Organometallic platinum(II) and palladium(II) polymers containing 2,6-diethynyl-4-nitroaniline bridging spacer and related dinuclear model complexes

Article abstract of DOI:10.1021/om049972w

The metal-carbon coupling in dehydrohalogenation conditions between Pt(II) or Pd(II) square planar bisphosphine dichloride complexes and 2,6-diethynyl-4-nitroaniline (DENA) yielded organometallic polymers, i.e., -[M(PTol₃)₂(-C≡C-R-C≡C-)]_n- with R = p-NH₂C₆H₂NO₂ and M = Pt(II) or Pd(II). Dinuclear platinum complexes were also synthesized as geometrical models. The polymers and complexes were fully characterized by means of spectroscopic techniques. Accurate investigations with 2D nuclear magnetic resonance (NMR) spectroscopy were used to define the chemical and spatial structure of the polymeric chains as a helical conformation for both Pt(II)- and Pd(II)-based organometallic polymers. Optical absorption studies and X-ray photoelectron spectroscopy measurements revealed the extent of conjugation and the nature of the ending groups.

Full text of DOI:10.1021/om049972w

2860
Organometallics 2004, 23, 2860-2869
Or ga n om eta llic P la tin u m (II) a n d P a lla d iu m (II) P olym er s
Con ta in in g 2,6-Dieth yn yl-4-n itr oa n ilin e Br id gin g Sp a cer
a n d Rela ted Din u clea r Mod el Com p lexes
Rosaria D’Amato,† Ilaria Fratoddi,*,† Alberto Cappotto,† Patrizia Altamura,†
Maurizio Delfini,† Cristiano Bianchetti,† Adriana Bolasco,‡
Giovanni Polzonetti,§ and Maria V. Russo†
Department of Chemistry, University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome,
Italy, and Department “Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive”,
University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome, Italy, and Department of
Physics, University of Rome “Roma Tre”, Via della Vasca Navale 84, 00146 Rome, Italy
Received J anuary 7, 2004
The metal-carbon coupling in dehydrohalogenation conditions between Pt(II) or Pd(II)
square planar bisphosphine dichloride complexes and 2,6-diethynyl-4-nitroaniline (DENA)
yielded organometallic polymers, i.e., -[M(PTol3)2(-CtC-R-CtC-)]n- with R ) p-NH2C6H2-
NO2 and M ) Pt(II) or Pd(II). Dinuclear platinum complexes were also synthesized as
geometrical models. The polymers and complexes were fully characterized by means of
spectroscopic techniques. Accurate investigations with 2D nuclear magnetic resonance (NMR)
spectroscopy were used to define the chemical and spatial structure of the polymeric chains
as a helical conformation for both Pt(II)- and Pd(II)-based organometallic polymers. Optical
absorption studies and X-ray photoelectron spectroscopy measurements revealed the extent
of conjugation and the nature of the ending groups.
In tr od u ction
cal calculations9 have demonstrated that there is a
significant overlap between the π system of the acety-
lene spacer and the d orbitals of the metal centers. As
a consequence, a good deal of back-bonding between the
metal orbitals and the π* alkynyl orbitals, leading to
an extended delocalization along the polymer chain
throughout the MLn groups, is expected. Optical absorp-
tion and photoluminescence studies revealed relatively
low band gaps, associated with metal to ligand charge
transfer (MLCT) transitions. The optical band gaps are
dependent on the nature of the organic spacer,10 which
also exerts an influence on the delocalization of π
electrons throughout the polymer backbone. Therefore
these materials are of potential interest for the develop-
ment of new semiconductor organic devices, which can
be realized using their thin films. Field effect transis-
tors, electroluminescent diodes, and photoconductive
devices have also been implemented by using organo-
metallic polymers.11
In the past decade a great deal of research work has
been devoted to the synthesis of organometallic poly-
mers.1,2 Polymers containing in the main chain transi-
tion metals σ bonded to conjugated alkynes -CtC-R-
CtC- have been largely investigated,3,4 being stable
materials with interesting electrical5 and linear and
nonlinear optical6 properties. Owing to their rigid rod
linear structure, they also behave as liquid crystals.7,8
Photoelectron spectroscopy measurements and theoreti-
* To whom correspondence should be addressed. E-mail:
ilaria.fratoddi@uniroma1.it.
† Department of Chemistry, University of Rome “La Sapienza”.
‡ Department “Studi di Chimica e Tecnologia delle Sostanze Bio-
logicamente Attive”, University of Rome “La Sapienza”.
§ University of Rome “Roma Tre”.
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Polymers with third-order NLO properties need an
extended π delocalization and organometallic rigid-rod
ones belong to this class.12 Organometallic polymers in
which donor-acceptor interactions can occur, resulting
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Chem. Soc. 1993, 115, 3276. (b) Springborg, M. J . Solid State Chem.
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10.1021/om049972w CCC: $27.50 © 2004 American Chemical Society
Publication on Web 05/08/2004

Organometallic Pt(II) and Pd(II) Polymers
Organometallics, Vol. 23, No. 12, 2004 2861
X-ray photoelectron spectroscopy (XPS) investigations were
performed with a custom designed XPS spectrometer. Typical
vacuum in the analysis chamber during the measurements
was in the 10-9-10-10 Torr range. The analysis chamber is
equipped with a 150 mm mean radius hemispherical electron
analyzer with a five-lens input system combined with a 16-
channel detector. Al KR nonmonochromatized X-ray radiation
(hν ) 1486.6 eV) was used during the measurements; the
resolution is 1.0 eV as measured for the Ag 3d5/2 line. The
samples were spin deposited onto polished stainless steel
substrates in the form of thin films obtained from chloroform
solutions. All the spectra were energy referenced to the C 1s
signal of aromatic carbons, i.e., at 284.7 eV binding energy
(BE) value. Quantitative evaluation of the atomic ratios was
obtained by using the well-known Scofield atomic cross-section
values.
Ma ter ia ls. Standard techniques, with Schlenk type equip-
ment for the manipulation of air-sensitive materials under
argon atmosphere, were used. Reagent grade (Carlo Erba)
solvents were freshly distilled under argon before use. The
precursor complexes cis-[Pt(PTol3)2Cl2] (1) and trans-[Pd-
(PTol3)2Cl2] (2) were prepared according to literature meth-
ods.15 2,5-[(Trimethylsilyl)ethynyl]thiophene, TSET (3), was
obtained following a reported procedure.16
from charge transfer between electron-donor and elec-
tron-withdrawing groups, exhibit second-order NLO
properties.13
In this framework, we have prepared and character-
ized new polymers using 2,6-diethynyl-4-nitroaniline
(DENA) and bis-phosphine Pt and Pd dihalides as the
precursors. To achieve a better characterization, Pt and
Pd model complexes were also synthesized by using
DENA and 2,5-diethynylthiophene (DET) as bridging
ligands between metal centers.
Exp er im en ta l Section
In str u m en ta tion . IR spectra were recorded with a Perkin-
Elmer 1700 FTIR spectrophotometer, in Nujol mulls, in CH2Cl2
solutions or KBr pellets. Spectra in the range 200-500 cm-1
were run on a Perkin-Elmer 1700X interferometer. Raman
spectra were run on a NIR FT Raman 1700X interferometer
(laser Nd:YAG λ ) 1064 nm) on samples mixed with BaSO4.
UV spectra were measured on a Perkin-Elmer Lambda 5
UV/vis spectrophotometer in CHCl3, N,N-dimethylformamide
(DMF), or tetrahydrofuran (THF) solutions, in quartz cells.
Photoluminescence spectra were registered on a Perkin-Elmer
LS 50 spectrofluorimeter in CHCl3 solutions. The molar
extinction coefficient ꢀo (with respect to the repeating unit) and
the relative quantum yield η of chloroform solutions were also
determined. We adopted as the standard a solution of couma-
rine in ethanol (c ) 0.0028 g/L), with a quantum yield equal
to 51%, calculated by comparison with a rhodamine 6G
solution (c ) 0.016 g/L, η ) 90%).14 All data were corrected by
taking into account the photomultiplier efficiency of the
fluorescence spectrometer.
Syn th eses. 2,6-Dieth yn yl-4-n itr oa n ilin e (4). The proce-
dure followed a modified pathway with respect to that reported
for the preparation of similar products.17 2,6-Diiodo-4-nitro-
aniline (4 g, 10.26 mmol, Sigma-Aldrich commercial product
purified with acetone, acetic acid and diethyl ether) was
dissolved in 33.3 mL of freshly distilled diisopropylamine in
the presence of 0.10 g (0.50 mmol) of copper(II) acetate
monohydrate and 0.35 g (0.49 mmol) of trans-[Pd(PPh3)2Cl2]
crystallized from chloroform. The solution was degassed by
passing a rapid stream of nitrogen through it, and then 3.1
mL (21.93 mmol) of trimethylsilylacetylene (TMSA) was added.
An insoluble reaction product was formed, which was filtered
off, dissolved in dichloromethane, and washed with HCl (5%)
and successively with water. The organic layer was dried over
sodium sulfate and the solvent removed at reduced pressure.
The yellow-brown solid obtained was first column chromato-
graphed (silica gel, hexane/diethyl ether, 20:1, as eluent) and
then crystallized from ethanol. The solid was dissolved in 80
mL of methanol, and KOH was added to hydrolyze the
trimethylsilyl groups. After 20 min of reaction, the volume of
the yellow solution was reduced, diluted with water, and
extracted with chloroform, and the organic layer was dried over
sodium sulfate and evaporated under reduced pressure. The
obtained solid was chromatographed on a SiO2 column, by
using isopropyl ether/hexane, 2:1, as eluent. The second eluted
fraction contained 2,6-diethylnyl-4-nitroaniline (DENA) as a
yellow solid. Yield: 75%. Mp: 213-214 °C. Anal. (calcd values
in parentheses): C 64.57 (64.52); H 3.15 (3.25); N 15.11 (15.05).
Raman: 2107 cm-1. FTIR (KBr mull, cm-1): 3481, 3371
(νNH2), 3293 (ν tCH), 1619 (ν NO2), 1288 (ν CN). UV (CHCl3,
nm): λmax ) 350. Luminescence emission (CHCl3, nm): λmax
NMR spectra were collected with a Varian XL 300 spec-
trometer in CDCl3. 1H and 13C spectra were calibrated with
internal standards and 31P spectra with H3PO4 (85%) probe.
NMR measurement conditions: 1H pulse width 7.5 µs (30°),
acquisition time 2 s, repetition time 0.5 s, spectral width 4000
Hz, number of data points 32K, number of scans 128; 31P pulse
width 10 µs (45°), acquisition time 2 s, repetition time 1 s,
spectral width 30 000 Hz, number of data points 32K, number
of scans 2000; 13C pulse width 4.3 µs (30°), acquisition time
1.815 s, repetition time 1.2 s, spectral width 19 000 Hz, number
of data points 64K, number of scans 20 000. 2D COSY spectra
were recorded on a Bruker AM-500 instrument, by using the
pulse sequence available in the routine of the instrument.
Measurement conditions: spectral width 8000 Hz, data matrix
4K × 512K points, 512 fid’s were collected for each value of t1.
2D NOESY spectra were obtained in the TPPI mode. The
acquisition parameters were the following: time domain 8K
mF2, 512 mF1 dimension, spectral width 8000 Hz in both
dimensions, resolution 0.98 and 15.65 Hz/pt mF2 and F1,
respectively. Number of scans 64, relaxation delay 1.5 s,
mixing time 150 ms.
1
) 484. Quantum yield: η ) 0.04%. H NMR (CDCl3, δ ppm):
Elemental analyses were performed at the “Laboratorio
Servizio Microanalisi, Dipartimento di Chimica” University
“La Sapienza” of Rome. TG and DTA measurements were
carried out on a Stanton Redcroft Rheometrics STA 1500
apparatus in air or in N2 atmosphere, with a heating rate of
10 °C/min.
3.48 (s, tCH), 5.51 (s, NH2), 8.21 (s, H aromatics). 13C NMR
(CDCl3, δ ppm): 78.5 (Ct), 85.5 (tCH), 106.5 (C-Ct), 129.5
(CH aromatics), 138.4 (C-NO2), 155.1 (C-NH2).
tr a n s-[Bis(tr i-pa r a -tolylp h osp h in e)(eth yn ylben zen e)-
p la tin u m ch lor id e] (5) a n d tr a n s-[Bis(tr i-pa r a -tolylp h os-
p h in e)bis(eth yn ylben zen e)p la tin u m ] (6). Complexes 5 and
6 were prepared using a modified synthetic method already
proposed for the analogous complexes containing the PPh3
Molecular weights were determined by a Perkin-Elmer
GPC-HPLC apparatus with a LC250 pump, LC oven, PL GEL
10 µm MIX analytical column, UV-vis LC 90 J detector, and
CHCl3 as eluent. Polystyrene standard samples were used for
the calibration curve.
(14) Svelto, O. Principles of Lasers; Plenum Press: New York, 1989;
Chapter 6.
(15) Hartley, F. R. Organomet. Chem. Rev. 1979, A6, 119.
(16) Altamura, P.; Giardina, G.; Lo Sterzo, C.; Russo, M. V. Orga-
nometallics 2001, 20, 4360.
(17) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627.
(12) Guha, S.; Frazier, C. C.; Kang, K.; Finberg, S. E. Opt. Lett. 1989,
14, 952.
(13) Caruso, U.; Di Matola, A.; Panunzi, B.; Rovello, A.; Sirigu, A.
Polymer 2001, 42, 3973.

2862 Organometallics, Vol. 23, No. 12, 2004
D’Amato et al.
ligand.18 cis-[Pt(PTol3)2Cl2] (0.601 g, 0.689 mmol) was dissolved
in 40 mL of CHCl3, and 0.1 mL (0.093 g, 0.912 mmol) of
phenylacetylene and 1.6 mL of diethylamine were added. The
mixture was stirred for 3 h at 70 °C, and the solvent was then
removed. The solid product was a mixture of the monochloro-
acetylide (5) and the diacetylide (6) complexes, which were
separated on a SiO2 column, using a mixture of CHCl3/toluene
(3:1) as eluent. In the first eluted fraction trans-[Pt(PTol3)2-
(CtC-C6H5)2] (6) was present. From the second fraction,
trans-[Pt(PTol3)2(CtC-C6H5)Cl] (5) was obtained. The prod-
ucts were further purified and crystallized from CHCl3/EtOH.
Ch a r a cter iza tion of Com p lex 5. Yield: 54%. Mp: 211-
212 °C. Anal. (calcd): C 63.74 (63.86); H 5.28 (5.04). FTIR
(Nujol mull, cm-1): 315 (ν Pt-Cl), 2130 (ν CtC). UV (CHCl3,
nm): λmax ) 313. NMR (CDCl3, δ ppm): 1H, 2.36 (s, CH3),
6.09-6.87 (m, C6H5), 7.17-7.66 (qt, p-C6H4Me of PTol3 ligand);
13C, 21.4 (CH3), 88.0-106.0 (-CtC-), 124.4, 126.8, 127.7,
131.0 (C6H5), 127.3, 128.6, 135.0, 140.3 (C6H4Me of PTol3
ligand); 31P, 20.23 (J Pt-P ) 2620 Hz).
°C. Anal. (calcd): C 66.12 (66.85); H 4.80 (4.99); S 1.59 (1.65).
FTIR (CHCl3 solution, cm-1): 1441 (ν CdC of thiophene) 2101
(ν CtC). UV (CHCl3, nm): λmax ) 409. NMR (CDCl3, δ ppm):
1H, 2.29 (s, CH3), 6.17, 6.87 (m, phenyl), 6.90 (s, thiophene),
7.11, 7.61 (qt, resonances of PTol3 ligand); 13C, 21.4 (CH3),
124.4, 126.8, 128.8, 130.9 (C6H5), 127.2, 128.0 (C4H2S), 126.9,
128.5, 134.9, 140.0 (C6H4Me); 31P, 16.67 (J Pt-P ) 2605 Hz).
P oly[2,6-dieth yn yl-4-n itr oan ilin ebis(tr i-pa r a -tolylph os-
p h in e)p la tin u m (II)] (9). cis-[Pt(PTol3)2Cl2] (0.611 g, 0.07
mmol) was dissolved in 40 mL of degassed diethylamine, and
0.127 g (0.7 mmol) of DENA and 0.013 g (0.07 mmol) of CuI
as catalyst were added. The mixture was warmed at 45 °C for
24 h. A yellow-brown solid separated gradually. The solid was
filtered off, thoroughly washed with EtOH, and dried under
vacuum. Yield: 75%. Mp: 245 °C (dec). Anal. (calcd for the
repeating unit PtP2O2N2C52H46): C 63.11 (63.24); H 4.41 (4.68);
N 2.69 (2.85). FTIR (Nujol mull, cm-1): 3468, 3357 (ν NH2),
2101 (ν CtC), 1288, 1310, 1344 (ν C-N). UV (CHCl3, nm):
λmax 390. Luminescence emission (CHCl3, nm): λmax ) 500.
Quantum yield: η ) 0.02%. NMR (CDCl3, δ ppm): 1H, 2.18,
2.26 (s, CH3), 3.40 (s, NH2), 6.60 (s, C6H2 NH2 NO2), 7.02, 7.09,
7.52 (m, resonances of PTol3 groups); 13C, 21.5, (CH3), 107.5,
124.0 (CtC), 110.5 128.2, 135.5, 153.0 (NH2C6H2NO2), 127.9,
128.9, 135.0, 141.1 (C6H4Me); 31P, 17.62 (J Pt-P ) 2589 Hz),
20.38 (J Pt-P ) 2605 Hz). GPC: molecular weight, Mw ) 14600
amu (n ) 16 repeat units), polydispersity p ) 2.4.
Ch a r a cter iza tion of Com p lex 6. Yield: 40%. Mp: 213-
215 °C. Anal. (calcd): C 70.20 (69.24); H 5.64 (5.21). FTIR
(Nujol mull, cm-1): 2110 (ν CtC). UV (CHCl3, nm): λmax
)
348. NMR (CDCl3 δ ppm): 1H, 2.40 (s, CH3), 6.95-6.32 (m,
tC-C6H5), 7.76-7.21 (dd, C6H4Me of PTol3 ligand); 13C, 21.25
(CH3), 111.57-112.68 (-CtC-), 124.20, 126.81, 128.32, 130.94
(C6H5), 128.37, 128.49, 134.90, 139.91 (C6H4Me of PTol3
ligand); 31P, 15.5 (J Pt-P ) 2625 Hz).
P oly[2,6-dieth yn yl-4-n itr oan ilin ebis(tr i-pa r a -tolylph os-
p h in e)p a lla d iu m (II)] (10). DENA (0.20 g, 1.07 mmol) was
dissolved in 50 mL of degassed diethylamine under argon, and
0.841 (1.07 mmol) of trans-[Pd(PTol3)2Cl2], 0.065 g (0.214
mmol) of tri-para-tolylphosphine (used to stabilize the result-
ing polymer), and 0.010 g (0.053 mmol) of CuI were added.
The reaction was carried out for 7 h at room temperature
under argon. At the end of the reaction, the solid product was
filtered off and washed with MeOH. The reaction product was
dissolved in CHCl3 and flash chromatographed on Florisil,
using CHCl3 and CH3OH as gradient eluents to remove the
byproducts NHEt2Cl and cuprous salts. After evaporation of
the solvent from the eluted fraction, a yellow-brown powder
was obtained. Yield: 69%. Mp: 187 °C (dec). Anal. (calcd for
the repeating unit PdP2O2N2C52H46): C 66.99 (69.48); H 5.38
(5.12); N 3.11 (3.67). FTIR (in Nujol mull, cm-1): 3468, 3357
(ν NH2), 2095 (ν CtC), 1288, 1310, 1344 (ν C-N). UV (CHCl3,
nm): λmax ) 390. Luminescence emission (CHCl3, nm): λmax
) 500. Quantum yield: η ) 0.02%. NMR (CDCl3, δ, ppm): 1H,
2.24 (m, CH3), 3.65 (s, NH2), 6.90 (s, NH2C6H2NO2), 7.10, 7.65
(m, resonances of PTol3 groups); 13C, 21.4 (CH3), 107.0, 124.0
(CtC), 110.2, 129.0, 134.6, 152.3 (NH2C6H2NO2), 127.9, 128.6,
132.0, 140.2 (C6H4Me); 31P, 25.70. GPC: molecular weight, Mw
) 6000 amu (n ) 8 repeat units), polydispersity p ) 2.3.
The data for 6 are in agreement with a literature report.19
tr a n s,tr a n s-[Dieth yn ylben zen edibis(tr i-pa r a -tolylph os-
p h in e)d ip la t in u m (II)-2,6-d iet h yn yl-4-n it r oa n ilin e] (7).
trans-[Pt(PTol3)2(CtC-C6H5)Cl] (0.166 g, 0.19 mmol) was
dissolved, under argon, in 20 mL of degassed diethylamine,
and 0.19 g (0.095 mmol) of DENA and 0.013 g (0.07 mmol) of
CuI as catalyst were added. The solution was warmed at 40
°C for 4 h. After removal of the solvent, the solid residue was
dissolved in CHCl3 and washed with water in a separatory
funnel. From the CHCl3 solution, yellow crystals were obtained
by addition of EtOH. Yield: 85%. Mp: 228-230 °C (dec). Anal.
(calcd): C 65.92 (66.26); H 5.24 (4.95); N 1.34 (1.40). FTIR
(Nujol mull, cm-1): 3479, 3363 (ν NH2); 2101 (ν CtC); 1287
(ν C-N). UV (CHCl3, nm): λmax ) 360. Luminescence emission
(CHCl3, nm): λmax ) 500. Quantum yield: η ) 0.02%. NMR
(CDCl3, δ ppm): 1H, 2.26 (s, CH3), 3.50 (s, NH2), 6.20-6.95
(m, C6H5), 6.58 (s, NH2C6H2NO2), 7.00-7.58 (qt, resonances
of PTol3 ligand); 13C, 21.2 (CH3), 106.2, 111.8, 112.8, 118.1
(-CtC-), 124.3, 126.9, 128.4, 131.3 (C6H5), 127.0, 128.8, 134.8,
140.4 (C6H4Me of PTol3 ligand), 110.7, 128.0, 136.0, 152.5
(NH2C6H2NO2); 31P, 17.48 (J Pt-P ) 2600 Hz).
tr a n s,tr a n s-[Dieth yn ylben zen edibis(tr i-pa r a -tolylph os-
p h in e)d ip la tin u m (II)-2,5-d ieth yn ylth iop h en e] (8). TSET
was used to perform the reaction, because this silyl derivative
is more stable and easy to handle than the corresponding 2,5-
diethynylthiophene, that is highly sensitive to oxygen and
reactive. TSET (0.292 g, 1.05 mmol) was dissolved in 40 mL
of deoxygenated methanol, to which 4 mL of a KOH solution
(0.5 M) was added. The reaction was carried out at room
temperature for 1 h, to obtain the 2,5-diethynylthiophene
revealed by means of 1H NMR spectra. To this reaction
mixture, 0.198 g (2.11 mmol) of trans-[Pt(PPTol3)2(CtC-
C6H5)Cl], dissolved in 45 mL of deoxygenated CH2Cl2, and 0.05
g of CuI as the catalyst were added under argon atmosphere.
The reaction was stirred at 25 °C for 25 h, and then the solvent
volume was reduced to 10 mL in a vacuum and the residue
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . The monomer
DENA was chosen for the presence of NH2 and NO2
groups in p-nitroaniline, which are suitable for the
formation of materials with second-order nonlinear
optical (NLO) properties, and because the two alkynyl
moieties are able to link transition metals (mainly Pt
and Pd) to form organometallic, highly ethynylated
polymers. The IR spectrum of DENA is characterized
by three bands in the 3500-3000 cm-1 region; two
bands at 3481 and 3371 cm-1, due to the stretching
chromatographed on
a silica gel column (eluent CHCl3/
vibrations of the NH2 group; and a band at 3293 cm-1
,
petroleum ether, 40-70, 3:2). The dinuclear complex 8 was
separated from the side products in 31% yield. Mp: 145-147
due to the stretching vibrations of the tC-H groups.
In the IR spectrum no bands are present in the 2200-
2000 cm-1 region, where the CtC stretching vibrations
should be observable, while a band at 2107 cm-1 is
present in the Raman spectrum of DENA, confirming
the presence of the symmetric triple CtC bond.
(18) D’Amato, R.; Furlani, A.; Colapietro, M.; Portalone, G.; Casal-
boni, M.; Falconieri, M.; Russo, M. V. J . Organomet. Chem. 2001, 627,
13.
(19) Osella, D.; Gobetto, R.; Nervi, C.; Ravera, M.; D’Amato, R.;
Russo, M. V. Inorg. Chem. Commun. 1998, 1, 239.

Organometallic Pt(II) and Pd(II) Polymers
Organometallics, Vol. 23, No. 12, 2004 2863
Ta ble 1. Collection of Sp ectr oscop ic Da ta for Com p ou n d s 4, 5, a n d 7-10
elemental analyses
C% (C% calc) H% (H% calc
N% (N% calc
31P NMR
δ J 31P-195Pt
(ppm) (Hz)
yield
(%)
)
1H NMR
δ (ppm)
13C NMR δ
(ppm)
sample
IR (cm-1
)
)
4
75
3481, 3371ν(NH2)
1619 ν(NO2)
64.57 (64.52)
3.15 (3.25)
3.48 (s H-CtC)
5.51(s -NH2)
78.5, 85.5 (CtC)
106.5, 129.5, 138.4,
155.1 (NH2C6H2NO2)
3293 ν(tCH)
1288, 1310, 1344
ν(CN)
15.11 (15.05)
8.21 (s -ArH)
2107 ν(CtC) Raman
2130 ν(CtC)
315 ν (Pt-Cl)
5
7
54
85
63.74 (63.86)
5.28 (5.04)
2.36 (s CH3)
6.09, 6.87 (m Ph)
7.17, 7.66 (qt PTol3)
20.23 (2620) 21.4 (CH3)
88.0, 106.0 (CtC)
124.4, 126.8, 127.7,
131.0 (C6H5)
127.3, 128.6, 135.0,
140.3 (C6H4Me)
3479, 3363 ν(NH2)
2101 ν(CtC)
65.92 (66.26)
5.24 (4.95)
2.26 (s CH3)
3.50 (s -NH2)
17.48 (2600) 21.2 (CH3)
106.2, 111.8, 112.8,
118.1 (CtC)
1287 ν(CN)
1.34 (1.40)
6.58 (s -ArH)
124.3, 126.9, 128.4,
131.3 (C6H5)
6.20, 6.95 (m Ph)
7.00, 7.58 (qt PTol3)
110.7, 128.0, 136.0,
152.5 (NH2C6H2NO2)
127.0, 128.8, 134.8,
140.4 (C6H4Me)
8
31
75
69
2101 ν(CtC)
66.12 (66.85)
4.80 (4.99)
2.29 (s CH3)
6.17, 6.87 (m Ph)
16.67 (2605) 21.4 (CH3)
1441 ν(CdC Th)
124.4, 126.8, 128.8,
130.9 (C6H5)
127.2, 128.0 (C4H2S)
126.9, 128.5, 134.9,
140.0 (C6H4Me)
S 1.59 (1.65)
6.90 (s Th)
7.11, 7.61 (qt PTol3)
9
3468, 3357ν(NH2)
2101 ν(CtC)
1288, 1310, 1344
ν(CN)
63.11 (63.24)
4.41 (4.68)
2.69 (2.85)
2.18, 2.26 (s CH3)
3.40 (s -NH2)
6.60 (s -ArH)
17.62 (2589) 21.5 (CH3)
20.38 (2605) 107.5, 124.0 (CtC)
110.5, 128.2, 135.5,
153.0 (NH2C6H2NO2)
127.9, 128.9, 135.0,
141.1 (C6H4Me)
7.02, 7.09, 7.52 (m PTol3)
10
3468, 3357ν(NH2)
2095 ν(CtC)
1288, 1310, 1344
ν(CN)
66.99 (69.48)
5.38 (5.12)
3.11 (3.67)
2.24 (m CH3)
3.65 (s -NH2)
6.90 (s -ArH)
25.70
21.4 (CH3)
107.0, 124.0 (CtC)
110.2, 129.0, 134.6,
152.3 (NH2C6H2NO2)
127.9, 128.6, 132.0,
140.2 (C6H4Me)
7.10, 7.65 (m PTol3)
1
The H NMR spectrum of DENA shows the aromatic
protons signal at 8.21 ppm, owing to the high influence
of the NO2 group in ortho position, a signal at 3.48 ppm
assigned to the tC-H proton, and the resonance at 5.51
ppm assigned to the NH2 group. The 13C NMR spectrum
exhibits the resonances of the CtC group at 85.5 and
78.5 ppm and the resonances of the aromatic carbons
at 106.5 (C linking the triple bond), 129.5 ppm (aromatic
C-H), 138.4 ppm (C bonded to NO2), and 155.1 ppm (C
bonded to NH2); these values are consistent with cor-
relation chart values. The experimental data are col-
lected in Table 1.
quite different polarity, show a shift of the absorption
maximum from 350 to 360 nm, supporting the fairly
extended ICT occurring for this molecule.
If we look at the geometry of DENA and of the square
planar Pt(II) and Pd(II) precursor complexes, the cou-
pling reaction that leads to the formation of rodlike
organometallic poly-ynes would produce in this case a
six-membered ring with total dipole moment µ ) 0 if
the p-nitroaniline moiety maintains the original con-
formation, i.e., if no turn around the -CtC- bonds in
meta position occurs (Scheme 1).
Looking at the recent literature on analogous systems,
cyclic complexes with diethynyl bridging spacers be-
tween the square planar metal centers have been
recently utilized to construct metallosupramolecular
assemblies,21 and the synthesis of organometallic macro-
cycles consisting of a nearly planar and symmetric
structure composed of metal acetylides has been re-
ported.22 However, in our case, we can suppose that the
total dipole moment would be µ * 0 if a free rotation
were possible, and a random sequence of the differently
oriented nitroaniline might result. In this way an
The polarizability of this molecule is confirmed by UV
measurements. As a general statement, an optical
excitation induces a different electronic distribution
between the donor and the acceptor groups in the
polarizable molecules and the dipole moment of the
ground and the excited state are largely different. The
position of the intramolecular charge transfer (ICT)
transition bands of these molecules is dependent on the
polarity of the solvent, and the solvatochromic effect is
characteristic of molecules that exhibit second-order
NLO properties.20 The UV spectra of DENA recorded
in CHCl3 and in N,N-dimethylformamide, solvents with
(21) (a) Bunz, U. H. F.; Roidl, G.; Altmann, M.; Enkelmann, V.;
Shimizu, K. D. J . Am. Chem. Soc. 1999, 121, 10719. (b) Lee, S. J .; Lin,
W. J . Am. Chem. Soc. 2002, 124, 4554.
(20) Wang, C. K.; Wang, Y. H.; Su, Y.; Luo, Y. J . Chem. Phys. 2003,
119, 4409.
(22) Onitsuka, K.; Yamamoto, S.; Takahashi, S. Angew. Chem., Int.
Ed. 1999, 38, 174.

2864 Organometallics, Vol. 23, No. 12, 2004
D’Amato et al.
Sch em e 2. Helica l a n d Zigza g Str u ctu r es for
Sch em e 1. Hyp oth esis of Hexa n u clea r Hexa gon a l
Str u ctu r e
P t(II) a n d P d (II) P oly-yn es
asymmetric complex with expected second-order NLO
properties would be synthesized. In our case the forma-
tion of an organometallic cyclic compound was observed
as a side product of the polymerization reaction based
on the Pt(II) complex. The structure of the cyclic
complex was assessed by X-ray crystal structure, and
it will be the subject of a forthcoming paper.23 If
distortion from planarity occurs, a metal poly-yne with
helical structure can be formed in analogy with the
results reported by Takahashi et al.24 Otherwise, zigzag
polymer structures are likely obtained, as depicted in
Scheme 2, in analogy with the structure of organo-
metallic polymers formed by chelate Pt and Pd centers
bridging diethynylbiphenyl spacers.25
As model molecules of the metal poly-ynes, the
dinuclear platinum complexes 7 and 8 were synthesized
from DENA and TSET in reaction with the monochloro
complex 5, which shows a trans configuration, as
determined from the J Pt-P coupling constant (2620 Hz).
The synthesis of the dinuclear complexes 7 and 8 follows
the pathway reported in Scheme 3, where the chemical
structure of the complexes is depicted.
of the protons of the nitroaniline ring at 6.58 ppm. The
double doublet typical pattern of the ending phenyl
ligand is detected at 6.20-6.95 ppm. In the 13C NMR
spectrum the resonances of the phosphine and ending
phenyl ligands are nearly the same as those of the
precursor 5, and those of the nitroaniline moiety are
nearly the same as those of DENA, while a shift toward
low field of the resonances of the carbon-carbon triple
bonds is found (Table 1), suggesting that the main effect
of charge transfer is induced on this moiety of the
complex. The 31P NMR spectrum of 7 is characterized
by a signal at 17.48 ppm, with two symmetrical signals
due to the 195Pt-31P coupling (J Pt-P ) 2600 Hz), in
agreement with a trans configuration of the ligands
around the Pt atoms.
The reaction leading to complex 8 is performed by
producing in situ diethynylthiophene from the silyl
derivative TSET, because the protected bisacetylene is
stable and easy to handle. The FTIR and NMR charac-
terizations of 8 confirm the proposed structure, which
is analogous to the structure of 7 and is deduced also
by comparison with the spectroscopic characterizations
of related diethynylthiophene Pd complexes and oligo-
mers prepared with two different reaction routes, i.e.,
dehydrohalogenation and Stille-EOP (extended one
pot).16 The thiophene spacer is recognized from the
presence of a singlet at 6.90 ppm in the 1H NMR
spectrum and of two resonances at 127.2 and 128.0 ppm
in the 13C NMR spectrum; the signals of the carbon
atoms linked by triple bonds are not detectable because
of the low solubility of the sample. The trans configu-
ration of complex 8 is confirmed by the 195Pt-31P
High yields of product 7 (85%) are found. The IR
spectrum of 7 shows a band centered at 2101 cm-1
,
suggesting a loss of symmetry in the dinuclear model
complex; the absence of the band at 315 cm-1, present
in the far-IR spectrum of the precursor 5, indicates the
performance of the coupling reaction. 1H NMR of 7
exhibits the same pattern as the precursor complex 5
in the range of the phosphine resonances, the resonance
of the -NH2 group at δ ) 3.50 ppm, and the resonance
(23) Hursthouse M., private communication.
(24) Takahashi, S.; Onitsuka, K.; Takei, F. Macromol. Symp. 2000,
156, 69.
(25) Iucci, G.; Infante, G.; Polzonetti, G. Polymer 2002, 43, 665.

Organometallic Pt(II) and Pd(II) Polymers
Organometallics, Vol. 23, No. 12, 2004 2865
Sch em e 3. Din u clea r Mod el Molecu les
coupling constant J Pt-P ) 2605 Hz, in analogy with
complex 7 (see Table 1).
measurements, indicate that the number of repeat units
is probably underestimated, according to previous re-
ports for rodlike organonickel polymers29 and recent
studies on Pt(II) poly-ynes.30
The reaction between DENA and complex 1 was
performed by the dehydrohalogenation procedure,26
which leads to the organometallic polymer 9. The IR
spectrum of the polymer shows the signal of the CtC
stretching mode at 2101 cm-1, and it is noteworthy that
this signal does not appear in the IR spectrum of DENA,
suggesting for polymer 9 a loss of symmetry; moreover,
the signal is sharp and this feature is considered to be
consistent with a low dispersion of polymer chain
lengths, as reported for rigid-rod organometallic plati-
num-ethynyl polymers containing ferrocenyl phosphine
ligands.27
The palladium-containing polymer 10 has been ob-
tained under similar reaction conditions (Scheme 2). An
excess of PTol3 was added to avoid the release of the
phosphine by the Pd centers, which are more reactive
than Pt ones and can form new bonds with the unsatur-
ated carbon-carbon bonds or with the amino groups,
as reported in the case of poly(monosubstituted)acet-
ylenes.28 In the synthesis of 10 it was found that the
optimum ratio between the free phosphine and CuI,
used as catalyst, is 1:4; these reaction conditions lead
to the organometallic polymer 10, avoiding side reac-
tions with the chain backbone or with the functional
groups of DENA.
Interesting features are observed in the 1H NMR
spectra. The resonances of the amine hydrogens, found
at 5.51 ppm in DENA, are shifted in the range 3.40-
3.65 ppm upon coordination to the metal center in
polymers 9 and 10. The univocal assignment of the NH2
signal has been performed by the exchange reaction
with increasing amounts of D2O, which showed the
decrease of the resonance at about 3.5 ppm. The time
of the exchange was low for the polymer solutions,
probably due to the base characteristic of the NH2 group.
Moreover, this result supports the hypothesis of a helical
structure for both the polymers, because of the difficult
access of the water molecules to the hindered NH2
group. The resonances of the two hydrogens of the
p-nitroaniline moiety are found in the range 6.60-7.28
ppm (8.21 ppm in DENA) and are low-field shifted. The
resonances of the PTol3 ligand are not affected by
coordination in long polymer chains and show almost
the same chemical shift value (7.00-7.61 ppm), with a
pattern quite similar to those of the model complex 7.
The Pt and Pd organometallic polymers show analo-
gous features in the 13C NMR spectra. The resonances
of the CtC atoms are found at about 107 and 124 ppm,
and those of the p-nitroaniline ring are nearly coincident
in the range 110-153 ppm and close to those of the
monomer DENA, indicating the negligible influence of
the different transition metals on the polymer chemical
structure.
Two resonances are detected in the 31P NMR spec-
trum of 9, at 17.62 and 20.38 ppm, corresponding to
internal and terminal Pt centers, respectively. The
195Pt-31P coupling constant J Pt-P ) 2605 Hz indicates
a trans configuration of the ligands around the Pt
centers. The 31P NMR spectrum of 10 shows only one
In general, palladium-containing polymers are less
stable than the analogous platinum polymers. In fact,
a decomposition may occur on a chromatographic col-
umn; however, the crude reaction product, which gave
nonsatisfactory elemental analyses, was purified by
using flash chromatography performed in mild condi-
tions. The FTIR spectrum of 10 is quite similar to that
of 9, suggesting the same structure for both polymers,
apart from the nature of the transition metal.
The molecular weights of polymers 9 and 10, 14.600
and 6000 amu, respectively, as determined by GPC
(26) Sonogashira, K. J . Organomet. Chem. 2002, 65, 46.
(27) Long, N. J .; White, A. J . P.; Williams, D. J .; Younus, M. J .
Organomet. Chem. 2002, 649, 94.
(28) Russo, M. V.; Furlani, A.; Altamura, P.; Fratoddi, I.; Polzonetti,
G. Polymer 1997, 38, 3677.
(29) Guo, X. A.; Sture, K. C.; Hunter, A. D.; Williams, M. C.
Macromolecules 1994, 27, 7825.
(30) Fratoddi, I.; Battocchio, C.; Furlani, A.; Mataloni, P.; Polzonetti,
G.; Russo, M. V. J . Organomet. Chem. 2003, 674, 10.

2866 Organometallics, Vol. 23, No. 12, 2004
D’Amato et al.
F igu r e 1. 1H NMR of compound 10.
signal at 25.70 ppm, indicating that a polymer with
relatively high molecular weight was obtained.
With the aim of achieving a deeper insight into the
chemical structure of our organometallic polymers,
COSY and NOESY NMR investigations have been
performed. COSY spectra do not exhibit scalar correla-
tions, except for the expected ones between ortho
aromatic protons. NOESY spectra give more interesting
information. Dipolar correlations between ortho aro-
matic protons (7.18:7.65; 7.35:6.95, and 7.50:7.10 ppm)
and between aromatic and aliphatic protons in polymer
10 (2.30:7.20; 2.30:7.60 ppm) are clearly detected as
shown in Figure 1 and in Figure 2.
These latter correlations look less intense for polymer
9 than those found for polymer 10 and suggest that the
aromatic and aliphatic protons are more far away in
polymer 9. Moreover, in both polymers dipolar correla-
tions are found for NH2 (3.65 ppm) and aromatic protons
of phosphine (7.20 and 7.60 ppm), with a higher
intensity for the signal at 7.60 ppm, indicating a close
spatial proximity, confirmed on the basis of simple
geometrical models and in analogy with literature
reports on pyrimidine-dicarbaldeyde-based polymers.31
Further information on the polymer structure can be
deduced from the NOESY spectra, which suggest a
chain entanglement that may be due either to helical
structure or to interchain stacking. To elucidate this
aspect, NMR spectra have been recorded for samples
at different concentrations; no modification of the
spectral features either in chemical shift or in peak
intensity was detected, and thus the interchain correla-
tions can be ruled out. Considering the steric hindrance
of the phosphine ligands and simple molecular models
based on the structure of Pt(II) and Pd(II) square planar
complexes, which show little distortions from planarity,
it can be deduced that the observed interactions are due
to phosphine groups bound to metallic centers probably
arranged in a helical configuration.
F igu r e 2. NOESY spectrum of compound 10 and in the
inset a magnification of the correlations.
that at the decomposition temperature (227 ( 3 °C) an
exothermic explosive reaction occurs with a weight loss
of about 50%. The total combustion occurs at higher
temperature, and a total weight loss is achieved at about
600 °C. The TG and DTA curves of polymer 9 indicate
that the polymer is stable until about 267 ( 3 °C, with
a negligible weight loss probably due to some solvent.
The following weight loss (34%) occurs with exothermic
reactions up to 500 °C, and further decomposition occurs
up to 800 °C (weight loss 10%). Over 800 °C the residue
is about 55%, due to the presence of the metal atoms of
the starting material. The TG and DTA curves of
Thermogravimetric (TG) and differential thermal
analyses (DTA) were carried out on the organometallic
polymers, to investigate the range of stability in air of
the metal poly-ynes, in view of their applications in NLO
devices.
The precursor monomer 4 was also investigated as a
comparison. The TG and DTA curves of DENA (4) show
(31) Schmitt, J . L.; Stadler A. M.; Kyritsakas N.; Lehn J . M. Helv.
Chim. Acta 2003, 86 1598.

Organometallic Pt(II) and Pd(II) Polymers
Organometallics, Vol. 23, No. 12, 2004 2867
Ta ble 2. Op tica l Absor p tion a n d Em ission
P r op er ties of Com p ou n d s of Mod el Molecu les a n d
Meta l-P olyyn es
absorption
emission
λmax (nm)
sample
λmax (nm)
ꢀ0 (L mol cm1)
η (%)
4
5
6
7
9
350
313
348
360
360
390
420
330
390
420
9200
15 875
26 600
41 335
25 000
18 800
10 900
9810
484
365
413
410-505
520
520
520
520
520
520
0.04
0.02
0.02
10
7975
6380
F igu r e 3. Pt 4f core level spectra of compounds 1, 7, and
9.
polymer 10 showed a lower thermal stability in com-
parison with polymer 9, with a first loss of weight (8%)
at 210 ( 3 °C, exothermic peak. The total combustion
leaves about 45% of material, probably the transition
metal oxide. These experimental data are in agreement
with the expected behavior of Pd-containing polymers
compared with those containing Pt; a higher stability
is achieved when DENA is bonded between two Pt
atoms in the polymer chain.
Absorption and emission spectra of the organometallic
polymers 9 and 10 have been recorded in order to
investigate the influence of the metal centers on the
position of absorption and emission. The results are
collected in Table 2. The UV-vis spectra of the polymers
show broad absorptions at higher wavelength in com-
parison with DENA, with a new tail band at about 420
nm. The maximum of absorption shifts from λ ) 350 to
λ ) 360 and to λ ) 390 nm on going from the monomer
DENA to the Pt dinuclear complex 7 and to polymers 9
and 10, respectively, indicating some enhancement of
effective conjugation through the metal centers by
increasing the chain length; the data concerning com-
plexes 5 and 6, reported in Table 2 as a comparison,
support this statement. It is noteworthy that the values
of the absorption maxima of 9 and 10 are quite similar,
as well as the quantum yields (0.02), thus suggesting
that the emission peaks are not due to d-d transitions
of the metal, but related to the chemical nature of the
organic spacer.
low light emission efficiency of the investigated poly-
mers, despite their π-conjugation characteristics.
XP S In vestiga tion s. The chemical and electronic
structure of the organometallic polymers 9 and 10 was
further investigated by means of XPS. As a comparison
and aid for the assessment of the polymer structure,
XPS measurements were performed on the precursor 4
and related model molecule 7. The C 1s, Pt 4f, Pd 3d, P
2p, Cl 2p, and N 1s core level spectra were acquired,
and a summary of the core level BE and fwhm (full
width at half-maximum) values is reported in Table 3.
The C 1s spectra for all our samples exhibit one main
feature positioned at 284.7 eV on the BE scale assigned
to aromatic carbons (phosphine and DENA). For the
polymer samples the C 1s contribution at lower BE
values is more evident (i.e., about 283.5 eV) due to the
C-M carbons (M ) Pd, Pt), and shake-up features, due
to π-π* transitions associated with the aromatic moiety,
occur at nearly 7 eV higher energy from the main line
for all the samples. The P 2p spectra show binding
energy values in the range 131.1-131.6 eV, consistent
with those measured for metal-bonded phosphine groups,
in agreement with the values reported in the litera-
ture.32
The Pt 4f spectra shown in Figure 3 have been
informative on the effect of the conjugation leading to
charge distribution in the organometallic system. Com-
parison between the BE values of Pt 4f7/2 core level
spin-orbit component, measured for the inorganic
precursor complex cis-[Pt(PTol3)Cl2] (1), the model
complex 7, and the polymer 9, shows values of 72.9, 72.4,
and 72.5 eV, respectively.
The positions of the luminescence maxima are shifted
with respect to the absorption maxima, but there is
however an overlap between the absorption and the
emission spectra, which probably is the reason for the
Ta ble 3. XP S Da ta Collection of Sp ectr oscop ic Da ta for Com p ou n d s 1, 2, 4, 7, 9, 10, a n d p-Nitr oa n ilin e
C 1s BE
(fwhm) (eV)
Pd 3d5/2 BE
(fwhm) (eV)
Pt 4f7/2 BE
(fwhm) (eV))
P 2p3/2 BE
(fwhm) (eV))
Cl 2p3/2 BE
(fwhm) (eV)
sample
N 1s BE (fwhm) (eV)
1
2
284.7 (2.0)
284.7 (1.7)
284.7
72.9 (1.8)
131.6 (2.0)
131.3 (1.9)
197.8 (2.0)
197.9 (1.8)
337.8 (1.7)
p-nitroanilineb
399.4 (-NH2)
405.0 (-NO2)
406.9 (NO2 shake up)
399.3 (2.0) (-NH2)
405.5 (2.0) (-NO2)
399.7 (2.8) (-NH2)
405.1 (4.8) (-NO2)
399.6 (3.2) (-NH2)
406.1 (4.8) (-NO2)
399.4 (2.2) (-NH2)
406.0 (4.2) (-NO2)
4a
7
284.7(2.4)
284.7 (1.8)
284.7 (1.9)
284.7 (1.9)
72.4 (1.9)
131.4 (1.9)
131.3 (1.8)
131.1 (2.0)
9
72.47 (2.0)
198.3c (2.0)
198.0c (2.0)
10
337.9 (1.8)
a
b
Decomposes under X-rays, measurements performed at -95 °C. Data from literature, referred to solid-state measurements (ref 33).
c Ending groups.

2868 Organometallics, Vol. 23, No. 12, 2004
D’Amato et al.
shows the N 1s BE value of NH2 0.5 eV higher than
that of DENA, while an opposite trend on the NO2 group
gives rise to a decrease of the N 1s BE value from 405.5
to 405.1 eV. These data should be considered together
with the changes detected at the platinum site of
complex 1 compared with the dinuclear system 7 (see
Table 3); a BE decrease of Pt 4f from 72.9 to 72.4 eV is
indicative of charge density increase at the metal.
Overall, the charge flows through the system toward
the metal, affecting both the metal center and the
substituents of the organic spacer, becoming more
positively charged (NH2) and more negatively charged
(NO2) (Figure 4). As far as the polymers are concerned,
considering the platinum-containing system 9 we detect
no variations for the nitrogen of the NH2 group, while
the nitro group gives a BE value (406.1 eV) that is
higher than that of sample 7; the BE value found for
platinum shows nearly the same value observed for the
dinuclear sample. Completely similar N 1s BE values
are measured for the palladium-containing polymer 9
(see Table 3), and the Pd 3d5/2 core level does not show
any significant variation compared with the precursor
complex 2. These data suggest that for both polymers
the variations at the organic spacer substituents are
nearly the same. However, there is evidence for a
relatively small charge perturbation on the platinum
site (Table 3, Figure 3); the role of the different transi-
tion metals seems to be detectable, although not dra-
matic. It is noteworthy to point out that there is still a
disagreement in the scientific community on whether
the transition metals favor or inhibit the charge flow
through conjugated bridges, and this topic needs further
studies. Photoelectron spectroscopy measurements pro-
vided information for the characterization of terminal
groups in polymers 9 and 10, which, according to GPC
measurements, have chain lengths corresponding to
about 8-16 repeat units. The analysis of the Cl 2p
spectra identified the presence of chlorine ending groups.
The Cl 2p BE values of the polymers are quite similar,
consistent with chlorine bonded to a metal atom, since
almost the same values are found for the precursor Pt
and Pd complexes reported in Table 3.
F igu r e 4. N 1s core level spectra of compounds 4, 5, 9,
and 10.
The observed trend is indicative of a limited increase
of the charge at the Pt atoms on changing from the
complex to the polymer, correlated to a delocalized
distribution through the organic spacer. In the effective
conjugation length of the rodlike molecules the metal
center is involved in the conjugation through the organo-
metallic system (d and p atomic orbitals of the metal
and π electrons of the organic spacer), although this
effect seems to occur in this case to a lesser extent in
comparison with other reported macromolecules30 that
have a rodlike structure.
As for the palladium-containing molecules, we have
analyzed the polymer 10 and the trans-[Pd(PTol3)Cl2]
(2) complex, and the Pd 3d BE measured values show
strong similarity, being 337.8 and 337.9 eV, respectively.
The observed trend differs from that of the already
discussed Pt systems; the electronic communication that
should occur through the polymeric system seems to be
confined on the organic spacer. Probably the push-pull
substituents of the nitroaniline moiety provoke a dipole
moment that opposes the charge flow along the organo-
metallic chain, and this effect is more evident in the case
of Pd polymer 10.
The N 1s spectra of the investigated samples exhibit
interesting features related to the chemical structure
of the polymers and are shown in Figure 4.
The XPS data provided results in good agreement
with the molecular structures suggested by other tech-
niques used for the chemical characterization and
evidenced the difference in charge distribution depend-
ing on the nature of the transition metal bound to the
same organic spacer, despite the expected same extent
of electron delocalization.
DENA (4), which can be considered the building block
of the polymer backbone, gives a N 1s spectrum with
two mains features, whose BE values are found at 399.3
eV (NH2 group) and 405.5 eV (NO2 group). Ågren et al.33
investigated para-nitroaniline in the solid state and
reported values of 399.4 eV for the amino (NH2), 405.0
eV for the nitro (NO2) groups, and 406.9 eV for the
shake-up features. Our results are in good agreement
with these data, but considering that the N 1s doublet
of NO2 is not resolved, we probably overestimate the
band position for NO2 and attribute this effect also to a
small charge perturbation induced by the triple bond
toward the NO2 group.
Con clu sion s
Organometallic polymers containing Pt and Pd cen-
ters in a square planar configuration linked through 2,6-
diethynyl-4-nitroaniline bridging units, namely, Pt-
DENA and Pd-DENA, were synthesized by the building
block approach. The polymer structure is a sequence of
organic spacers bound to metal centers, likely arranged
in a helical configuration, with chain length correspond-
ing to about 16 repeat units in the case of Pt-DENA and
about 8 repeat units in the case of Pd-DENA. The
polymer structure, which could be elucidated by means
of accurate NMR studies, allows only a moderate charge
delocalization through the metal centers along the
chain, as determined by means of optical and photo-
As the DENA molecule undergoes insertion between
metal complexes, some charge variation at the nitrogens
occurs. The XPS spectrum of the dinuclear complex 7
(32) Beamson, G.; Briggs, D. High-Resolution XPS of Organic
Polymers, the Scienta ESCA300 Database; Wiley: New York, 1992.
(33) A° gren, H.; Roos, B. O.; Bagus, P. S.; Gelius U.; Malmquist, P.
A.; Svensson, S.; Maripuu, R.; Siegbahn K. J . Chem. Phys. 1982, 77,
3893.

Organometallic Pt(II) and Pd(II) Polymers
Organometallics, Vol. 23, No. 12, 2004 2869
electron spectroscopy studies. Model dinuclear Pt com-
plexes were prepared and characterized, with the aim
of comparing the spectral features with those of the
polymers. The results confirm that the repeat unit of
the organometallic macromolecules has the same struc-
ture as the dinuclear complex.
Ack n ow led gm en t. The authors acknowledge the
financial support by MIUR (Ministero dell’Istruzione,
dell’Universita` e della Ricerca Scientifica), Italy COFIN
2002.
OM049972W