Ferrocene end-capped palladium(II) and platinum(II) complexes with thiophene spacers

Article abstract of DOI:10.1021/om990556z

A series of heterobimetallics containing ferrocene and Pd(II) or Pt(II) have been synthesized by oxidative addition of ferrocene-substituted halothiophenes with zerovalent palladium or platinum precursors. The stable solids were thoroughly characterized by elemental analysis, NMR, UV-vis spectroscopy, and cyclic voltammetry. The rich redox chemistry of the complexes depends on the conjugation length that separates the two metal sites. The crystal structure of a platinum σ-thienyl complex, (C₅H₅)Fe(C₅H₄CH=CH-th-Pt(PPh ₃)₂(Br)) (th = 2,5-disubstituted thiophene) has been determined.

Full text of DOI:10.1021/om990556z

Organometallics 1999, 18, 5285-5291
5285
F er r ocen e En d -Ca p p ed P a lla d iu m (II) a n d P la tin u m (II)
Com p lexes w ith Th iop h en e Sp a cer s
K. R. J ustin Thomas, J iann T. Lin,* and Kuan-J iuh Lin
Institute of Chemistry, Academia Sinica, 115, Taipei, Taiwan, Republic of China
Received J uly 19, 1999
A series of heterobimetallics containing ferrocene and Pd(II) or Pt(II) have been synthesized
by oxidative addition of ferrocene-substituted halothiophenes with zerovalent palladium or
platinum precursors. The stable solids were thoroughly characterized by elemental analysis,
NMR, UV-vis spectroscopy, and cyclic voltammetry. The rich redox chemistry of the
complexes depends on the conjugation length that separates the two metal sites. The crystal
structure of a platinum σ-thienyl complex, (C5H5)Fe(C5H4CHdCH-th-Pt(PPh3)2(Br)) (th
) 2,5-disubstituted thiophene) has been determined.
In tr od u ction
products of heteroaromatics have been isolated and
characterized.10 Trapping of the catalytic intermediates
would provide useful information regarding the reactiv-
ity differences of thienyl halides in such cross-coupling
reactions.
Organo-palladium complexes are versatile reagents
in organic chemistry, as exemplified by known pal-
ladium-catalyzed molecular rearrangements, oxidations,
substitutions, eliminations, and C-C and C-X (X ) N,
S, O) cross-coupling processes.1-5 The C-C and C-het-
eroatom coupling reactions involve oxidative addition
to afford Pd{P(aryl)3}2(R)X complexes in the initial
stage. It is known in some cases that initially the cis
isomer is formed which subsequently transforms into
the thermodynamically stable trans isomer. The stabil-
ity of these complexes was found to be crucial for the
subsequent transmetalation and reductive-elimination
steps in the catalytic cycle.
An array of σ-aryl complexes has been isolated from
aryl halides and zerovalent Pd or Pt precursors.6,7 Also,
it is known that binuclear complexes obtained from the
double oxidative addition of dihalo aromatics and M(P-
Ph3)4 (M ) Pd, Pt) are useful building blocks in the
design and self-assembly of novel cationic organome-
tallic macrocycles.8 Despite extensive studies of C-C
and related coupling reactions involving heteroaromat-
ics9,10 such as thiophene, only a few oxidative-addition
In this paper, we wish to present the synthesis and
characterization of a series of heterobimetallics obtained
by the oxidative addition of Pd(0) and Pt(0) precursors
such as M(PPh3)4 (M ) Pd, Pt) with ferrocenyl-
substituted bromothiophenes. These bromothiophenes
can be considered as relatively electron rich, as they are
linked by conjugation with ferrocene, an electron-
donating organometallic group. Thienylvinyl and thienyl
moieties were used as spacers in these heterobimetal-
lics, since oligo(thienylvinylene) and oligo(thiophene),
which find use in electronic materials,12 have stability
surpassing that of polyene and conduct electrons with
better efficiency than their phenyl analogues. Further-
more, the trinuclear congeners reported herein are
potential building blocks for organometallic supramol-
ecules.
Exp er im en ta l Section
The general procedures pertaining to the synthesis of the
compounds reported in this paper and their physical measure-
ments are identical with those previously published.13 Column
chromatography for 3 was performed with use of silica gel
(230-400 mesh, Macherey-Nagel GmbH & Co.) as the station-
ary phase in a column 30 cm in length and 2.0 cm in diameter.
All other chromatography separations were performed using
a column 30 cm in length and 4.0 cm in diameter. (Ferroce-
nylmethyl)triphenylphosphonium bromide,14 (5-bromo-2-thie-
* To whom correspondence should be addressed. Fax: Int.cod + (2)-
27831237. E-mail: jtlin@chem.sinica.edu.tw.
(1) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
(2) (a) Hartwig, J . F. Acc. Chem. Res. 1998, 31, 852. (b) Shaughnessy,
K. H.; Hammann, B. C.; Hartwig, J . F. J . Org. Chem. 1998, 63, 6546.
(b) Hartwig, J . F. Synlett 1997, 329.
(3) Wolfe, J . P.; Wagaw, S.; J ean-Francois, M.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805.
(4) Louie, J .; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118, 7217. (b)
Louie, J .; Hartwig, J . F. Tetrahedron Lett. 1995, 36, 3609.
(5) (a) Wolfe, J . P.; Wagaw, S.; Buchwald, S. L. J . Am. Chem. Soc.
1996, 118, 7215. (b) Guram, A. S.; Rennels, R. A.; Buchwald, S. L.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1348.
(10) Xie, Y.; Wu, B.; Xue, F.; Ng, S.-C.; Mak, T. C. W.; Hor, T. S. A.
Organometallics 1998, 17, 3988.
(6) (a) Chin, C. C. H.; Yeo, J . S. L.; Loh, Z. H.; Vittal, J . J .;
Henderson, W.; Hor, T. S. A. J . Chem. Soc., Dalton Trans. 1998, 3777.
(b) Casado, A. L.; Espinet, P. Organometallics 1998, 17, 954. (c) Paul,
F.; Patt, J .; Hartwig, J . F. Organometallics 1995, 14, 3030. (d) Portnoy,
M.; Milstein, D. Organometallics 1993, 12, 1665.
(7) (a) Cavell, K. J .; J in, H.; Skelton, B. W.; White, A. H. J . Chem.
Soc., Dalton Trans. 1992, 2923. (b) Tam, W.; Calabrese, J . C. Chem.
Phys. Lett. 1986, 25, 508.
(11) (a) Mu¨llen, K., Wegner, G., Eds. Electronic Materials: The
Oligomer Approach; Wiley-VCH: New York, 1998. (b) Brisset, H.;
Moustarder, S. L.; Blanchard, P.; Illien, B.; Riou, A.; Orduna, J .; Garin,
J .; Roncali, J . J . Mater. Chem. 1997, 7, 2027. (c) Elandaloussi, E. H.;
Fre`re, P.; Roncali, J .; Richomme, P.; J ubault, M.; Gorgues, A. Adv.
Mater. 1995, 7, 390. (d) Petty, M. C., Bryce, M. R., Bloor, D., Eds. An
Introduction to Molecular Electronics; Oxford University Press: New
York, 1995.
(8) Hicke, A.; Cava, M. P. J . Org. Chem. 1998, 63, 7413. (b) Roncali,
Chem. Rev. 1992, 92, 711.
(9) Abbotto, A.; Bradamante, S.; Facchetti, A.; Pagani, G. A. J . Org.
Chem. 1997, 62, 5755.
(12) Manna, J .; Kuehl, C. J .; Whiteford, J . A.; Stang, P. J . Organo-
metallics 1997, 16, 1897.
(13) J ustin Thomas, K. R.; Lin, J . T.; Wen, Y. S. J . Organomet.
Chem. 1999, 575, 301.
10.1021/om990556z CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/09/1999

5286 Organometallics, Vol. 18, No. 25, 1999
J ustin Thomas et al.
nylmethyl)triphenylphosphonium bromide,14 and ferrocene-
carboxaldehyde15 were prepared according to the literature
procedures. (4-Iodobenzyl)phosphonic acid diethyl ester was
prepared from 1-iodo-4-(bromomethyl)benzene and phosphorus
triethyl ester by a procedure similar to that described for (4-
bromobenzyl)phosphonic acid diethyl ester.16 Cyclic voltam-
metry experiments were performed with a BAS-100 electro-
chemical analyzer. All measurements were carried out at room
temperature with a conventional three-electrode configuration
consisting of platinum working and auxiliary electrodes and
a Ag/AgNO3 reference electrode (0.01 M AgNO3, 0.1 M TBAP/
CH3CN). The solvent in all experiments was CH2Cl2, and the
supporting electrolyte was 0.1 M tetrabutylammonium per-
sized by the same procedure as employed for 1b, except that
2-[(E)-2-(5-bromo-2-thienyl)-1-ethenyl]-2-thiophenecarbalde-
hyde was utilized instead of 5′-bromobithiophene-5-carbalde-
hyde. Compound 1c was isolated in 62% yield. MS (EI): m/e
1
482 (M+). H NMR (acetone-d6, TMS): δ 7.09 (d, J H-H ) 3.73
Hz, 1 H, SCCH), 7.04 (m, 3 H, SCCH and dCH), 6.99 (d, J H-H
) 3.75 Hz, 1 H, SCCH), 6.92 (d, J H-H ) 3.75 Hz, 1 H, SCCH),
6.92 (d, J H-H ) 15.8 Hz, 1 H, dCH), 6.74 (d, J H-H ) 15.8 Hz,
1 H, dCH), 4.54 (m, 2 H, C5H4), 4.32 (m, 2 H, C5H4), 4.14 (s,
5 H, Cp). Anal. Calcd for C22H17BrS2Fe: C, 54.91; H, 3.56.
Found: C, 54.71; H, 3.56.
2-[(E)-2-F er r ocen yl-1-eth en yl]-5-iod oth iop h en e (1d ).
Compound 1d was synthesized by the same procedure as
employed for 1b, except that 5′-iodothiophene-2-carbaldehyde
was utilized instead of 5′-bromobithiophene-5-carbaldehyde.
Compound 1d was isolated in 62% yield. MS (EI): m/e 420
a
chlorate. The E1/2 values were determined as 1/2(Ep + Epc),
a
where Ep and Epc are the anodic and cathodic peak potentials,
respectively. All potentials reported are not corrected for the
junction potential. Ferrocene was used as an external reference
both for potential calibration and for reversibility criteria.
Under similar conditions the ferrocene has E1/2 ) 217 mV
relative to Ag/Ag+ and the anodic peak-cathodic peak separa-
tion is 90 mV.
1
(M+). H NMR (acetone-d6, TMS): δ 7.08 (d, J H-H ) 3.6 Hz, 1
H, SCCH), 6.71 (d, J H-H ) 15.9 Hz, 1 H, dCH), 6.57 (d, J H-H
) 3.6 Hz, 1 H, SCCH), 6.57 (d, J H-H ) 15.9 Hz, 1 H, dCH),
4.42 (s, br, 2 H, C5H4), 4.29 (s, br, 2 H, C5H4), 4.13 (s, 5 H,
Cp). Anal. Calcd for C16H12ISFe: C, 45.75; H, 3.12. Found: C,
45.82; H, 2.97.
2-Br om o-5-[(E)-2-fer r ocen yl-1-eth en yl]th iop h en e (1a ).
Sodium methoxide was generated in situ by treating sodium
(0.23 g, 10 mmol) with MeOH (50 mL). To this vigorously
stirred solution was added (5-bromothienyl)methyltriphe-
nylphosphonium bromide (5.18 g, 10 mmol). After the mixture
was stirred at room temperature for 30 min, ferrocenecarbox-
aldehyde (2.14 g, 10 mmol) was added. The reddish mixture
was slowly heated to 60 °C and allowed to reflux for 6 h. The
cooled solution was then poured into ice water and extracted
with Et2O (2 × 50 mL). The combined ether extracts were dried
using MgSO4 and evaporated to leave the crude product. It
was chromatographed on silica gel using hexane/CH2Cl2 (4:1)
mixture as eluant. A 200 mL portion of the eluant was required
to collect the desired product. Removal of the solvent and
recrystallization of the crude product from hot hexane gave
an analytically pure sample in 64% yield. MS (EI): m/e 372
1-[(E)-2-fer r ocen y-1-eth en yl]-4-iod oben zen e (1e). To a
stirred mixture of (4-iodobenzyl)phosphonic acid diethyl ester
(3.54 g, 10.0 mmol) in THF (100 mL) was added a slight excess
of potassium tert-butoxide (1.20 g). After 30 min, ferrocen-
ecarboxaldehyde (2.14 g, 10.0 mmol) was added through a
sidearm. The mixture was slowly heated to 65 °C and
maintained at that temperature for 6 h. The cooled solution
was poured into ice water, extracted with diethyl ether,
washed with brine solutions, and finally dried over MgSO4.
Evaporation of the ethereal extract left behind a red residue,
which was chromatographed on silica gel using hexane/CH2-
Cl2 (4:1) mixture as eluant. A 200 mL portion of the eluant
was required to collect the desired product. Removal of the
solvent gave the title compound in 59% (2.46 g) yield. MS
1
(FAB): m/e 414 (M+). H NMR (CDCl3, TMS): δ 7.61 (d, J H-H
1
(M+). H NMR (CDCl3, TMS): δ 6.88 (d, J H-H ) 3.72 Hz, 1 H,
) 8.2 Hz, 2 H, C6H4), 7.13 (d, J H-H ) 8.2 Hz, 2 H, C6H4), 6.85
(d, J H-H ) 16.1 Hz, 1 H, dCH), 6.564 (d, J H-H ) 16.1 Hz, 1 H,
dCH), 4.47 (m, 2 H, C5H4), 4.31 (m, 2 H, C5H4), 4.14 (s, 5 H,
Cp). Anal. Calcd for C18H15IFe: C, 52.21; H, 3.65. Found: C,
52.34; H, 3.48.
SCCH), 6.65 (m, 2 H, SCCH and dCH), 6.55 (d, J H-H ) 15.9
Hz, 1 H, dCH), 4.39 (m, 2 H, C5H4), 4.27 (m, 2 H, C5H4), 4.12
(s, 5 H, Cp). Anal. Calcd for C16H14BrSFe: C, 51.51; H, 3.51.
Found: C, 51.70; H, 3.38.
5′-Br om o-5-(2-fer r ocen ylvin yl)-2,2′-bith iop h en e (1b).
To a suspension of (ferrocenylmethyl)triphenylphosphonium
bromide (2.70 g, 5.00 mmol) and THF (50 mL) was added
potassium tert-butoxide (0.63 g, 5.66 mmol) through a sidearm
with vigorous stirring. After 30 min, 1.36 g (5.00 mmol) of 5′-
bromobithiophene-5-carbaldehyde was added at once. The
resulting red mixture was refluxed for 6 h; after cooling it was
poured into crushed ice and extracted with CH2Cl2. The CH2-
Cl2 extracts were washed with brine solutions, dried over
MgSO4, and evaporated to dryness. The crude product, con-
taining mixture of cis and trans isomers (1.5 g, 66%), was
separated from triphenylphosphine oxide by column chroma-
tography on silica using hexane/CH2Cl2 (2:3) mixture as eluant.
A 200 mL portion of the eluant was required to collect the
desired product. Subsequent removal of the solvent and
recrystallization of the residue from hot hexane gave pure
trans isomer (1.3 g, 57%). MS (EI): m/e 456 (M+). 1H NMR
Gen er a l P r oced u r e for t h e Syn t h esis of P a lla d iu m -
(II) Com p lexes 2 a n d P la tin u m (II) Com p lexes 3 Der ived
fr om 1a -d . A mixture of M(PPh3)4 (M ) Pd, Pt; 1.00 mmol)
and 1a -d (1.01 mmol) was stirred in deoxygenated benzene
(50 mL) for 6 h at room temperature. The color of the solution
darkened during the progress of the reaction. The solvent was
removed under vacuum and the residue redissolved in 5 mL
of CH2Cl2. To the reddish CH2Cl2 solution was added dry Et2O
(20 m), and the mixture was cooled to 0 °C to give the desired
compounds in excellent yield. The precipitate was filtered,
washed thoroughly with Et2O (3 × 5 mL) and hexane (2 × 10
mL), and dried in vacuo. The platinum(II) complexes 3 are
further purified by column chromatography on silica gel using
hexane/CH2Cl2 (1:1) mixture as eluant. A 50 mL portion of the
eluant was required to collect the desired product.
1
2a : yield 71%. H NMR (CDCl3, TMS): δ 7.59-7.24 (m, 30
H, C6H5), 6.40 (d, J H-H ) 15.7 Hz, 1 H, dCH), 6.15 (d, J H-H
)
(acetone-d6, TMS): δ 7.10 (m, 3 H, SCCH), 6.96 (d, J H-H
)
3.4 Hz, 1 H, SCCH), 5.91 (d, J H-H ) 15.7 Hz, 1 H, dCH), 5.79
(d, J H-H ) 3.4 Hz, 1 H, SCCH), 4.26 (m, 2 H, C5H4), 4.16 (m,
2 H, C5H4), 4.05 (s, 5 H, Cp). 31P NMR (CDCl3, TMS): δ 23.1.
Anal. Calcd for C52H43BrP2SFePd: C, 62.20; H, 4.32. Found:
C, 62.34; H, 4.48.
3.87 Hz, 1 H, SCCH), 6.92 (d, J H-H ) 16.0 Hz, 1 H, dCH),
6.76 (d, J H-H ) 16.0 Hz, 1 H, dCH), 4.54 (m, 2 H, C5H4), 4.31
(m, 2 H, C5H4), 4.15 (s, 5 H, Cp). Anal. Calcd for C20H15BrS2-
Fe: C, 52.77; H, 3.32. Found: C, 52.95; H, 3.18.
1
2-[(E)-2-(5-Br om o-2-t h ien yl)-1-et h en yl]-5-[(E)-2-fer r o-
cen yl-1-eth en yl]th iop h en e (1c). Compound 1c was synthe-
2b: yield 92%. H NMR (CDCl3, TMS): δ 7.56-7.26 (m, 30
H, C6H5), 6.75-6.53 (m 5 H, SCCH and dCH), 6.27 (d, J H-H
) 15.6 Hz, 1 H, dCH), 6.20 (d, J H-H ) 3.5 Hz, 1 H, SCCH),
5.76 (d, J H-H ) 3.5 Hz, 1 H, SCCH), 4.39 (m, 2 H, C5H4), 4.26
(m, 2 H, C5H4), 4.12 (s, 5 H, Cp). 31P NMR (CDCl3, TMS): δ
23.3. Anal. Calcd for C58H47BrP2S2FePd: C, 62.63; H, 4.26.
Found: C, 62.88; H, 4.36.
(14) Zhang, J .-X.; Dubbois, P.; J erome, R. Synth. Commun. 1996,
26, 3091.
(15) Rosenblum, M.; Banerjee, A. K.; Danieli, N.; Fish, R. W.;
Schlatter, V. J . Am. Chem. Soc. 1963, 85, 316.
(16) Kennedy, G.; Perboni, A. D. Tetrahedron Lett. 1996, 42, 7611.

Pd(II) and Pt(II) Complexes with Thiophene Spacers
Organometallics, Vol. 18, No. 25, 1999 5287
1
2c: yield 90%. H NMR (CDCl3, TMS): δ 7.66-7.33 (m, 30
was collected. Removal of the solvent gave a red oil which
contained three inseparable isomers (eg., cis,cis, cis,trans, and
trans,trans). It was dissolved in toluene and heated at reflux
for 2 h. A small amount of iodine was used as catalyst. This
effectively converted the products into the all-trans isomer.
Crystallization from hot hexane gave reddish brown powdery
H, C6H5), 6.83 (d, J H-H ) 16.0 Hz, 1 H, dCH), 5.75 (d, J H-H
)
3.7 Hz, 1 H, SCCH), 6.57 (d, J H-H ) 16.0 Hz, 1 H, dCH), 6.48
(d, J H-H ) 3.7 Hz, 1 H, SCCH), 6.42 (d, J H-H ) 3.7 Hz, 1 H,
SCCH), 5.87 (d, J H-H ) 3.7 Hz, 1 H, SCCH), 4.49 (m, 2 H,
C5H4), 4.27 (m, 2 H, C5H4), 4.13 (s, 5 H, Cp). 31P NMR (CDCl3,
TMS): δ 23.3. Anal. Calcd for C56H45BrP2S2FePd: C 61.92;
H, 4.18. Found: C, 62.04, H, 3.91.
1
6 (0.76 g, 66%). MS (FAB): m/e 558 (M+). H NMR (CD2Cl2,
TMS): δ 6.85 (d, J ) 3.75 Hz, 2 H, SCCH), 6.59 (d, J ) 16.1
Hz, 2 H, dCH), 6.53 (d, J ) 3.75 Hz, 2H, SCCH), 6.35 (d, J )
16.1 Hz, 2 H, dCH), 4.41 (t, J ) 1.7 Hz, 4 H, C5H4), 4.27 (t, J
) 1.7 Hz, 4 H, C5H4). Anal. Calcd for C22H16Br2S2Fe: C, 47.17;
H, 2.88. Found: C, 47.06; H, 3.02.
2d : yield 93%. 1H NMR (CDCl3, TMS): δ 7.57 (m, 12 H,
o-C6H5), 7.31 (m, 18 H, m- and p-C6H5), 6.38 (d, J H-H ) 15.7
Hz, 1 H, dCH), 6.14 (d, J H-H ) 3.5 Hz, 1 H, SCCH), 5.90 (d,
J H-H ) 15.7 Hz, 1 H, dCH), 5.77 (d, J H-H ) 3.5 Hz, 1 H,
SCCH), 4.26 (m, 2 H, C5H4), 4.16 (m, 2 H, C5H4), 4.05 (s, 5 H,
Syn th esis of Tr in u clea r F eP d 2 Com p lex 7 fr om 6.
Compound 7 was synthesized in 71% yield by the same
procedure as employed for 5, except that 6 was used instead
of 4. 1H NMR (CD2Cl2, TMS): δ 7.68-7.23 (m, 60 H, C6H5),
6.35 (d, 8 H, J ) 15.9 Hz, 2 H, dCH), 6.16 (d, J ) 3.36 Hz,
2H, SCCH), 5.95 (d, 2 H, J ) 15.9 Hz, 2 H, dCH), 5.92 (d, J
) 3.36 Hz, 2H, SCCH), 4.13 (br, s, 4 H, C5H4), 4.04 (br, s, 4 H,
Cp). 31P NMR (CDCl3, TMS): δ 23.3. Anal. Calcd for C52H43
-
IP2SFePd: C, 59.42; H, 4.12. Found: C, 59.08; H, 4.01.
1
2e: yield 90%. H NMR (CDCl3, TMS): δ 7.54-7.19 (m, 30
H, C6H5), 6.50-6.29 (m 6 H, C6H4 and dCH), 4.35 (m, 2 H,
C5H4), 4.20 (m, 2 H, C5H4), 4.08 (s, 5 H, Cp). 31P NMR (CDCl3,
TMS): δ 23.0. Anal. Calcd for C54H45IP2FePd: C, 62.06; H,
4.34. Found: C, 61.88; H, 4.10.
C5H4). 31P NMR (CD2Cl2, TMS): δ 25.3. Anal. Calcd for C94H76
-
1
3a : yield 42%. H NMR (CDCl3, TMS): δ 7.65-7.30 (m, 30
Br2P4S2FePd2: C, 61.96; H, 4.20. Found: C, 62.12; H, 4.32.
H, C6H5), 6.41 (d, J ) 15.9 Hz, 1 H, dCH), 6.06 (d, J ) 3.4 Hz,
1 H, SCCH), 5.93 (d, J H-H ) 15.9 Hz, 1 H, dCH), 5.75 (d, J H-H
) 3.7 Hz, J H-Pt ) 46 Hz, 1 H, SCCH), 4.27 (m, 2 H, C5H4),
4.16 (m, 2 H, C5H4), 4.06 (s, 5 H, Cp). 31P NMR (CDCl3, TMS):
δ 23.8 (J H-Pt ) 2874 Hz). Anal. Calcd for C52H43BrP2SFePt:
C, 57.16; H, 3.97. Found: C, 56.78; H, 3.79.
Str u ctu r e Deter m in a tion of 3a . Crystals of 3a were
grown by slow diffusion of hexane into a concentrated solution
of 3a in CH2Cl2. Diffraction data were collected with an Enraf-
Nonius CAD4 diffractometer using graphite-monochromated
Mo KR (λ ) 0.7107 Å) radiation with the θ-2θ scan mode at
room temperature. Absorption corrections according to ψ scans
of three reflections were made. All the data processing was
performed using the Shelxl17 package. The Fe and Pt atoms
were located by Patterson techniques; all other atoms were
located by subsequent Fourier maps and cycles of least-squares
refinement. All non-hydrogen atoms were refined anisotropi-
cally, and all non-hydrogen atoms were placed in idealized
positions with dC-H ) 0.95 Å. At the end of refinement there
existed four peaks near platinum. Modeling them for a diffused
solvent, either CH2Cl2 or hexane, did not lead to any significant
improvement. The results provided here are for a CH2Cl2
solvate. Relevant experimental details are listed in Table 1.
All other crystal data for 3a are given in the Supporting
Information.
1
3b: yield 48%. H NMR (CDCl3, TMS): δ 7.64-7.29 (m, 30
H, C6H5), 6.78-6.56 (m, 5 H, SCCH and dCH), 6.26 (d, J H-H
) 15.9 Hz, 1 H, dCH), 6.15 (d, J H-H ) 3.5 Hz, 1 H, SCCH),
5.75 (d, J H-H ) 3.4 Hz, J H-Pt ) 45 Hz, 1 H, SCCH), 4.43 (m, 2
H, C5H4), 4.28 (m, 2 H, C5H4), 4.13 (s, 5 H, Cp). 31P NMR
(CDCl3, TMS): δ 23.9 (J H-Pt ) 2858 Hz). Anal. Calcd for C58H47
-
BrP2S2FePt: C, 58.01; H, 3.94. Found: C, 57.79; H, 3.76.
1
3c: yield 52%. H NMR (CDCl3, TMS): δ 7.69-7.34 (m, 30
H, C6H5), 6.83 (d, J H-H ) 15.9 Hz, 1 H, dCH), 6.73 (d, J H-H
)
3.8 Hz, 1 H, SCCH), 6.56 (d, J H-H ) 15.9 Hz, 1 H, dCH), 6.46
(d, J H-H ) 3.6 Hz, 1 H, SCCH), 6.32 (d, J H-H ) 3.6 Hz, 1 H,
SCCH), 5.78 (d, J H-H ) 3.6 Hz, J H-Pt ) 46 Hz, 1 H, SCCH),
4.40 (m, 2 H, C5H4), 4.27 (m, 2 H, C5H4), 4.12 (s, 5 H, Cp). 31P
NMR (CDCl3, TMS): δ 23.8 (J H-Pt ) 2842 Hz). Anal. Calcd
for C56H45BrP2S2FePt: C, 57.25; H, 3.86. Found: C, 57.33; H,
3.79.
Resu lts a n d Discu ssion
1,1′-Bis(p-iod op h en ylvin yl)fer r ocen e (4). Compound 4
was prepared in 59% yield by following a procedure similar to
that described for 1d using 1,1′-ferrocenedicarboxaldehyde and
diethyl (4-iodobenzyl)phosphonate. MS (FAB): m/e 642 (M+).
1H NMR (CDCl3, TMS): δ 7.48 (d, J ) 8.3 Hz, 4 H, C6H4),
6.90 (d, J ) 8.3 Hz, 4 H, C6H4), 6.63 (d, J ) 16.1 Hz, 2H, d
CH), 6.41 (d, J ) 16.1 Hz, 2 H, dCH), 4.41 (m, 4 H, C5H4),
4.26 (m, 4 H, C5H4). Anal. Calcd for C26H20I2Fe: C, 48.64; H,
3.14. Found: C, 48.36; H, 3.03.
Syn th esis of Tr in u clea r F eP d 2 Com p lex 5 fr om 4.
Compound 5 was synthesized in 75% yield by the same
procedure as employed for 2, except that 4 was used instead
of 1. 1H NMR (CD2Cl2, TMS): δ 7.68-7.31 (m, 60 H, C6H5),
7.31-7.19 (m, 8 H, C6H4 and dCH), 4.46 (m, 2 H, C5H4), 4.28
(m, 2 H, C5H4), 4.08 (s, 5 H, Cp). 31P NMR (CDCl3, TMS): δ
22.9. Anal. Calcd for C98H80I2P4FePd2: C, 61.82; H, 4.23.
Found: C, 61.79; H, 3.91.
1,1′-Bis[2-(5-br om o-2-th ien yl)eth en yl]fer r ocen e (6). So-
dium metal (0.12 g, 5.2 mmol) was dissolved in methanol (50
mL) under nitrogen. (5-Bromo-2-thienylmethyl)triphenylphos-
phonium bromide (2.7 g, 5.0 mmol) was added with vigorous
stirring followed by 1,1′-ferrocenedicarboxaldehyde (0.48 g, 2.0
mmol). The red mixture was refluxed overnight, cooled, and
poured into ice water. The resulting reddish residue was
extracted with CH2Cl2 and the extract dried over anhydrous
MgSO4. Evaporation of the organic extract left a red syrup. It
was purified by column chromatography on silica gel using
CH2Cl2/hexane (1:4) as eluant. A 100 mL portion of the eluant
Syn th esis of F er r ocen yl Der iva tives. The ferro-
cenyl derivatives required for the present study were
easily available from conventional Wittig or Wittig-
Horner reactions (Scheme 1). The Wittig reaction gener-
ally leads to a mixture of E and Z isomers. Careful
recrystallization from hot hexane by exploiting the
higher solubility of the Z isomers led to the separation
of analytically pure E isomers in good yields. Only the
E isomer was subjected to the oxidative-addition reac-
tions. The E isomers are characterized by their AB
quartet with a coupling constant of ca. 16.0 Hz. In the
proton NMR spectra recorded in CDCl3/acetone-d6 all
the three ligands 1a -c exhibited three upfield signals
corresponding to the ferrocene group. Two unresolved
multiplets were observed for the substituted Cp ring,
while the unsubstituted Cp ring resonated at a upfield
position as a sharp singlet. Thiophene protons appear
as two doublets in 1a , and four doublets are seen for
1b and 1c.
Syn th esis of M(P P h 3)2(th )Br Der iva tives. The
utility of zerovalent M(PPh3)4 in the preparation of
trans-M(PPh3)2(R)X complexes (X ) halide and R )
(17) Sheldrick, G. M. SHELXL-Structure Determination Package;
University of Gottingen, Gottingen, Germany.

5288 Organometallics, Vol. 18, No. 25, 1999
J ustin Thomas et al.
Ta ble 1. Cr ysta l Da ta for Com p ou n d 2d
Sch em e 2
chem formula
fw
C53H45BrCl2P2SFePt
1177.64
space group
a, Å
P1h
12.190(2)
b, Å
13.078(3)
c, Å
17.502(4)
R, deg
â, deg
γ, deg
V, Å3
79.64(1)
71.63(1)
65.22(2)
2400.6(9)
Z
2
T, °C
+20
F(000)
λ(Mo KR), Å
1164
0.7107
1.629
43.02
F
calcd, g cm-3
µ, cm-1
transmissn coeff
2θmax, deg
0.41-0.17
50
hkl range
-12 to +14, 0-15, -20 to +20
8883
8446
no. of rflns collected
no. of indep rflns
refinement method
order for group 10 M(PPh3)4 complexes with the C(aryl)-
halide bond is Ni(0) > Pd(0) > Pt(0) and C-I > C-Br
> C-Cl.19 It is also established that electron-withdraw-
ing groups (e.g., CN, CF3, NO3) para to the C-X bond
of the phenyl derivatives activate the aryl-X bond for
Pd(PPh3)4. Conversely, electron-donating groups sup-
press the reactivity of aryl halides. Enhanced reactivity
of triethylphosphine complexes was reported by Par-
shall19 and is attributed to the increase in nucleophi-
licity of the reactive species “M(PEt3)2” resulting from
the increase in basicity of phosphine (P(alkyl)3 vs PPh3).
Similar generalizations are not yet known for the
halothiophenes.
full-matrix least squares
on F2
GOF on F2 b
0.993
final R indices (I > 2σ(I))a
R indices (all data)
R1 ) 0.0815, wR2 ) 0.2187
R1 ) 0.1073, wR2 ) 0.2391
largest diff peak and hole (e Å)-3 4.075 and -4.938
R1 ) ∑(|Fo| - |Fc|)/|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑w(Fc2)2]1/2
.
a
2
GOF ) [∑w(|Fo| - |Fc|)2/(n - p)]1/2, where n ) no. of observed
b
reflections and p ) number of variables. w ) [σ2(Fo2 - Fc2) + (g1P)
+ g2P]-1; P ) [max(Fo2; 0) + 2Fc2]/3.
Sch em e 1
Reaction of 1 equiv of Pd(PPh3)4 with the respective
bromothiophenes (Scheme 2) in benzene at room tem-
perature generates the reddish orange trans-Pd(PPh3)2-
(th)Br (th ) 2,5-disubstituted thiophene) complexes in
excellent yields. However, Pt(PPh3)4 required harsh
conditions (refluxing for 24 h). The decreased reactivity
of the Pt(0) complex is in accordance with previous
findings for aryl halides.12 To the best of our knowledge,
oxidative-addition products of Pt(PPh3)4 and bro-
mothiophenes have not yet been reported. Owing to the
electron-donating nature of ferrocene, it was expected
that compounds 1a -c would exhibit reduced reactivity
in comparison to the unsubstituted bromothiophenes.
It was found, however, that the reactivity is very similar
to that observed for bromothiophenes.11 The heterobi-
metallic complexes are orange or red air- and moisture-
stable solids. However, in solution the Pd(PPh3)2(th)Br
complexes decompose if exposed to air for 1 week.
1
The H NMR spectra of the palladium and platinum
complexes 2 and 3 display a downfield resonance at ca.
7.7-7.3 ppm attributed to the PPh3 hydrogens. The
ferrocene hydrogens appear as a singlet and two unre-
solved multiplets. The â-proton in the thiophene moiety
adjacent to the metal site exhibits significant upfield
resonances when compared to the free ligands, 1. A
similar behavior was also reported recently by Hor and
co-workers for σ-thienyl complexes of palladium(II).20
This shielding is a consequence of the η1-M-C bond and
is more pronounced for thienyl derivatives (2a -d ) than
alkyl, aryl, alkenyl, acyl) is well-documented.12,18 In fact,
it has been demonstrated that the relative reactivity
(19) (a) Mantovani, A. J . Organomet. Chem. 1983, 255, 385. (b)
Parshall, G. W. J . Am. Chem. Soc. 1974, 96, 2360. (c) Gerlack, D. H.;
Kane, A. R.; Parshall, G. W.; J esson, J . P.; Mutterties, E. L. J . Am.
Chem. Soc. 1971, 93, 3543.
(20) Xie, Y.; Ng, S. C.; Wu, B.-M.; Xue, F.; Mak, T. C. W.; Hor, T. S.
A. J . Organomet. Chem. 1997, 531, 175.
(18) (a) Sen, A.; Chen, J .-T.; Vetter, W. M.; Whittle, R. R. J . Am.
Chem. Soc. 1987, 109, 148. (b) Stille, J . K. In The Chemistry of the
Metal-Carbon Bond; Hartley, F. R., Patai, S. Eds.; Wiley: Chichester,
England, 1985; Vol. 2, Chapter 9.

Pd(II) and Pt(II) Complexes with Thiophene Spacers
Organometallics, Vol. 18, No. 25, 1999 5289
Sch em e 3
Ta ble 2. Op tica l Absor p tion Sp ectr a l Da ta for th e
Com p lexesa
ꢀmax (×10-3
ꢀmax (×10-3
compd λmax (nm) M-1 cm-1
)
compd λmax (nm) M-1 cm-1
)
1a
1b
1c
463
333
460 (sh)
378
480 (sh)
411
314
463
337
460
1.32
20.58
25.92
2d
449
353
452
327
270 (sh)
356
403
433
324
470
302
470
340
2.57
28.08
1.46
2e
26.77
32.41
6.82
1.87
23.6
1.30
3a
3b
3c
23.22
25.09
39.23
7.27
2.08
40.00
2.48
1d
1e
4
5
6
370 (sh)
315
275
23.26
13.60
2.24
52.40
2.52
2a
441
468
353
308 (sh)
398
23.60
354 (sh)
325
454
38.52
4.73 (sh)
2b
2c
28.04
7
306
429
320 (sh)
375
346
318
40.00
15.56
41.98 (sh)
a
Measured in CH2Cl2. λmax values for the π-π* transition are
F igu r e 1. Electronic spectra (5.0 × 10-5 M in CH2Cl2) of
2a -c.
given in italics.
for the aryl derivative 2e. For the platinum complexes
3, the â-proton resonance is accompanied by a pair of
doublets centered about the major peak due to coupling
to platinum (ca. 45 Hz). The 31P{1H} NMR spectra of
the palladium complexes display a downfield shift at
ca. 23 ppm referenced to 85% phosphoric acid (δ 0 ppm).
For the corresponding platinum species, the 31P{1H}
signal is observed as a sharp singlet accompanied by
platinum satellites. The J P-Pt coupling ranges from 2842
to 2874 Hz, as expected for trans-PtP2 systems.21
When both Cp rings are derivatized with aryl halides,
a similar synthetic strategy can be applied for the
synthesis of trinuclear complexes (Scheme 3).
E lect r on ic Sp ect r oscop y. The UV-vis spectra
(Table 2) of the heterobimetallic complexes show two
prominent bands. The high-energy intense band is
ascribed to the π-π* transition of the organic ligand.
The low-energy weak absorption may arise from a
forbidden d-d transition.22 In the platinum and the
palladium complexes the π-π* transition is shifted to
lower energy and the intensity is increased (Figure 1),
suggesting additional charge-transfer character from
the platinum or palladium centers.23 As expected, within
a series the π-π* transition progressively shifts to
longer wavelengths with increasing chain length.
Cyclic Volta m m etr ic Stu d ies. Pertinent cyclic vol-
tammetric data for the complexes were presented in
Table 3. All the ligands 1 exhibit a reversible oxidation
of the ferrocene moiety slightly positive of the standard
ferrocene. It is noteworthy that the conjugated polyenes
and polyynes can be considered as electron-accepting
groups. When the conjugation length is increased, the
oxidation of ferrocene becomes easier; i.e., E1/2 shifts to
more negative potential. This is in analogy with what
is observed for phenylene derivatives, where oxidation
is favored by the delocalization of the charge along the
conjugation system.24
All the heterobimetallic complexes exhibit two revers-
ible redox processes (for example, see Figure 2). The
(22) Sohn, Y. S.; Hendrickson, D. A.; Gray, H. B. J . Am. Chem. Soc.
1971, 93, 3603.
(23) (a) Lopez, C.; Granell, J . J . Organomet. Chem. 1998, 555, 211.
(b) Burdeniuk, J .; Milstein, D. J . Organomet. Chem. 1993, 451, 213.
(21) (a) Crociani, B.; DiBianci, F.; Giovenco, A.; Berton, A.; Bertini,
R. J . Organomet. Chem. 1989, 361, 255. (b) Anderson, G. K.; Clark,
H. C.; Davies, J . A. Organometallics 1982, 1, 64.

5290 Organometallics, Vol. 18, No. 25, 1999
J ustin Thomas et al.
Ta ble 3. Electr och em ica l Da ta for th e Com p lexesa
Sch em e 4
compd
E1
E2
∆E
1a
1b
1c
1d
1e
2a
2b
2c
2d
2e
3a
3b
3c
4
0.023 (102)
0.009 (101)
-0.002 (93)
0.088 (101)
0.006 (120)
-0.076 (87)
-0.030 (90)
-0.018 (86)
-0.003 (89)
-0.026 (80)
-0.094 (88)
-0.025 (89)
-0.032 (90)
-0.003 (96)
-0.039 (107)
-0.015 (96)
-0.119 (90)
0.335 (84)
0.258 (87)
0.199 (79)
0.511 (132)
411
288
217
514
redox wave was observed for the thiophene segment of
1, indicating a significant contribution from ferrocene
and M(PPh3)2X (M ) Pd, Pt) to the stability of the
thiophene cations resulting from 2 and 3. It has been
reported previously that electron donor substituents
greatly stabilized the radical cations and dications of
short-chain oligo(thiophenes).26
0.255 (87)
0.125 (89)
0.200 (87)
349
150
232
5
6
7
0.810 (i)
0.291 (100)
410
Within a series of heterobimetallic complexes the Fe-
(III)/Fe(II) couple is shifted cathodically on increasing
the conjugation length. Thus, for instance, in compound
2a the Fe(III)/Fe(II) couple is located at 0.141 V, which
is 58 mV negative of that of 2c. It is interesting to note
that a reverse effect is observed for the monometallic
ferrocene derivatives 1. In 2a and 3a the smaller
conjugation length favors electron transfer from Pd/Pt
to ferrocene and, thus, the oxidation. The sensitivity of
the ferrocenyl fragment to the presence of remote
substituents attached via a conjugated linker is fre-
quently observed in complexes where ferrocenyl groups
have been used as redox spectators.27-29 The lower
oxidation potential of 2a (0.141 V) compared to that of
2e (0.191 V) and of 7 (0.098 V) compared to that of 5
(0.178 V) can be attributed to a more effective conjuga-
tion by the thiophene moiety compared to the benzenoid
moiety.30 The presence of two Pd moieties has a greater
influence on the oxidation potential of ferrocene: e.g.,
5 (0.178 V) vs 2e (0.191) and 7 (0.098 V) vs 2a (0.141
V). It is well-documented that oligo(thiophenes) and
oligo(thienylene-vinylene) have lower oxidation poten-
tials as the conjugation length increases.31,32 Recently
Wolf and co-workers have also reported a similar trend
in some ruthenium oligo(thienylacetylide) complexes.25
We found that the oxidation of the thiophene linker is
indeed easier as the conjugation length increases.
Consequently, the separation between the two redox
processes (∆E), EFc - Elinker, diminishes as the conjuga-
tion length increases.
a
All the potential values are in V for a scan rate of 100 mV/s.
The ∆Ep values are given in parentheses in mV. All potentials in
V vs ferrocene (0.00 V with ∆Ep ) 90 mV under similar conditions).
F igu r e 2. Cyclic voltammetric responses of 2a -c (scan
rate 100 mV/s).
peak separation and virtually equal currents indicate
two reversible one-electron oxidations. The less positive
oxidation wave is ascribed to the Fe(III)/Fe(II) couple.
The more positive redox process (E2) is proposed to arise
from the linker (thienyl moiety) between the Fe and Pd/
Pt metal centers. The reasons for this assumption are
as follows: (1) E2 is unlikely to be due to Pd(II) or Pt-
(II), since it differs only slightly between 2 and 3; (2)
no such oxidation wave is observed in complexes with
phenyl linkers, such as 2e and 5. The Fe(III)/Fe(II)
reduction potentials of 2 and 3 are considerably lower
than those of 1, implying the presence of delocalization
of Pd/Pt electron density into the spacer chain through
a dπfpπ interaction (Scheme 4). The reversibility of CV
waves for oligothienyl ligands was reported to be
enhanced as the length of the oligothiophene increased
in ruthenium oligo(thienylacetylide) complexes.25 The
reversibilities of the redox waves for the thienyl linker
in complexes 2 and 3 are remarkable in view of the
relatively short chain length of the linker. No reversible
On scanning to more positive potentials, we observed
polymer deposition on the working electrode, with
concomitant deterioration in current response.
X-r a y Cr ysta l Str u ctu r e of 3a . A ORTEP drawing
of 3a is shown in Figure 3. Selected bond distances and
angles are listed in Table 4. The structure is the first
(26) Garcia, P.; Pernaut, M.; Hapiot, P.; Wintgens, V.; Valat, P.;
Garnier, F.; Delabouglise, D. J . Phys. Chem. 1993, 97, 513.
(27) Bhadhade, M. M.; Das, A.; J effery, J . C.; McCleverty, J . A.;
Bodiola, J . A. N.; Wardd, M. D. J . Chem. Soc., Dalton Trans. 1995,
2769.
(28) Constable, E. C. Angew. Chem., Int. Ed. Engl. 1991, 30, 407.
(29) Lee, S.-M.; Marcaccio, M.; McCleverty, J . A.; Ward, M. D. Chem.
Mater. 1998, 10, 3272.
(30) Ito, S.; Kobayashi, H.; Kikuchi, S.; Morita, N.; Asao, T. Bull.
Chem. Soc. J pn. 1996, 69, 3225.
(31) (a) Nakanishi, H.; Sumi, N.; Aso, Y.; Otsubo, T. J . Org. Chem.
1998, 63, 8632. (b) Noma, N.; Kawaguchi, K.; Imae, I.; Nakano, H.;
Shirota, Y. J . Mater. Chem. 1996, 6, 117. (c) Martinez, F.; Voelkel, R.;
Naegele, D.; Naarmann, H. Mol. Cryst. Liq. Cryst. 1989, 167, 227.
(32) J estin, I.; Fre`re, P.; Mercier, N.; Levillain, E.; Stievenard, D.;
Roncali, J . J . Am. Chem. Soc. 1998, 120, 8150.
(24) Matas, J .; Uriel, S.; Peris, U.; Llusar, R.; Houbrechts, S.;
Persoons, A. J . Organomet. Chem. 1998, 562, 197.
(25) Zhu, Y.; Millet, D. B.; Wolf, M. O.; Rettig, S. J . Organometallics
1999, 18, 1930.

Pd(II) and Pt(II) Complexes with Thiophene Spacers
Organometallics, Vol. 18, No. 25, 1999 5291
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 3a
Distances
Pt1-C16
Pt1-P1
Pt1-P2
Pt1-Br1
1.98(1)
C13-C14
C14-C15
C15-C16
S1-C13
1.35(2)
1.41(2)
1.38(2)
1.73(2)
1.73(1)
2.309(3)
2.312(3)
2.512(1)
S1-C16
Angles
C16-Pt1-P1
C16-Pt1-P2
P1-Pt1-P2
89.0(4)
91.2(4)
177.0(1)
C16-Pt1-Br1
P1-Pt1-Br1
P2-Pt1-Br1
177.4(3)
88.70(8)
91.02(9)
length constructed from vinylthiophene subunits have
been successfully obtained in good to excellent yields.
They show reversible redox behavior that may be useful
for the study of intervalence electron transfer and near-
IR spectra. Efforts in this direction and in extending
this protocol to synthesize heterobimetallics incorporat-
ing other transition metals are underway.
F igu r e 3. ORTEP drawing of 3a . Thermal ellipsoids are
drawn with 50% probability boundaries.
platinum σ-thienyl complex. The platinum assumes a
square-pyramidal geometry with two trans-disposed
triphenylphosphine ligands. The Pt-C distance (1.98-
(1) Å) is in accordance with that of a related phenyl
analogue.12 The thienyl plane is nearly perpendicular
to the coordination plane derived from P(1), Br(1), C(16),
and P(2). All other distances and angles are similar to
those observed for related derivatives.10,12
Ack n ow led gm en t. We thank Academia Sinica and
the National Science Council (Grant NSC-88-2113-M-
001-045) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and thermal parameters, all bond distances and
angles, and experimental data for X-ray diffraction studies of
3a . This material is available free of charge via the Internet
at http://pubs.acs.org.
Con clu sion s
The heterobimetallic complexes incorporating fer-
rocene and Pd or Pt separated by a varying conjugation
OM990556Z