Model complexes for metallated polythiophenes: Gold(I) and palladium(II) complexes of bis(diphenylphosphino)oligothiophenes

Article abstract of DOI:10.1021/ic0258328

The preparations of two new phosphinothiophene ligands, 3,3′-bis(diphenylphosphino)-2,2′-bithiophene (dppbt; 1) and 3,3?-dihexyl-3′,3″-bis(diphenylphosphino)-2, 5′:2′,2″:5″,2?-quaterthiophene (hdppqt; 2) are reported. Oxidation of 1 gives 3,3′-bis(diphenylphosphine oxide)-2,2′-bithiophene (3), and the crystal structure of this compound was determined. Pd(II) and Au(I) complexes of these ligands have been synthesized and characterized. Crystal structures of [(dppbt)PdCl₂] (1-Pd), [(hdppqt)PdCl₂ (2-Pd), [(dppbt)(AuCl)₂] (1-Au), and [(hdppqt)(AuCl)₂] (2-Au) were obtained. [(dppbt)(AuCl)₂] crystallized in two solid-state forms; crystals grown from CH2Cl₂/Et₂O show a gold-gold interaction of 3.3221(4) A, but from CH₂Cl₂/toluene, the molecule crystallizes as a toluene adduct (1-Au-tol) and does not show any gold-gold interaction. All the complexes were characterized via UV-vis spectroscopy and cyclic voltammetry, and the effect of the metal on the energy of the π-π^*transition and oxidation potential was determined. These data are correlated to the interannular torsion angles in the oligothienyl groups from the crystal structure studies.

Full text of DOI:10.1021/ic0258328

Inorg. Chem. 2003, 42, 2704−2713
Model Complexes for Metallated Polythiophenes: Gold(I) and
Palladium(II) Complexes of Bis(diphenylphosphino)oligothiophenes
,§
,†
Olivier Clot,† Yumi Akahori,‡,§ Carolyn Moorlag,† Daniel B. Leznoff,* Michael O. Wolf,*
Raymond J. Batchelor,§ Brian O. Patrick,† and Mikita Ishii‡
Department of Chemistry, The UniVersity of British Columbia, VancouVer,
British Columbia, Canada V6T 1Z1, Department of Chemistry, Simon Fraser UniVersity,
8888 UniVersity DriVe, Burnaby, British Columbia, Canada V5A 1S6, and Department of
Industrial Chemistry, Meiji UniVersity, Higashi-mita, 1-1-1, Tama-ku, Kawasaki-shi,
Kanagawa-ken, 214-8571 Japan
Received June 28, 2002
The preparations of two new phosphinothiophene ligands, 3,3′-bis(diphenylphosphino)-2,2′-bithiophene (dppbt; 1)
and 3,3′′′-dihexyl-3′,3′′-bis(diphenylphosphino)-2,5′:2′,2′′:5′′,2′′′-quaterthiophene (hdppqt; 2) are reported. Oxidation
of 1 gives 3,3′-bis(diphenylphosphine oxide)-2,2′-bithiophene (3), and the crystal structure of this compound was
determined. Pd(II) and Au(I) complexes of these ligands have been synthesized and characterized. Crystal structures
of [(dppbt)PdCl2] (1-Pd), [(hdppqt)PdCl2] (2-Pd), [(dppbt)(AuCl)2] (1-Au), and [(hdppqt)(AuCl)2] (2-Au) were obtained.
[(dppbt)(AuCl)2] crystallized in two solid-state forms; crystals grown from CH Cl2/Et2O show a gold−gold interaction
2
of 3.3221(4) Å, but from CH Cl2/toluene, the molecule crystallizes as a toluene adduct (1-Au-tol) and does not
2
show any gold−gold interaction. All the complexes were characterized via UV−vis spectroscopy and cyclic voltammetry,
and the effect of the metal on the energy of the π−π* transition and oxidation potential was determined. These
data are correlated to the interannular torsion angles in the oligothienyl groups from the crystal structure studies.
Introduction
electronic properties of the metal and/or backbone, which
may have applications in electrocatalysis or chemical sensing
involving the pendant metal groups.7,8
Conjugated polymers and oligomers are an important class
of materials which are of use in a wide range of applications,
including polymer light-emitting diodes,1 chemical sensors,2
and thin-film transistors.3 Many studies have focused on
altering the optical and electronic properties of these materials
via synthetic modification of the conjugated backbone or
substituents. This may be achieved either via steric or
electronic influences of the substituent. One approach that
has been exploited is the attachment of metal groups to a
conjugated backbone so that the metal centers are electroni-
cally coupled to the backbone.4-7 This allows tuning of the
It has been shown that phosphines are useful in coordinat-
ing transition-metal centers to conjugated oligothiophene or
polythiophene backbones.7,9,10 Incorporating pendant biden-
tate bisphosphines where the two arms of the ligand are on
adjacent thiophene rings results in the formation of a seven-
membered ring in which the adjacent thiophene rings are
immobilized with respect to each other (Scheme 1). The
conjugation along the backbone is primarily determined by
(4) Ley, K. D.; Whittle, C. E.; Bartberger, M. D.; Schanze, K. S. J. Am.
Chem. Soc. 1997, 3423-3424.
(5) Wang, Q.; Wang, L.; Yu, L. J. Am. Chem. Soc. 1998, 120, 12860-
12868.
(6) Wolf, M. O. AdV. Mater. 2001, 13, 545-553.
(7) Weinberger, D. A.; Higgins, T. B.; Mirkin, C. A.; Stern, C. L.; Liable-
Sands, L. M.; Rheingold, A. L. J. Am. Chem. Soc. 2001, 123, 2503-
2516.
* To whom correspondence should be addressed. E-mail: mwolf@
chem.ubc.ca (M.O.W.); dleznoff@sfu.ca (D.B.L.). Fax: 604-822-2847
(M.O.W.); 604-291-3765 (D.B.L.).
† University of British Columbia.
‡ Meiji University.
§ Simon Fraser University.
(8) Kingsborough, R. P.; Swager, T. M. Prog. Inorg. Chem. 1999, 48,
123-231.
(1) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int. Ed.
1998, 37, 403-428.
(9) Clot, O.; Wolf, M. O.; Patrick, B. O. J. Am. Chem. Soc. 2000, 122,
10456-10457.
(2) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. ReV. 2000, 100,
2537-2574.
(10) Clot, O.; Wolf, M. O.; Yap, G. P. A.; Patrick, B. O. J. Chem. Soc.,
Dalton Trans. 2000, 2729-2737.
(3) Horowitz, G. AdV. Mater. 1998, 10, 365-377.
2704 Inorganic Chemistry, Vol. 42, No. 8, 2003
10.1021/ic0258328 CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/27/2003

Model Complexes for Metallated Polythiophenes
Scheme 1
from ethanol and dried at 90 °C under vacuum for 3 days.
Methylene chloride used in cyclic voltammetry was dried either
by refluxing over CaH2 or by passing through an activated alumina
tower. CH3CN was dried over 4 Å molecular sieves.
3,3′-Bis(diphenylphosphino)-2,2′-bithiophene (dppbt; 1). To
a solution of BuLi (1.6 M, 4.30 mL, 6.80 mmol) in 4 mL of dry
THF at -78 °C was slowly added a solution of 3,3′-dibromo-2,2′-
bithiophene (1.00 g, 3.10 mmol) in dry THF (4 mL) under nitrogen.
The mixture was stirred at -78 °C for 1 h. The temperature was
then raised to -50 °C and PPh2Cl (3.00 g, 13.6 mmol) added
dropwise. The cold bath was removed and the reaction mixture
allowed to warm to 25 °C and stirred for 1 h. The reaction was
then quenched with water and diethyl ether (40 mL) added. The
organic phase was washed with water and dried over anhydrous
MgSO4 and the solvent removed to leave a yellow solid. The crude
product was purified by chromatography on silica gel using a
CH2Cl2/hexanes mixture (6/4 v/v) as eluant. The first band was
collected and the solvent removed to yield 1 as an off-white solid.
the overlap between the ring π-systems,11 and control of
polymer properties such as absorption, emission, and con-
ductivity that are dictated by the conjugation are then
expected to be directed, in part, by the metal. A related
approach has been used to prepare conjugated polymers for
use in colorimetric sensors in which binding to a pendant
crown ether results in a change in the backbone conformation
and thus the color of the material.12 It is then of interest to
construct model complexes in order to probe these effects
and to elucidate whether polymers incorporating these groups
may possess interesting electronic properties.
Toward this goal, we describe here two new bis(phosphi-
no)thiophene ligands 1 and 2. We have prepared and deter-
mined the structures of Pd(II) and Au(I) complexes contain-
ing these ligands, and the characterization of these com-
pounds using UV-vis spectroscopy and cyclic voltammetry
is described.
1
Yield: 0.70 g (46%). H NMR (200 MHz, CDCl3): δ 7.36-7.18
(m, 11H), 6.68 (d, JHH ) 5.1 Hz, 1H). 31P{1H} NMR (81.015 MHz,
CDCl3): δ -26.4 (s). Anal. C32H24P2S2 requires: C, 71.91; H, 4.49.
Found: C, 71.69; H, 4.65%.
3,3′-Bis(diphenylphosphine oxide)-2,2′-bithiophene (3). To a
solution of 1 (1.0 g) in CHCl3 (50 mL) and acetone (50 mL) was
added 30% H2O2 (0.4 mL). A white solid began to precipitate
immediately, and the mixture stirred for 1 h. The solid was col-
lected by filtration, redissolved in CHCl3, filtered, and precipi-
1
tated with acetone to give a white solid. Yield: 0.54 g (51%). H
NMR (200 MHz, CDCl3): δ 7.71 (ddd, J ) 1.6, 8.2, 14.0 Hz,
8H), 7.53-7.36 (m, 12H), 7.18 (dd, JHH ) 5.4 Hz, JHP ) 2.2 Hz,
2H), 6.65 (dd, JHH ) 5.4 Hz, JHP ) 4.4 Hz, 2H). 31P{1H} NMR
(81.015 MHz, CDCl3): δ 20.5 (s). Anal. C32H24O2P2S2 requires:
C, 67.83; H, 4.27. Found: C, 67.59; H, 4.32%.
3,3′′′-Dihexyl-3′,3′′-dibromo-2,5′:2′2′′:5′′,2′′′-quaterthio-
phene (4). A solution of 2-bromo-3-hexylthiophene (7.34 g, 30
mmol) in THF was added dropwise to a mixture of magnesium
(1.41 g, 58 mmol) and trace iodine in THF (30 mL) at reflux, and
then heated further to reflux for 2 h. The resulting solution was
added dropwise at 25 °C via cannula to a mixture of 3,5,3′,5′-
tetrabromo-2,2′-bithiophene (5.72 g, 12 mmol) and [Pd(dppf)Cl2]
(200 mg, 0.6%) in diethyl ether (30 mL) and toluene (20 mL), and
heated to reflux for 3 h. The reaction was then quenched with
saturated aqueous ammonium chloride (50 mL), and filtered through
Celite to remove insoluble material. CH2Cl2 (50 mL) was then added
and the organic phase separated. The aqueous phase was extracted
with CH2Cl2. The combined organic phases were washed with
saturated NaHCO3 solution and H2O and dried with anhydrous
MgSO4 and the solvent removed to give a thick orange oil. The
crude product was purified by column chromatography on silica
gel with hexanes as eluant. The first three bands contained small
amounts of unreacted 3,5,3′,5′-tetrabromo-2,2′-bithiophene, 3-hexyl-
thiophene, and monosubstituted terthiophene side product, respec-
tively. The fourth band contained the desired product 4, and removal
of solvent left a bright-yellow, waxy solid. Penta- and hexathiophene
products were also isolated in subsequent bands. Yield: 4.02 g
Experimental Section
General. All reactions were performed using standard Schlenk
techniques with dry solvents under nitrogen. [AuCl(tht)] (tht )
tetrahydrothiophene),13 2-bromo-3-hexylthiophene,14 3,5,3′,5′-tet-
rabromo-2,2′-bithiophene,15 and 3,3′-dibromo-2,2′-bithiophene15
were prepared according to literature procedures. H and 31P{1H}
1
NMR experiments were performed on either a Bruker AC-200E
or a Bruker AV-300 spectrometer, and spectra were referenced to
residual solvent (1H) or external 85% H3PO4 (31P). Electronic
absorption spectra were obtained in CH2Cl2. Microanalyses (C, H,
N) were performed either at Simon Fraser University by Mr. Miki
Yang or at UBC by Mr. Peter Borda. Electrochemical measurements
were conducted on a Pine AFCBP1 bipotentiostat using a Pt disk
working electrode, a Pt coil wire counter electrode, and a silver
wire reference electrode. An internal reference, either decameth-
ylferrocene (-0.12 V vs SCE) or ferrocene (0.41 V vs SCE),16
was added to correct the measured potentials with respect to
saturated calomel electrode (SCE). The supporting electrolyte was
0.1 M [(n-Bu)4N]PF6, which was purified by triple recrystallization
(11) Bre´das, J. L.; Street, G. B.; The´mans, B.; Andre, J. M. J. Chem. Phys.
1985, 83, 1323-1329.
(12) Marsella, M. J.; Swager, T. M. J. Am. Chem. Soc. 1993, 115, 12214-
12215.
1
(52%). H NMR (200 MHz, CDCl3): δ 7.23 (d, JHH ) 5.2 Hz),
2H), 7.09 (s, 2H), 6.96 (d, JHH ) 5.2 Hz, 2H), 2.79 (t, JHH ) 7.7
Hz, 4H), 1.64 (m, 4H), 1.34 (m, 12H), 0.90 (t, 6.3 Hz, 6H). Anal.
C28H32Br2S4 requires: C, 51.22; H, 4.91. Found: C, 51.34; H,
4.72%.
3,3′′′-Dihexyl-3′,3′′-bis(diphenylphosphino)-2,5′:2′,2′′:5′′,2′′′-
quaterthiophene (hdppqt; 2). To a suspension of 4 (1.0 g, 1.52
mmol) in diethyl ether (30 mL) at -78 °C was added a solution of
(13) Uso´n, R.; Laguna, A. Organomet. Synth. 1986, 3, 322-342.
(14) Kellogg, R. M.; Schaap, A. P.; Harper, E. T.; Wynbert, H. J. Org.
Chem. 1968, 33, 2902-2909.
(15) Khor, E.; Ng, S. C.; Li, H. C.; Chai, S. Heterocycles 1991, 32, 1805-
1812.
(16) Robbins, J. L.; Edelstein, N.; Spencer, B.; Smart, J. C. J. Am. Chem.
Soc. 1982, 104, 1882-1893.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2705

Clot et al.
BuLi (1.6 M, 2.10 mL, 3.35 mmol) in dry THF. The mixture was
slowly warmed until the suspended solids dissolved at -30 °C to
give an orange solution, and PPh2Cl (1.34 g, 6.09 mmol) was
subsequently added. After 5 min (-30 °C), a yellow precipitate
formed, and the mixture was slowly allowed to warm to room
temperature and stirred for 1 h. The reaction was quenched with
water and dried over anhydrous MgSO4, and the solvent was
removed to leave a dark-yellow mixture. The crude product was
purified by chromatography on silica gel using hexanes/CH2Cl2
mixture (4:1) as eluent. The first two bands contained starting
materials, and the third band contained the monosubstituted side
product. Removal of solvent from the fourth band yielded 2 as a
dark-yellow oil. Yield: 0.91 g (61%). 1H NMR (200 MHz,
CDCl3): δ 7.31 (m, 10H), 7.10 (d, JHH ) 5.1 Hz, 1H), 6.85 (d,
JHH ) 5.1 Hz, 1H), 6.65 (s, 1H), 2.55 (m, 2H), 1.56-1.07 (m,
8H), 0.88 (m, 3H). 31P{1H} NMR (81.015 MHz, CDCl3): δ -25.1
(s). Anal. C52H52P2S4 requires: C, 72.06; H, 6.00. Found: C, 72.34;
H, 6.23%.
was also structurally characterized. Partial desolvation of 1-Au-tol
hindered the acquisition of reproducible elemental analysis data.
[(Hdppqt)(AuCl)2] (2-Au). A CH2Cl2 solution (10 mL) of 2
(0.05 g, 0.06 mmol) was added dropwise to a solution of [AuCl-
(tht)] (0.038 g, 0.12 mmol) in CH2Cl2 (20 mL). The yellow/orange
solution was stirred for 30 min, and then, the solvent was removed
in vacuo. Recrystallization of the resulting solid from 1:1 CH2Cl2/
hexanes at -20 °C gave air-stable red plates of [(hdppqt)(AuCl)2]
(2-Au) suitable for X-ray structural analysis. Yield: 44 mg (56%).
1H NMR (200 MHz, CDCl3): δ 7.70 (m, 4H), 7.47 (m, 6H), 7.17
(d, JHH ) 5.1 Hz, 1H), 6.86 (d, JHH ) 5.1 Hz, 1H), 6.66 (d, JHP
)
2.8 Hz, 1H), 2.50 (m, 2H), 1.56-1.17 (m, 8H), 0.88 (t, 3H).
31P{1H} NMR (81.015 MHz, CDCl3): δ 15.3 (s). Anal. C52H54-
Au2Cl2P2S4 requires: C, 46.82; H, 4.09. Found: C, 46.69; H, 3.97.
X-ray Crystallographic Analyses. Data for the X-ray crystal-
lographic analyses of 1-Pd, 2-Pd, 1-Au, 2-Au, and 3 were all
collected on a Rigaku/ADSC CCD diffractometer; data for 1-Au-
tol were collected on an Enraf Nonius CAD4F diffractometer. For
1-Pd and 1-Au, data were collected and processed using the
d*TREK program17 and were subsequently corrected for Lorentz
and polarization effects. The structures were solved using direct
methods18 and expanded using Fourier techniques.19 Molecules of
1-Pd crystallize in space group P21/n with one-half of a molecule
of methylene chloride in the asymmetric unit, that is disordered in
two orientations about an inversion center. Molecules of 1-Au
crystallize in space group C2/c with two molecules of methylene
chloride in the asymmetric unit.
[(Dppbt)PdCl2] (1-Pd). A warm solution of PdCl2 (50.0 mg,
0.28 mmol) in water (3 mL) and concentrated HCl (0.05 mL) was
slowly added to 1 (320 mg, 0.60 mmol) in an ethanol/acetonitrile
mixture (10/3 mL) at 50 °C. The mixture turned yellow immediately
and was stirred for 1 h at 50 °C after which time the mixture was
filtered warm to remove any unreacted ligand. The yellow filtrate
was concentrated to ∼3-4 mL, causing a yellow solid to precipitate
out which was collected by filtration. The crude material was further
purified by chromatography on a short column of neutral alumina
eluting first with CH2Cl2, and then with acetone to elute 1-Pd in a
yellow band. One recrystallization from CH2Cl2/hexanes yielded
1-Pd as yellow microcrystals. Yield: 151 mg (76%). 1H NMR (200
MHz, CDCl3): δ 7.96-7.64 (m, 4H), 7.56-7.31 (m, 6H), 7.00
(dd, JHH ) 5.4 Hz, JHP ) 1.7 Hz, 1H), 6.29 (dd, JHH ) 5.4 Hz, JHP
) 2.9 Hz, 1H). 31P{1H} NMR (81.015 MHz, CDCl3): δ 17.9 (s).
Anal. C32H24Cl2P2PdS2 requires: C, 53.98; H, 3.37. Found: C,
53.61; H, 2.99%.
For 1-Au-tol, the data were corrected empirically for the effects
of absorption.20 Data reduction included corrections for Lorentz
and polarization effects. Coordinates and anisotropic displacement
parameters were refined for all non-hydrogen atoms. The maximum
peak (0.7(2) e/Å3) in the final electron density difference map was
located 1.00 Å from Au. The programs used for absorption
corrections, data reduction, structure solution, and graphical output
were from the NRCVAX Crystal Structure System.21 The structure
was refined using CRYSTALS.22 Complex scattering factors for
neutral atoms23 were used in the calculation of structure factors.
For 2-Au, the structure was solved by direct methods.18 Both
hexyl groups display considerable thermal motion. One group,
C(17)-C(22), was modeled in two orientations using isotropic
thermal parameters. The second group, C(23)-C(28), was modeled
in one orientation using anisotropic thermal parameters. In addition,
the material crystallizes with 1.5 molecules of toluene in the
asymmetric unit. One solvent molecule was modeled using rigid
group restraints with isotropic thermal parameters. All calculations
were carried out using teXsan24 and SHELXL-97.25 For 2-Pd, both
[(Hdppqt)PdCl2] (2-Pd). A warm solution of PdCl2 (17.9 mg,
0.10 mmol) in water (2 mL) and concentrated HCl (0.02 mL) was
slowly added to 2 (96.0 mg, 0.11 mmol) in an ethanol/acetonitrile
mixture (8/3 mL) at 50 °C. The mixture turned dark orange
immediately and was stirred for 1 h after which time water was
added to precipitate a yellow solid. The slurry was stirred for 1 h
at 50 °C and filtered warm to collect an orange solid that was
washed with water and hexanes. Recrystallization from CH2Cl2/
hexanes yielded 2-Pd as a light orange powder. Yield: 51 mg
(48%). 1H NMR (200 MHz, CDCl3): δ 8.05-7.62 (m, 4H), 7.58-
7.27 (m, 6H), 7.14 (d, JHH ) 5.1 Hz, 1H), 6.84 (d, JHH ) 5.1 Hz,
1H), 6.23 (d, JHP ) 2.8 Hz, 1H), 2.45-2.21 (m, 2H), 1.51-1.10
(m, 8H), 1.03-0.76 (m, 3H). 31P{1H} NMR (81.015 MHz,
CDCl3): δ 17.5 (s). Anal. C52H52Cl2P2PdS4 requires: C, 59.80; H,
4.98. Found: C, 59.67; H, 5.12%.
(17) Area Detector Software, Version 4.13; Molecular Structure Corpora-
tion, The Woodlands, Texas, 1996-1998.
(18) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
[(Dppbt)(AuCl)2] (1-Au). A CH2Cl2 solution (10 mL) of 1 (0.10
g, 0.19 mmol) was added dropwise to a CH2Cl2 solution (20 mL)
of [AuCl(tht)] (0.12 g, 0.38 mmol). The yellow solution rapidly
decolorized and was stirred for 30 min, and then, the solvent was
removed in vacuo. Recrystallization of the resulting solid from 1:1
CH2Cl2/ether gave air-stable colorless needles of 1-Au suitable for
X-ray structural analysis. Yield: 90 mg (49%). 1H NMR (200 MHz,
CDCl3): δ 7.65-7.45 (m, 4H), 7.45-7.25 (m, 7H), 6.68 (d, JHH
) 5.1 Hz, 1H). 31P{1H} NMR (81.015 MHz, CDCl3): δ 13.8 (s).
Anal. C32H24Au2Cl2P2S2 requires: C, 38.46; H, 2.42. Found: C,
38.81; H, 2.79. Recrystallization from CH2Cl2/toluene gave air-
stable, colorless blocks of (dppbt)(AuCl)2‚C7H8 (1-Au-tol), which
(19) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-94 Program
System, Technical Report of the Crystallography Laboratory; Uni-
versity of Nijmegen, The Netherlands, 1994.
(20) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr. 1968,
A24, 351-359.
(21) Gabe, E. J.; LePage, Y.; Charland, J.-P.; Lee, F. L.; White, P. S. J.
Appl. Crystallogr. 1989, 22, 384-387.
(22) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.; Cooper,
R. I. CRYSTALS Issue 11; Chemical Crystallography Laboratory,
University of Oxford: Oxford, England, 1999.
(23) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1975; Vol. IV, p 99.
(24) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corporation, The Woodlands, Texas, 1985 and 1992.
2706 Inorganic Chemistry, Vol. 42, No. 8, 2003

Model Complexes for Metallated Polythiophenes
Table 1. Crystallographic Data
1-Pd
2-Pd
1-Au
1-Au-tol
2-Au
3
formula
mol wt
T, K
C32.5H25S2P2Cl3Pd C52H52P2S4Cl2Pd C34H28S2P2Cl6Au2 C39H32Au2Cl2P2S2 C65.2H64P2Cl2Au2 C32.75H25.50P2S2Cl1.50O2
754.38
1044.48
173(1)
1169.31
198(1)
1091.58
1516.29
173(1)
630.31
298(1)
173(1)
293(1)
space group
a, Å
b, Å
P21/n
P1h
C2/c
C2/c
P21/c
P1h
11.3597(3)
15.2372(4)
17.5400(7)
13.6973(8)
13.7726(9)
14.2939(8)
73.154(8)
76.805(9)
73.740(9)
2445.6(3)
1.418
13.1073(9)
17.672(1)
17.192(1)
15.4256(23)
13.8425(14)
19.425(3)
11.1645(3)
19.043(5)
29.733(4)
9.992(3)
10.943(3)
14.832(7)
76.48(1)
81.14(2)
85.04(2)
1555.9(9)
1.345
c, Å
R, deg
â, deg
γ, deg
V, Å3
93.21(1)
99.76(1)
112.314(12)
91.248(1)
3031.2(1)
1.653
4
1.144
0.024, 0.031
3924.6(4)
1.979
4
8.11
0.028, 0.038
3837.1
1.890
4
7.97
0.027, 0.027
6320(1)
1.593
4
4.960
0.047, 0.090
Fc (g cm-3
)
Z
2
7.60
0.041, 0.082
2
4.31
0.101, 0.120
µ (Mo KR) (mm-1
)
R1,a wR2b
[I > 3σ(I)]
R1,a wR2b
0.042, 0.068
0.073, 0.089
0.051, 0.080
0.117, 0.109
0.206, 0.246
(all data)
2
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
Scheme 2
hexyl groups are disordered, and each was modeled in two
orientations, with the major disordered fragment refined anisotro-
pically and the minor fragments isotropically. Hydrogen atoms were
placed in calculated positions.
For 3, data were collected and processed using the d*TREK
program.17 Complex 3 crystallizes in space group P1h with one
solvent molecule in the asymmetric unit. The structure was solved
by direct methods18 and refined using teXsan.24 All non-hydrogen
atoms were refined anisotropically, while all hydrogen atoms were
placed in calculated positions. Subsequent refinements revealed that
the solvent molecule was only partially occupied throughout the
lattice, with a population of approximately 0.75. The relatively high
residuals (R1 ) 0.101, wR2 ) 0.246) may be due to crystal
deterioration, as a result of loss of solvent from the lattice. The
crystal data for all six structures are collected in Table 1.
Results and Discussion
Ligand Syntheses. The preparative route used to obtain
diphosphines 1 and 2 is shown in Scheme 2. Compound 1
was prepared by addition of the previously prepared 3,3′-
dibromo-2,2′-bithiophene to a solution of n-butyllithium in
THF at -78 °C. This order of addition was necessary due
to the poor solubility of the dibromide in THF at low
temperatures. The resulting lithium salt was then treated with
excess PPh2Cl at -50 °C. The excess phosphine and higher
temperature are necessary to avoid scrambling of the lithium
on the oligothienyl group,26,27 which would be expected to
reduce the selectivity of the reaction. Compound 1 was
isolated as an off-white powder that is poorly soluble in
nonpolar solvents and stable in air. The bis(phosphine oxide)-
3 was readily prepared by oxidation with hydrogen peroxide,
and an X-ray crystal structure of this molecule was deter-
mined on crystals grown from methylene chloride (Figure
1). Bond lengths and angles are collected in Table 2. The
sterically demanding phosphine oxide substituents force
the thiophene rings to adopt close to a S-anti conforma-
tion in the solid state, with an interannular torsion angle
( S-C-C-S) of 124.1(8)°.
We were also interested in preparing a derivative of 1 with
a longer oligothienyl group in order to explore the effect of
this on the spectroscopic and electrochemical properties of
complexes containing the same metal binding site. Our initial
attempts were to prepare an unsubstituted quaterthiophene
derivative of 1; however, these were unsuccessful due to poor
solubility. To circumvent these difficulties, we chose to target
compound 2 that carries two hexyl substituents to enhance
its solubility in organic solvents. Compound 2 was prepared
from the quaterthiophene 4 and isolated by column chro-
matography as a bright yellow solid.
(26) Ng, S.-C.; Chan, H. S. O.; Huang, H.-H.; Swee-How, R. J. Chem.
Res. (S) 1996, 232-233.
(27) Folli, U.; Goldoni, F.; Iarossi, D.; Mucci, A.; Schenetti, L. J. Chem.
Res. (S) 1996, 69.
(25) SHELXL-97; Sheldrick, G. M., University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2707

Clot et al.
separate excess ligand from 1-Pd. Recrystallization of the
resulting solid from CH2Cl2/hexanes yielded 1-Pd as yellow,
air-stable microcrystals. Complex 2-Pd was purified by
precipitation from the reaction mixture followed by filtration
and washed with water and hexanes. The crude material was
further purified by recrystallization from a CH2Cl2/hexanes
mixture. Complex 2-Pd was obtained as an orange, air-stable
powder, which is soluble in polar solvents such as methylene
chloride and chloroform.
The 31P{1H} NMR spectra of 1-Pd and 2-Pd contain
singlets at δ 17.9 and 17.5, respectively. Crystals of 1-Pd
were grown from layered CH2Cl2/hexanes, and its solid-state
structure was determined by X-ray crystallography. The
structure of 1-Pd (Figure 2) shows that the bis(phosphine)
ligand chelates to one palladium center via the two phos-
phines, forming a seven-membered ring with a P-Pd-P bite
angle of 93.20(2)°. The Pd(II) center lies in a distorted square
planar geometry with the cis chlorine atoms slightly raised
above the (P-Pd-P) plane. Selected bond lengths and angles
are shown in Table 3. Coordination of 1 to Pd forces the
sulfur atoms of the bithienyl group close to a syn conforma-
tion with an intrannular torsion angle of 51.1(2)°.
The solid-state structure of 2-Pd is shown in Figure 3,
and selected bond lengths and angles are shown in Table 4.
There are three distinct interannular torsion angles in 2-Pd.
The central, internal pair of rings are locked at 56.6(3)°,
slightly greater than the comparable angle in 1-Pd. The
outer rings are also twisted at similar angles, 58.8(3)° and
69.0(3)°. All four of the rings are oriented approximately
S-syn to each other, with the sulfur atoms alternating above
and below a plane along the quaterthiophene moiety. Most
quaterthiophenes are nearly planar in the solid-state, although
deviations are sometimes observed due to steric interactions
between substituents.28 The C(8)-C(9) bond in 2-Pd is
shorter (1.452(4) Å) than either of the two other interannular
C-C bonds in this structure, but comparable to the inter-
annular bond length in 1-Pd. It is possible that this shorter
bond is indicative of enhanced conjugation between the inner
two rings in this oligomer; however, structural effects due
to the formation of the metallacycle may also result in some
distortion of this bond.
Figure 1. (a) ORTEP view of 3. The hydrogen atoms are omitted for
clarity, and thermal ellipsoids are drawn at 50% probability. (b) ORTEP
view down C(4)-C(5) axis illustrating the interannular torsion angle (phenyl
groups omitted for clarity).
Table 2. Selected Bond Lengths and Angles for 3
Distances, Å
P(1)-O(1)
P(2)-O(2)
P(1)-C(3)
P(2)-C(6)
C(5)-C(6)
S(2)-C(5)
S(2)-C(8)
C(7)-C(8)
1.495(6)
1.475(7)
1.762(9)
1.80(1)
1.41(2)
1.70(1)
1.73(1)
1.25(2)
C(6)-C(7)
C(4)-C(5)
S(1)-C(1)
S(1)-C(4)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
1.48(1)
1.46(1)
1.706(9)
1.704(9)
1.36(1)
1.46(1)
1.41(1)
Angles, deg
O(2)-P(2)-C(6)
O(1)-P(1)-C(3)
S(2)-C(5)-C(6)
S(2)-C(8)-C(7)
S(1)-C(4)-C(3)
117.8(6)
114.9(4)
111.1(6)
112.0(8)
113.3(6)
S(1)-C(1)-C(2)
P(1)-C(3)-C(4)
P(1)-C(3)-C(2)
P(2)-C(6)-C(5)
P(2)-C(6)-C(7)
111.2(6)
127.0(6)
125.4(7)
126.4(6)
124.7(8)
Scheme 3
Gold Complexes. [(dppbt)(AuCl)2] (1-Au) was synthe-
sized via the reaction of 1 with [AuCl(tht)] (Scheme 4).
The 31P{1H} NMR spectrum of 1-Au contains one singlet
at δ 13.8, and the elemental analysis is consistent with two
Au centers per ligand. Attempts to synthesize the mono-
gold(I) complex [(dppbt)(AuCl)], as was obtained for pal-
ladium(II), lead to mixtures, with bimetallic 1-Au being the
major product. Two solid-state structures were established
for 1-Au; in both cases, each gold(I) center binds to one
phosphine and one chloride in a nearly linear geometry. The
first structure was determined from crystals grown from
CH2Cl2/Et2O and shows a gold-gold interaction of 3.3221-
(4) Å (Figure 4).29,30 The second one, established from
Palladium Complexes. In order to explore the coordina-
tion of 1 and 2 to transition metals, we reacted these
compounds with Pd(II) and Au(I) precursors. Reaction of
PdCl2 with a slight excess of 1 or 2 in an ethanol/water mix-
ture at 50 °C yielded 1-Pd and 2-Pd, respectively (Scheme
3). For complex 1-Pd, the ethanol was removed resulting in
precipitation of a solid from the solution, which was collected
by filtration and washed with water and hexanes. Chroma-
tography on a short neutral alumina column was used to
(28) Lukevics, E.; Barbarella, G.; Arsenyan, P.; Belyakov, S.; Pudova, O.
Chem. Heterocycl. Compd. (N.Y.) 2000, 36, 630-662.
(29) Pathaneni, S. S.; Desiraju, G. R. J. Chem. Soc., Dalton Trans 1993,
319-322.
2708 Inorganic Chemistry, Vol. 42, No. 8, 2003

Model Complexes for Metallated Polythiophenes
Figure 2. (a) ORTEP view of 1-Pd. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability. (b) ORTEP view
down C(4)-C(5) axis illustrating the interannular torsion angle (phenyl groups omitted for clarity).
Scheme 4
Figure 3. ORTEP view of 2-Pd. The hydrogen atoms are omitted for
clarity, and thermal ellipsoids are drawn at 50% probability.
Table 3. Selected Bond Lengths and Angles for 1-Pd
Distances, Å
Table 4. Selected Bond Lengths and Angles for 2-Pd
Pd(1)-Cl(1)
Pd(1)-P(1)
P(1)-C(3)
S(1)-C(1)
C(1)-C(2)
C(3)-C(4)
S(2)-C(5)
C(5)-C(6)
C(7)-C(8)
2.3536(6)
2.2889(6)
1.832(2)
1.707(3)
1.355(3)
1.379(3)
1.730(2)
1.371(3)
1.353(4)
Pd(1)-Cl(2)
Pd(1)-P(2)
P(2)-C(6)
S(1)-C(4)
C(2)-C(3)
C(4)-C(5)
S(2)-C(8)
C(6)-C(7)
2.3445(7)
2.2595(6)
1.823(2)
1.723(2
1.432(3)
1.456(3)
1.704(3)
1.434(3)
Distances, Å
2.2490(9)
Pd(1)-P(1)
Pd(1)-P(2)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
S(1)-C(1)
S(1)-C(4)
S(2)-C(5)
S(2)-C(8)
S(3)-C(9)
S(3)-C(12)
S(4)-C(16)
S(4)-C(13)
P(1)-C(7)
P(2)-C(10)
C(4)-C(5)
C(8)-C(9)
C(12)-C(13)
1.733(4)
1.699(4)
1.724(4)
1.820(4)
1.825(3)
1.470(5)
1.452(4)
1.466(5)
2.2510(9)
2.3426(9)
2.3342(9)
1.704(4)
1.732(4)
1.726(3)
1.727(3)
1.721(3)
Angles, deg
Cl(1)-Pd(1)-P(2)
Cl(1)-Pd(1)-Cl(2)
Cl(2)-Pd(1)-P(2)
C(1)-S(1)-C(4)
S(1)-C(1)-C(2)
C(2)-C(3)-C(4)
176.20(2)
87.41(2)
89.82(2)
91.8(1)
112.1(2)
111.1(2)
Cl(2)-Pd(1)-P(1)
Cl(1)-Pd(1)-P(1)
P(1)-Pd(1)-P(2)
C(5)-S(2)-C(8)
C(1)-C(2)-C(3)
S(1)-C(4)-C(3)
170.53(2)
89.95(2)
93.20(2)
91.8(1)
113.3(2)
111.7(2)
Angles, deg
P(1)-Pd(1)-P(2)
P(1)-Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(2)
Cl(1)-Pd(1)-Cl(2)
P(2)-Pd(1)-Cl(1)
P(2)-Pd(1)-Cl(2)
93.96(3)
86.04(3)
170.38(4)
91.30(4)
169.06(4)
90.40(3)
Pd(1)-P(2)-C(10)
C(9)-S(3)-C(12)
C(5)-S(2)-C(8)
Pd(1)-P(1)-C(7)
C(1)-S(1)-C(4)
C(13)-S(4)-C(16)
113.77(10)
92.07(16)
92.21(7)
118.23(10)
91.3(2)
91.98(18)
crystals grown from CH2Cl2/toluene, appears as a toluene
adduct (1-Au-tol) and does not show any gold-gold interac-
tion (Au-Au distance is 4.685 Å). In solution, only an
averaged 31P{1H} NMR signal is observed for 1-Au; there
is no significant shift or decoalescence of the singlet in
CD2Cl2 or in CD2Cl2/C7D8 from 183 to 298 K.31 This result
suggests that the gold-gold bond in 1-Au can be easily
(30) Leznoff, D. B.; Xue, B.-Y.; Batchelor, R. J.; Einstein, F. W. B.; Patrick,
B. O. Inorg. Chem. 2001, 40, 6026-6034.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2709

Clot et al.
Figure 4. (a) ORTEP view of 1-Au. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability. (b) ORTEP view
of 1-Au-tol. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability.
Table 5. Selected Bond Lengths and Angles for 1-Au and 1-Au-tol
disrupted by intermolecular forces and is thus quite weak
compared to gold-gold interactions in systems such as the
Distances, Å
auracarborane 1,1′-(AuPPh3)2-[2-(1′,2′-C2B10H10)-1,2-C2B10H10],
1-Au
1-Au-tol
for which Au-Au bond strengths of 11 ( 1 kcal/mol have
been measured using data obtained from variable temperature
31P{1H} NMR.32
Au(1)-Au(1)
Au(1)-P(1)
Au(1)-Cl(1)
P(1)-C(3)
P(1)-C(11)
P(1)-C(21)
C(1)-C(1)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
S(1)-C(5)
S(1)-C(2)
3.3221(4)
2.230(1)
2.283(1)
1.808(5)
1.813(5)
1.815(5)
1.466(9)
1.381(6)
1.419(6)
1.357(8)
1.695(6)
1.722(5)
2.2244(19)
2.2782(22)
1.800(5)
1.810(6)
1.814(7)
1.465(13)
1.374(8)
1.412(10)
1.343(8)
1.703(8)
1.717(5)
Selected bond lengths and angles for 1-Au and 1-Au-tol
are shown in Table 5. For both structures, the average Au-P
and Au-Cl bond lengths are comparable with those observed
in other phosphinogold(I) halide complexes.33,34 Given their
strong preference for phosphine donors,34,35 the gold(I) cen-
ters do not interact significantly with the thiophene moieties
directly, as occurs in related ruthenium(II) complexes.7,10,36
In the structure of complex 1-Au, the two planar thiophene
rings are oriented S-anti to each other with an interannular
torsion angle of 110.8(5)°. For 1-Au-tol, the torsion angle
is 115.3(7)°. Thus, despite the lack of a formal Au-Au bond
(<3.6 Å), the preferred ligand conformation is similar to
1-Au. This illustrates that the presence of the gold-gold unit,
however weakly interacting, locks the conformation of the
thiophene rings into place, as with the palladium(II) systems
described. However, in this case, the presence of two metals
Angles, deg
1-Au
1-Au-tol
Cl(1)-Au(1)-P(1)
Au(1)-Au(1)-P(1)
Au(1)-Au(1)-Cl(1)
Au(1)-P(1)-C(3)
Au(1)-P(1)-C(11)
Au(1)-P(1)-C(21)
P(1)-C(3)-C(4)
P(1)-C(3)-C(2)
C(3)-P(1)-C(11)
C(3)-P(1)-C(21)
C(11)-P(1)-C(21)
C(2)-S(1)-C(5)
178.95(5)
90.82(3)
90.15(4)
111.7(1)
114.8(2)
113.6(2)
125.9(4)
121.1(3)
105.6(2)
106.5(2)
103.9(2)
92.5(2)
178.14(6)
113.23(21)
114.00(24)
113.65(21)
123.8(4)
124.3(5)
105.1(3)
104.0(3)
105.9(3)
92.0(3)
(31) Bardaj´ı, M.; Laguna, A. J. Chem. Educ. 1999, 76, 201-203.
(32) Harwell, D. E.; Mortimer, M. D.; Knobler, C. B.; Anet, F. A. L.;
Hawthorne, M. F. J. Am. Chem. Soc. 1996, 118, 2679-2685.
(33) Leznoff, D. B.; Rancurel, C.; Sutter, J.-P.; Rettig, S. J.; Pink, M.;
Paulsen, C.; Kahn, O. J. Chem. Soc., Dalton Trans. 1999, 3593-
3599.
denies the ligand the ability to form a cis-chelate, and instead
of being locked into a more planar arrangement as in 1-Pd,
a highly twisted configuration results.
In a similar fashion, reaction of the quaterthiophene ligand
2 with two equiv of [AuCl(tht)] yielded [(hdppqt)(AuCl)2]
(2-Au), which showed one singlet in its 31P{1H} NMR
spectrum at δ 15.3. The solid-state structure (Figure 5) is
(34) Chen, B.-L.; Mok, K.-F.; Ng, S.-C. J. Chem. Soc., Dalton Trans. 1998,
4035-4042.
(35) Fuchita, Y.; Ieda, H.; Wada, S.; Kameda, S.; Mikuriya, M. J. Chem.
Soc., Dalton Trans. 1999, 4431-4435.
(36) Weinberger, D. A.; Higgins, T. B.; Mirkin, C. A.; Liable-Sands, L.
M.; Rheingold, A. L. Angew. Chem., Int. Ed. 1999, 38, 2565-2568.
2710 Inorganic Chemistry, Vol. 42, No. 8, 2003

Model Complexes for Metallated Polythiophenes
Figure 5. ORTEP view of 2-Au. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability.
Table 6. Selected Bond Lengths and Angles for 2-Au
mately 50 nm relative to bithiophene (302 nm) and quater-
thiophene (390 nm), respectively (Table 7).37 These shifts
may be due to either electronic or steric effects caused by
the presence of the phosphines on the oligothiophene units.
The negligible shift in absorbance observed for 3′-diphenyl-
phosphino-2,2′:5′2′′-terthiophene (dppterth) (λmax ) 354
nm)10 relative to terthiophene (355 nm)37 suggests that the
electronic influence of the phosphine group on the oligo-
thienyl moiety is rather small. It is then likely that the larger
blue-shifts observed for 1 and 2 are mainly due to twisting
between the thiophene rings caused by unfavorable steric
interactions between the two phosphine groups. This is sup-
ported by the large torsional angle found between the rings
in the crystal structure of 3; it is reasonable that a similar
angle would be present in 1 and between the central two
rings of 2.
Distances, Å
3.0879(7)
Au(1)-Au(2)
Au(1)-P(1)
Au(2)-P(2)
Au(1)-C(l1)
Au(2)-C(l2)
P(2)-C(10)
P(1)-C(7)
C(9)-C(10)
C(10)-C(11)
C(11)-C(12)
S(3)-C(9)
S(3)-C(12)
S(2)-C(5)
S(2)-C(8)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
1.347(13)
1.418(13)
1.369(14)
1.711(11)
1.724(11)
1.730(10)
1.720(10)
1.348(13)
1.414(14)
1.392(13)
2.228(3)
2.236(3)
2.286(3)
2.298(3)
1.833(11)
1.826(11)
1.479(13)
1.468(14)
1.348(13)
1.466(14)
C(8)-C(9)
C(12)-C(13)
C(5)-C(6)
C(4)-C(5)
Angles, deg
174.28(10) Cl(2)-Au(2)-Au(1)
P(1)-Au(1)-Cl(1)
P(1)-Au(1)-Au(2)
Cl(1)-Au(1)-Au(2)
P(2)-Au(2)-Cl(2)
P(2)-Au(2)-Au(1)
85.49(9)
92.5(5)
91.2(6)
113.3(3)
113.5(3)
95.57(8)
88.16(8)
C(9)-S(3)-C(12)
C(16)-S(4)-C(13)
176.87(12) C(10)-P(2)-Au(2)
97.63(8)
C(7)-P(1)-Au(1)
similar to 1-Au, with a quaterthiophene ligand in place of
the bithiophene. Bond lengths and angles are collected in
Table 6. The Au-Au bond in 2-Au of 3.0879(7) Å is
substantially shorter than that in 1-Au and likely persists in
solution. The deviation from linearity of the Cl-Au-P angle
is larger in 2-Au (174.28°, 176.87°) compared with 1-Au
or 1-Au-tol, both of which are nearly 179°; this is consistent
with the presence of a stronger Au-Au interaction.
Quaterthiophene 2-Au also has three distinct interannular
torsion angles. The central, internal pair of rings are locked
with a high twist of 100.8(9)°, similar to the torsional angle
in 1-Au and 3 (110.8(5)° and 124.1(8)°, respectively). The
sterically less hindered outer rings are only twisted by
28.5(12)° and 12.5(11)°. Thus, the quaterthiophene unit in
2-Au can be considered as a pair of bithiophene units. In
each unit, the outer thiophene rings are oriented close to a
S-syn fashion, while the two central rings are oriented S-anti
to each other. The C(8)-C(9) bond in 2-Au is longer (1.479-
(13) Å) than either of the two other interannular C-C bonds
in this structure, and longer than these bonds in previously
reported quaterthiophenes.28 This is in contrast to 2-Pd where
the C-C bond between the central two rings is shorter than
either of the other two interannular bonds. These observations
are all consistent with weak conjugation between the two
central rings in 2-Au.
In complexes 1-Pd and 2-Pd, several bands are observed
in the UV-vis spectra (Table 7). Related Pd(II) chloro
phosphine complexes38 are known to exhibit C f Pd LMCT
bands in the visible region near 340 nm, and such a transi-
tion should also be present here, although perhaps shifted
slightly in energy; the spectra of both 1-Pd and 2-Pd have
bands near 340 nm. The presence of the electron-rich
oligothiophene ligands indicates that thiophene f Pd LMCT
transitions are also expected. The lowest energy bands are
tentatively assigned in this way, and the red-shift observed
for the lowest energy band in 2-Pd relative to 1-Pd supports
this assignment. In addition, π-π* bands are expected but
may be shifted due to a combination of inductive and steric
effects resulting from the presence of the metal and phos-
phine groups. Complete assignment of the bands in the
spectra of the Pd complexes is difficult; however, the
absorption spectra of the Au complexes are simpler due to
the absence of any low energy LMCT bands. In both Au
complexes, the spectra are very close to those observed for
the respective ligands 1 and 2. Assuming that the Au does
not exert a significant electronic effect, it can be concluded
that the torsion angles between the central thiophene rings
(37) Van Pham, C.; Burkhardt, A.; Shabana, R.; Cunningham, D. D.; Mark,
H. B.; Zimmer, H. Phosphorus, Sulfur Silicon Relat. Elem. 1989, 46,
153-168.
(38) Leung, K. H.; Szulbinski, W.; Phillips, D. L. Mol. Phys. 2000, 98,
1323-1330.
Spectroscopic and Electrochemical Characterization.
The absorption bands of 1 and 2 are blue-shifted by approxi-
Inorganic Chemistry, Vol. 42, No. 8, 2003 2711

Clot et al.
Table 7. UV-Vis and Cyclic Voltammetry Data
complex
UV-visa λmax/nm (ꢀ/M-1 cm-1
)
Ep,oxb V vs SCE
interannular torsion angle (θ)c
1
2
252 (sh) (3.98 × 104)
1.10d,e
1.02e,f
1.67d,e
254 (6.20 × 104), 340 (2.83 × 104)
1-Pd
258 (2.51 × 105), 280 (2.51 × 105),
354 (sh) (4.19 × 104), 414 (sh)
(9.22 × 103)
51.1(2)
2-Pd
267 (2.06 × 104), 302 (1.68 × 104),
340 (sh) (1.42 × 104), 451
(2.52 × 103)
1.40d,g
58.8(3), 56.6(3), 69.0(3)
1-Au
2-Au
239 (sh) (3.52 × 104)
>2d,g
1.49d,g
>2e,f
1.31
110.8(5),h 115.3(7)i
28.5(12), 100.8(9), 12.5(11)
124.1(8)
252 (2.88 × 104), 344 (1.66 × 104)
254 (1.65 × 104), 286 (sh) (6.29 × 103)
302 (1.25 × 104)
3
2,2′-bithiophenej
180k
2,2′:5′,2′′:5′′,2′′′-quaterthiophenej
390 (4.55 × 104)
0.95
181.1(2), 180, 181.1(2)l
a In CH2Cl2. b Scan rate ) 200 mV/s; only oxidation waves <2 V included. c Interannular torsion angle ) S-C-C-S. For all quaterthiophene structures,
the four linked rings are labeled ABCD, with the torsion angles listed: A-B, B-C, C-D. d In CH3CN containing 0.1 M [(n-Bu)4N]PF6. e Referenced
to decamethylferrocene. f In CH2Cl2 containing 0.1 M [(n-Bu)4N]PF6. g Referenced to ferrocene. h 1-Au. i 1-Au-tol. j UV-vis, ref 37; cyclic voltammetry,
ref 40. k Ref 42. l Ref 43.
are similar in the Au complexes to those in the respective
ligands. Indeed, the torsion angles in 1-Au and the phosphine
oxide 3 are reasonably comparable.
cesses (Table 7). Generally, extending the length of a
π-system results in a decrease in the oxidation potential.40
This effect is observed in both sets of complexes where
extension from two to four rings results in a decrease in
oxidation potential. The crystal structure of 2-Au shows that
the outer two thiophene rings are close to coplanar; thus,
the presence of the metal groups results in these complexes
behaving like two bithiophene units that are weakly conju-
gated to each other.
When the working electrode was scanned repeatedly past
the first oxidation wave in solutions of the complexes 1-Pd,
1-Au, 2-Pd, or 2-Au, there was no evidence of film forma-
tion on the electrode surface. There are two possible rea-
sons why these complexes did not electropolymerize. First,
the interannular twisting which results in blue-shifted absorp-
tion peaks and higher oligothiophene oxidation potentials
may be severe enough to prevent any coupled materials
that form from being sufficiently conductive to allow film
growth. Second, the solid-state structures of 1-Pd and
1-Au indicate that the phenyl rings of the phosphines ex-
tend past the R-positions of the bithienyl moieties, which
may reduce their accessibility for coupling. The quater-
thiophene complexes should not be influenced by this effect,
so in 2-Au and 2-Pd, it is likely that the interannular twisting
observed in the crystal structures is sufficient to prevent
conductivity along the backbone and growth of a conductive
film.
Both 1 and 2 have a first oxidation potential close to that
observed for the oxidation of PPh3, which has been assigned
to formation of the triphenylphosphonium cation followed
by reaction with trace water to give triphenylphosphine
oxide.39 In phosphine oxide 3, the oxidation wave is shifted
to a much more positive potential than in bithiophene, due
to the electron-withdrawing effect of the phosphine oxide
group on the conjugated system, and to the large deviation
from planarity in 3.
The cyclic voltammogram of 1-Pd contains an irreversible
oxidation wave (Table 7) assigned to an oligothiophene-based
process; no analogous wave is observed for 1-Au below 2
V. For both complexes, oxidation occurs significantly
positive of bithiophene (+1.31 V).40 There are two factors
which can contribute to this shift: (a) the inductive effect
of the metal and (b) the change in the interannular conjuga-
tion which results upon coordination. In 1-Pd, both the
electron-withdrawing effect of the PdCl2 group41 and the
large torsion angle relative to bithiophene result in the
observed increase in the oxidation potential relative to
bithiophene. In 1-Au, the interannular torsion angle is
substantially larger than in 1-Pd, and comparable to that in
3. In solution, rotation between rings may be allowed;
however, the fully planar anti conformation is also unlikely
in this case due to unfavorable steric interactions. In this
case, it is likely that the shift to higher oxidation potential
relative to 1-Pd results from poorer conjugation between
thiophene rings as seen in the larger torsion angle. This is
supported by the longer intrannular C-C bonds (vide supra)
in 1-Au versus 1-Pd.
Conclusions
Binding bulky metal groups to oligothiophenes via chelat-
ing phosphines results in substantial effects on the electronic
properties of the conjugated system. Perturbations result from
a combination of factors including changes in the interannular
torsion angles due to the backbone substituents and the metal
groups, as well as inductive effects. The interannular torsion
angles in the complexes examined here are large relative to
those typically observed in solid-state structures of oligo-
thiophenes.28 In the metal complexes, both blue-shifts in the
π-π* absorption bands and increases in the oxidation
The CVs of compounds 2-Pd and 2-Au also contain
irreversible oxidation waves, assigned to ligand-based pro-
(39) Schiavon, G.; Zecchin, S.; Cogoni, G.; Bontempelli, G. J. Electroanal.
Chem. Interfacial Electrochem. 1973, 48, 425-431.
(40) Diaz, A. F.; Crowley, J.; Bargon, J.; Gardini, G. P.; Torrance, J. B. J.
Electroanal. Chem. 1981, 121, 355-361.
(41) Corain, B.; Longato, B.; Favero, G.; Ajo`, D.; Pilloni, G.; Russo, U.;
Kreissl, F. R. Inorg. Chim. Acta 1989, 157, 259-266.
(42) Pelletier, M.; Brisse, F. Acta Crystallogr., Sect. C 1994, 50, 1942-
1945.
(43) Antolini, L.; Horowitz, G.; Kouki, F.; Garnier, F. AdV. Mater. 1998,
10, 382-385.
2712 Inorganic Chemistry, Vol. 42, No. 8, 2003

Model Complexes for Metallated Polythiophenes
potentials of the oligothiophene π-system due to the large
interannular torsion angles are observed, relative to unsub-
stituted oligomers. As expected, increasing the length of the
conjugated system from two to four rings resulted in a
decrease in oxidation potential, and a red-shift in the
absorption spectrum for both the Pd and the Au complexes.
These results suggest that the electronic behavior of
polythiophenes incorporating similar pendant metal groups
into the backbone would be drastically influenced by the
presence of these moieties. We are currently investigating
alternatives to electropolymerization to prepare these ex-
tended materials.
Acknowledgment. M.O.W. and D.B.L. thank the Natural
Sciences and Engineering Research Council of Canada and
D.B.L. thanks Simon Fraser University and Meiji University
for support of this research.
Supporting Information Available: X-ray crystallographic data
files (CIF) for 3, 1-Pd, 2-Pd, 1-Au, 1-Au-tol, and 2-Au. Fully
labeled ORTEP views of all crystal structures (PDF). This ma-
terial is available free of charge via the Internet at http://pubs.
acs.org.
IC0258328
Inorganic Chemistry, Vol. 42, No. 8, 2003 2713