A bridging ligand featuring terminal 2-pyridylphosphole moieties: Synthesis, optical properties and Ru(II)-complex

Article abstract of DOI:10.1016/S0022-328X(01)01123-8

2,2′-Di[2-(5-(2-pyridyl)phospholyl)]thiophene (2a) has been obtained in 63% yield via the Fagan-Nugent's route. Derivative 2a possesses an extended π-conjugated system and behaves as a bis(P,N-chelate) towards cationic (p-cymene)RuCl fragments affording the air-stable complex 3a in 60% yield. A diastereoselective coordination was observed and the solid state structure of the model Ru-complex 2b featuring a related 2-(2-pyridyl)-5-(2-thienyl)phosphole ligand is presented.

Full text of DOI:10.1016/S0022-328X(01)01123-8

Journal of Organometallic Chemistry 643–644 (2002) 494–497
www.elsevier.com/locate/jorganchem
Note
A bridging ligand featuring terminal 2-pyridylphosphole moieties:
synthesis, optical properties and Ru(II)-complex
Caroline Hay a, Mathieu Sauthier a, Vale´rie Deborde a, Muriel Hissler a, Lo¨ıc Toupet b,
Re´gis Re´au a,*
a Organome´talliques et Catalyse: Chimie et Electrochimie Mole´culaires, UMR 6509 CNRS-Uni6ersite´ de Rennes 1, Institut de Chimie de Rennes,
Campus de Beaulieu, 35042 Rennes Cedex, France
b Groupe Matie`re Condense´e et Mate´riaux, UMR 6626, CNRS-Uni6ersite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
Received 28 June 2001; accepted 19 July 2001
Abstract
2,2%-Di[2-(5-(2-pyridyl)phospholyl)]thiophene (2a) has been obtained in 63% yield via the Fagan–Nugent’s route. Derivative 2a
possesses an extended p-conjugated system and behaves as a bis(P,N-chelate) towards cationic (p-cymene)RuCl fragments
affording the air-stable complex 3a in 60% yield. A diastereoselective coordination was observed and the solid state structure of
the model Ru-complex 2b featuring a related 2-(2-pyridyl)-5-(2-thienyl)phosphole ligand is presented. © 2002 Elsevier Science
B.V. All rights reserved.
Keywords: Phosphole; p-Conjugated system; Ruthenium; Bridging ligand; Heterocycle
ligands to build bimetallic complexes. Herein, we de-
scribe the synthesis and optical properties of the first
example of such derivatives and the preparation of a
corresponding bimetallic Ru(II)-complex.
1. Introduction
Great attention has recently been paid to the synthe-
sis and photophysical properties of dinuclear complexes
containing bridging p-conjugated ligands owing to their
potential applications for molecular devices [1]. The
design of the bridging ligands allows tuning of the
electronic properties of these dyads and has led to
important progress in the field of photoinduced elec-
tron- or energy-transfer processes. Typical examples of
such systems are polypyridine ligands and their Ru and
Os complexes which have been widely studied due to
the possible multiple structural variations [1a,1b,1c].
We have recently shown that co-oligomers alternating
phosphole and thienyl rings are tunable chromophores
possessing extended p-systems [2a,2b,2c,2d] and that
2-pyridylphospholes can act as tightly bonded 1,4-
chelates towards Pd(II) centres [2e]. These properties
prompted us to investigate a new family of derivatives
possessing two terminal 2-pyridylphosphole moieties
joined by a 2,5-thienyl spacer as potential bridging
2. Results and discussion
The target phosphole was prepared according to the
‘one-pot’ Fagan–Nugent’s route, an efficient method
for phosphole synthesis [3]. The intramolecular oxida-
tive coupling of 2,2%-di[8-(2-pyridyl)octa-1,7-diynyl]-
thiophene (1a), obtained in 70% via a Sonogashira
coupling involving 2,5-dibromothiophene and two
equivalents of 1-(2-pyridyl)octa-1,7-diyne, with ‘zir-
conocene’ followed by addition of bromodiphenylphos-
phine
affords
2,2%-di[2-(5-(2-pyridyl)phospholyl)]-
thiophene (2a) (Scheme 1). This compound was isolated
as an air stable solid in 63% yield after purification by
flash column chromatography on basic alumina.
Derivative 2a has been characterised by high-resolution
mass spectrometry and elemental analysis. Its 31P-NMR
spectrum consists of two lines of comparable intensity
observed at +10.6 and +10.9 ppm, a typical range for
l3,s3-phospholes [3b,3c], indicating that 2a exists as a
* Corresponding author.
E-mail address: regis.reau@univ-rennes1.fr (R. Re´au).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01123-8

C. Hay et al. / Journal of Organometallic Chemistry 643–644 (2002) 494–497
495
1/1 mixture of diastereoisomers. High-temperature 31P-
NMR experiments reveal a phosphorus inversion bar-
rier of 16.9 kcal mol−1. This low value is classical for
phospholes [3b,3c] and 2a can be regarded as a mixture
of diastereoisomers interconverting slowly at room tem-
perature. The 1H- and 13C-NMR spectra are quite
simple and consistent with the proposed structure [4].
Subsequent additions of [(p-cymene)RuCl2]2 and two
equivalents of KPF6 to a CH2Cl2 solution of di(2-
pyridylphospholyl)thiophene (2a) gave rise to the air
stable complex 3a isolated in 60% yield after crystallisa-
tion (Scheme 1). In the 31P-NMR spectrum of complex
3a, the signals attributed to the phosphole rings consist
in two sharp lines (+58.8, +59.1) and reveal a large
coordination shift effect (Dl:49 ppm). This shift is
much larger than those usually observed upon coordi-
nation of monodentate phosphole ligands such as 1-
phenyl-3,4-dimethylphosphole on cationic Ru(II)
centres (Dl:20 ppm) [5]. However, such high coordi-
nation shift effects have already been observed when
2-pyridylphosphole derivatives act as chelating P,N-lig-
ands towards Pd(II) centres [2e]. Coordination of an
unsymmetrical 2-pyridylphosphole moiety to an
‘(arene)RuCl’ fragment can give rise to two isomers.
The simplicity of the 31P-NMR spectrum of complex 3a
strongly suggests a diastereoselective coordination, each
diastereoisomer of 2a giving one diastereoisomer of 3a.
All attempts to separate these isomers by crystallisation
failed, and the sole valuable information given by the
1H- and 13C-NMR spectra of the mixture is the coordi-
nation downfield shift of the 1H-NMR-signal due to the
NCH6-pyridyl fragments (2a/3a, Dl:0.7 ppm) [6]. In
order to confirm that 2-pyridylphospholes act as P,N-
chelates towards cationic ‘(arene)RuCl’ fragments and
undergo a diastereoselective coordination, the be-
haviour of the model 2-(2-pyridyl)-5-(2-thienyl)phos-
phole (2b) (Scheme 1) was investigated. Derivative 2b
was allowed to react with [(p-cymene)RuCl2]2 and
KPF6 in dichloromethane at room temperature. In the
31P-NMR spectrum of the crude reaction mixture, only
one sharp signal at +59.4 ppm is observed. This
chemical shift compares nicely with those recorded for
complex 3a, and shows that only one of the possible
diastereoisomers was formed. The half-sandwich-type
complex 3b (Scheme 1) was isolated in 95% yield after
1
crystallisation. The simplicity of the H- and 13C-NMR
spectra confirms that 3b was obtained as a single
diastereoisomer [7] and the deshielding upon coordina-
tion of the pyridyl-NCH6 1H-NMR-signal reaches 0.6
ppm. The solid state structure of the cation of 3b with
selected bond lengths and angles is shown in Fig. 1 [8].
The chlorine atom and the P-phenyl substituent are
pointing in the same direction. The bond lengths and
,
bond angles around the Ru centre [RuꢀP, 2.3058(8) A;
,
RuꢀN, 2.131(3) A, PꢀRuꢀN, 80.29(7)°] are consistent
with known literature values [5,9] and reveal no strain
due to the formation of the five-membered metallacycle.
The thiophene and the slightly puckered phosphole
rings are almost coplanar [twist angle, 3.8°(3)] and the
dihedral angle between the coordinated pyridine and
phosphole moieties [P1ꢀC1ꢀC13ꢀN1] reaches 24.3°(4).
The C2ꢀC1ꢀC13ꢀC14 twist angle [45.6(5)°] is larger
than those recorded for other 2-pyridylphosphole
derivatives [1.8(16)–25.6(5)°] [2], but does not prevent
an extended p-conjugation since the orbital overlap
varies approximately with the cosine of the twist angle.
Scheme 1.

496
C. Hay et al. / Journal of Organometallic Chemistry 643–644 (2002) 494–497
Ru(II) to p*-orbital of the coordinated 2-pyridylphos-
phole moiety. In contrast, coordination of bis(2-
pyridylphospholyl)thiophene 2a has almost no influence
on the umax (Table 1). This is probably due to the
symmetrical structure of 2a which prevents efficient
ILCT. It is noteworthy that, in contrast to the corre-
sponding free ligands, complexes 3a and 3b do not
display emission in CH2Cl2 solutions at room
temperature.
3. Conclusion
We have described the synthesis, UV–vis absorption
and fluorescence data of a new p-conjugated oligomer
2a featuring terminal 2-pyridylphosphole moieties and
a thienyl spacer. The 2-pyridylphosphole fragments act
as P,N-chelates and undergo diastereoselective coordi-
nation to chiral Ru(II) centres. The evaluation of the
electrochemical properties of the Ru(II)-complexes 3a,b
and the coordination of 2a to Ru(II)–(bipyridine)2
fragments are under active investigations.
Fig. 1. ORTEP drawing (thermal ellipsoid 40% probability) of the
cation of complex 3b. Hydrogen atoms have been omitted for clarity.
,
Selected bond lengths (A) and angles (°): P1ꢀC1, 1.788(3); C1ꢀC13,
1.464(4); C13ꢀN1, 1.360(4); N1ꢀRu1, 2.131(3); Ru1ꢀP1, 2.3058(8);
Ru1ꢀP1ꢀC(1), 98.45(10); P1ꢀC1ꢀC13, 115.5(2); C1ꢀC13ꢀN1, 113.5(3);
C13ꢀN1ꢀRu1, 122.4(2); N1ꢀRu1ꢀP1, 80.29(7); N1ꢀRu1ꢀCl1,
83.60(8).
Table 1
Photophysical data for compounds 2a,b and 3a,b in CH2Cl2 solutions
at room temperature a
4. Supplementary material
umax (nm), m (mol−1 l cm−1
)
uem (nm)
Crystallographic data (excluding structure factors)
for the structure reported in this paper have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC no. 165626. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
2a
2b
3a
3b
480 (8100)
396 (4400)
482 (4900)
435 (7500)
555–585
500
a Absorption and emission maxima, 93 nm.
2-Pyridyl-5-thienylphosphole (2b) shows an absorp-
tion maximum in the visible region at 396 nm at-
tributed to p–p* transitions of the p-conjugated
system. This value is considerably red-shifted for the
Acknowledgements
bis(2-pyridylphospholyl)thiophene
derivative
2a
(Dumax=84 nm, Table 1), suggesting a delocalisation of
the p-system over the whole molecule. Both derivatives
are photoluminescent in CH2Cl2 solutions at room
temperature, and they display emissions in the visible
region upon excitation at their umax. It is noteworthy
that compound 2a exhibits two emission bands of
comparable intensities (Table 1), the Stoke shifts are
comparable for the two derivatives 2a and 2b (:100
nm). Coordination of 2-pyridylphosphole 2b to the
cationic ruthenium fragment induces a bathochromic
shift of 39 nm (Table 1). This red shift can be attributed
to an intra-ligand-charge-transfer (ILCT) enforced by
the presence of electron-rich thiophene and electron
withdrawing coordinated pyridyl groups at the 2,5-posi-
tion of the phosphole ring. It is very likely that this
broad ligand-centred transition overlaps the possible
metal-to-ligand-charge-transfer transition arising from
This work was financially supported by the Conseil
Re´gional Bretagne, the Ministe`re de l’Education Na-
tionale, de la Recherche et de la Technologie and the
Centre National de la Recherche Scientifique.
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1.79. Calc. for C62H64Cl2F12N2P4Ru2S (1494.1): C, 49.80; H, 4.32;
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3H, J(H,H)=6.9 Hz, CHCH3), 1.13 (d, 3H, J(H,H)=6.9 Hz,
CHCH3), 1.58 (s, 3H, CH3ꢀC6H4), 2.57 (sept, 1H, J(H,H)=6.9
Hz, CHCH3), 5.34 (dd, 1H, J(H,H)=5.6 Hz, CH arom p-
cymene), 5.61 (d, 1H, J(H,H)=5.6 Hz, CH arom. p-cymene),
5.88 (d, 1H, J(H,H)=6.2 Hz, CH arom. p-cymene), 5.96 (d, 1H,
J(H,H)=6.2 Hz, CH arom. p-cymene), 7.10–7.47 (m, 8H, thienyl
H4, H3, pyridyl H5 and phenyl Hortho, Hmeta, Hpara), 7.53 (d,
J(H,H)=5.3 Hz, 1H, thienyl H5), 7.59 (d,3J(H,H)=7.6 Hz, 1H,
pyridyl H3), 7.83 (t, J(H,H)=7.6 Hz, J(H,H)=7.6 Hz, 1H,
pyridyl H4), 9.10 (d, J(H,H)=5.4 Hz, 1H, pyridyl H6); 13C–
{1H}-NMR (75 MHz, CD2Cl2): l=17.7 (s, CH3), 20.5 (s, CH3),
21.7 (s, CꢁCCH2CH2), 22.3 (s, CꢁCCH2CH2), 23.5 (s, CH3), 27.5
(d, J(P,C)=7.3 Hz, CꢁCCH2), 29.4 (d, J(P,C)=8.5 Hz,
CꢁCCH2), 30.9 (s, CHCH3), 82.1 (s, CH arom p-cymene), 88.2
(d, J(P,C)=2.4 Hz, CH arom p-cymene), 92.5 (d, J(P,C)=4.8
Hz, CH arom p-cymene), 93.8 (d, J(P,C)=6.1 Hz, CH arom
p-cymene), 99.1 (s, CꢀCH(CH3)2 arom. p-cymene), 111.0 (s,
CH3ꢀC arom. p-cymene), 117.2 (q, 1J(P,F)=321.6 Hz, CF3SO3),
122.1 (d, J(P,C)=42.2 Hz, phenyl Cipso), 123.7 (d, J(P,C)=8.5
Hz, pyridyl C3), 124.9 (s, pyridyl C5), 128.1 (s, thienyl C4), 128.8
(d, J(P,C)=10.8 Hz, phenyl Cmeta), 129.0 (d, J(P,C)=7.3 Hz,
thienyl C3), 129.4 (s, thienyl C5), 132.0 (d, J(P,C)=3.1 Hz phenyl
Cpara), 133.1 (d, J(P,C)=9.4 Hz, phenyl Cortho), 136.5 (d,
J(P,C)=18.8 Hz, thienyl C2), 137.1 (d, J(P,C)=50.8 Hz, Ca),
137.7 (d, J(P,C)=49.3 Hz, Ca), 139.6 (s, pyridyl C4), 145.9 (d,
J(P,C)=10.9 Hz, Cb), 150.8 (d, J(P,C)=9.4 Hz, Cb), 153.3 (d,
J(P,C)=20.3 Hz, pyridyl C2), 159.1 (s, pyridyl C6). 31P–{1H}-
NMR (81 MHz, CDCl3): l= +59.4 (s). MS–HR (FAB,
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[4] Selected data for 2a: 1H-NMR (200 MHz, CD2Cl2): l=6.95 (m,
4H, thienyl H3 and pyridyl H5), 7.15 (m, 6H, phenyl Hmeta and
Hpara), 7.35 (m, 6H, pyridyl H3 and phenyl Hortho), 7.50 (ddd,
J(H,H)=8.1, J(H,H)=8.1, J(H,H)=1.9 Hz, 2H, pyridyl H4),
8.45 (ddd, J(H,H)=4.8, J(H,H)=1.9, J(H,H)=1.0 Hz, 2H,
pyridyl H6). 13C–{1H}-NMR (75 MHz, CD2Cl2): l=23.0 (s,
CꢁCCH2CH2), 23.1 (s, CꢁCCH2CH2), 29.7 (s, CꢁCCH2), 29.6 (s,
CꢁCCH2), 120.3 (s, pyridyl C5), 122.9 (d, J(P,C)=8.2 Hz, pyridyl
C3), 126.3 (d, J(P,C)=10.1 Hz, thienyl C3), 128.4 (d, J(P,C)=8.6
Hz, phenyl Cmeta), 129.3 (s, phenyl Cpara), 133.7 (d, J(P,C)=19.2
Hz, phenyl Cortho), 135.7 (d, J(P,C)=1.6 Hz, pyridyl C4), 149.3
(d, J(P,C)=1.6 Hz, pyridyl C6). 31P–{1H}-NMR (81 MHz,
CD2Cl2): l= +10.6 (s) and +10.9 (s). MS–HR (FAB, mNBA):
m/z, found 662.2084 [M]+; Anal. Found: C, 76.32; H, 5.38; N,
4.34. Calc. for C42H36N2P2S (662.2074): C, 76.11; H, 5.48; N,
4.23%.
mNBA): m/z, found 644.0898 [M−OTf]+
; C33H34ClNPRuS
Calc. 644.0887. Anal. Found: C, 51.62; H, 4.45; N, 1.79. Calc. for
C34H34ClF3NO3PRuS2 (793.23): C, 51.45; H, 4.32; N, 1.77%.
[8] X-ray structural analysis for 3b: C34H34ClF3NO3PRuS2, M=
793.23, 0.24×0.22×0.18 mm, monoclinic P21/c; a=12.927(2),
3
,
,
b=18.300(2), c=14.217(4) A; i=95.20(2)°; V=3350(1) A ;
Z=4; v=7.73 mm−1. CAD4 NONIUS diffractometer; Mo–Ka
,
radiation; u(Mo–Ka)=0.71073 A;
D
calc=1.573
g
cm−3
;
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177.
F(000)=1616; T=293 K; 2qmax=54°. 7287 unique reflections
from which 5512 with I\2.0|(I) (scan ꢀ/2q=1; hkl: h, 0.16; k,
0.23; l, −18.18, calc w=1/[|2(F2o)+(0.0568P)2+2.29P] where
P=(F2o+2Fc2)/3 with the resulting R=0.0379, Rw=0.0986 and
[6] Selected data for 3a: 1H-NMR (200 MHz, CD2Cl2): l=1.17 (d,
6H, J(H,H)=6.9 Hz, CHCH3), 1.26 (d, 6H, J(H,H)=6.9 Hz,
CHCH3), 1.60 (m, 6H, CH3ꢀC6H4), 1.80 (m, 4H, CꢁCCH2CH2),
2.00 (m, 4H, CꢁCCH2CH2), 2.77 (sept, 2H, J(H,H)=6.9 Hz,
CHCH3), 2.94 (m, 8H, CꢁCCH2CH2), 5.44–6.10 (m, 8H, CH
arom p-cymene), 7.00–7.95 (m, 18H, CH arom), 9.15 (m, 2H,
pyridyl H6); 31P–{1H}-NMR (81 MHz, CD2Cl2): l= −140 (s,
Sw=1.041 (residual Dz51.04 e A−3)). After Lorentz and polar-
,
ization corrections, the structure was solved with SIR-97, and
refined with SHELXL97 by the full-matrix least-squares techniques.
[9] D. Carmona, C. Cativiela, S. Elipe, F.J. Lahoz, M.P. Pilar, L.-R.
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2351.