Preparation and photophysical properties of phosphino- and phosphine oxide-linked siloles

Article abstract of DOI:10.1021/om900956u

1,1-dimethyl-2,5-disubstituted-3,4-diphenylsiloles terminated at the 2,5-positions with a phosphino or phosphine oxide group were prepared. All reactions were carried out under an inert atmosphere of argon or nitrogen using standard Schlenk techniques or a drybox using solvents dried by standard procedures. The phosphine oxide-linked silole was prepared in 17% yield from the reaction of 1,1-dimethyl-2,5-bis(4-bromophenyl)-3,4-diphenylsilole with diphenyl(4-ethynyl phenyl)-phosphine oxide in the presence of CuI, Pd(PPh ₃)₄, and NEt₃. The ¹³C{ ¹H} NMR spectra for the siloles 1-5 and 9 all exhibit resonances generally above about 135 ppm for the silole ring carbons, and the Si{ ¹H} resonances were generally observed near 8-9 ppm except for siloles 1a and 1b, which were shifted slightly downfield at 15 and 20 ppm.

Full text of DOI:10.1021/om900956u

1612 Organometallics 2010, 29, 1612–1621
DOI: 10.1021/om900956u
Preparation and Photophysical Properties of Phosphino- and
Phosphine Oxide-Linked Siloles
Janet Braddock-Wilking,* Li-Bin Gao, and Nigam P. Rath
Department of Chemistry and Biochemistry and Center for Nanoscience,
University of Missouri;St. Louis, St. Louis, Missouri 63121
Received November 2, 2009
Introduction
applications in organic light emitting diodes (OLEDs),2-4
organic field-effect transistors (OFETs),5 and photovoltaic
devices,6 and as sensors,4,7 due to high electron mobility8 and
affinity9 and strong photoluminescence.10
The last two decades have witnessed a dramatic increase in
the research of silole-based π-conjugated systems due to their
distinctive electronic and photophysical properties arising
from a low LUMO energy level due to σ*-π* conjuga-
tion between the exocyclic bonds at silicon with the π*or-
bital of the butadiene unit.1 Siloles have shown promising
Extensive studies on the preparation, characterization,
and reactivity of siloles have been reported over the last
two decades.11 Two key synthetic routes are generally used
for the preparation of siloles. The reductive cyclization of
bis(phenylethynyl)silanes has been used to prepare a number
of 2,5-disubstituted-3,4-diphenylsiloles.12,13 Another meth-
od involves the regioselective coupling of internal and termi-
nal alkynes through a titanacyclopentadiene intermediate
followed by halogenolysis to produce the corresponding 1,4-
dihalobutadienes. Subsequent lithium-halogen exchange
with nBuLi followed by reaction with Si(OMe)4 or a dihalo-
silane produces the silole.14 The electronic properties of
siloles can be fine-tuned depending upon the nature of the
exocyclic substituents at the silicon center15 or more signifi-
cantly from the groups at the 2,5-positions of the silole
ring.16 In order to further explore the optimization of the
electronic properties of siloles, we have examined the effects
of incorporating phosphino or phosphine oxide groups
into the conjugated framework either by direct attachment
to the silole ring or by linking the heteroatom unit to the
terminal positions of the conjugated groups in the 2,5-
positions. In addition, the presence of the reactive phosphino
groups enables these systems to be building blocks for the
construction of a variety of conjugated materials includ-
ing the incorporation of transition metal centers. Recently,
*To whom correspondence should be addressed. E-mail: wilkingj@
umsl.edu.
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pubs.acs.org/Organometallics
Published on Web 03/04/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 7, 2010 1613
Chart 1
The five-membered silole ring of compounds 1-5 was
formed utilizing the reductive cyclization method reported
by Tamao and co-workers from reaction of bis(phenyl-
ethynyl)dimethylsilane with lithium naphthalenide.12 Sub-
sequent reactions were performed on the resulting 2,5-
dilithio-substituted silole to produce the final products as
shown in Chart 1 and described in the following para-
graphs. The intermediate 2,5-dilithio-substituted silole (R=
Li, Chart 1) was reacted with 2 equiv of PPh2Cl to afford
air- and moisture-sensitive compound 1a in 66% yield
(Scheme 1). Oxidation of 1a with 30% H2O2 afforded the
corresponding phosphine oxide compound 1b in 62% yield
(Scheme 1). The mixed phosphine/phosphine oxide com-
pound 1a,b was produced in 48% yield by the slow oxidation
of 1a in air. The phosphine oxides prepared in this study were
found to be hygroscopic.
Compound 2a was prepared in 54% yield from the reac-
tion of 1,1-dimethyl-2,5-bis(p-bromophenyl)-3,4-diphenylsi-
lole21 with a slight excess of n-BuLi followed by 2 equiv of
PPh2Cl, as shown in eq 1. The related silole, 1,1-dimethyl-
2,5-bis(m-diphenylphosphinophenyl)-3,4-diphenylsilole, 3a,
was prepared in 63% yield by a similar procedure starting
from the corresponding 2,5-bis(m-bromophenyl)-substi-
tuted silole. Both phosphine oxides 2b and 3b were synthe-
sized in 93% and 89% yields from 2a and 3a, respectively, by
treatment with 30% H2O2 solution.
bis(diarylphosphino)dithioenosilole derivatives and the cor-
responding phosphine oxide systems have been prepared,
and the photoluminescence was found to be significantly
affected by the oxidation state of the phosphorus center.17
The coordination chemistry of related phosphine-substi-
tuted oligothiophenes with gold18 and π-conjugated phosp-
holes19 through coordination of the phosphorus to a variety
of transition metal centers has resulted in the formation of a
diverse array of supramolecular architectures. The reductive
cyclization method has also been used to prepare 2,5-disub-
stituted siloles containing 7-azaindolylaryl or 2,20-dipyri-
dylamino groups and the latter complex coordinated to
zinc centers at the open nitrogen sites.20 We now report the
preparation and characterization of several 1,1-dimethyl-
2,5-disubstituted-3,4-diphenylsiloles containing diphenyl-
phosphino or diphenylphosphine oxide groups directly
bound to or linked to the terminal positions of a conjugated
organic group bound to the 2,5-positions of the silole ring.
We also report the coordination chemistry of 1,1-dimethyl-
2,5-bis(40-diphenylphosphinophenyl)-3,4-diphenylsilole with
(chloro)gold(tetrahydrothiopene) to produce the novel digold
complex 1,1-dimethyl-2,5-bis(40-diphenylphosphino(chloro-
gold)phenyl)-3,4-diphenylsilole.
Compound 4b was prepared in 72% yield by the coupling
reaction13 of 1,1-dimethyl-2,5-bis(chlorozinc)-3,4-diphenylsi-
lole22 with (40-bromobiphenyl-4-yl)diphenylphosphine oxide
in the presence of the catalyst, (Ph3P)2PdCl2 (Scheme 2). The
silole 4a was then prepared in 41% yield from 4b by treatment
with excess HSiCl3 and NEt3 (Scheme 2).23
Results and Discussion
The phosphine oxide-linked silole 5b was prepared in 17%
yield from the reaction of 1,1-dimethyl-2,5-bis(4-bromo-
phenyl)-3,4-diphenylsilole21 with diphenyl(4-ethynyl phenyl)-
phosphine oxide24 in the presence of CuI, Pd(PPh3)4, and
NEt3 (eq 2). The corresponding diphenylphosphino-termi-
nated silole 5a was prepared in 15% yield by treatment of 5b
with an excess of HSiCl3 and NEt3.
Several substituted silacyclopentadienes have been pre-
pared that contain a diphenylphosphino (1a-5a) or phos-
phine oxide (1b-5b) group bound directly to the 2,5-
positions of the silole ring or linked at the terminal positions
to a conjugated organic group, as shown in Chart 1. The new
siloles were isolated as yellow to greenish-yellow solids for
1-5 and were generally characterized by multinuclear
NMR, UV-vis, and fluorescence spectroscopy, mass spec-
trometry, elemental analysis, and X-ray crystallography (2b
and 4a).
(21) Wang, F.; Luo, J.; Chen, J.; Huang, F.; Cao, Y. Polymer 2005,
46, 8422–8429.
(22) Yamaguchi, S.; Endo, T.; Uchida, M; Izumizawa, T.; Furukawa,
K.; Tamao, K. Chem.;Eur. J. 2000, 6, 1683–1692.
(23) Shi, M.; Chen, L.-H.; Li, C.-Q. J. Am. Chem. Soc. 2005, 127,
3790–3800.
(24) Ha-Thi, M.-H.; Souchon, V.; Hamdi, A.; Metivier, R.; Alain, V.;
Nakatani, K.; Lacroix, P. G.; Genet, J.-P.; Michelet, V.; Leray, I.
Chem.;Eur. J. 2006, 12, 9056–9065.
(17) Ohshita, J.; Kurushima, Y.; Lee, K.-H.; Kunai, A.; Ooyama, Y.;
Harima, Y. Organometallics 2007, 26, 6591–6595.
(18) Stott, T. L.; Wolf, M. O.; Patrick, B. O. Inorg. Chem. 2005, 44,
620–627.
(19) Crassous, J.; Reau, R. Dalton Trans. 2008, 6865–6876.
(20) Lee, J.; Liu, Q.-D.; Motala, M.; Dane, J.; Gao, J.; Kang, Y.;
Wang, S. Chem. Mater. 2004, 16, 1869–1877.
(25) Boydston, A. J.; Yin, Y.; Pagenkopf, B. L. J. Am. Chem. Soc.
2004, 126, 10350–10354.

1614 Organometallics, Vol. 29, No. 7, 2010
Braddock-Wilking et al.
Scheme 1
Scheme 2
The 13C{1H} NMR spectra for the siloles 1-5 and 9 all
exhibit resonances generally above about 135 ppm for the
silole ring carbons,27 and the 29Si{1H} resonances were
generally observed near 8-9 ppm except for siloles 1a and
1b, which were shifted slightly downfield at 15 and 20 ppm,
respectively. The phosphine-linked siloles 2a-4a exhibi-
ted singlet resonances in the 31P{1H} NMR spectra between
- 5 and - 6 ppm, whereas the signal of 1a was observed
slightly upfield at -12 ppm. The 31P{1H} NMR resonances
of the phosphine oxide-linked siloles 2b-5b were observed
near 29 ppm; however, the signal of 1b was observed slightly
upfield at 22 ppm. Coordination of the phosphorus centers
to gold in complex 9 resulted in a downfield shift of the
resonance to 32 ppm.
The electronic absorption and fluorescence data of 1-5
and 9 are summarized in Table 1. The UV-vis spectra
exhibit absorption bands between 308 and 385 nm that are
attributed to the π-π* transition of the silole ring (Figures 1
and 2).3g,20,22,28 Siloles 5a and 5b show an additional absorp-
tion at 307 and 304 nm, respectively, which is assigned to the
π-π* transition for the alkyne units.29 The absorption
maximum for silole 2a is red-shifted by 15 nm compared to
1,1-dimethyl-2,3,4,5-tetraphenylsilole22 (2c, λabs =359 nm)
due to the presence of the phosphino group in 2a. However,
placement of the phosphino group in the meta-position of
the aryl group as in 3a or at the para-position of the biphenyl
unit in 4a results in essentially no change in the absorp-
tion maximum compared to 2c and 1,1-dimethyl-2,5-bis-
(biphenyl)-3,4-diphenylsilole22 (4c, λabs = 381 nm), respec-
tively. The presence of a phosphino group has resulted in
Coordination of the phosphine centers to gold was accom-
plished by reaction of silole 2a with 2 equiv of (chloro)-
gold(tetrahydrothiophene), [(Cl)Au(tht)],26 to form the digold
complex 9 as a yellow solid in 89% yield (eq 3). The structure 9
was confirmed by X-ray crystallography.
(27) Troitski, N. A.; Tandura, S. N.; Kolesnikov, S. P.; Choi, S.-B.;
Boudjouk, P. Main Group Met. Chem. 2001, 24, 1–4.
(28) Tamao, K.; Ohno, S.; Yamaguchi, S. Chem. Commun. 1996,
1873–1874.
(26) Uson, R.; Laguna, A.; Laguna, M. Inorg. Synth. 1989, 26, 85–91.
(29) Crisp, G. T.; Turner, P. D. Tetrahedron 2000, 56, 8335–8345.

Article
Organometallics, Vol. 29, No. 7, 2010 1615
Table 1. Photoluminescent Data for Compounds 1-5 and 9
absorptiona emissionb
c
φF
compound
λabs/nm
log(ε)
λem/nm
1a
1a/1b
2a
3a
4a
5a
1b
2b
3b
4b
5b
9
384
381
374
360
382
385
308
367
360
375
383
364
4.26
4.36
4.18
4.14
4.24
4.38
4.44
4.48
4.36
4.53
4.56
4.29
503
485
511
514
0.69 ꢀ 10-2
0.65 ꢀ 10-2
1.59 ꢀ 10-2
2.38 ꢀ 10-2
0.24 ꢀ 10-2
0.52 ꢀ 10-2
1.41 ꢀ 10-2
1.61 ꢀ 10-2d
1.21 ꢀ 10-2
487
474
505
512
416
a Concentration: [M] = 1 ꢀ 10-5 M in CH2Cl2 at 298 K. b Concen-
tration: [M] = 1 ꢀ 10-4 M in CH2Cl2 at 298 K. c Determined with
reference to anthracene. d Absorption minimal above 350 nm. Defined
maximum not observed between 260 and 375 nm.
Figure 3. Emission spectra of compounds 2a-5a in CH2Cl2
solution at 298 K. Excitation wavelengths (nm): 2a (429), 3a
(394), 4a (447), 5a (419).
maxima to higher energy compared to the corresponding
siloles, 2a, 3a, and 4a, respectively. However, a remarkable
hypsochromic shift is observed for silole 1b compared to 1a,
where the phosphorus centers are bound directly to the silole
ring. A smaller shift of the absorption maximum to higher
energy is observed for complex 9 (λabs = 364 nm) and the
phosphine oxide 2b (λabs=367 nm) compared to the silole 2a
(λabs = 374 nm). Hypsochromic shifts in the absorption
maxima have been observed for bis(diarylphosphine oxide)-
dithienosiloles (λabs=361 nm) and the corresponding phos-
phine derivatives (λabs = 380 nm).17 A similar trend was
also observed for the absorption maxima for 2,5-bis-
(diphenylphosphino)thiophene (PTP, λabs = 300 nm), the
related phosphine oxide (OTPTO, λabs = 273 nm), and
coordination complex (ClAu(PTP)AuCl, λabs = 276 nm),
where the latter complex exhibited a smaller hypsochromic
shift compared to the oxide. The larger hypsochromic shift
for the oxide (OTPTO) was suggested to possibly be due to
the higher electronegativity of O compared to Au.18
Figure 1. Electronic absorption spectra of compounds 1a-5a
in CH2Cl2 solution at 298 K.
The fluorescence spectra of 2-5 and 9 exhibit emission
bands between 416 and 514 nm (Figures 3 and 4). The
emission spectra for 2-5 also exhibit a shift to lower energy
as the chain length increases. The siloles 1a, 1b, and the mixed
phosphine/phosphine oxide 1a,b with the phosphino or
phosphine oxide unit bound directly to the 2,5-positions of
the silole ring, respectively, do not show any emission max-
ima. The absence of any emission in these compounds
may be due to negligible overlap between the phosphorus
lone pair and the π* LUMO orbital of the ring. The emis-
sion spectra for the related 2-diphenylphosphino- and
2,5-(diphenylphosphino)thiophenes (PT and PTP, respec-
tively) exhibit weak emission and a large Stoke’s shift, and
the emission bands were assigned to the π*-n transition.
These results are consistent with DFT calculations, which
supported a HOMO with significant P lone-pair character
and a LUMO localized primarily on the thienyl group.30
The emission maximum for complex 9 is blue-shifted
significantly compared to silole 2a. Coordination of the
phosphorus centers in some phosphino(oligothiophenes) to
gold centers has also resulted in blue shifts in the emission
maxima compared to the free ligand.18,30 Complexation of
zinc centers to a 2,20-dipyridylamino-functionalized silole
has also been reported to result in a blue shift of the
absorption and emission maxima due to an alteration of
the conjugation with the silole ring.20 The photoluminescent
Figure 2. Electronic absorption spectra of compounds 1b-5b
in CH2Cl2 solution at 298 K.
bathochromic shifts in the absorption maxima of phosphine-
substituted thiophenes relative to the unsubstituted systems
by enhancing the conjugation.30 As expected, the absorption
wavelength for 1-5 increases as the conjugation chain length
at the 2,5-positions of the silole ring increases,25 and silole 5a
exhibits the lowest energy absorption band in the current
study at 385 nm. Upon oxidation, the phosphorus centers in
siloles 2b, 3b, and 4b exhibit little or no shift of the absorption
(30) Stott, T. L.; Wolf, M. O. J. Phys. Chem. B 2004, 108, 18815–
18819.

1616 Organometallics, Vol. 29, No. 7, 2010
Braddock-Wilking et al.
Figure 5. Molecular structure of 2b (with thermal ellipsoids
shown at the 50% probability level) showing one of the two
˚
unique molecules in the unit cell. Selected bond distances (A)
Figure 4. Emission spectra of compounds 2b-5b in CH2Cl2
solution at 298 K. Excitation wavelengths (nm): 2b (403), 3b
(394), 4b (435), 5b (436).
and angles (deg): Si1-C1=1.865(5), Si1-C4=1.873(5), Si1-
C5 = 1.839(5), Si1-C6 = 1.858(5), C1-C2 = 1.360(7), C2-
C3 = 1.513(7), C3-C4 = 1.364(7), P1-O1 = 1.435(5), P1-
C22 = 1.803(5), P1-C25 = 1.780(6), P1-C31 = 1.794(6),
P2-O2 = 1.415(5), P2-C40 = 1.805(5), P2-C43 = 1.794(6),
P2-C49 = 1.792(6); C5-Si1-C6 = 111.5(2), C1-Si1-C4=
92.1(2), C2 -C1-Si1 = 108.3(4), C3-C4-Si1 = 108.3(4),
C1-C2-C3 = 115.8(4), C4-C3-C2 = 115.2(4), C25-P1-
C22 = 106.9(3), C25-P1-C31 = 106.5(3), C31 -P1-C22 =
106.3(3), O1-P1-C22 = 111.6(3), O1-P1-C25 = 115.2(3),
O1-P1-C31=109.9(3), C49-P2-C40=105.6(2), C49-P2-
C43 = 106.7(3), C43-P2-C40 = 105.4(2), O2-P2-C40 =
113.2(3), O2-P2-C49=111.9(3), O2-P2-C43=113.4(3).
quantum efficiencies were determined for siloles 1-5 and 9 in
CH2Cl2 solution at room temperature, and the mode-
rate values observed are similar of those reported for other
siloles.22,25 Solid-state luminescent measurements could not
be performed due to the limitations of our spectrometer.
However, solid samples of compounds 2a, 2b, 3a, 3b, 4b, 5a,
and 5b were exposed to UV light from a hand-held black
light, and all showed fluorescence, whereas compounds 1a,b
and 1b did not.
X-ray Crystallography. The molecular structures of 2b,
4a, and 9 were determined by X-ray crystallography and are
shown in Figures 5, 6, and 7 respectively. Two unique
molecules of 2b were found in the asymmetric unit, and only
one of these molecules is shown in Figure 5. The phosphorus
center P2 and an associated phenyl group are disordered in
4a. The central silole ring in 2b, 4a, and 9 is planar with a
tetrahedral environment at the silicon centers. The four aryl
substituents bound to the silole ring carbons adopt a non-
coplanar propeller-like arrangement. The dihedral angles
between the aryl groups in the 2,5-positions of 2b and 4a
and the silole ring were 54.9-55.7° and 41.9-49.6o respec-
tively. The molecular structures of 2b and 4a are similar to
1,1-dimethyl-2,3,4,5-tetraphenylsilole31 and a series of struc-
turally characterized 1,1-dimethyl-2,5-bis(p-monosubsti-
tuted phenyl)-3,4-diphenylsiloles.22 The P-O distances in
Figure 6. Molecular structure of 4a (with thermal ellipsoids
shown at the 30% probability level). Selected bond distances
˚
˚
(A) and angles (deg): Si1-C1 = 1.875(7), Si1-C4 = 1.883(7),
2b (1.41-1.43 A) are slightly shorter than those observed for
32
˚
OPPh3 (1.48 A).
Si1-C5 = 1.864(7), Si1-C6 = 1.868(7), C1-C2 = 1.341(9),
C2-C3 = 1.535(9), C3-C4 = 1.355(9), P1-C28 = 1.829(8),
P1-C31=1.843(9), P1-C37=1.830(9), P2-C52=1.875(11),
P2-C55=1.831(12), P2-C61=1.778(10), P20-C52=1.825(16),
P20-C55 =1.900(19); C5-Si1-C6=108.3(3), C1-Si1-C4=
91.8(3), C2-C1-Si1 = 109.2(5), C3-C4-Si1 = 107.8(5),
C1-C2-C3 = 115.0(6), C4-C3-C2 = 116.1(6), C28-P1-
C37 = 102.2(4), C28-P1-C31 = 102.2(4), C37-P1-C31=
100.7(4), C61-P2-C55=105.9(7), C61-P2-C52=111.0(7),
C55-P2-C52=96.5(6), C52-P20-C55=95.9(8).
The two gold centers in 9 (Figure 7) are coordinated to one
phosphorus center at each end of ligand 2a in an almost
linear coordination with Cl-Au-P angles of 177.64(7)° and
178.73(8)o. The Au-Cl and Au-P bond lengths of ca.
˚
2.28-2.29 and 2.25-2.26 A, respectively, are similar to those
observed for the related chloro(triphenylphosphine)gold,
˚
which exhibited an Au-Cl distance of 2.279(3) A, an
˚
Au-P distance of 2.235(3) A, and a P-Au-Cl angle of
179.68(8)o.33 The dihedral angles between the aryl groups in
the 2,5-positions of 9 and the silole ring were 49.2-59.0° and
are only slightly larger than those observed for 2b. The solid-
state structure of 9 shows no short intermolecular Au Au
interactions.
In conclusion, we prepared 1,1-dimethyl-2,5-disubstitu-
ted-3,4-diphenylsiloles terminated at the 2,5-positions with a
phosphino or phosphine oxide group that show blue-green
luminescence in solution with the notable absence of emis-
sion from the siloles 1a and 1b, where the phosphine units are
directly bound to the ring. The phosphino-linked siloles can
3 3 3
(31) (a) Parkanyi, L. J. Organomet. Chem. 1981, 216, 9–16. (b) Yu, G.;
Yin, S.; Liu, Y.; Chen, J.; Xu, X.; Sun, X.; Ma, D.; Zhan, X.; Peng, Q.; Shuai,
Z.; Tang, B.; Zhu, D.; Fang, W.; Luo, Y. J. Am. Chem. Soc. 2005, 127, 6335–
6346.
(32) Thomas, J. A.; Hamor, T. A. Acta Crystallogr. 1993, C49, 355–
357.
(33) (a) Baenziger, N. C.; Bennett, W. E.; Soboroff, D. M. Acta
Crystallogr. 1976, B32, 962–963. (b) Khan, M.; Oldham, C.; Tuck, D. G.
Can. J. Chem. 1981, 59, 2714–2718.

Article
Organometallics, Vol. 29, No. 7, 2010 1617
Isotopes, Inc., and dried over activated molecular sieves before
use. The following compounds were prepared by literature
methods, 1,1-dimethyl-2,5-bis(40-bromophenyl)-3,4-diphenyl-
silole,21 1,1-dimethyl-2,5-dibromo-3,4-diphenylsilole,34 dimethyl-
bis(phenylethynyl)silane,35 4-(bromophenyl)diphenylphosphine,36
(4-bromophenyl)diphenylphosphine oxide,37 ZnCl2(TMEDA),38
(Ph3P)2PdCl2,39 and [AuCl(tht)] (tht = tetrahydrothiophene).26
The 1H, 13C{1H}, 29Si{1H}, and 31P{1H} NMR spectra were
recorded on a Bruker ARX-500 MHz in CDCl3 at room tempera-
ture. Proton and carbon NMR chemical shifts (δ) were referenced
to the residual peaks of the solvents used. Silicon NMR chemical
shifts were referenced to external SiMe4. Phosphorus NMR
chemical shifts are referenced relative to external H3PO4. Mass
spectral data were obtained in either EI or FAB mode with
nitrobenyl alcohol (NBA) on a JEOL M Station-JMS700. UV-vis
and fluorescence spectra were recorded on Cary 50 Bio UV-visible
and Cary Eclipse Fluorescence spectrophotometers, respectively.
Emission spectra were measured using the λmax value for each
compound obtained from the absorption spectra and also by the
computer-optimized excitation energy, resulting in spectra of
identical shape and position but with differing intensity. Elemental
analysis determinations were obtained from Atlantic Microlabs,
Inc., Norcross, GA. X-ray crystallographic determinations were
performed on a Bruker Apex II diffractometer equipped with a
CCD area detector.
Figure 7. Molecular structure of 9 (with thermal ellipsoids
shown at the 50% probability level). Selected bond distances
(A) and angles (deg): Au1-P1 = 2.2267(18), Au1-Cl1 =
˚
2.2941(17), Au2-P2=2.225(2), Au2-Cl2=2.282(2), Au1
3 3 3
Au2=16.8, Si1-C1=1.875(7), Si1-C4=1.875(8), Si1-C5=
1.860(8), Si1-C6 = 1.858(9), C1-C2 = 1.350(10), C2-C3 =
1.508(10), C3-C4 = 1.366(10), P1-C10 = 1.809(7), P1-
C31=1.813(7), P1-C37=1.825(7), P2-C28=1.781(7), P2-
C49=1.821(7), P2-C43=1.834(9); P1-Au1-Cl1=177.64(7),
P2-Au2-Cl2 = 178.73(8), C10-P1-C37 = 107.3(3), C10-
P1-C31=104.4(3), C10-P1-Au1=112.1(2), C37-P1-C31=
105.3(3), C37-P1-Au1=114.1(2), C31-P1-Au1=113.0(2),
C28-P2-C49=107.3(3), C28-P2-C43=105.9(4), C49-P2-
C43 = 105.5(4), C28-P2-Au2 = 112.6(3), C49-P2-Au2 =
114.2(3), C43-P2-Au2 = 110.8(3), C5-Si1-C6 = 109.9(4),
C1-Si1-C4=91.3(3), C2 -C1-Si1=108.7(5), C3-C4-Si1=
108.8(5), C1-C2-C3 = 116.2(6), C4-C3-C2 = 114.9(7),
C28-P1-C37 = 102.2(4), C28-P1-C31 = 102.2(4), C37-
P1-C31=100.7(4), C61-P2-C55=105.9(7), C61-P2-C52=
111.0(7), C55-P2-C52=96.5(6), C52-P20-C55=95.9(8).
Preparation of 1,1-Dimethyl-2,5-bis(diphenylphosphine)-3,4-
diphenylsilole (1a). A mixture of lithium wire that was cut into
small pieces (84 mg, 12 mmol) and naphthalene (1.54 g, 12.1
mmol) in 40 mL of dry THF was stirred at room temperature for
5 h to produce a deep green solution containing lithium
naphthalenide. A solution of dimethylbis(phenylethynyl)silane
(0.79 g, 3.0 mmol) in 5 mL of THF was added to the LiNaph
solution dropwise over 5 min at room temperature. After
stirring for 10 min the mixture was cooled to -78 °C. A solution
of Ph2PCl (1.6 g, 7.0 mmol) in 10 mL of THF was added
dropwise and the mixture stirred for 2 h at low temperature.
The mixture was allowed to warm to room temperature and
stirred overnight. The solvent was removed by under reduced
pressure, and the crude reaction mixture was subjected to silica
gel column chromatography under argon (neat hexane then
hexane/CH2Cl2, 4:1). Compound 1a was obtained as an air-
sensitive yellow solid in 66% yield (1.25 g). Mp: 159-161 °C. 1H
NMR (500 MHz): δ 7.39-7.34 (m, 8H, ArH), 7.29-7.25 (m, H,
ArH, overlapping with CHCl3 solvent), 7.00-6.95 (m, 6H,
ArH), 6.89-6.86 (m, 4H, ArH), -0.59 (s, 6H, SiMe). 13C{1H}
NMR (125 MHz): δ 166.6 (dd, JPC = 27, 5.5 Hz), 140.8 (d,
JPC = 21 Hz), 139.6 (d, JPC = 7 Hz), 138.7 (d, JPC = 11 Hz),
134.0 (d, JPC = 20 Hz), 129.2 (d, JPC = 3 Hz), 128.5, 128.3 (d,
be used as precursors to the corresponding phosphine oxides
(and vice versa) as well as building blocks for the formation
of luminescent organometallic complexes through coordi-
nation of the phosphorus centers to transition metals, as
demonstrated by the formation of the digold complex 9. The
nature of the environment at the phosphorus center has a
notable impact on the electronic properties of the siloles
studied. The absorption and emission maxima for the phos-
phino-terminated siloles were found to be at lower energy
than the corresponding phosphine oxides especially when the
conjugated chain linking the silole to the phosphino group
was small or zero. The coordination of the phosphino groups
in 2a to gold to give complex 9 resulted in a relatively small
blue shift in the absorption maximum of 9 but a significant
shift to higher energy in the emission spectrum probably due
to reduced conjugation and an increase in the HOMO-
LUMO energy gap. Thus, the coordination chemistry of the
phosphino-linked siloles with metal centers will enable us to
tune the emission color by altering the nature of the silole and
metal center used. Further studies involving the coordina-
tion of the phosphino groups to other transition metals and
their effects on the absorption and emission of these silole-
based systems are in progress.
J
PC = 7 Hz), 127.2, 126.9, -2.7. 29Si{1H} NMR (99 MHz,
DEPT): δ 15.1 (t, JPSi = 5 Hz). 31P{1H} NMR (202 MHz):
δ -12.2. HRMS (EI): m/z calcd for C42H36P2Si, 630.20615;
found, 630.2067. Anal. Calcd for C42H36P2Si: C, 79.97; H, 5.75.
Found: C, 79.88; H, 5.76.
1,1-Dimethyl-2,5-bis(diphenylphosphineoxide)-3,4-diphenylsi-
lole (1b). Compound 1b was prepared according to the proce-
dure described for the preparation of diphenyl-[(4-trimethyl-
silylethynyl)phenyl]phosphine oxide.24 To a solution of 1a (1.9
g, 3.0 mmol) in 50 mL each of dichloromethane and methanol
was slowly added hydrogen peroxide (30% solution, 1.8 mL).
(34) Boydston, A. J.; Yin, Y.; Pagenkopf, B. L. J. Am. Chem. Soc.
2004, 126, 3724–3725.
Experimental Section
(35) (a) Son, H.-J.; Han, W.-S.; Kim, H.; Kim, C.; Ko, J.; Lee, C.;
Kang, S. O. Organometallics 2006, 25, 766–774.
(36) Thomas, C. M.; Peters, J. C. Inorg. Chem. 2004, 43, 8–10.
(37) Martin, S. E.; Bonaterra, M.; Rossi, R. A. J. Organomet. Chem.
2002, 664, 223–227.
(38) Isobe, M.; Kondo, S.; Nagasawa, N.; Goto, T. Chem. Lett. 1977,
679–682.
(39) Dangles, O.; Guibe, F.; Balavoine, G.; Lavielle, S.; Marquet, A.
General Procedures. All reactions were carried out under an
inert atmosphere of argon or nitrogen using standard Schlenk
techniques or a drybox using solvents dried by standard proce-
dures. Dichlorodimethylsilane and trichlorosilane were pur-
chased from Aldrich Chemical Co. and distilled over K2CO3
prior to use. Other commercially available reagents were used
as received. Chloroform-d1 was purchased from Cambridge
J. Org. Chem. 1987, 52, 4984–4993.

1618 Organometallics, Vol. 29, No. 7, 2010
Braddock-Wilking et al.
After stirring for 2 h the resulting mixture was quenched with
aqueous Na2SO3 solution and then extracted with dichloro-
methane. The organic layer was dried over anhydrous MgSO4,
filtered, and concentrated under reduced pressure. The crude
reaction mixture was subjected to silica gel column chromato-
graphy (CH2Cl2/acetone, 5:1) to afford compound 1b as a white
solid (1.23 g, 62% yield). Mp: 266-267 °C. An analytically pure
sample of 1b was dried under vacuum over P2O5 overnight and
was found to contain 0.7 molecule of water per molecule of 1b
based on integration of the H2O and SiMe resonances in the 1H
CH2Cl2 solution of 2b at room temperature. 1H NMR (500
MHz): δ 7.66-7.60 (m, 8H, ArH), 7.55-7.52 (m, 4H, ArH),
7.47-7.36 (m, 12H, ArH), 7.04-6.96 (m, 10H, ArH), 6.78-6.74
(m, 4H, ArH), 0.47 (s, 6H, SiMe). 13C{1H} NMR (125 MHz):
δ 155.7, 144.0 (d, JPC = 3 Hz), 141.9, 138.0, 133.2, 132.4, 132.2
(d, JPC = 10 Hz), 132.0 (d, JPC = 7 Hz), 131.9, 129.9, 128.8 (d,
JPC = 12 Hz), 128.6 (d, JPC = 12 Hz), 127.7, 126.9, -3.8.
29Si{1H} NMR (99 MHz, DEPT): δ 8.8. 31P{1H} NMR (202
MHz): δ 29.2. HRMS(NaI): m/z calcd for C54H44O2P2SiNa,
837.2483; found, 837.2480 (M þ Na)þ. Anal. Calcd for
C54H44OP2Si: C, 79.58; H, 5.44. Found: C, 78.49; H, 5.50.
Compound 2b was also synthesized by an alternative route as
described for the preparation of 4b using lithium naphthalenide
(8 mmol), bis(phenylethynyl)dimethylsilane (0.52 g, 2.0 mmol),
ZnCl2(TMEDA) (2.2 g, 8.8 mmol), 40-bromophenyl)diphenyl-
phosphine oxide (1.6 g, 4.4 mmol), and PdCl2(PPh3)2 (80 mg,
0.11 mmol). The crude residue was subjected to silica gel column
chromatography (CH2Cl2/acetone, 5:1) to afford compound 2b
as a yellow powder (1.27 g, 78% yield).
1,1-Dimethyl-2,5-bis(30-diphenylphosphinophenyl)-3,4-diphenyl-
silole (3a). Compound 3a was prepared by a similar procedure as
that used for the preparation of 2a but using 1,1-dimethyl-2,5-
bis(30-bromophenyl)-3,4-diphenylsilole (7) (1.5 g, 2.6 mmol),
TMEDA (1.2 mL, 7.8 mmol), n-butyllithium (2.5 M in hexane,
3.2 mL, 7.8 mmol), and chlorodiphenylphosphine (3.0 g,
7.8 mmol). The crude product was subjected to alumina column
chromatography (hexane/CH2Cl2, 5:1). Compound 3a was iso-
lated as a yellow powder (1.29 g, 63% yield). Mp: 84-86 °C. 1H
NMR (500 MHz): δ 7.36-7.29 (m, 12H, ArH), 7.23-7.17 (m,
8H, ArH), 7.12-7.06 (m, 4H, ArH), 7.00-6.94 (m, 6H, ArH),
6.89-6.83 (m, 4H, ArH), 6.76-6.70 (m, 4H, ArH), 0.18 (s, 6H,
SiMe). 13C{1H} NMR (125 MHz): δ 154.3, 141.9, 140.3 (d,
JPC=5 Hz), 138.6, 137.4 (d, JPC = 11 Hz), 136.8 (d, JPC = 10
Hz), 134.1, 133.9 (d, JPC = 20 Hz), 131.3 (d, JPC=25 Hz), 130.0,
129.0, 128.7, 128.6 (d, JPC = 7 Hz), 128.2 (d, JPC = 9 Hz), 127.6,
126.4, -4.1. 29Si{1H} NMR (99 MHz, DEPT): δ 8.1. 31P{1H}
NMR (202 MHz): δ -5.3. Anal. Calcd for C54H44P2Si: C, 82.84;
H, 5.66. Found: C, 82.09; H, 5.66.
1
NMR spectrum. H NMR (500 MHz): δ 7.52-7.46 (m, 8H,
ArH), 7.36-7.31 (m, 4H, ArH), 7.28-7.22 (m, overlapping with
CHCl3, 8H, ArH), 6.74-6.69 (m, 2H, ArH), 6.66-6.58 (m, 8H,
ArH), 0.09 (s, 6H, SiMe). 13C{1H} NMR (125 MHz): δ 169.2 (d,
JPC = 20 Hz), 140.9 (dd, JPC = 86, 2 Hz), 137.0 (d, JPC = 8 Hz),
134.0 (d, JPC = 105 Hz), 131.5 (d, JPC = 10 Hz), 131.3, 129.2,
128.2 (d, JPC = 12 Hz), 127.1, 126.7, -3.3. 29Si{1H} NMR (99
2
MHz, DEPT): δ 20.5 (t, JPsi = 19 Hz). 31P{1H} NMR (202
MHz): δ 22.5. Anal. Calcd for C42H36O2P2Si 0.7H2O: C, 74.69;
3
H, 5.58. Found: C, 74.73; H, 5.40.
1,1-Dimethyl-2-(diphenylphosphine)-5-(diphenylphosphineoxide)-
3,4-diphenylsilole (1a,b). Compound 1a (1.0 g, 1.6 mmol) was
dissolved in 25 mL of CH2Cl2, and the resulting solution was
exposed to air for one week. The solvent was removed under
reduced pressure, and the residue was purified by silica gel column
chromatography (CH2Cl2) to afford 1a,b as a slightly air sensitive
yellow solid (0.49 g, 48%). Mp: 211-212 °C. 1HNMR (500MHz):
δ 7.54-7.46 (m, 6H, ArH), 7.36-7.30 (m, 8H, ArH), 7.28-7.19
(m, overlapping with CHCl3, 14H, ArH), 6.90-6.84(m, 4H, ArH),
6.77-6.64 (m, 8H, ArH),-0.22 (s, 6H, SiMe). 13C{1H} NMR (125
MHz): δ 169.4 (d, JPC = 5 Hz), 166.0 (dd, JPC = 25, 19 Hz), 146.0
(dd, JPC = 24, 2 Hz), 138.7 (d, JPC = 6 Hz), 137.9 (d, JPC = 8 Hz),
137.5 (d, JPC=11 Hz), 137.0, 136.3, 135.0, 134.1 (d, JPC= 19 Hz),
131.5 (d, JPC = 9 Hz), 131.0 (d, JPC = 3 Hz), 129.2, 129.1 (d, JPC
=
3 Hz), 128.7, 128.3 (d, JPC = 7 Hz), 128.1 (d, JPC = 11 Hz), 127.2,
127.0, 126.9, 126.8, -3.1. 29Si{1H} NMR (99 MHz, DEPT): δ 17.7
(dd, JSiP = 18 Hz). 31P{1H} NMR (202 MHz): δ 23.1, -10.9.
HRMS (FAB): m/z calcd for C42H36OP2SiH, 647.2088; found,
647.2100 (M þ H)þ.
1,1-Dimethyl-2,5-bis(30-diphenylphosphinophenyloxide)-3,4-di-
phenylsilole (3b). Compound 3b was prepared by a similar pro-
cedure to that used for the preparation of 1b but using 3a (2.3 g,
3.0 mmol) and H2O2 (30% solution, 1.7 mL). The crude product
was subjected to alumina column chromatography (hexane/
CH2Cl2, 4:1). Compound 3b was recrystallized from acetone/
hexane and was isolated as a yellow powder (2.1 g, 89% yield).
Mp: 94-95 °C. An analytically pure sample of 3b was dried
under vacuum over P2O5 overnight and was found to contain
0.63 molecule of water and 0.14 molecule of acetone per
molecule of 3b based on integration of these signals and the
SiMe resonances in the 1H NMR spectrum. 1H NMR (500
MHz): δ 7.53-7.44 (m, 14H, ArH), 7.38-7.43 (m, 8H, ArH),
7.27-7.23 (m, overlapping with CHCl3, 2H, ArH), 7.10-7.07
(m, 2H, ArH), 7.10-7.06 (m, 2H, ArH), 7.02-6.92 (m, 6H,
ArH), 6.68-6.64 (m, 4H, ArH), 0.21 (s, 6H, SiMe). 13C{1H}
NMR (125 MHz): δ 154.5, 141.0, 139.6 (d, JPC = 12 Hz), 137.6,
132.6, 132.5, 131.9 (d, JPC = 11 Hz), 131.7, 131.6 (d, JPC = 10
Hz), 131.5 (d, JPC = 3 Hz), 129.5, 129.0 (d, JPC = 9 Hz), 128.2
(d, JPC = 12 Hz), 128.1 (d, JPC = 12 Hz), 127.3, 126.2, -4.5.
29Si{1H} NMR (99 MHz, DEPT): δ 8.5. 31P{1H} NMR (202
MHz): δ 29.2. HRMS (FAB): m/z calcd for C54H44O2P2SiH,
815.2664; found, 815.2635 (M þ H)þ. Anal. Calcd for C54H44-
1,1-Dimethyl-2,5-bis(40-diphenylphosphinophenyl)-3,4-diphenyl-
silole (2a). To a solution of 1,1-dimethyl-2,5-bis(40-bromo-
phenyl)-3,4-diphenylsilole (1.5 g, 2.62 mmol) in diethyl ether
(100 mL) was added TMEDA (1.2 mL, 7.8 mmol). The mixture
was cooled to -78 °C, and a solution of n-butyllithium in hexane
(2.5 M, 3.2 mL, 7.8 mmol) was added dropwise. The mixture was
stirred for 1.5 h, then warmed to 0 °C, stirred for 1 h, and recooled
to -78 °C. A solution of chlorodiphenylphosphine (3.0 g,
7.8 mmol) in 5 mL of THF was added dropwise and the solution
stirred at -78 °C for 1 h. The mixture was allowed to warm to
room temperature and stirred overnight. The solvent was re-
moved under vacuum and the crude reaction mixture subjected to
alumina column chromatography (hexane/CH2Cl2, 5:1) to afford
compound 2a as a yellow powder (1.1 g, 54% yield). Mp:
103-105 °C. 1H NMR (500 MHz): δ 7.38-7.33 (m, 10H, ArH),
7.32-7.26 (m, 8H, ArH), 7.11-7.00 (m, 12H, ArH), 6.95-6.91
(m, 4H, ArH), 6.85-6.80 (m, 4H, ArH), 0.51 (s, 6H, SiMe).
13C{1H} NMR (125 MHz): δ 154.8, 141.8, 140.7, 138.8, 137.6 (d,
JPC = 11 Hz), 133.9 (d, JPC = 9 Hz), 133.9 (d, JPC = 19 Hz),
133.5 (d, JPC = 19 Hz), 130.1, 129.1 (d, JPC = 7 Hz), 128.8, 128.6
(d, JPC = 7 Hz), 127.6, 126.6, -3.6. 29Si{1H} NMR (99 MHz,
DEPT): δ 8.0. 31P{1H} NMR (202 MHz): δ -5.7 (s). Anal. Calcd
for C54H44P2Si: C, 82.84; H, 5.66. Found: C, 82.65; H, 5.94.
1,1-Dimethyl-2,5-bis(40-diphenylphosphinophenyloxide)-3,4-di-
phenylsilole (2b). Compound 2b was prepared by a similar
procedure as that used for the preparation of 1b but using 2a
(2.3 g, 3.0 mmol) and H2O2 (30% solution, 1.7 mL). The crude
product was subjected to alumina column chromatography
(hexane/CH2Cl2, 4:1) to afford compound 2b as a yellow
powder (2.27 g, 93% yield). Mp: 282 °C (dec). X-ray quality
crystals of 2b were obtained by slow diffusion of hexanes into a
O2P2Si 0.63H2Oþ0.14(CH3)2CO: C, 78.33; H, 5.57. Found:
3
C, 77.98; H, 5.49.
1,1-Dimethyl-2,5-bis(40-diphenylphosphine-4-biphenyl)-3,4-di-
phenylsilole (4a). To a mixture of 4b (1.0 g, 1.0 mmol) and Et3N
(5.4 mL, 35 mmol in dry toluene (45 mL) was added HSiCl3
(2 mL, 17.8 mmol) at 0 °C. The reaction mixture was refluxed for
18 h, then cooled to room temperature. The mixture was diluted
with Et2O (50 mL) and quenched with aqueous NaHCO3. The
resulting mixture was filtered through Celite, and the organic

Article
Organometallics, Vol. 29, No. 7, 2010 1619
layer was dried over MgSO4, then concentrated under reduced
pressure. The crude mixture was subjected to silica gel column
chromatography (CH2Cl2/hexane, 1:1) to afford compound 4a
as a yellow solid (0.39 g, 41% yield). Mp: 217 °C (dec). X-ray
quality crystals of 4a were obtained by slow evaporation of a
CH2Cl2 solution of 4a at room temperature. 1H NMR (500
MHz): δ 7.47-7.44 (m, 4H, ArH), 7.32-7.29 (m, 4H, ArH),
7.27-7.22 (m, overlapping with CHCl3, 24H, ArH), 6.97-6.91
(m, 10H, ArH), 6.79-6.76 (m, 4H, ArH), 0.47 (s, 6H, SiMe).
13C{1H} NMR (125 MHz): δ 154.5, 141.4, 141.2, 139.3, 139.0,
137.4 (d, JPC = 3 Hz), 137.3, 135.9 (d, JPC = 10 Hz), 134.3 (d,
(m, 4H, ArH), 0.50 (s, 6H, SiMe). 13C{1H} NMR (125 MHz):
δ 154.9, 141.8, 140.4, 138.6, 137.9 (d, JPC = 12 Hz), 136.9 (d, JPC
=
11 Hz), 134.0 (d, JPC=19Hz), 133.6(d, JPC=19.3 Hz), 131.6, 131.5,
130.1, 129.1 (d, JPC=7 Hz), 128.8 (d, JPC=7 Hz), 127.8, 126.7,
123.9, 120.3, 91.0, 89.5, -3.6. 29Si{1H} NMR (99 MHz, DEPT): δ
8.2. 31P{1H} NMR (202 MHz): δ -4.9. HRMS (FAB, NaI):
m/z calcd for C70H52P2SiH, 983.3392; found, 983.3412 (M þ H)þ.
1,1-Dimethyl-2,5-bis{[(4-diphenylphosphineoxide)phenylethynyl]-
phenyl}-3,4-diphenylsilole (5b). To a solution of 1,1-dimethyl-
2,5-bis(40-bromophenyl)-3,4-diphenylsilole (0.50 g, 0.87 mmol)
and diphenyl-(4-ethynylphenyl)phosphine oxide (0.55 g, 1.8
mmol) in a mixture of toluene (75 mL) and triethylamine
(20 mL) were added CuI (9.5 mg, 0.05 mmol) and Pd(PPh3)4
(0.06 g, 0.05 mmol). The resulting mixture was stirred for 24 h at
50 °C, then allowed to cool to room temperature and concen-
trated under vacuum. The residue was subjected to silica gel
column chromatography (CH2Cl2/(CH3)2CO, 10:1) to afford
compound 5b as a yellow solid (0.15 g, 17% yield). Mp: 149 °C
(dec). An analytically pure sample of 5b was dried under vacuum
over P2O5 overnight and was found to contain 1.7 molecules of
water per molecule of 5b based on integration of the H2O and
SiMe resonances in the 1H NMR spectrum. 1H NMR (500 MHz):
δ 7.72-7.61 (m, 12H, ArH), 7.59-7.54 (m, 8H, ArH), 7.52-7.45
(m, 8H, ArH), 7.33-7.25 (m, overalapping with CHCl3, 4H,
ArH), 7.07-6.99 (m, 6H, ArH), 6.95-6.90 (m, 4H, ArH),
6.83-6.78 (m, 4H, ArH), 0.50 (s, 6H, SiMe). 13C{1H} NMR
(125 MHz): δ 155.0, 141.8, 140.8, 138.5, 132.3 (d, JPC = 8 Hz),
132.2, 131.9, 131.6 (d, JPC = 7 Hz), 130.9 (d, JPC = 9 Hz), 130.2,
129.2, 129.1 (d, JPC = 11 Hz), 128.9 (d, JPC = 12 Hz), 128.5 (d,
JPC = 12 Hz), 128.0, 127.7, 126.9, 119.9, 92.9, 89.0, -3.6. 29Si{1H}
NMR (99 MHz): δ 8.2. 31P{1H} NMR (202 MHz): δ 28.8. HRMS
(FAB, NaI): m/z calcd for C70H52O2P2SiNa, 1037.3109; found,
JPC = 19 Hz), 133.9 (d, JPC = 19 Hz), 130.1, 129.6, 128.9, 128.7
(d, JPC = 7 Hz), 127.7, 126.9 (d, JPC = 7 Hz), 126.6, 126.5, -3.3.
29Si{1H} NMR (99 MHz, DEPT): δ 8.0. 31P{1H} NMR (202
MHz): δ -6.0. Anal. Calcd for C66H52P2Si 1/2CH2Cl2: C,
3
81.70; H, 5.46. Found: C, 82.12; H, 5.54.
1,1-Dimethyl-2,5-bis(40-diphenylphosphineoxide-4-biphenyl)-
3,4-diphenylsilole (4b). A mixture of lithium wire cut into small
pieces (56 mg, 8 mmol) and naphthalene (1.038 g, 8 mmol) in
12 mL of THF was stirred at room temperature for 5 h to form
a deep green solution of lithium naphthalenide (LiNaph). A
solution of dimethylbis(phenylethynyl)silane (0.52 g, 2.0 mmol)
in 5 mL of THF was added to the LiNaph solution dropwise
over 5 min at room temperature. After stirring for 10 min, the
mixture was cooled to 0 °C and ZnCl2(TMEDA) (2.2 g, 8.8
mmol) was added as a solid to the mixture, followed by dilution
with THF (15 mL) to give a dark green suspension. After stirring
for an additional hour at room temperature, (40-bromobi-
phenyl-4-yl)diphenylphosphine oxide (1.9 g, 4.4 mmol) and
Pd(PPh3)2Cl2 (80 mg, 0.11 mmol) were added to the resulting
suspension. The mixture was heated to reflux and stirred for
12 h. After cooling to room temperature, the solvent was
removed by rotary evaporation, and the crude residue subjected
to silica gel column chromatography (CH2Cl2/EtOAc, 5:1) to
afford compound 4b as a yellow powder (1.39 g, 72% yield). Mp:
261 °C (dec). An analytically pure sample of 4b was dried under
vacuum over P2O5 overnight and was found to contain 1
molecule of water per molecule of 4b based on integration of
1037.3127 (M þ Na)þ. Anal. Calcd for C70H52O2P2Si 1.7H2O:C,
3
80.39; H, 5.34. Found: C, 80.73; H, 5.25.
Compound 5b was was also prepared by a similar procedure to
that used for the preparation of 4b, starting from lithium naph-
thalenide (8 mmol), bis(phenylethynyl)dimethylsilane (0.52 g,
2.0 mmol), ZnCl2(TMEDA) (2.2 g, 8.8 mmol), (40-bromophenyl-
ethynylphenyl)diphenylphosphine oxide (8, 2.01 g, 4.4 mmol),
and Pd(PPh3)2Cl2 (80 mg, 0.11 mmol). The crude residue was
subjected to silica gel column chromatography (CH2Cl2/acetone,
5:2) to afford compound 5b as a yellow powder (1.36 g, 67%
yield).
1
1
the H2O and SiMe resonances in the H NMR spectrum. H
NMR (500 MHz): δ 7.73-7.62 (m, 18H, ArH), 7.57-7.53 (m,
4H, ArH), 7.50-7.44 (m, 8H, ArH), 7.42-7.38 (m, 4H, ArH),
7.05-7.01 (m, 10H, ArH), 6.87-6.83 (m, 4H, ArH), 0.55 (s, 6H,
SiMe). 13C{1H} NMR (125 MHz): δ 154.8, 144.4 (d, 3JPC = 3
Hz), 141.4, 140.0, 138.9, 136.8, 133.2, 132.7 (d, JPC = 11 Hz),
132.3 (d, JPC = 10 Hz), 132.1 (d, JPC = 3 Hz), 131.3, 130.4,
130.1, 129.6, 128.7 (d, JPC = 21 Hz), 127.7, 126.93, 126.91 (d,
JPC = 12 Hz), 126.6, -3.4. 29Si{1H} NMR (99 MHz, DEPT): δ
8.2. 31P{1H} NMR (202 MHz): δ 29.2. HRMS (NaI): m/z calcd
for C66H52O2P2SiNa, 989.3109; found, 989.3110 (M þ Na)þ.
1,1-Dimethyl-2,5-bis(3-bromophenyl)-3,4-diphenylsilole (6). A
mixture of lithium wire that was cut into small pieces (56 mg,
8.0 mmol) and naphthalene (1.04 g, 8.0 mmol) in 12 mL of THF
was stirred at room temperature for 5 h to produce a deep
green solution containing lithium naphthalenide. A solution
of dimethylbis(phenylethynyl)silane (0.52 g, 2.0 mmol) in 5 mL
of THF was added to the LiNaph solution dropwise over 5 min
at room temperature. After stirring for 10 min, the mixture
was cooled to 0 °C and ZnCl2(TMEDA) (2.2 g, 8.8 mmol) was
added as a solid to the reaction mixture, followed by the addition
of THF (15 mL) to give a dark green suspension. After stirring
for an additional hour at room temperature, 3-bromoiodo-
benzene (1.24 g, 4.4 mmol) and Pd(PPh3)2Cl2 (80 mg, 0.11
mmol) were added to the resulting suspension. The mixture
was heated to reflux and stirred for 12 h. After cooling to room
temperature, the solvent was removed by rotary evaporation,
and the crude reaction mixture subjected to silica gel column
chromatography with hexane as the eluent to afford com-
pound 6 as a yellow powder (0.59 g, 52% yield). Mp: 45-46
°C. 1H NMR (500 MHz): δ 7.28-7.24 (m, 2H, ArH), 7.20
(br s, 2H, ArH), 7.12-7.07 (m, 6H, ArH), 7.06-7.01 (m,
2H, ArH), 6.95-6.92 (m, 2H ArH), 6.92-6.87 (m, 4H, ArH),
0.55 (s, 6H, SiMe). 13C{1H} NMR (125 MHz): δ 155.0,
142.0, 140.9, 137.9, 131.6, 129.8, 129.6, 128.7, 127.7, 127.4,
126.7, 122.2, -3.9. 29Si{1H} NMR (99 MHz, DEPT): δ 8.5.
HRMS (EI): m/z calcd for C30H2479Br2Si, 570.00140; found,
570.0002 (Mþ).
Anal. Calcd for C66H52O2P2Si H2O: C, 80.46; H, 5.52. Found:
3
C,79.85; H, 5.26.
1,1-Dimethyl-2,5-bis{[(4-diphenylphosphine)phenylethynyl]-
phenyl}-3,4-diphenylsilole (5a). Compound 5a was prepared by a
similar procedure to that used for the preparation of 4a. To a
solution of compound 5b (1.0 g, 1.0 mmol) and Et3N (5.4 mL,
35 mmol) in dry toluene (45 mL) was added HSiCl3 (2 mL,
17.8 mmol) at 0 °C. The reaction mixture was refluxed for 18 h,
then cooled to room temperature. The mixture was diluted with
Et2O (50 mL) and quenched with aqueous NaHCO3. The
organic layer was separated and dried over MgSO4, then con-
centrated under reduced pressure. The crude mixture was sub-
jected to silica gel column chromatography (CH2Cl2/hexane,
1:1) to afford compound 5a as a yellow solid (0.15 g, 15% yield).
Compound 5a could not be obtained in analytically pure form,
but the major impurities were assigned to common reagents/
solvents (as determined by NMR spectroscopy, see Supporting
Information) that should not affect the photophysical proper-
1
ties. Mp: 131-132 °C. H NMR (500 MHz): δ 7.46-7.42 (m,
4H, ArH), 7.38-7.23 (m, overlapping with CHCl3, 26H, ArH),
7.06-7.00 (m, 8H, ArH), 6.93-6.89 (m, 4H, ArH), 6.83-6.79

1620 Organometallics, Vol. 29, No. 7, 2010
Braddock-Wilking et al.
Table 2. Crystallographic Data and Structure Refinement for 2b, 4a, and 9
2b
4a
9
formula
C
54H44O2P2Si
C66 H52P2 Si
0.5CH2Cl2
977.57
C56H44Au2Cl2P2Si
2CH2Cl2
1417.61
3
3
fw
814.92
cryst size/mm
cryst syst
space group
0.17 ꢀ 0.13 ꢀ 0.11
monoclinic
P21/n
11.5999(13)
16.7822(19)
44.176(5)
90
97.087(7)
90
8534.2(16)
1.269
8
0.173
1.86 to 25.00
166 532/14 998
[R(int) = 0.201]
numerical
0.46 ꢀ 0.12 ꢀ 0.03
monoclinic
C2/c
46.444(8)
9.5894(18)
24.803(5)
90
106.484(15)
90
10 593(3)
1.226
4
0.197
2.17 to 25.00
60 845/9294
[R(int) = 0.187]
semiempirical from
equivalents
0.9935 and 0.9142
0.0993
0.52 ꢀ 0.29 ꢀ 0.22
triclinic
P1
˚
a/A
10.2869(11)
13.7618(15)
19.957(2)
73.571(3)
83.772(3)
88.086(3)
2693.9(5)
1.748
2
5.856
2.97 to 26.22
35 516/10 433
[R(int) = 0.0391]
numerical
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
V/A
Dcalcd/g cm-3
Z
abs coeff/mm-1
θ range/deg
reflns collected/ indep reflns
abs correct
max. and min. transm
final R indices [I > 2σ(I)]
R indices (all data)
0.8703 and 0.8119
0.0840
0.1835
0.3538 and 0.1500
0.0422
0.0631
0.2647
0.806 and -0.404
-3
˚
largest diff peak and hole/e A
0.419 and -0.599
2.071 and -1.556
Preparation of (40-Bromobiphenyl-4-yl)diphenylphosphine Oxide
(7). Compound 7 was prepared by similar procedures used
for the synthesis of the related compounds 4-(bromo-
phenyl)diphenylphosphine and (4-bromophenyl)diphenylphos-
phine oxide. A solution of 4,40-dibromobiphenyl (4.05 g, 13.0
mmol) in 150 mL of THF was cooled to -95 °C with an acetone/
liquid nitrogen bath. A solution of n-BuLi (2.5 M in hexane, 5.2
mL, 13.0 mmol) was added dropwise, and the resulting solution
was stirred at -95 °C for 1 h; then chlorodiphenylphosphine (2.88
g, 13.0 mmol) was added dropwise. The solution was allowed to
warm to room temperature over 3 h and concentrated under
vacuum. The residue was subjected to silica gel column chroma-
tography (CH2Cl2/hexane, 1:5) to give a white solid. The white
solid was dissolved in a mixture of dichloromethane (60 mL) and
methanol (60 mL); then hydrogen peroxide (30% solution,
3.5 mL) was slowly added to the solution. The resulting mixture
was stirred at room temperature for 2 h, then quenched with
aqueous Na2SO3 solution and extracted with dichloromethane.
The organic layer was dried over anhydrous MgSO4, filtered,
and concentrated under vacuum to give (40-bromobiphenyl-4-
yl)diphenylphosphine oxide (7) as a white solid (3.48 g, 62%
yield). Mp: 131-132 °C. 1H NMR (500 MHz): δ 7.87-7.76 (m,
6H, ArH), 7.71-7.67 (m, 2H, ArH), 7.60-7.55 (m, 4H, ArH),
7.53-7.47 (m, 6H, ArH). 13C{1H} NMR (125 MHz): δ 142.9
(d, JPC = 2 Hz), 138.2, 132.5, 132.2 (d, JPC = 10 Hz), 131.71 (d,
91.3, 89.9. 31P{1H} NMR (202 MHz): δ 29.0. HRMS (FAB):
m/z calcd for C26H1879BrOPH, 457.0357; found, 457.0339
(M þ H)þ.
1,1-Dimethyl-2,5-bis(40-diphenylphosphino(chlorogold)phenyl)-
3,4-diphenylsilole (9). A solution of 2a (0.15 g, 0.2 mmol) in
CH2Cl2 (10 mL) was added to a solution of [AuCl(tht)] (0.13 g,
0.4 mmol) in CH2Cl2 (10 mL) at room temperature. After 12 h,
the volatiles were removed by vacuum. The residue was dis-
solved in CH2Cl2 (2 mL), and Et2O (20 mL) was added. The
resulting precipitate was washed with Et2O (3 ꢀ 5 mL) to
1
provide 9 as an air-stable yellow solid (0.22 g, 89% yield). H
NMR (500 MHz): δ 7.56-7.44 (m, 20H, ArH), 7.31-7.25 (m,
4H, ArH), 7.10-6.99 (m, 10H, ArH), 6.80-6.76 (m, 4H, ArH),
0.51 (s, 6H, SiMe). 13C{1H} NMR (125 MHz): δ 156.1, 144.1
(d, JPC = 3 Hz), 141.6, 137.9, 134.3 (d, JPC = 14 Hz), 133.9
(d, JPC = 14 Hz), 132.1 (d, JPC = 2 Hz), 129.9, 129.5 (d, JPC
=
12 Hz), 129.364, 129.367 (d, JPC = 11 Hz), 128.8, 127.8, 127.1,
125.5, 125.0, -3.7. 29Si{1H} NMR (99 MHz): δ 9.0. 31P{1H}
NMR (202 MHz): δ 32.7. HRMS (FAB, NaI): m/z calcd for
C54H44Au235ClP2Si, 1211.1707; found, 1211.1676 (M - Cl)þ.
Anal. Calcd for C56H44Au2Cl2P2Si 2CH2Cl2: C, 47.44; H, 3.41.
3
Found: C, 47.45; H, 4.14.
X-ray Structure Determination of 2b, 4a, and 9. Crystals of
X-ray diffraction quality of 2b, 4a, and 9 were obtained by slow
evaporation from either a mixture of CH2Cl2 and hexane or
from neat CH2Cl2 at room temperature, respectively. Crystals of
appropriate dimensions were mounted on Mitgen loops in
random orientations. Preliminary examination and data collec-
tion were performed using a Bruker Kappa Apex II charge
coupled device (CCD) detector system single-crystal X-ray
diffractometer equipped with an Oxford Cryostream LT device.
All data were collected using graphite-monochromated Mo KR
J
PC = 8 Hz), 131.60 (d, JPC = 3 Hz), 131.5, 130.9, 128.4, 128.1
(d, JPC =12 Hz), 126.5 (d, JPC = 12 Hz), 122.1. 31P{1H} NMR
(202 MHz): δ 28.3. Anal. Calcd for C24H18BrOP: C, 66.53; H,
4.19. Found: C, 66.02; H, 4.24.
Preparation of (40-Bromophenylethynylphenyl)diphenylphos-
phine Oxide (8). A solution of diphenyl-(4-ethynylphenyl)pho-
sphine oxide (1.5 g, 3.5 mmol) in 25 mL of THF was slowly
injected into a solution containing 1-bromo-4-iodobenzene (1.0
g, 3.5 mmol), Pd(PPh3)2Cl2 (0.1 g, 0.14 mmol), CuI (0.027 g, 0.14
mmol), NEt3 (25 mL), and THF (25 mL). The reaction mixture
was stirred at room temperature for 24 h. The volatiles were
removed under vacuum, and the residue was subjected to silica
gel column chromatography (CH2Cl2/hexane, 1:4) to give 8 as a
white solid (0.95 g, 59%). Mp: 146-147 °C. 1H NMR (500
MHz): δ 7.68-7.52 (m, 10H, ArH), 7.47-7.44 (m, 6H, ArH),
7.38-7.28 (m, 2H, ArH). 13C{1H} NMR (125 MHz): δ 133.5,
132.8, 132.5, 132.4 (d, JPC = 10 Hz), 132.1, 132.0, 131.8 (d,
˚
radiation (λ = 0.71073 A) from a fine-focus sealed tube X-ray
source. Preliminary unit cell constants were determined with
a set of 36 narrow frame scans. Typical data sets consist of
combinations of ω and φ scan frames with a typical scan width of
0.5° and counting time of 15-30 s/frame at a crystal to detector
distance of 4.0 cm. The collected frames were integrated using an
orientation matrix determined from the narrow frame scans.
Apex II and SAINT software packages40 were used for data
(40) APEX II and SAINT; Bruker Analytical X-Ray: Madison, WI,
JPC=12 Hz), 128.9 (d, JPC=12 Hz), 128.8, 127.1, 123.5, 121.9,
2008.

Article
Organometallics, Vol. 29, No. 7, 2010 1621
collection and data integration. Analysis of the integrated data
did not show any decay. Final cell constants were determined
by global refinement of reflections from the complete data
set. Collected data were corrected for systematic errors using
SADABS41 based on the Laue symmetry using equivalent
reflections.
Structure solution and refinement were carried out using the
SHELXTL- PLUS software package.42 The structures were
solved by direct methods and refined successfully in the space
complex 9, and one was found to be disordered. The disordered
solvent was refined with partial occupancies of 80:20. All
hydrogen atoms were treated using the appropriate riding model
(AFIX m3). The final residual values, structure refinement
parameters, and crystal data and intensity data collection para-
meters are listed in Table 2. A table of calculated and observed
structure factors are available in electronic format from the
authors.
groups P21/n (Z = 8), C2/c (Z = 4), and P1 (Z = 2). Full matrix
least-squares refinement was carried out by minimizing w(Fo
- Fc ) . All non-hydrogen atoms were refined anisotropically to
convergence. Some of the atoms in compound 4a had to be
refined with restraints (EADP, SADI, ISOR, SIMU). Com-
pound 4a contains a half a molecule of CH2Cl2 per molecule of
4a in the crystal lattice that is disordered as well as disorder in the
phosphorus center P2 and an associated phenyl group. The
disorder was modeled with two orientations in the ratio of 60:40.
Two molecules of CH2Cl2 were located in the lattice with
Acknowledgment. Funding from the National Science
Foundation is greatly appreciated (CHE-0719380 and
MRI, CHE-0420497 for the purchase of the Apex II
diffractometer).
P
2
2 2
Supporting Information Available: CIF files and complete
listings of geometrical parameters, positional and isotropic
displacement coefficients for hydrogen atoms, anisotropic dis-
placement coefficients for the non-hydrogen atoms for com-
plexes 2b, 4a, and 9, absorption spectra for 1a, 1b, 1ab, and 9,
excitation and emission spectra for 2-5 and 9, and multinuclear
NMR spectroscopic data for 1-9 are available free of charge via
the Internet at http://pubs.acs.org.
(41) Blessing, R. H. Acta Crystallogr. 1995, A51, 33–38.
(42) Sheldrick, G. M. Bruker-SHELXTL. Acta Crystallogr. 2008,
A64, 112–122.