3,4-Dithiaphosphole and 3,3′,4,4′-tetrathia-1,1′- biphosphole π-conjugated systems: S makes the impact

DOI: 10.1002/chem.201001463

3,4-Dithiaphosphole and 3,3’,4,4’-Tetrathia-1,1’-Biphosphole p-Conjugated

Systems: S Makes the Impact

Omrane Fadhel,^[a]Zoltꢀn Benkç,^[b]Michael Gras,^[a]Valꢁrie Deborde,^[a]Damien Joly,^[a]

Christophe Lescop,^[a]Lꢀszlꢂ Nyulꢀszi,*^[b]Muriel Hissler,*^[a]and Rꢁgis Rꢁau*^[a]

Abstract: Conjugated systems based on

phospholes and 1,1’-biphospholes bear-

ing 3,4-ethylenedithia bridges have

been prepared using the Fagan–Nugent

route. The mechanism of this organo-

metallic route leading to intermediate

zirconacyclopentadienes has been in-

vestigated by using theoretical calcula-

tions. This study revealed that the oxi-

dative coupling leading to zirconacyclo-

pentadienes is favored over oxidative

particular interest, this comparative

study revealed that the introduction of

S atoms has an impact on the electron-

ic properties of phosphole-based conju-

as well as an increase of the reduction

and oxidation potentials. The S atoms

of the 3,4-ethylenedithia bridge of the

2,5-phosphole have been oxidized

using m-chloroperoxybenzoic acid. The

resulting 3,4-ethylenesulfoxide oxo-

phosphole was characterized by an X-

ray diffraction study. Experimental and

theoretical studies show that this novel

chemical manipulation results in an in-

crease of the HOMO–LUMO separa-

tion and an important decrease of the

LUMO level. The electropolymeriza-

tion of 2-thienyl-capped 3,4-ethylenedi-

thiathioxophosphole and 1,1’-biphos-

phole is reported. The impact of the S

substituents on the polymer properties

is discussed.

gated systems.

A decrease of the

HOMO–LUMO separation and a sta-

bilization of the LUMO level were ob-

served. These general trends are also

observed with 1,1’-biphospholes exhib-

iting s–p conjugation. The P atom of

the 3,4-ethylenedithiaphospholes can

be selectively oxidized by S₈or O₂.

These P modifications result in a lower-

ing of the HOMO–LUMO separation

ꢀ

addition within the S CꢁC bond both

thermodynamically and kinetically. The

impact of the presence of the S atoms

on the optical and electrochemical be-

havior of the phospholes and 1,1’-bi-

phospholes has been systematically

evaluated both experimentally and the-

Keywords: conjugation

functional calculations

·

density

electro-

polymerization · phospholes · poly-

merization · thiophenes

oretically.

A comparison with their

“all-carbon” analogues is provided. Of

Introduction

The demand for new organic p-conjugated materials with

improved electrical and optical properties for plastic elec-

tronic applications necessitates extensive experimental mo-

lecular engineering and theoretical investigations of the un-

derlying structure–property relationships.^[1]The two main

strategies to diversify the properties and to expand the func-

tion of linear p-conjugated systems A (Scheme 1) involve

1) the modification of the conjugated framework composi-

tion, including the synthesis of mixed derivatives, and 2) the

attachment of lateral substituents R¹and R²with specific

electronic or steric demands.^[1,2]Heterocyclopentadienes (A:

X,Y=NR, S, SiR₂, PR(E), and so forth; Scheme 1) have

been extensively used for modifying the conjugated frame-

work composition since they exhibit electronic properties re-

lated to the nature of the heteroatom.^[1–3]Heteroles includ-

ing second-row elements like silicon^[4]or phosphorus^[4a,5]

[a] Dr. O. Fadhel, M. Gras, V. Deborde, D. Joly, C. Lescop,

Prof. M. Hissler, Prof. R. Rꢀau

Sciences Chimiques de Rennes

UMR 6226 CNRS, Universitꢀ de Rennes 1

Campus de Beaulieu, 35042 Rennes Cedex (France)

Fax : (+33)2-23-23-69-39

E-mail: muriel.hissler@univ-rennes1.fr

regis.reau@univ-rennes1.fr

[b] Dr. Z. Benkç, Prof. L. Nyulꢁszi

Department of Inorganic and Analytical Chemistry

Budapest University of Technology and Economics

Gellꢀrt tꢀr 4, 1111 Budapest (Hungary)

Fax : (+36)14633408

E-mail: nyulaszi@mail.bme.hu

Supporting information for this article is available on the WWW

under http://dx.doi.org/10.1002/chem.201001463.

11340

ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 11340 – 11356

FULL PAPER

substituents R¹and R²with specific electronic or steric de-

mands, Scheme 1) has not been fully investigated with

phosphole building blocks. In fact, all the phosphole moiet-

ies B that have been used to date for the tailoring of p sys-

tems A (Scheme 1) feature alkyl groups at their 3- and 4-po-

sitions, except one example concerning per-aryl deriva-

AHCTUNGTRENNUNG

tives.^[8a]This is mainly due to synthetic reasons since these

3,4-dialkylphosphole synthons are easily accessible using the

two well-established methods depicted in Scheme 2.^{[5a–c,11–13]}

Scheme 1. Structure of linear p-systems A and P building blocks used for

molecular engineering.

Scheme 2. Synthetic routes to the two families of mixed p-systems incor-

porating phosphole moieties.

play a specific role in this molecular engineering due to

ꢀ

their low-lying exocyclic P R or Si R s* orbitals that can

effectively overlap with the p system. This results in a low-

energy LUMO and consequently, a high electron affinity

(suitable for n-type conductivity).^[6]Furthermore, a reduced

HOMO–LUMO separation of p-conjugated system A is ob-

served since these heteroles (silole and phosphole) exhibit a

low level of aromaticity,^[4,6]which results in a better elec-

tronic interaction of their endocyclic p electrons with other

aromatic subunits at the 2,5-positions. For example, thio-

phene–silole oligomers A (Scheme 1) exhibit different phys-

ical properties (improved p conjugation, lower lying LUMO

level, etc.) than the corresponding oligo(thiophene)s,

making these mixed systems of interest for applications such

as the development of sensors, solar cells, or optimized ma-

terials for organic light-emitting diodes.^[7]

The phosphole ring B (Scheme 1), which is the most re-

cently investigated heterole for the molecular engineering of

linear p systems A (Scheme 1), possesses two further advan-

tages: 1) the possibility to readily tune the electronic proper-

ty of phosphole-based p-conjugated systems by chemical

modifications of the reactive P atoms, and 2) the increased

effectiveness of the hyperconjugative interaction in 1,1’-bi-

phosphole moieties C (Scheme 1) leading to further reduc-

tion of the HOMO–LUMO gaps.^[8]These specific properties

have been fully exploited by several groups for the optimi-

zation of phosphole-based p-conjugated materials exhibiting

(electro)fluorescence, sensor, or electron-transporting prop-

erties.^[9]Note that this general approach can also be per-

formed using fused-ring systems (for example, dibenzo-

phospholes D or dithienophospholes E, Scheme 1),^[10]al-

though these compounds are better described as whole delo-

calized entities and not as phosphole derivatives.

Therefore we have investigated the synthesis of unprece-

dented phosphole derivatives bearing Group 16 heteroele-

ment substituents at their 3,4-positions with the aim of

tuning the electronic properties of P-based conjugated sys-

tems. This type of substituent was selected by considering

the vast literature on thiophene-containing p-conjugated

systems. Indeed, thiophene derivatives bearing Group 16

heteroelement substituents (alkoxy, thioalkoxy, or selenoal-

koxy) at their 3,4-positions have been extensively used for

the development of advanced materials since they exhibit

improved properties relative to their parent analogue.^[14]

Furthermore, such a substitution pattern will suppress possi-

ble thermally induced phosphole–phospholene isomeriza-

tion, a process that can be a drawback for the development

of these P building blocks since it modifies the extended p-

conjugated pathway (Scheme 3).^[6d]

Scheme 3. s⁴-Phosphole–s⁴-phospholene isomerization.

In this paper, we describe the synthesis of the first phos-

pholes B and 1,1’-biphospholes C (Scheme 1) bearing an SR

function at their 3- and 4-positions. The choice of S- rather

than O-substituents was made following a theoretical study,

reported in this paper, revealing that 3,4-dithiaphospholes

exhibit appealing electronic properties (stabilized LUMO

The second main strategy to diversify the properties of

linear p-conjugated systems (i.e., the attachment of lateral

Chem. Eur. J. 2010, 16, 11340 – 11356

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11341

R. Rꢀau, L. Nyulꢁszi, M. Hissler et al.

level, low HOMO–LUMO gap). The synthetic route to-

wards these novel phosphole derivatives containing SR func-

tions is based on the organometallic approach described in

Scheme 2 (route (2)). To the best of our knowledge, the oxi-

dative coupling of S-functionalized diynes upon reaction

with low-valent zirconium, affording intermediate metallacy-

clopentadienes G (Scheme 2), is unprecedented. This reac-

tion, which extends the scope of this widely used organome-

tallic route towards heteroles, has been investigated by theo-

retical calculations since S-functionalized triple bonds can

potentially give oxidative addition reactions upon reaction

with zirconocene. The impact of the two S-substituents at

the 3,4-position on the electronic properties of the phosp-

hole ring and phosphole-based p-conjugated systems has

been elucidated following combined experimental and theo-

retical studies. Of particular interest, it will be shown that

the presence of these S-substituents impacts the electropoly-

merization ability of thienyl-capped phosphole monomers,

and allows for a subtle tailoring of the phosphole electronic

properties following chemical S-oxidation.

Figure 1. LUMO, HOMO, and HOMOꢀ1 orbitals of phosphole (left)

and thiophene (right) at the B3LYP/6-31G*//B3LYP/6-31+G* level.

with energies that are lower than those of the parent rings

(Figure 2). It is remarkable that the effect of the S-substitu-

ents is similar for thiophene and phosphole rings that have

very different electronic properties since the S-heterole is a

highly aromatic system while its P-analogue is almost nonar-

omatic. This behavior is rather surprising, since an interac-

tion between the sulfur lone pair and the unoccupied ring p

orbital should result in the destabilization of the LUMO

energy for both S- and P-heteroles. However, this behavior

has already been reported for thiophene with theoretical

calculations showing that bis-3,4-ethylenedisulfanylthio-

phene (EDTT) possesses a lower LUMO level than bis-3,4-

ethylenedioxythiophene (EDOT).^[14f]Note that, in accord-

ance with these theoretical results, the reduction potential

of an EDTT-containing oligomer was reported to be lower

than that of its EDOT-containing analogue.^[14k]The under-

standing of this phenomenon is not straightforward and can

Results and Discussion

Preliminary theoretical study: To evaluate the effect of the

Group 16 substituents at the 3,4-positions on the HOMO–

LUMO gap of the phosphole ring, model calculations have

been performed. For comparison purposes, thiophene was

selected as a prototype heterocyclopentadiene. The Kohn–

Sham (KS)^[15]HOMOꢀ1, HOMO, and LUMO for phos-

phole and thiophene are shown in Figure 1, and the energies

of these KS orbitals upon replacing the H atoms at the 3,4-

positions by alkyl/alkoxy/thioalkoxy-fused six-membered

rings are given in Figure 2.

The introduction of Group 16 substituents at the 3,4-posi-

tions has a similar effect on the

orbital energies of both phos-

phole and thiophene rings

(Figure 2). As expected, the oc-

cupied orbitals are destabilized

upon replacing H or alkyl by

Group 16 substituents. Note

that the HOMO of the S-substi-

tuted phosphole (ꢀ5.69 eV)

and thiophene (ꢀ5.67 eV) de-

rivatives have similar energy

(Figure 2). The unoccupied or-

bital energies behave in a dif-

ferent way. The C- and O-sub-

stitutions result in a gradual de-

stabilization of the LUMO en-

ergies compared to the parent

heteroles (Figure 2), a behavior

that is in accordance with the

general expectation. In con-

trast, the S-substituted hetero-

les exhibit a stabilized LUMO the B3LYP/6-31G*//B3LYP/6-31+G* level of theory.

Figure 2. LUMO, HOMO, and HOMOꢀ1 Kohn–Sham orbital energies and HOMO–LUMO gaps (in eV) at

11342

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Chem. Eur. J. 2010, 16, 11340 – 11356

Thiaphosphole p-Conjugated Systems

FULL PAPER

find its origin in different reasons. For example, theoretical

calculations have shown that the d orbital involvement in

the LUMO is somewhat increased in the case of the sulfur

derivatives,^[16]with respect to their oxygen analogues and it

can contribute to the stabilization of the LUMO. Moreover

the investigation of the photodissociation dynamics of

phenol and thiophenol revealed mixing between the pp*

and ps* states in the case of the sulfur derivative only,

which also explained a stabilization of the LUMO level.^[17]

Likewise, in the photodissociation dynamics of 2-methyl-3-

furanethiol, the (n/p)s* excited state played a significant

role.^[18]In conclusion, this theoretical study brings to light

the special behavior of the second-row S-substituents and

justifies that its introduction at the 3,4-position of the phos-

phole ring is worth studying to tune the electronic properties

of this P building block. Another key point revealed by the

theoretical calculations is that the introduction of an S-sub-

stituent at the 3,4-position of heteroles significantly reduces

their HOMO–LUMO gap (Figure 3). This appealing proper-

ty is nicely illustrated by time-dependent (TD)-DFT calcula-

tions clearly showing that the UV-visible spectrum of 3,4-

ethylenedithiaphosphole is redshifted relative to that of its

“all-carbon” analogue (Dl_max=34 nm; the excitation wave-

lengths and oscillator strengths are given in the Supporting

Information, together with simulated spectra). Very interest-

ingly, this effect is also observed

Figure 3. HOMO–LUMO separations of phospholes with and without S

atoms at their 3,4-positions.

(Negishi reagent)^[13]can potentially react 1) with the triple

bonds (oxidative coupling leading to the zirconacyclopenta-

ꢀ

diene G, Scheme 2), or 2) with the C_spS bond of 2a,b (oxi-

dative addition leading to -CꢁC-(ZrCp₂)-S- derivatives;

Cp=cyclopentadienyl), a process that is well exemplified

with vinyl sulfides (Scheme 5).^[19]

The thienyl- or phenyl-capped 1,2-bis(ethynylthio)ethanes

2a,b^[20]were obtained in medium yields (ca. 30–50%) by

and even amplified for the cor-

responding thiooxophosphole

series (Figure 3, see the Sup-

porting Information for simulat-

ed spectra Dl_max=92 nm). In

fact, the HOMO–LUMO sepa-

ration of the 3,4-ethylenedithia-

thioxophosphole is very low

due an important decrease of

its LUMO level (Figure 3). This

theoretical study highlights the

impact of S-substituents on the

electronic behavior of the

phosphole ring and motivated

our synthetic efforts towards

unknown

3,4-ethylenedithia-

phosphole derivatives.

Synthesis of 3,4-ethylenedithia-

phosphole derivatives: Our syn-

thetic approach towards the

target 3,4-ethylenedithiaphos-

ACHTUNGTRENNUNGphole derivatives was to use the

Fagan–Nugent route described

in Scheme 2 (route (2)) starting

with

the

1,2-bis-

A

2a,b

(Scheme 4). Note that this

choice raises a chemoselectivity

issue since the intermediate

Scheme 4. Synthesis of 3,4-ethylenedithiaphosphole and 3,3’,4,4’-tetrathia-1,1’-biphosphole derivatives 4a,b and

low-valent zirconocene species 5a,b. Structure of reference phospholes I and J.^[8l]

Chem. Eur. J. 2010, 16, 11340 – 11356

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11343

R. Rꢀau, L. Nyulꢁszi, M. Hissler et al.

The insertion of the sulfur substituents in the exocyclic

bridge induces a shielding of the PC_band PC_asignals by ap-

proximately d=12 and 2 ppm in compounds 4a and 4b, re-

spectively, relative to the reference molecules I and J that

bear a carbocycle bridge (Scheme 4).^[8l]Phosphole 4b bear-

ing phenyl substituents was characterized by an X-ray dif-

fraction study (Figure 4, Table 2). The angles and bond

lengths of the P ring are classical and compare well with

Scheme 5. Oxidative addition of intermediate low-valent zirconocene

ꢀ

species into an C_sp₂S bond.

means of a synthetic method described by Gleiter et al.^[21]

involving the nucleophilic attack of lithium acetylides on the

1,2-bis(thiocyanato)ethane 1 (Scheme 4). The treatment of

2a,b with “zirconocene”, followed by addition of PhPBr₂or

PBr₃, gave rise to the target 1-phenylphospholes 4a,b and

1,1’-biphospholes 5a,b, respectively (Scheme 4). Note that,

in the course of formation of 1,1’-biphospholes 5a,b, inter-

mediate 1-bromophospholes were observed (³¹P NMR: d=

+49.4 (R=2-thienyl), +46.1 ppm (R=Ph)). After filtration

of the solution over basic alumina to remove Zr-containing

species, the phospholes 4a,b and 1,1’-biphospholes 5a,b

were isolated as air-stable solids in 45–60% yields (Table 1).

Figure 4. Molecular structure of phosphole 4b in the solid state. Hydro-

gen atoms have been omitted for clarity.

those observed for other phos-

Table 1. ³¹P{¹H} NMR spectroscopic, optical, and electrochemical data for 3,4-S-substituted phosphole and

1,1’-biphosphole derivatives.

phole derivatives.^[8a,k,l]For ex-

ample, the P atom has a strong

[b]

[d]

d^[a][ppm] Yield [%] l_max/l_onset[nm]

loge

l_em[nm]/ F^[c][%] E_pa[V] E_pc[V]

pyramidal character (ꢀP_ang

=

4a

4b

5a

5b

6a

6b

7b

8b

I^[8l]

J^[8l]

S^[8j]

T^[8j]

+9.9

+10.2

+5.0

60

50

45

53

95

85

75

40

60

40

93

87

437/502

385/445

403–480/600

376–441/496

471/542

413/477

419/489

390/450

412/468

3.68

3.90

3.96–3.48

4.30–3.82

3.93

3.35

3.56

3.85

3.93

536/1.0

493/1.8

–

+0.39

+0.60

+0.30

+0.54^[e]

+0.63

+0.97

+0.94

–

+0.40

+0.69

+0.24

+0.57

+0.70

+1.09

ꢀ2.28

ꢀ2.47

ꢀ1.57

ꢀ1.81

ꢀ1.87^[e]

ꢀ2.04

ꢀ1.94^[e]

ꢀ1.14^[e]

–

ꢀ2.88

ꢀ2.10

ꢀ2.24

ꢀ1.94^[e]

ꢀ2.14

ꢀ

294.78) and the endocyclic P C

bond lengths (1.808(2)–

1.816(2) ꢃ, Table 3) approach

that of P–C single bond

+7.2

–

+47.3

+47.7

+34.1

+39.1

+12.7

+13.6

ꢀ0.5

612/<1

559/<1

557/<1

537/<1

501/5

466/14.3

–

a

(1.84 ꢃ). Note that the twist

angles between the phosphole

ring and the aromatic substitu-

ents are rather low (38.58(6)8,

40.95(0)8), thus allowing a p-

conjugated pathway involving

the phosphole ring and its 2,5-

aryl substituents. The S atoms

are in the plane of the sp²-C

atoms forming this extended p-

conjugated system (S-C3-C2-S

354/430

4.20

360–391–448/560 4.11–4.08–3.81

329–390/460

432/496

ꢀ13.6

4.22–3.81

3.98

4.13

–

U^[8l]+52.6

V^[9h]+55.3

548/4.6

516/<1

380/440

[a] From ³¹P{¹H} NMR spectroscopy in CDCl₃. [b] Measured in CH₂Cl₂. [c] Fluorescence quantum yields deter-

mined using fluorescein as standard, ꢂ15%. [d] All potentials were obtained during cyclic voltammetric inves-

tigations in 0.2m Bu₄NPF₆in CH₂Cl₂. Platinum electrode diameter: 1 mm; sweep rate: 200 mVs^ꢀ1. All report-

ed potentials are referenced to the reversible formal potential of the ferrocene/ferrocenium couple. [e] Rever-

sible processes, E^ꢃ_oxand E_r^ꢃ_edvalues provided.

dihedral

Figure 4). The S-C(phosphole)

angle,

ꢀ4.878,

distances (1.766 (2) ꢃ, Table 2)

ꢀ

The newly prepared P-compounds 4a,b and 5a,b were

characterized by high-resolution mass spectrometry and ele-

mental analysis, and their multinuclear NMR spectra sup-

port the proposed structures. Their ³¹P{¹H} NMR spectra

display a singlet at classical chemical shifts for 1-phenyl-

phosphole derivatives (4a, d=+9.9 ppm; 4b, d=

+10.2 ppm) and 1,1’-biphospholes (5a, d=+5.0 ppm; 5b,

d=+7.2 ppm).^[5,8a,j,l]Their ¹³C NMR spectra recorded at

room temperature are very simple, thereby indicating sym-

are shorter than a simple C S bond (1.81 ꢃ) and compare

ꢀ

to those encountered in arylsulfide (1.75 ꢃ) for which an S

C

(sp²) electronic interaction takes place.^[22]These X-ray

data suggest that the sulfur atoms at the 3,4-positions inter-

act with the p-conjugated pathway formed by the phosphole

ring and its 2,5-substituents.

To the best of our knowledge, it is the first time that the

metal-promoted coupling of alkynes with low-valent zirconi-

um complexes leading to metallacyclopentadiene intermedi-

ates has been applied to sulfide substrates (Scheme 4). At

first glance, the success of this synthetic approach is quite

surprising since it is well known that low-valent “zircono-

cene” inserts into the alkenyl–sulfur bond of vinyl sulfides,

sulfoxides, and sulfone alkene substrates (Scheme 5).^[19]

ꢀ

metric structures and/or a rapid rotation around the P P

bond for 1,1’-biphospholes. The ¹³C{¹H} data of the carbon

skeleton of 5a,b and those of the corresponding phospholes

4a,b are very similar, except the PC_asignals that are shield-

ed by approximately d=3–5 ppm in 4a,b relative to 5a,b.

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Chem. Eur. J. 2010, 16, 11340 – 11356

Thiaphosphole p-Conjugated Systems

FULL PAPER

Table 2. Crystal data and structure refinement for 3b, 4a, and 6b.

Since this synthetic result is an important and novel exten-

sion of the Fagan–Nugent route, we decided to investigate

the mechanism of this reaction by theoretical calculations.

One key question was to elucidate whether the observed

chemoselectivity leading to intermediate metallacyclopenta-

dienes 3a,b is driven only by the presence of the organic

linker between the two triple bonds of 2a,b (Scheme 4; en-

tropy factor).

Several groups have already investigated the Cp₂Zr-medi-

ated coupling reaction of two acetylene molecules theoreti-

cally.^[23]The intimate mechanism and kinetics of the elemen-

tal steps are substrate dependent. However, in accordance

with experimental data, these theoretical studies clearly

point to stepwise activation of the two alkynes by the Cp₂Zr

fragment (Scheme 6). The first alkyne is strongly bonded to

4b

6a

8b

molecular formula

M_r

T [K]

crystal system

space group

a [ꢃ]

b [ꢃ]

c [ꢃ]

a [8]

C₂₄H₁₉PS₂

402.88

100(2)

monoclinic

P21/c

9.6734(4)

9.8046(5)

20.6158(10)

90

C₄₁H₃₂P₂Cl₂S₁₀C₂₄H₁₉O₅PS₂

978.11

100(2)

monoclinic

P2/n

482.48

120(2)

monoclinic

P21/c

10.118(1)

8.566(2)

25.171(1)

90

9.321(1)

18.804(1)

12.915(1)

90

b [8]

97.879(2)

90

1936.82(16)

4

98.202(1)

90

2159.3(5)

2

107.632

90

2157.3(3)

4

g [8]

V [ꢃ³]

Z

1_calcd[gcm^ꢀ3

]

1.380

1.504

1.486

l (Mo_Ka) [ꢃ]

0.71073

0.71069

crystal size [mm]

0.2ꢄ0.1ꢄ0.03 0.2ꢄ0.1ꢄ0.05 0.3ꢄ0.19ꢄ0.12

m [mm^ꢀ1

]

0.364

0.740

0.357

F

(000)

840

1004

1000

q limit [8]

index ranges hkl

1.99–26.48

2.89–27.48

3.15–27.50

ꢀ12ꢄhꢄ12

ꢀ12ꢄhꢄ11 ꢀ13ꢄhꢄ13

ꢀ11ꢄkꢄ11

ꢀ25ꢄlꢄ25

12892

ꢀ11ꢄkꢄ11 ꢀ24ꢄkꢄ24

ꢀ32ꢄlꢄ32

ꢀ15ꢄlꢄ16

reflns collected

8695

35434

independent reflns

reflections (I>2s(I))

data/restraints/params

GOF on F²

3929

3463

3929/0/244

1.185

4923

3654

4923/0/251

1.061

4924

3934

4924/0/289

0.548

Scheme 6. Oxidative coupling leading to zirconacyclopentadiene complex

M illustrated here with acetylene.

final R indices

R1=0.0395

R1=0.0548

R1=0.0309

A

wR2=0.1112 wR2=0.1453 wR2=0.0855

R1=0.0484 R1=0.0760 R1=0.0459

wR2=0.1292 wR2=0.1598 wR2=0.1025

0.410/ꢀ0.524 0.475/ꢀ0.519 0.504/ꢀ0.363

the metal center (K: Zr–C, ca. 2.18 ꢃ). In contrast, the in-

teraction of the second alkyne with the Zr center is weak

(L: metal–C>3.5 ꢃ, Scheme 6). The oxidative coupling

leading to zirconacyclopentadiene M (Scheme 6) takes place

through a nonsymmetrical transition state. It is noteworthy

ACHTUNGTRENNUNG

]

that, in some cases, the bisACTHNURGTNE(UNG alkyne)complex L is neither an

intermediate nor a transition state on the reaction pathway.

The major differences between the previously investigated

alkynes and those presented in this theoretical study are the

fact that 1) the two -CꢁC- moieties belong to the same

molecule (the entropy factor will be affected), and 2) the

two -CꢁC- moieties are linked to p-donor S atoms that are

potentially a ligand for the low-valent Zr center, and that

will influence the alkyne electronic property. The mecha-

nism of the reaction depicted in Scheme 4 was studied with

the model substrate CH₃-CꢁC-S-(CH₂)₂-S-CꢁC-CH₃(N;

the difference between the real system and this one is only

the nature of the terminal groups). For this diyne, a confor-

mation analysis was performed with the MM1 force field

and the different isomers located were further optimized

using the combination of the B3LYP functional and the cc-

pVDZ basis set. Eleven different rotamers have been found

on the potential-energy surface (see the Supporting Infor-

mation) being close in energy to each other (2–5 kcalmol^ꢀ1).

These data suggest that in the case of the different inter-

mediate Zr complexes bearing this ligand, several rotamers

with similar energy can also exist.

Table 3. Selected bond lengths [ꢃ] and angles [8] for compounds 4b, 6a,

and 8b.

4b^[a]

6a^[b]

8b^[c]

ꢀ

P1 C1

ꢀ

C1 C2

1.808(2)

1.369(3)

1.481(3)

1.363(3)

1.816(2)

1.474(3)

1.476(3)

1.766(2)

91.43(10)

110.04(16)

114.0(2)

114.09(19)

109.99(16)

101.79(10)

101.48(9)

1.804(3)

1.361(4)

1.486(4)

1.360(4)

1.812(3)

1.460(4)

1.452(4)

1.741(3)

1.744(3)

93.14(13)

109.0(2)

114.3(2)

115.2(2)

108.3(2)

106.89(13)

105.87(14)

1.8344(18)

1.353(3)

1.506(2)

1.345(3)

1.8275(19)

1.475(2)

1.483(2)

1.7849(18)

1.799(2)

ꢀ

C2 C3

ꢀ

C3 C4

ꢀ

C4 P1

ꢀ

C1 C6

ꢀ

C4 C5

ꢀ

C2 S

ꢀ

C3 S

C1-P-C4

P-C1-C2

C1-C2-C3

C2-C3-C4

C3-C4-P

C1-P-C7

C4-P-C7

92.93(8)

108.01(13)

115.31(15)

115.09(15)

108.65(13)

105.85(9)

105.96(8)

The geometry and total energy of the zirconium com-

plexes were calculated using the B3LYP and BP86 function-

als and the cc-pVDZ basis set with pseudopotentials for Zr.

Since both the solvent and—besides the alkene—the poten-

[a] Y, Z=lone pair, X=CH₂=CH₂. [b] X=S, Y =S, Z =lone pair. [c] Y,

Z=O, X =CH₂=CH₂.

Chem. Eur. J. 2010, 16, 11340 – 11356

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11345

R. Rꢀau, L. Nyulꢁszi, M. Hissler et al.

tial other ligands of the starting Cp₂Zr are THF molecules,

it is important to gain insights into the magnitude of the sol-

vent effects. Therefore, single-point energies were deter-

mined using the polarizable continuum model (PCM) and

THF as solvent, which resulted in changes between ꢀ4.2

and +4.8 kcalmol^ꢀ1with respect to the gas-phase values

(Figure 5). However, the overall description of the elemen-

tal steps of the reactions (vide infra) is not influenced by the

solvent model used.

first elemental step of the classic mechanism depicted in

Scheme 6.

Starting from complex O, two reaction pathways can be

envisaged. The first one is the oxidative coupling leading to

the zirconacyclopentadiene complex R (Figure 5, right). The

second one is the oxidative addition of the zirconocene into

the -S-C(ꢁC)- bond (Figure 5, left). Although the oxidative

addition has a rather low barrier (nearly 20 kcalmol^ꢀ1), indi-

cating that this is a plausible reaction pathway (in accord-

ance with the results of Marek

et al.^[19]), the comparison of the

energy profile of these two

pathways

(B3LYP/cc-pVDZ-

AHCTUNGTERG(NNUN -PP) level) clearly show that

the oxidative coupling of diynes

leading to zirconacyclopenta-

diene R is favored over the oxi-

dative addition both from ther-

modynamic and kinetic points

of view (Figure 5). Therefore,

these theoretical data fit with

the experimental results and ra-

tionalize the selective formation

of phosphole derivatives 4a,b/

5a,b using 1,2-bis(ethynylthio)-

ethanes 2a,b (Scheme 4). At

the

B3LYP/cc-pVDZACHTUNGTRENNUNG(-PP)

Figure 5. Energy profile of the competitive reactions: oxidative addition (left) and formation of zirconacyclo-

level, the optimization runs al-

lowed us to locate an inter-

mediate P and a transition state

Q leading to the zirconacyclo-

pentadiene complex R (right) and relative energies (in kcalmol^ꢀ1) are compared with the h²-complex O (in

the middle in frame) at different levels of theory. For all the levels of theory the cc-pVDZ

used. [a] Neither an intermediate nor transition state was found using BP86/cc-pVDZ(-PP).

ACHTUNGTREN(NUGN -PP) basis set was

AHCTUNGTRENNUNG

pentadiene

ring

R

(see

Figure 5, right). The profile of

The first investigated step is the reaction of [Cp₂Zr

(H₂C=

the reaction is in good accordance with the former studies

on alkyne coupling reactions with zirconocene (Scheme 6).

Along the pathway leading to zirconacyclopentadiene R, no

structure exhibiting a Zr–S interaction is observed. No tran-

sition states could be determined between the (O-type) h²

complex and intermediate P on the very flat potential-

energy surface. The activation barrier to the zirconacyclo-

CH₂)(thf)] with substrate N. The energy of the reaction de-

ACHTUNGTRENNUNG

picted in Scheme 7 leading to the key intermediate O at the

pentadiene R is very small at the B3LYP/cc-pVDZ

ACHTUNGTRENNUNG(-PP)

level. Moreover, at the BP86/cc-pVDZ(-PP) level, neither

AHCTUNGTRENNUNG

an intermediate (P) nor transition state (Q) was found. Re-

laxed optimization scans also support the barrier-free mech-

anism at this level (see the Supporting Information), which

is in good agreement with some previous studies.^[23]In con-

clusion, this theoretical study revealed that the oxidative

coupling of a substrate of type N with zirconocene follows a

classic mechanism in spite of its peculiar structure.

Scheme 7. Coordination of model diyne N to the zirconocene fragment.

(THF) level is 2.5 kcalmol^ꢀ1. Howev-

B3LYP/cc-pVDZACHTUNGTRENNUNG(-PP)AHCTUNGTRENNGUN

er, because of the formation of ethylene, the Gibbs free

energy of the reaction is negative (ꢀ12.8 kcal.mol^ꢀ1), and it

is reasonable to assume that the formation of the zirconacy-

clopentadiene ring will take place through this intermediate

O. The complexation on the CꢁC triple bond of N for the

formation of an O-type h²complex is remarkably favored

Physical properties of 3,4-ethylenedithiaphosphole and

3,3’,4,4’-tetrathia–1,1’-biphosphole derivatives: Compounds

4a,b (Scheme 4) display intense absorption bands in the visi-

ble part of the absorption spectra (Figure 6) that are as-

signed to p–p* transitions (vide infra). As generally ob-

served in phosphole-based conjugated systems,^[8]the spec-

trum of the 2-thienyl-capped derivative 4a (l_max=434 nm,

over the complexation of the

S atom (the latter is

45 kcalmol^ꢀ1higher in energy than the former). Indeed, the

presence of the S atoms does not change the nature of the

11346

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Chem. Eur. J. 2010, 16, 11340 – 11356

Thiaphosphole p-Conjugated Systems

FULL PAPER

The

phospholes 5a,b (Scheme 4)

display absorption spectra

ethylenedithia-1,1’-bi-

showing several absorption

bands with one redshifted

broad shoulder (l_onset

:

5a,

600 nm; 5b, 496 nm; Figure 7).

The fact that 1) these low-

energy bands are considerably

redshifted relative to the ab-

sorption of the corresponding

1-phenylphospholes

4a,b

(Figure 6), and that 2) the

shape of the spectra of 5a,b are

very similar to those of the cor-

responding reference deriva-

tives S,T^[8j](Figure 7), clearly

show that s–p conjugation is ef-

fective in the newly prepared

Figure 6. Absorption and emission spectra of 4a (dashed line) and 4b (solid line) in CH₂Cl₂.

l_onset=502 nm) is shifted to

lower frequencies relative to

that of its phenyl-substituted

analogue 4b (l_max=385 nm,

l_onset=445 nm;

Table 1,

Figure 6). It is worth noting

that the absorption maximum

(l_max) and the optical end ab-

sorption (l_onset) of derivatives

4a,b (Table 1) are redshifted

relative to those of related

phospholes I and J featuring no

sulfur atoms in the carbocyclic

bridge

Dl_max=22 nm, Dl_onset=34 nm;

4b/J, Dl_max=31 nm, Dl_onset

(Scheme 4)^[8l]

(4a/I,

=

15 nm, Table 1). The cyclic vol-

tammetry (CV) performed at

Figure 7. Absorption spectra of 5a (dashed line), 5b (solid line), and reference compounds S (dotted line) and

200 mVs^ꢀ1revealed that the de- T (dashed–dotted line) in CH₂Cl₂.

rivatives with or without sulfur

in the carbocycle bridge exhibit

similar oxidation potentials, but that derivatives 4a,b are

more easily reduced than reference compounds I and J

(Scheme 4, Table 1) revealing a stabilization of the LUMO

level. Note that the redox processes observed for 4a,b are ir-

reversible. Therefore, both the UV-visible and electrochemi-

cal data show a decrease of the HOMO–LUMO separation

of phosphole-based conjugated systems upon introducing an

S substituent at the 3,4-positions of the P ring (I!4a, J!

4b, Scheme 4).

The two phospholes 4a,b are also photoluminescent and

emit in the visible region (l_em.: 4a, 536 nm; 4b, 493 nm).

Note that the Stokes shifts are relatively important (ca.

4385–5690 cm^ꢀ1, Figure 6), which suggests a large rearrange-

ment of these molecules upon photoexcitation. The quan-

tum yields of 4a,b are notably lower than those of deriva-

tives I and J (Table 1).

derivatives 5a,b. These data confirm that the P–P skeleton

is a powerful s scaffold to establish through-bond electronic

interaction between p chromophores.^[8a,j]

P-derivatives exhibiting s–p conjugation are still

rare^[8a,j,11]and it was thus of interest to elucidate whether

the presence of the S-substituents has an impact on this in-

triguing mode of conjugation. It is noteworthy that the l_max

of the 3,4-ethylenedithia-1,1’-biphospholes, including the

low-energy transitions, are redshifted relative to those of

their “all-carbon” analogues (Figure 7: 5a/S; 5b/T). This

effect is more pronounced for the phenyl-substituted deriva-

tives but is also effective in the thienyl series. Indeed, these

optical data show that the extent of the s–p conjugation is

notably affected by the presence of the S-substituents on the

phosphole ring. It is very likely that the stabilization of the

phosphole LUMO upon introduction of the S atoms shown

by the theoretical calculation (Figure 2) plays a key role in

Chem. Eur. J. 2010, 16, 11340 – 11356

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11347

R. Rꢀau, L. Nyulꢁszi, M. Hissler et al.

this behavior since the main

contribution to the s–p conju-

gation involves the interaction

of sPP and s*PP with the

LUMO of the P ring. This as-

sumption is nicely supported by

the

electrochemical

data

(Table 1) showing that the S-

substituted derivatives 5a,b are

more easily reduced than the

reference molecules S and T

(5a/S,

DE_pc=53 mV;

5b/T,

DE_pc=43 mV), whereas the oxi-

dation processes happen at the

same potential (Table 1). There-

fore, as observed in the 1-phe-

nylphosphole series, there is a

considerable stabilization of the

LUMO of 1,1’-biphospholes

upon introduction of the

S

atoms within the carbocycles

fused to the P rings. These re-

sults show that the introduction

of sulfur substituents at phos-

phole 3,4-positions has a con-

siderable impact on the elec-

tronic properties of these P-

containing p-conjugated sys-

tems.

Scheme 8. Chemical derivatization of phospholes 4a,b and mesomeric forms of thiooxo- and oxo-phospholes

6a,b and 7b.

Tuning the electronic property

of 3,4-ethylenedithiaphospholes

by P and S chemical modifica-

tions: Tuning the electronic properties of phosphole-contain-

ing p-conjugated systems by chemical modification of their

P atom is an appealing property that we first demonstrated

in 1999,^[8o]and which was then used by many other

groups.^[8,10]In this regard, derivatives 4a,b behave as classic

phospholes and their P center can be chemoselectively oxi-

dized using elemental sulfur or dioxygen giving rise to com-

pounds 6a,b and 7b, respectively (Scheme 8). These phosp-

holes were isolated in high yields (95%) as air-stable deriva-

tives (Table 1) and their multinuclear data, as well as their

high-resolution mass spectra and elemental analysis, support

the proposed structures. Derivative 6a was also character-

ized by an X-ray diffraction study (Figure 8, Table 2). This

solid-state structure is of particular interest since the s⁴-P

atom of the P ring exhibits a partial positive charge, due to

the presence of the highly polarized P=S bond (Scheme 8).

Therefore, a push–pull effect can potentially take place

within the ring due the presence of the exocyclic p-donor S

atoms (Scheme 8). These two S atoms of 6a are in the plane

of the planar phosphole ring and it is noteworthy that the

Figure 8. Molecular structures of phospholes 6a and 8b in the solid state.

Hydrogen atoms have been omitted for clarity.

4b; neither lengthening of the C1–C2 and C3–C4 distances

nor shortening of the P–C1 and P–C4 separations are re-

corded (Table 3). Indeed, these solid-state data do not speak

for the presence of a push–pull system within the P ring of

6a.

One 2-thienyl substituent of 6a lies in the plane of the

phosphole ring (dihedral angle, 1.68) whereas the second

one exhibits a twist angle of 37.98 (Figure 8). It is notewor-

thy that two S atoms (i.e., one of the thiophene ring and

one of the exocyclic 3,4-ethylenedithia bridge) point towards

each other. The fact that the distance between these two S

centers (3.04 ꢃ) is markedly smaller than the sum of the

ꢀ

S C_sp₂bond lengths are slightly shorter than those observed

for the s³-phosphole derivative 4b in which no push–pull

effect can take place (Table 3). However, the metric data of

the P ring of 6a compare well with those of s³-derivative

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Thiaphosphole p-Conjugated Systems

FULL PAPER

van der Waals radii (3.7 ꢃ) prompted us to perform a calcu-

lation on 6a to elucidate whether any S···S interaction takes

place. Note that this type of interaction, although being

rather weak, is an invaluable tool for the design of p-conju-

gated oligothiophene materials.^[14]Three rotamers 6a’–6a’’’

V. Therefore, the general trends expected following the

analysis of the impact of the S-substituent on the phosphole

building blocks (Figures 2 and 3) have been confirmed both

by experimental and theoretical results obtained with two

different series of p-conjugated systems.

The presence of a reactive heteroatomic center is the

most important attribute of phosphole-based conjugated sys-

tems for chemical engineering aiming at varying their elec-

tronic property. Quite surprisingly, although heteroles fea-

turing 3,4-ethylenedithia bridges have been extensively used

for the tailoring of conjugated systems, the presence of po-

tentially reactive S atoms has been fairly exploited to tune

their electronic property.^[24]We have therefore investigated

this approach with phenyl-capped thioxophosphole 6b and

oxophosphole 7b using m-chloroperoxybenzoic acid

(mCPBA) at room temperature (Scheme 8). The reaction

performed with oxophosphole 7b will be discussed first. The

isolated product 8b is an air-stable orange powder that was

purified by column chromatography (85% yield). Its

³¹P NMR spectroscopic chemical shift is similar to that of its

precursor 7b (Table 1). The presence of a P ring is also sup-

ported by the observation in the ¹³C NMR spectrum of two

ꢀ

doublets corresponding to the P C_aand P C_bcarbon atoms

ꢀ

with classic P C coupling constants. The HRMS and ele-

mental analysis indicate that both S atoms were fully oxi-

dized. The proposed disulfone structure of 8b (Scheme 8)

was confirmed by an X-ray diffraction study performed on

single crystals (Figure 8, Tables 2 and 3). Under the same re-

action conditions (mCPBA, RT), thioxophosphole 6b is also

transformed into oxophosphole 8b in 85% yield. This result

was not expected, since we are not aware of this type of re-

activity in phosphole chemistry; nevertheless it can be un-

derstood by considering the high stability of the P=O

moiety.

The analysis of the solid state of 8b reveals certain bond

localization within the P ring (Table 3), but the presence of

the strongly withdrawing sulfonic groups does not induce

other special structural features. In contrast, the electronic

property of the p-conjugated systems are affected by the -S-

!-S(O₂)- transformation. Compared to its precursor 7b, the

absorption maximum of compound 8b is blueshifted

(Figure 10, Table 1, Dl_max=22 nm) and its reduction poten-

tial increased by 0.8 V (Table 1). In other words, the oxida-

tion of the 3,4-S atoms results in an increase of the HOMO–

LUMO separation and of the electron affinity (lowering of

the LUMO level). To get more insight into this tuning prop-

erty, theoretical calculations have been performed. The iso-

lated phosphole building block as a model compound was

firstly investigated. The -S-!-S(O₂)- transformation results

in a decrease of both the HOMO and LUMO energy level

of the phosphole ring, accompanied by a large increase of

the HOMO–LUMO separation (Figure 11). As expected,

and in line with the experimental results, the presence of the

electron-withdrawing groups induces a notable decrease of

the LUMO level. The blueshift of the l_maxis also nicely re-

produced by the TD-DFT calculations (see Figure S3 in the

Supporting Information). Indeed, these experimental and

Figure 9. The three optimized rotamers of 6a. View of 6a’’’ showing the

critical points between the S atoms.

could be optimized for 6a (Figure 9). The details of these

optimized geometries and their total energies are given in

the Supporting Information. The short distances between

the S centers pointing in the same direction are reproduced

in the optimized structures 6a’’ and 6a’’’ (calculated values:

3.117–3.176 ꢃ). By the topological analysis of the B3LYP/6-

31+G* electron density, critical points were found between

the S atoms for both isomers 6a’’ and 6a’’’ (see Figure 9 for

conformer 6a’’’). However, the electron density is quite

small in these points revealing that the S···S interaction is

rather weak. Accordingly, conformers 6a’’ and 6a’’’ do not

possess extra stabilization and the energy difference be-

tween the three conformers is 1–2 kcalmol^ꢀ1only.

As usually observed for phosphole-based p-conjugated

systems, the oxidation of the P center of 4a,b results in a

bathochromic shift of the UV-visible l_maxand l_onsetas well as

an increase of the oxidation and reduction potentials

(Table 1: 4a/6a, 4b/6b, and 4b/7b). It is worth noting that

the absorption maximum (l_max) and the optical end absorp-

tion (l_onset) of derivatives 6a,b (Table 1) are redshifted com-

pared to those of related thioxophospholes U and V featur-

ing no sulfur atoms in the exocyclic bridge (Scheme 8)^[8l,9h]

(6a/U: Dl_max=39 nm, Dl_onset=46 nm; 6b/V: Dl_max=33 nm,

Dl_onset=37 nm, Table 1). These experimental data can be

nicely reproduced by TD-DFT calculations given in the Sup-

porting Information. The redox properties are also affected

by the presence of the S atoms: compounds 6a,b are slightly

easier to oxidize and to reduce than reference molecules U/

Chem. Eur. J. 2010, 16, 11340 – 11356

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11349

R. Rꢀau, L. Nyulꢁszi, M. Hissler et al.

the P centers (s³,l³-P/s⁴,l⁴-P/s⁴,l⁵-P). By considering the

impact of the 3,4-ethylenedithia bridge on the electronic

properties of di(2-thienyl)phosphole and ꢀ1,1’-biphosphole,

it was of interest to elucidate whether the same trends will

be observed for the corresponding electro-generated poly-

mers. The 2-thienyl-substituted s³,l³- and s⁴,l⁵-phospholes

4a and 6a, as well as the s³,l³-biphosphole 5a (Scheme 9)

Figure 10. Electronic spectra of compounds 6a (solid line), 6b (dotted

line), 7b (dashed line), and 8b (dashed–dotted line) in CH₂Cl₂.

Scheme 9. Synthesis of poly

tion.

ACHUTGTNRENNUG(6a) and polyACHTUNTGREN(NUGN 5a) by means of electrooxida-

were selected for this study.

The electropolymerization experiments were conducted

using solutions of the mixed phosphole–thiophenes 4a–6a in

CH₂Cl₂(1 mm) with Bu₄NPF₆(0.2m) as the supporting elec-

trolyte. When using the s³,l³-phosphole 4a, application of

repetitive potential scans between 0 and 1 V did not result

in polymer formation. Under the same conditions, its “all-

carbon” analogue I (Scheme 4) also could not be polymer-

ized. This similar behavior can be rationalized by the fact

that the remote S atoms do not increase the formation and/

or the stability of the radical cation (which is mainly local-

ized on the terminal thienyl rings). In contrast, repetitive

potential scans applied to the solutions of monomers 6a and

5a in CH₂Cl₂(between 0 to 0.83 V and 0.89 V, respectively)

resulted in a new anodic process well below the onset of the

oxidation of the monomers (Figure 12a, b). The fact that the

intensity of this new redox system regularly increased is con-

sistent with insoluble electroactive material deposition on

the working Pt electrode. The two dark blue films formed

are insoluble in all common solvents (CH₂Cl₂, THF, DMF,

acetone, acetonitrile, MeOH). It is important to recall that

under the same reaction conditions, the “all-carbon” s⁴,l⁵-

thioxophosphole U (Scheme 8) and s³,l³-biphosphole S

(Figure 7) also undergo oxidative polymerization.^[8l]The

Figure 11. HOMO–LUMO separations of thiooxophospholes illustrating

the impact of having the sulfur moiety at their 3,4-positions.

theoretical studies show that the oxidation of the S atoms of

a 3,4-ethylenedithia P-heterole bridge is a powerful means

to tune the electronic property of the five-membered ring

and especially to enhance its electron affinity.

Electropolymerization of 3,4-ethylenedithiathiooxophos-

phole and ꢀ1,1’-biphosphole derivatives 6a and 5a: One of

the most versatile routes towards p-conjugated polymers in-

volves the electropolymerization of thienyl-capped mono-

mers by means of an oxidation process involving the cou-

pling of radical cations.^[25]This method has been successfully

applied for the preparation of hybrid phosphole–thiophene

polymers having phosphole^[8d,l]or 1,1’-biphosphole^[8j]sub-

units. As observed for their corresponding molecular di(2-

thienyl)-capped P precursors, the optical and electrochemi-

cal properties of these phosphole-modified poly(thiophene)s

depend both on the nature of the P building block (phos-

electrochemical responses of polyACTHNUTRGENNGU(5a) and polyACHTUNGTRENNUNG(6a)

(Scheme 9, Figure 12) were studied by CV, recorded in mo-

nomer-free electrolytic medium. The cyclic voltammograms

of these materials show anodic waves that are stable and re-

versible upon cycling (five recurrent sweeps between ꢀ0.5

and +0.8 V; Figure 12c, d). The threshold potential oxida-

tion of poly

(5a) (ꢀ0.2 V) is less anodic than that of poly

ACHTUNGTRENNUNG(6a)

(+0.1 V), which shows that the nature of the P building

A

block has an impact on the electronic properties of the

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Thiaphosphole p-Conjugated Systems

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Figure 12. Multiple-scan voltammogram of 10^ꢀ2m solutions of derivatives a) 5a and b) 6a in 0.2m Bu₄NPF₆in CH₂Cl₂(scan rate, 200 mVs^ꢀ1). Cyclic vol-

tammogramm of electropolymerized c) poly(5a) and d) poly

(6a) recorded in 0.2m Bu₄NPF₆in CH₂Cl₂(scan rate, 200 mVs^ꢀ1). Working electrode: plati-

A

ACHTUNGTRENNUNG

num disk (d=1 mm). Potentials referred to the ferrocene/ferrocenium couple.

phosphole–thiophene copolymer. Poly(S), the “all-carbon”

atoms has an influence on the electron affinity of the 1,1’-bi-

analogue of poly

N

phosphole-based films. The influence of the S atoms within

threshold (ꢀ0.35 V). Interestingly, poly

N

the bridge is more important for poly

ly, poly(6a) possesses a lower threshold potential than that

of its “all-carbon” analogue poly(U) (Table 4)^[8l]and the

shape of the anodic wave of poly(6a) (Figure 12) clearly

shows that its p-doping stability is higher than that of

poly(U).^[8l]Secondly, the reduction of poly

(6a) takes place

ACHTUNGERTN(NUNG 6a) (Scheme 9). First-

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

at a less negative potential than poly(U) (Table 4). There-

fore, the most important modification of the electronic prop-

erty of a mixed polymer based on thienyl and phosphole or

1,1’-biphosphole moieties upon introduction of the S atoms

within the bridge is the lowering of the LUMO level. The

electropolymerization of 6a and 5a can also be conducted

on indium–tin oxide (ITO) by recurrent CV, allowing the

Table 4. Polymerization potential of monomers 5a–6a and reference

compounds S and U. The p-doping and n-doping potential ranges and

photophysical data of the corresponding dedoped polymers are also

given.^[a]

[b]

[e]

E_electopol

[V]

p doping^[c]

[V]

n doping^[c]

[V]

l_max

l_onset

[nm]

poly

poly(S)

poly(U)

N

0.89

0.83

0.80

1.15

ꢀ0.20!+0.76 ꢀ1.63^[d]

611

600

594

529

800

760

730

750

+0.11!+0.73 ꢀ1.35^[d]

UV-visible spectrum of the insoluble poly

to be recorded. The UV-visible spectra of dedoped poly

and poly(5a) are considerably redshifted relative to those of

their respective monomers (Figure 13). The spectra exhibit a

large band with an unresolved maximum (poly(5a): l_max

611 nm; poly(6a): l_max=600 nm) and a high value of l_onset

(poly(5a): l_onset800 nm; poly(6a): l_onset=760 nm)

A

ACHTUNGTRENNUNG(5a)

ꢀ0.35!+0.32

–

ACHTUNGTRENNUNG

+0.30!+0.65 ꢀ1.80!ꢀ2.42

AHCTUNGTRENNUNG

[a] All potentials were obtained during cyclic voltammetric investigations

of solutions of monomers in CH₂Cl₂(1 mm) with Bu₄NPF₆(0.2m ) or in

CH₂Cl₂free of monomer with Bu₄NPF₆(0.2m) for the polymer response.

Platinum electrode diameter: 1 mm; sweep rate: 200 mvs^ꢀ1. [b] Potential

at the electropolymerization takes place. [c] Potential range at which the

p- and n-doping processes are reversible. Potentials were referred to the

ferrocene/ferrocenium couple. [d] Threshold reduction potential of the ir-

reversible process. [e] ꢂ5 nm.

A

=

AHCTUNGTRENNUNG

A

ACHTUNGTRENNUNG

(Figure 13). These wavelengths (l_maxand l_onset) are slightly

redshifted relative to the analogous “all-carbon” polymers

Chem. Eur. J. 2010, 16, 11340 – 11356

ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

11351

R. Rꢀau, L. Nyulꢁszi, M. Hissler et al.

Experimental Section

X-ray crystallography studies: Single

crystals suitable for X-ray crystal anal-

ysis were obtained by slow diffusion of

vapors of pentane into a solution of

4b, 6a, or 8b in dichloromethane.

Single-crystal data collection was per-

formed at 100 K with an APEX II

Bruker-AXS (Centre de Diffractomꢀ-

trie, Universitꢀ de Rennes 1, France)

with Mo_Karadiation (l=0.71073 ꢃ).

Reflections were indexed, Lorentz-po-

larization-corrected, and integrated by

the DENZO program of the Kap-

paCCD software package. The data-

merging process was performed using

the SCALEPACK program.^[27]Struc-

ture determinations were performed

by direct methods with the solving

program SIR97,^[28]which revealed all

Figure 13. Electronic absorption measurements in CH₂Cl₂for derivatives 5a (dashed line) and 6a (solid line)

and on ITO modified by poly(5a) (dashed line) and poly

(6a) (solid line) dedoped at ꢀ0.4 V. Deposits were

prepared by anodic oxidation of 10^ꢀ2m solutions of 5a, 6a in 0.2m Bu₄NPF₆in CH₂Cl₂.

G

ACHTUNGTRENNUNG

the

non-hydrogen

atoms.

The

SHELXL program^[29]was used to

refine the structures by full-matrix

least-squares methods based on F². All

non-hydrogen atoms were refined with anisotropic displacement parame-

ters. Hydrogen atoms were included in idealized positions and refined

with isotropic displacement parameters. In the case of derivative 6b, one

of the two thienyl moieties was found disordered over two superimposed

orientations. This disorder was treated for the thienyl ring with a parti-

tion of these two orientations. For each of these orientations, the relative

population was refined.

(Table 4), which indicates that the S-substituents of the P-

moieties induce a lowering of the gap of these electroactive

materials.

Conclusion

Atomic scattering factors for all atoms were taken from International

Tables for X-ray Crystallography.^[30]Details of crystal data and structural

refinements are given in Table 1. CCDC-777639 (4b), -777640 (6a), and

-777641 (8b) contain the supplementary crystallographic data for this

paper. These data can be obtained free of charge from The Cambridge

Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

In this paper, we have described the use of the Fagan–

Nugent route for the synthesis of the first phosphole and

1,1’-biphosphole derivatives bearing S-substituents at their

3,4-positions. The theoretical study of the mechanism of this

organometallic method showed that 1,2-bis(ethynylthio)-

ethane substrates follow the classic mechanism proposed for

nonfunctional alkynes. The presence of the S atoms has a

large impact on the electronic properties of the P rings,

which allows small p-conjugated systems with low HOMO–

LUMO separation and a stabilized LUMO level to be pre-

pared. The 3,4-ethylenedithiaphosphole derivatives possess

two reactive nucleophilic heterotaoms, that is, the s³,l³-P

and the s²,l²-S centers, that can be successively oxidized.

These chemioselective modifications result in a stepwise

tuning of both the optical and the electrochemical proper-

ties of phosphole-based conjugated systems. Therefore, the

incorporation of 3,4-ethylenedithiaphosphole within p-con-

jugated systems endowed these materials with multiaddress-

able ability. Lastly, polymers incorporating 3,4-ethylenedi-

thiaphosphole and ꢀ1,1’-biphosphole units can be readily

prepared by electropolymerization. These results show that

these multifunctional P,S building blocks are valuable syn-

thons for the molecular engineering of p-conjugated molec-

ular or polymeric conjugated systems, and extend the family

of organophosphorus-based materials.^[26]

Computations: All the density functional calculations were carried out

using the Gaussian 03 code.^[31]This level of the theory has provided satis-

factory results for phosphole–thiophene oligomers before.^[4c,h,5d,7]The ge-

ometries were fully optimized, and vibrational analysis was performed on

the optimized structures to check whether the stationary point located is

a minimum of the potential-energy hypersurface or a first-order saddle

point (in the case of transition states). At the saddle points intrinsic reac-

tion coordinate (IRC) calculations were performed to locate the minima

connected by the transition structure. For the phosphole and thiophene

derivatives the B3LYP/6-31+G* level of theory was used; the molecular

orbitals were calculated at the B3LYP/6-31G* and HF/6-31G* levels. The

vertical excitation energies were calculated on the optimized structures

using the time-dependent (TD) density functional method applying the

B3LYP functional and the 6-31G* basis set. The zirconocene complexes

were calculated using the B3LYP and BP86 functionals and the cc-pVDZ

basis set; for zirconium the cc-pVDZ basis with pseudopotentials.^[32]The

solvent effect of THF was modeled with the PCM.^[33]For the visualiza-

tion of the structures, the Molden program^[34]was used.

Syntheses and characterization: All experiments were performed under

an atmosphere of dry argon using standard Schlenk techniques. Column

chromatography was performed in air, unless stated otherwise. Solvents

were freshly distilled under argon from sodium/benzophenone (THF, di-

ethyl ether) or from phosphorus pentoxide (pentane, dichloromethane).

[(Cp)₂ZrCl₂] was obtained from Alfa Aesar Chem. Co. nBuLi, PBr₃, and

S₈were obtained from Acros Chem. Co. Ammonium chloride, magnesi-

um sulfate, 3-chloroperoxybenzoic acid (77% max) and elemental sulfur

were obtained from Aldrich Chem. Co. All compounds were used as re-

ceived without further purification. PPhBr₂,^[35]ethynylthiophene,^[36a,b]

ethynylbenzene,^[36a,c]and 1,2-biscyanoethane^[21](1) were prepared as de-

scribed in the literature. Preparative separations were performed by grav-

11352

www.chemeurj.org

ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 11340 – 11356

Thiaphosphole p-Conjugated Systems

FULL PAPER

ity column chromatography on basic alumina (Aldrich, Type 5016A, 150

mesh, 58 ꢃ) or silica gel (Merck Geduran 60, 0.063–0.200 mm) in 3.5–

20 cm columns. ¹H, ¹³C, and ³¹P NMR spectra were recorded on Bruker

C₁₈H₁₄S₂(294.439): C 73.43, H 4.79, S 21.78; found: C 73.67, H 5.17, S

21.40.

Compound 4a: At ꢀ788C, a solution of BuLi in hexane (2.5m, 0.85 mL;

2.1 mmol) was added dropwise to a solution of [Cp₂ZrCl₂] (0.30 mg,

1 mmol) and 1,2-bis(thiophen-2-ylethynylthio)ethane (2a; 0.31 mg,

1 mmol) in THF (20 mL). The solution was warmed to room temperature

and stirred for 12 h. To this deep red solution was added, at ꢀ788C,

freshly distilled PhPBr₂(230 mL, 1.1 mmol). The solution was allowed to

warm to room temperature and stirred for an additional 12 h. Then, the

solution was filtered on basic alumina (THF, R_f=0.8). All the volatile

materials were removed under vacuum. Compound 4a was washed sever-

al times with pentane and diethyl ether and isolated as a dark red solid

(0.25 g, 60%). ¹H NMR (300 MHz, C₆D₆): d=2.44 (m, 2H; CH₂), 2.59

1

AM300 or DPX200 instruments. H and ¹³C NMR spectroscopic chemical

shifts were reported in parts per million (ppm) relative to SiACHTNUGTRNEG(UN CH₃)₄as ex-

ternal standard. ³¹P NMR spectroscopic downfield chemical shifts were

expressed with a positive sign, in ppm, relative to external 85% H₃PO₄.

Assignment of proton atoms is based on COSY experiments. Assignment

of carbon atoms is based on HMBC, HMQC, and DEPT-135 experi-

ments. High-resolution mass spectra were obtained on a Varian MAT

311, Waters Q-TOF 2, or ZabSpec TOF Micromass instrument at

CRMPO, University of Rennes 1. Elemental analyses were performed by

the CRMPO, University of Rennes 1.

(m, 2H; CH₂), 6.74 (ddd, ³J

N

ACHTUNGTRENNUNG(P,H)=

Determination of optical data: UV-visible spectra were recorded at room

temperature on a UVIKON 942 spectrophotometer and luminescence

spectra were recorded in freshly distilled solvents at room temperature

with a PTI spectrofluorometer (PTI-814 PDS, MD 5020, LPS 220B)

using a xenon lamp. Quantum yields were calculated relative to fluores-

cein (F=0.90 in 0.1n NaOH).^[37]

1.2 Hz, 2H;

G

H

, H

phenyl

³J

H

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

CD₂Cl₂): d=28.4 (s; CH₂), 125.8 (d, JACTHUNGTRENNNUG

J

N

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

Cyclic voltammetry: The electrochemical studies were carried out under

argon using an Eco Chemie Autolab PGSTAT 30 potentiostat for cyclic

voltammetry with the three-electrode configuration: the working elec-

trode was a platinum disk or ITO, the reference electrode a saturated cal-

omel electrode, and the counter electrode a platinum wire. All potentials

were internally referenced to the ferrocene/ferrocenium couple. For the

measurements, concentrations of 10^ꢀ3m of the electroactive species were

used in freshly distilled and degassed dichloromethane (Lichrosolv,

Merck) and 0.2m tetrabutylammonium hexafluorophosphate (TBAHFP,

Fluka), which was twice recrystallized from ethanol and dried under

vacuum prior to use.

E

ACHTUNGTRENNUNG

R

ACHTUNGTRENNUNG

22.3 Hz; C₂); ³¹P{¹H} NMR (CD₂Cl₂, 121.5 MHz): d=9.9 ppm (s); HRMS

(EI): m/z calcd for C₂₀H₁₅PS₄: 413.97943; found: 413.9790 [M]⁺; elemen-

tal analysis calcd (%) for C₂₀H₁₅PS₄(414.572): C 57.94, H 3.65, S 30.94;

found: C 58.28, H 4.05; S 30.79.

Compound 4b : At ꢀ788C, a solution of BuLi in hexane (2.5m, 1.12 mL;

2.8 mmol) was added dropwise to a solution of [Cp₂ZrCl₂] (0.39 mg,

1.3 mmol) and 1,2-bis(phenylethynylthio)ethane (2b) (0.39 mg, 1.3 mmol)

in THF (30 mL). The solution was warmed to room temperature and

stirred for 12 h. Freshly distilled PhPBr₂(300 mL, 1.5 mmol) was added to

this red solution at ꢀ788C. The solution was allowed to warm to room

temperature and stirred for an additional 24 h. Then, the solution was fil-

tered on basic alumina (THF, R_f=0.8). All the volatile materials were re-

moved under vacuum. Compound 4b was washed several times with pen-

tane and diethyl ether and isolated as a yellow solid (0.26 g, 50%).

¹H NMR (300 MHz, CD₂Cl₂): d=3.11 (m, 2H; CH₂), 3.31 (m, 2H; CH₂),

Compound 2a: A solution of BuLi in hexanes (2.5m, 3.5 mL, 8.7 mmol)

was added dropwise at ꢀ788C to

(0.941 g, 8.7 mmol) in THF (40 mL). The heterogeneous red mixture was

stirred for 1 h. Then, solution of 1,2-bis(thiocyano)ethane (0.63 g,

a solution of 2-ethynylthiophene

a

4.4 mmol) in THF (10 mL) was added to this reaction mixture at ꢀ208C.

After stirring overnight at room temperature, the red solution was

washed 3 times with an aqueous saturated ammonium chloride solution

(30 mL). After extraction, the organic layer was dried over magnesium

sulfate. All volatile materials were removed under vacuum, and the prod-

uct was purified by silica gel chromatography (n-heptane/ethyl acetate,

9:1, v/v R_f=0.5). The product was obtained as a brown solid (0.373 g,

28%). ¹H NMR (200 MHz, C₆D₆): d=2.72 (s, 4H; CH₂), 6.56 (dd,

7.12–7.30 (m, 7H; H_{ortho,meta,para}_phenyl, H_4phenyl), 7.37 (pseudo-t, J

7.3 Hz, J(H,H)=7.8 Hz, 4H; H_3phenyl), 7.54 ppm (d, J(H,H)=7.3 Hz, 4H;

_2phenyl); ¹³C NMR (75 MHz, CD₂Cl₂): d=28.5 (s; CH₂), 127.0 (d,

(P,C)=0.7 Hz; C₄H_phenyl), 128.3 (s; C₃H_phenyl), 128.5 (d, J(P,C)=8.2 Hz;

(P,C)=1.5 Hz;

(P,C)=15.6 Hz; C_ipsophenyl), 132.4 (d, (P,C)=

(P,C)=19.7 Hz; C_orthoH_phenyl), 135.6 (d,

(P,C)=17.2 Hz; C_1phenyl), 142.9 ppm (d, J

(P,C)=1.8 Hz; PC=C); ³¹P{¹H}

ACHTUNGTRENNUNG(H,H)=

N

ACHTUNGTRENNUNG

H

J

A

ACHTUNGTRENNUNG

C_metaH_phenyl), 129.0 (d, J

C_paraH_phenyl), 131.4 (d,

ACHUTTGNERN(NUG P,C)=9.5 Hz; C₂H_phenyl), 129.6 (d, JACHTUNGTRENNUNG

³J

5.1 Hz, ⁴J

⁴J(H,H)=1.1 Hz, 2H; H_3thienyl); ¹³C{¹H} NMR (75.46 MHz, CDCl₃): d=

(H,H)=3.6 Hz, ³J

E

H

_4thienyl), 6.71 (dd, ³J

ACHTUNGTRNE(NUNG H,H)=

J

R

JACHTUNGTRENNUNG

10.2 Hz; PC=C), 133.4 (d,

JACHTUNGTRENNUNG

R

(H,H)=3.6 Hz,

J

A

ACHTUNGTRENNUNG

NMR (CD₂Cl₂, 121.5 MHz): d=10.2 ppm (s); HRMS (EI): m/z calcd for

C₂₄H₁₉PS₂: 402.06658; found: 402.0651 [M]⁺; elemental analysis calcd

(%) for C₂₄H₁₉PS₂(402.519): C 71.62, H 4.76, S 15.93; found: C 71.26, H

4.65, S 15.99.

35.2 (s; CH₂), 82.2 (s; CꢁC), 87.0 (s; CꢁC), 123.1 (s; C_thienyl), 127.0 (s;

CH_thienyl), 128.2 (s;CH_thienyl), 133.4 ppm (s; CH_thienyl); HRMS (EI): m/z

calcd for C₁₂H₆S₄: 277.93524; found: 277.9347 [MꢀCH₂CH₂]⁺; calcd for

C₁₄H₁₀S₄: 305.9665; found: 306.0 [M]⁺; elemental analysis calcd (%) for

C₁₄H₁₀S₄(306.492): C 54.86, H 3.29, S 41.85; found: C 54.96, H 3.40, S

40.56.

Compound 5a: A solution of BuLi in hexanes (2.5m, 0.52 mL; 1.2 mmol)

was added dropwise at ꢀ788C to a solution of [Cp₂ZrCl₂] (0.182 g,

0.62 mmol) and 1,2-bis(thienyl-2-ylethynylthio)ethane (2a) (0.181 g,

0.6 mmol) in THF (20 mL). After being stirred overnight, the solution

turned deep red and neat PBr₃(0.12 mL, 1.2 mmol) was added at ꢀ788C.

The solution was stirred for 3 d at room temperature and turned light

red. The solution was then filtered on basic alumina (THF, R_f=0.8) and

all volatile materials were removed under vacuum. The precipitate was

washed several times with pentane and diethyl ether. Compound 5a was

isolated as a red solid (0.09 g, 45%). ¹H NMR (300 MHz, CD₂Cl₂): d=

Compound 2b: A solution of BuLi in hexanes (2.5m, 2.5 mL, 6.3 mmol)

was added dropwise at ꢀ788C to a solution of ethynylbenzene (0.64 g,

6.3 mmol) in THF (30 mL). The heterogeneous red mixture was stirred

for 1 h. Then, a solution of 1,2-bis-thiocyanoethane (0.45 g, 3.1 mmol) in

THF (10 mL) was added to this reaction mixture at ꢀ208C. After stirring

overnight at room temperature, the red solution was washed 3 times with

an aqueous saturated ammonium chloride solution (3ꢄ30 mL). After ex-

traction, the organic layer was dried over magnesium sulfate. All volatile

materials were removed under vacuum, and the product was purified on

silica gel chromatography (n-heptane/ethyl acetate, 95:5, v/v R_f=0.5).

The product was obtained as a yellow solid (0.91 g, 58%). ¹H NMR

(300 MHz, C₆D₆): d=3.22 (s, 4H; CH₂), 7.31 (m, 6H; H_meta,para_phenyl),

7.42 ppm (m, 4H; H_ortho_phenyl); ¹³C{¹H} NMR (75.46 MHz, CDCl₃): d=

35.1 (s; CH₂), 77.9 (s; CꢁC), 94.3 (s; CꢁC), 123.1 (s; C_phenyl), 128.4 (s;

CH_phenyl), 131.6 ppm (s; CH_phenyl); HRMS (EI): m/z calcd for C₁₈H₁₄S₂:

294.05369; found: 294.0518 [M]⁺; elemental analysis calcd (%) for

3.08 (m, 8H; CH₂), 7.13 (dd, ³J

_3thienyl), 7.16 (dd, ³J(H,H)=3.6 Hz, ³J

7.43 ppm (dd, ⁴J(H,H)=0.9 Hz, ³J(H,H)=5.1 Hz, 4H; H_5thienyl); ¹³C{¹H}

NMR (75.46 MHz, CD₂Cl₂): d=27.7 (s, CH₂) 125.7 (s, CH_thienyl), 126.9 (t-

like, J(P,C)=5.6, 5.5 Hz; CH_thienyl), 127.1 (s, CH_thienyl), 130.7 (brs; PC=C),

134.6 (brs; PC=C), 137.6 ppm (t-like, JACHTUGTNRENNU(G P,C)=12.0, 12.0 Hz; C_thienyl);

A

ACHTUNGTRENNUNG

H

N

H

A

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

³¹P{¹H} NMR (CD₂Cl₂, 121.5 MHz): d=5.0 ppm (s); HRMS (ES, positive

mode): m/z calcd for C₂₈H₂₀P₂S₈Na: 696.87037; found: 696.8704 [M+Na]⁺;

Chem. Eur. J. 2010, 16, 11340 – 11356

ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

11353

R. Rꢀau, L. Nyulꢁszi, M. Hissler et al.

elemental analysis calcd (%) for C₂₈H₂₀P₂S₈(674.931): C 49.83, H 2.99, S

38.01; found: C 49.57, H 2.86, S 38.25.

CH_meta_phenyl), 129.5 (d, J

10.5 Hz; CH_ortho_phenyl), 132.0 (d, J

(P,C)=9.2 Hz; C_phenyl), 139.2 ppm (d, JACTHUNGTRENNUNG

NMR (CD₂Cl₂, 81.0 MHz): d=34.1 ppm (s); HRMS (ES, positive mode):

m/z calcd for C₂₄H₁₉OPS₂Na: 441.0513; found: 441.0517 [M+Na]⁺; ele-

mental analysis calcd (%) for C₂₄H₁₉OPS₂(418.518): C 68.88, H 4.58, S

15.32; found: C 68.75, H 4.20, S 14.98.

U

ACHTUNGTRENNUNG(P,C)=

AHCTUNGTRENNUNG

J

N

Compound 5b: A solution of BuLi in hexanes (2.5m, 0.52 mL; 1.2 mmol)

was added dropwise at ꢀ788C to a solution of [Cp₂ZrCl₂] (0.182 g,

0.62 mmol) and 1,2-bis(phenylethynylthio)ethane (2b) (0.184 g,

0.62 mmol) in THF (20 mL). After being stirred overnight, the solution

turned deep red and neat PBr₃(0.12 mL, 1.20 mmol) was added at

ꢀ788C. The solution was stirred for 3 d at room temperature and turned

light red. The solution was then filtered on basic alumina (THF, R_f=0.8)

and all volatile materials were removed under vacuum. The precipitate

was washed several times with pentane and diethyl ether. Compound 5b

was isolated as an orange solid (0.10 g, 53%). ¹H NMR (300 MHz,

CD₂Cl₂): d=2.85 (m, 4H; CH₂), 3.00 (m, 4H; CH₂), 7.32 (m, 8H; H_phenyl),

7.38 (m, 4H; H_4phenyl), 7.47 ppm (m, 8H; H_phenyl); ¹³C{¹H} NMR

(75.46 MHz, CD₂Cl₂): d=27.9 (s; CH₂), 127.0 (s; CH_phenyl), 128.1 (s;

Compound 8b: A solution of 3-chloroperoxybenzoic acid (77% max,

6 equiv, 0.094 g, 0.44 mmol) in CH₂Cl₂(5 mL) was added dropwise to a

solution of phosphole 6b (0.032 g, 0.074 mmol) in CH₂Cl₂(5 mL) at room

temperature. The reaction mixture was stirred for 2 h, then treated with a

saturated solution of NaHCO₃(2 mL) to remove the benzoic acids and

was allowed to stir for another 2 h. The mixture was then extracted with

dichloromethane (3ꢄ5 mL), dried over MgSO₄, and solvents were re-

moved to give an orange solid. The crude solid was subjected to chroma-

tography on silica gel (MeOH/CH₂Cl₂, 0.2:99.8, v/v, R_f=0.60). Compound

8b was obtained as an air-stable yellow-orange powder (0.030 g,

85%).¹H NMR (200 MHz, CD₂Cl₂): d=4.00 (m, 4H; CH₂), 7.38–7.78 (m,

CH_phenyl), 129.3 (t-like, J

4.5, 4.2 Hz; PC=C), 135.3 (t-like, J

(d,

(P,C)=6.0 Hz; PC=C); ³¹P{¹H} NMR (CD₂Cl₂, 121.5 MHz): d=

A

ACHTUNGTRNE(NUNG P,C)=

AHCTUNGTRENNUNG

JACHTUNGTRENNUNG

12H; H_phenyl), 7.64 (dd, ³J

_phenyl), 7.73 ppm (ddd, ³J

12.7 Hz, 2H; H_{ortho phenyl}); ¹³C{¹H} NMR (75.46 MHz, CD₂Cl₂): d=48.7 (s,

CH₂), 122.8 (d, J(P,C)=98.1 Hz; PC=C), 127.8 (s; CH_phenyl), 128.0 (d,

(P,C)=6.8 Hz; CH_phenyl), 128.3 (d, J(P,C)=4.9 Hz; CH_phenyl), 129.0 (d,

(P,C)=12.7 Hz; CH_meta_phenyl), 129.9 (d, J(P,C)=10.6 Hz; CH_{ortho phenyl}),

(P,C)=1.3 Hz; C_phenyl), 133.2 (d, J(P,C)=2.8 Hz; CH_{para phenyl}),

140.2 (d, J(P,C)=27.0 Hz; PC=C), 144.7 ppm (d, J(P,C)=79.9 Hz; C_ipso

R

ACHTUNGTRENNUNG

7.2 ppm (s); HRMS (ES, positive mode): m/z calcd for C₃₆H₂₈P₂S₄Na:

673.04468; found: 673.0452 [M+Na]⁺; elemental analysis calcd (%) for

C₃₆H₂₈P₂S₈(650.826): C 66.44, H 4.34, S 19.71; found: C 66.23, H 4.00, S

19.82.

E

JACHTUNGTRENNUNG

AHCTUNGTRENNUNG

J

U

ACHTUNGTRENNUNG

Compound 6a: An excess amount of elemental sulfur was added to a so-

lution of phosphole 4a (0.50 g, 1.2 mmol) in THF (10 mL) at room tem-

perature. The reaction mixture was stirred for 1 d, filtered, and the sol-

vent was removed under vacuum. After purification on silica gel (hep-

tane/CH₂Cl₂, 60:40, v/v, R_f=0.7), 6a was obtained as an air-stable orange

solid (0.51 g, 95%). ¹H NMR (300 MHz, CDCl₃): d=3.46 (s, 4H; CH₂),

ACHTUNGTRENNUNG

130.0 (d, J

A

ACHTUNGTRENNUNG

R

ACHTUNGTRENNUNG

_phenyl); ³¹P{¹H} NMR (CD₂Cl₂, 81.0 MHz): d=39.1 ppm (s); HRMS (ES,

positive mode): m/z calcd for C₂₄H₂₀O₅PS₂: 483.0490; found: 483.0484

[M+H]⁺; elemental analysis calcd (%) for C₂₄H₁₉O₅PS₂(482.516): C

59.74, H 3.97, S 13.29; found: C 59.85, H 4.10, S 12.96.

6.99 (dd, ³J

³J

(H,H)=5.1 Hz, 2H;

7.93 ppm (ddd, ³J(H,H)=7.5 Hz, ⁴J

H_ortho_phenyl); ¹³C{¹H} NMR (75.46 MHz, CD₂Cl₂): d=27.9 (s; CH₂), 124.7

(d, J(P,C)=83.9 Hz; PC=C), 126.9 (s; CH_thienyl), 127.3 (s; CH_thienyl), 128.4

(d, J(P,H)=6.0 Hz; CH_thienyl), 129.1 (d, J(P,C)=77.9 Hz; C_{ipso phenyl}), 129.2

(d, J(P,C)=12.8 Hz; CH_{meta phenyl}), 130.8 (d, J(P,C)=12.1 Hz; CH_{ortho phenyl}),

132.2 (d, J(P,C)=3.2 Hz; CH_para_phenyl), 133.7 (d, J(P,C)=14.7 Hz; C_thienyl),

135.2 ppm (d, J

(P,C)=24.7 Hz; C_b); ³¹P{¹H} NMR (CD₂Cl₂, 121.5 MHz):

A

N

H

_4thienyl), 7.36 (d,

_5thienyl),

ACTHNUGTREN(NGNU H,H)=1.0 Hz, JCAHTUNGTREN(NUGN P,H)=9.0 Hz, 2H;

R

H

, H

phenyl

N

ACHTUNGTRENNUNG

Acknowledgements

A

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

This work was supported by the Ministꢅre de la Recherche et de l’En-

seignement Supꢀrieur, the Institut Universitaire de France, the CNRS,

the Rꢀgion Bretagne (CREATE project) and the project ANR PSICO.

Support from the Scientific and Technological French–Hungarian Bilater-

al Cooperation (BALATON program TeT FR08/2) and COST CM0802

(Phoscinet) is also acknowledged.

A

ACHTUNGTRENNUNG

d=+47.3 ppm (s); HRMS (EI): m/z calcd for C₂₀H₁₅PS₅: 445.9515;

found: 445.9491 [M]⁺; elemental analysis calcd (%) for C₂₀H₁₅PS₅

(446.636): C 53.78, H 3.39, S 35.90; found: C 53.89, H 3.25, S 35.95.

Compound 6b: An excess amount of elemental sulfur was added to a so-

lution of phosphole 4b (0.50 g, 1.24 mmol) in THF (10 mL) at room tem-

perature. The reaction mixture was stirred for 1 d, filtered, and the sol-

vent was removed under vacuum. After purification on silica gel (hep-

tane/CH₂Cl₂, 60:40, v/v, R_f=0.7), 6b was obtained as an air-stable yellow

powder (0.51 g, 95%). ¹H NMR (300 MHz, CD₂Cl₂): d=3.31 (s, 4H;

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CH₂), 7.31–7.50 (m, 13H; H_meta,para

H

_2,3,4phenyl), 7.86 ppm (ddd,

(P,H)=15.0 Hz, 2H; H_{ortho phenyl});

¹³C{¹H} NMR (75.46 MHz, CD₂Cl₂): d=27.8 (s; CH₂), 128.0 (d, J

(P,C)=

77.6 Hz; PC=C), 128.3 (s; CH_phenyl), 128.8 (s; CH_{para phenyl}), 128.9 (s;

CH_phenyl), 129.0 (s; CH_phenyl), 130.7 (d, J(P,C)=80.8 Hz; C_{ipso phenyl}), 130.8

(d, J(P,C)=11.7 Hz; CH_meta_phenyl), 131.7 (d, J(P,C)=9.9 Hz; C_phenyl), 132.0

(d, J(P,C)=9.7 Hz; CH_ortho_phenyl), 138.7 ppm (d, J(P,C)=26.9 Hz; PC=C);

phenyl,

³J(H,H)=7.5 Hz, ⁴J

ACHTUNGTRENNUNG ACHTUNGTRENNUNG(H,H)=1.8 Hz, JACUTHNGTRENNNUG

AHCTUNGTRENNUNG

G

ACHTUNGTRENNUNG

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E

ACHTUNGTRENNUNG

³¹P{¹H} NMR (CD₂Cl₂, 121.5 MHz): d=+47.7 ppm (s); HRMS (EI): m/z

calcd for C₂₄H₁₉PS₃: 434.03865; found: 434.0370 [M]⁺; elemental analysis

calcd (%) for C₂₄H₁₉PS₃(434.58): C 66.33, H 4.41, S 22.13; found: C

66.08, H 4.34, S 21.98.

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Compound 7b: A solution of phosphole 4b (0.030 g, 0.07 mmol) in THF

(5 mL) was stirred for 5 d in air and all volatile materials were removed

under vacuum. The precipitate was dissolved in ethyl acetate and com-

pound 7b was precipitated by adding pentane. Compound 7b was ob-

tained as an air-stable yellow-orange powder (0.29 g, 95%).¹H NMR

(200 MHz, CD₂Cl₂): d=3.32 (m, 4H; CH₂), 7.29–7.58 (m, 9H; H_meta,para

3

4

H

_3,4phenyl), 7.56 (dd, J

7.69 ppm (ddd, ³J(H,H)=7.7 Hz, ⁴J

H_ortho_phenyl); ¹³C{¹H} NMR (75.46 MHz, CD₂Cl₂): d=27.7 (s; CH₂), 128.0

(d, J(P,C)=84.6 Hz; PC=C), 128.1 (d, J(P,C)=0.8 Hz; CH_phenyl), 128.5 (s;

(P,C)=5.5 Hz; CH_phenyl), 128.9 (d, J(P,C)=12.4 Hz;

G

ACHTUNGTRENNUNG

phenyl,

E

ACHTUNGTRENNUNG

U

ACHTUNGTRENNUNG

CH_phenyl), 128.6 (d, J

N

ACHTUNGTRENNUNG

11354

www.chemeurj.org

ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 11340 – 11356

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Received: May 26, 2010

Published online: August 16, 2010

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3,4-Dithiaphosphole and 3,3′,4,4′-tetrathia-1,1′- biphosphole π-conjugated systems: S makes the impact

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