Phosphorus copies of PPV: π-conjugated polymers and molecules composed of alternating phenylene and phosphaalkene moieties

Article abstract of DOI:10.1021/ja060816l

A new class of π-conjugated macromolecule, poly(p- phenylenephosphaalkene) (PPP), is reported. PPPs are phosphorus analogues of the important electronic material poly(p-phenylenevinylene) (PPV) where P=C rather than C=C bonds space phenylene moieties. Spe

Full text of DOI:10.1021/ja060816l

Published on Web 06/16/2006
Phosphorus Copies of PPV: π-Conjugated Polymers and
Molecules Composed of Alternating Phenylene and
Phosphaalkene Moieties
Vincent A. Wright, Brian O. Patrick, Celine Schneider, and Derek P. Gates*
Contribution from the Department of Chemistry, UniVersity of British Columbia,
2036 Main Mall, VancouVer, British Columbia, Canada V6T 1Z1
Received February 10, 2006; Revised Manuscript Received April 26, 2006; E-mail: dgates@chem.ubc.ca
Abstract: A new class of π-conjugated macromolecule, poly(p-phenylenephosphaalkene) (PPP), is reported.
PPPs are phosphorus analogues of the important electronic material poly(p-phenylenevinylene) (PPV) where
PdC rather than CdC bonds space phenylene moieties. Specifically, PPPs [sC6R4sPdC(OSiMe3)sC6R′4s
C(OSiMe3)dPs]n (1: R ) H, R′ ) Me; 11: R ) Me, R′ ) H) were synthesized by utilizing the Becker
reaction of a bifunctional silylphosphine, 1,4-C6R4[P(SiMe3)2]2, and diacid chloride 1,4-C6R′4[COCl]2. Several
model compounds for PPP are reported. Namely, mono(phosphaalkene)s RsPdC(OSiMe3)sR′ (4: R )
Ph, R′ ) Mes; 7: R ) Mes, R′ ) Ph), C-centered bis(phosphaalkene)s RsPdC(OSiMe3)sC6R′4s
C(OSiMe3)dPsR (5: R ) Ph, R′ ) Me; 8: R ) Mes, R′ ) H), and P-centered bis(phosphaalkene)s Rs
C(OSiMe3)dPsC6R′4sPdC(OSiMe3)sR (6: R ) Mes, R′ ) H; 10: R ) Ph, R′ ) Me). Remarkably, selective
Z-isomer formation (i.e., trans arylene moieties) is observed for PPPs when bulky P-substituents are
employed while E/Z-mixtures are otherwise obtained. X-ray crystal structures of Z-7, Z,Z-8, and Z,Z-10
suggest moderate π-conjugation. The twist angles between the PdC plane and unsubstituted arenes are
16°-26°, while those between the PdC plane and methyl-substituted arenes are 59°-67°. The colored
PPPs and their model compounds were studied by UV/vis spectroscopy, and the results are consistent
with extended π-conjugation. Specifically, weakly emissive polymer E/Z-1 (λmax ) 338 nm) shows a red
shift in its absorbance from model E/Z-4 (λmax ) 310 nm), while a much larger red shift is observed for
Z-11 (λmax ) 394 nm) over Z-7 (λmax ) 324 nm).
Introduction
has been a growth of activity in π-conjugated phosphorus
macromolecules because of their potential electronic applica-
The development of new polymers incorporating inorganic
elements into the main chain is a challenging research frontier
that promises to lead to materials with exciting properties and
possible specialty applications.1,2 Inorganic macromolecules
composed of phosphorus atoms in the backbone have attracted
considerable attention with the polyphosphazenes (A) being the
most important class (see Chart 1).3 Recently, major advances
in the breadth of phosphorus polymer chemistry have been made
including the synthesis of poly(ferrocenylphosphine)s (B),4
polythionylphosphazenes (C),5 polyphosphinoboranes (D),6 and
poly(methylenephosphine)s (E).7 In the past few years, there
tions.8 Perhaps the most thoroughly investigated of these are
the polyphospholes. Although the parent polyphosphole is not
known, several oligomeric and polymeric species containing
phospholes have been reported (F).9-18 The fabrication of the
(6) See, for example: Dorn, H.; Singh, R. A.; Massey, J. A.; Lough, A. J.;
Manners, I. Angew. Chem., Int. Ed. 1999, 38, 3321-3323. Dorn, H.; Singh,
R. A.; Massey, J. A.; Nelson, J. M.; Jaska, C. A.; Lough, A. J.; Manners,
I. J. Am. Chem. Soc. 2000, 122, 6669-6678. Dorn, H.; Rodezno, J. M.;
Brunnho¨fer, B.; Rivard, E.; Massey, J. A.; Manners, I. Macromolecules
2003, 36, 291-297. Denis, J.-M.; Forintos, H.; Szelke, H.; Toupet, L.;
Pham, T.-N.; Madec, P.-J.; Gaumont, A.-C. Chem. Commun. 2003, 54-
55. Clark, T. J.; Rodenzo, J. M.; Clendenning, S. B.; Aouba, S.; Brodersen,
P. M.; Lough, A. J.; Ruda, H. E.; Manners, I. Chem.sEur. J. 2005, 4526-
4534.
(1) Mark, J. E.; Allcock, H. R.; West, R. Inorganic Polymers, 2nd ed.; Oxford
University Press: 2005.
(7) Tsang, C.-W.; Yam, M.; Gates, D. P. J. Am. Chem. Soc. 2003, 125, 1480-
1481.
(2) Manners, I. Angew. Chem., Int. Ed. Engl. 1996, 35, 1603-1621.
(3) Allcock, H. R. Chemistry and Applications of Polyphosphazenes; John
Wiley & Sons: New Jersey, 2003.
(4) See, for example: Withers, H. P.; Seyferth, D. Organometallics 1982, 1,
1275-1282. Withers, H. P.; Seyferth, D. Organometallics 1982, 1, 1283-
1288. Honeyman, C. H.; Foucher, D. A.; Dahmen, F. Y.; Rulkens, R.;
Lough, A. J.; Manners, I. Organometallics 1995, 14, 5503-5512. Hon-
eyman, C. H.; Peckham, T. J.; Massey, J. A.; Manners, I. Chem. Commun.
1996, 2589-2590. Peckham, T. J.; Massey, J. A.; Honeyman, C. H.;
Manners, I. Macromolecules 1999, 32, 2830-2837.
(5) See, for example: McWilliams, A. R.; Gates, D. P.; Edwards, M.; Liable-
Sands, L. M.; Guzei, I.; Rheingold, A. L.; Manners, I. J. Am. Chem. Soc.
2000, 122, 8848-8855. Chunechom, V.; Vidal, T. E.; Adams, H.; Turner,
M. L. Angew. Chem., Int. Ed. 1998, 37, 1928-1930. Gates, D. P.;
McWilliams, A. R.; Manners, I. Macromolecules 1998, 31, 3494-3497.
Liang, M.; Manners, I. J. Am. Chem. Soc. 1991, 113, 4044-4045.
(8) Hissler, M.; Dyer, P.; Re´au, R. Coord. Chem. ReV. 2003, 244, 1-44.
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33, 1158.
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Int. Ed. 2000, 39, 1812-1815.
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Nyula´szi, L.; Re´au, R. Chem.sEur. J. 2001, 7, 4222-4236.
(13) Morisaki, Y.; Aiki, Y.; Chujo, Y. Macromolecules 2003, 36, 2594-2597.
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8836
J. AM. CHEM. SOC. 2006, 128, 8836-8844
10.1021/ja060816l CCC: $33.50 © 2006 American Chemical Society

Phosphorus Copies of Poly(p-phenylenevinylene) (PPV)
A R T I C L E S
phosphorus being coined “the carbon copy”.31,34,35 The parallels
between phosphaalkenes and alkenes are evidenced by the
occurrence of phospha-variants of reactions common for olefins
such as Peterson and Wittig olefination, 1,2-addition, [4+2]
cycloaddition, η2 metal coordination, and Cope and allylic
rearrangements.
Chart 1. Selected Examples of Polymers Containing Group 15
Elements in the Main Chain
Our research group is interested in expanding the phosphorus-
carbon analogy to polymer science and has been utilizing the
isolobal relationship between PdC and CdC bonds. To this
end, we recently reported the successful polymerization of a
PdC bond, by analogy with olefin polymerization, to afford
poly(methylenephosphine) (E, Chart 1).7 The preparation of
macromolecules where the PdC bond is directly incorporated
into the backbone is also of considerable interest.36 The formal
replacement of the CdC moiety by a PdC moiety in the
important organic π-conjugated polymer poly(p-phenylenevi-
nylene) (PPV)37 would result in a poly(p-phenylenephosphaal-
kene) (PPP) and is expected to lead to a new generation of
electronic materials. Moreover, the successful preparation of
first organophosphorus-based LEDs using oligophospholes
represents an exciting recent achievement in this field.19,20 Novel
phosphorus analogues of polyaniline have been prepared, and
these poly(p-phenylenephosphine)s (G) possess electronic prop-
erties that are consistent with extended π-conjugation.21-23
Although the phosphorus analogue has not been reported, it is
worth noting that luminescent poly(vinylene arsine)s (H) have
also been prepared.24-26 Many of the aforementioned polymers
contain pyramidal phosphorus atoms. We postulated that more
effective π-conjugation might be observed if the phosphorus
atoms were directly involved in (p-p)π bonding by incorporat-
ing PdC bonds into the polymer structure.
The investigation of compounds possessing heavy element
(np-mp)π bonds (n > 2; m g 2) continues to be an important
central theme in main group chemistry.27 These low-coordinate
species pose a considerable synthetic challenge yet are attractive
because their intriguing structural features challenge our un-
derstanding of chemical bonding28,29 and offer a means to
expand the diverse chemistry of olefins and alkynes to other
systems.30,31 This year marks the thirtieth anniversary of the
landmark development of the first isolable phosphaalkenes by
Becker32 and the detection of the parent HPdCH2 by Kroto
and Nixon.33 Conceptually, a phosphaalkene is derived by
replacing one of the methylene fragments (R2C) of an alkene
with the isolobal phosphinidene (RP) group. The development
of phosphaalkenes has unveiled a fertile new area of phosphorus
chemistry and has played a major role in low-coordinate
PPPs, although synthetically challenging, would provide a
unique opportunity to further investigate the parallel between
PdC and CdC bonds. The first examples of PPPs (1 and 2)
have recently been reported by us38 and Protasiewicz.39-41 These
phosphaalkene-containing polymers, as well as the diphosphene-
containing polymer 3,40 exhibit electronic properties consistent
with extended π-conjugation in the main chain.
(18) Baumgartner, T.; Wilk, W. Org. Lett. 2006, 8, 503-506.
(19) Fave, C.; Cho, T.-Y.; Hissler, M.; Chen, C.-W.; Luh, T.-Y.; Wu, C.-C.;
Re´au, R. J. Am. Chem. Soc. 2003, 125, 9254-9255.
(20) Su, H.-C.; Fadhei, O.; Yang, C.-J.; Cho, T.-Y.; Fave, C.; Hissler, M.; Wu,
C.-C.; Re´au, R. J. Am. Chem. Soc. 2006, 128, 983-995.
(21) Lucht, B. L.; St. Onge, N. O. Chem. Commun. 2000, 2097-2098.
(22) Jin, Z.; Lucht, B. L. J. Organomet. Chem. 2002, 653, 167-176.
(23) Jin, Z.; Lucht, B. L. J. Am. Chem. Soc. 2005, 127, 5586-5595.
(24) Umeyama, T.; Naka, K.; Bravo, M. D.; Nakahashi, A.; Chujo, Y. Polym.
Bull. 2004, 52, 191-199.
Herein, we report our detailed studies of PPPs, phosphorus
copies of PPV, including their synthesis, electronic properties,
(34) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy;
Wiley: West Sussex, 1998.
(35) Regitz, M.; Scherer, O. J. Multiple Bonds and Low Coordination in
Phosphorus Chemistry; Georg Thieme Verlag Thieme Medical Publish-
ers: New York, 1990.
(36) Recently, novel polymers have been reported where PdC bonds are
incorporated into the side-group structure. See: Toyota, K.; Ujita, J.;
Kawasaki, S.; Abe, K.; Yamada, N.; Yoshifuji, M. Tetrahedron Lett. 2004,
7609-7612.
(37) For reviews, see: (a) Handbook of Conducting Polymers, 2nd ed.; Skotheim,
T. A., Elsenbaumer, R. L., Reynolds, J. R., Eds.; Dekker: New York, 1998.
(b) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int. Ed.
1998, 37, 402-428.
(25) Umeyama, T.; Naka, K.; Chujo, Y. Macromolecules 2004, 37, 3623-3629.
(26) Naka, K.; Umeyama, T.; Chujo, Y. J. Am. Chem. Soc. 2002, 124, 6600-
6603.
(27) Power, P. P. Chem. ReV. 1999, 99, 3463-3504.
(28) Power, P. P. J. Chem. Soc., Dalton Trans. 1998, 2939-2951.
(29) Power, P. P. Chem. Commun. 2003, 2091-2101.
(30) Mathey, F. Acc. Chem. Res. 1992, 25, 90-96.
(31) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578-1604.
(32) Becker, G. Z. Anorg. Allg. Chem. 1976, 423, 242-254.
(33) Hopkinson, M. J.; Kroto, H. W.; Nixon, J. F.; Simmons, N. P. C. J. Chem.
Soc., Chem. Commun. 1976, 513-515.
9
J. AM. CHEM. SOC. VOL. 128, NO. 27, 2006 8837

A R T I C L E S
Wright et al.
Table 1. Selected Characterization Data for Model Compounds and Polymers
δ PdC (ppm)
Mn
λmax
(nm)
Z:E
(%)
isolated
compound
31P NMR
13C NMRa
(g/mol)
yield (%)
reference
4
134.0 (Z)
149.2 (E)
134.0, 131.8, 129.9, 129.6 (Z)
155.2, 154.9, 150.7, 149.5 (E)
132.3 (Z,Z)
148.3, 134.8 (E,Z)
149.2 (E,E)
132 (Z)
197.3 (Z, 49 Hz)
210.2 (E, 41 Hz)
198.6 (Z, 49 Hz)
211.8 (E, 44 Hz)
195.5 (49 Hz)
209.7 (41 Hz)
210.4 (41 Hz)
197.9 (Z)
328
310
314
332
46:54
56:44
12:88
75
42
54
this work
5
6
550
578
this work
this work
1 (trial 1)
2900b
328
53:47
35
this work
152 (E)
211.9 (E)
1 (trial 2)
1 (trial 3)
1 (trial 4)
7
6300b
6300b
10 500b
328
334
334
338
324
388
337
394d
306
349
326
411
445
445
51:49
51:49
53:47
100:0
100:0
100:0
100:0
100:0
0:100
0:100
0:100
0:100
0:100
this work
this work
this work
this work
this work
this work
this work
51
66
75, 76
39
39
39
141.5 (Z)
197.3 (Z, 56 Hz)
196.4 (Z,Z, 60 Hz)
195.9 (Z,Z, 55 Hz)
194 (Z)
188.5 (Z, 52 Hz)
N/A
40
71
62
88
8
146.3 (Z,Z)
150.2 (Z,Z)
153 (Z)
141.3 (Z)
248.6 (E)
579
10
11
12
19
23
25
26
2
551
N/Ac
496
846
259.2 (E)
243.5 (E)
243.3 (E)
250.5 (E), 270.6 (E)
173.7 (E)
N/A
N/A
N/A
655
790
991
6500
a Our 13C NMR assignments of the PdC carbon for E- and Z-isomers of 4, 5, and 1 were incorrect in ref 38. Reexamination of the spectra and comparison
1
to that observed for Z-7, Z,Z-8, Z,Z-10, and Z-11 led to this new assignment. JCdP is given in parentheses. b Mn was estimated using end group analysis.
c Could not use end group analysis using CP-MAS NMR. d UV/vis spectroscopy performed on the THF soluble fraction of the mostly insoluble 11.
Scheme 1. Becker Route to Phosphaalkenes: Condensation
Followed by the [1,3]-Silatropic Rearrangement of an
Acylphosphine to a Phosphaalkene
and methods to control the stereochemistry of the PdC bond.
As is common in the study of π-conjugated polymers,42 we have
systematically prepared molecular model compounds for the
polymer. Structural and spectroscopic investigations of these
systems are consistent with extended π-conjugation between
the PdC and phenylene moieties in the backbone of PPP.
and tolerates a variety of substituents.44 This reaction involves
Results and Discussion
initial condensation of an acid chloride with a bis(trimethylsilyl)-
phosphine to form a transient acylphosphine that rapidly
When we embarked on this project, we realized that the
biggest challenge to the preparation of a PdC analogue of PPV
tautomerizes to the phosphaalkene. Another attractive feature
would lie in choosing the synthetic route. To achieve a
of the Becker route is that the sole byproduct (Me3SiCl) is easily
satisfactory degree of polymerization through condensation
removed which simplifies polymer purification.
polymerization, the phosphorus-carbon bond forming step must
Synthesis and Characterization of Mixed E/Z-PPPs. The
simplest model for PPP is PhPdC(OSiMe3)Ph; however,
previous studies showed that this compound is unstable and
readily dimerizes.45 We realized that steric protection would
be necessary to stabilize the PdC bond. However, extremely
bulky groups such as supermesityl (Mes* ) 2,4,6-tri-tert-
butylphenyl) would cause backbone twisting and, consequently,
diminish π-conjugation. Therefore, the smaller mesityl sub-
stituent (Mes ) 2,4,6-trimethylphenyl) was chosen for this task.
To accurately model the backbone of the target polymer and to
evaluate π-conjugation in the backbone, mono(phosphaalkene)
(4) and two bis(phosphaalkene)s (5 and 6) were prepared.
Important spectroscopic data for these model compounds are
given in Table 1. Interestingly, the 31P NMR spectrum of
phosphaalkene 4 (yield ) 75%) shows signals for both E- and
Z-isomers (δ 149.2, 54%, E; 134.0, 46%, Z) assigned by
be quantitative and the monomers must be of very high purity.43
Of the numerous routes known for the preparation of phos-
phaalkenes, the aforementioned Becker method (Scheme 1)
attracted our attention since it is convenient, is high yielding,
(38) Wright, V. A.; Gates, D. P. Angew. Chem., Int. Ed. 2002, 41, 2389-2392.
(39) Smith, R. C.; Chen, X.; Protasiewicz, J. D. Inorg. Chem. 2003, 42, 5468-
5470.
(40) Smith, R. C.; Protasiewicz, J. D. J. Am. Chem. Soc. 2004, 126, 2268-
2269.
(41) Smith, R. C.; Protasiewicz, J. D. Eur. J. Inorg. Chem. 2004, 998-1006.
(42) See, for example: van Hutten, P. F.; Hadziioannou, G. Semiconducting
Polymers 2000, 561-613. van Hutten, P. F.; Krasnikov, V. V.; Hadziio-
annou, G. Acc. Chem. Res. 1999, 32, 257-265. Martin, R. E.; Diederich,
F. Angew. Chem., Int. Ed. 1999, 38, 1350-1377. Mu¨llen, K., Wegner, G.,
Eds. Electronic Materials. The Oligomer Approach; Wiley-VCH: New
York, 1998. Tour, J. M. Chem. ReV. 1996, 96, 537-554. Mu¨llen, K. Pure
Appl. Chem. 1993, 65, 89-96.
(43) In a step growth polymerization, the extent of reaction (p) determines the
number-average degree of polymerization (Xn) according to the Carothers
equation: Xn ) 1/(1 - p). Therefore, to achieve a polymer with 100 repeat
units, the reaction must proceed to 99% completion. In addition, stoichio-
metric imbalance (r ) NA/NB; where NA ) mol of monomer A and NB
)
mol of monomer B) also leads to lower average degrees of polymerization
according to the following equation: Xn ) (1 + r)/(1 + r - 2rp).
Stoichiometric imbalance may arise due to difficulty measuring accurate
quantities of monomers or, more likely, the presence of impurities. For the
aforementioned polymerization (two bifunctional monomers A-A + B-B)
which proceeds to 99% completion, an imbalance in stoichiometry of 0.99
(i.e., a 1% excess of B-B) will decrease the degree of polymerization (Xn)
from 100 to 67. For a nice discussion of the challenge of achieving high
molecular weight using step polymerization, see: Odian, G. Principles of
Polymerization; Wiley: New York, 1991; Chapter 2.
(44) See, for example: (a) Becker, G. Z. Anorg. Allg. Chem. 1977, 430, 66-
76. (b) Becker, G.; Mundt, O. Z. Anorg. Allg. Chem. 1978, 443, 53-69.
(c) Becker, G.; Becker, W.; Uhl, G. Z. Anorg. Allg. Chem. 1984, 518, 21-
35. (d) Pietschnig, R.; Niecke, E.; Nieger, M.; Airola, K. J. Organomet.
Chem. 1997, 529, 127-133. (e) Gruenhagen, A.; Pieper, U.; Kottke, T.;
Roesky, H. W. Z. Anorg. Allg. Chem. 1994, 620, 716-722. (f) Mack, A.;
Pierron, E.; Allspach, T.; Bergstra¨ber, U.; Regitz, M. Synthesis-Stuttgart
1998, 1305-1313.
(45) Becker, G.; Becker, W.; Mundt, O. Phosphorus Sulfur 1983, 14, 267-
283.
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Phosphorus Copies of Poly(p-phenylenevinylene) (PPV)
A R T I C L E S
comparison to similar phosphaalkenes from the literature.32,46,47
The E-isomer features the two aryl substituents in cis positions,
while in the Z-isomer the aryl groups are trans configured and
this isomer is expected to be more π-conjugated.
phine monomers in the melt (85 °C) affords PPP (1) as a viscous
yellow gum. The 31P NMR spectrum of 1 shows broad
overlapping signals assigned to E- and Z-configured PdC bonds
and a sharp signal assigned to sP(SiMe3)2 end groups.
Importantly, broad resonances at 212 and 198 ppm assigned to
the vinylic carbons of the E- and Z-isomers are detected in the
13C{1H} NMR spectrum of E/Z-1. Attempts to estimate the
molecular weight of the poly(p-phenylenephosphaalkene) 1 by
GPC and MALDI-TOF MS were precluded by the air and
moisture sensitivity of the polymer. The relative integration of
the sP(SiMe3)2 and PdC signals in the 31P NMR spectrum
suggests that the number average molecular weights (Mn) for
various samples of 1 range from 2900 to 10 500 g mol-1 (see
Table 1). The molecular weights determined by end group
analysis match well with elemental analyses, including chlorine
analysis. Unfortunately, attempts to obtain higher molecular
weight 1 by heating for 48 h afford insoluble yellow-orange
gels that swelled reversibly in THF. Nevertheless, the 31P NMR
spectra of these swollen gels exhibit broad resonances similar
to those for the soluble polymer E/Z-1 suggesting that the gel
is higher molecular weight or partially cross-linked E/Z-1.
The bis(phosphaalkene)s (5 and 6) can be prepared quanti-
tatively (by 31P NMR spectroscopy). However, these compounds
are difficult to isolate as solids due to their high solubility in
hexanes even at low temperatures, and consequently, low
isolated yields are obtained (5, 42%; 6, 54%). Similar to that
observed for mono(phosphaalkene) 4, the NMR spectra of bis-
(phosphaalkene)s 5 and 6 indicate that a mixture of E- and
Z-isomers is present. The 31P NMR spectrum of a bis-
(phosphaalkene) should show four resonances [E,E- (1 signal);
Z,Z- (1 signal); E,Z- (2 signals)]. As predicted, four signals are
observed in the phosphaalkene region of the 31P NMR spectrum
of 6 and are assigned as follows: E,E-6 (δ 149.2, 78%), E,Z-6
(δ 148.3, 134.8; 20%), and Z,Z-6 (δ 132.3, 2%). These
assignments were made on comparison with other phosphaalk-
enes prepared in this and previous studies.32,46,47 Unexpectedly,
the 31P NMR spectrum of bis(phosphaalkene) 5 exhibits eight
resonances distributed over the regions expected for E- (44%)
and Z-phosphaalkene (56%) isomers. The presence of eight
rather than four signals can be rationalized by assuming that
the bulky C6Me4 spacer restricts free rotation of the PdC
moieties. As a consequence, each isomer has syn- and anti-
conformers, and the number of signals increases from four to
eight. Presumably, the C6H4 central spacer in 6 does not hinder
rotation of the PdC groups on the NMR time scale, and thus
four signals are observed as expected. The UV/vis data
(discussed below) also support this hypothesis since E/Z-6
appears to be more π-conjugated than E/Z-5.
Synthesis and Characterization of Z-PPPs. Thus far, we
have shown that mixed E/Z-PPP and molecular models could
be prepared; however, we sought an all Z-PPP which we
anticipated would show more extensive π-conjugation. It has
previously been noted that Becker phosphaalkenes show a
preference for the Z-isomer when bulky P-substituents (i.e., tBu
and Mes*) are employed.32,48 Therefore, we speculated that
PPPs bearing bulky P-substituents would selectively form as
Z-isomers, and we embarked on the preparation of the model
compound 7.
Previously unknown mono(phosphaalkene) 7 can be prepared
by stirring MesP(SiMe3)2 and PhCOCl in THF for 1 d at 25
°C. Remarkably, only a single resonance in the phosphaalkene
region (δ 141.5) is detected in the 31P NMR spectrum of the
reaction mixture suggesting that, unlike E/Z-4, only one isomer
of 7 is present. Additional evidence for the stereoselective
formation of 7 is obtained from the relatively simple 13C{1H}
NMR spectrum. Notably, a distinctive doublet resonance is
detected at 197.3 ppm (1JPC ) 56 Hz) which can be assigned
to the vinylic carbon of the Z-PdC isomer. In contrast to liquid
E/Z-4, solid 7 is crystalline and the analysis of single crystals
With model compounds E/Z-4, E/Z-5, and E/Z-6 in hand, the
target poly(p-phenylenephosphaalkene) (1) could be prepared.
Heating the bifunctional carboxylic acid chloride and silylphos-
(46) Becker, G.; Beck, H. P. Z. Anorg. Allg. Chem. 1977, 430, 77-90.
(47) Fluck, E. Topics in Phosphorus Chemistry; Wiley: New York, 1980; Vol.
(48) Yoshifuji, M.; Toyota, K.; Inamoto, N. Phosphorus Sulfur 1985, 25, 237-
10.
243.
9
J. AM. CHEM. SOC. VOL. 128, NO. 27, 2006 8839

A R T I C L E S
Wright et al.
Scheme 2 a
Figure 1. Molecular structure of 7 (50% probability). All hydrogen atoms
are omitted for clarity.
a
t
Conditions and reagents: (i) THF, -78 °C, 4 equiv BuLi; subse-
quently, 2 equiv of ClP(NEt2)2. (ii) CH2Cl2, 0 °C, excess dry HCl(g). (iii)
Et2O, -78 °C, 1.1 equiv of LiAlH4. (iv) Et2O, -78 °C, 4 equiv of MeLi;
subsequently, 4 equiv of ClSiMe3.
Figure 2. Molecular structure of Z,Z-8 (50% probability). All hydrogen
atoms are omitted for clarity.
by X-ray crystallography confirmed that the Z-isomer was
formed selectively (Figure 1).
In contrast to the conditions necessary for the preparation of
bis(phosphaalkenes) E/Z-5 and E/Z-6 (several days of heating),
bis(phosphaalkene) 8 forms quantitatively in just 5 h at 25 °C.
The 31P NMR spectrum of the reaction mixture shows a single
resonance at 146.3 ppm suggesting a single isomer. Crystals of
bis(phosphaalkene) 8 suitable for X-ray crystallography were
obtained directly from the reaction mixture, and the molecular
structure (Figure 2) confirms the identity of 8 as a Z,Z-isomer.
Figure 3. Molecular structure of Z,Z-10 (50% probability). All hydrogen
atoms are omitted for clarity.
careful fractional sublimation at the dichlorophosphine stage
[i.e., from 1,4-C6Me4(PCl2)2], silylphosphine 9 can be isolated
in very high purity.
With bis(silylphosphine) 9 in hand, the bis(phosphaalkene)
(10) is obtained quantitatively by 31P NMR spectroscopy and
in 62% isolated yield after recrystallization. Analogous to Z-7
and Z,Z-8, the resonances assigned to the PdC bond in the 31
P
13
1
31
13
and C{ H} NMR spectra of 10 (δ ) 150.2; δ ) 195.9,
P
C
1JPC ) 55 Hz) suggest that a single Z,Z-isomer is obtained.49
The selective formation of Z,Z-10 is confirmed by the X-ray
crystal structure (Figure 3).
To access bis(phosphaalkene) (10) and PPP (11) and fully
test our hypothesis that bulky P-substituents preferentially give
Z-phosphaalkenes, the hindered bis(phosphino)arylene (9) had
to be prepared. Highly pyrophoric 9 was prepared following
the procedure outlined in Scheme 2 (overall yield ) 20%).
Silylphosphine 9 is extremely difficult to obtain in high purity
because of incomplete lithiation of 1,4-Br2C6Me4 and the
unavoidable presence of traces of [HNEt3]Cl in the ClP(NEt2)2.
Consequently, the first step yields some HC6Me4P(NEt)2 and
BrC6Me4P(NEt2)2 in addition to desired 1,4-C6Me4[P(NEt2)2]2.
We have found that when these impurities are removed by
The synthesis of the corresponding all trans-isomer PPP (11)
was attempted by heating neat 9 and terephthaloyl chloride to
85 °C. After just 2 h, the initially free-flowing melt solidifies
into a bright orange glass. The brittle solid, presumed to be
Z-11, is insoluble in common organic solvents which is not
surprising since many stereoregular organic π-conjugated
polymers are poorly soluble (e.g., trans-PPV and trans-
(49) In addition to the large signal assigned to the Z,Z-isomer, the 31P NMR
spectrum of the initial reaction mixture showed additional minor signals
in the region expected for phosphaalkenes. This may indicate that a very
small amount of E-isomer is present initially.
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8840 J. AM. CHEM. SOC. VOL. 128, NO. 27, 2006

Phosphorus Copies of Poly(p-phenylenevinylene) (PPV)
A R T I C L E S
Figure 4. 13C{1H} CP-MAS NMR spectrum (νo ) 15 kHz) of polymer 11 (10 000 scans, 5 s delay, contact time 1 s). * represents tentatively assigned to
-P(SiMe3)2 end groups in 11 and/or unreacted 9.
polyacetylene).50 Solid-state NMR spectroscopy confirms that
the orange glass is indeed Z-11. In particular, the dominant
signal detected at 153 ppm in the 31P CP-MAS NMR spectrum
of 11 is assigned to the Z-phosphaalkene group upon comparison
with Z-7 (δ ) 141.5), Z,Z-8 (δ ) 146.3), and Z,Z-10 (δ )
150.2). Signals at -147 and -155 ppm are assigned to
sP(SiMe2)2 end groups and residual 9, respectively. A small
signal is also observed at δ 30 in the 31P CP-MAS NMR
spectrum. We speculate that either a bis(acyl)phosphine cross-
link/branch point or a 1,2- or 1,3-diphosphetane cross-link is
responsible for this signal since both moieties are plausible and
are expected to resonate in this region of the 31P NMR spectrum.
Given that we have not observed PdC dimerization in any of
our model studies, we favor the assignment of the resonance at
30 ppm to the bis(acyl)phosphine. Moreover, we have prepared
spectroscopy (Figure 5) gave some very intriguing results. As
expected, over the course of 8 h silylphosphine 9 is entirely
consumed and only a trace of bis(acyl)phosphine is observed
(δ ) 30). Surprisingly, early in the reaction (i.e., Figure 5a and
5b), the majority of the phosphaalkene signals are observed at
175 ppm. This is significantly downfield from model compounds
Z-7, Z-8, Z-10, and thermal polymer Z-11 (δ ) ca. 150) and
suggests E-isomer formation. As the polymerization progresses,
the E-PdC moieties (δ ) 175) are consumed and the Z-PdC
signals (δ ) 150) become dominant. The detection of E- before
Z-isomers in Becker reactions has been mentioned previously45,51
and implies that the Z-phosphaalkene is formed from the
E-phosphaalkene. In addition, it suggests that [1,3]-silatropy to
form Becker phosphaalkenes is an intramolecular reaction since
the acylphosphine can only adopt the conformation necessary
to form an E- (but not Z-) phosphaalkene. If the silatropic
rearrangement was intermolecular, there would be no preference
for initial formation of the E- over the Z-isomer. Interestingly,
after several hours an insoluble orange/brown solid precipitates
from the reaction mixture (presumably, high molecular weight
Z-11). The THF soluble portion of this precipitate of 11 was
analyzed by UV/vis spectroscopy (λmax ) 394 nm).
31P
MesP(C(O)Ph)2 (δ ) 24.9) as a model for the cross-link/
branch points, and its 31P chemical shift is similar to that
observed in the solid-state NMR spectrum of Z-11.
π-Conjugation in PPPs. In this section, the π-conjugation
in poly(p-phenylenephosphaalkenes) will be assessed by ex-
amining the molecular structures of model compounds for the
polymer and by using UV/vis spectroscopy. This section aims
to show that there is strong evidence of π-conjugation between
the PdC and phenylene groups in these novel molecules and
polymers.
(i) Structural Studies Using X-ray Crystallography. A
coplanar relationship between the vinylene and phenylene groups
in the PPV backbone would maximize the overlap of neighbor-
ing p-orbitals and, therefore, maximize π-conjugation. However,
in PPV, deviations from coplanarity are observed, and short
model oligomers of PPV [i.e., PhHCdCHPh and Ph(HCdCHs
C6H4)nHCdCHsPh; n ) 3] show dihedral angles between the
arylene and vinylene moieties of 3°-10°.52 To gain insight into
the π-conjugation in PPPs and to further investigate their
Additional support for our assertion that polymer 11 is
primarily Z-configured is provided by the 13C{1H} CP MAS
solid-state NMR spectrum (Figure 4). The signal observed at
194 ppm is typical of the chemical shifts of vinylene carbon of
Z-PdC moieties in the model compounds as the E-PdC moieties
are all observed further downfield at ca. 210 ppm (see Table
1). The other signals in the aryl and alkyl regions of the 13C-
{1H} CP MAS NMR spectrum are also consistent with the
assigned structure of Z-11.
It is possible that the partial cross-linking/branching of 11
observed in the thermal polymerization is due to slight
stoichiometric imbalances in the melt [i.e., localized excess of
sC(O)Cl moieties with respect to sP(SiMe3)2]. We speculated
that better monomer mixing in a solution polymerization might
minimize the formation of bis(acyl)phosphine cross-links/
branches. Treating a THF solution of silylphosphine 9 with 1,4-
C6H4(COCl)2 and monitoring the reaction progress by 31P NMR
(51) Yoshifuji, M.; Toyota, K.; Shibayama, K.; Inamoto, N. Chem. Lett. 1983,
1653-1656.
(52) van Hutten, P. F.; Wildeman, J.; Meetsma, A.; Hadziioannou, G. J. Am.
Chem. Soc. 1999, 121, 5910-5918. Kwasniewski, S. P.; Franc¸ois, J. P.;
Deleuze, M. S. J. Phys. Chem. A 2003, 107, 5168-5180. Traetteberg, M.;
Frantsen, E. B. J. Mol. Struct. 1975, 26, 57-68. Bernstein, J. Acta
Crystallogr. 1975, B31, 1268-1271. Hoekstra, A.; Meertens, P.; Vos, A.
Acta Crystallogr. 1975, B31, 2813-2817. Finder, C. J.; Newton, M. G.;
Allinger, N. L. Acta Crystallogr. 1974, B30, 411-415. Robertson, J. M.;
Woodward, I. Proc. R. Soc. London, Ser. A 1937, 162, 568-570
(50) Skotheim, T. A. Handbook of Conducting Polymers; Marcel Dekker: New
York, 1986; Vol. I and II.
9
J. AM. CHEM. SOC. VOL. 128, NO. 27, 2006 8841

A R T I C L E S
Wright et al.
Figure 5. 31P{1H} NMR spectra showing the progress of the reaction of 9 with 1,4-C6H6(COCl)2 in THF. Spectra collected after (a) 15 min, (b) 1 h, (c)
2 h, (d) 4 h, (e) 6 h, and (f) 8 h. * represents hydrolysis product.
Table 2. Crystal Data and Structural Refinement Details for 7, 8,
and 10
feature carbon substituents on both the phosphorus and carbon
atoms of the PdC bond (12,48 13,53 14,54 15,55 16,40b 17,56 and
1857). To our knowledge, two other 1,4-arylene-bridged bis-
(phosphaalkene)s have previously been crystallographically
characterized (1857 and 1966).
7
8
10
formula
FW
crystal system
space group
color
a (Å)
b (Å)
C
19H25OPSi
C30H40O2P2Si2
550.74
monoclinic
P21/n
C
32H44O2P2Si2
328.45
monoclinic
P21/n
yellow
7.806(1)
16.799(2)
14.801(2)
90.0
101.780(10)
90.0
1900.0(4)
4
578.82
triclinic
P1h
yellow
yellow
9.769(1)
9.0886(8)
17.490(2)
90.0
94.19(1)
90.0
8.1006(7)
12.280(1)
17.181(2)
101.513(5)
93.354(4)
98.714(4)
1648.4(3)
2
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
1548.7(3)
2
T (K)
173(2)
1.148
173(1)
1.181
173(1)
1.166
d
calcd (Mg m-3
)
crystal size (mm3) 0.50 × 0.50 × 0.10 0.30 × 0.20 × 0.10 0.35 × 0.20 × 0.10
no. reflns
45 391
32 704
3671
15 587
6806
no. unique reflns 4456
R(int)
0.0330
0.032
3671/168
0.048
0.138
1.05
0.055
6806/353
0.042
0.103
0.92
reflection/params 4456/204
R1 [I > 2σ(I)]a
wR2 [all data]b
GOF
0.035
0.108
1.123
2
2
2
a R1 ) Σ ||Fo| - |Fc||/|Fo|. b wR2 ) [Σ(w(Fo - Fc )2)/Σw(Fo )2]1/2
.
structural features and bonding, the molecular structures of Z-7,
Z-8, and Z-10 (Figures 1, 2, and 3, respectively) were determined
by X-ray crystallography. A summary of data collection and
refinement parameters is listed in Table 2, and the bond lengths
and angles for these and other phosphaalkenes pertinent to this
discussion are summarized in Table 3. A survey of the
Cambridge Crystallographic Database (CCD) for possible
molecular models for the PPPs reported herein revealed 22
Becker-type phosphaalkenes.40b,48,53-65 Of these, just seven
The PdC bonds in model compounds 7, 8, and 10 are
comparable in length [avg 1.701(4) Å] and are similar to those
found in the Becker phosphaalkenes 12-18 [avg 1.690(6) Å].
This places these molecules near the upper limit of a typical
PdC bond length [1.61-1.71 Å].35 The bond angles at
phosphorus for 7, 8, and 10 (avg 104°) are consistent with a
high degree of p-character for the PsC σ-bonds and a high
(53) Manz, B.; Bergstasser, U.; Kerth, J.; Maas, G. Chem. Ber. 1997, 130, 779-
788.
(54) Haber, S.; Schmitz, M.; Bergstasser, U.; Hoffman, J.; Regitz, M. Chem.s
Eur. J. 1999, 5, 1581-1589.
(55) Appel, R.; Folling, P.; Schuhn, W.; Knoch, F. Tetrahedron Lett. 1986, 27,
1661-1664.
(56) Appel, R.; Hunnerbein, J.; Knoch, F.; Nieger, M. J. Organomet. Chem.
1988, 346, 379-384.
(57) Knoch, F.; Appel, R.; Wenzel, H. Z. Krystallogr. 1995, 210, 224-224.
(58) Appel, R.; Barth, V.; Knoch, F. Chem. Ber. 1983, 116, 938-950.
(59) Weber, L.; Reizig, K.; Boese, R.; Polk, M. Angew. Chem., Int. Ed. 1985,
24, 604-605.
(63) Appel, R.; Niemann, B.; Schuhn, W.; Knoch, F. Angew. Chem., Int. Ed.
Engl. 1986, 25, 932-932.
(64) Appel, R.; Fo¨lling, P.; Josten, B.; Schuhn, W.; Wenzel, H. V.; Knoch, F.
Z. Anorg. Allg. Chem. 1988, 556, 7-22.
(60) Weber, L.; Reizig, K.; Frebel, M.; Boese, R.; Polk, M. J. Organomet. Chem.
1986, 306, 105-114.
(65) Gru¨nhagen, A.; Pieper, U.; Kottke, T.; Roesky, H. W. Z. Anorg. Allg. Chem.
1994, 620, 716-722.
(61) Weber, L.; Reizig, K.; Boese, R.; Polk, M. Organometallics 1986, 5, 1098-
1103.
(66) Shah, S.; Concolino, T.; Rheingold, A. L.; Protasiewicz, J. D. Inorg. Chem.
2000, 39, 3860-3867.
(62) Appel, R.; Porz, C.; Knoch, F. Chem. Ber. 1986, 119, 2748-2755.
9
8842 J. AM. CHEM. SOC. VOL. 128, NO. 27, 2006

Phosphorus Copies of Poly(p-phenylenevinylene) (PPV)
A R T I C L E S
Table 3. Comparison of Important Structural Data
CPdCC
angle between
planes [deg]
P
bond
[Å]
d
C
C
s
angle
[deg]
P
d
C
torsion
angle
[deg]
b
c
compd
φP
φC
reference
7
1.7081(12) 65.6(2) 27.8(2) 104.20(6)
178.1(1) this work
179.1(1) this work
8a (P1) 1.700(2)
62.18(2) 16.5(2) 106.31(9)
(P2)
10
1.696(2)
66.67(2) 26.55(2) 104.19(9) -176.2(1) this work
1.7014(19) 59.88(8) 25.54(9) 102.94(9)
179.9(1) this work
12
18
19
1.686(2)
1.683(2)
1.676(2)
81.6(3) 54.8(2) 103.9(2) -175.2(1) 48
56.8(2) N/Ad
104.6(2) -174.6(1) 57
69.9(2) 21.8(2) 101.4(2)
172.07(2) 66
a The PdC units are unique in 8. b This is the angle between the planes
defined by the 6-atom P-substituted aromatic ring and the 5-atom plane
containing the PdC bond, calculated using ConQuest. c This is the angle
between the planes defined by the 6-atom C-substituted aromatic ring and
the 5-atom plane containing the PdC bond, calculated by ConQuest. d Due
to the alkyl substituent on the carbon atom, φC cannot be defined.
degree of s-character for the lone pair. The sum of the bond
angles at the PdC carbon and the CsPdCsC torsion angles
in 7, 8, and 10 are as expected for a planar double bonded
system and do not deviate significantly from 360° and 180°,
respectively.
The angles between the planes of the PdC bond and the aryl
substituents are most relevant to the structural assessment of
the π-conjugation in phosphaalkenes 7, 8, and 10 in the solid
state. The degree of π-conjugation is proportional to the cosine
of the angle (φ) between planes (i.e., φ ) 90° f no π-conjuga-
tion). The dihedral angles between the PdC plane and the bulky
aryl P-substituent for each of the model compounds [7 φP )
65.6(2)°; 8 φP ) 62.18(2)°, 66.67(2)°; 10 φP ) 59.88(8)°] does
not preclude π-conjugation between these moieties but will
prevent efficient delocalization of the pi-system. For comparison,
Figure 6. UV/vis spectra (ca. 10-5 M THF) of (a) E/Z-model compounds
(4, 5, 6) and PPP (1) and (b) all Z-model compounds (7, 8, and 10) and the
THF soluble portion of PPP (11).
stilbene derivatives with a Mes substituent (i.e., 20, φMes
)
76°;67 21, φMes ) 6268) exhibit similar dihedral angles and are
much larger than those found in trans-stilbene (φPh ) 3°-10°).
Other trans-aryl substituted phosphaalkenes also show signifi-
cant twist angles for the P-substituents [Z-12: φP ) 81.6(2)°;
Z,Z-18: φP ) 56.8(2)°; E,E-19: φP ) 69.9(2)°], but only Z-12,
possessing the extremely bulky Mes* group, approaches 90°
(i.e., no π-conjugation).
comparison, the structurally related mono(phosphaalkene) Z-12
[φC ) 54.8(2)°] shows a much larger angle and is less
π-conjugated. The bis(phosphaalkene) E,E-19 [φC ) 21.8°]
exhibits a small twist angle that is comparable to the φC for 7,
8, and 10 and suggests a similar degree of π-conjugation.
In conclusion, the observed angles between the PdC and
arylene planes in model phosphaalkenes Z-7, Z,Z-8, and Z,Z-
10 suggest that PPP will show properties consistent with
π-conjugation. Unfortunately, it is not possible to ascertain to
what extent the structural features are determined by electronics
(i.e., conjugation effects) versus crystal packing effects. In
solution, it may be possible to access more conjugated planar
structures at least in excited states.
(ii) Electronic Properties Using UV/Vis Spectroscopy. For
extended π-conjugated systems, a red shift in λmax of the π-π*
band is observed as the length of the conjugation pathway is
increased.69,70 Therefore, if the PdC bond and arylene unit are
π-conjugated, the λmax should increase from mono(phospha-
alkene)s to bis(phosphaalkene)s to the corresponding PPP.
Previous studies of a series of model compounds of PPP (2)
The angles between the planes of the PdC bond and the
sterically unhindered C-substituent [7 φC ) 27.8(2)°; 8 φC )
16.5(2)°, 26.55(2)°; 10 φC ) 25.54(9)°] are much smaller
enabling greater π-conjugation between these moieties. For
(67) Brook, A. G.; Chatterton, W. J.; Sawyer, J. F.; Hughes, D. W.; Vorspohl,
K. Organometallics 1987, 6, 1246-1256.
(68) Schmittel, M.; Keller, M.; Burghart, A. J. Chem. Soc., Perkin Trans. 2
1995, 2327-2333.
(69) Meier, H.; Stalmach, U.; Kolshorn, H. Acta Polym. 1997, 48, 379-384.
(70) Mu¨llen, K., Wegner, G., Eds. Electronic Materials. The Oligomer Approach;
Wiley-VCH: New York, 1998.
9
J. AM. CHEM. SOC. VOL. 128, NO. 27, 2006 8843

A R T I C L E S
Wright et al.
by Smith and Protasiewicz41 and investigations of ortho, meta,
and para-22,71-74 23, and 2475,76 have provided strong evidence
that phosphaalkenes are capable of long-range electronic com-
munication in π-systems. The UV/vis spectra for the phos-
phaalkenes prepared in this study are shown in Figure 6, and
the λmax data are tabulated in Table 1. A red shift is observed
in the absorbance maximum assigned to the π-π* band as the
chain length is increased for the E/Z-phosphaalkenes [4, 310
nm; 5, 314 nm; 6, 332 nm; 1, 338 nm] and the Z-phosphaalkenes
[7, 324; 8, 388 nm; 10, 337 nm; 11, 394 nm]. For comparison,
the λmax for Z-11 (394 nm) is less than that for E-PPV (426
nm)77 and PPP (E-2, 445 nm).39 Importantly, the magnitude of
the red shift is greater for the all Z-PPP (∆λmax ) 70 nm for
11 vs 7) than for the mixed E/Z-PPP (∆λmax ) 28 nm for 1 vs
4) and E-2 (∆λmax ) 0 nm vs 26). Interestingly, the red shifts
observed for known PPPs are smaller than the red shift for
E-PPV (∆λmax ) 119 nm vs E-stilbene). The smaller red shift
for PPPs is likely a consequence of twisting in the backbone
caused by the C6Me4 moieties. The incorporation of some C6-
Me4 groups into PPV is known to lead to a blue shift of 20-
30 nm.77,78
electronically isolated no significant bathochromic shift in the
λmax for these pairs of compounds would be expected. Neverthe-
less, the longer wavelength absorbances observed for bis-
(phosphaalkene)s with C6H4-spacers over those with C6Me4-
spacers (∆λmax ) 18 nm for 6 vs 5; ∆λmax ) 51 nm 8 vs 10)
suggest more effective π-conjugation through the less sterically
bulky spacer. A similar observation was also made with bis-
(phosphaalkene)s 25 and 19.41,79 In preliminary luminescence
measurements a weak emission is detected at 445 nm when THF
solutions of polymer 1 are exited at 310 nm.
Summary
We have synthesized a new class of π-conjugated polymer,
poly(p-phenylenephosphaalkene) (PPP), a phosphorus copy of
poly(p-phenylenevinylene) (PPV). The formal replacement of
CdC bonds by the isolobal PdC bonds extends the phosphorus-
carbon analogy to polymer science. Importantly, we have
discovered that the positioning of the bulky substituent required
to kinetically stabilize the PdC bond provides a measure of
stereochemical control. The more highly conjugated Z-isomer,
which features the aryl substituents in a trans arrangement to
one another, is formed selectively when the ortho-dimethyl-
substituted arene is placed on phosphorus while E/Z-mixtures
are observed otherwise. Strong evidence for π-conjugation
between the PdC and phenylene groups in PPPs has been
gathered from UV/vis spectroscopy and X-ray crystallography
on molecular model compounds. Specifically, the molecular
structures obtained for mono- and bis(phosphaalkene)s show
small twist angles between the PdC plane and unsubstituted
arenes (16°-26°) and larger twist angles between the PdC plane
and methyl-substituted arenes (59°-67°). A remarkable 70 nm
red shift is observed for a THF soluble fraction of Z-PPP when
compared with a mono(phosphaalkene) model compound.
Future work will focus on preparing soluble Z-PPPs and gaining
further insight into the electronic properties of this new class
of phosphorus macromolecule.
Acknowledgment. This work was supported by the Natural
Sciences and Engineering Research Council (NSERC) of
Canada, the Canada Foundation for Innovation (CFI), and the
British Columbia Knowledge and Development Fund (BCKDF).
V.W. is grateful to the Laird Endowment at UBC for a graduate
fellowship. We would like to thank Prof. Colin Fyfe for the
use of the solid state NMR instrumentation and Profs. Mark
MacLachlan and Michael Wolf for the use of UV/vis and IR
equipment.
Although the C6Me4 group partially impedes π-conjugation,
the modest red shifts observed between the bis- and mono-
(phosphaalkene)s (∆λmax ) 4 nm for 5 vs 4; ∆λmax ) 13 nm
for 10 vs 7) suggest that there is still π-conjugation through
the central C6Me4 ring in PPPs. If the PdC bonds were
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8844 J. AM. CHEM. SOC. VOL. 128, NO. 27, 2006