrifluo-
rosilane (1.97 g, 12.2 mmol) was added to the re-
action mixture at −78◦C. The reaction mixture was
stirred at the same temperature for 1 h, at −58◦C
for 3 h and then at room temperature overnight. Af-
ter filtration with Celite, the solution was removed
under reduced pressure. The residue (4.61 g) was re-
crystallized from a hexane (60 mL)/toluene (13 mL)
mixed solvent at −30◦C to afford 2 in 87% yield (2.36
g, 4.92 mmol) as colorless crystals: mp 74.1–74.8◦C
(760 mmHg); 1H NMR (CDCl3, 300 MHz) δ 7.10–7.19
(t-like, 3 JH−H = 7.5 Hz, 4H, Ar–H), 7.20–7.30 (m, 6H,
Ar–H), 7.32 (s, 1H, Ar–H), 7.34–7.40 (m, 2H, Ar–H),
7.41–7.49 (m, 1H, Ar–H), 7.45–7.55 (m, 2H, Ar–H),
7.65–7.75 (d-like, J = 7.0 Hz, 2H, Ar–H), 7.97–8.02
◦
3
˚
γ = 114.911(10) , V = 992.7(13) A , Z = 2, D(calc) =
1.353, F000 = 420.00. Total reflections collected =
7183 (unique = 4192, R = 0.111), GOF = 0.651,
int
Max S/E = 0.000, R/P ratio = 16.50, R (I > 2.00
σ(I)) = 0.0665, Rw (all reflections) = 0.1705.
SUPPLEMENTARY MATERIAL
CCDC-876980 (1) and CCDC-876981 (2) contain the
supplementary crystallographic data for this pa-
per. 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
336033; or deposit@ccdc.cam.ac.uk).
SUPPORTING INFORMATION
NMR for new compounds and NBO analysis are
available in the Supporting Information.
1
(m, 1H, Ar–H); 13C{ H} NMR (C6D6, 75 MHz) δ 128.1,
128.4, 128.5, 128.7, 129.2, 130.6 (td, J = 3.5 Hz, J =
19.1 Hz), 132.0 (d, J = 60.8 Hz), 133.3 (d, J = 19.8
Hz), 134.5 (m), 135.0, 136.2 (dt, J = 18.3 Hz, J = 2.3
Hz), 136.6 (d, J = 8.8 Hz), 137.4 (dt, J = 52.3 Hz,
ACKNOWLEDGMENTS
This work was performed under the Cooperative Re-
search Program of “Network Joint Research Center
1
J = 16.8 Hz), 144.9 (d, J = 10.7 Hz); 29Si{ H} NMR
Heteroatom Chemistry DOI 10.1002/hc

Intramolecular Interactions of Si/P in 1,2-Phenylene Frameworks
5
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for Materials and Devices” and supported by Spe-
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Materials, Devices and System Research Alliance)
from the Ministry of Education, Culture, Sports, Sci-
ence, and Technology of Japan. We also thank the
Center for Advanced Materials Analysis, Technical
Department, Tokyo Tech.
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