The synthesis and structural characterisation of some azo-containing phosphine chalcogenides and comparison to non-phosphorus-containing analogues

Article abstract of DOI:10.1039/b104918f

p-HO-Ph(Ph₂)P(E) (E=S, 1b, Se, 1c) reacts with the diazonium salts [4-R-PhN=N][BF₄] (R=H, Me, Et, ⁱPr, ^tBu, NMe₂, NO₂) to afford the new compounds [1-HO-2-(4-R-PhN=N)-4-Ph₂P(E)C<

Full text of DOI:10.1039/b104918f

View Article Online / Journal Homepage / Table of Contents for this issue
The synthesis and structural characterisation of some
azo-containing phosphine chalcogenides and comparison
to non-phosphorus-containing analogues
1
2
Mark J. Alder, Vanessa M. Bates, Wendy I. Cross, Kevin R. Flower* and Robin G. Pritchard
Department of Chemistry, UMIST, PO Box 88, Manchester, UK M60 1QD.
E-mail: k.r.flower@umist.ac.uk
Received (in Cambridge, UK) 5th June 2001, Accepted 6th September 2001
First published as an Advance Article on the web 25th September 2001
p-HO-Ph(Ph )P(E) (E = S, 1b, Se, 1c) reacts with the diazonium salts [4-R-PhN᎐N][BF ] (R = H, Me, Et, iPr, tBu,
᎐
2
4
NMe , NO ) to afford the new compounds [1-HO-2-(4-R-PhN᎐N)-4-Ph P(E)C H ] (E = S, R = H, 2a; Me, 2b; Et,
᎐
2
2
2
6
3
2c; iPr, 2d; tBu, 2e; NMe2, 2f; NO2, 2g; E = Se, R = H, 2h; Me, 2i) in acceptable yield. Similarly m-HO-Ph(Ph2)P(S)
3 reacts with two molar equivalents of the diazonium salts [4-R-PhN᎐N][BF ] (R = H, Me, NMe , NO ) to give the
᎐
4
2
new compounds 1-HO-2,4-(4-R-PhN᎐N)-3-Ph P(S)-C H 4a–d (R = H, 4a; Me, 4b; NMe , 4c; NO , 4d). All of the
᎐
2
6
2
2
2
new compounds have been characterised by elemental analysis, 1H, 31P-{1H}, 13C-{1H}-NMR spectroscopy and in
selected cases UV–visible spectroscopy. The selectivity in the substitution reactions of 3 with the diazonium salts
is influenced not only by the steric bulk of the Ph2PS moiety but by the ortho-effect too. These data have been
compared to those obtained from analogous coupling reactions between m-cresol and one and two
molar equivalents of [4-Me-PhN᎐N][BF ] which afford 1-HO-3-CH -4-(4-Me-PhN᎐N)C H 5 and
᎐
᎐
4
3
6
3
1-HO-3-CH -2,4-(4-Me-PhN᎐N)C H 6 respectively. The compounds 2bؒ0.55CH Cl ؒ0.2C H ,
᎐
3
6
2
2
2
6
14
4bؒCH2Cl2, 5 and 6b have been further characterised by X-ray crystallography.
Introduction
Phosphorus() species that contain the azo (N᎐N) moiety have
᎐
been known since the mid-1950s,1 and since then sporadic
reports of this class of compound have appeared in the liter-
ature,2 see Fig. 1 for an illustration of representative examples.
Recent interest has been shown in these types of compounds
because of their potential opto-electronic properties.2g–l We
recently reported3 an efficient synthesis of the azo-containing
phosphines I, Fig. 2, and have subsequently described some
facets of their coordination chemistry.4 We were curious to see
if the deprotonation of a hydroxy group bound to a phenyl ring
of a triarylphosphine would suitably activate the ring to a C–N
azo-coupling reaction as in the naphthyl system,2 or whether
the simple P–N Lewis acid–Lewis base adduct would form
preferentially,5 in which case it would be necessary to protect
the lone pair of electrons at phosphorus. Herein we report
that deprotonation of the hydroxy group is not sufficient to
activate the ring to undergo a C–N coupling reaction with a
diazonium tetrafluoroborate salt, but that coupling readily
takes place between p-hydroxyphenyl(diphenyl)phosphine
sulfide or selenide and m-hydroxyphenyl(diphenyl)phosphine
sulfide with a range of diazonium tetrafluoroborate salts to
afford azo-containing phosphine chalcogenides.
Fig. 1 Representative examples of azo-containing phosphorus()
species.
Results and discussion
It is well known that a deprotonated hydroxy group is an ortho/
para director in electrophilic aromatic substitution reactions;6
for example, in the reaction between [C H N᎐N][BF ] and
᎐
6
5
4
phenol,7 the para-product is predominant (99.1% in H2O; and
86.7% in C5H5N). Initial work, therefore, focused on coupling
reactions between p-hydroxyphenyl(diphenyl)phosphine and
diazonium salts so that only one product was likely, namely
where coupling should occur ortho to the hydroxy group,
since the para-position was blocked. Thus, dissolution of
p-hydroxyphenyl(diphenyl)phosphine in dry THF and addition
Fig. 2 Azo-containing naphthylphosphines.
of NaH led to gas evolution and the generation of the phen-
oxide anion. Cooling of the solution to 0–5 ЊC and addition of
a stoichiometric amount of [C H N᎐N][BF ] did not lead to the
᎐
6
5
4
DOI: 10.1039/b104918f
J. Chem. Soc., Perkin Trans. 1, 2001, 2669–2675
This journal is © The Royal Society of Chemistry 2001
2669

View Article Online
Fig. 4 13C-{1H} NMR numbering scheme for 2a–i.
Fig. 3 ORTEP representation of compound 2b showing the atomic
numbering scheme.
Scheme 1 (i) H2O2, acetone; S8, THF; grey Se, toluene; (ii) NaH, [4-R-
PhN᎐N][BF4], THF.
᎐
characteristic orange colour of a phenylazo-containing com-
pound, even on stirring for several days. After addition of water
and work up p-hydroxyphenyl(diphenyl)phosphine oxide was
isolated and this is consistent with the formation of a P–N
coupled adduct which is hydrolysed on addition of water.5 This
observation is also consistent with our previous report where
we have shown that the P–N adduct is not an intermediate
in the formation of azo-containing phosphines, but is an
undesired competing pathway.4b It was obvious, therefore, that
deprotonation of the hydroxy group on the phenyl ring does
not activate the ring sufficiently to compete with the P–N
adduct forming reaction. We then turned our attention to pro-
tecting the phosphorus and investigating the coupling reactions
with aryldiazonium salts. The phosphine chalcogenides p-HO-
Ph(Ph2)P(E) (E = O, S, Se) 1a–c were prepared, Scheme 1, by
reaction of the p-HO-Ph(Ph2)P with the appropriate chalcogen
in good yield, Table 1. To facilitate the coupling reactions 1a–c
were dissolved in THF and then reacted with a molar equiv-
alent of NaH to generate the phenoxide ion. The anion gener-
ated from 1a (the phosphine oxide) was found to precipitate
from solution and not to undergo the expected coupling reac-
tion; however, on deprotonation of 1b or 1c a soluble phenoxide
ion was generated and these ions did readily couple with the
Scheme 2 (i) NaH, [4-R-PhN᎐N][BF4], THF.
᎐
to OH resonance and is indicative of a proton in a strongly
bound hydrogen-bonded environment,9 and this proton readily
exchanges on addition of D2O. The 31P-{1H} NMR data for
2a–g all show a singlet resonance around 43 ppm which is as
expected for phosphine sulfides and compounds 2h and 2i dis-
play singlets around 35 ppm straddled by satellites J(P–Se) of
average value 732.2 Hz. The 13C-{1H} NMR spectra (Table 3),
see Fig. 4 for the numbering scheme, have been assigned with the
aid of DEPT 135 spectra, substituent effects10 and coupling to
the spin active 31P nucleus.
Having established that p-hydroxyphenyl(diphenyl)phosphine
chalcogenides readily undergo azo-coupling reactions we
decided to investigate the coupling reaction with m-hydroxy-
phenyl(diphenyl)phosphine sulfide 3, Scheme 2. In these
coupling reactions, unlike those for the p-hydroxyphenyl-
(diphenyl)phosphine chalcogenides, there is the distinct possi-
bility of the generation of isomeric products, Scheme 2, due
to the meta-disposition of ortho/para-(OH) and meta-(SPPh2)
directing groups.11 Normally the incoming group goes ortho to
the meta-directing moiety, rather than para12 which implies that
either isomer A or B should result rather than C. Further, where
the groups are sterically demanding A should be favoured.12
These observations were further developed by Kruse and Cha
who suggested,13 that substitution ortho to the meta-director
could be explained by consideration of the relative resonance
energies of the potential transition states which they approx-
imated as σ-complexes and in the absence of overwhelming
steric effects they suggested that the reaction will occur
i
t
diazonium salts [4-R-PhN᎐N][BF ] (R = H, Me, Et, Pr, Bu,
᎐
4
NMe , NO ) to afford the new compounds [1-HO-2-(4-R-PhN᎐
᎐
2
2
i
N)-4-Ph2P(E)C6H3] (E = S, R = H, 2a; Me, 2b; Et, 2c; Pr, 2d;
tBu, 2e; NMe2, 2f; NO2, 2g; E = Se, R = H, 2h; Me, 2i) in
acceptable yield, Scheme 1. All of the new compounds have
been characterised by elemental analysis, Table 1, 1H, 31P-{1H},
Table 2, and 13C-{1H} NMR spectroscopy, Table 3, and in
selected cases UV–visible spectroscopy, Table 4, and compound
2b by a single crystal X-ray diffraction study, see Fig 3 for an
ORTEP8 representation of the molecule.
1
The H NMR data (Table 2) are consistent with the com-
pounds 2a–i being azo-containing phosphine chalcogenides. Of
particular note is the singlet around 13.4 ppm which is assigned
2670
J. Chem. Soc., Perkin Trans. 1, 2001, 2669–2675

View Article Online
Table 1 Physical and analytical data for compounds 1a–6a
Analysis (%)
C
Compound
Colour
Yield (%)
Mp/ЊC
H
N
S
1a
White
69
69
85
60
68
51
63
42
62
54
23
16
62
58
51
53
45
56
40
158
158
178
92
73.4
(73.5)
69.4
(69.7)
60.0
(60.5)
68.6
(69.6)
64.9
(65.2)
70.3
(70.6)
70.8
(71.1)
69.4
(69.1)
67.7
(68.3)
59.4
(59.7)
59.8
(59.8)
61.2
(61.4)
69.7
(68.4)
68.8
(69.5)
70.9
(70.3)
67.0
(67.5)
56.3
4.7
(5.1)
4.9
(5.4)
3.6
(4.2)
4.7
(4.6)
5.0
(4.7)
5.4
(5.2)
5.4
(5.5)
5.9
(5.6)
5.3
(5.3)
3.3
(3.8)
4.0
(4.0)
4.4
(4.4)
4.9
(4.9)
4.5
(4.5)
4.7
(5.0)
5.8
1b
White
10.1
(10.3)
1c
Off-white
Orange
Orange
Orange
Orange
Orange
Red
2a
6.7
(6.8)
5.9
7.4
(7.7)
6.3
2bؒ0.5CH2Cl2
80
(5.9)
6.2
(6.2)
6.1
(6.5)
7.1
(7.3)
6.8
2c
142
126
150
90
2d
(6.1)
5.5
(5.7)
9.2
(7.0)
5.9
(6.8)
6.4
2e
2f
(9.2)
8.3
(8.3)
5.9
(7.0)
6.3
(6.6)
2gؒ0.25CHCl3
Yellow
Orange
Orange
White
190
100
162
132
226
253
224
200
95
2hؒ0.25CH2Cl2
(5.7)
5.4
2iؒ0.25CH2Cl2
(5.6)
0
(0)
3
9.3
(10.0)
5.7
(6.2)
6.1
(5.9)
5.0
(5.3)
5.7
4a
Brown
Brown
Brown
Brown
Orange
Brown
10.8
(10.8)
10.1
(10.2)
13.1
(13.9)
12.3
(12.9)
12.3
(12.4)
16.0
(16.3)
4b
4c
(5.5)
3.0
(3.4)
6.1
(6.2)
5.5
(5.9)
4dؒ0.5CH2Cl2
(56.5)
74.2
(74.3)
72.9
(4.9)
5
6
102
(73.2)
a Calculated values in parentheses.
mutually ortho to both substituents. Applying their interpret-
ation to the reaction between 3 and diazonium salts the most
likely product is B, Scheme 2, since the transition states for A
and C are “cross-conjugated”.
Treatment of 3 with one molar equivalent of NaH in THF
led to effervescence and generation of the phenoxide anion,
which on reaction with a stoichiometric amount of [4-Me-
PhN᎐N][BF ] led to an orange solution, which after work-up,
᎐
4
afforded an orange powder. The 31P-{1H} NMR spectrum
displayed two equal intensity resonances at 44.7 and 44.3 ppm.
This observation suggested that coupling had occurred to
afford isomers A and B, Scheme 2. The presence of B was to be
expected, and evidence for its presence came from the 1H NMR
spectrum which displayed a sharp singlet around 14 ppm (this is
indicative of an azo group ortho to the hydroxy moiety). The
presence of A must be a result of the large steric requirement of
the Ph2PS moiety. From the integration of the 31P-{1H} NMR
spectrum it was apparent that a roughly 50 : 50 mixture of the
two isomers was present. Either treatment of the crude mixture
Fig. 5 13C-{1H} NMR numbering scheme for 4a–d.
[4-R-PhN᎐N][BF ] (R = H, NMe , and NO ) to afford the new
᎐
4
2
2
compounds 1-HO-2,4-(4-R-PhN᎐N)-3-Ph P(S)-C H , 4a, c, d
᎐
2
6
2
(R = H, 4a; NMe2, 4c; NO2 4d). Due to similar Rf and solubility
properties of the mono-substituted isomers it has, to-date, not
been possible to isolate any in an analytically pure state. All of
the new compounds 4a–d have been characterised by elemental
1
with a second equivalent of NaH followed by [4-Me-PhN᎐N]-
analysis, Table 1, H, 31P-{1H} NMR spectroscopy, Table 2,
᎐
[BF4] or reaction of 3 with two molar equivalents of NaH
13C-{1H} NMR spectroscopy, Table 3, see Fig. 5 for the number-
ing scheme, and in selected cases UV–visible spectroscopy,
Table 4, and the data are consistent with their formulation.
Compound 4b was further characterised by a single crystal
X-ray diffraction, see Fig. 6 for ORTEP8 representation of the
molecule showing the atomic numbering scheme.
followed by two molar equivalents of [4-Me-PhN᎐N][BF ] led
᎐
4
to the isolation of 4b, Scheme 2. Compound 4b displays a single
resonance at 37.9 ppm in its 31P-{1H} NMR spectrum and three
singlets at 14.2, 2.36 and 2.355 ppm (integral ratio 1 : 3 : 3)
corresponding to the OH and the two different CH3 moieties
1
respectively in its H NMR spectrum: this is consistent with a
Although the data collected for 4b were not of high quality it
confirmed that the coupling reaction had taken place in both
positions ortho to the meta-directing group. Further, it was
double coupling reaction having taken place. Compound 3 also
reacts in an analogous manner with two molar equivalents of
J. Chem. Soc., Perkin Trans. 1, 2001, 2669–2675
2671

View Article Online
Table 2 1H NMRa (δ) and 31P-{1H} NMR datab (δ) for compounds 1b–6
Compound
31P
1H
1b
1c
44.1
7.8–7.3 (br m, 12H, aryl H), 6.9 (dd, JHH 8.5, JPH 2.1, 2H, aryl H), 5.9 (br s, 1H, OH).
7.8–7.7 (br m, 4H, aryl H), 7.6–7.3 (br m, 8H, aryl H), 6.8 (dd, JHH 7.5, JPH 2.0, 2H, aryl H), 5.8 (br s, 1H,
OH).
35.4 (1JP–Se 712.1)
2a
2b
2c
2d
2e
2f
42.8
13.3 (s, 1H, OH), 8.3 (dd, JPH 13.6, JHH 1.9, 1H, aryl H), 7.9–7.3 (br m, 16H, aryl H), 7.1 (dd, JHH 8.6, JHH
2.5, 1H, aryl H).
42.8
13.4 (s, 1H, OH), 8.3 (dd, JPH 15.7, JHH 2.2, 1H, aryl H), 7.9–7.3 (br m, 15H, aryl H), 7.1 (dd, JHH 8.6, JHH
2.5, 1H, aryl H), 5.29 (s, ¹ H, CH2Cl2), 2.4 (s, 3H, CH3).
¯
²
42.9
13.4 (s, 1H, OH), 8.3 (dd, JPH 13.6, JHH 2.1, 1H, aryl H), 7.8–7.2 (br m, 15H, aryl H), 7.1 (dd, JHH 8.6, JHH
2.7, 1H, aryl H), 2.7 (q, JHH 7.2, 2H, CH2), 1.3 (t, JHH 7.2, 3H, CH3).
42.9
13.4 (s, 1H, OH), 8.3 (dd, JPH 15.7, JHH 2.3, 1H, aryl H), 7.8–7.3 (br m, 15H, aryl H), 7.1 (dd, JHH 8.6, JHH
2.7, 1H, aryl H), 3.0 (m, JHH 7.0, 1H, CH), 1.3 (d, JHH 7.0, 6H, CH3).
13.4 (s, 1H, OH), 7.8 (dd, JPH 14.7, JHH 2.1, 1H, aryl H), 7.7–7.3 (br m, 15H, aryl H), 7.1 (dd, JHH 8.5, JHH
2.5, 1H, aryl H), 1.6 (s, 9H, CH3).
42.9
43.7
13.7 (s, 1H, OH), 8.2 (dd, JPH 13.8,JHH 2.0, 1H, aryl H), 7.8–7.5 (br m, 13H, aryl H), 7.0 (dd, JHH 8.5, JHH
3.0, 1H, aryl H), 6.7 (dd, JHH 8.5, JHH 3.0, 1H, aryl H), 3.1 (s, 6H, CH3).
2g
2h
2i
43.2
12.9 (s, 1H, OH), 8.4–8.3 (br m, 3H, aryl H), 8.0 (d, JHH 8.5, 2H, aryl H), 7.8–7.5 (br m, 1014 H, aryl H,
14 CHCl ), 7.1 (dd, JHH 8.7, JHH 2.8, 2H, aryl H).
35.2 (1JP–Se 731.7)
35.2 (1JP–Se 732.7)
13.4 (s, 31H, OH), 8.3 (dd, JPH 13.8, JHH 2.0, 1H, aryl H), 7.8–7.5 (br m, 15H, aryl H), 7.1 (dd, JHH 8.5, JHH
2.5, 1H, aryl H), 5.29 (s, 13 H, CH Cl ).
13.4 (s, 1H, OH), 8.3 (dd, JPH 14.20, 2JHH 2.0, 1H, aryl H), 7.8–7.7 (br m, 7H, aryl H), 7.5–7.4 (br m, 5H,
1
4
aryl H), 7.3 (d, JHH 8.5, 1H, aryl H), 7.1 (dd, JHH 8.7, JHH 2.6, 1H, aryl H), 5.29 (s, H, CH2Cl2), 2.4
(s, 3H, CH3).
3
4a
4b
44.5
37.9
37.9
7.8–7.9 (br m, 4H, aryl H), 7.6–7.5 (br m, 7H, aryl H), 7.3–7.2 (br m, 3H, aryl H).
14.2 (s, 1H, OH), 8.0–7.9 (br m, 6H, aryl H), 7.4–7.2 (br m, 16H, aryl H).
14.2 (s, 1H, OH), 8.0–7.9 (br m, 5H, aryl H), 7.8–7.0 (br m, 15H, aryl H), 2.36 (s, 3H, CH3), 2.355 (s, 3H,
CH3).
4c
37.8
38.0
14.3 (s, 1H, OH), 8.0–7.7 (br m, 8H, aryl H), 7.7–7.0 (br m, 7H, aryl H), 6.5–6.4 (br m, 5H, aryl H), 3.06
(s, 6H, CH3), 3.04 (s, 6H, CH3).
4d
5
14.0 (s, 1H, OH), 8.2–7.9 (br m, 10H, aryl H), 7.4–7.2 (br m, 10H, aryl H), 5.29 (s, ¹ H, CH2Cl2).
¯
²
7.77 (d, JHH 9.0, 2H, aryl H), 7.65 (d, JHH 9.0, 1H, aryl H), 7.29 (d, JHH 9.0, 2H, aryl H), 6.7 (m, 2H, aryl
H), 5.1 (s, 1H, OH), 2.7 (s, 3H, CH3), 2.42 (s, 3H, CH3).
6
14.4 (s, 1H, OH), 7.8 (m, 5H, CH), 7.3 (m, 4H, CH), 6.9 (d, JHH 9.0, 1H, CH), 3.1 (s, 3H, CH3), 2.45
(s, 3H, CH3), 2.44 (s, 3H, CH3).
a Spectra recorded in CDCl3 (293 K) and referenced to CHCl3; coupling constants in Hz. b Spectra recorded in CDCl3 (293 K) and referenced to 85%
H3PO4; coupling constants in Hz.
Fig. 7 Representation of the rotation about P–C bond observed in
molecular structure of 4b.
Fig. 6 ORTEP representation of compound 4b showing the atomic
substitution at the sterically least hindered site ortho to the
numbering scheme.
hydroxy group, since the ortho-effect should no longer be
operating.
evident that there is a strong hydrogen bond14 present in the
molecule: O(1)–H ؒ ؒ ؒ N(2) with O(1)–H 0.753(2), O(1)–N(2)
2.578(2), N(2)–H 1.994(2) Å, O–H–N 134.6(11) which is
common in these types of compounds.15 Since 4b contains two
azo-moieties, of which only one is ortho to the hydroxy group,
direct structural evidence for the presence of hydroxyazo–
ketohydrazone tautomerisation in phenol based systems should
be possible.15 Unfortunately in the crystal, rotation about the
P(1)–C(3) bond, Fig. 7, was evident about 20% of the time
which means that the bond lengths around each azo-moiety in
the final structural model contain a contribution from both
types of azo environment and so no such interpretation can be
made.
Since the coupling reaction of 3 with diazonium salts had
occurred at the expected ortho-positions to the meta-directing
Ph2PS group, we were curious as to whether replacing the
Ph2PS moiety with the formally ortho/para-directing methyl
group, and carrying the reaction out under identical conditions
would lead to (i) exclusively mono-substitution para to the
hydroxy group and (ii) on reaction of a second equivalent to
Treatment of m-cresol with a stoichiometric amount of NaH
in THF led to effervescence and the generation of the phen-
oxide ion, which on cooling to 0–5 ЊC and addition of [4-Me-
PhN᎐N][BF ] led exclusively, as expected, to formation of
᎐
4
1-HO-3-CH -4-(4-Me-PhN᎐N)-C H 5, i.e. the para-coupled
᎐
3
6
3
product and no evidence for any ortho-coupled product either
at the 2- or 6-position was obtained, Scheme 3, see Tables 1–3
for characterising data. Treatment of 5 with a stoichiometric
amount of NaH followed by [4-Me-PhN᎐N][BF ] led to the
isolation of the brown solid 1-HO-3-CH -2,4-(4-Me-PhN᎐N)-
C6H2 6 where a second coupling reaction had occurred and
once again exclusively in the sterically most congested ortho-
position; Scheme 3, see Tables 1–3 for characterising data. The
second coupling in the 2-position is clear from the proton
NMR spectrum by the presence of a doublet at 6.9 ppm JHH 9.0
Hz (the other expected doublet is obscured under the multiplet
centred at 7.32 ppm), whereas if coupling had occurred in the
6-position lower frequency long range coupling would of been
evident for the two protons on the substituted ring: no evidence
for this product was seen in the crude 1H NMR spectrum. This
᎐
4
᎐
3
2672
J. Chem. Soc., Perkin Trans. 1, 2001, 2669–2675

View Article Online
Table 3 13C-{1H} NMR data (δ)a for compounds 1b–6
C(7) C(8) C(9) C(10)
C(7Ј) C(8Ј) C(9Ј) C(10Ј) C(11) C(12) C(13) C(14) Others
Compound C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
1bb
1cb
2ab
2bb
2cb
2db
2eb
2fc
159.3 115.8 134.1 122.4
J 3.1 J 13.6 J 12.6 J 91.0
159.2 115.8 134.5 121.3
J 2.2 J 13.8 J 12.4 J 83.6
132.9 132.1 128.5 131.6
J 84.7 J 12.6 J 3.1 J 3.1
131.8 132.5 128.5 131.6
J 77.8 J 10.9 J 13.1 J 2.9
155.6 136.5 136.4 123.8 137.9 119.0 150.2 122.5 129.5 131.9 132.9 132.2 128.6 131.6
J 2.1 J 15.1 J 11.6 J 91.5 J 12.6 J 13.7 J 86.3 J 10.5 J 12.6 J 3.1
155.6 136.2 136.0 123.6 137.5 118.9 148.2 122.5 130.1 142.7 133.1 132.2 128.6 131.6 21.7
J 2.1 J 15.7 J 11.5 J 91.5 J 12.6 J 13.7 J 86.3 J 10.5 J 12.6 J 3.1 (CH3)
155.6 136.5 136.0 123.6 137.6 118.9 148.4 122.5 128.9 149.0 133.1 132.2 128.6 131.6 28.9 15.3
J 2.1 J 15.8, J 11.6 J 90.5 J 12.6 J 13.7 J 86.3 J 10.5 J 12.6 J 2.7 (CH2) (CH3)
155.6 136.6 136.0 123.6 137.6 118.9 148.5 122.6 127.5 153.5 133.1 132.2 128.6 131.6 34.3 23.8
J 2.1 J 15.8 J 11.6 J 90.5, J 12.6 J 13.7 J 86.3 J 10.5 J 12.6 J 3.2 (CH) (CH3)
155.6 136.6 136.0 123.4 137.7 118.9 148.0 122.2 126.4 155.8 133.1 132.2 128.6 131.6 35.3 31.2
J 2.1 J 15.7 J 11.6 J 90.5 J 12.6 J 13.7 J 86.3 J 10.5 J 12.6 J 3.2 (CCH3) (CH3)
155.6 136.7 134.2 122.7 136.0 118.4 140.0 124.5 111.6 152.7 133.1 132.1 128.5 131.4 40.1
J 1.9 J 15.5 J 11.6 J 91.8 J 12.6 J 13.5 J 86.0 J 10.6 J 12.6 J 2.9 (CH3)
155.6 136.9 137.8 124.2 138.8 119.3 153.5 123.1 125.0 149.0 133.1 132.2 128.7 131.6
J 2.1 J 15.5 J 10.6 J 80.2 J 9.7 J 12.6 J 86.3 J 10.6 J 12.6
155.6 136.4 134.6 122.4 136.7 115.7 150.1 122.4 129.4 131.7 131.8 132.5 128.6 131.7
2gc d
2hb
2ib d
3c d
J 1.9 J 15.3 J 12.3 J 82.1 J 12.4 J 14.5
155.6 136.4 136.3 122.8 137.9 118.9 148.1 122.4 130.1 142.7
J 2.2 J 15.3 J 11.6 J 82.8 J 12.4 J 14.5
J 77.8 J 10.9 J 13.1 J 2.9
132.5 128.6 131.6 21.5
J 10.9 J 13.1 J 3.6 (CH3)
133.6 132.1 128.4 131.6
J 85.0 J 10.6 J 12.6 J 2.2
156.0
J 10.1
132.3 124.0 129.7 119.8
J 86.0 J 9.7 J 15.5 J 2.6
4ac d
4bc d
4cc d
4dc d
5b
156.1 135.3 134.0 146.8 122.2 123.6 151.9 123.5 128.9 131.7 138.3 130.1 128.6 129.6
J 7.7 J 80.2 J 8.7 J 1.9 149.4 123.2 128.4 131.1 J 88.9 J 10.6 J 12.6 J 2.9
157.4 135.6 133.3 147
J 7.7 J 80.2
121.9
J 8.7
150.1 123.5 129.6 142.6 138.5 130.0 128.0 129.1 21.5 21.4
147.6 123.2 129.0 141.7 J 88.9 J 10.6 J 13.8 J 3.9 (CH3) (CH3)
154.5 136.0 134.2 147.7 119.8 122.8 143.5 125.7 111.2 152.6 139.1 130.0 128.6 129.1 40.18 40.15
J 10.3
157.4 135.6 136.8 146.6
J 7.7 J 77.3
J 90.5
J 9.7
140.4 125.4 110.7 152.2 J 88.9 J 10.6 J 12.6 J 2.9 (CH3) (CH3)
154.7 124.1 124.7 148.8 137.9 130.1 128.4
152.6 123.8 124.0 148.7 J 89.8 J 10.6 J 13.6
157.9 117.2 140.8 145.2 117.3 113.6 151.4 122.6 129.7 140.7
21.4 17.5
(CH3) (CH3)
21.5 21.4 11.9
(CH3) (CH3) (CH3)
6b
156.4 142.6 135.0 144.0 121.7 116.4 151.1 122.7 129.6 140.7
148.4 121.2 130.0 141.8
a Spectra recorded in CDCl3 (293 K) and referenced to CDCl3 (δ 77.0); (JC–P) coupling constants in Hz. b Spectrum recorded at 75.6 MHz. c Spectrum
recorded at 100.6 MHz. d One or more resonances obscured or partially obscured by overlapping with other signals; see Fig. 5 for the numbering
schemes.
Table 4 UV–visible dataa for selected compounds 2a–4d
Compound
λb
εc
2a
2b
324
377
337
380
469
336
399
324
380
336
380
358
430
349
427
374
10426
5260
15870
11270
37470
16790
8200
14420
7460
21490
13510
24040
9930
2f
2g
2h
2i
4a
4b
4d
67120
23040
14040
a Spectra recorded in CHCl3. b λmax/nm. c ε/dm3 molϪ1 cmϪ1
.
Scheme 3 (i) NaH, [4-R-PhN᎐N][BF4], THF; (ii) 2 NaH, 2 [4-R-
᎐
PhN᎐N][BF4], THF.
᎐
Compounds 5 and 6 were also characterised by single crystal
X-ray diffraction studies, see Figs. 8 and 9 for ORTEP8 repre-
sentations of the molecules showing the atomic numbering
schemes. Compound 5 displays a strong intermolecular hydro-
gen bond O(1)–H(1) ؒ ؒ ؒ N(2) where O(1)–H(1) 0.905, H(1) ؒ ؒ ؒ
N(2) 1.987, O(1) ؒ ؒ ؒ N(2) 2.876 Å, O(1)–H(1)–N(2) 167.3Њ,
whereas, compound 6 shows a strong intramolecular hydro-
gen bond O(1)–H(1) 1.183, H(1) ؒ ؒ ؒ N(2) 1.487, O(1) ؒ ؒ ؒ N(2)
result was somewhat surprising, however, reaction at the 2-
position in competition with the 6- is not without precedent in
related systems. For example, the reaction of 1-hydroxy-3-
methyl-4-nitrobenzene with either HNO3 or Cl2 affords substi-
tution at the 2-position (66 and 80% respectively),16,17 and the
only explanation offered for these observations was: electronic
rather than steric effects dominate.13
J. Chem. Soc., Perkin Trans. 1, 2001, 2669–2675
2673

View Article Online
Preparations
p-Hydroxyphenyl(diphenyl)phosphine sulfide 1a. To p-
hydroxyphenyl(diphenyl)phosphine (1 g, 3.6 mmol) dissolved in
THF (15 mL) with continuous stirring under dinitrogen was
added S8 (0.13 g, 3.6 mmol). When all of the S8 had dissolved
the solution was filtered through Celite and the solvent removed
under reduced pressure. Recrystallisation of the crude material
from CH2Cl2–hexane afforded 1a as a white solid (1 g, 92%).
In an analogous manner m-hydroxyphenyl(diphenyl)phosphine
sulfide 3 was obtained; see Table 1 for physical and analytical
data.
Fig. 8 ORTEP representation of compound 5 showing the atomic
numbering scheme.
p-Hydroxyphenyl(diphenyl)phosphine selenide 1c. To p-
hydroxyphenyl(diphenyl)phosphine (1 g, 3.6 mmol) dissolved in
toluene (15 mL) with continuous stirring under dinitrogen was
added grey Se (0.32 g, 4 mmol) and the mixture refluxed for 3 h.
The solution was cooled, filtered through Celite and the solvent
removed under reduced pressure. Recrystallisation of the crude
material from CH2Cl2–hexane afforded 1c as an off-white solid
(1.1 g, 85%); see Table 1 for physical and analytical data.
2-Phenylazo-4-(diphenyl)phosphinothioylphenol 2a. To p-
hydroxyphenyl(diphenyl)phosphine (0.3 g, 0.97 mmol) dissolved
in THF (10 mL) with continuous stirring under dinitrogen NaH
(60% w/w in mineral oil; 0.046 g, 1.16 mmol) was added and the
mixture stirred for 1 h. The solution was then cooled to 0–5 ЊC
Fig. 9 ORTEP representation of compound 6 showing the atomic
numbering scheme.
2.543 Å, O(1)–H(1)–N(2) 144.3Њ which is a common feature of
ortho-hydroxyazo benzene systems.14
and [PhN᎐N][BF ] (0.2 g, 1.1 mmol) dissolved in NCMe
᎐
4
(10 mL) was rapidly added. After stirring for 1 h, HCl (0.2 mL,
1 M) was added and the solvent was removed under reduced
pressure. The crude material was then extracted into CH2Cl2
and filtered through Celite to remove NaBF4. Reduction of the
solvent volume to 1 mL, in vacuo, and passing the solution
down a silica column (3 × 20 cm) with CH2Cl2 as eluent
afforded 2a as an orange solid (0.24 g, 60%) on removal of the
solvent. In an analogous manner compounds 2b–i were
obtained; see Table 1 for physical and analytical data.
Conclusion
We have prepared a series of azo-containing phosphine chalco-
genides by a classical azo-coupling reaction. Coupling in
m-hydroxyphenyl(diphenyl)phosphine sulfide occurs at both
positions ortho to the phosphine sulfide group qualitatively, at
least, at the same rate and this is a result of the ortho-effect11
and steric bulk of the (diphenyl)phosphine sulfide moiety. A
similar coupling pattern is seen for m-cresol, although coupling
in the sterically encumbered ortho-position only takes place
once coupling para- to the hydroxy-group has occurred even
though there is not a meta-disposition between an ortho/para
and meta-directing groups.
2,4-Bis(4-methylphenylazo)-3-(diphenyl)phosphinothioyl-
phenol 4b. To 3 (0.3 g, 0.97 mmol) dissolved in dry THF
(10 mL), with continuous stirring under an atmosphere of dry
dinitrogen was added NaH (60% w/w in mineral oil; 0.12 g,
2.9 mmol). After stirring for 10 min, the solution was cooled to
0–5 ЊC and [4-CH -C H N᎐N][BF ] (0.49 g, 2.4 mmol) was
᎐
3
6
4
4
Experimental
added and stirred for 2 h. HCl (1 M, 0.2 mL) was added and the
solvent removed under reduced pressure, followed by extraction
into CH2Cl2 (10 mL) and filtration through Celite to remove
NaBF4. The resulting solution, after reduction in volume to
ca. 1 mL, was passed through a silica column with CH2Cl2–
hexane (8 : 2) as eluent. Elution initially gave a light red band,
which was a mixture of mono-substituted products (0.1 g). Fur-
ther elution with CH2Cl2–hexane (8 : 2) gave a dark red–brown
band, which on removal of the solvent under reduced pressure,
followed by recrystallisation from CH2Cl2–hexane afforded 4b
as a brown solid (0.26 g, 51%). In an analogous manner, com-
pounds 4a, 4c–d were obtained; see Table 1 for physical and
analytical data.
General considerations
All solvents, except water, were dried over an appropriate
drying agent and distilled prior to use: THF (K); CH2Cl2
(P2O5); hexane (NaK). The aryldiazonium tetrafluoroborate
salts,18 p-methoxyphenyl(diphenyl)phosphine, p-hydroxyphenyl-
(diphenyl)phosphine and p-hydroxyphenyl(diphenyl)phosphine
oxide,19 m-methoxyphenyl(diphenyl)phosphine and m-hydroxy-
phenyl(diphenyl)phosphine20 were prepared by the literature
methods using reagents purchased from commercial sources.
Melting points were recorded on a Griffin Melting Point
Apparatus and are uncorrected. The H (200.1 MHz) and 31P-
1
{1H} NMR (81.3 MHz) were recorded on a Bruker DPX 200
spectrometer. 13C-{1H} NMR spectra (75.5, 100.5 MHz) were
recorded on either a Bruker DPX 300 or DPX 400 spectro-
meter. 1H and 13C-{1H} NMR spectra were referenced to
CHCl3 (δ 7.26) and CHCl3 (δ 77.0) and 31P-{1H} NMR extern-
ally to 85% H3PO4. UV–visible spectra were recorded on a
Shimadzu UV20101 PC spectrophotometer in CHCl3 (AR) in
1 cm cuvettes. Elemental analyses, were performed by the
Microanalytical Service, Department of Chemistry, UMIST;
solvents of crystallisation were confirmed by repeated elem-
ental analysis and observation of relevant signals in the NMR
spectra. Syntheses were carried out under a dinitrogen atmos-
phere using standard Schlenk techniques and subsequent work-
ups were carried out in the open unless otherwise stated.
3-Methyl-4-(4-methylphenylazo)phenol 5. To m-cresol (0.8 g,
7.39 mmol) dissolved in dry THF (10 mL), with continuous
stirring under an atmosphere of dry dinitrogen, was added
NaH (60% w/w in mineral oil; 0.30 g, 7.39 mmol). After stirring
for 10 min, the solution was cooled to 0–5 ЊC and [4-CH3-
C H N᎐N][BF ] (1.5 g, 7.39 mmol) was added and stirred for
᎐
6
4
4
2 h. HCl (1 M, 0.2 mL) was added and the solvent removed
under reduced pressure, followed by extraction into CH2Cl2
(10 mL) and filtration through Celite to remove NaBF4. The
solvent was removed to yield a brown solid and purification was
effected by passing down a silica column with Et2O–hexane
(1 : 1) as eluent affording 6 (0.93 g, 56%); see Table 1 for
physical and analytical data.
2674
J. Chem. Soc., Perkin Trans. 1, 2001, 2669–2675

View Article Online
Table 5 Crystallographic data for compounds 2b, 4b, 5, and 6
2bؒ0.55CH2Cl2ؒ0.2C6H14
4bؒCH2Cl2
5
6
Formula
M
Space group
T /K
C26.8H29Cl1.1N2OPS
492.92
P-1
C33H29Cl2N4OPS
631.53
P21/c
C14H14N2O
226.27
P21/n
C21H20N4O
344.41
Pna21
293
203
293
293
a/Å
b/Å
c/Å
α/Њ
8.8661(12)
10.5570(18)
14.267(3)
110.513(16)
94.713(13)
91.063(12)
1244.9(4)
2
16.037(2)
7.6280(10)
26.332(2)
5.809(4)
18.173(7)
11.540(5)
18.942(4)
20.515(3)
4.6558(10)
90
90
90
1809.2(6)
4
1.54178
6653
3048
8.5
β/Њ
93.860(10)
96.99(4)
γ/Њ
V/Å3
3213.9(6)
4
0.70169
5205
2744
5.4
1209.1(11)
4
1.54178
2194
1981
4.4
Z
µ(Mo-Kα)/cmϪ1
No. reflections
No. ind. reflections
R (%)
0.71069
4676
4368
6.1
Rw (%)
18.1
10.8
7.5
16.5
Kukhtin, J. Gen. Chem. (USSR), 1976, 46, 1224; (g) C. Lambert,
E. Schmalzin, K. Meerholtz and C. Bräuchle, Chem. Eur. J., 1998, 4,
512; (h) K. C. Ching, M. Lequan, R. M. Lequan, C. Runser, M.
Baraoukas and A. Fort, J. Mater. Chem., 1995, 5, 649; (i) K. C.
Ching, M. Lequan, R. M. Lequan and F. Kajzar, Chem. Phys. Lett.,
1995, 242, 598; (j) D. W. Allen, J. Hawkrigg, H. Adams, B. F. Taylor,
D. E. Hibbs and M. B. Hursthouse, J. Chem. Soc., Perkin Trans. 1,
1998, 335; (k) D. W. Allen and X. Li, J. Chem. Soc., Perkin Trans. 2,
1997, 1099; (l ) D. W. Allen, J. P. Miffin and P. J. Skabara,
J. Organomet. Chem., 2000, 601, 293.
3 (a) M. J. Alder, K. R. Flower and R. G. Pritchard, Tetrahedron Lett.,
1998, 39, 3571; (b) M. J. Alder, W. I. Cross, K. R. Flower and R. G.
Pritchard, J. Chem. Soc., Dalton Trans., 1999, 2563.
4 (a) M. J. Alder, W. I. Cross, K. R. Flower and R. G. Pritchard,
J. Organomet. Chem., 1998, 568, 279; (b) M. J. Alder, W. I. Cross,
K. R. Flower and R. G. Pritchard, J. Organomet. Chem., 1998,
590, 123; (c) M. J. Alder, K. R. Flower and R. G. Pritchard,
J. Organomet. Chem., 2001, 629, 153.
5 (a) L. Horner and R. Stoher, Chem. Ber., 1953, 86, 1066; (b)
L. Horner and H. Hoffman, Angew. Chem., 1956, 68, 473; (c) L.
Horner and H. Hoffman, Chem. Ber., 1958, 91, 45.
6 A. Streitweiser and C. H. Heathcock, Introduction to Organic
Chemistry, 2nd edn., Macmillan, New York, 1981, p. 705.
7 H. Hamada, Y. Hashida, S. Schiguchi and K. Matsui, Bull. Chem.
Soc. Jpn., 1974, 47, 2351.
8 C. N. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
9 D. H. Williams and I. Fleming, Spectroscopic Methods in Organic
Chemistry, 4th edn., McGraw-Hill, New York, 1989.
2,4-Bis(4-methylphenylazo)-3-methylphenol 6. To 5 (0.5 g,
2.21 mmol) dissolved in dry THF (10 mL), with continuous
stirring under an atmosphere of dry dinitrogen, was added
NaH (60% w/w in mineral oil; 0.088 g, 2.21 mmol). After stir-
ring for 10 min, the solution was cooled to 0–5 ЊC and [4-CH3-
C H N᎐N][BF ] (0.46 g, 2.21 mmol) was added and stirred for
᎐
6
4
4
2 h. HCl (1 M, 0.2 mL) was then added and the solvent removed
under reduced pressure, followed by extraction into CH2Cl2
(10 mL) and filtration through Celite to remove NaBF4.
Removal of the solvent under reduced pressure, followed by
recrystallisation from EtOH afforded 6 as a brown solid (0.3 g,
40%); see Table 1 for physical and analytical data.
Crystallography†
All of the crystals were grown by slow diffusion of hexane into
a saturated CH2Cl2 solution of 2b, 4b, 5, or 6 at room temper-
ature. The X-ray crystallography experiments for 2b and 4b
were carried out on a Nonius Mach 4-circle diffractometer
using Mo-Kα radiation and for 5 and 6 on a Rigaku AFC6S
diffractometer using Cu-Kα radiation. Crystallographic data
for compounds 2b, 4b, 5 and 6 are summarised in Table 5. The
SHELX 97 suite of programs21 was used to solve the structures
by direct methods and refined them by full matrix least squares.
10 H. O. Kalinowski, S. Berger and S. Braun, Carbon-13 NMR
Spectroscopy, Wiley, New York, 1988.
Acknowledgements
11 M. S. Newman, Steric Effects in Organic Chemistry, Wiley, New
York, 1956, pp. 164–200.
12 J. March, Advanced Organic Chemistry: Reactions, Mechanisms, and
Structure, 2nd edn., McGraw-Hill, 1977, p. 465.
M. J. A. and W. I. C would like to thank the EPSRC for the
award of Studentships.
13 L. I. Kruse and J. K. Cha, J. Chem. Soc., Chem. Commun., 1982,
1333.
14 J. C. Speakman, The Hydrogen Bond and other Intermolecular Forces,
Monograph for Teachers No. 27, The Chemical Society, 1975.
15 H. Zollinger, Azo and Diazo Chemistry, Aliphatic and Aromatic
Compounds, Interscience, London, 1961.
16 H. E. Dadswell and J. Kenner, J. Chem. Soc., 1927, 280.
17 M. E. Flaugh, T. A. Crowell, J. A. Clemens and B. D. Sawyer,
J. Med. Chem., 1979, 22, 63.
† CCDC reference numbers 165166–165169. See http://www.rsc.org/
suppdata/p1/b1/b104918f/ for crystallographic files in .cif or other
electronic format.
References
1 G. M. Kosolapoff and G. G. Priest, J. Am. Chem. Soc., 1953, 75,
4847.
2 (a) A. N. Podovick and T. M. Moshkina, Zh. Obsch. Khim., 1965,
35, 2024; (b) A. M. Lukin, N. A. Bolotino and G. B. Zavarkhina,
Chem. Abstr., 1968, 68, 88177a; (c) V. Jagodic and L. Tusek, J. Org.
Chem., 1972, 37, 1222; (d ) L. Tusek-Bozic, M. Curic and P. Traldi,
Inorg. Chim. Acta, 1997, 254, 49; (e) V. V. Kormachev, T. V. Vasil’eva,
B. I. Ionin and V. A. Kukhtin, J. Gen. Chem. (USSR), 1975, 45, 293;
( f ) V. V. Kormachev, T. V. Vasil’eva, B. I. Bryantsev and V. A.
18 A. Vogel, Practical Organic Chemistry, 5th edn., Longman Scientific
and Technical, New York, 1989, p. 920.
19 A. E. Senar, W. Valient and J. Wirth, J. Org. Chem., 1960, 25,
2001.
20 E. N. Tsvetkov, M. M. Makhamatkhanov, D. F. Lobanov and M. I.
Kabachnik, J. Gen. Chem. (USSR), 1971, 41, 2376.
21 G. M. Sheldrick, SHELX 97, University of Göttingen, 1998.
J. Chem. Soc., Perkin Trans. 1, 2001, 2669–2675
2675