Study of chemical structure and conjugation length in organometallic Pt(II) oligomers and polymers containing 1,4-diethynylbenzene derivatives as bridging units

Article abstract of DOI:10.1016/S0022-328X(03)00156-6

The synthesis of platinum containing organometallic rigid rod oligomers and polymers, of general formula-[PtL₂(-C≡C- pC₆H₄(2,5-R)₂-C-C-)]_n, where L=PPh₃, PBu_3; R=H, OC₄H₉ or OC₁₆H₃₃, has been carried out. The multinuclear macromolecules have been prepared by the Stille coupling in the extended one pot version. Oligomers of different chain lengths were obtained and fully characterised by means of spectroscopic techniques. Different organic spacers and precursor metal complexes have been employed in order to study and compare the reaction products. Well-defined oligomers were isolated and X-ray photoelectron spectroscopy technique provided information about the chain length and the nature of the end-groups. Luminescence and absorption studies of the newly synthesised Pt based poly-ynes are also reported. A correlation between the chain length, the nature of ligand phosphines and organic spacers with the optical properties was rationalised. The Pt metal centre played an important role in the conjugation, showing a red shift of absorption maxima upon increasing the number of repeating units. Band gaps of about 2.8-3.0 eV were found, corresponding to blue-light emission with a quantum efficiency up to about 3% for measurements performed in solution.

Full text of DOI:10.1016/S0022-328X(03)00156-6

Journal of Organometallic Chemistry 674 (2003) 10ꢁ23
/
www.elsevier.com/locate/jorganchem
Study of chemical structure and conjugation length in organometallic
Pt(II) oligomers and polymers containing 1,4-diethynylbenzene
derivatives as bridging units
I. Fratoddi a,*, C. Battocchio a, A. Furlani a, P. Mataloni b, G. Polzonetti c,
M.V. Russo a
a Department of Chemistry, University of Rome ‘La Sapienza’, P.le Aldo Moro 5, 00185 Rome, Italy
b Department of Physics, University of Rome ‘La Sapienza’ P.le Aldo Moro 5, 00185 Rome, Italy
c Department of Physics and INFM-INSTM, University of Rome ‘Roma Tre’, Via della Vasca Navale 84, 00146 Rome, Italy
Received 19 December 2002; accepted 10 March 2003
Abstract
The synthesis of platinum containing organometallic rigid rod oligomers and polymers, of general formula*
/
[PtL2(ꢀ
/
Cꢁ
/
Cꢀ
/
pC6H4(2,5-R)2ꢀCꢁCꢀ)]n, where LꢀPPh3, PBu3; RꢀH, OC4H9 or OC16H33, has been carried out. The multinuclear
/
/
/
/
/
macromolecules have been prepared by the Stille coupling in the extended one pot version. Oligomers of different chain lengths
were obtained and fully characterised by means of spectroscopic techniques. Different organic spacers and precursor metal
complexes have been employed in order to study and compare the reaction products. Well-defined oligomers were isolated and X-
ray photoelectron spectroscopy technique provided information about the chain length and the nature of the end-groups.
Luminescence and absorption studies of the newly synthesised Pt based poly-ynes are also reported. A correlation between the chain
length, the nature of ligand phosphines and organic spacers with the optical properties was rationalised. The Pt metal centre played
an important role in the conjugation, showing a red shift of absorption maxima upon increasing the number of repeating units. Band
gaps of about 2.8ꢁ3.0 eV were found, corresponding to blue-light emission with a quantum efficiency up to about 3% for
/
measurements performed in solution.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Platinum poly-yne; Synthesis; Luminescence
1. Introduction
number of interesting properties such as liquid crystal [3]
and third order non-linear optical behaviour [4ꢁ6].
/
Organometallic polymers are recently gaining an
increasing interest in materials science because poly-
meric conjugated materials, containing transition metals
in the main chain or in the pendant groups [1] may
display unique electric, redox and optical behaviour
which make them good candidates for the development
of advanced opto-electronic devices [2].
Moreover, highly ethynylated organometallic polymers
have shown luminescence [7], magnetic [8] electronic
[9,10] properties and their innovative characteristics are
due to a synergy of delocalisation effects of the organic
spacer and mobility of d metal electrons, that give rise to
metal/ligand charge transfer ([11,12]) effects. These
materials offer the opportunity of tailoring their physi-
cal properties by changing the transition metal and/or
the organic spacer, which are the building blocks of
these peculiar polymers [13].
When the metal is bridged between organic conju-
gated spacers such as dialkynes within aromatic moi-
eties, we are in the presence of metalꢁpoly-ynes with a
/
Photoelectron spectroscopy results and theoretical
calculations have shown an overlap between p occupied
orbitals of the organic spacer and empty p or d orbitals
rigid rod conjugated architecture that gives rise to a
of the metal in systems like [LnMꢀ
/
Cꢁ
/
Cꢀ
/
Rꢀ
/
Cꢁ
/
Cꢀ
/
]
x
* Corresponding author.
E-mail address: ilaria.fratoddi@uniroma1.it (I. Fratoddi).
[14,15]. The electronic features of model mononuclear
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00156-6

I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ
/23
11
complexes have been studied and the alkynyl ligands
show a good s and p donor, but low p acceptor
characteristics [16]. As a consequence, only limited
back-donation is expected and poly-ynic structure
show band gaps around 3 eV [17]. In order to enhance
p-conjugation, several research groups choose modified
organic spacers with extended conjugation length, to
decrease the energy of the p* molecular orbital [18] or
introducing a donor atom on the spacer [19,20].
Depending on the ligand, the metal and the organic
spacer, delocalisation throughout the organic moiety
and the metallic centres may be enhanced [21].
From the original synthesis of Hagihara [22], a
number of organometallic polymers containing metals
from groups 8 to 10 have been prepared using more
often square planar or octahedral coordinated precursor
complexes [23,24].
properties of surface acoustic wave sensors based on
some of the materials reported here [36,37] have raised
further interest for their study and synthesis.
2. Results and discussion
2.1. Synthesis
A series of platinum poly-ynes were synthesised,
namely poly-{[2,5-bis(ethynyl)benzene]-trans-bis(tribu-
tylphosphine)platinum(II)} Ptꢁ
{[1,4-bis(ethynyl)-2,5-di(butoxy)benzene]-trans-bis(tri-
butylphosphine)platinum(II)} PtꢁBꢁBOBn(a), poly-
{[1,4-bis(ethynyl)-2,5-di(butoxy)benzene]-trans-bis(tri-
phenylphosphine)platinum(II)} PtꢁPꢁBOBn(a,b),
poly-{1,4-diethynyl-2,5-dihexadecyloxy)benzene-bis(tri-
butylphosphine)platinum(II)} PtꢁBꢁHDOBn(a), and
poly-{1,4-diethynyl-2,5-bis(hexadecyloxy)benzene-bis-
(triphenylphosphine) platinum(II)} PtꢁPꢁHDOBn(a),
where n indicates the number of platinum atoms in the
chain (nꢀ2ꢁ80), and a or b the synthetic path. The
/
Bꢁ/DEBn(a,b), poly-
/
/
/
/
A different synthetic approach was developed by
Lewis and co-workers [25], and series of platinum
poly-ynes have been synthesised by this way by varying
the organic spacer, i.e. benzene, fluorene, thiophene etc.
[26,27]. The influence of the organic spacer is reflected in
the lowering of the band gap [28], while the role of the
/
/
/
/
/
/
molecular structures are depicted in Fig. 1.
heavy metal seems to be related to a spinꢁorbit coupling
/
The diethynylbenzene (DEB) monomer, already used
by Hagihara was chosen as reference and the corre-
sponding 2,5-disubstituted diethynylbenzenes, i.e. 1,4-
diethynyl-2,5-bis(hexadecyloxy)benzene (BOB) and 1,4-
diethynyl-2,5-bis(hexadecyloxy)benzene (HDOB) were
used as organic spacers in order to study the effect of
that gives rise to efficient intersystem crossing and
luminescence phenomena [29].
An alternative way to form carbonꢁ
/
carbon or metalꢁ
/
carbon bonds is the versatile Stille [30,31] reaction. In
this framework we studied an extension of the Stille
coupling reaction based on a one pot procedure, recently
reported for poly(arylene-ethynylene) and polymetal-
la(arylene-ethynylene) copolymers [32,33]. In this study
we applied the extended one pot (EOP) procedure to
form metalꢁ/carbon bonds. It was demonstrated that
also metalꢁiodide functionality can give rise to the
/
formation of new bonds by coupling with stannane-
acetylides [34,35] and now we applied the reaction to a
metalꢁchloride functionality coupling with in situ dis-
/
tannane-protected diethynyl organic spacers.
With this aim, derivatives of 1,4-diethynilbenzene
with aliphatic substituents R in position 2,5 on the
aromatic ring were synthesised and the results are
reported in this paper. Different aliphatic chains (Rꢀ
/
ꢀ
/
OC4H9, ꢀOC16H33) were introduced in order to
/
optimise the solubility and processability of the reaction
products. The organic spacers were co-polymerised with
square planar platinum complexes containing tributyl or
triphenylphosphine as ancillary ligands.
The Hagihara-type dehydrohalogenation reaction was
carried out between some of the organic spacers and
metallic complexes in order to compare the two
synthetic procedures.
Luminescence and X-ray photoelectron spectroscopy
(XPS) characterisations were carried out in order to
well-define the emission properties and the effective
chain length. Preliminary investigations on the sensing
Fig. 1. Chemical structures of Ptꢁpoly-ynes.
/

12
I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ23
/
both the presence and elongation of the oxyalkyl chains
on solubility and reactivity.
sponding (bis)trialkyltinethynyl derivatives. The mixture
changed colour with a little darkening. 3rd step) the
metaldichloride complex PtL2Cl2 is subsequently added
to this reaction mixture and formation of the polymer
takes place by the palladium-catalysed coupling between
Two synthetic pathways were compared for Ptꢁ
/
Bꢁ
/
DEBn and PtꢁPꢁBOBn, i.e. dehydrohalogenation (b)
/
/
and the EOP modification of the Stille coupling reaction
(a) In the dehydrohalogenation route terminal alkynes
need to be prepared and isolated, before the reaction
with PtL2Cl2 complexes, whereas in the EOP coupling,
aromatic diiodides can be the reaction precursors. The
conventional Stille reaction is based on a coupling, in
the presence of palladium, between electrophiles and
organotin reagents. Herein, we report this synthetic
procedure where three consecutive steps were cumulated
(see Fig. 2): 1st step) the coupling between an organic
diiodide and tributyl(ethynyl)tin, is carried out in order
to obtain an organic dialkyne and the iodotributyltin
side-product. The coupling is carried out by overnight
stirring the reaction mixture in THF at 70 8C. The
the Mꢀ
/
Cl and Bu3Snꢀ
/
Cꢁ
/
Cꢀ
/
moieties.
DEBn(b) a polymeric compound
In the case of Ptꢁ
/
Bꢁ
/
was obtained by the dehydrohalogenation method from
DEB and trans-[Pt(PBu3)2Cl2] as confirmed by gel
permeation chromatography (GPC) measurements
(n $
the aromatic region was found at dꢀ
the tributyl chains on the phosphinic ligand showed
/
80 repeating units). The 1H-NMR resonance of
7.07 ppm, whereas
/
multiplets at dꢀ2.09, 1.57, 1.41 ppm (CH2) and 0.89
/
(CH3). The main resonance in the 31P-NMR spectra was
assessed to phosphorus atoms bonded to internal
platinum units, at dꢀ3.50 ppm. The coupling constant
/
J(195Ptꢁ31
metal (ꢀ
/
P) was typical of a trans geometry around the
2360 Hz) [38]. In order to compare the two
mixture slowly turned from colourless to brownꢁ
/
/
orange. 2nd step) a stoichiometric amount of lithium-
diisopropylamide (LDA) is directly added to this reac-
tion mixture, previously cooled at 0 8C. This provokes
the removal of the acetylenic proton from the terminal
acetylenic functionalities and their immediate recombi-
nation with the Bu3SnI with formation of the corre-
reaction paths, the Stille EOP coupling was carried out
on the same precursors, and the formation of a main
coupling product was observed, i.e. the trinuclear
compound Ptꢁ
NMR resonances at dꢀ
intensity ratio 1:2. The formation of a trinuclear
/
Bꢁ
/
DEB3(a), which showed two 31P-
3.50 and 0.76 ppm with
/
Fig. 2. Synthetic pathways: method (a) EOP Stille coupling and (b) dehydrohalogenation reaction.

I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ
/23
13
1
compound could be assessed, as confirmed also by
elemental analyses.
were isolated. The H-NMR spectra showed resonances
of the organic spacers and of the ancillary phosphines at
the same values of the already reported compounds. For
The studies on the two reaction methods have been
extended to the reactivity of BOB monomer, by
introducing alkoxyalkyl pending chains on the aromatic
spacer and the chemical structure of the metal moiety by
using cis-[Pt(PPh3)2Cl2]. In this reaction (EOP path-
way), the crude product obtained was a red oil, which
was chromatographated to separate the oligomers. Two
main products were isolated, i.e. dinuclear and tetra-
nuclear compounds with terminal stannane groups, as
XPS measurements and elemental analyses let us to
Ptꢁ
31P-NMR, centred at dꢀ
BOB3(a) and PtꢁBꢁBOB4(a) terminal and internal
/
Bꢁ
/
BOB2(a), a single resonance was observed in the
/
0.92 ppm, whereas in PtꢁBꢁ
/
/
/
/
phosphines were assessed to the signals at about 0.90
and 1.00 ppm, respectively, with intensity ratios 2:1 and
1:1.
Reactions in the same experimental conditions, per-
formed using the same Pt precursor complex with
HDOB monomer, gave the Ptꢁ
materials. The 31P-NMR spectra of Ptꢁ
showed two resonances centred at dꢀ0.90 (terminal)
and 0.99 (internal) ppm (JPtꢀP 2300 and 2311 Hz,
/
Bꢁ/HDOBn(a) based
assess. Ptꢁ
the 1H-NMR spectra, the singlet of the aromatic
protons at dꢀ6.56 ppm, and the ꢀOCH2ꢀ triplet at
3.75 ppm. The resonances arising from the aliphatic
region were centred at dꢀ2.09, 1.59, 1.35 (CH2) and
0.90 (CH3) ppm, as unresolved multiplets. In the case of
PtꢁPꢁ
BOB4(a), two 31P-NMR resonances were ob-
served, at dꢀ18.07 and 17.67 ppm with intensity ratio
/
Pꢁ
/
BOB2(a) and Ptꢁ
/
Pꢁ/BOB4(a), showed in
/
BꢁHDOB4(a)
/
/
/
/
/
ꢀ
/
respectively), both due to the tributylphosphines bonded
to platinum in a trans configuration. The two reso-
nances are in 1:1 ratio as expected for a tetranuclear
compound.
/
/
/
/
Ptꢁ
/
Bꢁ
/
HDOB7(a) also showed two signals in the 31P-
0.90
1:1, confirming the formation of a tetranuclear com-
pound. Trans geometry around the metal was assessed
NMR spectra, with the intensity ratio 2:5, (at dꢀ
/
and 1.00 ppm). In this case the molecular structure is
consistent with an heptanuclear compound.
When the ancillary ligand on Pt was PPh3, we
from the value of the coupling constant J(195Ptꢁ31
/
P) of
about 2600 Hz, typical of a trans geometry in diacety-
lyde-platinum complexes [39]. A cis ꢁtrans isomerisation
/
observed the formation of a red oil (Ptꢁ
Only one signal in the 31P-NMR spectrum was observed
for PtꢁPꢁHDOBn(a) (centred at dꢀ18 ppm) due to
internal phosphorus atoms of a polymeric compound.
This hypothesis was confirmed by GPC (n $20) and
elemental analysis (see Section 4).
Comparing these results with those relative to the
compounds obtained from the BOB spacer, we observed
the formation of products with longer chain length. The
influence of longer alkoxy chains on the aromatic
spacer, improves the solubility of the as-formed cou-
pling products and make them more suitable for further
couplings.
/
Pꢁ
/
HDOBn(a)).
occurred around the Pt centre, that is expected beha-
viour of cis-[Pt(PPh3)2Cl2] reacting with acetylenes [40].
An oligomeric compound containing about 12 repeat-
/
/
/
ing units (Ptꢁ
/
PꢁBOBn(b)) was obtained in the case of
/
/
the dehydrohalogenation reaction on the same precur-
sors, as suggested from the 31P-NMR signals intensity
ratio. In fact, two main signals were found as in the
previously described compound, at about 18.2 and 17.7
ppm, with intensity ratio 5:1.
In the case of DEB and BOB organic spacers, the two
methods exhibit a marked difference in reactivity that is
a preferential yield in long chain polymer formation in
the dehydrohalogenation route, while multinuclear Pt
complexes are the main products of the EOP synthetic
The GPC analysis carried out on our polymeric
materials (Ptꢁ
/
Pꢁ
/
BOBn(b), Ptꢁ
/
Pꢁ
/
HDOBn(a), Ptꢁ
/
Bꢁ
/
procedure. The different length of Ptꢁ
/
Bꢁ/DEBn(b) and
DEBn(b)) underestimates the molecular weight. In fact
previously reported measurements carried out on Ni-
arylenes [42], showed that the polystyrene standard, a
random coil material, significatively differs from the
rigid rod structure of the materials under study. A rough
scale up of our GPG molecular weights was possible by
the following approach. In Table 2 the GPC measure-
ments of the organometallic compounds are compared
with the values obtained for the precursor complexes
trans-[Pt(PBu3)2Cl2] and cis-[Pt(PPh3)2Cl2]. GPC results
PtꢁPꢁBOBn(b) (nꢀ80 and 12, respectively) is probably
/
/
/
due to the different phosphinic ligand that affect the
solubility of the growing chain. As a general rule, PBu3
ligand enhance the solubility of the metal complex units
of the polymer.
The synthesis of p-conjugated oligomers of well-
defined chemical structure is actually of interest, in
view of the dramatic increase of research devoted to the
synthesis of materials in the nano-scale for the new
frontier of molecular electronics [41]. On the basis of our
preliminary results, the studies with EOP synthetic
method have been extended to BOB and HDOB
monomers and Pt complexes.
gave Mwꢀ
/
312 (Mnꢀ
/
310) and Mwꢀ
/
360 (Mnꢀ320),
/
respectively, while the calculated molecular weights are
664.0 and 784.0 a.m.u. On the basis of these compar-
isons, the reported values of Mw and Mn are expected to
underestimate of about one half the real molecular
weights of our compounds.
In the case of Ptꢁ
/
BꢁBOBn(a) based materials, the
/
EOP method gave rise to oligomeric coupling products
and dinuclear, trinuclear and tetranuclear compounds

14
I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ23
/
Table 1
Chemical and spectroscopic characterization of Ptꢁ
31P-NMR a
d (ppm) J(31Pꢀ
/
poly-ynes
Sample
Elemental analyses
IR (film) (cmꢂ1
)
Formula
C%
H%
(C% calc.)
(H% calc.)
/
195Pt) (Hz)
n (CꢁC) n (Ptꢀ
/
/
Cl)
n (CꢀSn)
/
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
Ptꢁ
/
Bꢁ
Bꢁ
Bꢁ
Bꢁ
Bꢁ
Pꢁ
Pꢁ
Bꢁ
Bꢁ
Pꢁ
Pꢁ
/
DEB3(a)
DEBn(b)
BOB2(a)
BOB3(a)
BOB4(a)
51.71
8.17
(52.16)
(8.09)
3.50
0.76
(2362)
(2303)
2104
2100
2104
2106
2104
2104
2104
2104
2109
2099
2106
328
C92H170P6Pt3Cl2
/
/
56.15
8.54
(56.42)
(8.08)
3.50
(2361)
C34H58 P2Pt
/
/
51.58
8.49
(51.52)
(8.38)
0.92
(2313)
326
328
C66H128O2P4Pt2Cl2
C156H249O6P6Pt3SnCl
C210H370O10P8Pt4Sn2
C150H174O6P4Pt2Sn2
C258H274O10P8Pt4Sn2
C222H420O6P8Pt4Cl2
C420H786O12P14Pt7Cl2
C54H50O2P2Pt
/
/
56.79
8.50
(56.58)
(8.57)
0.91
0.99
(2316)
(2314)
525
540
/
/
58.98
8.52
(58.38)
(8.63)
0.94
1.01
(2316)
(2314)
525
533
/
/BOB2(a)
63.00
5.60
(63.78)
(6.20)
12.00
(3454)
525
540
/
/BOB4(a)
63.95
5.74
(64.55)
(5.75)
18.07
17.67
(2654)
(2610)
528
540
/
/
HDOB4(a)
HDOB7(a)
BOBn(b)
63.00
9.70
(62.23)
(9.88)
0.90
0.99
(2300)
(2311)
327
327
/
/
64.02
9.91
(63.86)
(10.03)
0.90
1.00
(2300)
(2311)
/
/
66.12
5.13
(65.64)
(5.10)
18.18
17.67
(2682)
(2610)
/
/HDOBn(a)
71.20
7.31
(70.72)
(7.46)
18.00
(2595)
C78H78O2P2Pt
a
31P-NMR spectra (in CDCl3) are referred to H3PO4 85%.
Ptꢁ
and Ptꢁ
length (2ꢁ
/
Bꢁ
/
BOBn(a), Ptꢁ
PꢁHDOBn(a) oligomers of different chain
7 units) were investigated by absorption
/
Pꢁ
/
BOBn(a), Ptꢁ
/
Bꢁ
/
HDOBn(a)
Table 2
Molecular weights of Ptꢁ
/
poly-ynes determined by GPC
/
/
/
a
Sample
Mw
Mn
n
Repeating unit b (pm)
spectroscopy and experimental data are collected in
Table 3. Spectra recorded both in solution or thin solid
films, showed similar absorption maxima and shapes
indicating negligible complex/solvent interaction.
The spectra of organometallic compounds displayed
[PtCl2(Pbu3)2]
[PtCl2(PPh3)2]
312
360
310
320
C24H54Cl2P2Pt (664.00)
C36H30Cl2P2Pt (784.00)
25 C34H58P2Pt (723.85)
C54H50O2P2Pt (988.00)
Pt-Bꢁ
PtꢁPꢁ
PtꢁPꢁ
/
DEBn(b)
BOBn(b)
HDOBn(a) 26700 15800 20ꢁ
57000 18000 80ꢁ
7700 3200 8ꢁ
/
/
/
/
3
/
/
/12 C78H98O2P2Pt (1324.64)
pꢁp* absorption bands red shifted with respect to the
/
a
n, number of r.u.
Calculated molecular weight of r.u.
organic monomeric precursors, and the red shift in-
creased by increasing the number of repeating units
going from about 360 to 390 nm, as shown in Fig. 3. The
oligomers showed a bathocromic shift absorption
(nearly 40 nm) by comparison with the absorption
b
2.2. Optical absorption and emission studies
A growing interest in different research areas has risen
for the use of organic materials as active layers in
luminescence based devices. The use of conjugated
polymers was deeply investigated for the advantages of
ease of fabrication and low cost, but the number of
materials effectively used is still limited. In fact solubility
and high luminescence efficiency, required for practical
applications, are usually very difficult to achieve.
Photoluminescence (PL) and electroluminescence
(EL) studies give information about the nature of the
excited states [43], a basis for the interpretation of the
behaviour of EL devices.
maxima of BOB (lꢀ
/
335.2 nm) and HDOB (lꢀ332.6
/
nm). This effect is indicative of an electronic delocalisa-
tion occurring through the Pt centres, involving a
contact between the p orbitals of the organic conjugated
spacer with the Pt 5d and 6p orbitals as discussed by
Lewis and co-workers [44]. A further evaluation of the
delocalisation effect can be estimated from the IR n(Cꢁ
/
Q
C) stretching modes [45]. -delocalisation
C) and n(Mꢀ
/
induces a structural variation from alkyne to allene that
can be revealed by a shift towards lower frequency for
the n(Cꢁ
/
C) and to higher frequency for the n(Mꢀ
/
C)

I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ
/23
15
Table 3
Optical characterization of Ptꢁ
/
poly-ynes: UVꢁvis and luminescence in CHCl3 solution or thin film
/
Sample
labs max. (nm)
o0 (l molꢂ1 cmꢂ1
)
Eg (eV)
lem max. (nm)
h (%)
Solution
Film
Solution
Film
Solution
Film
Ptꢁ
/
Bꢁ
Bꢁ/
/
BOB2(a)
368.0
377.0
365.4
371.8
2.03ꢃ
/
104
104
3.20
2.80
3.20
2.75
470.0
465.0
445.0
440.0
440.0
0.25
0.35
Ptꢁ
/
BOB3 (a)
7.64ꢃ
/
Ptꢁ
/
Bꢁ/BOB4(a)
389.0
387.2
1.41ꢃ
/
105
2.75
2.25
470.0
440.0
425.0
0.85
Ptꢁ
/
Pꢁ
Pꢁ/
/
BOB2(a)
389.0
396.0
387.8
398.2
a
1.96ꢃ
/
104
104
2.90
2.80
2.80
2.75
a
470.0
460.0
440.0
440.0
a
0.11
0.30
Ptꢁ
/
BOB4(a)
3.46ꢃ
/
Ptꢁ
/
Bꢁ/
HDOB4(a)
377.0
5.30ꢃ
/
104
2.95
450.0
427.0
2.33
Ptꢁ
/
Bꢁ/HDOB7(a)
380.0
376.4
6.38ꢃ
/
105
2.90
2.30
460.0
430.0
440.0
420.0
3.16
a
The complex exhibits films of poor optical quality.
stretching modes. In our case a value of about 2100
cmꢂ1 was found for n(Cꢁ
C) in all the investigated
materials, lowered with respect to the organic monomers
by about 40 cmꢂ1. This trend can be associated with the
presence of a higher conjugation degree in the coupled
products.
These observations may be correlated with the pre-
sence of the valence shell orbitals of the transition metal
conjugated with the p-system of the organic spacers, as
theoretically expected [46]. According to literature
report [47], the absorption peak may be associated
observed. However, it is noteworthy that the Eg values
decreased by increasing the number of platinum units.
Eg values similar were found for oligomers of the same
chain length, by varying the aliphatic chains on the
organic spacer or the phosphine ligands. The variation
of the ancillary phosphines on the metal and of the
aliphatic chains does not significantly affect the energy
of HOMO and LUMO molecular orbitals, as expected.
Luminescence spectra were recorded for solutions and
thin films, and relative quantum yields h were calcu-
lated. In analogy with absorption spectra, luminescence
features of films and solutions showed strong simila-
/
with the S00
/
S1 transition from the highest occupied
rities. The luminescence of our materials is in the blueꢁ
green region of the visible spectrum, with peaks ranging
from lem 430ꢁ470 nm (see Table 3). The emission
features are shifted to longer wave-lengths on going
from monomers (lem 392 (HDOB) and 387 nm
/
molecular orbital (HOMO) to the lowest unoccupied
molecular orbital (LUMO), which are delocalised p and
p* orbitals.
ꢀ
/
/
The HOMOꢁ
from the absorbance vs. eV spectra, recorded for both
solution and thin film samples. Values in the range 2.8ꢁ
3.2 eV, in analogy with literature data [48], were
/LUMO energy gap Eg was estimated
ꢀ
/
/
(BOB)) to multinuclear compounds and a rise of h
with increasing the molecular weight was observed. The
Fig. 3. UVꢁ
/
vis absorption spectra of Ptꢁ
/
BꢁBOB2-3-4 in CHCl3 solution.
/

16
I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ23
/
Fig. 4. UVꢁ
/
vis absorption and emission spectra of Ptꢁ
/
Bꢁ/
HDOB4 and Ptꢁ
/
BꢁHDOB7 in CHCl3 solution.
/
well-resolved spectra exhibited two peaks, while broad
emission features were found in some cases (Table 3).
2.3. X-ray photoelectron spectroscopy
The actual interest in oligomers, which exhibit most of
the relevant properties of the corresponding polymers,
prompted us to investigate in depth the electronic
structure of our Pt-based oligomers with BOB and
HDOB organic spacers by means of XPS technique.
The C1s, O1s, Pt4f, P2p, Cl2p and Sn3d core level
spectra of the oligomers of different length were
acquired and a summary of the core level binding
energies (BE) and full width at half maximum
(FWHM) values is reported in Table 4.
The peak at lower wave-length (ꢀ
to the emission due to a singlet excited state (S1ꢁ
fluorescence) and the second one (ca. 470 nm) to the
emission from a triplet excited state (T1ꢁS0 phosphor-
/
440 nm) is assigned
/S0
/
escence) in agreement with the literature [49]. A method
to ascertain the attribution of emission features (fluo-
rescence and phosphorescence) was developed by che-
mical doping of our materials with molecular iodine. In
analogy with other p-conjugated materials, a redox-
based charge transfer reaction may affect the pꢁp*
/
The C1s spectra of all our samples appeared struc-
tured and could be deconvoluted by curve fitting into
three individual peaks assigning the main feature at
electronic transition [50], with formation of a polyiodide
molecule according to the reaction reported as an
example: 3I2ꢄ
2I3ꢂ. In our case the reaction with I2 led to a quenching
of the fluorescence peak (S1ꢁS0) at about lem 430 nm,
whereas the phosphorescence peak at about lem 450
/
2Ptꢁ
/
Bꢁ
/
HDOB40
/
2Ptꢁ
/
Bꢁ
/
HDOB4ꢄꢄ
/
BEꢀ/285.0 eV to aromatic carbon (triphenylphosphine
containing samples) or the peak at BEꢀ/284.7 eV to the
/
ꢀ
/
carbons of tributylphosphine based compounds. The
asymmetries in the C1s peak are due to the carbons
ꢀ
/
nm remained unchanged. In order to unambiguously
attribute these peaks, measurements of half lifetime of
the excited states by means of time-resolved measure-
ments will be performed.
The emission spectra, measured in solution, of the
oligomers showed an increase of quantum yield by
increasing the number of Pt centres (Table 3). Oligomers
bonded to less electronegative atoms (ꢁ
and to carbon atoms bound to oxygen (Cꢀ
oligomers. As an example the C1s signal of Ptꢁ
HDOB7(a) is reported in Fig. 5a, where the main C1s
peak is found at BEꢀ285.0 eV, the CꢀPt signal at 283.7
eV and CꢀO at BEꢀ286.4 eV.
/
Cꢀ
O), in all the
Bꢁ
/
Pt, Cꢀ
/
Sn),
/
/
/
/
/
/
/
Ptꢁ
longer aliphatic chain (OC16H33), showed higher emis-
sion intensity and relative quantum yield (3.16% for Ptꢁ
BꢁHDOB7(a)) in comparison with the same oligomers
with BOB spacer (shorter aliphatic chain OC4H9). In
Fig. 4 luminescence and absorption spectra of PtꢁBꢁ
HDOB4(a) and PtꢁBꢁHDOB7(a) are reported. As it
can be seen, a difference between absorption and
emission maxima of about 70ꢁ80 nm was found and
the highest quantum efficiency was observed in PtꢁBꢁ
/
Bꢁ
/
HDOBn(a), which have the organic spacer with
The P2p spectra show binding energy values of about
131.0 eV consistent with those measured for metal-
bonded phosphine groups, in agreement with the values
reported in the literature [51].
The analysis of Pt4f spectra provided some useful
information on the effect of the conjugation length of
the organometallic system on the charge distribution.
The BE values of the Pt4f7/2 component of different
oligomers and of the inorganic starting complexes were
compared in order to find a correlation between the
position of the Pt4f7/2 peak and the length of the rod-like
molecule. From the observed trend of the data (see
/
/
/
/
/
/
/
/
/
HDOB7(a) sample, suggesting a role, not obvious, of
the ancillary ligand phosphines.

I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ
/23
17
Table 4
XPS measurements of Ptꢁ
/
poly-ynes: BE values for core levels and atomic ratios (in parenthesis calculated ratios)
Pt4f7/2 BE (eV) P2p3/2 BE (eV) Cl2p3/2 BE (eV) Sn3d5/2 BE (eV) n8 Cl/Pt
Sample
C1s
n8 Sn/Pt
BE (eV) FWHM
Exp. (Calc.) Exp. (Calc.)
Ptꢁ
/
Bꢁ
/
BOB2(a)
BOB3(a)
BOB4(a)
285.0
283.5
286.7
1.82
1.77
1.82
1.86
1.87
1.70
1.80
72.3
72.5
72.1
72.4
72.1
72.6
72.1
131.0
131.1
130.8
131.3
131.6
131.4
131.1
199.2
199.3
0.89 (1.0)
Ptꢁ
/
Bꢁ/
285.0
283.5
286.5
486.9
486.1
486.3
486.5
0.28 (0.33) 0.38
(0.33)
(0.5)
(1.0)
(0.5)
Ptꢁ
/
Bꢁ/
285.0
283.3
286.5
0.48
Ptꢁ
/
Pꢁ
/
BOB2(a)
284.7
283.4
286.2
0.97
0.41
Ptꢁ
/
Pꢁ/
BOB4(a)
284.7
283.1
286.2
Ptꢁ
/
Bꢁ/
HDOB4(a) 285.0
283.3
286.4
199.2
199.3
0.46 (0.5)
Ptꢁ
/
Bꢁ/
HDOB7(a) 285.0
283.7
286.4
0.28
(0.29)
[Pt(PPh3)Cl2]
[Pt(PBu3)Cl2]
284.7
285.0
73.3
73.4
131.3
131.8
198.4
199.1
Table 4), it comes out that the transition metal favours
the conjugation through the organometallic system. The
d and p atomic orbitals of the metal are, at least in part,
involved in the delocalisation of p electrons of the
organic spacers. In fact, the Pt4f7/2 binding energy in the
precursor square planar complexes trans-[Pt(PBu3)2Cl2]
and cis-[Pt(PPh3)2Cl2] are 73.4 and 73.3 eV, respectively,
as already reported in the literature [52]; while the lower
BE values measured in our samples indicated that Pt
atoms have an increased electron density. However, the
2ꢁ7) are relatively close to each other, suggesting a
charge distribution that tends to an average extent (Fig.
5b).
/
Photoelectron spectroscopy measurements provided
useful information for a complete characterisation of
terminal groups of the here investigated multinuclear
oligomers. The analysis of the Cl2p and Sn3d spectra
allowed to identify the chloride or SnBu3 ending groups;
in fact from the synthetic pathway showed in Fig. 2, it is
possible to obtain compounds with terminal chloride or
SnBu3 moieties.
Pt4f7/2 BE values for oligomers of different length (nꢀ
/
Fig. 5. C1s and Pt 4f core level spectra of Ptꢁ
/
BꢁHDOB7.
/

18
I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ23
/
The Cl2p BE values for Ptꢁ
BOBn(a) were found in the range 198.0ꢁ
/
Bꢁ
/
HDOBn(a) and Ptꢁ
/
Pꢁ
/
carbon atoms bonded to platinum and to oxygen (Table
4), as already discussed.
/199.0 eV,
consistent with chlorine bonded to a metal atom; similar
values have been reported for Pt-complexes [53,54]. The
presence of SnBu3 terminal groups was also stated by
the analysis of the Sn3d5/2 XPS signal with a BE value at
486.5 eV. This signal is attributed to a Sn atom bonded
The Pt4f7/2 main signal of Ptꢁ
/
BꢁHDOB4(a) was
/
centred at 72.6 eV, shifted of about 0.8 eV to the low
BE side from the corresponding signal found for the
trans-[Pt(PBu3)2Cl2] precursor (see Table 4). This in-
creased charge density at the Pt atoms indicates the
occurrence of electron communication throughout the
metal and the organic spacers.
only to carbon atoms [55], as expected for ꢀ
/
Cꢁ
/
Cꢀ
/
SnBu3 moieties.
The P2p3/2 signal found at 131.4 eV, appears un-
modified with respect to the pristine complex, and with a
Pt/P ratio of 0.5 as expected.
The evaluation of Pt/Cl and Pt/Sn atomic ratios was
fundamental in the assessment of the chemical structure
of the systems, the presence of these elements being
strictly connected to the terminal groups, and therefore
giving a reasonable estimate of the number of Pt(pho-
sphine)2 units in the chains, then yielding the oligomers
length.
The C1s signal of Ptꢁ
deconvoluted into three components, at 285.0, 283.7 and
286.4 eV, respectively, due to CꢀC, CꢀPt and Cꢀ
contributions (Fig. 5a). The Pt4f signal was found at
/
BꢁHDOB7(a) sample can be
/
/
/
/O
7/2
72.1 eV, shifted by about 1.3 eV from the starting
platinum complex, indicating an enhanced electronic
charge transfer from the organic spacer to the Pt centre.
Evaluation of the Cl/Pt intensity ratio that is 0.28, leads
to the assessment of a molecular structure correspond-
ing to an heptanuclear complex, result that is also
supported by the elemental analyses and 31P-NMR
results.
The XPS data provided results in good agreement
with the molecular structures suggested by other tech-
niques, i.e. 31P-NMR and elemental analysis. IR spec-
troscopy also confirmed the nature of ending groups,
showing the Ptꢀ
/
Cl stretching mode at about 340 cmꢂ1
in those oligomers where appreciable chlorine XPS
Sn stretching modes at 525
signal was found, and Cꢀ
/
and 540 cmꢂ1 in those samples having XPS Sn3d signal.
Hereafter, the most significative results concerning
Ptꢁ
/
Bꢁ
/
HDOB4(a) and Ptꢁ
/
BꢁHDOB7(a) will be dis-
/
cussed, as these macromolecules are representative of
different series and show the best optical properties. The
3. Summary
analysis of Ptꢁ
/
BꢁHDOBn(a) materials showed the
/
presence of chlorine terminal groups. In this case the
presence of chlorine atoms was observed at BE value
Highly ethynylated polynuclear Pt(II) complexes,
with metal centres linked through 1,4-diethynyl-2,5
alkoxyalkyl benzenes have been synthesised by using
the EOP route. Organometallic oligomers with variable
chain length and terminal groups have been charac-
terised with XPS and NMR investigations. The presence
of Cl or SnBu3 ending groups represents a chance to
prepare materials with tailored chain length by applying
the building block approach, as an extension of this
research. The dehydrohalogenation route, performed by
comparison in few cases, leads to polymeric materials.
199.2 eV typical of a Clꢀ
IR spectrum, where the Ptꢀ
found at 327 cmꢂ1. Evaluation of the XPS atomic ratios
/Pt moiety, as confirmed also by
/Cl stretching band was
(Cl/Ptꢀ0.46), comparison with elemental analyses re-
/
sults and 31P-NMR spectra, allow to conclude that the
chemical structure of this compound is corresponding to
a tetranuclear complex, as depicted in Fig. 6.
The C1s signal of the aliphatic carbon atoms was
calibrated at 285.0 eV, showed asymmetries arising from
Fig. 6. Chemical structure of Ptꢁ
/
BꢁHDOB7.
/

I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ
/23
19
The correlation between chemical structures and
optical characteristics was assessed. Absorption spectra
and luminescence quantum yields were correlated with
the chain length, the nature of organic spacers and
ancillary phosphines. Longer chains show red shift of
the absorption maxima, and longer alkyl groups en-
hance the photoemission of the materials. Enhancement
of charge density of the Pt atoms, flowing from the
organic spacers, was also detected by XPS measure-
ments, suggesting electron communication along the
molecular backbone.
CHCl3 (HPLC grade), using monodisperse polystyrene
standards at 25 8C, flow rate 1 ml minꢂ1
Elemental analyses were performed at the Depart-
ment of Chemistry, University of Rome ‘La Sapienza’.
XPS spectra were obtained using a custom designed
.
spectrometer. A nonmonochromatised Mgꢁ
source (1253.6 eV) was used and the pressure in the
instrument was maintained at 1ꢃ
10ꢂ9 Torr throughout
/
Ka X-rays
/
the analysis. The experimental apparatus consists of an
analysis chamber and a preparation chamber separated
by a gate valve. An electrostatic hemispherical analyser
(radius 150 mm) operating in the fixed analyser trans-
mission mode and a 16-channel detector were used. The
film samples were prepared by dissolving our materials
in CHCl3 and spinning the solutions onto polished
stainless steel substrates. The samples showed good
stability during the XPS analysis, preserving the same
spectral features and chemical composition. BE were
corrected by adjusting the position of the C1s peak to
285.0 eV in those samples containing mainly aliphatic
carbons and to 284.7 eV in those containing more
aromatic carbon atoms, in agreement with literature
data [57].
4. Experimental
4.1. General procedures
FTIR spectra were recorded as nujol mulls by using
CsI cells, on a PerkinꢁElmer 1700X Fourier Transform
/
spectrometer. Multiple internal reflection spectra were
performed by the same spectrometer as films deposited
by CHCl3 solutions on a TlI crystal recording the
1
spectra at 608. H and 31P-NMR spectra were recorded
The C1s, O1s, Pt4f, P2p, Cl2p and Sn3d spectra were
deconvoluted into their individual peaks using the Peak
Fit curve fitting program for PC.
on a Bruker AC 300P spectrometer at 300 and 121
MHz, respectively, in appropriate solvents (CDCl3,
C6D6); the chemical shifts (ppm) were referenced to
Quantitative evaluation of the atomic ratios was
obtained by analysis of the XPS signal intensity,
employing Scofield’s atomic cross-section values [58]
and experimentally determined sensitivity factors.
All reactions were performed under an inert argon
atmosphere using standard Schlenk glassware. Solvents
were freshly degassed, dried by standard procedures and
saturated with argon before use. Chromatographic
1
1
TMS for H-NMR assigning the residual H impurity
signal in the solvent at 7.24 ppm (CDCl3). The 31P-
NMR chemical shifts are relative to H3PO4 (85%). UVꢁ
vis spectra were recorded on Perkin-Elmer Lambda 16
instrument. PL spectra were performed on a Perkinꢁ
/
/
Elmer LS 50 Fluorescence Spectrometer. All measure-
ments were performed at room temperature using
quantitative solutions of the oligomers in CHCl3 or
thin films spin casted onto glass substrates by a
commercial spinner. The molar extinction coefficient oo
(with respect to the repeating unit) and the relative
quantum yield h of both chloroform solutions and thin
films were also determined. We adopted as the standard
separations were obtained with 70ꢁ230 mesh alumine
/
(Merck), by using the appropriate eluents. The com-
pounds 1,4-diiodo-2,5-bis(butyloxy)benzene and 1,4-
diiodo-2,5-bis(hexadecyloxy) benzene were prepared by
using the method described by Li [59] and used to
prepare in situ the organic spacers 1,4-diethynyl-2,5-
bis(butyloxy)benzene (BOB) and 1,4-diethynyl-2,5-
bis(hexadecyloxy)benzene (HDOB). DEB was prepared
by following a literature method [60]. Platinum com-
plexes cis-[dichlorobis(triphenylphosphine)platinum(II)]
and trans-[dichlorobis(tributylphosphine)platinum(II)]
were prepared by reported methods [61].
a solution of coumarine in ethanol (cꢀ
with a quantum yield equal to 51%, calculated by
comparison with a rhodamine 6G solution (cꢀ0.016 g
lꢂ1, hꢀ
90%) [56] as described below.
/
0.0028 g lꢂ1),
/
/
Quantitative solutions of coumarine and of oligomers
were prepared on purpose, with the same absorbance at
the excitation wavelength lmax
quantum yields were calculated from the measurements
ꢀ350 nm. The relative
/
4.2. Synthesis: general preparation of metal poly-ynes*
/
of the emission intensities of the sample and of the
standard, considering the relationship: hsample
[ML2(ꢀCꢁCꢀpC6H4(2,5OR)2ꢀCꢁCꢀ)]n
/
/
/
/
/
/
ꢀ
/
(Isample/
Istandard)ꢃhstandard. All the data were corrected by
taking into account the photomultiplier efficiency of
the fluorescence spectrometer.
/
4.2.1. EOP reaction, method (a)
The following procedure for the preparation of Ptꢁ
BꢁHDOBn is representative of PtꢁBꢁBOBn, PtꢁPꢁ
BOBn, PtꢁPꢁHDOBn and PtꢁBꢁDEBn. The synthetic
/
/
/
/
/
/
Molecular weights were determined by GPC on a
/
/
/
/
Perkinꢁ
/
Elmer instrument equipped with a PL-gel col-
procedure is based on the ‘EOP’ method. In a Schlenk
vessel 712 mg (0.88 mmol) of 1,4-diiodo-2,5-dihexade-
umn and UV detector. Measurements were performed in

20
I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ23
/
ciloxybenzene were introduced in 40 ml of THF in the
presence of 100 mg (0.08 mmol) of [tetrakis(triphenyl-
phosphine)palladium(0)]. Several vacuum/argon cycles
were performed and then 552 mg (1.754 mmol) of
tributyl(ethynyl)tin were added. The reaction mixture
for 18 h the reaction mixture was cooled at 0 8C and
LDA 2 M poured in (1.24 ml, 2.35 mmol). After adding
trans-bis(tributylphosphine)platinum(II) (630 mg, 0.94
mmol), the mixture was warmed up at 70 8C for 24 h,
then the solution was allowed to cool at room tempera-
ture and reduced in volume under vacuum. Addition of
pentane caused the precipitation of a brown powder
(970 mg, 46% yield).
1
was heated at 70 8C for 15 h, until H-NMR analysis
indicated the complete consumption of the tin reagent.
After cooling to 0 8C, 1.14 ml (2.28 mmol) of LDA were
introduced. After 10 min the reaction was allowed to
warm up and to reach room temperature. 1H-NMR
analysis indicated the complete transformation of the
alkyne moieties into the tributyltin alkynyl functional-
ities. At this point, 559 mg (0.833 mmol) of trans-
[dichlorobis-(tributylphosphine)platinum(II)] and 50 mg
(0.044 mmol) of [dibenzilideneacetonepalladium(0)]
were added, then the temperature was raised up to
70 8C, and the reaction was refluxed for 24 h. After
cooling, the final reaction mixture was filtered through
celite to eliminate the catalyst, the solvent volume of the
filtrate was reduced to small volume and pentane was
added to precipitate the polymeric material. With this
4.3.1. Characterisation
IR n(Cꢁ
/
C): 2104, n(Ptꢀ
/
Cl): 328 cmꢂ1; UV (CHCl3):
H),
CH2), 1.41 (m 36H
9.08 Hz); 31P-NMR
P) Hz): 3.50 (2362.0), 0.76
(2303.0) (intensity ratioꢀ1:2); Elemental analysis (%),
1
373.8 nm; H-NMR (CDCl3 ppm): 7.08 (s 8H Arꢀ
2.13 (36H PꢀCH2ꢀ), 1.55 (m 36H ꢀ
CH2), 0.89 (t 54HꢀCH3 Jꢀ
(CDCl3 ppm, J(195Ptꢁ31
/
/
/
/
ꢀ
/
/
/
/
/
found (calculated for the trinuclear structure
C92H170P6Pt3Cl2, pm 2118.32): C, 51.71 (52.16); H,
8.17 (8.09).
4.4. Reaction between 1,4-bis(ethynyl)benzene and
trans-bis(tributylphosphine)platinum(II) with method
procedure a red oily product, (Ptꢁ
/
BꢁHDOBn), was
/
obtained.
(b): Ptꢁ
/
BꢁDEBn(b)
/
4.2.2. Dehydrohalogenation reaction, method (b)
1,4 bis(ethynyl)Benzene (100 mg, 0.8 mmol) and
trans-[Pt(PBu3)2Cl2] (526 mg, 0.8 mmol) were dissolved
in argon-bubbled diethylamine with CuI as catalyst (5%
in mol) and the temperature was risen up to 55 8C for 12
h. After removing ammonium salts, the addition of
methanol yields a brown powder (300 mg, 52% yield).
0.8 mmol of 1,4 bis(ethynyl)benzene and an equimolar
amount of the square planar complex trans-
[Pt(PBu3)2Cl2] were added in the reaction flask in the
presence of argon-bubbled diethylamine as solvent and
base (30 ml). CuI was then added as catalyst (5% in mol)
and the reaction allowed to react for 12 h at 55 8C.
Ammonium salts were then removed by filtration and
the residual dark brown solution reduced in volume. By
4.4.1. Characterization
1
IR n(Cꢁ
/
C): 2100 cmꢂ1; UV (CHCl3): 378.4 nm; H-
adding methanol a brown powder (Ptꢁ
/
Bꢁ/DEBn) was
NMR (CDCl3 ppm): 7.07 (s 4H Arꢀ
/
H), 2.09 (m 12H Pꢀ
/
formed and then filtered.
CH2ꢀ
18HꢀCH3 Jꢀ
J(195Ptꢁ31
/
), 1.57 (m 12H ꢀ
/
CH2), 1.41 (q 12H ꢀ
/
CH2), 0.89 (t
9.00 Hz); 31P-NMR (CDCl3 ppm,
The crude products prepared either with method (a)
or (b) were purified with column chromatography on
alumine using pentane/dichloromethane in increasing
polarity ratio. Oligomers with different chain length and
chlorine or tributylstannane as terminal groups, as XPS
and conventional spectroscopic analysis assessed, could
be separated and characterised from the crude products
obtained by method (a). The characterisation of oligo-
mers and polymers are hereafter reported in the elution
order. The main characterisations and molecular for-
mulas are collected in Table 1.
/
/
/
P) Hz): 3.50 (2360.8); Elemental analysis
(%), found (calculated for the repeating unit C34H58
P2Pt): C, 56.15 (56.42); H, 8.54 (8.08); GPC molecular
weight (in CHCl3): Mwꢀ
/
57000, Mnꢀ
/
18000, Pꢀ3.2,
/
n $80.
/
4.5. Reaction between 1,4-diiodo-2,5-di(butoxy)benzene
and trans-bis(tributylphosphine)platinum(II) with
method (a): Ptꢁ
/
BꢁBOBn(a)
/
1,4-diiodo-2,5di(butoxy)benzene (745 mg, 1.58 mmol)
and 1 g (3.17 mmol) of tributylethynyltin were dissolved
in THF under Ar, followed by the catalyst [Pd(PPh3)4]
(180 mg, 0.16 mmol). After stirring for 18 h at 70 8C, the
reaction mixture was cooled at 0 8C and LDA 2 M was
added (1.96 ml, 4.0 mmol). At this point trans-bis(tri-
butylphosphine)platinum(II) (1 g, 1.50 mmol) was
introduced in the reaction vessel and the mixture
warmed up at 70 8C for 24 h. The solution was then
allowed to cool at room temperature and reduced in
4.3. Reaction between 1,4-diiodobenzene and trans-
bis(tributylphosphine)platinum(II) with method (a):
Ptꢁ
/
BꢁDEB3(a)
/
1,4-diiodobenzene (300 mg, 0.990 mmol) was dis-
solved in freshly distilled THF and 570 mg (1.82 mmol)
of tributylethynyltin were added under Ar, followed by
the catalyst [Pd(PPh3)4] (105 mg, 0.09 mmol). The
temperature was risen up to 70 8C and after stirring

I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ
/23
21
volume. With the addition of pentane to the solution, a
red oil was separated (980 mg, 75% yield), and
chromatographic separation gave three main products.
solution was left to cool at room temperature and the
volume reduced in vacuum. Addition of pentane
allowed the separation of a red oil (1.36 g, 73% yield),
whose chromatographic separation gave two main
products.
4.5.1. Characterisations
4.5.1.1. Ptꢁ
457, n(PꢀC): 394, 280,n(Ptꢀ
(CHCl3): o0ꢀ2.03ꢃ
104 l molꢂ1 cmꢂ1; lmax
nm; luminescence (CHCl3): lmax 470.0 nm, hꢀ
1H-NMR (CDCl3): 6.70 (s Arꢀ
H), 3.87 (t OꢀCH2ꢀ
2.18 (m PꢀCH2ꢀ), 1.54 (m ꢀCH2), 1.41 (m ꢀCH2), 0.88
(t ꢀ P) Hz):
CH3); 31P-NMR (CDCl3 ppm, J(195Ptꢁ31
0.92 (2313.7); 10% of the crude product; Elemental
analysis (%), found (calculated for the binuclear struc-
ture C66H128O2P4Pt2Cl2 ppm, 1538.68): C, 51.58 (51.52);
H, 8.49 (8.38).
/
Bꢁ
/
BOB2(a). IR n(Cꢁ
/
C): 2104, n(Ptꢀ
/
P):
4.6.1. Characterisation
/
/
Cl): 326 cmꢂ1
;
UV
/
/
ꢀ
/
368.0
4.6.1.1. Ptꢁ
525, 533; 394, 280 cmꢂ1; UV (CHCl3): o0ꢀ
molꢂ1 cmꢂ1; lmax
396.0 nm; luminescence (CHCl3):
lmax 440, 460 nm, hꢀ
0.30%; 1H-NMR (CDCl3 ppm):
7.72 (m PꢀArꢀH), 7.35 (m PꢀArꢀH) 6.56 (ArꢀH), 3.75
(t OꢀCH2ꢀ), 2.09, 1.59 (m ꢀCH2), 1.35 (m ꢀCH2), 0.90
(m ꢀ P) Hz):
CH3); 31P-NMR (CDCl3 ppm, J(195Ptꢁ31
18.07 (2654.0), 17.67 (2610.0), (intensity ratioꢀ1:1);
40% of the crude product; Elemental analysis (%), found
(calculated for the tetranuclear structure
258H274O10P8Pt4Sn2: C, 63.95 (64.55); H, 5.74 (5.75).
/
Pꢁ
/
BOB4(a). IR n(Cꢁ
/
C): 2104, n(Cꢀ
/
Sn):
ꢀ
/
/0.25%;
/
3.46ꢃ
/
104 l
/
/
/),
ꢀ
/
/
/
/
/
ꢀ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
4.5.1.2. Ptꢁ
525, 540, n(Ptꢀ
cmꢂ1; UV (CHCl3): o0ꢀ
lmax 377.0 nm; luminescence (CHCl3): lmax
445 nm, hꢀ
0.35%; 1H-NMR (CDCl3 ppm): 6.69 (s
ArꢀH), 3.87 (t OꢀCH2ꢀ), 2.16 (m PꢀCH2ꢀ), 1.54 (m ꢀ
CH2), 1.41 (m ꢀCH2), 0.88 (t ꢀ
CH3); 31P-NMR (CDCl3
ppm, J(195Ptꢁ31
P) Hz): 0.91 (2316.5), 0.99 (2314.1),
(intensity ratioꢀ2:1); 40% of the crude product; Ele-
/
Bꢁ
/
BOB3(a). IR n(Cꢁ
P): 457, n(PꢀC): 394, 280,n(Ptꢀ
7.64ꢃ
104 l molꢂ1 cmꢂ1
465,
/
C): 2106, n(Cꢀ
/
Sn):
C
/
/
/
Cl): 328
/
/
;
4.6.1.2. Ptꢁ
525, 533; 279 cmꢂ1; UV (CHCl3): o0ꢀ
molꢂ1 cmꢂ1; lmax
389.0 nm; luminescence (CHCl3):
lmax 470 nm, hꢀ
0.11%; 1H-NMR (CDCl3 ppm): 7.72
(m PꢀArꢀH), 7.35 (m PꢀArꢀH) 6.56 (ArꢀH), 3.75 (t
OꢀCH2ꢀ), 2.05 (s), 1.59 (m ꢀCH2), 1.35 (m ꢀCH2), 0.90
(m ꢀ P) Hz):
CH3); 31P-NMR (CDCl3 ppm, J(195Ptꢁ31
/
Pꢁ
/
BOB2(a). IR n(Cꢁ
/
C): 2104, n(Cꢀ
/
Sn):
ꢀ
/
ꢀ
/
/
1.96ꢃ l
/
104
/
ꢀ
/
/
/
/
/
/
/
ꢀ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
mental analysis (%), found (calculated for the trinuclear
structure C156H249O6P6Pt3SnCl: C, 56.79 (56.58); H,
8.50 (8.57).
12.00 (3454.0); 10% of the crude product; Elemental
analysis (%), found (calculated for the structure
C
150H174O6P4Pt2Sn2: C, 63.00 (63.78); H, 5.60 (6.20).
4.5.1.3. Ptꢁ
525, 533, n(Ptꢀ
o0ꢀ1.41ꢃ
105 l molꢂ1 cmꢂ1; lmax
nescence (CHCl3): lmax 470.0 nm, hꢀ
NMR (CDCl3 ppm): 6.70 (ArꢀH), 3.87 (Oꢀ
2.16 (m PꢀCH2ꢀ), 1.54 (m ꢀCH2), 1.41 (m ꢀCH2), 0.88
(ꢀ
CH3); 31P-NMR (CDCl3 ppm, (J195Pt-31P) Hz): 0.94
(2316.5), 1.01 (2314.1), (intensity ratioꢀ1:1); 10% of the
crude product; Elemental analysis (%), found (calcu-
/
Bꢁ
/
BOB4(a). IR n(Cꢁ
C): 394 cmꢂ1; UV (CHCl3):
389.0 nm; lumi-
0.85%; 1H-
CH2ꢀ),
/
C): 2104, n(Cꢀ
/
Sn):
4.7. Reaction between 1,4-diiodo-2,5-di(butoxy)benzene
and trans-bis(triphenylphosphine)platinum(II) with
/
P): 457, n(Pꢀ
/
/
/
ꢀ
/
method (b): Ptꢁ
/
PꢁBOBn(b)
/
ꢀ
/
/
/
/
/
1,4-bis(ethynyl)-2,5di(butoxy)benzene (434 mg, 0.92
mmol) and cis-[Pt(PPh3)2Cl2] (723 mg, 0.92 mmol) were
dissolved in argon-bubbled diethylamine with CuI as
catalyst (5% in mol) and the temperature was risen up to
55 8C for 12 h. After removing the ammonium salts, the
addition of methanol yielded a red oil (500 mg, 55%
yield).
/
/
/
/
/
/
lated for the tetranuclear structure
P8Pt4Sn2: C, 58.98 (58.38); H, 8.52 (8.63).
C210H370O10-
4.6. Reaction between 1,4-diiodo-2,5-di(butoxy)benzene
and trans-bis(triphenylphosphine)platinum(II) with
4.7.1. Characterisation
method (a): Ptꢁ
/
PꢁBOBn(a)
/
4.7.1.1. Ptꢁ
(CHCl3): 370.2 nm; H-NMR (CDCl3): 7.72 (m Pꢀ
H), 7.35 (m PꢀArꢀH) 6.93 (ArꢀH), 3.96 (t OꢀCH2ꢀ
1.61 (m ꢀCH2), 1.38 (m ꢀCH2), 0.93 (m ꢀ
/
Pꢁ
/
BOBn(b). IR n(Cꢁ
/
C): 2099 cmꢂ1; UV
Arꢀ
),
1
To 900 mg of 1,4-diiodo-2,5di(butoxy)benzene (1.91
mmol), dissolved in THF, 1.196 g (3.80 mmol) of
tributylethynyltin were added under Ar, followed by
the catalyst [Pd(PPh3)4] (88 mg, 0.07 mmol). After
stirring at 70 8C for 18 h, the reaction mixture was
cooled at 0 8C and LDA 2 M added (2.47 ml, 5.0 mmol).
Cis-bis(triphenylphosphine)platinum(II) (1.425 g, 1.88
mmol) was then introduced into the vessel and the
mixture warmed up at 70 8C for 24 h. At this point the
/
/
/
/
/
/
/
/
/
/CH3), 0.86 (m
ꢀ
/
CH3); 31P-NMR (CDCl3 ppm, J(195Ptꢁ31
/
P) Hz): 18.18
(2682.0), 17.67 (2610.0) (intensity ratio 5:1); Elemental
analysis (%), found (calculated for the repeating unit
C54H50O2P2Pt): C, 66.12 (65.64); H, 5.13 (5.10); GPC
molecular weight (in CHCl3): Mwꢀ
/
7700, Mnꢀ3200,
/
Pꢀ2.4, nꢀ8ꢁ3.
/
/
/

22
I. Fratoddi et al. / Journal of Organometallic Chemistry 674 (2003) 10ꢁ23
/
4.8. Reaction between 1,4-diiodo-2,5-
di(hexadecyloxy)benzene and trans-
bis(tributylphosphine)platinum(II) with method (a):
mmol) and the mixture was warmed up to 70 8C for
24 h. The solution was then cooled at room temperature
and reduced in volume. Addition of pentane led to the
separation of a red oil (880 mg, 80% yield). In this case,
no chromatographic separation was performed, and the
oily product was characterised.
Ptꢁ
/
BꢁHDOBn(a)
/
To a THF solution of 1,4-diiodo-2,5di(hexadecylox-
y)benzene (712 mg, 0.88 mmol), 552 mg (1.754 mmol) of
tributylethynyltin were added under Ar, followed by
[Pd(PPh3)4] (100 mg, 0.08 mmol). After stirring 18 h at
70 8C, the reaction mixture was cooled at 0 8C and 1.14
ml (2.28 mmol) of LDA 2 M were added. Trans-
bis(tributylphosphine)platinum(II) (559 mg, 0.833
mmol) was then introduced and the mixture warmed
up at 70 8C for 24 h. At this point the solution was
allowed to cool at room temperature and reduced in
volume. Addition of pentane allowed the separation of a
red oil (720 mg, 72% yield), whose chromatographic
separation gave two main products.
4.9.1. Ptꢁ
IR n(Cꢁ
molꢂ1 cmꢂ1; lmax
lmax 450, 440 nm, hꢀ
ppm): 7.7 (m 18H, phosphine), 7.4 (m 12H, phosphine),
6.65 (m 2H, ArꢀH), 3.98 (t 4H, OꢀCH2ꢀ), 1.55ꢁ1.41
(m 56H, ꢀCH2ꢀ), 0.90 (m 6H, ꢀ
CH3); 31P-NMR
(CDCl3 ppm, J(195Ptꢁ31
P) Hz): 18.00 (2595.0); Elemen-
/
Pꢁ
C): 2106 cmꢂ1; UV (CHCl3): o0ꢀ
371.2 nm; luminescence (CHCl3):
0.34%; 1H-NMR (CDCl3, d
/
HDOBn(a)
/
/
3.00ꢃ
105 l
/
ꢀ
/
ꢀ
/
/
/
/
/
/
/
/
/
/
tal analysis (%), found (calculated for the repeating unit
C78H78O2P2Pt): C, 71.20 (70.72); H, 7.31 (7.46); GPC
molecular weight (in CHCl3): Mwꢀ
/
26700, Mnꢀ15800
/
Pꢀ1.7.
/
4.8.1. Characterisation
4.8.1.1. Ptꢁ
327, n(Ptꢀ
P): 415 cmꢂ1; UV (CHCl3): o0ꢀ
molꢂ1 cmꢂ1; lmax
377.0 nm; luminescence (CHCl3):
lmax 450, 427 nm, hꢀ
2.33%; 1H-NMR (CDCl3 ppm):
6.69 (ArꢀH), 3.73 (t OꢀCH2ꢀ), 2.15 (m ꢀCH2), 1.65 (m
CH2), 1.41 (m ꢀCH2), 0.88 (m ꢀ
CH3); 31P-NMR
(CDCl3 ppm, J(195Ptꢁ31
P) Hz): 0.90 (2300.0), 0.99
(2311.4), (intensity ratioꢀ1:1); Elemental analysis (%),
found (calculated for the tetranuclear structure
222H420O6P8Pt4Cl2: C, 63.00 (62.23); H, 9.70 (9.88).
/
Bꢁ
/
HDOB4(a). IR n(Cꢁ
/
C): 2104, n(Ptꢀ
/
Cl):
Acknowledgements
/
/
5.30ꢃ
/
104 l
ꢀ
/
The authors gratefully acknowledge Prof. Claudio Lo
Sterzo for helpful discussions. This work was financially
supported by CNR (Italy), Progetto Finalizzato
MSTA2.
ꢀ
/
/
/
/
/
/
ꢀ
/
/
/
/
/
References
C
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4.8.1.2. Ptꢁ
327, n(Ptꢀ
P): 415 cmꢂ1; UV (CHCl3): o0ꢀ
molꢂ1 cmꢂ1; lmax
380.0 nm; luminescence (CHCl3):
lmax 460, 430 nm, hꢀ
3.16%; 1H-NMR (CDCl3 ppm):
6.69 (ArꢀH), 3.75 (t OꢀCH2ꢀ), 2.16 (m ꢀCH2), 1.55 (m
CH2), 1.41 (m ꢀCH2), 0.90 (m ꢀ
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/
Bꢁ
/
HDOB7(a). IR n(Cꢁ
/
C): 2109, n(Ptꢀ
/
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/
/
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/
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