Synthesis and solvatochromism of some dipolar aryl-phosphonium and -phosphine oxide systems

Article abstract of DOI:10.1016/S0022-328X(00)00085-1

The synthesis is reported of a series of dipolar arylphosphonium salts bearing ferrocenylethenyl, 2-thienylethenyl, 4-dimethylaminophenylethenyl, or (4-dimethylaminophenyl)butadienyl electron-donor centres, together with a study of their course of alkaline hydrolysis, which provides a convenient synthetic route to related dipolar phosphine oxides. The phosphonium salts exhibit a modest degree of negative solvatochromism, whereas the related phosphine oxides show a small positive solvatochromic effect. In the case of the ferrocenyl systems, the electronic effects of the phosphorus acceptor group on the ferrocene unit have been studied by cyclic voltammetry.

Full text of DOI:10.1016/S0022-328X(00)00085-1

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 601 (2000) 293–298
Synthesis and solvatochromism of some dipolar aryl-phosphonium
and -phosphine oxide systems
David W. Allen * , Josephine P. Mifflin, Peter J. Skabara
Di6ision of Chemistry, Sheffield Hallam Uni6ersity, Pond Street, Sheffield S1 1WB, UK
Received 13 December 1999; received in revised form 26 January 2000
Abstract
The synthesis is reported of a series of dipolar arylphosphonium salts bearing ferrocenylethenyl, 2-thienylethenyl, 4-dimethyl-
aminophenylethenyl, or (4-dimethylaminophenyl)butadienyl electron-donor centres, together with a study of their course of
alkaline hydrolysis, which provides a convenient synthetic route to related dipolar phosphine oxides. The phosphonium salts
exhibit a modest degree of negative solvatochromism, whereas the related phosphine oxides show a small positive solvatochromic
effect. In the case of the ferrocenyl systems, the electronic effects of the phosphorus acceptor group on the ferrocene unit have
been studied by cyclic voltammetry. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Phosphonium salt; Phosphine oxide; Solvatochromism; Ferrocenyl; Cyclic voltammetry
1. Introduction
tron-deficient centre, to which is bonded a polarisable
p-system that carries an electron-donating substituent.
We have embarked on a study of the solva-
tochromism of dipolar compounds of the heavier Main
Group 15 elements. Compounds that are solva-
tochromic are also of potential interest in that they may
also exhibit non-linear optical properties under appro-
priate circumstances. In recent papers, we have de-
scribed the synthesis and solvatochromic properties of a
series of phosphonioaryl-imidazolide and phospho-
nioaryl-phenolate betaines [6,7], and an extension of
these studies to the analogous compounds of arsenic
and antimony [8]. In this paper, we report the synthesis
of a series of dipolar phosphonium salts 5–8, and a
study of their course of alkaline hydrolysis, which
provides a convenient synthetic route to the related
There is growing interest in the opto-electronic prop-
erties of organic derivatives of the heavier Main Group
15 elements, notably those of phosphorus. Recent pa-
pers have reported the synthesis of the dipolar systems
1 [1], 2 [2,3], 3 [4], and 4 [5], which have proved to be
of interest in connection with their non-linear and other
optical properties. All of these systems involve either a
phosphonium or phosphine oxide moiety as the elec-
* Corresponding author. Tel.: +44-114-2253000; fax: +44-144-
2253066.
E-mail address: d.w.allen@shu.ac.uk (D.W. Allen)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00085-1

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D.W. Allen et al. / Journal of Organometallic Chemistry 601 (2000) 293–298
dipolar phosphine oxides 3, 9, 10 and 11. The solva-
tochromism of the phosphonium salts and phosphine
oxides has also been investigated, and, in the case of the
ferrocenyl systems 7 and 10, the electronic effects of the
phosphorus acceptor group on the ferrocene unit have
been studied by cyclic voltammetry.
products. However, in these reactions, it is clear that
the remote electron-donating substituent must desta-
bilise the forming carbanion relative to phenyl such
that loss of phenyl is favoured. There is clearly a
statistical effect here as well in that three phenyl groups
are available for cleavage in relation to the single
substituted phenyl group. Traces of the competitive
cleavage products, triphenylphosphine oxide and the
hydrocarbons (13, X=H) were detected, but the de-
sired phosphine oxides were isolated cleanly and in
good yield.
As expected, introduction of the phosphonium centre
shifted the visible absorption bands of the stilbene-like
systems (13, X=Br) towards longer wavelength, the
colour of the salt depending on the nature of the donor
group present. Whereas the thienylethenyl salt 8 was
isolated as a pale yellow powder, the dimethyl-
aminoaryl salts 5 and 6 were orange and bright red,
respectively, and were noticeably fluorescent in solution
in dichloromethane. The ferrocenyl salt 7 was also red.
The phosphonium salts exhibited negative solva-
tochromism, but to a much smaller extent than the
phosphonioiminophenolate betaines (14, X=Cl, Br, or
Ph) [7], or the phosphoniobenzimidazolide 15 [6]. Thus,
the ferrocenylethenyl system 7 showed umax=336 and
486 nm in methanol compared with 340 and 498 nm in
dichloromethane. A similar range was observed for the
dimethylaminophenyl systems 5 and 6, the stilbene 5
having umax=406 nm in methanol and 422 nm in
dichloromethane, and the dienyl system 6 having
umax=422 nm in methanol and 442 nm in
dichloromethane. The 2-thienylethenyl salt 8 showed an
even smaller solvatochromic effect, having umax=352
nm in methanol and 358 nm in dichloromethane. The
extent of negative solvatochromism observed in these
salts is consistent with a small degree of intramolecular
charge transfer from the donor centre through the
p-system to the ring bearing the phosphonium group,
as in 16, the less polar excited states, e.g. 16B, being of
higher energy in the more polar solvents, which tend to
stabilise the more polar ground state (16A) to a greater
extent. Clearly, the extent of charge transfer is smaller
for the thienyl system than for ferrocenyl and 4-
dimethylaminophenyl.
2. Results and discussion
The discovery of the non-linear optical properties of
4-dimethylamino-4%-nitrostilbene (DANS) (12) [9,10]
has stimulated a wide range of studies of related polar-
isable dipolar systems that bear a potential donor cen-
tre linked to an electron-withdrawing group, via a
polarisable p-system. Following our earlier work on
solvatochromic heavier Group 15 compounds, we de-
cided to explore the synthesis and solvatochromism of a
series of molecules related to DANS, in which the
electron-withdrawing group is either a phosphonium
cation or a phosphine oxide moiety, and the electron-
donating systems include ferrocenyl and 2-thienyl
groups.
The arylphosphonium salts 5–8 were prepared by the
Horner reaction [11] in which the appropriate bro-
moarene (13, X=Br) was heated with triphenylphos-
phine and anhydrous nickel(II) bromide in benzonitrile.
Conversion of the phosphonium salts to the phosphine
oxides 3, 9, 10 and 11 was achieved by alkaline hydrol-
ysis, a well-established reaction that proceeds with
cleavage of the group most stable as a developing
carbanion, which is then protonated to form the related
hydrocarbon [12–14]. In the case of the above salts,
there is clearly a choice of potential aryl carbanion
between phenyl and arylethenyl substituted phenyl (13,
X=lone pair), which could result in a mixture of
In contrast, the related phosphine oxides 3 and 10
show a small degree of positive solvatochromism,
reflecting the lack of formal positive charge (and
smaller electron-withdrawing power) of the diphenyl-
phosphinyl group compared with the formally positive
triphenylphosphonio group. The solvatochromic prop-
erties of 3 have been described previously [4], this

D.W. Allen et al. / Journal of Organometallic Chemistry 601 (2000) 293–298
295
compound exhibiting a small degree of positive solva-
tochromism, having umax=367 nm in cyclohexane and
383 nm in DMSO. This is consistent with charge trans-
fer from nitrogen to the phosphorus centre in the
excited state, which is then more polar than the ground
state. This compound has also been shown to exhibit a
significant second-order non-linear optical effect [4].
The ferrocenylethenyl phenylphosphine oxide 10 also
exhibited a small degree of positive solvatochromism,
exhibiting a long-wavelength band at 439 nm in cyclo-
hexane, at 466 nm in dichloromethane, and at 472 nm
in DMSO, consistent with electron transfer from the
ferrocenyl system to the phosphorus group. In contrast,
the solvatochromic properties of the related dienyl sys-
tem 9, and the thienyl system 11 were almost non-exis-
tent, implying that the extent of charge displacement
towards the phosphine oxide unit is much smaller.
Thus, the dienyl system 9 showed a visible absorption
band at 396 nm in both dichloromethane and DMSO.
Similarly, the thienyl system 11 absorbed at 338 nm in
dichloromethane, and 340 nm in DMSO. Solubility
problems precluded the use of less polar solvents for
these compounds. The similarity in solvatochromic
properties of compound 10 to those of 3 would suggest
that the former might also display significant non-linear
optical properties. The synthetic route reported in this
paper provides a simple approach to a range of dipolar
p-bridged systems which provides scope for consider-
able variation in the nature of the phosphorus-contain-
ing electron-withdrawing group, including chiral
centres, which would enhance the likelihood of encoun-
tering significant solid state non-linear optical proper-
ties.
2.1. Electrochemistry
The redox properties of ferrocenyl compounds 7 and
10 were studied by cyclic voltammetry in acetonitrile
solution, using unsubstituted ferrocene as internal stan-
dard (see Fig. 1 and Table 1). In each case, a reversible
oxidation process is observed, which represents the
transformation of the ferrocene unit to the ferrocenium
species. The voltammogram for the salt 7 shows an
additional irreversible peak at +885 mV; this process
represents the oxidation of the bromide species and is
irreversible due to coupling of the radical species to
form bromine.
In comparison to ferrocene, both E11/2 processes are
shifted anodically (56 mV for 7 and 39 mV for 10), due
to the electron-withdrawing nature of the phosphorus-
containing substituents that decrease the electron re-
leasing ability of the ferrocene unit. Notably, the shift is
greater in derivative 7, which bears the stronger elec-
tron-withdrawing unit. However, if we consider the
nucleophilic constants (|p) of the phosphonium and
phosphine oxide groups (0.53 for P(O)Ph2 and 1.18 for
P+(Me)Ph2) [15], we would expect the oxidation of the
ferrocene moiety in 7 to occur at an even higher
potential. This hypothesis can be made on the basis of
a similar study utilising more ‘traditional’ electron with-
drawing groups, in which ferrocene derivatives 17 [16]
and 18 [17], bearing formyl and dicyanovinyl groups,
respectively, have been investigated for their solva-
tochromic and electrochemical properties (in di-
chloromethane, with ferrocene as internal reference; see
Table 1) [17].
Fig. 1. Cyclic voltammograms of compounds 7 (—) and 10 (- - -) in
MeCN vs. Ag/AgCl, Pt wire counter electrode, Pt disk working
electrode, at 20°C, 0.1 M Bu4NPF6 supporting electrolyte, ca. 0.001
M substrate, 200 mV s−1 scan rate with iR compensation.
Table 1
Cyclic voltammetric data for ferrocene, 7, 10, 17 and 18, and elec-
tronic absorption maxima (obtained in dichloromethane) correspond-
ing to intramolecular charge transfer
Compound
E11/2 (mV)
E2 (mV)
E11/2 shift
umax (nm)
from FcH
Ferrocene
(FcH)
7
10
17 [17]
18 [17]
443 a
–
–
–
499 ep
482 a
306 b
334 b
885 a
–
–
–
56
39
42
70
498
466
480
535
From the values of the nucleophilic constants for the
substituents CHO (|p=0.42) and CHꢀC(CN)2 (|p=
0.84), it is not surprising that the greater anodic shift
for the ferrocene/ferrocenium redox couple is observed
in compound 18. The same analogy can be made in the
electronic absorption spectra of the two compounds —
a Obtained in acetonitrile.
b Obtained in dichloromethane.

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D.W. Allen et al. / Journal of Organometallic Chemistry 601 (2000) 293–298
relative to the formyl derivative 17, the longest wave-
length maximum (corresponding to intramolecular
charge-transfer) is shifted bathochromically in 18 by 55
nm.
cooled, solvent extraction was carried out with
dichloromethane and aqueous KBr (10%). The organic
layer was dried (MgSO4) and the solvent was evapo-
rated in vacuo. The remaining benzonitrile mixture was
poured into diethyl ether and the solid precipitated was
triturated many times with fresh diethyl ether. On
filtering, the solid was found to be very hygroscopic
and, therefore, the salt was purified and isolated as a
red crystalline solid by column chromatography with
an eluting solvent of dichloromethane–methanol. The
solid was dried under reduced pressure. Yield: 0.38 g
(14%); m.p.\75°C (dec.). 31P NMR (CDCl3): 22.42
Clearly, the dicyanovinyl group is a powerful elec-
tron-withdrawing species; however, |p for a phospho-
nium group is greater than that of the former [15].
Since the difference in the nucleophilic constants for the
formyl and phosphine oxide groups is quite small
(D|p=0.11), we would expect Dumax and D|p between
derivatives 7 and 10 to be greater than the correspond-
ing values for 17 and 18. Remarkably, the reverse is
true, showing that under the experimental conditions,
the phosphonium species is a weaker electron-with-
drawing group than the dicyanovinyl fragment. These
results are in direct contrast with the values of the
nucleophilic constants for the respective acceptor
groups and may be explained by the inability of the
phosphonium centre to act as a p-acceptor as a result of
the now recognised minimal d-orbital involvement in
the bonding in potentially five-covalent, four-coordi-
nate Main Group 15 compounds [18].
1
ppm. H-NMR (CDCl3): 4.16 (s, 5H), 4.39 (s, 2H), 4.53
(s, 2H) (cyclopentadienyl), 7.0 (centre of AB pattern,
J
AB=16.1 Hz, CHꢀCH), 7.52–7.92 (m, 19H, aromatic)
ppm. FABMS: Calc. for C36H30FeP cation: 549.09376.
Found: 549.09369 (0.00 ppm).
3.3. 1-(4-Bromophenyl)-2-(2-thienyl)ethene (13,
Ar=2-thienyl, X=Br)
To a solution of (2-thienylmethyl)triphenylphos-
phonium bromide (9.79 g, 0.022 mol) and 4-bromoben-
zaldehyde (4 g, 0.022 mol) in dry THF (100 ml) was
added potassium tertiary butoxide (3.4 g, 0.03 mol),
and the reaction mixture stirred for 4 h. The reaction
mixture was poured into water (200 ml) and extracted
with diethyl ether (3×50 ml). The yellow organic layer
was dried (MgSO4). The crude solid was washed with
methanol until the washings went from pale yellow to
colourless to afford a pale yellow solid. Yield: 1.66 g
(28.5%); m.p. 144–146°C. 1H-NMR (CDCl3): 6.83–
7.49 (m, 9H, aromatic and olefinic) ppm. MS (EI) [M+]
264 and 266. Anal. Calc. for C12H9BrS: C, 54.36; H,
3.42. Found: C, 54.52; H, 3.50%.
3. Experimental
1
31P- and H-NMR studies were carried out using a
Bruker AC 250 FTNMR spectrometer. Low-resolution
mass spectra were recorded on a VG Micromass 7070F
instrument. High-resolution FABMS determinations
were carried out by the EPSRC Mass Spectrometry
Service, University of Wales, Swansea. Cyclic voltam-
metry was performed on a BAS CV50W voltammetric
analyser, with iR compensation, using anhydrous ace-
tonitrile as the solvent, Ag/AgCl as the reference elec-
trode and platinum wire and disk as the counter and
working electrodes, respectively. All solutions were de-
gassed (N2) and contained the substrate in concentra-
tions of ca. 10–3 M, together with Bu4NPF6 (0.1 M) as
the supporting electrolyte. The scan rate was 300 mV
3.4. 1-(2-Thienyl)-2-(4-triphenylphosphoniophenyl)-
ethene bromide (8)
The bromo compound (13, Ar=2-thienyl, X=Br)
(1.5 g, 0.0057 mol) was heated under reflux in benzoni-
trile (50 ml) with triphenylphosphine (3 g, 0.01 mol)
and nickel(II) bromide (0.63 g, 0.0029 mol) for 8 h
under nitrogen to form a bottle green reaction mixture.
The mixture was poured into aqueous KBr (10%) (200
ml) and the product extracted with dichloromethane
(3×50 ml). The yellow organic layer was dried
(MgSO4) and the solvent was evaporated in vacuo. The
remaining benzonitrile mixture was poured into diethyl
ether and triturated several times with fresh diethyl
ether. The solid was filtered to afford a pale yellow
powder. Yield: 1.18 g (60%); m.p. 310–312°C (dec.).
31P-NMR (CDCl3): 22.35 ppm. 1H-NMR (CDCl3):
6.50–8.30 (m, 24H, aromatic and olefinic) ppm.
FABMS: Calc. for C30H24PS [M+] cation): 447.133636.
Found 447.133450 (0.4 ppm). Anal. Calc. for
s−1
.
3.1. 1-Ferrocenyl-2-(4-bromophenyl)ethene (13,
Ar=ferrocenyl, X=Br)
This was prepared as described in the literature [19].
3.2. 1-Ferrocenyl-2-(4-triphenylphosphoniophenyl)ethene
bromide (7)
The bromophenylalkene (13, Ar=ferrocenyl, X=
Br) (1.57 g, 0.0043 mol) was heated under reflux with
triphenylphosphine (1.69 g, 0.0065 mol) and nickel(II)
bromide (0.47 g, 0.0021 mol) in benzonitrile (37 ml) for
4 h under nitrogen. The solution remained a deep red in
colour instead of turning the usual bottle green. Once

D.W. Allen et al. / Journal of Organometallic Chemistry 601 (2000) 293–298
297
C30H24BrPS: C, 68.31; H, 4.59. Found: C, 68.02; H,
4.60%.
3.8. 1-(4-Dimethylaminophenyl)-4-(4-triphenyl-
phosphoniophenyl)-1,3-butadiene bromide (6)
3.5. 1-(4-Bromophenyl)-2-(4-dimethylaminophenyl)-
ethene (13, Ar=4-dimethylaminophenyl, X=Br)
The diene (13, Ar=4-dimethylaminophenylethenyl,
X=Br) (2 g, 0.006 mol) was heated under reflux in
benzonitrile (40 ml) with triphenylphosphine (2.36 g,
0.009 mol) and nickel(II) bromide (0.066 g, 0.003 mol)
for 4 h under nitrogen. The cooled reaction mixture
was poured into aqueous potassium bromide (10% w/v)
(200 ml) and extracted with dichloromethane (3×50
ml). The combined organic layers were washed with
aqueous potassium bromide, dried (MgSO4) and the
solvent was removed in vacuo. After repeated tritura-
tion of the oil with diethyl ether, the filtered solid was
found to be hygroscopic, and so was purified by flash
chromatography using MeOH–CH2Cl2 (1:9) as the
eluting solvent. A bright red crystalline solid was ob-
tained. Yield: 3.43 g (97%); m.p.\330°C (dec.). 31P-
This was prepared as described by Lequan et al. [20].
3.6. 1-(4-Dimethylaminophenyl)-2-(4-phenyl-
phosphoniophenyl)ethene bromide (5)
The bromostilbene (13, Ar=4-dimethylaminophenyl,
X=Br) (3 g, 0.01 mol) was heated under reflux with
triphenylphosphine (3.93 g, 0.015 mol) and nickel(II)
bromide (1.09 g, 0.005 mol) in benzonitrile (70 ml) for
4 h under nitrogen. The cooled reaction mixture was
poured into aqueous KBr (10% w/v) (200 ml) and
extracted with dichloromethane (3×50 ml). The com-
bined organic layers were washed with KBr (aq), dried
(MgSO4), and the solvent was evaporated in vacuo.
After repeated trituration of the oil with diethyl ether, a
rusty–orange solid was obtained, which was dried un-
der vacuum. Yield: 4.54 g (94%); m.p.\70°C (dec.).
1
NMR (CDCl3): 22.29 ppm. H-NMR (CDCl3): 2.95 (s,
6H, NMe2), 6.62–6.80 (m, 4H, olefinic), 7.34–7.92 (m,
23H, aromatic) ppm. 13C-NMR (CDCl3): 40.59, 112.93,
118.93, 128.54, 131.04, 131.25, 134.57, 134.72, 136.07
ppm. FABMS: required for [M+] cation C36H33NP:
510.235064. Found: 510.235002 (0.1 ppm). Anal. Calc.
for C36H33BrNP·H2O: C, 71.05; H, 5.80; N, 2.30.
Found: C, 70.86; H, 5.72; N, 2.21%.
1
31P-NMR (CDCl3): 22.25 ppm. H-NMR (CDCl3): 2.95
(s, 6H, NMe2), 6.65–7.86 (m, 25H, aromatic and
olefinic) ppm. 13C-NMR (CDCl3): 40.55, 112.13,
112.43, 117.53, 118.96, 121.1, 124.2, 127.76, 127.76,
127.96, 129.02, 130.32, 131.04, 131.23, 134.54, 134.69,
135.31, 136.06, 146.34, 151.35 ppm. FABMS: Calc.
for [M+] cation: C34H31NP: 484.219414. Found:
484.218048 (2.8 ppm). Anal. Calc. for C34H31BrNP·
2H2O: C, 68.00; H, 5.87; N, 2.33. Found: C, 67.84; H,
5.30; N, 2.32%.
3.9. 1-(4-Diphenylphosphinoylphenyl)-2-
( ferrocenyl)ethene (10)
Phosphonium salt 7 (0.81 g, 1.6 mmol) was heated
under reflux in ethanol (3 ml) for 3 h with sodium
hydroxide (1 M, 1.5 ml). After several hours the colour
of the reaction mixture turned from red to orange–
brown. The cooled reaction mixture was poured into
water and extracted with dichloromethane (3×20 ml)
and washed with water. The combined organic layers
were dried (MgSO4), and the solvent evaporated in
vacuo to afford the crude phosphine oxide as an orange
powder. Yield: 0.4 g (52%); m.p. 154–157°C. 31P-NMR
3.7. 1-(4-Bromophenyl)-4-(4-dimethylaminophenyl)-
1,3-butadiene (13, Ar=4-dimethylaminophenylethenyl,
X=Br)
To
a solution of (4-bromobenzyl)triphenylphos-
phonium bromide (16.6 g, 0.032 mol) and 4-dimethyl-
aminocinnamaldehyde (5.68 g, 0.032 mol) in dry THF
(120 ml) at room temperature was added potassium
tertiary butoxide (4 g, 0.035 mol), and the resulting
solution left to stir overnight. The reaction mixture was
poured into a large volume of water, and the solid
filtered under suction. The crude solid was recrystallised
from dichloromethane, and washed with a small
amount of cold acetone to afford a pale yellow solid
(one isomer only, from GC–MS, assumed to be trans–
1
(CDCl3): 29.02 ppm. H-NMR (CDCl3): 4.11 (s, 5H),
4.33 (s, 2H), 4.49 (s, 2H) (cyclopentadienyl), 6.86 (cen-
tre of AB pattern, JAB=16.25 Hz, CHꢀCH), 7.40–8.2
(m, 14H, aromatic) ppm. MS (EI) Calc. for
C30H25 54FeOP: 486.10391. Found: 486.10211 (3.7 ppm,
7.19%). Calc. for C30H25 56FeOP: 488.09924. Found:
488.10001 (−1.6 ppm, 100%). Calc. for C30H25 57FeOP:
489.09970. Found: 489.10274 (−6.2 ppm, 35.97%).
1
trans). Yield: 2.1 g (20%); m.p. 239–240°C. H-NMR
3.10. 1-(4-Diphenylphosphinoyl)-2-(2-thienyl)ethene
(11)
(CDCl3): 2.99 (s, 6H, NMe2), 6.46–6.95 (m, 4H,
olefinic), 7.28–7.45 (m, 8H, aromatic) ppm. MS (EI)
required for [M+] C18H18 79BrN: 327.06226. Found:
327.06000 (6.9 ppm). Anal. Calc. for C18H18BrN: C,
65.86; H, 5.53; N, 4.27. Found: C, 65.74; H, 5.53; N,
4.21%.
Analogously to the procedure for 10, salt 8 (0.5 g,
0.95 mmol) was heated under reflux in ethanol with
sodium hydroxide (1 M, 2 ml) for 2 h. No colour
change was observed during the reaction. After solvent

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D.W. Allen et al. / Journal of Organometallic Chemistry 601 (2000) 293–298
extraction a pale yellow solid was obtained. Yield: 0.14
g (27%); m.p. 156–160°C. 31P-NMR (CDCl3): 28.63
ppm. 1H-NMR (CDCl3): 6.95–7.73 (m, 17H, aromatic),
7.18 (CHꢀCH, JAB=16.1 Hz) ppm. MS (EI) Calc. for
C24H19OPS: 386.08942. Found: 386.08705 (6.1 ppm).
ture and pressure using analytical grade (Aldrich) sol-
vents, at concentrations of ca. 1×10−4 M.
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3.11. 1-(4-Dimethylaminophenyl)-2-
(4-diphenylphosphinoylphenyl)ethene (3)
Analogously to the procedure for 10, salt 5 (0.11 g,
0.195 mmol) was heated under reflux in ethanol with
sodium hydroxide (1 M, 0.5 ml) for 2 h. No colour
change was observed during the reaction and a pale
orange solid was obtained. The phosphine oxide 3 was
isolated by column chromatography as a yellow solid.
Yield: 0.05 g (70%); m.p. 253–254°C (lit. [4], 255°C).
1
31P-NMR (CDCl3): 29.17 ppm. H-NMR (CDCl3): 2.87
(s, 6H, NMe2), 6.4–8.1 (m, 18H, aromatic), 7.04 (centre
of AB pattern, JAB=15.9 Hz, CHꢀCH) ppm. MS (EI)
Calc. for C28H26NOP: 423.17520. Found: 423.17500
(0.5 ppm).
[9] J.L. Oudar, J. Chem. Phys. 67 (1977) 446.
[10] A. Dulcic, C. Flytzanis, C.L. Tang, D. Pe´pin, M. Fe´tizon, Y.
Hoppiliard, J. Chem. Phys. 74 (1981) 1559.
[11] L. Horner, G. Mummenthey, H. Moser, P. Beck, Chem. Ber. 99
(1966) 2782.
3.12. 1-(4-Dimethylaminophenyl)-4-
(4-diphenylphosphinoylphenyl)-1,3-butadiene (9)
[12] M. Zanger, C.A. VanderWerf, W.E. McEwen, J. Am. Chem.
Soc. 81 (1959) 3806.
[13] W.E. McEwen, K.F. Kumli, A. Blade-Font, M. Zanger, C.A.
VanderWerf, J. Am. Chem. Soc. 86 (1964) 2378.
[14] W.E. McEwen, G. Axelrad, M. Zanger, C.A. VanderWerf, J.
Am. Chem. Soc. 87 (1965) 3948.
[15] C. Hansch, A. Leo, R.W. Taft, Chem. Rev. 91 (1991) 165. This
reference does not include the |p value for P+Ph3; however, we
suspect that the value for this substituent should be at least, if
not greater than, 1.18 (|p for P+(Me)Ph2), since the substitution
of methyl groups for phenyl groups has an increasing effect on
the value of |p (P+Me3=0.73).
[16] H.E. Bunting, M.L.H. Green, S.R. Marder, M.E. Thompson, D.
Bloor, P.V. Kolinsky, C.J. Jones, Polyhedron 11 (1992) 1489.
[17] K.R.J. Thomas, J.T. Lin, Y.S. Wen, J. Organomet. Chem. 575
(1999) 301.
Analogously to the procedure for 10, salt 6 (0.5 g,
0.85 mmol) was treated with sodium hydroxide (1 M, 4
ml) under refluxing ethanol (3 ml). As soon as the base
was added, a bright yellow solid precipitated, which
was left stirring under reflux for a further hour. A
bright yellow waxy solid was obtained from which the
phosphine oxide 9 was isolated by column chromatog-
raphy as a bright yellow waxy solid. Yield: 0.2 g (53%);
1
m.p. 202–205°C. 31P-NMR (CDCl3): 28.80 ppm. H-
NMR (CDCl3): 3.12 (s, 6H, NMe2), 6.3–8.0 (m, 22H,
aromatic and olefinic) ppm. MS (EI) Calc. for
C30H28NOP: 449.19086. Found: 449.19026 (1.3 ppm).
3.13. Sol6atochromism studies
[18] D.G. Gilheaney, Chem. Rev. 94 (1994) 1339.
[19] K.L. Kott, R.J. McMahon, J. Org. Chem. 57 (1992) 3097.
[20] M. Lequan, R.M. Lequan, K. Chane-Ching, J. Mater. Chem. 1
(1991) 997.
UV–vis studies were carried out on the salts 5–8 and
the phosphine oxides 3, 9, 10 and 11 at room tempera-
.
.