Synthesis of 2-aryl-5-styrylphospholes: Promising candidates for the phosphole-based NLO chromophores

Article abstract of DOI:10.1021/jo070822f

(Chemical Equation Presented) 2-Aryl-1-phenyl-5-styrylphospholes were prepared in good yields in a one-pot procedure from the corresponding 1,9-diarylnona-8-ene-1,6-diynes and dichloro(phenyl)phosphine via intermediary titana-cyclopentadienes. According t

Full text of DOI:10.1021/jo070822f

Synthesis of 2-Aryl-5-styrylphospholes: Promising Candidates for
the Phosphole-Based NLO Chromophores
Yoshihiro Matano,*,† Tooru Miyajima,† Hiroshi Imahori,† and Yoshifumi Kimura‡
Department of Molecular Engineering, Graduate School of Engineering, Kyoto UniVersity,
Nishikyo-ku, Kyoto 615-8510, Japan, and DiVision of Research InitiatiVes, International InnoVation Center,
Kyoto UniVersity, Sakyo-ku, Kyoto 606-8501, Japan
matano@scl.kyoto-u.ac.jp
ReceiVed April 19, 2007
2-Aryl-1-phenyl-5-styrylphospholes were prepared in good yields in a one-pot procedure from the
corresponding 1,9-diarylnona-8-ene-1,6-diynes and dichloro(phenyl)phosphine via intermediary titana-
cyclopentadienes. According to the UV-vis absorption and fluorescence spectra of this class of compounds,
the optical properties of the phosphole-vinylene-bridged π-conjugated system have been revealed to
depend strongly on the electronic character of the terminal functionalities. In particular, the polarizability
at the excited-state has been found to be considerably greater than that in the ground state. High molecular
hyperpolarizabilities obtained for the push-pull type of 2-aryl-5-styrylphospholes in the hyper-Rayleigh
scattering measurements demonstrate the potential utility of the stilbene-type phosphole derivatives as a
new class of second-order NLO chromophores.
Introduction
Phosphole is known as a basically nonaromatic heterole and
to possess the polarizable and electron excessive cis-dienic
π-system connected by a phosphorus atom. As a consequence,
phospholes exhibit characteristic optical and electrochemical
properties that differ considerably from those of pyrroles.1 Both
experimental and theoretical studies have revealed that π-con-
jugated substituents attached at the 2- and 5-positions (R
positions) of the phosphole ring play an important role in
controlling the HOMO and LUMO energies as well as the
polarizability of the cis-dienic π-system of phospholes.2 In
particular, unsymmetrically substituted phospholes bearing
electron donor (D) and electron acceptor (A) functionalities at
FIGURE 1. Phosphole-based NLO chromophores.
the R positions have been suggested to act as nonlinear optics
(NLO). In 1997, Marks and co-workers reported quantitative
analysis of aromaticity and auxiliary D-A effects on molecular
hyperpolarizabilities of several π-conjugated stilbene-type chro-
mophores, including phosphole derivatives, based on theoretical
calculations. They concluded that electron density of the
heterocycles plays the major role in determining second-order
NLO response properties.3 For instance, model compound 1a
(Figure 1), in which the phosphole ring acts as an electron-
excessive heterocycle, was predicted to exhibit higher NLO
responses than the thiophene analogue.4 The high electron-
excessive nature of the phosphole ring was further confirmed
by comparing the hyperpolarizability of the D-phosphole-
* Corresponding author. Phone: 81 75 383 2567. Fax: 81 75 383 2571.
† Graduate School of Engineering.
‡ International Innovation Center.
(1) For reviews, see: (a) Quin, L. D. The Heterocyclic Chemistry of
Phosphorus; Wiley: New York, 1981. (b) Mathey, F. Chem. ReV. 1988,
88, 429. (c) Mathey, F. J. Organomet. Chem. 1990, 400, 149. (d) Quin, L.
D. In ComprehensiVe Heterocyclic Chemistry; Katritzky, A. R., Rees, C.
W., Scriven, E. F. V., Eds.; Elsevier: Oxford, 1996; Vol. 2. (e) Mathey,
F.; Mercier, F. C. R. Acad. Sci. Paris, Se´r. II b 1997, 701. (f) Hissler, M.;
Dyer, P. W.; Re´au, R. Coord. Chem. ReV. 2003, 244, 1. (g) Mathey, F.
Angew. Chem., Int. Ed. 2003, 42, 1578. (h) Mathey, F. Acc. Chem. Res.
2004, 37, 954. (i) Hissler, M.; Lescop, C.; Re´au, R. C. R. Chimie 2005, 8,
1186.
10.1021/jo070822f CCC: $37.00 © 2007 American Chemical Society
Published on Web 07/11/2007
6200
J. Org. Chem. 2007, 72, 6200-6205

Synthesis of 2-Aryl-5-styrylphospholes
SCHEME 1. Synthesis of 4a-i
vinylene-benzene-A system 1a with that of the reverse dipolar
system 1b. Thus, to enhance the second-order NLO response
properties of the stilbene-type phosphole derivatives, it would
be desirable to attach an electron-donating group at the
phosphole terminus and an electron-withdrawing group at the
benzene terminus. In 2002, Re´au and co-workers experimentally
determined molecular hyperpolarizabilities of phosphole deriva-
tives for the first time. Interestingly, the NLO responses of
5-aryl-2-(2-pyridyl)phospholes are enhanced remarkably by the
stereoselective complexation with a cationic palladium(II) salt
through P,N-chelates.5 For example, the cationic complex 2
exhibits a â value of 180 × 10-30 esu (at 1.91 µm), which is
much larger than the sum over the contribution of two sub-
chromophores (â ) 31 × 10-30 esu). Such an enhancement
was rationalized by considering metal-to-ligand or ligand-to-
metal-to-ligand charge-transfers (CT). Despite these early sug-
gestive results, however, no experimental information is avail-
able for the phosphole-based stilbene-type NLO chromophores
like 1. This is apparently because of the lack of a convenient
method for introducing functionalized vinyl groups at the R
position of the phosphole ring.
To our knowledge, there are only two examples for R-vi-
nylphospholes, both of which were prepared via several steps
starting from 3,4-dimethyl-1-phenylphosphole.6 Recently, To-
mita7 and we8 independently reported a convenient method for
the synthesis of 2,5-disubstituted phospholes via titanacyclo-
pentadiene intermediates. Synthetically, it is of particular interest
that the R-ester functions are compatible with the reaction
conditions employed.8 We expected that a similar methodology
would be applicable to the introduction of functionalized vinyl
groups to the R position of the phosphole ring. Herein, we report
the synthesis, structure, and optical properties of unsymmetri-
cally 2,5-disubstituted phospholes bearing an aryl group at one
side and a styryl group at the other side. Hyper-Rayleigh
scattering experiments on the D-π-A type of 2-aryl-5-
styrylphospholes have disclosed that the stilbene-type phosphole
derivatives are promising candidates as a new class of second-
order NLO chromophores.
(2) For example, see: (a) Hay, C.; LeVilain, D.; Deborde, V.; Toupet,
L.; Re´au, R. Chem. Commun. 1999, 345. (b) Hay, C.; Fischmeister, C.;
Hissler, M.; Toupet, L.; Re´au, R. Angew. Chem., Int. Ed. 2000, 10, 1812.
(c) Hay, C.; Hissler, M.; Fischmeister, C.; Rault-Berthelot, J.; Toupet, L.;
Nyula´szi, L.; Re´au, R. Chem. Eur. J. 2001, 7, 4222. (d) Delaere, D.; Nguyen,
M. T.; Vanquickenborne, L. G. Phys. Chem. Chem. Phys. 2002, 4, 1522.
(e) Hay, C.; Sauthier, M.; Deborde, V.; Hissler, M.; Toupet, L.; Re´au, R.
J. Organomet. Chem. 2002, 643-644, 494. (f) Delaere, D.; Nguyen, M.
T.; Vanquickenborne, L. G. J. Phys. Chem. A 2003, 107, 838. (g) Hay, C.;
Fave, C.; Hissler, M.; Rault-Berthelot, J.; Re´au, R. Org. Lett. 2003, 5, 3467.
(h) Hissler, M.; Rescop, C; Re´au, R. J. Organomet. Chem. 2005, 690, 2482.
(i) Su, H.-C.; Fadhel, O.; Yang, C.-J.; Cho, T.-Y.; Fave, C.; Hissler, M.;
Wu, C.-C.; Re´au, R. J. Am. Chem. Soc. 2006, 128, 983. (j) Baumgartner,
T.; Re´au, R. Chem. ReV. 2006, 106, 4681 (Correction: 2007, 107, 303),
and references therein.
Results and Discussion
Synthesis and Characterization of 2-Aryl-5-styrylphosp-
holes. 1,9-Diarylnona-8-ene-1,6-diynes 4a-i, the precursors of
2-aryl-5-styrylphospholes, were prepared by sequential Sono-
gashira/Sonogashira coupling or Sonogashira/Negishi coupling
reactions of 1,6-heptadiyne with the corresponding iodoarenes
and â-bromostyrenes via monosubstituted diynes 3a,b or
enediynes 3c,d (Scheme 1). In the synthesis of 4a-h, (E)-
(6) (a) Deschamps, E.; Ricard, L.; Mathey, F. J. Chem. Soc., Chem.
Commun. 1995, 1561. (b) Niemi, T.-A.; Coe, P. L.; Till, S. J. J. Chem.
Soc., Perkin Trans. 1 2000, 1519.
(7) Tomita reported the synthesis of phosphole-containing polymers via
titanacyclopentadienes, generated from diethynylbenzene and the Ti(II)
reagent. See: (a) Tomita, I.; Ueda, M. Macromol. Symp. 2004, 209, 217.
(b) Tomita, I. Polym. Prep. 2004, 45, 415.
(3) Albert, I. D. L.; Marks, T. J.; Ratner, M. A. J. Am. Chem. Soc. 1997,
119, 6575.
(4) The âx values (× 10-30 esu) of 1a and 1b were evaluated using the
INDO/1 Hamiltonian to be 45.90 and 39.24, respectively, at the AM1
optimized structures. See ref 3.
(5) Fave, C.; Hissler, M.; Se´ne´chal, K.; Ledoux, I.; Zyss, J.; Re´au, R.
Chem. Commun. 2002, 1674.
(8) Matano, Y.; Miyajima, T.; Nakabuchi, T.; Matsutani, Y.; Imahori,
H. J. Org. Chem. 2006, 71, 5792.
J. Org. Chem, Vol. 72, No. 16, 2007 6201

Matano et al.
TABLE 1. Synthesis of 5a-i
isomers were isolated exclusively, irrespective of the stereo-
chemistry of â-bromostyrenes. Reaction of 4a-i with (η2-
propene)Ti(O-i-Pr)2, generated in situ from Ti(O-i-Pr)4 and 2
equiv of i-PrMgCl as previously reported by Sato, Urabe, and
co-workers,9 followed by treatment with dichloro(phenyl)-
phosphine, afforded 2-aryl-5-styrylphospholes 5a-i in 58-66%
isolated yields (Table 1). Note that the ester function in 4f,h
and 5f,h is compatible with the reaction conditions employed.
The present titanacycle method is highly convenient in that the
desired phospholes are readily accessible from commercially
available substrates in a few steps.10 The σ3-phosphole 5c
smoothly underwent complexation with AuCl(SMe2) to give Au-
(I)-phosphole complex 6 in 89% yield (eq 1).
Phospholes 5a-i and 6 are air stable, yellow or orange solids
1
and have been fully characterized by H, 13C, and 31P NMR,
1
MS, and elemental analysis. In the H NMR spectra, vinyl
protons R to the phosphole ring of 5a-h were observed at δ
6.97-7.11 with relatively large 3JH-P values of 15.6-16.0 Hz,
whereas those â to the phosphole ring of 5a-h were observed
at δ 6.53-6.65 with no detectable 1H-31P coupling. The large
1H-1H coupling constants between the two vinyl protons (J )
15.6-16.0 Hz) of 5a-h definitely support the (E)-stereochem-
istry of the styryl groups. The σ3-phospholes 5a-h displayed
the 31P peaks at δ 27.6-29.6, which are more shielded than
those observed for the 3,4-C3-bridged σ3-phospholes bearing
ester functions at the R positions (δ 32.0-33.4).8 On the other
hand, the 31P peak of 5i was observed at downfield (δ 39.3) as
compared to those of 5a-h.
The structure of Au(I) complex 6 was further elucidated by
X-ray crystallography.11 There are two sulfur atom positions
due to disorder of the thiophene ring, and the major form is
depicted in Figure S1. In both forms, the phosphole, thiophene,
and benzene rings are nearly coplanar, implying that the
π-conjugation could occur efficiently through the phosphole-
vinylene bridge.12 The Julg index13 (0.71) calculated for the
phosphole ring in 6 is comparable to that (0.72) of a structurally
characterized 2,5-bis(ethoxycarbonyl)phosphole containing the
same five-membered backbone.8 The phosphorus center adopts
a distorted tetrahedral geometry with C-P-C bond angles of
93.40(16)-107.69(13)° and Au-P-C bond angles of 111.82-
(7)-118.29(13)°. The Au-P bond length [2.2351(7) Å] and
the P-Au-Cl bond angle [171.08(4)°] are close to the corre-
sponding values reported for Au(I)-phosphole (monophosphine)
complexes.14
Optical Properties of 2-Aryl-5-styrylphospholes. To ex-
amine the substituent effects on the optical properties of 2-aryl-
5-styrylphospholes, we first measured UV-vis absorption and
fluorescence spectra of 5a-i and 6 in THF. The results are
summarized in Table 2 and Figure 2. The absorption maxima
due to the π-π* transition of the extended π-conjugated system
of 2-thienyl-5-styrylphospholes 5c,e are red-shifted (∆λmax
)
15-16 nm) relative to those of 2-phenyl-5-styrylphospholes 5a,b
with the same para substituents. Introduction of a methoxy
group at the R position of the thienyl ring and/or introduction
of an electron-withdrawing substituent at the para position of
the benzene ring of the styryl group causes further red-shifts of
the absorption maxima (∆λmax ) 20-22 nm, 5g,h vs 5e,f; ∆λmax
) 4-11 nm, 5e,f vs 5c). These results suggest that the push-
pull (D-A) effect between the two terminal aryl groups operates
efficiently through the phosphole-vinylene bridge. The fluo-
renyl derivative 5i shows a red-shifted π- π* transition (λmax
(9) (a) Urabe, H.; Suzuki, K.; Sato, F. J. Am. Chem. Soc. 1997, 119,
10014. (b) Urabe, H.; Takeda, T.; Hideura, D.; Sato, F. J. Am. Chem. Soc.
1997, 119, 11295. (c) Sato, F.; Urabe, H.; Okamoto, S. Pure Appl. Chem.
1999, 71, 1511. (d) Sato, F.; Urabe, H.; Okamoto, S. Chem. ReV. 2000,
100, 2835. (e) Mikami, K.; Matsumoto, Y.; Shiono, T. Sci. Synth. 2003, 2,
457, and references therein.
(10) Functionalized â-bromostyrenes and 9-(bromomethylene)-9H-fluo-
rene were prepared from the corresponding aromatic aldehydes and
9-fluorenone, respectively, in two steps.
(11) Formula C25H21AuClPS, space group C2/c, a ) 23.149(3) Å, b )
12.4217(11) Å, c ) 18.529(2) Å, â ) 125.6476(4)°, V ) 4329.7(8) Å3, Z
) 8, Dc ) 1.893 g cm-3, 4922 observed and 263 variables, Rw ) 0.0482,
R ) 0.0212 (I > 2.00σ(I)), GOF ) 1.070.
(12) The thiophene and benzene rings are slightly twisted from the
phosphole ring with dihedral angles of 4.2° and 7.3°, respectively.
(13) (a) Julg, A.; Franc¸ois, P. Theor. Chim. Acta (Berlin) 1967, 7, 249.
(b) Schleyer, P. V. R.; Freeman, P. K.; Jiao, H.; Goldfuss, B. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 337.
(14) (a) Attar, S.; Bearden, W. H.; Alcock, N. W.; Alyea, E. C.; Nelson,
J. H. Inorg. Chem. 1990, 29, 425. Au-P, 2.220(9)-2.227(2) Å; P-Au-
Cl, 172.4(1)-178.8(1)°. (b) See ref 2i. Au-P, 2.2290(16)-2.2300(16) Å;
P-Au-Cl, 171.64(7)-174.63(8)°. (c) Dienes, Y.; Eggenstein, M.; Neu-
mann, T.; Englert, U.; Baumgartner, T. Dalton Trans. 2006, 1424. Au-P,
2.2249(12) Å; P-Au-Cl, 177.26(4)°.
6202 J. Org. Chem., Vol. 72, No. 16, 2007

Synthesis of 2-Aryl-5-styrylphospholes
TABLE 2. Absorption and Fluorescence Maxima of
5-Alkenyl-2-arylphospholesa
interaction between the electron-donating thienyl group and the
electron-withdrawing phenyl group plays a crucial role in
controlling the HOMO-LUMO gap.
λ
max, nm
(log ꢀ)
λ
em, nmb
Stokes shift,
cm-1
phosphole
(φf/%c)
To get further insight into the substituent effects on the
polarizability of the π-conjugated system in 2-aryl-5-styrylphos-
pholes, we next examined solvatochromism of absorption and
fluorescence spectra of 5c,e-h and 6 using nine solvents with
different polarity (Table S1). When the solvent was changed
from nonpolar cyclohexane to polar N,N-dimethylformamide
(DMF), the emission maximum of 5c exhibited larger batho-
chromic shift (∆λem ) 14 nm) than the absorption maximum
(∆λmax ) 3 nm). As shown in Figure S3, a Kamlet-Taft
analysis15 for the fluorescence spectra of 5c gave a linear
solvation energy relationship (LSER) vs the solvatochromic
parameter π* [νem ) 19.68-0.56π* (103 cm-1)] with an R value
of 0.952 (n ) 9). On the contrary, a reliable LSER could not
be given from the absorption spectra, due to little difference in
their λmax values. It is most likely that the polarizability of the
excited-state of 5c is more significant than that of the ground
state. Similarly, 5e-h and 6 showed appreciable solvato-
chromism in their fluorescence spectra (Figure S3), displaying
the following LSERs: 5e [νem ) 19.09 - 1.10π* (103 cm-1);
R ) 0.937 (n ) 9)]; 5f [νem ) 18.96 - 1.65π* (103 cm-1); R
) 0.954 (n ) 9)]; 5g [νem ) 17.42 - 1.76π* (103 cm-1); R )
0.956 (n ) 9)]; 5h [νem ) 17.18 - 1.98π* (103 cm-1); R )
0.964 (n ) 9)]; 6 [νem ) 18.46 - 0.91π* (103 cm-1); R )
0.967 (n ) 9)]. Thus, the slope of LSER increases in the order
5c < 6 < 5e < 5f < 5g < 5h, indicating that both the electron-
withdrawing para substituents of the styryl group and the
electron-donating R substituent of the thienyl group are indis-
pensable for providing high polarizability in the excited state.
It has been clarified that the combination of 5-methoxy-2-thienyl
and 4-methoxycarbonylphenyl groups is best for the polarization
of the phosphole-vinylene-bridged π-conjugated system.
NLO Properties of 2-Aryl-5-styrylphospholes. One of the
promising approaches to construct efficient second-order NLO
chromophores is to attach electron donor and electron acceptor
substituents at the opposite ends of a suitable π-conjugated
bridge.16 Namely, the larger the difference in dipole moments
between the ground state and the excited-state of the π-conju-
gated system is, the higher the performance of the NLO
chromophore becomes. To systematically evaluate the NLO
response properties of the 2-aryl-5-styrylphospholes at the
molecular level, we finally measured the first molecular
hyperpolarizabilities (â) of 5e-h in dioxane using the hyper-
Rayleigh scattering (HRS) method17 at a fundamental wave-
length of a Nd:YAG laser (1064 nm).18 Although our samples
are weakly fluorescent, the effect of two-photon excitation19
was well removed by using a multichannel detector as is
described in the experimental section.18 The â values were
5a
5b
5c
5d
5e
5f
5g
5h
5i
402 (4.40)
405 (4.44)
417 (4.43)
420 (4.49)
421 (4.48)
428 (4.52)
441 (4.49)
450 (4.56)
437 (4.35)
435 (4.35)
490 (2.9)
504 (0.20)
516 (4.3)
522 (2.3)
545 (0.27)
552 (0.25)
613 (0.17)
622 (0.13)
d
4.47 × 103
4.85 × 103
4.60 × 103
4.65 × 103
5.40 × 103
5.25 × 103
6.36 × 103
6.15 × 103
6
555 (3.8)
4.97 × 103
a Measured in THF at 25 °C. b Excited at 420 nm. c Fluorescence
quantum yields relative to quinine sulfate. d No emission was detected.
FIGURE 2. UV-vis absorption spectra (a) and fluorescence spectra
(b) of 5c,e-h in THF. The peak maxima are normalized. The color:
5c, purple; 5e, blue; 5f, green; 5g, orange; 5h, red.
) 437 nm) with a lower extinction coefficient (log ꢀ ) 4.35)
as compared to the styryl derivative 5c. The functionalization
at phosphorus from σ3 to σ4 also causes a red-shift of the
absorption maximum (∆λmax ) 18 nm, 6 vs 5c). The spectral
shapes of 5i and 6 are slightly different from those of 5a-h
(Figure S2), implying that the character of the vibronic states
of the 2-aryl-5-styrylphosphole derivatives varies depending on
the structure of the vinylene moiety and the electronic property
of the phosphorus center.
2-Aryl-5-styrylphospholes 5a-i and 6 are weakly fluorescent,
exhibiting emission bands at 490-622 nm with fluorescence
quantum yields of 0.13-4.3% in THF. With increasing the
electron-withdrawing ability of the para substituents of the styryl
group and/or the electron-donating ability of the thienyl group,
the emission maxima (λem) are shifted to longer wavelengths.
For instance, the λem value increases in the order: 2-(2-thienyl)-
5-styrylphosphole 5c (516 nm) < 2-(2-thienyl)-5-(4-methoxy-
carbonylstyryl)phosphole 5f (552 nm) < 2-(5-methoxy-2-
thienyl)-5-(4-methoxycarbonylstyryl)phosphole 5h (622 nm). As
shown in Table 2, the degree of bathochromic shift of λem is
considerably larger than that of λmax, indicating that the CT
interaction in the excited-state is more pronounced than that in
the ground state. It is apparent that the π-conjugative CT
(15) Kamlet, M. J.; Abboud, J.-L. M.; Abraham, M. H.; Taft, R. W. J.
Org. Chem. 1983, 48, 2877.
(16) For example, see: (a) Molecular Nonlinear Optics: Materials,
Physics and DeVices; Zyss, J., Ed.; Academic Press: Boston, 1993. (b)
Nonlinear Optical Properties of Organic Molecules and Crystals; Chemla,
D. S., Zyss, J., Eds.; Academic Press: New York, 1987. (c) Prasad, P. N.;
Williams, D. J. Introduction to Nonlinear Optical Effects in Molecules and
Polymers; Wiley: New York, 1991. (d) Kanis, D. R.; Ratner, M. A.; Marks,
T. J. Chem. ReV. 1994, 94, 195. (e) Cariati, E.; Pizzotti, M.; Roberto, D.;
Tessore, F.; Ugo, R. Coord. Chem. ReV. 2006, 250, 1210. (f) Maury, O.;
Le Bozec, H. Acc. Chem. Res. 2005, 38, 691.
(17) (a) Clays, K.; Perssoons, A. ReV. Sci. Instrum. 1992, 63, 3285. (b)
Clays, K.; Perssoons, A. Phys. ReV. Lett. 1991, 66, 2980.
(18) The details of the HRS measurements for 5e-h are provided in the
Experimental Section.
J. Org. Chem, Vol. 72, No. 16, 2007 6203

Matano et al.
TABLE 3. Nonlinear Optical Data of 2-Aryl-5-styrylphospholes
highest molecular hyperpolarizability, which exemplifies the
potential utility of this class of phosphole derivatives as
promising candidates for efficient second-order NLO chro-
mophores.
phosphole
â1064a (â1907b), (×10-30 esu)
5e
5f
44 (18)
79 (30)
5g
5h
129 (45)
204 (66)
Experimental Section
a Obtained by the HRS method in dioxane. The estimated errors are ca.
10% of the values. b Calculated using the two-level model.
Synthesis of 2-Aryl-5-styrylphospholes. Typical Procedure.
To a mixture of 4a (270 mg, 1.0 mmol), Ti(O-i-Pr)4 (0.29 mL, 1.0
mmol), and Et2O (15 mL) was slowly added an ether solution of
i-PrMgCl (2.0 M × 1.0 mL, 2.0 mmol) at -78 °C, and the resulting
mixture was stirred for 2 h at -50 °C. Dichloro(phenyl)phosphine
(0.14 mL, 1.0 mmol) was then added to the mixture at this
temperature, and the resulting suspension was allowed to warm to
0 °C and stirred for 1 h at this temperature. After stirring for an
additional 2 h at room temperature, a saturated aq NH4Cl solution
(10 mL) was poured into the reaction mixture, and insoluble
substances were filtered off through a Celite bed. The Celite bed
was washed with AcOEt repeatedly, and the filtrate was washed
with brine (50 mL). The aqueous phase was extracted with AcOEt
(20 mL × 2), and the combined organic extracts were dried over
Na2SO4 and evaporated under reduced pressure. The solid residue
was subjected to short silica gel column chromatography (CH2-
Cl2). The yellow fraction was collected and evaporated to give a
yellowish solid, which was then washed with MeOH. 2-Phenyl-5-
styrylphosphole 5a was isolated as a yellow solid (240 mg, 63%).
Mp 161-162 °C; 1H NMR (CDCl3, 300 MHz) δ 2.35 (tt, 2H, J )
7.2, 7.2 Hz), 2.57-2.87 (m, 3H), 2.92-3.05 (m, 1H), 6.65 (d, 1H,
determined by the external reference method against p-nitroa-
niline (PNA) and are summarized in Table 3.20 On the basis of
a simple two-level model,21 we estimate hyperpolarizabilities
of 5e-h at 1.91 µm as 18 (5e), 30 (5f), 45 (5g), and 66 (5h).
Although care must be taken for evaluating these calculated
values,22 it is likely that the NLO response properties of the
D-π-A type of 2-aryl-5-styrylphospholes 5g,h are large
according to the classifications proposed by Marks and co-
workers.16d The 2-thienyl-5-styrylphospholes 5e,f bearing an
electron-withdrawing substituent at the para position of the
phenyl group showed moderate NLO responses (â ) 44 × 10-30
and 79 × 10-30 esu), which are 2.6-4.6 times greater than that
of PNA (â ) 16.9 × 10-30 esu). The 2-(5-methoxy-2-thienyl)-
5-styrylphospholes 5g,h exhibit larger NLO responses (â ) 129
× 10-30 and 204 × 10-30 esu) than the corresponding R-free
thienyl derivatives 5e,f. Thus, introduction of the methoxy group
at the R position of the thiophene ring enhances the NLO
response property largely. These data represent that the resonance/
inductive effects derived from the electron-donating and electron-
withdrawing substituents at the termini operate effectively in
hyperpolarization through the phosphole-vinylene bridged
π-conjugated system.
3
J ) 15.6 Hz), 7.03 (dd, 1H, J ) 15.6 Hz, J(P,H) ) 15.6 Hz),
7.08-7.18 (m, 2H), 7.20-7.30 (m, 7H), 7.27-7.37 (m, 2H), 7.42-
7.50 (m, 4H); 13C{1H} NMR (CDCl3, 75 MHz) δ 27.0 (d, JP-C
)
1.3 Hz), 29.2, 29.3 (d, JP-C ) 1.3 Hz), 123.6 (d, JP-C ) 17.4 Hz),
126.2, 126.2 (d, JP-C ) 1.3 Hz), 127.1, 127.5 (d, JP-C ) 9.9 Hz),
128.4, 128.5, 128.7 (d, JP-C ) 8.1 Hz), 129.3 (d, JP-C ) 1.9 Hz),
129.4 (d, JP-C ) 10.6 Hz), 133.3 (d, JP-C ) 18.7 Hz), 133.6
(d, JP-C ) 11.8 Hz), 136.2, 136.9 (d, JP-C ) 18.7 Hz), 137.2, 137.8,
154.2 (d, JP-C ) 9.4 Hz), 157.8 (d, JP-C ) 8.7 Hz); 31P{1H} NMR
(CDCl3, 162 MHz) δ + 27.7; UV/vis (THF) λmax (ꢀ) 402 (25300);
Fluorescence (THF) λem(φf/%) 490 (2.9); MS (MALDI-TOF) m/z
378 (M+); Anal. Calcd for C27H23P: C, 85.69; H, 6.13. Found: C,
85.56; H, 6.12.
Conclusions
We have established a reliable route for the synthesis of
2-aryl-5-styrylphospholes from 1,9-diarylnona-8-ene-1,6-diynes
and dichloro(phenyl)phosphine via intermediary titanacyclo-
pentadienes. The observed optical properties of the push-pull
type of derivatives represent that the charge-transfer interaction
between the two terminal aryl groups dramatically affect the
polarizability of the phosphole-vinylene-bridged π-conjugated
system. Among the newly prepared phospholes, 2-(5-methoxy-
2-thienyl)-5-[4-(methoxycarbonyl)styryl]phosphole exhibits the
Synthesis of Au(I) Complex 6. A mixture of 5c (38 mg, 0.10
mmol), AuCl(SMe2) (32 mg, 0.11 mmol), and CH2Cl2 (10 mL)
was stirred for 1 h at room temperature. The mixture was then
concentrated under reduced pressure and subjected to short silica
gel column chromatography (CH2Cl2). The first yellow fraction was
collected and washed with MeOH to give 5 as an orange solid (55
mg, 89%). Mp 220 °C (dec); 1H NMR (CDCl3, 400 MHz) δ 2.32-
2.53 (m, 2H), 2.75-3.00 (m, 4H), 6.80-6.96 (m, 3H), 7.19-7.35
(m, 7H), 7.40-7.55 (m, 3H), 7.76-7.83 (m, 2H); 13C{1H} NMR
(CDCl3, 100 MHz) δ 27.8 (d, JP-C ) 8.8 Hz), 28.0 (d, JP-C ) 1.3
Hz), 29.9 (d, JP-C ) 8.1 Hz), 120.1 (d, JP-C ) 14.9 Hz), 122.3,
123.2, 125.9 (d, JP-C ) 2.5 Hz), 126.6, 126.7 (d, JP-C ) 1.9 Hz),
(19) (a) Flipse, M. C.; de Jonge, R.; Woudenberg, R. H.; Marsman, A.
W.; van Walree, C. A.; Jenneskens, L. W. Chem. Phys. Lett. 1995, 245,
297. (b) Song, N. W.; Kang, T.-I.; Jeoung, S. C.; Jeon, S.-J.; Cho, B. R.;
Kim, D. Chem. Phys. Lett. 1996, 261, 307.
(20) The â value of PNA at 1064 nm (dioxane) is reported to be 16.9,
which was determined using the electric field induced second harmonic
generation (EFISH) method. See: (a) Teng, C. C.; Garito, A. F. Phys. ReV.
B 1983, 28, 6766. (b) Sta¨helin, M.; Burland, D. M.; Rice, J. E. Chem. Phys.
Lett. 1992, 191, 245.
128.0, 128.3, 128.7, 129.6 (d, JP-C ) 11.2 Hz), 132.5 (d, JP-C
)
8.1 Hz), 132.8 (d, JP-C ) 2.5 Hz), 133.8 (d, JP-C ) 14.3 Hz),
136.4 (d, JP-C ) 20.5 Hz), 136.5, 155.9 (d, JP-C ) 15.5 Hz), 160.4
(d, JP-C ) 16.1 Hz); 31P{1H} NMR (CDCl3, 162 MHz) δ + 52.4;
(21) (a) Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1977, 66, 2664. (b)
Oudar, J. L. J. Chem. Phys. 1977, 67, 446. (c) Oudar, J. L.; Zyss, J. Phys.
ReV. A 1982, 26, 2016. The â values at 1.91 µm were calculated according
UV/vis (THF) λ
(ꢀ) 435 (22400); Fluorescence (THF) λem(φf/
max
%) 555 (3.8); MS (MALDI-TOF) m/z 617 (M+).
to the following equation neglecting damping factors: â1.91 ) â1.06(R1.06
/
2
R
1.91); Rω ) ω0 /(ω02 - ω2)(ω02 - 4ω2), where ω0 is the frequency of the
Hyper-Rayleigh Light Scattering (HRS) Measurements. The
first hyperpolarizabilities (â) of 2-aryl-5-styrylphospholes were
determined using the hyper-Rayleigh light scattering (HRS) method
using a fundamental output (1064 nm) from a Nd:YAG laser (10
Hz, ca. 5-7 ns). The beam at a fundamental wavelength (1064
nm) was focused in the solution in a 1 cm glass cell with a beam
diameter of ca. 1.6 mm by a lens with a focal length of 200 mm.
The hyper-Rayleigh signal from the solution was collected at a 90°
scattering geometry and focused on a slit of a 64 cm monochromator
absorption maximum.
(22) It has been pointed out that the intrinsic hyperpolarizabilities (â0)
calculated from 1064 nm HRS data somewhat differ from the 1907 nm
results. This discrepancy has been attributed to the difficulty of the
estimation of the resonance enhancement associated with the 1064 nm
radiation employed in the HRS experiments. However, the traditional way
(note 21) still gives rough estimations. For example, see: (a) Wang, C. H.;
Woodford, J. N.; Jen, A. K.-Y. Chem. Phys. 2000, 262, 475. (b) Clays, K.;
Hendrickx, E.; Verbiest, T.; Persoons, A. AdV. Mater. 1998, 10, 643. (c)
Wolff, J. J.; Wortmann, R. AdV. Phys. Org. Chem. 1999, 121.
6204 J. Org. Chem., Vol. 72, No. 16, 2007

Synthesis of 2-Aryl-5-styrylphospholes
(a 1800 lines/mm grating) equipped with a CCD camera (1340 ×
400 imaging pixels, 20 × 20-µm pixels). The hyper-Rayleigh signal
detected at 532 nm was easily resolved from other background
signals (e.g., two-photon fluorescence) by using a multichannel
detector, since the signal appears as a strong spike over the smooth
background. It was ensured that the hyper-Rayleigh signal was
proportional to the square of the laser pulse energy at least up to
ca. 25 mJ. In the determination of â, the concentration dependence
of the hyper-Rayleigh signal intensity was measured at the fixed
pulse energy (ca. 20 mJ). Freshly distilled dioxane was used as a
solvent, and the â values of 5e-h were measured using the external
reference method against a standard solution of p-nitroaniline (PNA)
in the same solvent: the relative hyperpolarizabilities of two
chromophores are given by â ) âref × (m/mref)1/2, where m is slope
of the hyper-Rayleigh signal intensity against the solute concentra-
tion. The concentrations of PNA were less than 14 mM, and those
of 5e,f were less than 1 mM. In the measurements of 5g,h, the
diluted sample solutions (<0.1 mM) were used to avoid self-
absorption of the second harmonic generation signal at 532 nm,
and the effect of the reabsorption was corrected.
Acknowledgment. This work was partially supported by a
Grant-in-Aid (No. 19027030) from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan.
Supporting Information Available: Experimental details,
synthetic procedures and characterization data for 3a-d, 4a-i, and
5b-i, 1H NMR charts for new compounds, and CIF file for 6. This
material is available free of charge via the Internet at http://
pubs.acs.org.
JO070822F
J. Org. Chem, Vol. 72, No. 16, 2007 6205