Bis(azidophenyl)phosphole building block for extended π-conjugated systems

Article abstract of DOI:10.1002/ejoc.201201148

Novel bis(azidophenyl)phosphole sulfide building block 8 has been developed to give access to a plethora of phosphole-containing π-conjugated systems in a simple synthetic step. This was explored for the reaction of the two azido moieties with phenyl-, pyridyl- and thienylacetylenes, to give bis(aryltriazolyl)-extended π-systems, having either the phosphole sulfide (9) or the phosphole (10) group as central ring. These conjugated frameworks exhibit intriguing photophysical and electrochemical properties that vary with the nature of the aromatic end-group. The λ³-phospholes 10 display blue fluorescence (λ_em = 460-469 nm) with high quantum yield (φ_F = 0.134-0.309). The radical anion of pyridyl-substituted phosphole sulfide 9b was observed with UV/Vis spectroscopy. TDDFT calculations on the extended π-systems showed some variation in the shape of the HOMOs, which was found to have an effect on the extent of charge transfer, depending on the aromatic end-group. Some fine-tuning of the emission maxima was observed, albeit subtle, showing a decrease in conjugation in the order thienyl < phenyl < pyridyl. These results show that variations in the distal ends of such π-systems have a subtle but significant effect on photophysical properties. We report a novel approach to phosphole-containing π-conjugated materials. From bis(azidophenyl)phosphole 8, a plethora of π-conjugated systems are possible in a single step, incorporating different aromatic capping groups installed using click chemistry. End-group variations introduce photophysical and electronic changes into resulting fluorophores 10, which have been investigated in detail. Copyright

Full text of DOI:10.1002/ejoc.201201148

FULL PAPER
DOI: 10.1002/ejoc.201201148
Bis(azidophenyl)phosphole Building Block for Extended π-Conjugated Systems
[a]
[b]
[c]
[a]
ˇ
Wannes Weymiens, Frantisek Hartl, Martin Lutz, J. Chris Slootweg,
Andreas W. Ehlers,[a] Jos R. Mulder,[a] and Koop Lammertsma*[a]
Keywords: Phospholes / Molecular electronics / Conjugation / Fluorescence / Click chemistry
Novel bis(azidophenyl)phosphole sulfide building block 8
has been developed to give access to a plethora of phos-
phole-containing π-conjugated systems in a simple synthetic
step. This was explored for the reaction of the two azido moi-
eties with phenyl-, pyridyl- and thienylacetylenes, to give
bis(aryltriazolyl)-extended π-systems, having either the
phosphole sulfide (9) or the phosphole (10) group as central
ring. These conjugated frameworks exhibit intriguing photo-
physical and electrochemical properties that vary with the
nature of the aromatic end-group. The λ3-phospholes 10 dis-
play blue fluorescence (λem = 460–469 nm) with high quan-
tum yield (ΦF = 0.134–0.309). The radical anion of pyridyl-
substituted phosphole sulfide 9b was observed with UV/Vis
spectroscopy. TDDFT calculations on the extended π-systems
showed some variation in the shape of the HOMOs, which
was found to have an effect on the extent of charge transfer,
depending on the aromatic end-group. Some fine-tuning of
the emission maxima was observed, albeit subtle, showing a
decrease in conjugation in the order thienyl Ͻ phenyl Ͻ pyr-
idyl. These results show that variations in the distal ends of
such π-systems have a subtle but significant effect on photo-
physical properties.
phosphole lone-pair participation in the π-system by in-
creasing the steric bulk around the phosphorus centre.[7]
Such attempts to generate fused phosphole–thiophene
building block 2 did result in varying HOMO–LUMO gaps,
but not in the desired fine-tuning of photophysical proper-
ties.[8] The π-conjugated backbone itself can also be modi-
fied, which is a commonly applied strategy for carbon-
based π-systems.[9] This approach has been explored for the
thiophene-substituted phosphole 1[2] and the thiophene–
phosphole–thiophene-fused π-systems 3[10] by functionali-
zation of the thiophene ring. Also noteworthy is the π-sys-
tem extension of 2,5-diethynylphosphole with phenyltriazo-
lyl moieties through application of the copper-catalyzed
1,3-dipolar Huisgen reaction with phenyl azide.[11] This ap-
proach enabled further fine-tuning of the photophysical
properties by introducing various substituents at the para
position of the distal phenyl groups. Here, we examine how
far-reaching the electronic effect may be with subtle
changes in the backbone.
Introduction
Neglected for decades, phosphorus is now recognized as
a valuable component in π-conjugated molecular frame-
works.[1] The phosphole ring, in particular, has potential as
a building block in organic materials,[2] as exemplified by
the organic light-emitting devices (OLEDs) based on chlor-
ido(dithienylphosphole)gold(I) complex 1 (Figure 1).[3] The
electronic structure[4] of the phosphole ring combines a low
but not negligible degree of aromaticity, originating from
hyperconjugation between the carbon-based π-system and
the exocyclic σ(P–R) orbital,[5] with a tunable λ3σ3-phos-
phorus center.[3b] This combination provides a handle to
fine-tune the photophysical properties of phosphole-con-
taining π-systems by influencing the extent of conjugation
over the diene moiety.[6] There are limitations to this modifi-
cation, as 2,5-bis(aryl)phospholes having a λ5σ4-phos-
phorus center generally suffer from severely reduced lumi-
nescence quantum yields,[2,3b] making them unsuitable for
electronic devices. However, a viable option is to modify the
[a] Department of Chemistry and Pharmaceutical Sciences, VU
University Amsterdam,
De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
Fax: +31-20-598-7488
E-mail: K.Lammertsma@vu.nl
Homepage: http://www.chem.vu.nl/en/research/division-
organic-chemistry/index.asp
[b] Department of Chemistry, University of Reading,
Whiteknights, Reading, RG6 6AD, UK
[c] Crystal and Structural Chemistry, Bijvoet Center for
Biomolecular Research,
Figure 1. Examples of phosphole-containing π-conjugated molecu-
lar frameworks.
Utrecht University, Padualaan 8, 3584 CH Utrecht, The
Netherlands
As a novel phosphole-containing building block we
chose 2,5-diarylphosphole 8, the first phosphole-containing
compound bearing azido moieties. These moieties enable
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201148.
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K. Lammertsma et al.
FULL PAPER
access to diverse derivatives by application of copper-cata- sulfur afforded corresponding phosphole sulfide 6; this step
lyzed 1,3-dipolar Huisgen addition[12] between the azido proved to be necessary to prevent oxidation during the sub-
groups and various aromatic acetylenes. The present study sequent two steps that employ aqueous media. Acidic hy-
reports the synthesis and photophysical properties of a se- drolysis of 6 afforded primary bis(amine) 7, which was
lect number of such derivatives.
transformed into the corresponding bis(diazonium) salt and
reacted with sodium azide to give target bis(azidophenyl)-
phosphole sulfide 8 in 31% isolated yield. The structure of
8 was unequivocally established by X-ray crystal structure
determination (Figure 2). Characteristic bond lengths,
angles and torsion angles of 8 are given in Table 1. The
most intriguing characteristic of the crystal structure is the
fact that both azido moieties are pointing in more or less
the same direction. As will be discussed later, this “down-
ward” (or syn) orientation of the two aromatic substituents
at these positions is the most stable possibility for the ex-
tended π-systems. The interplanar angles between the
phenyl rings and the central phosphole are 51.48(10)° and
22.02(9)°, respectively, which restricts efficient inter-ring π-
orbital overlap. As a consequence, the C–C bonds of the π-
conjugated path are only slightly smaller than regular single
bonds, and the corresponding C=C bonds are only slightly
longer than unconjugated double bonds (see Table 1).
Results and Discussion
Synthesis of Bis(azidophenyl)phosphole Building Block 8
Targeted building block 8 was synthesized by the multi-
step procedure depicted in Scheme 1. The phosphole moiety
was introduced in the third step using a Fagan–Nugent re-
action,[13] an efficient and elegant method for heterocycle
synthesis, particularly phospholes.[1,14] Bis(imine) 5 was
used as the reactant, since the Fagan–Nugent reaction had
proven incompatible with primary amine and azide func-
tionalities.
Figure 2. Crystal structure of bis(azidophenyl)phosphole sulfide 8
with numbering of the atoms. Hydrogen atoms are omitted for clar-
ity, and ellipsoids are at 50% probability.
Scheme 1. Synthesis of bis(azidophenyl)phosphole sulfide 8.
(a) Pd(OAc)2, PPh3, THF, TEA, r.t., 16 h; (b) benzophenone imine,
NaOtBu, Pd2dba3, BINAP, toluene, 80 °C, 48 h; (c) ZrCp2, THF,
–78 °C (1 h) Ǟ r.t. (3 h); (d) CuCl, THF, 0 °C, 0.5 h; (e) PhPCl2,
THF, 0 °C Ǟ r.t., 18 h; (f) S8, THF, r.t., 5 h; (g) HCl, H2O, THF,
66 °C, 2 h; (h) NaNO2, HCl, H2O, THF, –5 °C, 10 min; (i) NaN3,
NaOAc, H2O, THF, –5 °C, 2 h.
Table 1. Selected bond lengths [Å], angles, and torsion angles [°] of
bis(azidophenyl)phosphole sulfide 8 in the crystal.[a]
C8–C7
C2–C1
C8–C9
P1–C8
C1–P1–C8
C1–P1–C21
P1–C1–C15–C16
P1–C8–C9–C10
C1–C2–C7–C8
1.353(2)
1.363(2)
1.479(2)
C7–C2
C1–C15
P1–C1
1.498(2)
1.473(2)
1.8225(17)
1.8309(18)
103.54(8)
Bis(imine) 5 was efficiently prepared by Sonogashira cou-
pling of octa-1,7-diyne with 2 equiv. of 1-bromo-3-iodo-
benzene, followed by a Buchwald–Hartwig coupling with
benzophenone imine in 98% yield. Treatment of 5 with
ZrCp2 resulted in the formation of a distinctly red transient
zirconocyclopentadiene species that gave, after transmetal-
lation with CuCl and addition of PhPCl2, the desired bis-
1.8038(18) P1–C21
93.44(8)
106.08(8)
20.3(2)
53.8(2)
2.0(2)
C8–P1–C21
C2–C1–P1–C8 –5.25(13)
P1–C1–C2–C7 2.93(18)
(imino)phosphole. Oxidation of this species with elemental [a] Atom numbering in accordance with Figure 2.
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Extended π-Conjugated Systems from Bis(azidophenyl)phospholes
“Click” Chemistry
54.4 (9b), 54.4 (9c), 13.6 (10a), 13.5 (10b), 13.8 (10c) ppm].
Next, we set out to analyze the electronic structure and
photophysical properties of the extended π-systems 9a–c
and 10a–c by UV/Vis absorption and fluorescence spec-
troscopy, cyclic voltammetry, spectroelectrochemistry, and
DFT calculations in order to investigate the influence of the
aromatic end-groups on the core. All spectroscopic data are
summarized in Table 2.
Extension of the π-system of 8 was accomplished using
copper-catalyzed 1,3-dipolar Huisgen addition, coined click
chemistry,[12] by a reaction with phenyl-, 2-pyridyl- and 2-
thienyl-substituted acetylenes using [Cu(NCMe)4][PF6] as
the catalyst and 2,6-lutidine as the ligand (Scheme 2).[12b]
The resulting products, obtained in 82–99% yield, are rep-
resentative examples with the phenyl (9a), electron-rich pyr-
idine (9b), and thiophene (9c) rings introduced at the distal
ends of the extended π-system. The sulfur atoms were effec-
tively removed from the phosphorus center in 71–100%
yield, using P(NMe2)3, to obtain the corresponding λ3σ3-
phospholes 10a–c, which are expected to exhibit higher
quantum yields than sulfur-protected analogues 9. Both the
phosphole and phosphole sulfide based extended π-systems
exhibit distinctive 31P NMR chemical shifts, which are not
influenced by the aromatic end-groups [δ31P = 54.4 (9a),
UV/Vis Absorption and Fluorescence Spectroscopy
The electronic absorption spectra of phosphole sulfides
9a–c show broad unresolved low-energy transitions in the
range λabs = 300–420 nm, wherein two shoulders could be
identified (see Figure 3a). Their fluorescence spectra show
emission from two distinct species. The broad emission
band around λem = 415 nm is dominant at higher concen-
trations (10–4 m; Figure 4a), whereas the one at λem
=
302 nm becomes dominant at lower concentrations (10–5 m;
Figure 4b). At higher concentration, two excitation bands
are observed; one at λexc = 261–266 nm and a broad band
around λexc = 340 nm, whereas two higher-energy bands are
present at λexc = 229–230 nm and λexc = 279–281 nm at
lower concentration. Quantum yields are very low for the
phosphole sulfides and could be determined only at 10–4
m
[ΦF = 0.0019 (9a), 0.0036 (9b), 0.00071 (9c); Table 2], since
the fluorescence intensity at lower concentrations was too
low for accurate quantum yield determination.
Scheme 2. Extension of the π-system by application of click chemis-
try. (a) phenyl-, 2-pyridyl- or 2-thienylacetylene, [Cu(NCMe)4]
[PF6], 2,6-lutidine, CH2Cl2, r.t., 48 h; (b) P(NMe2)3, toluene, reflux,
25 h. lp = lone pair.
Table 2. Photophysical data for phosphole sulfides 9a–c and phos-
pholes 10a–c.
λabs [nm][a]
ε [m–1 cm–1][a] λem [nm][b]
ΦF
τ [ns]
r.t.[d] or
4 K[e]
r.t.[b] or
4 K[c]
9a 248
6.08ϫ104
8.23ϫ103
4.46ϫ103
4.66ϫ104
3.06ϫ104
1.66ϫ104
1.96ϫ104
3.58ϫ103
2.12ϫ103
2.63ϫ104
1.62ϫ104
2.81ϫ104
1.13ϫ104
3.23ϫ104
1.02ϫ104
303
0.0019[b]
n.d.[g]
326 (sh)
385 (sh)
9b 286
324 (sh)
382 (sh)
9c 275
339 (sh)
382 (sh)
10a 290 (sh)
355
10b 286
355
416[f]
Figure 3. Normalized UV/Vis absorption spectra for (a) phosphole
sulfides 9a (blue), 9b (green) and 9c (red) and (b) phospholes 10a
(blue), 10b (green) and 10c (red). Recorded as 10–5 m solutions in
CH2Cl2.
302
0.0036[b]
0.0055[c]
4.6[d]
7.8[e]
414[f]
302
0.00071[b]
n.d.[g]
416[f]
The lowest-energy absorption maxima of the desulfur-
ized phospholes 10a–c (Figure 3b) exhibit a lowest-energy
emission, which is more resolved when compared to their
sulfur-protected analogues. These lowest-energy maxima
are located approximately halfway between the two shoul-
ders observed for the corresponding sulfur-protected ana-
logue. A pronounced bathochromic shift is observed in the
fluorescence maxima (Figure 5), which shows a 160–167 nm
shift to longer wavelengths relative to the emission maxima
of monomeric 9a–c (Figure 4b). Interestingly, the phos-
phole sulfide based π-systems 9a–c exhibit both absorption
and emission maxima of much higher energy than the re-
lated 2,5-diarylphosphole sulfides,[6] suggesting that the
463
469
460
0.273[b]
0.484[c]
0.134[b]
0.209[c]
0.309[b]
0.731[c]
3.8[d]
6.8[e]
3.7[d]
5.7[e]
2.7[d]
6.3[e]
10c 276
356
[a] Measured in CH2Cl2 as 10–6 m solutions. [b] At r.t., determined
for 10–5 m phosphole sulfides 9a–c and 10–7 m phospholes 10a–c in
cyclohexane, using perylene (ΦF = 94%) as the reference. [c] At
4 K, computed according to Equation (1). [d] At r.t., determined
for 10–4 m phosphole sulfides 9a–c and 10–6 m phospholes 10a–c in
cyclohexane. [e] At 4 K, determined for 10–4 m phosphole sulfides
9a–c and 10–6 m phospholes 10a–c in cyclohexane. [f] Recorded as
a 10–4 m solution. [g] Not determined.
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Figure 6. Lifetimes for phospholes 10a (᭛), 10b (ϫ) and 10c (+),
and phosphole sulfide 9b (᭺).
Figure 4. Normalized emission (solid) and excitation (dotted) spec-
tra for phosphole sulfides 9a (blue), 9b (green) and 9c (red); (a) re-
corded as 10–4 m solutions in THF (λexc = 260–266 nm; λem = 405–
410 nm); (b) recorded as 10–5 m solutions in THF (λexc = 230 nm;
λem = 302 nm).
The radiative decay constant (kF) of the emissive sub-
stance can be determined from the room-temperature value
of τ and ΦF according to Equation (1). As kF is tempera-
ture-independent, the non-radiative decay constant (knr)
can be computed at all temperatures using Equation (2) (see
Supporting Information, Tables S1–S4).
conjugation in these systems is somehow disrupted. In con-
trast, phospholes 10a–c behave similarly to related diaryl-
phosphole π-systems (λ3 analogues of 1).[6] These phos-
τ = ΦF/kF (at r.t.)
(1)
pholes emit blue-green light and exhibit sizeable Stokes ΦF = (knr + kF)/kF
(2)
shifts of 104–109 nm.
Since τ and knr are of similar magnitude for the phos-
phole sulfide 9b and the phospholes 10a–c, the low quan-
tum yield for 9a–c cannot be explained by a rapid non-
radiative decay of the S1 to the S0 state (internal conver-
sion). A more plausible explanation is a high rate of in-
tersystem crossing to a triplet state for the phosphole sulf-
ides, which may be caused by the presence of the “heavy
atom” sulfur. The small fraction of molecules that decay to
the vibrational ground state of the S1 state must then be
presumed to fluoresce just as efficiently as the correspond-
ing σ3-phospholes. However, because no phosphorescence
is detected, we conclude that the triplet state decays non-
radiatively.
It is evident that the influence of the aromatic end-group
on the optical properties is subtle and less pronounced than
in related systems in which the (hetero)aromatic rings are
directly attached in the 2- and 5-position at the phosphole
ring. Incorporation of cross-conjugation over the phenyl
rings of the extended π-systems of 9a–c and 10a–c slightly
reduces the efficient interaction with the phospholes as
compared to the interaction with directly attached (hetero)-
aromatic substituents.
Figure 5. Normalized emission spectra of phospholes 10a (blue),
10b (green) and 10c (red). Recorded as 10–7 m solutions in cyclohex-
ane (λexc = 350–356 nm).
As expected, fluorescence quantum yields are dramati-
cally enhanced for the σ3-phospholes 10a–c [ΦF = 0.273
(10a), 0.134 (10b), 0.309 (10c); Table 2]. Notably, these
quantum yields are among the highest reported thus far for
2,5-diarylphosphole-based π-systems.[6]
Excited-state lifetimes (τ) for the emission from phos-
pholes 10a–c were determined from single exponential fits
for the emission decay curves recorded between 4 K and
room temperature (Figure 6). These lifetimes are all around
Cyclic Voltammetry
Phosphole sulfides 9a–c can be reduced between –1.91 V
6 ns up to approximately 120 K, above which they gradually and –2.04 V vs. Fc/Fc+ (Table 3), which is consistent with
become shorter. Those at 4 K and room temperature are the fairly low-lying LUMO of the phosphole-based π-sys-
given in Table 2, and those at intermediate temperatures are tems. On the other hand, no anodic waves were detected
disclosed in the Supporting Information (Tables S1–S4). below +1.0 V. Phospholes 10a–c exhibit slightly more nega-
For comparison, these measurements were also conducted tive cathodic waves between –2.25 V and –2.35 V vs. Fc/Fc+
for bis(pyridyl) derivative 9b, the brightest fluorescent phos- (Table 3), in line with the DFT data (see below, Figure 9).
phole sulfide (see also Figure 6), which has the longest life- Notably, the cathodic potentials of the extended π-systems
time over the entire temperature range.
10a–c reveal that their LUMO levels are still significantly
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Extended π-Conjugated Systems from Bis(azidophenyl)phospholes
lower-lying compared to those of their less extended coun- conversion of bis(pyridyl)phosphole sulfide 9b to [9b]–
a
terparts 2,5-diphenylphosphole (E0Ј = –2.88 V) and 2,5-di- new low-energy absorption band appeared gradually at λmax
thienylphosphole (E0Ј = –2.45 V).[6a] The reductions of = 609 nm [see inset (a) in Figure 8]. The stability of [9b]–
phosphole sulfides 9 are fully reversible at room tempera- on the time scale of the experiment has been indicated by
ture, but only partly reversible for the free phospholes 10 the presence of an isosbestic point at ca. 410 nm. When
(ip,a/ip,c Ͻ 1 at v = 100 mV s–1). The subsequent reduction the electrode potential was further shifted to more negative
of the radical anions [9a–c]– to the corresponding dianions values corresponding to the second reduction, i.e. below
is totally irreversible and affected by weak adsorption –2.35 V, the radical anion converted to an unidentified sec-
(Table 3). This second reduction was also observed for the ondary reduction product, exhibiting an absorption maxi-
short-lived radical anions of phosphole sulfides 10a and mum at λmax = 377 nm [see inset (b) in Figure 8].
10c. Exemplary for this redox behavior is the cyclic voltam-
mogram of bis(phenyl)phosphole sulfide 9a (Figure 7), in
which the solid line represents the reversible first reduction
and the dotted line represents the irreversible second cath-
odic wave. Notably, oxidation of a secondary species
formed by degradation of unstable [9a]2– is perceptible at
–1.02 V (vs. Fc/Fc+) on the reverse anodic scan. For [10a]2–
the corresponding anodic wave is shifted to –0.75 V. Lower-
ing the temperature enhances the stability of the radical
anions and dianions, but it also results in a decreased rate
of electron transfer, thus giving quasi-reversible reduction
waves for both the phosphole sulfides 9a–c and the free
phospholes 10a–c (see Supporting Information, Figure S1
for the cyclic voltammogram of 9a at 223 K).
Figure 8. UV/Vis absorption spectral changes accompanying the
stepwise reduction of bis(pyridyl)phosphole sulfide 9b to [9a]– and
[9a]2– within an OTTLE cell (continuous scanning at 2 mV s–1).
(a) Spectra 1–8 show the isosbestic appearance of a new band at
609 nm belonging to stable [9a]–. (b) Spectra 8–15 show the appear-
ance of a new band at 377 nm belonging most likely to a secondary
reduction product arising from highly unstable [9a]2–.
Table 3. Electrochemical data[a] for phosphole sulfides 9a–c and
phospholes 10a–c.
9a
9b
9c
10a
10b
10c
E1/2 (1) [V]
–1.91[b]
–1.93[b] –2.04[b] –2.25[c] –2.33[c]
–2.35[c]
–2.66
[e]
Ep,c (2) [V][d] –2.24
–2.35
–2.49
–2.62
In accordance with the irreversible nature of the electro-
chemical reduction of bis(pyridyl)phosphole 10b at ambient
temperature (see above), the corresponding radical anion
was not observed in the course of in situ spectroelectro-
chemistry.
[a] Experimental conditions: 10–1 m Bu4NPF6 in C3H7CN, Pt mic-
rodisc electrode, scan rate = 100 mVs–1, T = 293 K. [b] Fully re-
versible first reduction, potentials given vs. Fc/Fc+. [c] Irreversible
cathodic wave (ip,a/ip,c Ͻ 1), potential vs. Fc/Fc+. [d] Irreversible
second reduction, cathodic peak potential vs. Fc/Fc+. [e] Not re-
corded.
DFT Calculations
To assist in elucidating the electronic structure of the
phosphole-containing π-systems 9a–c and 10a–c, their opti-
mized structures and frontier orbitals were computed by
symmetry-restricted PCM-TDDFT calculations.[15] The ge-
ometry with both π-conjugated arms pointing “down-
wards” and the triazole nitrogen atoms pointing out (as de-
picted in Scheme 2 and Figure 9) belongs to the most stable
conformer of all six π-systems. The frontier orbitals of the
π-systems are depicted together with the corresponding rel-
ative energies in Figure 9.
The LUMOs of all the π-systems are almost identical in
nature, irrespective of the aromatic end-group, exhibiting
conjugation between the phosphole ring and the adjacent
phenyl rings. Some mixing of the σ*(PS) orbital into the π*
orbital results in a lowering in energy of the phosphole sulf-
ide based LUMOs. Also, the energies of the HOMOs of the
phosphole compounds (10a–c) are slightly higher in energy
compared to the phosphole sulfide compounds (9a–c).
Figure 7. Cyclic voltammogram of bis(phenyl)phosphole sulfide 9a,
showing the reversible first reduction to [9a]·– (solid) and the
irreversible second reduction to [9a]2– (dashed), recorded at r.t. in
C3H7CN at a Pt microdisc electrode (scan rate = 100 mV s–1).
UV/Vis Spectroelectrochemistry
The nature of the pyridyl-substituted radical anion [9b]– Some variation occurs in the shape of the HOMOs, as thi-
was further examined by UV/Vis spectroelectrochemistry at enyl-substituted 9c exhibits a HOMO, which is delocalized
room temperature (Figure 8). In the course of the cathodic over the entire molecule, as opposed to the other π-systems.
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Table 4. PCM-TDDFT analysis of phosphole sulfides 9a–c and
phospholes 10a–c.
[a]
λabs
λabs
f[b]
Configuration[c]
Transition
[eV] [nm]
9a 3.14
3.68
395 0.4555 HOMO Ǟ LUMO
π Ǟ π*
n Ǟ π*
π Ǟ π*
n Ǟ π*
π Ǟ π*
(80%)
337 0.1315 HOMO–3 Ǟ LUMO
(90%)
9b 3.03
3.66
409 0.5406 HOMO Ǟ LUMO
(92%)
338 0.1024 HOMO–3 Ǟ LUMO
(92%)
9c 3.02
411 0.5439 HOMO Ǟ LUMO
(54%)
HOMO–2 Ǟ LUMO
(40%)
339 0.0934 HOMO–3 Ǟ LUMO
(92%)
364 0.6574 HOMO Ǟ LUMO
(93%)
362 0.6859 HOMO Ǟ LUMO
(94%)
363 0.6849 HOMO Ǟ LUMO
(88%)
Figure 9. Frontier orbitals (LUMOs top and HOMOs bottom) of
phosphole sulfide based π-systems 9a–c and phosphole based π-
systems 10a–c, with corresponding relative energies and corre-
sponding HOMO–LUMO gap (ΔEHL) in eV, calculated with PCM-
TDDFT at CAM-B3LYP/cc-pVTZ.
3.66
10a 3.41
10b 3.43
10c 3.42
n Ǟ π*
π Ǟ π*
π Ǟ π*
π Ǟ π*
This leads to significant charge-transfer for this specific
compound, which may relate to the observed very low
quantum yield of ΦF = 0.0071. Also some spreading of the
HOMO to the triazole rings and aromatic end-groups, al-
though to a lesser extent, is observed for 9a, 9b and 10c.
Several occupied p-orbitals are close in energy and type of
aromatic end-group has some influence on the extent to
which they contribute to the HOMO.
[a] The calculated excitation energies of the phosphole sulfide com-
pounds 9a–c and the phosphole compounds 10a–c are underesti-
mated by an average of 10–30 nm. [b] Oscillator strength. [c] Domi-
nant orbital transitions.
In summary, these results demonstrate clearly that the
influence of the aromatic end-groups is subtle but not negli-
gible. The nature of the group at the terminal position has
some influence on the shape of the HOMO and, as such,
determines the amount of charge transfer occurring during
excitation. Also, some tuning of the emission wavelength is
accomplished, which exerts an influence on the HOMO–
LUMO gap. Such fine-tuning of the photophysical proper-
ties is indeed observed, despite the presence of cross-conju-
gation between both triazole moieties and the central phos-
phole ring.
The calculated HOMO–LUMO gaps (ΔEHL) of the λ3-
phosphole π-systems 10a–c are significantly larger than
those of the sulfur-protected ones (Figure 9), which is in
accordance with the absorption spectra. However, the emis-
sion spectra show an opposite effect, as the values for λem of
the λ3-phospholes are shifted towards lower energies with
respect to those of the phosphole sulfides. This discrepancy
may be explained by a higher degree of relaxation for the
excited states of the free phospholes. Variations in absorp-
tion and emission maxima, caused by the presence of dif-
ferent aromatic end-groups, are not reflected in the calcu-
lated ΔEHL values of the phosphole-based π-systems.
The singlet vertical excitation energies were calculated
with linear response PCM-TDDFT.[15] The lowest-lying sin-
glet vertical excitation energy and oscillator strengths along
Conclusions
We have synthesized a bifunctional 2,5-diphenylphos-
with the main excitation configuration of the phosphole- phole-based π-system with functional moieties that effec-
containing π-systems are listed in Table 4. The calculated tively extend the π-conjugated framework. Bis(azidophen-
absorption maxima of phosphole sulfides [λabs(9a–c) = 395– yl)phosphole sulfide building block 8, obtained in 31%
411 nm] and phospholes [λabs(10a–c) = 362–364 nm] corre- yield in a multi-step reaction sequence, was efficiently func-
spond very well to the experimentally obtained ones tionalized using the copper-catalyzed Huisgen 1,3-dipolar
[λabs(9a–c) = 382–385 nm; λabs(10a–c) = 355–356 nm]. The cycloaddition to provide extended π-systems with phenyltri-
excitations of the compounds are mainly related to transi- azolyl (9a), pyridyltriazolyl (9b) and thienyltriazolyl (9c)
tions involving the two frontier orbitals (HOMO and end-groups and the corresponding sulfur-free λ3σ3-phos-
LUMO), except for compound 9c, where also the HOMO– phorus-based 10a–c.
2 plays an important role in the excitation, having a contri-
The π-systems 10a–c fluoresce efficiently in the blue-
bution of 40%. The HOMO–2 orbital of 9c is similar in green region (λem = 460–469 nm; ΦF = 0.13–0.31), which
shape and 0.21 eV lower in energy, compared to the corre- represents a significant bathochromic shift and strongly in-
sponding HOMO. The lowest-energy transitions can all be creased luminescence intensity compared to their phosphole
assigned to be of π Ǟ π* character. For the phosphole sulf- sulfide based analogues 9a–c (λem = 414–416 nm; ΦF
=
ides (9a–c) a second transition can be allocated to be of 0.00071–0.0036). The origin of the low fluorescence quan-
n Ǟ π* type from the sulfur lone pair into the empty π- tum yields of the phosphole sulfide based π-systems has
orbital.
been attributed to intersystem crossing to a non-radiatively
6716
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 6711–6721

Extended π-Conjugated Systems from Bis(azidophenyl)phospholes
connected to an air-tight single-compartment cell containing a Pt
microdisc (0.14 mm2 surface) working electrode (polished freshly
between scans with a 0.25 μm grain diamond paste), a Pt wire aux-
iliary electrode and an Ag wire pseudoreference electrode calibrated
with ferrocene as an internal standard. The compounds were
studied as 10–3 m solutions in dry C3H7CN, distilled freshly from
CaH2. Bu4NPF6 (Aldrich) was recrystallized twice from absolute
ethanol and dried under vacuum at 80 °C overnight prior to using
it as the 10–1 m supporting electrolyte. UV/Vis absorption spectroe-
lectrochemical experiments were carried out with an optically
decaying triplet state. The π-systems of 9a–c and 10a–c are
easily reducible, and the electrogenerated radical anions of
the pyridyl-substituted phosphole sulfide 9b could be iden-
tified spectroscopically at room temperature [λabs(9b·–) =
609 nm].
The nature of the (aromatic) end-group determines to
some extent which p-orbitals contribute to the HOMO of
the π-system. The TDDFT calculations reveal that some
fine-tuning of the photophysical properties of the extended
π-systems is achieved by determining the extent of charge- transparent thin-layer electrochemical (OTTLE) cell equipped with
CaF2 windows.[18] The potential of the Pt minigrid (32 wires per
transfer occurring during excitation, which has a subtle ef-
cm) working electrode was controlled with a PA4 potentiostat
fect on the shape and location of the HOMO and on the
(Laboratory Devices, Polná, Czech Republic). The potential scan
size of the HOMO–LUMO gap.
rate was 2 mV s–1. The UV/Vis absorption spectra were recorded
Their intense fluorescence, the relative stability of their
with an HP8453 diode array spectrophotometer in intervals of a
radical anions, and their tunability make the λ3-phosphole-
few seconds at continuous potential sweep.
based π-systems 10a–c potential candidates for incorpora-
tion into electronic devices such as OLEDs. Moreover, use
of the bis(azidophenyl)phosphole sulfide building block 8
in the so-called click reaction may give access to diverse
fluorescent probes suitable in solid-state, biomolecular, and
enzymatic systems.
1,8-Bis(3-bromophenyl)octa-1,7-diyne (4): To a solution of 1-bromo-
3-iodobenzene (3.18 mL, 25.0 mmol, 2.0 equiv.) and octa-1,7-diyne
(1.69 mL, 12.75 mmol, 1.02 equiv.) in NEt3 (30 mL) and THF
(100 mL), Pd(OAc)2 (56 mg, 0.25 mmol, 2%), PPh3 (131 mg,
0.50 mmol, 4%) and CuI (95 mg, 0.50 mmol, 4%) were added, and
the mixture was stirred at room temp. for 16 h. The dark yellow
turbid solution was diluted with pentane and washed with 0.5 m
HCl (aq.), H2O, 5% NaHCO3 (aq.) and H2O. The organic layer
was dried with MgSO4, filtered, and the solvents were removed in
vacuo. The dark red residue was purified by column chromatog-
raphy on silica gel eluting with hexane/CH2Cl2, 10:0 to 7:3 [RF (3:1)
Experimental Section
General Remarks: All reactions were carried out under nitrogen
using standard Schlenk techniques and dry solvents, unless stated
otherwise. THF and Et2O were distilled from Na/benzophenone,
= 0.32], which afforded 4 as white semi-crystalline solid (5.08 g,
12.2 mmol, 98%). M.p. 41.7–42.7 °C. 1H NMR (250.13 MHz,
NEt3 from CaH2, CH2Cl2 from CaCl2 and toluene from Na. 2-
3
CDCl3): δ = 7.55 (s, 2 H, ArH2), 7.40 (d, JHH = 8.0 Hz, 2 H,
Ethynyl-thiophene[16] and P(NMe2)3[17] were prepared according to
ArH4), 7.32 (d, 3JHH = 7.8 Hz, 2 H, ArH6), 7.14 (t, 3JHH = 7.8 Hz,
literature procedures and were kept as stock solutions (0.15 m in
2 H, ArH5), 2.48 (br. s, 4 H, ϵC-CH2-CH2-), 1.78 (br. s, 4 H, ϵC-
CH2Cl2 and 1.5 m in THF respectively). NMR measurements were
CH2-CH2-) ppm. 13C NMR (62.90 MHz, CDCl3): δ = 134.8 (s,
performed with a Bruker Avance 250 or a Bruker Avance 400 spec-
ArC2), 131.2 (s, ArC4), 130.5 (s, ArC6), 130.0 (s, ArC5), 126.4 (s,
trometer. NMR chemical shifts were externally referenced to SiMe4
ArC1), 122.4 (s, ArC3), 91.7 (s, Ar-CϵC-), 80.0 (s, Ar-CϵC-), 28.1
(1H and 13C) or 85% H3PO4 (31P). Atom numbering of the 2,5-
(s, ϵC-CH2-CH2-), 19.4 (s, ϵC-CH2-CH2-) ppm. HRMS (EI):
diarylphosphole system is according to Figure 2. IR spectra were
recorded with a Mattson-6030 Galaxy FT-IR spectrophotometer
(KBr) or a Shimadzu FTIR-8400s spectrophotometer (neat), and
calcd. for C20H16Br2 [M] 413.9619; found 413.9614; m/z (%) = 418
(12) [M]+ (81Br2), 416 (23) [M]+ (81Br79Br), 414 (12) [M]+ (79Br2).
IR (KBr): ν = 2943 (w), 1588 (m), 1550 (m), 1470 (m), 1402 (w),
˜
high-resolution mass spectra were measured using a Finnigan Mat
900 mass spectrometer operating at an ionization potential of 70 eV
(EI) or a JEOL JMS SX/SX 102A four-sector mass spectrometer,
equipped with a Xenon primary atom beam, utilizing a 3-ni-
trobenzyl (3-NOBA) matrix (FAB). Melting points were measured
with a Stuart Scientific SMP3 melting point apparatus in unsealed
capillaries and are uncorrected. UV/Vis absorption spectra were
recorded at room temperature with a Carey 300 UV/Vis spectro-
photometer and room temperature fluorescence spectra with a Per-
kin–Elmer LS50-B spectrofluorimeter, using 10 mm quartz cu-
vettes. Spectra were recorded with a scan speed of 200 nm/min,
using a spectral width of 5 nm for both excitation and emission.
Quantum yields were determined in cyclohexane as 10–4 m solu-
tions for phosphole sulfides 9a–c and as 10–7 m solutions for phos-
pholes 10a–c, using perylene as standard (ΦF = 94%). Tempera-
ture-dependent luminescence life-time measurements were per-
formed with an Edinburgh FLS 920 spectrofluorimeter using time-
correlated photon counting under pulsed excitation at 375 nm with
an EPL375 picosecond diode laser. The temperature was varied
using an Oxford Instruments Optistat CF liquid helium flow cryo-
stat in combination with an ITC temperature controller. The sam-
ple solution was inserted in a homemade quartz cuvette of ca. 1 cm
diameter. Conventional cyclic voltammetric experiments were per-
formed using a computer-controlled EG&G PAR 283 potentiostat
1324 (w), 1217 (w), 1073 (w), 993 (w), 869 (w), 784 (s), 722 (w),
680 (m), 436 (w) cm–1. UV/Vis (CH2Cl2): λabs = 255 nm (ε =
2.11ϫ104 m–1 cm–1).
1,8-Bis{3-[(diphenylmethylene)amino]phenyl}octa-1,7-diyne
(5):
Compound 4 (2.08 g, 5.00 mmol) was dissolved in Et2O (20 mL),
and the solvent was removed under reduced pressure. This was re-
peated two more times to remove traces of water; 4 was then dis-
solved in toluene (150 mL), and benzophenone imine (2.00 mL,
12.0 mmol, 2.4 equiv.), Pd2dba3 (46 mg, 0.050 mmol, 1%), BINAP
(93 mg, 0.15 mmol, 3%) and NaOtBu (1.35 g, 14.0 mmol,
2.8 equiv.) were added. The black reaction mixture was stirred at
80 °C for 48 h. The colour changed to yellow turbid, and the reac-
tion mixture was diluted with pentane and washed with H2O and
0.25 m HCl (aq.). The organic layer was dried with MgSO4, filtered,
and the solvents were removed in vacuo. The dark orange residue
was purified by column chromatography on silica gel eluting with
hexane/EtOAc, 9:1 (RF = 0.30) to obtain 5 as a slightly yellow
powder (3.08 g, 5.00 mmol, 100%). M.p. 71.8–72.4 °C. 1H NMR
3
(400.13 MHz, CDCl3): δ = 7.66 (d, JHH = 7.3 Hz, 4 H, o-Z-PhH),
3
4
3
7.39 (tt, JHH = 7.3, JHH = 1.8 Hz, 2 H, p-Z-PhH), 7.32 (t, JHH
= 7.3 Hz, 4 H, m-Z-PhH), 7.15–7.20 (m, 6 H, m-E-PhH, p-E-PhH),
7.01–7.05 (m, 4 H, o-E-PhH), 6.94 (t, JHH = 7.7 Hz, 2 H, ArH5),
3
3
4
4
6.88 (dt, JHH = 7.7, JHH = 1.6 Hz, 2 H, ArH6), 6.76 (t, JHH
=
Eur. J. Org. Chem. 2012, 6711–6721
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6717

K. Lammertsma et al.
FULL PAPER
1.6 Hz, 2 H, ArH2), 6.48 (ddd, JHH = 7.7, JHH = 1.6, JHH
3
4
4
=
128.43 (d, 2JCP = 12.7 Hz, o-PPh), 128.41 (d, 4JCP = 1.3 Hz, ArC5),
1.3 Hz, 2 H, ArH4), 2.34 (m, 4 H, ϵC-CH2-CH2-), 1.64 (m, 4 H, 128.3 (s, p-E-PhC), 128.2 (d, JCP = 73.5 Hz, ipso-PPh), 128.0 (s,
1
3
ϵC-CH2-CH2-) ppm. 13C NMR (62.90 MHz, CDCl3): δ = 169.0
(s, Ph2C=N–), 151.6 (s, ArC3), 139.9 (s, ipso-Z-PhC), 136.3 (s, ipso-
E-PhC), 131.2 (s, p-Z-PhC), 129.8 (s, o-E-PhC), 129.7 (s, o-Z-PhC),
129.1 (s, p-E-PhC), 128.7 (s, ArC5), 128.6 (s, m-Z-PhC), 128.4 (s,
m-Z-PhC), 127.8 (s, m-E-PhC), 123.6 (d, JCP = 3.8 Hz, ArC6),
3
3
121.2 (d, JCP = 6.8 Hz, ArC2), 120.5 (s, ArC4), 27.3 (d, JCP
=
13.2 Hz, Cq-CH2-CH2-), 22.4 (s, Cq-CH2-CH2-) ppm. 31P NMR
(CDCl3; 101.25 MHz): δ = 53.5 (s) ppm. In the H and 13C NMR
1
m-E-PhC), 126.8 (s, ArC6), 124.50 (s, ArC2), 124.47 (s, ArC1), 120.6 spectroscopic data, the imine-phenyl ring pointing towards the
(s, ArC4), 89.9 (s, Ar–CϵC–), 81.3 (s, Ar–CϵC–), 28.2 (s, ϵC– phenyloctadiyne moiety is labeled Z, and the phenyl ring pointing
CH2-CH2-), 19.4 (s, ϵC–CH2-CH2-) ppm. In the 1H and 13C NMR away is labeled E. HRMS (EI): calcd. for C52H42N2PS [M + H]
spectroscopic data, the imine phenyl ring pointing towards the
phenyloctadiyne moiety is labeled Z, and the phenyl ring pointing
away is labeled E. HRMS (EI): calcd. for C46H37N2 [M] 617.2957,
757.2806, found 751.2811; m/z (%) = 757 (100) [M + H]+, 756 (39)
[M]+, 679 (5) [M – Ph]+. IR (neat): ν = 3052 (w), 2943 (w), 2868
˜
(w), 1613 (w), 1587 (m), 1572 (s), 1476 (w), 1445 (m), 1317 (m),
found 617.2960; m/z (%) = 617 (100) [M + H]+, 616 (77) [M]+, 539 1287 (m), 1142 (w), 1104 (m), 1075 (w), 1026 (w), 955 (m), 892 (w),
(16) [M – Ph]+. IR (neat): ν = 3057 (w, CAr–H), 2938 (w, CH2),
784 (m), 765 (m), 746 (m), 697 (s), 662 (s) cm–1. UV/Vis (CH2Cl2):
˜
2861 (w, CH2), 1585 (s, N = H), 1570 (s), 1491 (w), 1474 (m), 1447 λabs = 229 (ε = 5.08ϫ104 m–1 cm–1), 248 (ε = 5.47ϫ104 m–1 cm–1),
(m), 1418 (w), 1314 (w), 1302 (w), 1296 (w), 1254 (m), 1186 (m), 336 nm (ε = 1.35ϫ104 m–1 cm–1).
1134 (m), 1074 (w), 966 (s), 949 (m), 926 (m), 874 (m) cm–1. UV/
2,5-Bis(3-aminophenyl)-1-phenyl-1-thiooxophosphole (7): 0.5 m HCl
(aq. 20 mL, 5 equiv.) was added to a solution of 6 (1.44 g,
1.90 mmol) in wet THF (50 mL). The reaction mixture was re-
Vis (CH2Cl2): λabs = 254 (ε = 7.35ϫ104 m–1 cm–1), 336 nm (ε =
5.86ϫ103 m–1 cm–1).
fluxed for 3 h, subsequently diluted with Et2O and washed with
H2O and 5% NaHCO3 (aq.). The organic layer was dried with
2,5-Bis{3-[(diphenylmethylene)amino]phenyl}-1-phenyl-1-thiooxo-
phosphole (6): Compound 5 (1.07 g, 1.74 mmol) was dissolved in
MgSO4, filtered, and the solvents were removed in vacuo. The yel-
Et2O (15 mL) and the solvent removed under reduced pressure.
low residue was purified by column chromatography on Al2O3 elut-
This was repeated two more times to remove traces of water. In a
separate Schlenk vessel, ZrCp2Cl2 (508 mg, 1.74 mmol, 1.0 equiv.)
ing with hexane/EtOAc, 4:1 to 0:1 [RF (EtOAc) = 0.91] to remove
benzophenone, which afforded 7 as a yellow foam (530 mg,
was suspended in THF (25 mL). At –78 °C, nBuLi (1.6 m in hexane,
1.24 mmol, 65%). M.p. 80.3–80.6 °C (decompos.); 96.2–97.5 °C
2.28 mL, 3.65 mmol, 2.1 equiv.) was added dropwise to the mixture
3
(melt.). 1H NMR (400.13 MHz, CDCl3): δ = 7.82 (ddd, JHP
=
of ZrCp2Cl2 in THF over 20 min. After stirring at –78 °C for
30 min, a solution of 5 in THF (30 mL) was added dropwise to the
yellow reaction mixture of ZrCp2 over 40 min. The reaction mix-
ture was slowly warmed to room temperature, during which the
reaction mixture turned dark red, indicating the formation of the
zirconocyclopentadiene species. After stirring at room temperature
for 3 h, the reaction mixture was cooled to 0 °C, and CuCl (361 mg,
3.65 mmol, 2.1 equiv.) was added. Stirring was continued at 0 °C
for 30 min, after which PhPCl2 (236 μL, 1.74 mmol, 1.0 equiv.) was
added dropwise at 0 °C over 15 min. The dark reaction mixture
was slowly warmed to room temperature with continued stirring
for 16 h. Then, S8 (89.1 mg, 347 μmol, 0.2 equiv.) was added, and
the clear yellow reaction mixture was stirred for another 5 h. The
solvent was removed and the dry residue redissolved in CHCl3,
which was washed extensively with H2O. The combined H2O layers
were extracted with additional CHCl3, and the combined organic
layers were dried with MgSO4, filtered, and the solvent was re-
moved in vacuo. The green residue was purified by column
chromatography on silica gel eluting with pentane/EtOAc, 9:1 to
2:1 [RF (9:1) = 0.08] to obtain 6 as a yellow powder (1.04 g,
1.37 mmol, 79%). M.p. 154.8–155.2 °C (decompos.), 165.7–
13.6, 3JHH = 7.6, 4JHH = 1.5 Hz, 2 H, o-PPhH), 7.36–7.47 (m, 3 H,
m-PPhH, p-PPhH), 7.05 (t, JHH = 7.8 Hz, 2 H, ArH5), 6.75 (s, 2
3
3
3
H, ArH2), 6.64 (d, JHH = 7.6 Hz, 2 H, ArH6), 6.57 (dd, JHH
=
8.0, JHH = 1.1 Hz, 2 H, ArH4), 3.51 (br. s, 4 H, NH2), 2.77 (br. s,
4
4 H, Cq-CH2-CH2), 1.76 (br. s, 4 H, Cq-CH2-CH2) ppm. 13C NMR
2
(62.90 MHz, CDCl3): δ = 147.9 (d, JCP = 23.5 Hz, PC=C), 146.0
(s, ArC3), 133.9 (d, 1JCP = 66.6 Hz, PC=C), 133.4 (d, 2JCP = 1.4 Hz,
ArC1), 131.4 (d, JCP = 3.0 Hz, p-PPh), 130.6 (d, JCP = 11.4 Hz,
4
3
m-PPh), 129.0 (s, ArC5), 128.5 (d, JCP = 12.4 Hz, o-PPh), 128.2
2
(d, 1JCP = 73.4 Hz, ipso-PPh), 119.4 (d, 3JCP = 5.3 Hz, ArC6), 115.5
(d, JCP = 4.9 Hz, ArC2), 114.6 (d, JCP = 1.1 Hz, ArC4), 27.8 (d,
3JCP = 13.4 Hz, Cq-CH2-CH2-), 22.6 (s, Cq-CH2-CH2) ppm. 31P
NMR (101.25 MHz, CDCl3): δ = 53.9 (s) ppm. HRMS (EI): calcd.
for C26H26N2PS [M + H] 428.1554, found 429.1548; m/z (%) = 429
3
5
(100) [M + H]+, 428 (54) [M]+. IR (neat): ν = 2923 (w), 2858 (w),
˜
1614 (m), 1596 (m), 1580 (m), 1487 (m), 1435 (m), 1303 (m), 1228
(w), 1166 (w), 1095 (m), 1025 (w), 997 (w), 907 (w), 867 (w), 776
(m), 744 (m), 716 (s), 689 (s), 668 (s) cm–1. UV/Vis (CH2Cl2): λabs
= 230 (ε = 1.40ϫ104 m–1 cm–1), 278 (sh, ε = 5.80ϫ103 m–1 cm–1),
333 nm (ε = 4.40ϫ103 m–1 cm–1).
165.9 °C (melt.). 1H NMR (400.13 MHz, CDCl3): δ = 7.69 (d, 3JHH 2,5-Bis(3-azidophenyl)-1-phenyl-1-thiooxophosphole (8): 0.5 m HCl
= 7.2 Hz, 4 H, o-Z-PhH), 7.63–7.68 (m, JHP = 13.7 Hz, 2 H, o- (aq. 4 mL, 4.0 equiv.) was added slowly to a solution of 7 (230 mg,
537 μmol) in wet THF (6 mL) at –5 °C. To this viscous solution,
NaNO2 (88.9 mg, 1.29 mmol, 2.4 equiv.) in H2O (2 mL) was added
7.30–7.35 (m, 2 H, m-PPhH), 7.23 (t, JHH = 7.3 Hz, 2 H, p-E- dropwise over 7 min and stirring was continued for 20 min. Then,
3
4
3
PPhH); 7.41–7.46 (m, JHH = 1.9 Hz, 1 H, p-PPhH), 7.45 (t, JHH
3
= 7.2 Hz, 4 H, p-Z-PhH), 7.37 (t, JHH = 7.2 Hz, 4 H, m-Z-PhH),
3
3
3
PhH), 7.19 (t, JHH = 7.3 Hz, 4 H, m-E-PhH), 7.04 (t, JHH
=
urea (10 mg, 0.17 mmol, 0.3 equiv.) was added to destroy the excess
nitrous acid. The reaction mixture was carefully poured into a solu-
7.8 Hz, 2 H, ArH5), 7.03 (d, JHH = 7.3 Hz, 4 H, o-E-PhH); 6.99
3
(dd, 3JHH = 7.8, 4JHH = 0.8 Hz, 2 H, ArH6), 6.65 (d, 3JHH = 7.8 Hz, tion of NaN3 (140 mg, 2.15 mmol, 4.0 equiv.) and NaOAc (264 mg,
2
4
2 H, ArH4), 6.58 (s, 2 H, ArH2), 2.32 (dd, JHH = 18.0, JHP
=
3.22 mmol, 6 equiv.) in H2O (5 mL) at –5 °C, and rinsed with THF
(2 mL). Stirring of the orange viscous suspension was continued at
–5 °C for 2 h, after which the reaction mixture was diluted with
Et2O and the organic layer washed with H2O. The organic layer
was dried with MgSO4, filtered, and the solvent removed in vacuo.
2
4
3.1 Hz, 2 H, Cq-CH2-), 2.23 (dd, JHH = 18.0, JHP = 3.1 Hz, 2 H,
Cq-CH2-), 1.56 (br. s,
4
H, -CH2-CH2-) ppm. 13C NMR
(62.90 MHz, CDCl3): δ = 168.3 (s, Ph2C=N-), 151.1 (s, ArC3),
2
147.8 (d, JCP = 23.3 Hz, PC=C), 139.5 (s, ipso-Z-PhC), 135.9 (s,
ipso-E-PhC), 133.5 (d, JCP = 92.4 Hz, PC=C), 132.9 (s, ArC1), The orange residue was purified by column chromatography on
1
4
131.4 (d, JCP = 2.5 Hz, p-PPh), 130.59 (s, p-Z-PhC), 130.57 (d,
silica gel eluting with hexane/EtOAc, 9:1 to 1:1 [RF (9:1) = 0.33] to
3JCP = 11.0 Hz, m-PPh), 129.5 (s, o-E-PhC), 129.2 (s, o-Z-PhC), obtain 8 as a yellow powder (160 mg, 333 μmol, 62%). Cubic crys-
6718 Eur. J. Org. Chem. 2012, 6711–6721
www.eurjoc.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Extended π-Conjugated Systems from Bis(azidophenyl)phospholes
4
3
tals of 8, suitable for X-ray analysis, were grown by slow cooling
2JHH = 18.1, JHP = 3.2 Hz, 2 H, Cq-CH2-CH2), 1.83 (t, JHH
=
of a hexane solution. M.p. 110.4–110.9 °C. 1H NMR (250.13 MHz,
2.7 Hz, 4 H, Cq-CH2-CH2) ppm. 13C NMR (62.90 MHz, CDCl3 ):
3
3
2
CDCl3): δ = 7.84 (dd, JHP = 13.8, JHH = 6.8 Hz, 2 H, o-PPhH),
δ = 149.4 (d, JCP = 22.0 Hz, PC=C), 148.4 (s, NCH=C), 136.9 (s,
7.41–7.55 (m, 3 H, m-PPhH, p-PPhH), 7.29 (t, 3JHH = 8.0 Hz, 2 H,
ArC3), 134.1 (d, JCP = 12.6 Hz, ArC1), 133.2 (d, JCP = 81.8,
2
1
ArH5), 7.13 (d, JHH = 8.0 Hz, 2 H, ArH6), 6.96 (s, 2 H, ArH2),
PC=C), 132.2 (d, JCP = 3.2 Hz, p-PPh), 130.6 (d, JCP = 11.3 Hz,
3
4
2
6.93 (d, JHH = 8.0 Hz, 2 H, ArH4), 2.79 (br. s, 4 H, Cq-CH2- o-PPh), 130.1 (s, ipso-Ph), 129.8 (s, ArC4), 129.1 (d, JCP = 6.3 Hz,
3
3
CH2), 1.81 (br. s, 4 H, Cq-CH2-CH2) ppm. 13C NMR (62.90 MHz,
m-PPh), 129.0 (s, ArC5), 128.8 (s, m-Ph), 128.4 (s, p-Ph), 127.1 (d,
CDCl3): δ = 148.7 (d, JCP = 22.5 Hz, PC=C), 140.1 (s, ArC3),
1JCP = 73.6 Hz, ipso-PPh), 125.8 (s, o-Ph), 120.5 (d, JCP = 5.0 Hz,
2
3
134.3 (s, ArC1), 133.6 (d, JCP = 68.1 Hz, PC=C), 132.1 (d, JCP
=
ArC2), 119.8 (d, 3JCP = 1.3 Hz, ArC6), 117.4 (s, NCH), 27.8 (d, 3JCP
1
4
3.1 Hz, p-PPh), 130.7 (d, JCP = 11.5 Hz, m-PPh), 129.8 (s, ArC5), = 13.2 Hz, Cq-CH2-CH2), 22.4 (s, Cq-CH2-CH2) ppm. 31P NMR
3
2
1
129.0 (d, JCP = 12.4 Hz, o-PPh), 127.4 (d, JCP = 73.5 Hz, ipso-
(101.25 MHz, CDCl3): δ = 54.4 (s) ppm. HRMS (FAB): calcd. for
C42H34N6PS [M + H] 685.2303, found 685.2296; m/z (%) = 685
(100) [M + H]+, 684 (23) [M]+, 542 (29) [M – TrPh + 2 H]+. IR
PPh), 125.6 (d, JCP = 5.0 Hz, ArC6), 119.3 (d, JCP = 5.1 Hz,
ArC2), 118.6 (d, 5JCP = 1.1 Hz, ArC4), 27.8 (d, 3JCP = 13.1 Hz, Cq-
CH2-CH2), 22.6 (s, Cq-CH2-CH2) ppm. 31P NMR (101.25 MHz,
3
3
(neat): ν = 2976 (w), 2933 (w), 1576 (m), 1477 (m), 1261 (m), 1227
˜
CDCl3): δ = 54.2 (s) ppm. HRMS (EI): calcd. for C26H21N6PS [M] (w), 1093 (s), 1038 (s), 1019 (s), 881 (w), 797 (s), 761 (s), 718 (m),
480.1286, found 480.1307; m/z (%) = 480 (100) [M]+, 452 (3) [M –
690 (s), 668 (m) cm–1. UV/Vis (CH2Cl2): λab s = 248 (ε =
6.08ϫ104 m–1 cm–1), 326 nm (ε = 8.23ϫ103 m–1 cm–1). FS (cyclo-
hexane): λem = 303 nm (ΦF = 0.0019).
N ]+. IR (KBr): ν = 3047 (w), 2942 (w), 2856 (w), 2108 (s, N ),
˜
2
3
1595 (m), 1575 (m), 1480 (w), 1436 (w), 1419 (w), 1297 (m), 1095
(w), 789 (w), 746 (w), 717 (m), 690 (m), 670 (w) cm–1. UV/Vis
(CH2Cl2): λabs = 244 (ε = 3.85ϫ104 m–1 cm–1), 328 nm (ε =
8.85ϫ103 m–1 cm–1).
2,5-Bis[4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl]-1-phenyl-1-thiooxo-
phosphole (9b): A solution of 8 (70.0 mg, 146 μmol), 2-ethynylpyr-
idine (30.3 μL, 300 μmol, 2 equiv.), 2,6-lutidine (34.9 μL, 300 μmol,
2 equiv.) and [Cu(NCMe)4][PF6] (2.7 mg, 7.3 μmol, 0.05 equiv.) in
CH2Cl2 (7 mL) was stirred at room temperature for 64 h and sub-
sequently diluted with CH2Cl2 and washed with water. The organic
layer was dried with MgSO4, filtered, and the solvents were re-
moved. The yellow crude product was purified by column
chromatography on silica gel eluting with hexane/EtOAc, 1:2 (RF
= 0.18) affording 9b as a yellow powder (83.9 mg, 122 μmol, 84%).
Crystal Structure Determination of 8: C26H21N6PS (480.52), yellow
plate, 0.18ϫ0.12ϫ0.06 mm, monoclinic, P21/c (no. 14), a =
10.0280(1), b = 15.1083(2), c = 17.6600(2) Å, β = 119.0155(5)°, V
= 2339.78(5) Å3, Z = 4, DX = 1.364 g/cm3, μ = 0.24 mm–1. 39210
reflections were measured with a Nonius Kappa CCD dif-
fractometer with rotating anode and graphite monochromator (λ
= 0.71073 Å) up to a resolution of (sin θ/λ)max = 0.65 Å–1 at a
temperature of 150(2) K. Intensity data were integrated with the
HKL2000 software.[19] Absorption correction and scaling were per-
formed based on multiple measured reflections with SADABS[20]
M.p. 77.1–77.5 °C. 1H NMR (400.13 MHz, CDCl3): δ = 8.62 (d,
3
3JHH = 4.5 Hz, 2 H, PyH6), 8.50 (s, 2 H, NCH), 8.22 (d, JHH
=
=
3
3
4
7.9 Hz, 2 H, PyH3), 7.84 (ddd, JHP = 13.9, JHH = 6.8, JHH
(0.77–0.98 correction range). 5358 reflections were unique (Rint
=
1.5 Hz, 2 H, o-PPhH), 7.81 (br. s, 2 H, ArH2), 7.80 (dt, 3JHH = 7.9,
3
4
0.057), of which 3995 were observed [IϾ2σ(I)]. The structure was
solved with Direct Methods using the program SHELXS-97[21] and
refined with SHELXL-97[21] against F2 of all reflections. Non-hy-
drogen atoms were refined with anisotropic displacement param-
eters. All hydrogen atoms were located in difference Fourier maps
and refined with a riding model. 307 parameters were refined with
no restraints. R1/wR2 [IϾ2σ(I)] = 0.0402/0.0914. R1/wR2 (all refl.)
= 0.0647/0.1026. S = 1.029. Residual electron density between
–0.25 and 0.32 e/Å3. Geometry calculations and checking for
higher symmetry were performed with the PLATON program.[22]
CCDC-853315 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
4JHH = 1.7 Hz, 2 H, PyH4), 7.72 (dd, JHH = 7.9, JHH = 0.9 Hz,
2 H, ArH4), 7.53 (dd, 3JHH = 7.8, 4JHH = 1.0 Hz, 2 H, ArH6), 7.46
(t, JHH = 7.9 Hz, 2 H, ArH5), 7.40–7.51 (m, 3 H, m-PPhH, p-
3
PPhH), 7.26 (t, JHH = 5.9 Hz, 2 H, PyH5), 2.90 (dd, JHH = 18.1,
3
2
2
4
4JHP = 3.5 Hz, 2 H, Cq-CH2-CH2), 2.82 (dd, JHH = 18.1, JHP
=
3
3.1 Hz, 2 H, Cq-CH2-CH2), 1.82 (t, JHH = 2.8 Hz, 4 H, Cq-CH2-
CH2) ppm. 13C NMR (100.62 MHz, CDCl3): δ = 149.9 (s, PyC2),
149.5 (s, PyC6), 149.3 (d, JCP = 22.1 Hz, PC=C), 149.0 (s,
2
2
NCH=C), 136.94 (s, PyC4), 136.94 (s, ArC3), 134.3 (d, JCP
=
=
1
4
12.7 Hz, ArC1), 133.4 (d, JCP = 81.2 Hz, PC=C), 132.3 (d, JCP
3.0 Hz, p-PPh), 130.6 (d, JCP = 11.6 Hz, o-PPh), 129.9 (s, ArC5),
2
129.3 (d, JCP = 4.5 Hz, ArC6), 129.1 (d, JCP = 12.5 Hz, m-PPh),
3
3
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ 127.0 (d, JCP = 74.1 Hz, ipso-PPh), 123.1 (s, PyC5), 120.6 (d, JCP
data_request/cif.
1
3
3
= 5.6 Hz, ArC2), 120.4 (s, PyC3), 119.8 (s, NCH), 119.8 (d, JCP
=
1.1 Hz, ArC4), 27.9 (d, JCP = 12.8 Hz, Cq-CH2-CH2), 22.5 (s, Cq-
CH2-CH2) ppm. 31P NMR (101.25 MHz, CDCl3): δ = 54.3 (s) ppm.
HRMS (FAB): calcd. for C42H32N8PS [M + H] 687.2208, found
687.2214; m/z (%) = 687 (100) [M + H]+, 686 (16) [M]+. IR (neat):
3
2,5-Bis(4-phenyl-1H-1,2,3-triazol-1-yl)-1-phenyl-1-thiooxophosphole
(9a): A solution of 8 (48.0 mg, 100 μmol), phenylacetylene
(44.0 μL, 400 μmol, 4 equiv.), 2,6-lutidine (23.4 μL, 200 μmol,
2 equiv.) and [Cu(NCMe)4][PF6] (1.9 mg, 5.0 μmol, 0.05 equiv.) in
CH2Cl2 (3 mL) was stirred at room temperature for 64 h and sub-
sequently diluted with CH2Cl2 and washed with water. The organic
layer was dried with MgSO4, filtered, and the solvents were re-
moved in vacuo. The yellow crude product was purified by column
chromatography on silica gel eluting with hexane/EtOAc, 1:1 (RF
= 0.38) to obtain 9a as a yellow powder (67.9 mg, 99.2 μmol, 99%).
ν = 2920 (w), 2853 (w), 1718 (w), 1600 (w), 1584 (w), 1472 (w),
˜
1437 (w), 1414 (w), 1260 (m), 1150 (m), 1065 (m), 1023 (s), 784 (s),
748 (w), 692 (m) cm–1. UV/Vis (CH2Cl2): λabs = 245 (ε =
4.66 ϫ 104 m–1 cm–1), 286 (ε = 3.06ϫ 104 m–1 cm–1), 324 nm (ε =
7.52 ϫ 103 m–1 cm–1). FS (cyclohexane): λem = 302 nm (ΦF
=
0.0036).
1
M.p. 136.0–136.4 °C. H NMR (400.13 MHz, CDCl3): δ = 8.07 (s,
2,5-Bis[4-(thien-2-yl)-1H-1,2,3-triazol-1-yl]-1-phenyl-1-thiooxophos-
phole (9c): A solution of 8 (21.5 mg, 44.7 μmol), 2-ethynylthio-
3
4
2 H, NCH), 7.89 (dd, JHH = 8.3, JHH = 1.3 Hz, 2 H, o-PhH),
3
4
4
7.85 (dd, JHH = 8.2, JHH = 1.5 Hz, 2 H, o-PPhH), 7.83 (t, JHH phene (0.15M in CH2Cl2, 1.0 mL, 150 μmol, 3.35 equiv.), 2,6-luti-
= 1.1 Hz, 2 H, ArH2), 7.70–7.76 (m, 2 H, ArH6), 7.51 (tt, JHH
=
dine (10.4 μL, 89.5 μmol, 2 equiv.) and [Cu(NCMe)4][PF6]
3
7.3, 4JHH = 1.5 Hz, 1 H, p-PPhH), 7.42–7.49 (m, 10 H, m-PhH, m- (0.83 mg, 2.2 μmol, 0.05 equiv.) in CH2Cl2 (4 mL) was stirred at
PPhH, ArH4,5), 7.37 (tt, JHH = 7.4, JHH = 1.3 Hz, 2 H, p-PhH),
room temperature for 64 h and subsequently diluted with CH2Cl2
3
4
2.90 (dd, 2JHH = 18.1, 4JHP = 3.7 Hz, 2 H, Cq-CH2-CH2), 2.83 (dd, and washed with water. The organic layer was dried with MgSO4,
Eur. J. Org. Chem. 2012, 6711–6721
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6719

K. Lammertsma et al.
FULL PAPER
filtered, and the solvents were removed. The yellow crude product
was purified by column chromatography on silica gel eluting with
hexane/EtOAc, 2:1 (RF = 0.15) to obtain 9c as a yellow powder
yellow residue was purified by column chromatography on silica
gel eluting hexane/EtOAc, 1:2 (RF = 0.25), which afforded 10b as a
yellow powder (80.0 mg, 122 μmol, 100%). 1H NMR (400.13 MHz,
(25.5 mg, 36.6 μmol, 82 %). M.p. 150.5–151.0 °C. 1H NMR CDCl3): δ = 8.61–8.68 (m, 2 H, PyH6), 8.64 (s, 2 H, NCH), 8.29
3
4
3
(400.13 MHz, CDCl3): δ = 7.97 (s, 2 H, NCH), 7.89 (ddd, JHP
=
=
(t, JHH = 7.4 Hz, 2 H, PyH4), 7.88 (s, 2 H, ArH2), 7.84 (dd, JHH
3
4
4
13.9, JHH = 7.7, JHH = 1.4 Hz, 2 H, o-PPhH), 7.79 (t, JHH
= 7.8, 4JHH = 1.9 Hz, 2 H, PyH5), 7.64–7.70 (m, 2 H, ArH4), 7.47–
1.0 Hz, 2 H, ArH2), 7.75 (dt, JHH = 6.6, JHH = 1.0 Hz, 2 H,
7.57 (m, 4 H, ArH5,6), 7.24–7.34 (m, 3 H, o-PPhH, p-PPhH), 7.20
3
4
ArH6), 7.53–7.57 (m, JHH = 7.2, JHH = 1.6 Hz, 1 H, p-PPhH), (dt, 3JHH = 5.9, JHH = 1.4 Hz, 2 H, m-PPhH), 2.71–3.14 (m, 4 H,
3
4
4
3
7.46–7.52 (m, 8 H, thienylH5, m-PPhH, ArH4,5), 7.37 (dd, JHH
=
=
Cq-CH2-CH2), 1.68–1.97 (m, 4 H, Cq-CH2-CH2) ppm. 13C NMR
(62.90 MHz, CDCl3): δ = 149.9 (s, PyC2), 149.3 (s, PyC6), 148.7 (s,
3
3
3
5.1, JHH = 1.1 Hz, 2 H, thienylH3), 7.14 (dd, JHH = 5.1, JHH
3.6 Hz, 2 H, thienylH4), 2.92 (dd, 2JHH = 18.2, 4JHP = 3.7 Hz, 2 H, NCH=C), 145.6 (d, JCP = 10.9 Hz, PC=C), 143.0 (d, JCP
=
2
1
Cq-CH2-CH2), 2.84 (dd, 2JHH = 18.2, 4JHP = 3.2 Hz, 2 H, Cq-CH2-
2.1 Hz, PC=C), 138.8 (d, JCP = 18.8 Hz, ArC1), 137.0 (s, PyC4),
2
CH2), 1.86 (t, JHH = 2.9 Hz, 4 H, Cq-CH2-CH2) ppm. 13C NMR 136.9 (s, ArC3), 133.4 (d, JCP = 18.9 Hz, o-PPh), 130.8 (d, JCP
=
3
2
2
(100.62 MHz, CDCl3): δ = 149.4 (d, 2JCP = 22.2 Hz, PC=C), 143.41
71.4 Hz, ipso-PPh), 130.1 (s, p-PPh), 129.7 (s, ArC5), 129.4 (d, 3JCP
(s, NCH=C), 136.7 (s, ArC3), 134.1 (d, JCP = 12.5 Hz, ArC1), = 10.2 Hz, ArC6), 128.6 (d, 3JCP = 8.3 Hz, m-PPh), 123.0 (s, PyC5),
2
133.1 (d, JCP = 81.1 Hz, PC=C), 132.3 (d, JCP = 3.3 Hz, p-PPh), 120.4 (s, PyC3), 120.4 (d, JCP = Hz, ArC2), 119.6 (s, ArC4), 118.1
1
4
3
132.2 (s, thienylC2), 130.6 (d, JCP = 11.6 Hz, o-PPh), 129.8 (s, (s, NCH), 27.9 (d, JCP = 0.9 Hz, Cq-CH2-CH2), 23.0 (s, Cq-CH2-
2
3
ArC4), 129.1 (s, ArC5), 129.0 (d, JCP = 8.3 Hz, m-PPh), 127.6 (s,
CH2) ppm. 31P NMR (101.25 MHz, CDCl3 ): δ = 13.5 (s) ppm.
HRMS (FAB): calcd. for C40H31N8P [M] 655.2488, found
3
thienylC5), 127.0 (d, 1JCP = 73.9 Hz, ipso-PPh), 125.3 (s, thienylC4),
124.5 (s, thienylC3), 120.4 (d, 3JCP = 5.2 Hz, ArC2), 119.8 (s, ArC6), 655.2473; m/z (%) = 655 (75) [M + H]+, 654 (30) [M]+, 615 (100)
116.8 (s, NCH), 27.8 (d, 3JCP = 12.9 Hz, Cq-CH2-CH2), 22.4 (s, Cq- [M
CH2-CH2) ppm. 31P NMR (101.25 MHz, CDCl3): δ = 54.4 (s) ppm.
HRMS (FAB): calcd. for C38H30N6PS3 [M + H] 697.1432, found
697.1443; m/z (%) = 697.14 (100) [M + H]+, 696.15 (10) [M]+. IR
–
C2H2N]+. UV/Vis (CH2Cl2): λabs
=
238 (ε
=
5.29ϫ104 m–1 cm–1), 286 (ε = 2.81ϫ104 m–1 cm–1), 355 nm (ε =
1.13ϫ104 m–1 cm–1). FS (cyclohexane): λem = 469 nm (ΦF = 0.134).
2,5-Bis[4-(thien-2-yl)-1H-1,2,3-triazol-1-yl]-1-phenylphosphole (10c):
Compound 9c (13.4 mg, 19.2 μmol) was dissolved in toluene
(3.5 mL) and a 1.5 m solution of P(NMe2)3 in THF (70 μL,
100 μmol, 5 equiv.) was added. The yellow reaction mixture was
refluxed for 16 h, after which the solvent was removed, and the
yellow residue was purified by column chromatography on silica
gel eluting with hexane/EtOAc, 2:1 to 1:1 [RF (1:1) = 0.56] to obtain
10c as a yellow powder (9.0 mg, 13.5 μmol, 71%). 1H NMR
(400.13 MHz, CDCl3): δ = 8.03 (s, 2 H, NCH), 7.71 (br. s, 2 H,
(neat): ν = 2993 (w), 2863 (w), 1576 (m), 1477 (m), 1260 (m), 1233
˜
(m), 1093 (m), 1039 (s), 1016 (s), 999 (w), 965 (w), 930 (w), 892
(w), 857 (w), 787 (s), 747 (w), 716 (m), 689 (s), 670 (s) cm–1. UV/
Vis (CH2Cl2): λ = 227 (ε = 2.16 ϫ 104
m
–1 cm–1), 275 (ε =
1.96ϫ104 m–1 cm–1), 339 nm (ε = 3.58ϫ103 m–1 cm–1). FS (cyclo-
hexane): λem = 302 nm (ΦF = 0.00071).
2,5-Bis(4-phenyl-1H-1,2,3-triazol-1-yl)-1-phenylphosphole (10a):
Compound 9a (32.6 mg, 47.6 μmol) was dissolved in toluene
(5 mL), and a 1.5 m solution of P(NMe2)3 in THF (160 μL,
ArH2), 7.62 (dd, 3JHH = 8.8, 4JHH = 2.4 Hz, 2 H, ArH4), 7.47–7.51
238 μmol, 5 equiv.) was added. The yellow reaction mixture was (m, 6 H, ArH5,6, thienylH2), 7.36 (d, JHH = 5.0 Hz, 2 H, thien-
3
3
refluxed for 16 h, after which the solvent was removed, and the
yellow residue was purified by column chromatography on silica
gel eluting with hexane/EtOAc, 3:1 (RF = 0.28) to obtain 10a a
ylH3), 7.26–7.29 (m, 2 H, o-PPhH), 7.24 (t, JHH = 7.2 Hz, 1 H, p-
3
3
PPhH), 7.19 (t, JHH = 7.2 Hz, 2 H, m-PPhH), 7.14 (dd, JHH
=
5.0, JHH = 3.8 Hz, 2 H, thienylH4), 2.98–3.08 (m, 2 H, Cq-CH2-
3
yellow powder (25.9 mg, 39.6 μmol, 83%). 1H NMR (400.13 MHz, CH2), 2.76–2.84 (m, 2 H, Cq-CH2-CH2), 1.86–1.92 (m, 2 H, Cq-
3
4
CDCl3): δ = 8.12 (s, 2 H, NCH), 7.91 (dd, JHH = 8.3, JHH
=
CH2-CH2), 1.76–1.82 (m, 2 H, Cq-CH2-CH2) ppm. 13C NMR
1.3 Hz, 4 H, o-PhH), 7.79 (s, 2 H, ArH2), 7.61 (dd, JHH = 7.0,
(62.90 MHz, CDCl3): δ = 145.7 (d, JCP = 11.0 Hz, PC=C), 143.4
3
2
4JHH = 2.2 Hz, 2 H, ArH4), 7.45–7.56 (m, 8 H, ArH5,6, m-PhH),
(s, thienylC2), 142.7 (d, JCP = 1.9 Hz, PC=C), 138.8 (d, JCP
=
1
2
3
4
2
7.38 (tt, JHH = 7.3, JHH = 1.3 Hz, 2 H, p-PhH), 7.22–7.29 (m, 2
18.7 Hz, ArC1), 136.8 (s, ArC3), 133.5 (d, JCP = 19.0 Hz, o-PPh),
3
3
4
1
H, o-PPhH), 7.21 (t, JHH = 7.2 Hz, 1 H, p-PPhH), 7.16 (t, JHH 132.4 (s, NCH=C), 131.8 (d, JCP = 2.8 Hz, p-PPh), 130.5 (d, JCP
= 7.2 Hz, 2 H, m-PPhH), 2.74–3.04 (m, 4 H, Cq-CH2-CH2), 1.68– = 12.0 Hz, ipso-PPh), 129.6 (s, ArC5), 129.3 (d, JCP = 9.4 Hz,
3
1.90 (m, 4 H, Cq-CH2-CH2) ppm. 13C NMR (62.90 MHz, CDCl3): ArC6), 128.6 (d, JCP = 8.3 Hz, m-PPh), 127.6 (s, thienylC5), 125.3
3
δ = 148.3 (s, NCH=C), 145.7 (d, 2JCP = 10.8 Hz, PC=C), 142.7 (d,
(s, thienylC4), 124.5 (s, thienylC3), 120.5 (d, JCP = 8.9 Hz, ArC2),
3
1JCP = 2.1 Hz, PC=C), 138.8 (d, JCP = 18.6 Hz, ArC1), 137.0 (s,
118.2 (s, ArC4), 116.9 (s, NCH), 27.9 (d, JCP = 1.4 Hz, Cq-CH2-
2
3
ArC3), 133.5 (d, JCP = 18.9 Hz, o-PPh), 130.2 (s, ipso-Ph), 129.6 CH2), 23.0 (s, Cq-CH2-CH2) ppm. 31P NMR (101.25 MHz,
2
(s, ArC5), 129.5 (d, 4JCP = 1.4 Hz, p-PPh), 129.2 (d, 3JCP = 9.4 Hz, CDCl3): δ = 13.8 (s) ppm. HRMS (FAB): calcd. for C38H30N6PS2
ArC6), 128.8 (s, m-Ph), 128.6 (d, JCP = 8.3 Hz, m-PPh), 128.3 (s, [M + H] 665.1711, found 665.1718; m/z (%) = 665 (100) [M +
3
p-Ph), 125.8 (s, o-Ph), 120.6 (d, JCP = 9.1 Hz, ArC2), 118.2 (s,
H]+, 664 (31) [M]+. UV/Vis (CH2Cl2): λabs
= 276 (ε =
3
ArC4), 117.4 (s, NCH), 27.9 (d, 3JCP = 0.9 Hz, Cq-CH2-CH2), 23.0 3.23ϫ104 m–1 cm–1), 356 nm (ε = 1.02ϫ104 m–1 cm–1). FS (cyclo-
(s, Cq-CH2-CH2) ppm; ipso-PPh was unresolved. 31P NMR
(101.25 MHz, CDCl3): δ = 13.6 (s) ppm. HRMS (FAB): calcd. for
C42H34N6P [M + H] 653.2583, found 653.2592; m/z (%) = 653 (100)
[M + H]+, 652 (22) [M]+. UV/Vis (CH2Cl2): λabs = 243 (ε =
8.58 ϫ 104 m–1 cm–1), 290 (ε = 2.63ϫ 104 m–1 cm–1), 355 nm (ε =
1.62ϫ104 m–1 cm–1). FS (cyclohexane): λem = 463 nm (ΦF = 0.273).
hexane): λem = 460 nm (ΦF = 0.309).
Computational Details: All theoretical calculations were performed
using the Amsterdam Density Functional (ADF) program suite.[23]
Geometries were optimized using the TZ2P basis set. The inner
cores of the carbon, nitrogen, and oxygen atoms (1s2) and those of
the sulfur and phosphorus atoms (1s22s22p6) were kept frozen. An
auxiliary set of STOs was used to fit the density for the Coulomb-
type integrals. The GGA exchange functional OPTX was used in
combination with the non-empirical PBE correlation functional
2,5-Bis[4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl]-1-phenylphosphole
(10b): Compound 9b (83.9 mg, 122 μmol) was dissolved in toluene
(10 mL), and a 1.5 m solution of P(NMe2)3 in THF (400 μL,
600 μmol, 5 equiv.) was added. The yellow reaction mixture was (OPBE) with an integration accuracy of 5.0 and convergence cri-
refluxed for 16 h, after which the solvent was removed, and the
teria of 1ϫ10–5. Coordinates of the optimized structures can be
6720
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 6711–6721

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Received: August 22, 2012
Published Online: October 25, 2012
Eur. J. Org. Chem. 2012, 6711–6721
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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