Synthesis of highly ethynylated mono and dinuclear Pt(II) tethers bearing the 4,4′-bis(ethynyl)biphenyl (debp) unit as central core

Article abstract of DOI:10.1016/S0022-328X(00)00533-7

Mono and bisubstituted bis(ethynyl)biphenyl Pt(II) complexes, i.e. trans-[(R-CC-)Pt(PPh₃)₂(-CC-p-C₆H ₄-p-C₆H₄-CC-H)], R=p-NO₂C₆H₄ (3b), (η⁵-C₅H₅)Fe(η⁵-C ₅H₄) (3c), and trans-[(R-CC-)Pt(PPh₃)₂(-CC-p-C₆H ₄-p-C₆H₄-CC-)Pt(PPh₃) ₂(-CC-R)], R=C₆H₅ (4a)_, p-NO₂C₆H₄ (4b), (η⁵-C₅H₅)Fe(η⁵-C ₅H₄) (4c), have been synthesized by the dehydrohalogenation reaction from the appropriate Pt monochloro acetylides trans-[(R-CC-)Pt(PPh₃)₂Cl], R=C₆H₅ (1a), R=p-NO₂C₆H₄ (1b), R=(η⁵-C₅H₄)Fe(η⁵-C ₅H₅) (1c) and HCC-p-C₆H₅-p-C₆H₅-CCH, (4,4′-bis-ethynylbiphenyl), (DEBP) (2). In order to make possible a direct evaluation of the role of Pt centers on the properties of these highly ethynylated complexes, the corresponding species without Pt were prepared, i.e. C₆H₅-CC-CC-C₆H₄-C₆H ₄-CC-CC-C₆H₅, (4,4′-(bis-phenylethynyl)-diethynylbiphenyl) (7), and (η⁵-C₅H₅)Fe(η⁵-C ₅H₄)-(CC-CC-C₆H₄-C₆H ₄-CC-CC)-(η⁵-C₅H₄)Fe(η ⁵-C₅H₅), (4,4′-(bis-ferrocenylethynyl)-diethynylbiphenyl) (8). Preparation of the latter compounds was only achieved by the use of the palladium catalyzed Stille coupling reaction, since the dehydrohalogenation route afforded only homocoupled and polymeric products. The electron-donor or electron-withdrawing ligands coordinated to Pt were chosen for the purpose of tuning the optical properties of the complexes through the different charge distribution along the π-electron conjugation. Characteristic spectroscopic features (UV-vis, FT-IR and NMR) of these complexes are discussed.

Full text of DOI:10.1016/S0022-328X(00)00533-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 619 (2001) 49–61
Synthesis of highly ethynylated mono and dinuclear Pt(II) tethers
bearing the 4,4%-bis(ethynyl)biphenyl (debp) unit as central core
M.V. Russo a,*, C. Lo Sterzo b, P. Franceschini a, G. Biagini a, A. Furlani a
a Department of Chemistry, Uni6ersity of Rome, ‘La Sapienza’, Piazzale Aldo Moro 5, 00185 Rome, Italy
b Department of Chemistry, Centro CNR di Studio sui Meccanismi di Reazione, Uni6ersity of Rome, ‘La Sapienza’, Piazzale Aldo Moro 5,
00185 Rome Italy
Received 18 May 2000; received in revised form 24 July 2000
Abstract
Mono and bisubstituted bis(ethynyl)biphenyl Pt(II) complexes, i.e. trans-[(RꢀCꢁCꢀ)Pt(PPh3)2(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀH)],
R=p-NO2C6H4
(3b),
(h5-C5H5)Fe(h5-C5H4)
(3c),
and
trans-[(RꢀCꢁCꢀ)Pt(PPh3)2(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀ)Pt-
(PPh3)2(ꢀCꢁCꢀR)], R=C6H5 (4a), p-NO2C6H4 (4b), (h5-C5H5)Fe(h5-C5H4) (4c), have been synthesized by the dehydrohalogena-
tion reaction from the appropriate Pt monochloro acetylides trans-[(RꢀCꢁCꢀ)Pt(PPh3)2Cl], R=C6H5 (1a), R=p-NO2C6H4 (1b),
R=(h5-C5H4)Fe(h5-C5H5) (1c) and HCꢁCꢀp-C6H5ꢀp-C6H5ꢀCꢁCH, (4,4%-bis-ethynylbiphenyl), (DEBP) (2). In order to make
possible a direct evaluation of the role of Pt centers on the properties of these highly ethynylated complexes, the corresponding
species without Pt were prepared, i.e. C6H5ꢀCꢁCꢀCꢁCꢀC6H4ꢀC6H4ꢀCꢁCꢀCꢁCꢀC6H5, (4,4%-(bis-phenylethynyl)-diethynylbiphenyl)
(7), and (h5-C5H5)Fe(h5-C5H4)ꢀ(CꢁCꢀCꢁCꢀC6H4ꢀC6H4ꢀCꢁCꢀCꢁC)ꢀ(h5-C5H4)Fe(h5-C5H5), (4,4%-(bis-ferrocenylethynyl)-di-
ethynylbiphenyl) (8). Preparation of the latter compounds was only achieved by the use of the palladium catalyzed Stille coupling
reaction, since the dehydrohalogenation route afforded only homocoupled and polymeric products. The electron-donor or
electron-withdrawing ligands coordinated to Pt were chosen for the purpose of tuning the optical properties of the complexes
through the different charge distribution along the p-electron conjugation. Characteristic spectroscopic features (UV–vis, FT-IR
and NMR) of these complexes are discussed. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Platinum; Acetylide; Dinuclear; Ferrocene
photoluminescence, optical and photoinduced absorp-
tion effects, which can be successfully used in light
1. Introduction
emitting diodes (LEDs) [4]. Similar organometallic
A great deal of interest has grown recently in the
polymers containing group 10 transition metals, with a
scientific community, towards organometallic oligomers
rigid rod conjugated backbone, show interesting prop-
and polymers in which transition metals are bound to
erties of alignment in a magnetic and electrical field [5],
organic spacers [1]. Since the pioneering work of Hagi-
fast and reproducible response to relative humidity
hara’s group [2] who developed the dehydrohalogena-
variations in SAW (surface acoustic wave) sensors [6],
tion reaction pathway, an alternative reaction route
and molecular orientation even when spin deposited in
proposed by Lewis and co-workers [3], based on bis-
thick layers [7]. Moreover Group 10 metal alkynyls and
SnMe3 derivatives of dialkynes, has been widely used
for the synthesis of mono- and poly-nuclear s-bonded
acetylides. These materials show a wide domain of
properties useful for application in modern technology.
For example Pt-containing poly-ynes exhibit promising
related polymers have been studied in view of their
second- and third-order non-linear optical (NLO) prop-
erties, which depend on the transition metal, on the
organic ligand, on the spacer in the polymer chain and
on the symmetry of the molecules [8].
Within this frame, it is interesting the study of
organometallic oligomers and complexes, which can be
considered the molecular models and the building
blocks of long chain organometallic polymers.
* Corresponding author. Tel.: +39-06-49913551; fax: +39-06-
490324.
E-mail address: mariavittoria.russo@uniroma1.it (M.V. Russo).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00533-7

50
M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
A good deal of excellent research has been performed
acetylide and allenylidenes has been recently investi-
gated by Friend and co-workers [12], who present
evidence for the presence of mixed valence species and
elucidate the presence of quinoid structure with the aid
of theoretical calculations. Homo and hetero-dinuclear
acetylene and (Z)-1,3-enyne bridged bis(cyclopentadi-
enyl) metal complexes, where the transition metals are
Fe, W, Mo, Mn, and Re have been prepared, in the
framework of an extensive project, using the palladium-
catalyzed coupling reaction (Stille reaction) between
organic electrophiles and organostannanes [13]. Re-
cently this synthetic procedure has been also extended
to the coupling of metal halides and alkynylstannanes,
allowing an easy access to metal acetylides (homo and
heterobimetallic) with the acetylenic moiety s-bound to
the metals [14].
In this paper we describe the procedures which allow
the formation of model molecules with p-electron con-
jugation extended through ethynyl bonds of
organometallic and pure organic highly ethynylated
molecules. The presence of electron-donor or electron-
withdrawing ligands linked to Pt(II) are expected to
produce a tuning of the NLO properties of these mate-
rials, which are representative building blocks of highly
ethynylated organometallic polymers with promising
NLO response, that is one of the ultimate goals for
advanced materials.
on this topic. Mixed-metal oligomers and complexes
containing Ru and Pd, Fe and Pd, Fe and Ru, Pt and
Ru, Os and Ru coordination centers linked by unsatu-
rated carbon-rich bridges have been synthesized, and
their electron communication between the metal centers
was recently investigated [9]. Bimetallic complexes show
intramolecular electronic communication through the
metal centers that can act as electron donors or accep-
tors depending on the nature of the redox active transi-
tion metal and on the organic bridge connecting the
terminal organometallic fragments [9b,c]. Hetero-
bimetallic complexes containing ferrocenyl ligands as
typical donor fragments and M(CO)5 (M=Cr, Mo, W)
as electron accepting moiety have been recently synthe-
sized, and they exhibit higher first hyperpolarizability b
values [10], compared to those reported for other
organometallic based materials. A wide series of homo-,
bi- and poly-nuclear s-acetylide complexes with
Fe(dppe)Cp* and Fe(CO)2Cp* linked to p-electron de-
localized carbon bridges, have been prepared and char-
acterized by Lapinte and coworkers [11]; investigation
of the redox processes involving metal-acetylide com-
plexes indicate a significant electronic communication
between the metal centers [11b,c]. The synthesis and
electrochemistry of dinuclear metal (Fe, Ru, Os) s-
2. Results and discussion
The feasibility of obtaining Ptꢀacetylene s-bonds is
well known, and allowed us to prepare some model
molecules for the polymeric materials which have been
already studied [6,7] and for organometallic polymers
whose synthesis is in progress. The synthetic procedures
proposed here are suitable for the preparation of asym-
metric Pt-bisacetylides [15], starting from mono-
cloroacetilydes [16]. The reactivity of mono-
chloroacetylides requires mild and easy reaction condi-
tions, but it is not trivial; in fact it depends on the trans
influence of the acetylenic ligand s-bonded to Pt(II)
[16b]. The preparation of Pt(II) acetylides linking elec-
tron-donor or electron-withdrawing ligands was per-
formed by the dehydrohalogenation reaction of the
corresponding [(RꢀCꢁCꢀ)Pt (PPh3)2 Cl] complexes (1a–
c) and DEBP (2) (Scheme 1).
General conditions to perform the dehydrohalogena-
tion reaction are similar to those reported earlier [2,3a],
that is the use of CuI as the catalyst and NHEt2 as the
base; however some modifications have been introduced
for the purpose of obtaining better yields. The presence
of organic solvents (CHCl3, C6H5CH3) allows the solu-
bility of the monochloroacetylides in the reaction
medium. With the purpose of forming the disubstituted
DEBP derivatives 4a–c, we initially tried the reaction
Scheme 1.

M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
51
Table 1
Compound
UV–vis umax (nm)
FT-IR (cm−1
)
trans-[Pt(PPh3)2(ꢀCꢁCꢀC6H4NO2)(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀH)] (3b)
trans-[Pt(PPh3)2(ꢀCꢁCꢀFc)(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀH)] (3c) a
388
351
3266 (wHꢀCꢁC
2105 (wCꢁC
3276 (wHꢀCꢁC
)
)
)
2109 (wCꢁC
2112 (wCꢁC
2105 (wCꢁC
)
)
)
trans–trans-[(PPh3)2(PhꢀCꢁCꢀ)PtꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀPt(ꢀCꢁCꢀPh) (PPh3)2] (4a)
trans–trans-[(PPh3)2(p-NO2ꢀC6H4ꢀCꢁCꢀ)PtꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀPt(ꢀCꢁCꢀC6H4ꢀ
p-NO2)(PPh3)2] (4b)
373
397
trans–trans-[(PPh3)2(FcꢀCꢁCꢀ)PtꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀPt(ꢀCꢁCꢀFc)(PPh3)2] (4c) a
PhꢀCꢁCꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀCꢁCꢀPh (7)
380
350
2115 (wCꢀC
2213 (wCꢀC
)
)
2191 (wCꢁC
2141 (wCꢁC
)
)
FcꢀCꢁCꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀCꢁCꢀFc (8) a
a Fc=(h5-C5H4)Fe(h5-C5H5).
337
2.1. Mono substituted organometallic DEBP deri6ati6es
between the Ptꢀmonochloroacetylides 1a–c and DEBP
(2) in the molar ratio 2:1. Surprisingly, under these
conditions only 1a straightforwardly afforded the corre-
sponding dinuclear derivative 4a, while in the reaction
of complexes 1b and 1c with 2 in the 2:1 stoichiometric
ratio, formation of the dinuclear derivatives 4b and 4c
was always accompanied by formation of a variable
amount of the mononuclear complexes 3b and 3c.
Since mononuclear DEBP derivatives 3b–c represent
interesting intermediates which could be used to pre-
pare more elaborate metallaacetylide oligomers, condi-
tions that could favor their formation were searched.
For this purpose the stoichiometric ratio between Pt-
monochloroacetylides 1a–c and DEBP was first re-
verted to 1:1 and then to 1:2. However, despite these
modifications the reaction of 1a and 2, independently
from the stoichiometric ratio between the reactants,
always afforded the sole dinuclear derivative 4a, while
only using the most unbalanced stoichiometric ratio 1:6
and 1:2 between the Pt monochloroacetylides 1b and 1c
versus DEBP, respectively, it was possible to orient the
reaction toward the prevalent formation of 3b and 3c.
Trying to order these results in a rationale, we can
suppose that formation of the dinuclear derivatives
4a–c is occurring through the previous formation of
the mononuclear derivatives 3a–c. Then in the case of
1a, following the first attack of the Pt-
monochloroacetylyde on DEBP, the mononuclear com-
plex 3a is much more reactive toward the remaining
Pt-monochloroacetylide 1a than the unreacted DEBP,
thus formation of dinuclear derivative 4a is always
preferred. On the contrary, in the case of 1b and 1c, the
reactivity of unreacted DEBP can compete with the
intermediates 3b and 3c versus the remaining
monochloroacetylides 1b–c; thus with the help of a
favorable stoichiometry, an appreciable amount of the
mononuclear derivatives 3b–c can be obtained.
The FT-IR spectra of the asymmetric (bis)acetylides,
trans-[(p-NO2C6H4 ꢀCꢁC)Pt(PPh3)2(CꢁCꢀp-C6H4 ꢀp-
C6H4ꢀCꢁCꢀH)] (3b) and trans-[(FcꢀCꢁC)Pt(PPh3)2-
(CꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀH)] (3c) (Table 1) show
sharp signals at 3266 and 3276 cm−1, respectively, due
to ꢁCꢀH stretching of the DEBP ligand and at 2105
and 2109 cm−1, attributed to CꢁC stretching vibration;
no bands at 540 cm−1 appear, suggesting a trans
structure of the complexes by comparison with litera-
ture reports [16b][17].
UV spectra in CHCl3 of 3b show three absorption
maxima at 314, 345 and 388 nm, this last one the more
intense, while 3c shows a single broad absorption at 351
nm. It is worth noting the comparison of values of the
UV maximum observed for compounds 3b and 3c and
those of compounds 4a and 4c (vide infra), with those
of the corresponding constituting units, p-nitropheny-
lacetylene (umax=289 nm), ethynylferrocene (umax
=
262 nm) and DEBP (umax=290 nm). The strong
variations of the UV shift observed when the constitut-
ing units are joined to form the metallaacetylide assem-
bly, is accounting for the larger p delocalization
probably occurring through the p orbitals of Pt. Nowa-
days there is still a large debate ongoing in the scientific
community on whether electron mobility may be pro-
moted or inhibited when a transition metal is bound
into a poly-yne backbone. Molecular calculations of the
extended Hu¨ckel type performed on metal (Fe, Rh, Pt)
oligo-yne polymers indicate that Pt containing
molecules, with a square planar configuration around
the metal, present a larger conduction bandwidth than
the molecules where the metal is in octahedral configu-
ration [18]. However, electrochemical studies performed
on heterotrimetallic Ru/Pd/Ru and Fe/Pd/Fe com-
plexes connected by ꢀCꢁCꢀC6H4ꢀCꢁCꢀ bridges, indi-
cate that the insertion of the palladium moiety inhibits

52
M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
the communication between the two ruthenium centers
[19], while analogous measurements made on a Ru/Pt/
Ru trinuclear mixed metal complex showed that the
platinum moiety transfers electron density to the ruthe-
nium center [9d]. Our results seem to suggest that there
is at least a fairly good electronic communication flow-
ing through the platinum centers and the organic
spacer.
Pt(PPh3)2(CꢁCꢀFc)] (4c), which contains the electron-
donor ethynylferrocene (Fc) groups at the terminal
ends of the molecule, has been prepared in view of the
expected opposite behavior in charge transfer activity in
comparison with 4b. The FT-IR spectrum of complex
4c shows a strong wCꢀC at 2115 cm−1, no bands in the
range 3300–3200 cm−1 (ꢁCꢀH stretching mode) and no
bands at 540 and 320 cm−1. Since the FT-IR spectra of
4c and 3c are exactly the same apart from the wꢁCꢀH
stretching, the two molecules must be quite similar in
their coordination around Pt. These results are in
agreement with the proposed trans structure, with no
PtꢀCl bonds and no free acetylenic hydrogens. The UV
spectrum of 4c exhibits a broad maximum absorption
band at 379 nm, which again suggests an increase of
conjugation and electronic interaction between metal
centers with respect to the related asymmetric bis-
acetylide 3c (umax=351 nm), thus confirming the role
of Pt centers in the increase of electron density in the
conjugated system ( compare also the UV absorptions
of the molecules 7 and 8 with no Pt atoms). The
electron donor property of the ligand (ferrocene) in-
duces a little but detectable opposite effect on electron
density and mobility with respect to the electron with-
drawing ꢀNO2 group (Table 1).
2.2. Disubstituted organometallic DEBP deri6ati6es
The binuclear complex trans–trans-[(PhꢀCꢁC)Pt-
(PPh3)2(CꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁC)Pt(PPh3)2(CꢁCꢀPh)]
(4a) has been obtained in good yield (80%) by the
general reaction route described in Scheme 1. An alter-
native approach based on the condensation of 1a and
4,4%-bis(trimethyltin)ethynylbiphenyl (11) gave a lower
yield (54%) (vide infra). Using the dehydrohalogenation
route, the corresponding mononuclear (bis)acetilyde
[(PhꢀCꢁC)Pt(PPh3)2(CꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀH)]
(3a) was never found in the reaction mixture. The
FT-IR spectrum of complex 4a shows no bands in the
range 3200–3300 cm−1, characteristic of ꢁCꢀH stretch-
ing vibration, thus confirming that the DEBP spacer is
capped by two Pt moieties via s bonds. The wCꢁC
stretching mode appears at 2112 cm−1 as a sharp single
band. The absorption at 540 cm−1 (overtone of the
deformation mode of PꢀC bonds in the PPh3 ligands
for cis square planar complexes) is absent, as well as
bands around 320 cm−1, due to PtꢀCl stretching vibra-
tions. The UV spectrum shows an absorption band at
373 nm, close to the values found for mixed metal
acetylide complexes with Pt and Ru centers bridged by
(bis)ethynylbenzene, attributed to charge transfer tran-
sitions, i.e. ligand–metal charge transfer (LMCT) for Pt
moiety and metal–ligand (MLCT) for Ru moiety [9d].
The binuclear complex trans–trans-[(p-NO2ꢀC6H4ꢀ
CꢁC)Pt(PPh3)2(CꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁC)Pt(PPh3)2-
(CꢁCꢀC6H4ꢀp-NO2)] (4b), containing two electron
withdrawing groups, is obtained in basic conditions,
without the use of CuI, in a mixture containing the
mononuclear (bis)acetylide 3b as a minor product when
the reactants are in 1:1 stoichiometric ratio; we surpris-
ingly found that, running the reaction in the absence of
CuI, the reaction is slower, but the yield is not affected
and the reaction is much cleaner. The pattern of the
FT-IR spectrum is quite similar to that of the complex
3b, apart from the absence of the band at 3266 cm−1
(wꢁCꢀH); this results indicates that the DEBP moiety is
bridge-linked to the two Pt atoms. The trans structure
is again confirmed by the absence of the band at 540
cm−1. In the optical spectrum of 4b an absorption
maximum at 398 nm is found indicating an enhance-
2.3. Synthesis and characterization of
4,4%-(bis-phenylethynyl)-diethynylbiphenyl (7) and
4,4%-(bis-ferrocenylethynyl)-diethynylbiphenyl (8)
As mentioned before, there is still a controversial
discussion in the scientific community on whether the
electronic communication through p-conjugated carbon
bonds is favored or inhibited by (i) the insertion of
s-bonded transition metal into the conjugation path
[4a,9a,b,c,d], and/or (ii) the nature of the inserted metal
(for example Pd) and the structure of the organometal-
lic complex [9b]. Compounds 7 and 8 were prepared in
order to form with compounds 4a and 4c two pairs of
molecules differentiating only for the presence of the
platinum-bistriphenylphosphine moiety into the conju-
gation path. In this way a direct evaluation of the role
of a metal center on the properties of conjugated
compounds might be elucidated.
In a first series of experiments we attempted the
preparation of compounds 7 and 8 by the use of the
Glaser–Hay oxidative coupling of C6H5ꢀCꢁCꢀH (5)
and (h5-C5H5)Fe(h5-C5H4ꢀCꢁCꢀH) (6) with DEBP (2)
(Path a of Scheme 2). However, although operating
under a variety of experimental conditions, a complex
mixture of products were invariably obtained: among
the others biphenylbutadyine and polymeric materials
of type [ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀ]n were found
without any traces of the desired products 7 and 8.
Evidently homocoupling is always favored with respect
to cross coupling. A different synthetic approach was
ment of p conjugation in comparison with 3b (umax
=
388 nm). The tetranuclear complex trans–
trans-[(FcꢀCꢁC)Pt(PPh3)2(CꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁC)-

M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
53
Scheme 2.
then accomplished by using the palladium catalyzed
Stille coupling reaction [13,19,20], as outlined in Path b
of Scheme 2. Although this synthetic path required the
previous conversion of phenylacetylene and ferroceny-
lacetylene into the corresponding iodo derivatives 9 and
10 and the conversion of DEBP into the corresponding
bis-trimethyltin derivative 11, this route remains a
unique path to achieve the otherwise inaccessible com-
pounds 7 and 8.
The characteristic features of the FT-IR spectrum of
7 are the bands at 2213 and 2191 cm−1 (wCꢁC); the high
frequency band is shown only by compound 7 and is
characteristic of disubstituted aromatic alkynes [21].
The absence of this band in the corresponding Pt
containing complexes indicates that probably the coor-
dination of a metal atom to the triple bonds causes the
vanishing of this band (Table 1). The intensity of the
two bands is low because a pseudo center of symmetry
is established, about which the stretching of the triple
bond is symmetrical. The high energy of the CꢁC bands
also suggests that there is no contribution to partial
cumulenic linkages CꢂCꢂCꢂC in the molecule [9c].
Compound 7 revealed to be very air and light sensitive
either in the pure form and/or in solution. The FT-IR
spectrum of complex 8 shows a strong absorbance and
low resolution in the high energy region (4000–2000
cm−1), which is a characteristic of conducting proper-
ties [22]. However, the stretching vibration of the CꢁC
bonds is still detectable at 2141 cm−1 and the bands of
the ferrocene unit at 821 and 1027 cm−1 are also
present.
Having in hand compound 11, an alternative ap-
proach to the synthesis of compound 4a could be
performed. Coupling of 11 and 1a was carried out by
the procedure described by Lewis [3c]; following work
up, the binuclear complex 4a was isolated in 52% yield.
Despite the fact that the present route affords 4a in
lower yield than the dehydroalogenation procedure
Table 2
1H-NMR data (l, ppm) for compounds 3b,c

54
M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
Table 3
13C-NMR data (l, ppm) for compounds 3b,c
(Scheme 1), it represents an alternative route to disub-
stituted DEBP derivatives, that in case of 4b and 4c
might be prepared avoiding the concomitant formation
of the mononuclear derivatives 3b and 3c.
in compounds 7 and 8 not bearing the platinum sub-
stituent the HA,B resonances appear as a confused mul-
tiplet in the 7.7–7.4 ppm range, just like as signals of
the HA%,B% protons of compounds 3b and 3c. The 13C-
NMR spectroscopic features of either the unsymmetri-
cal compounds 3b and 3c (Table 3) and the symmetrical
compounds 7 and 8 (Table 5) show some very impres-
sive features. In particular in the 13C-NMR spectra of
compound 3b (Fig. 1(a)) it has been possible to detect
and assign five of the six nonequivalent acetylenic car-
bons 8, 7, 6, 5, and 5% (carbon marked as 6% is overlap-
ping with the CDCl3 triplet).
Of particularly interest are the signals of the
acetylenic carbons 7 and 8. Because of the 13C and 31P
coupling, both signals appear as a triplet. Carbon 7
closer to the platinum-bistriphenylphosphine moiety
shows a coupling constant of 14 Hz, while the more
distant carbon 8 shows a lower coupling constant of
J=2.5 Hz. In compound 3c this fine splitting was not
observed because of the presence of the iron center
which induces signal broadening, while the scarce solu-
bility of compounds 4a–c did not allow detection of
signals for alkyne carbons.
2.4. NMR characterization
In Tables 2 and 3 are reported NMR data (1H, and
13C) of compounds 3b and 3c, and Table 4 reports
1H-NMR data of compounds 4a–c, 7 and 8. The scarce
solubility of compounds 4a–c led to some difficulties
for their complete 13C-NMR characterization; however,
the main signals could be detected and assigned (Table
5). The higher solubility of compounds 7 and 8 allowed
their full 13C-NMR characterization, and specific attri-
bution of each signal of the carbon skeleton was possi-
ble (Table 5).
1
It is interesting to compare the H- and 13C-NMR
data of compounds 3b and c, bearing a unsymmetrical
substituted 4,4%-diethynylbiphenyl (DEBP) unit (Tables
2 and 3), with those of compounds 4a–c, 7 and 8
bearing a symmetrical substituted DEBP core (Tables 4
and 5). In the proton spectra of compounds 3b and 3c
(Table 2) the signals of the two different aromatic rings
of the DEBP units are clearly distinct. In both com-
pounds the protons on the phenyl ring attacked next to
the platinum moiety appear as two distinct doublets
(HA,B) at 7.1 and 6.3 ppm, while protons (HA%,B%) on the
ring bearing the free acetylene moiety appear as multi-
plet overlapping the signals of the triphenylphosphine
ligands. Proton resonances of the DEBP unit of com-
pounds 4a–c (HA,B) (Table 4) appear almost identical
to the HA,B proton of compounds 3b and 3c, thus
evidencing that in all compounds the proximity to the
platinum moiety impress the same spectroscopic fea-
tures to the protons of the nearest DEBP ring. In fact
Another remarkable feature seen in the 13C spectra of
compound 3b bearing the platinum-bistriphenylphos-
phine moiety, is the splitting of the signal observed for
the carbon resonances of the phenyl ring of the
triphenylphosphine ligand (Fig. 1(b)). Four distinct sig-
nals, are observed for the ipso, ortho, meta and para
carbons. While the latter appears as a singlet, the other
three appear as triplets, whose different coupling con-
stant (29, 6 and 5 Hz, respectively) reflects the progres-
sive distance from the phosphorous center. As before in
compound 4c this fine splitting was not observed be-
cause of the presence of the iron center which induces
signal broadening.

M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
55
Fig. 1. (a) 13C-NMR spectrum of the mononuclear bis-acetylyde complex 3b. (b) Expanded portion of the 13C-NMR spectrum of complex 3b
evidencing carbon resonances of the phenyl ring of the triphenylphosphine ligand.

56
M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
Table 4
1H-NMR data (l, ppm) for compounds 4a–c, 7 and 8
The 31P-NMR spectra show resonances with chemi-
cal shifts and J(195Ptꢀ31P) values in agreement with
those found for square planar Pt(II) trans isomers
[23] (Section 3).
Finally it is worth noting that an interesting char-
acteristic has been revealed upon observing the NMR
data of compounds reported in Tables 3 and 5. We
found that from the 13C-NMR data of the overall
series of compounds, it is possible to deduct a sys-
tematic and additive effect of substituents on the
chemical shift of each carbon of the different benzene
moieties. As consequence the 13C-NMR chemical shift
of each carbon of the benzene moieties of an hypo-
thetical compound made by combination of any of
the moieties of compounds 3–6 is fully predictable
[24].

M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
57
Table 5
13C-NMR data (l, ppm) for compounds 4a–c, 7 and 8
2.5. Conclusions
electron donor ligands were bound to Pt, with the aim
of tuning the electron delocalization along the highly
ethynylated sequence of the organic moieties. Related
molecules with no Pt inserted were also synthesized
and characterized with the purpose of doing a com-
parative study on the role of the metals on the elec-
tronic and optical properties of highly ethynylated
materials.
Several mono and dinuclear Pt(II) complexes were
obtained and characterized by using different synthetic
approaches. The complexes contain the 4,4%-bi-
s(ethynyl)biphenyl (DEBP) unit as the common ligand,
which is the central core bridging the metal units of
the bimetallic compounds. Electron withdrawing and

58
M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
3. Experimental
3.1. General procedure
argon atmosphere for 5 h. The reaction solution was
filtered and by addition of EtOH the product precipi-
tated as yellow powder. The powder was dissolved in
the minimum volume of 1:1 dichloromethane–toluene
and submitted to column chromatography (1:2
dichloromethane–toluene); further purification was
achieved by crystallization (CHCl3–EtOH) (0.147 g,
yield 80%).
FT-IR spectra were recorded on a Perkin–Elmer
1700 X spectrophotometer: the samples were prepared
as Nujol mulls using CsI cells.
UV–vis spectra were recorded on a Perkin-Elmer
Lambda 16 instrument. H-, 13C- and 31P-NMR spectra
1
were recorded on a Bruker AC 300P spectrometer at
300, 75 and 121 MHz, respectively. The 1H-NMR
chemical shifts (ppm) are assigned considering the refer-
4.1.2. Reaction of trans-[ClꢀPt(PPh3)2 (ꢀCꢁCꢀC6H5)]
(1a) with 4,4%-bis(trimethyltin)ethynylbiphenyl (11)
Complex 1a (0.106 g, 0.1 mmol) and 11 (0.033 g, 0.06
mmol; a little excess of 11 improves the reaction yield)
were added into 30 ml of toluene with 0.008 g of CuI.
The reaction mixture was heated at 60°C for 6 h and
then a pale yellow powder was obtained by precipita-
tion with EtOH. The crude powder was then purified as
above reported in method (4.1.1), yielding pure 4a
(yield 52%). Elemental analysis: Found: C, 68.05; H,
4.28 Calc. for C120H78P4Pt2: C, 67.82; H, 4.27%. FT-IR
(cm−1): 2112 (wCꢁC). 31P-NMR (CDCl3): l (ppm) 17.31,
J(PtꢀP)=2646 Hz.
1
ence Me4Si signal at 0 ppm and the residual H impu-
rity signal in the solvent at 7.24 ppm (CDCl3). The
13C-NMR chemical shifts are calibrated to the 13C
triplet of CDCl3 at 77 ppm. The 31P-NMR chemical
shifts are relative to 85% H3PO4. Low resolution mass
spectra (FAB, m-nitrobenzyl alcohol) was obtained
with a VG-Quattro Instrument, at the Universita` di Tor
Vergata, Roma.
Elemental analyses were determined by Servizio di
Microanalisi of the Department of Chemistry, Univer-
sity of Rome, La Sapienza.
Solvents including those used for chromatography,
were distilled over standard drying agents and degassed
before use. Chromatographic separations were per-
formed with 70–230 mesh silica gel (Merck). All reac-
tions were performed under Argon atmosphere, using
standard glassware and equipment. Et2NSnMe3 was
prepared according to a published method [25].
Preparations of trans-[(C6H5ꢀCꢁC)Pt(PPh3)2Cl] (1a),
trans-[(p-NO2C6H4ꢀCꢁC)Pt(PPh3)2Cl] (1b) and trans-
{ClPt(PPh3)2[(CꢁCꢀh5-C5H4)Fe(h5-C5H5)]} (1c) were
performed by reacting cis-[Pt(PPh3)2Cl2] and the corre-
sponding alkynes, according to the synthetic routes
reported in the literature, references [15,16b], respec-
tively. DEBP (2) was obtained by the reaction reported
in the literature [26]. Phenylacetylene (5) was a com-
mercial product (Aldrich) dry distilled before use.
Ethynylferrocene (6) was prepared according to a pub-
lished method [27].
4.2. Formation of trans-[(p-NO2ꢀC6H4ꢀCꢁCꢀ)-
Pt(PPh3)2 (ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀH)] (3b) and
trans–trans-[(p-NO2ꢀC6H4ꢀCꢁCꢀ)Pt(PPh3)2-
(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀ)Pt(CꢁCꢀC6H4ꢀp-NO2)
(PPh3)2] (4b)
4.2.1. Reaction of trans-[ClꢀPt(PPh3)2(ꢀCꢁCꢀC6H4ꢀp-
NO2] (1b) with 4,4%-bis(ethynyl)biphenyl (2)
This reaction can be orientated toward the prevalent
formation of (i) 3b or (ii) 4b depending on the reaction
conditions. (i) Compound 2 (0.500 g, 2.47 mmol) was
dissolved in the minimum amount of CHCl3 and to this
solution 10 ml of NHEt2 were added. Another solution,
containing complex 1b (0.400 g, 0.44 mmol) dissolved
in a mixture of solvents, (i.e. 25 ml of CHCl3 and 100
ml of EtOH), was prepared and poured dropwise into
the former one; the final mixture was stirred for 15 h at
r.t. The reaction mixture was then filtered through a
glass frit (c4) to separate traces of 4b and the solvent
was reduced to a small volume (20 ml); by addition of
EtOH a crude material precipitated as brown powder
that was dissolved in the minimum amount of 1:1
dichloromethane–toluene and then further purified by
chromatography (1:1 dichloromethane–toluene eluent).
The eluted fraction containing 3b was dry evaporated
and the residue crystallized with CHCl3, giving pure 3b
in 50% yield. Elemental analysis: Found: C, 67.40; H,
4.05; N, 1.30. Calc. for C60H43NO2P2Pt: C, 67.54; H,
4.06; N, 1.31%. FT-IR (cm−1): 3266(wꢁCꢀH), 2105
(wCꢁC). 31P-NMR (CDCl3): l (ppm) 19.40, J(PtꢀP)=
2618 Hz.
4. Syntheses
4.1. Formation of
trans–trans-[(C6H5ꢀCꢁCꢀ)Pt(PPh3)2-
(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀ)Pt(ꢀCꢁCꢀC6H5)-
(PPh3)2] (4a)
4.1.1. Reaction of trans-[ClꢀPt(PPh3)2(ꢀCꢁCꢀC6H5]
(1a) with 4,4%-bis(ethynyl)biphenyl (2)
Complex 1a (0.170 g, 0.2 mmol) and DEBP (2) (0.02
g, 0.1 mmol) were dissolved in 20 ml of CHCl3 and 1.6
ml of NHEt2 and CuI (0.007 g) was added immediately
after. The reaction mixture was warmed at reflux under
(ii) The complex trans-[ClꢀPt(PPh3)2(ꢀCꢁCꢀC6H4-
NO2)] (1b) (0.260 g, 0.28 mmol) and DEBP (2) (0.03 g,

M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
59
0.14 mmol) were dissolved in 30 ml of CHCl3. NHEt2
(5 ml) was added to the solution and the reaction
mixture was warmed at reflux for 48 h. The progress of
the reaction was monitored by TLC performed on
periodical checks. The final solution was concentrated
to small volume and by addition of EtOH, a crude
red–brown precipitate was obtained. The solid residue
was dissolved in a mixture of 1:1 dichloromethane–tol-
uene and purified by column chromatography using the
same solvents mixture as the eluent. Following a first
band constituted by unreacted DEBP (0.0169, 50%) a
second fraction showing UV absorption at u=390 nm
was collected and the pure complex (3b) was obtained
after evaporation of the solvent (0.045 g, 15%). A
further fraction eluted from the chromatographic
column, showing umax=397 nm, contains the dinuclear
complex (4b), that is recovered after evaporation under
vacuum as a bright yellow powder (0.27 g, 50%). Ele-
mental analysis: Found: C, 64.70; H, 3.99; N, 1.46.
Calc. for C104H76N2O2P4Pt: C, 64.66; H, 3.97; N,
1.45%. FT-IR (cm−1): 2104 (wCꢁC), 1101. 31P-NMR
(CDCl3): l (ppm) 19.36, J(PtꢀP)=2620 Hz.
and by addition of EtOH a solid yellow product was
obtained. The crude product was dissolved in the mini-
mum volume of 1:1 dichloromethane–toluene and then
purified by column chromatography (2:1 dichloro-
methane–toluene eluent). Complex 4c was further
purified by crystallization with CHCl3–EtOH (yield
40%). Elemental analysis: Found: C, 65.67; H, 4.23.
Calc. for C112H86Fe2P4Pt2: C, 65.38; H, 4.21%. FT-IR
(cm−1): 2115 (wCꢁC); 1101 (PPh3) 804, 818 (wCꢀH Ar),
31P-NMR (DMF-d7 at 343 K):
J(PtꢀP)=2652 Hz.
l (ppm) 19.56,
4.4. Preparation of phenylacetilene iodide (9)
A solution of phenylacetylene (5) (7.2 mmol, 0.8 ml)
in methanol (40 ml) was cooled to 0°C and treated with
solid KOH (18 mmol, 1 g). After 20 min of stirring at
a low temperature solid N-iodosuccinimide (8.6 mmol,
1.940 g) was added to the mixture, and the stirring
continued at 0°C for 15 min. The cold bath was then
removed and the stirring continued at r.t. for an addi-
tional 20 min. Then 200 ml of Et2O was added and the
mixture extracted three times with brine. The organic
layer was separated, dried over MgSO4, filtered, and
evaporated. The product was isolated in quantitative
yield as brown oil. FT-IR (neat film, cm−1): 2171
(wCꢁC); 1070, 1026, 754 (wCꢀH Ar); 3080, 3056, 3031
4.3. Formation of trans-{[(p5-C5H5)Fe(p5-C5H4ꢀCꢁCꢀ)]-
Pt(PPh3)2(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀH)} (3c) and
trans–trans-{[(p5-C5H5)Fe(p5-C5H4ꢀCꢁCꢀ)]Pt(PPh3)2-
(ꢀCꢁCꢀp-C6H4ꢀp-C6H4ꢀCꢁCꢀ)Pt[(ꢀCꢁCꢀp5-C5H4)-
Fe(p5-C5H5)] (PPh3)2} (4c)
(wCꢀH Ar); 1489, 1443 (wCꢀH Ar).UV–vis (THF): umax
=
1
257 nm. H-NMR: l (ppm) 7.26–7.34 (m, 3H), 7.39–
7.45 (m, 2H), aromatic protons. Elemental analyses:
Found: C, 41.98; H, 2.20. Calc. for C8H5I: C, 42.14; H,
2.21%. A different reaction route was already proposed
for the synthesis of 9 [28].
4.3.1. Reaction of trans-{ClꢀPt(PPh3)2[(ꢀCꢁCꢀp5-
C5H4)Fe(p5-C5H5)]} (1c) with 4,4%-bis(ethynyl)biphenyl
(2)
(i) DEBP (2) (0.200 g,
1
mmol) and the
monochloroacetylide Pt complex (1c) (0.450 g, 0.5
mmol) were mixed in 700 ml of THF with 18 ml of
NHEt2. The reaction was run at reflux for 48 h under
argon atmosphere, giving a brown powder (4c) that was
filtered off and washed with ethanol (yield 10%). The
remaining reaction solution was evaporated to dryness,
under vacuum, and the solid residue was dissolved in
the minimum volume of the 1:2 dichloromethane–tolu-
ene mixture and submitted to chromatography (1:2
dichloromethane–toluene eluent). Pure complex (3c)
was obtained from the eluted fractions by precipitation
with EtOH (yield 40%). The characterization of 3c is
the following: Elemental analysis: Found: C, 68.31; H,
4.27. Calc. for C64H48FeP2Pt: C, 68.03; H, 4.28%. FT-
IR (cm−1): 3276 (wHꢀCꢁ), 2109 (wCꢁC). 31P-NMR
(CDCl3): l (ppm) 19.59, J(PtꢀP)=2660 Hz.
(ii) DEBP (2) (0.080 g, 0.40 mmol) was dissolved in
45 ml of previously degassed toluene with complex 1c
(0.750 g, 0.80 mmol), and 4 ml of Et2NH were added to
the solution. The reaction mixture was heated at reflux
for 36 h, yielding a deep red solution and a white
precipitate (ammonium salt) that was filtered off. The
volume was reduced to 20 ml with a rotary evaporator
4.5. Preparation of ethynylferrocene iodide (10)
Using the procedure described above, ethynylfer-
rocene (6) (3.0 mmol, 0.63 g) in methanol (40 ml) was
first treated with KOH (7.9 mmol, 0.44 g) at 0°C and
then with N-iodosuccinimmide (3.6 mmol, 0.820 g).
Subsequent Et2O–brine extraction, drying over MgSO4,
filtration and evaporation afforded quantitative
product as brown solid. FT-IR (cm−1): 2176 (wCꢁC).
UV–vis (CHCl3): umax=269 nm. 1H-NMR: l (ppm)
4.15–4.19 (m, 2H), 4.20 (s, 5H), 4.40–4.45 (m, 2H).
Elemental analysis: Found: C, 43.04; H, 2.71. Calc. for
C12H9FeI: C, 42.90; H, 2.70%.
4.6. Preparation of 4,4%-bis(trimethyltin)ethynylbiphenyl
(11)
A 100 ml Schlenk tube was loaded with 4,4%-bi-
s(ethynyl)biphenyl (2) (1 mmol, 0.20 g) and capped with
a rubber septum. The side arm was then connected with
a vacuum–argon manifold and several evacuation–ar-
gon filling cycles were performed. With the use of a

60
M.V. Russo et al. / Journal of Organometallic Chemistry 619 (2001) 49–61
syringe Et2NSnMe3 (2.1 mmol, 0.65 g) was introduced
through the septa and the resulting mixture was stirred
at r.t. for 1 h. After this time, the mixture was exposed
to the vacuum, and the diethylamine side product
formed during the reaction was removed. The product
was thus isolated in quantitative yield as a pale yellow
solid. FT-IR (cm−1): 2136 (wCꢁC); 1917; 825 (wCꢀH Ar).
Acknowledgements
The authors wish to thank CNR (Consiglio
Nazionale delle Ricerche), Italy, PF-MSTA II, for the
financial support to this work.
1H-NMR:
l
(ppm) 0.35 (s, J(117Snꢀ1H)=29.0,
References
J(119Snꢀ1H)=30.3 Hz, 18H), 7.49 (m, 8H). 13C-NMR:
l (ppm) −7.65 (t, J(117Snꢀ13C)=192.5 Hz), −7.65 (t,
J(119Snꢀ13C)=202.5 Hz) (CH3); 94.55 (t, J(117–
119Snꢀ13C)=202 Hz) (C of the alkyne). UV–vis
(CHCl3): umax=300 nm. Elemental analysis: Found: C,
49.96; H, 4.95. Calc. for C22H26Sn2: C, 50.06; H, 4.96%.
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4.7. Preparation of 4,4%-(bis-phenylethynyl)-
diethynylbiphenyl (7)
Phenylacetyleneiodide (9) (1.1 g, 4.9 mmol) was
added into the reaction vessel, where 4,4%-
bis(trimethyltin)ethynyl-biphenyl (11) (1.3 mmol) was
previously prepared, with 40 ml of dry THF and
Pd(PPh3)4 (0.015 g, 0.013 mmol) as the catalyst. The
reaction was performed at 50°C overnight (16 h). Then
the reaction solvent and the Sn(CH3)2I by-product were
removed under vacuum pumping. To the brown residue
THF (50 ml) was added and the solution was passed
through a celite filter. Then dry, degassed n-pentane (30
ml) was added and the mixture stirred overnight at
−30°C. Compound 7 (very air sensitive) was thus
precipitated and recovered by filtering under argon
atmosphere (yield 50%). Because of its sensitivity the
compound must be stored under argon at ca. 2°C.
FT-IR (cm−1): 2186 (wCꢁC), 821, 755 (wCꢀH Ar). MS
(FAB) m/e=403 [M+H]+
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Polymers with Special Properties: NATO ASI Series E, vol. 208,
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4.8. Preparation of 4,4%-(bis-ferrocenylethynyl)-
diethynylbiphenyl (8)
Using the same procedure for the preparation of (7),
ethynylferrocene iodide (10) (2.7 mmol, 0.905 g) and
(11) (1.34 mmol, 0.70 g) were added to a solution of
Pd(PPh3)4 (0.13 mmol, 0.156 g) in 30 ml of THF and
the resulting mixture was stirred at 70°C for 16 h. Then
the reaction solvent and the (CH3)2SnI side product
were removed under vacuum pumping and a crude
powder was obtained. The powder was dissolved in the
minimum amount of a 1:3 THF–n-hexane mixture and
was purified by chromatography using the same solvent
mixture as the eluent. Following evaporation of the
solvent, compound (8) was obtained as a red–orange
solid (yield 10%). An analytical sample was prepared by
crystallization with CHCl3–EtOH. FT-IR (cm−1): 2141
(wCꢁC), 1027, 821 (wCꢀH ferrocene). UV–vis (CHCl3):
umax=337 nm. Elemental analysis: Found: C, 78.01; H,
4.22. Calc. for C40H26Fe2: C, 77.70; H, 4.24%.
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