A porphyrin-bridged Pd dimer complex stabilizes gold nanoparticles

Article abstract of DOI:10.1002/ejic.201100339

A porphyrin-bridged bimetallic palladium(II) diphenylacetylide complex and the oligomer with 3-5 repeat units have been prepared and spectroscopically characterized. The porphyrin-bridged Pd complex has been used for the stabilization of gold nanoparticle

Full text of DOI:10.1002/ejic.201100339

FULL PAPER
DOI: 10.1002/ejic.201100339
A Porphyrin-Bridged Pd Dimer Complex Stabilizes Gold Nanoparticles
Ilaria Fratoddi,*[a] Chiara Battocchio,[b] Giovanni Polzonetti,[b] Fabio Sciubba,[c]
Maurizio Delfini,[a] and Maria Vittoria Russo[a]
Keywords: Gold / Nanoparticles / Porphyrinoids / Palladium / NMR spectroscopy
A porphyrin-bridged bimetallic palladium(II) diphenylacet-
ylide complex and the oligomer with 3–5 repeat units have
been prepared and spectroscopically characterized. The por-
phyrin-bridged Pd complex has been used for the stabiliza-
tion of gold nanoparticles, thus giving rise to unexpected
stable structures with no evidence of covalent bonds be-
tween the porphyrin and the gold nanoparticles. The mor-
phology investigated by TEM analysis shows that gold nano-
particles with a mean diameter of about 5 nm have been ob-
tained. UV/Vis spectra reveal the achievement of stabilized
gold nanoparticles through the presence of the plasmon reso-
nance at 500 nm together with the absorption features of the
porphyrin molecule at 436 and 620 nm (Q band). Photolumi-
nescence spectra exhibit an emission feature centred at
572 nm with a shoulder at 325 nm with no quenching effects.
XPS measurements at the Au 4f core level suggest an elec-
tronic interaction between the gold atoms of the nanoparticle
surface and the porphyrin-based complex; NMR spectro-
scopic studies indicate that interactions and assemblies also
occur that involve the porphyrin rings. Elemental analysis
suggests that about 120 tilted porphyrins are physisorbed
onto the Au core.
the gold core.[8] Free-base porphyrins with two thioacetate-
terminated linkers in different positions on the porphyrin
molecule have been used for the stabilization of gold nano-
particles and short fluorescence lifetimes have been mea-
sured, thus indicating efficient energy transfer to the gold
cores.[9] The control of the size of gold nanoparticles is also
an important feature; it has been achieved by the link of a
tetradentate porphyrin monolayer on the gold surface with
well-defined orientation,[10] and gold nanoparticles stabi-
lized with porphyrins with four sulfur atoms provide quite
small size-controlled gold nanoparticles.[11,12] The tuning of
the plasmon coupling between the Au nanocrystals of linear
chains of Au nanorods is proposed for tetrakis(4-sulfonato-
phenyl)porphyrin aggregates in solution, thereby providing
potential applications of metal nanocrystals in the areas of
photonics, electronics and optics.[13] The transduction of
optical radiation to current in a molecular circuit made by
a network array of AuNPs bridged through a dithiol–Zn
porphyrin trimer has been recently reported, which suggests
that the plasmon-controlled electrical properties of these
molecules can be tailored to be applied in optoelectronic
and energy-harvesting devices.[14] Gold nanoparticles are
usually stabilized by a sulfur–Au covalent bond, and a few
examples of physisorption of a porphyrin derivative without
covalent bonding are known.[15] The assembly of gold
nanoparticles stabilized by noncovalently bonded electro-
optically active conjugated molecules is a suitable model to
study the electronic structure of the molecules that interact
with gold nanoparticles.
Introduction
Porphyrins are a class of multifunctional and versatile π-
conjugated molecules with interesting optical, photocata-
lytic and light-harvesting properties that have shown great
potential in the fabrication of multifunctional electronic
and optical devices through covalent linking to metal nano-
particles.[1–3] Understanding the factors that affect the inter-
action between chromophores and metal nanoparticles is
essential in the design of effective applications. The rational
design of gold nanoparticles that link different stabilizers
has driven extended studies because these complex struc-
tures offer the chance to bind and incorporate various or-
ganic, inorganic or bioactive molecules.[4,5] Recently PdII-
containing organometallic thiols have also been used for the
stabilization of gold nanoparticles (AuNPs).[6]
In the case of porphyrin-functionalized gold nanopar-
ticles, energy-transfer processes from the photoexcited chro-
mophore to the gold core lead to quenching of porphyrin
fluorescence in porphyrin-functionalized gold nanopar-
ticles.[7] Porphyrins as linkers on gold nanoparticles also
have the advantage of exploiting multiple binding sites to
achieve a better control of the orientation of porphyrins on
[a] Department of Chemistry, “Sapienza” University of Rome,
P.le A. Moro 5, Box 34 Roma 62, 00185 Rome, Italy
E-mail: ilaria.fratoddi@uniroma1.it
[b] Department of Physics,
unità INSTM and CISDiC University Roma Tre,
Via della Vasca Navale 85, 00146 Rome, Italy
[c] Università Telematica Internazionale UniNettuno,
Facoltà di Ingegneria Corso Vittorio Emanuele II,
39 00186, Rome, Italy
In this paper we report the synthesis and characterization
of a Zn–porphyrin-bridged diacetylide PdII complex with
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100339.
4906
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A Porphyrin-Bridged Pd Dimer Complex Stabilizes Gold Nanoparticles
extended π conjugation capable of efficiently interacting
with gold nanoparticles by physisorption to yield stable
conjugates without the need for S–Au bonding.
Results and Discussion
Synthesis and Characterization of Pd–Porphyrin Complex 4
and Oligomer 5
The synthetic route to yield the porphyrin-bridged Pd
complexes is based on the widely applicable dehydrohaloge-
nation reaction.[16] This reaction was successfully used for
the achievement of porphyrin-bridged Pt complexes and
oligomers, the chemical and electronic structure of which
has been investigated in depth in our group.[17–19] These
multinuclear Pt complexes are also capable of self-assembly
into nanostructured features.[20] However, the synthesis of
analogous Pd complexes proved to be very difficult, because
of decomposition that occurs during purification (crystalli-
zation and chromatography). Previous attempts to prepare
complex 4 gave preliminary results and few insights into the
self-assembly properties of this complex in comparison with
the Pt analogues studied.[21] The synthesis has now been
reinvestigated, and the products carefully characterized.
The reaction routes that started from Zn–porphyrin 1 and
led to complexes 4 and 5 are depicted in Scheme 1.
The reaction courses were monitored with UV/Vis ab-
sorption measurements at subsequent times; the intensity
of the Soret band at 424 nm of precursor 1 decreased,
whereas those of the bands at 452 nm for complex 4 and
462 nm for oligomer 5 increased. Oligomer 5 showed a
moderate increase in electron delocalization through the
macromolecule, with a considerable redshift in the band rel-
ative to that of ZnDEP. The FTIR spectra of 4 and 5 con-
Scheme 1. Reaction scheme and chemical structures of ZnDEP (1),
complex 4 and oligomer 5.
firm the achievement of the coupling reaction by the ab- at δ = 10.46 and 11.60 ppm, which are attributed to phos-
sence of the band at 3200 (free NH in non-metalated por- phorus atoms on terminal and internal sites, respectively.[16]
phyrin) and of the bands at 3264 and 622 cm–1 characteris- The relative integrals are about 1:1.5 (i.e. corresponding to
tic of the H–CϵC stretching mode and bending mode, an oligomer made of 3–5 units). A GPC analysis was car-
respectively, of 1, whereas enhancement of intensity and a ried out and Mw and Mn data (Mw=5570 a.m.u.,
slight shift in the band for the CϵC stretching mode Mn=3700 a.m.u.) agree with the 31P NMR spectroscopic re-
[2083 cm–1 for 1, 2079 cm–1 for complex 4 and 2066 cm–1 sults.
for complex 5, respectively] were found.
NOESY spectra with several mixing times (150, 200, 250
The full characterization of 4 was accomplished by and 500 ms) were acquired with the aim of exploring the
means of NMR spectroscopic investigations. The 1H 1D molecule spatial arrangement of complex 4. Strong dipolar
NMR and COSY spectra of 4 can roughly be divided into correlations, which correspond to interproton distances that
two regions; the first one ranges from about δ = 0.60 ppm range from 2 to 3 Å, were observed among the n-butyl pro-
to about 5.00 ppm in which aliphatic protons resonate, tons and between the –CH3 protons and the n-butyl ones.
whereas in the latter region (from δ = 7 to 10 ppm) aromatic Smaller cross peaks, which correspond to interproton dis-
protons can be observed. The COSY spectrum allowed us tances that range from 3 to 5 Å, were observed between the
to unequivocally assign all proton resonances; experimental resonance of ortho aromatic protons and n-butyl protons
details are reported in the Supporting Information. The 31
P
and between meso protons and –CH2 ethyl protons. Those
NMR spectrum evidenced a single resonance at δ = correlations suggest that some n-butyl chains could be posi-
10.86 ppm for the two equivalent phosphane ligands. The tioned near the porphyrin ring and others near the phenyl
observed resonances confirmed the structure of complex 4. groups. To evaluate the possibility of intermolecular stack-
1
The H NMR spectrum of 5 shows the characteristic com- ing, several 1D proton and 2D NOESY experiments were
plexity of polydispersed species, yet it was possible to recog- acquired with a concentration that ranged from 0.5 mg/
nize the polymer resonances by comparison with the spec- 0.6 mL to 2 mg/0.6 mL according to previous studies.[22] In
trum of 4. The 31P NMR spectrum shows two resonances this concentration range, no chemical shift, half-height
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Table 1. XPS data collected on complex 4 and oligomer 5; the same data collected and already published for the trans-[Pd(PBu3)2Cl2]
complex are also reported for comparison.
Sample
C 1s
EB (fwhm) [eV]
Pd 3d5/2
EB (fwhm) [eV]
P 2p3/2
EB (fwhm) [eV]
Zn 2p3/2
EB (fwhm) [eV]
N 1s
EB (fwhm) [eV]
4
283.40
284.70
(1.76)
283.20
284.70
(2.16)
285.00
(1.50)
337.70
(1.78)
130.75
(1.65)
1022.00
(1.65)
398.24
(1.65)
5
337.83
(1.77)
130.86
(1.55)
1022.20
(3.2)
398.26
(1.64)
trans-[PdCl2(PBu3)2]
338.07
(1.42)
130.90
(1.42)
–
–
width or dipolar correlation variations were observed, thus
suggesting that the molecule does not show auto-assembly
behaviour. The half-height width variations provide the re-
lationship between this parameter and transversal relax-
ation time T2;[23] thus by comparing two peaks with dif-
ferent widths, the broader resonance can be assigned to the
molecular moiety that rotates more slowly. The absence of
half-height width variations for the resonance of the meso
protons is very important since a broadening of their line
shape is indicative of an interaction that involves the por-
phyrin ring. Since this behaviour is common for all proton
resonances, this is a further indication that the molecule
does not auto-assemble in the examined concentration
range, as reported in the literature in analogous studies on
porphyrin materials.[24]
The binuclear complex 4 and compound 5 were investi-
gated by means of X-ray photoelectron spectroscopy with
the aim of investigating both the electronic and molecular
structure. C 1s, Pd 3d, P 2p, Cl 2p, Zn 2p and N 1s signals
were collected and analyzed, as reported in Table 1. The
collected data were compared to the ones measured for the
trans-[Pd(PBu3)2Cl2] precursor to investigate the expected
electronic structure modifications. A Pd 3d5/2 signal was
found at a binding energy (EB) of 337.70 eV in both por-
phyrin complex 4 and compound 5, only slightly shifted
from that of the precursor that is at EB = 338.07 eV, which
Figure 1. Pd 3d spectra of complex 4 and oligomer 5. The same
spectrum measured for [Pd(PBu3)2Cl2] is superimposed for com-
parison.
Cl 2p/Pd 3d signal ratio a chain length of 3–4 metal units
was calculated, as also suggested by the GPC and 31P NMR
spectroscopic results.
Synthesis and Characterization of Porphirin-Stabilized Gold
Nanoparticles (AuNPs-4)
Gold nanoparticles coated with complex 4 were prepared
suggests slight electron conjugation through the π-conju- by NaBH4 reduction of HAuCl4 in a two-phase procedure
gated organic moieties and the metal centre. The 0.37 eV to give red porphyrin-stabilized gold nanoparticles AuNPs-
EB shift is clearly shown in Figure 1, in which the Pd 3d 4. Gold nanoparticles AuNPs-4 were stable and the surface
spectra of the three samples are displayed.
plasmon band did not change over weeks. Figure 2 shows
The C 1s signals of both complex 4 and compound 5 the UV/Vis absorption and emission (photoluminescence,
show two main components. The component at 284.70 eV PL) spectra of the purified AuNPs-4 nanoparticles in com-
is due to aliphatic and (most) aromatic C atoms; the less parison with those of complex 4. The spectrum shows both
intense component at EB = 283.40 eV is attributed to C features characteristic of the porphyrin and gold nanopar-
atoms bonded to the metal centre, as already reported in ticles (i.e. the Soret and Q bands at 436 and 620 nm, respec-
the literature for organometallic compounds.[16] N 1s sig- tively, and the surface plasmon band at around 500 nm).
nals appear at about EB = 398.26 eV for both samples, as The Soret band of AuNPs-4 was significantly broadened
expected for N atoms of the metalloporphyrin ring.[21]
and blueshifted relative to that of 4 before reduction:
The Cl 2p core level was carefully analyzed for com- 436 nm for AuNPs-4 versus 452 nm for 4 were detected,
pound 5, with the aim of individuating the terminal groups thereby suggesting that electronic interactions between gold
and estimating the number of repetitive units. A Cl 2p3/2 nanoparticles and the porphyrin and/or side-by-side align-
signal at EB = 198.05 was detected, as expected for chlorine ment of 4 on the gold surface occur.[26] Moreover, a ligand-
terminal groups in organometallic compounds.[25] From the dependent decrease of the Soret-band intensity is observed
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A Porphyrin-Bridged Pd Dimer Complex Stabilizes Gold Nanoparticles
that also points to an electronic interaction between the
porphyrin and the Au nanoparticles.[27] The PL spectra
show an emission peak at about 572 nm with a shoulder at
625 nm and no quenching effects and features significantly
narrower and blueshifted bands relative to those of complex
4 (Δλ = 67 nm). By considering that porphyrins very close
to each other and to the gold nanoparticle surface show a
broadening in the absorption features because of aggrega-
tion effects,[28] the optical results confirm an interaction be-
tween the Au core and the porphyrin ligand.
Figure 2. UV absorption and emission spectra of 4 and AuNPs-4
in CHCl3.
Figure 3. (a) TEM images of AuNPs-4 with mean diameter
(5.0Ϯ1.4) nm, circles have been added to easily distinguish some
of the many particles with low sizes; the arrows indicate small par-
ticles characterized by some shape and faceting. (b) Tilted confor-
mation model of complex 4 on the gold surface. (c) Dimensions
distribution.
Figure 3 shows a TEM image of AuNPs-4. The particle
distribution consists of two populations; the mean diameter
of the observed spherical particles is 5.0Ϯ1.4 nm and con-
tains roughly 2000 gold atoms, calculated according to a
literature report[29] with a surface area of about 50 nm2. By
considering the elemental analysis results,[30] a single gold
nanoparticle should interact with approximately 120 mole-
cules of complex 4; the ratio between the number of gold
atoms and the number of complex 4 molecules is equal to
16.7. In analogy to what was reported in the literature for
1.63 ppm superimposed with the water singlet at δ =
1.47 ppm. In this region the resonances due to the n-butyl
CH3 and CH2 protons and several broad multiplets at δ =
1.72 and 1.88 ppm, respectively, assigned to terminal CH3
protons of the ethyl groups on the porphyrinic ring are ob-
served. Between δ = 3.30 and 4.00 ppm broad resonances
can be observed at δ = 3.64 and 3.94 ppm, which are associ-
meso-5,10,15,20-tetrakis-2-thienylporphyrin
physisorbed
onto gold nanoparticles and by using the cross-sectional
area of a similar compound that can be adsorbed onto gold
nanoparticles in flat or edge-on configurations (approxi-
mately 1.7 and 0.8 nm2),[15] we can assume that 120 mole-
cules of complex 4 are arranged on the gold surface with a
tilted conformation (see Figure 3b) and in which porphyrin
rings interact with each other, as reported for similar por-
phyrin complexes adsorbed onto flat gold surfaces.[21,31]
The 1D proton spectra of AuNPs-4 nanoparticles were
1
acquired and are reported in Figure 4 together with the H
NMR spectrum of complex 4. The spectral profile of
AuNPs-4 is similar yet different to the one observed for the
isolated molecule. As before, the spectrum can be divided
into an aliphatic region between δ = 0.50 and 4.00 ppm, an
aromatic region between δ = 6.8 and 7.5 ppm and the meso
proton region at about δ = 10 ppm. In the region between
δ = 0.70 and 2.00 ppm several complex resonances can be
observed: a broad signal at δ = 0.77 ppm, a multiplet at
Figure 4. 1H NMR spectra of complex 4 (black) and AuNPs-4
δ = 0.89 ppm and another broad resonance from 1.20 to (grey).
Eur. J. Inorg. Chem. 2011, 4906–4913
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Table 2. XPS data (EB, fwhm) collected on sample AuNPs-4. For comparison, complex 4 XPS data are also reported.
Sample
C 1s
EB (fwhm) [eV]
Pd 3d5/2
EB (fwhm) [eV]
P 2p3/2
EB (fwhm) [eV]
Zn 2p3/2
EB (fwhm) [eV]
N 1s
EB (fwhm) [eV]
Au 4f7/2
EB (fwhm) [eV]
4
284.70
(1.76)
284.70
(1.96)
337.70
(1.78)
338.36
(1.83)
130.75
(1.65)
130.81
(1.62)
1022.00
(1.65)
1021.66
(2.10)
398.24
(1.65)
398.41
(2.15)
–
AuNPs-4
83.56
84.98
(1.52)
ated to CH2 and methyl groups on the porphyrinic ring. In sisorption occurring between the gold nanoparticles and the
the aromatic region a broad, complex resonance is found porphyrin-based complex with no significant EB shifts in
between δ = 7.06 and 7.40 ppm. The signal at δ = 7.06 ppm the core-level spectra of complex 4 atoms.
is attributed to the aromatic para protons of the terminal
phenyl ring, the deformed doublet at δ = 7.16 ppm to the
meta protons and the other doublet at δ = 7.27 ppm to the
ortho protons. At lower fields, a broad singlet at δ =
9.94 ppm can be identified and attributed to the meso pro-
tons.
The spectrum of AuNPs-4 differs from that acquired for
the isolated molecule, slight chemical-shift variations and,
more importantly, a general broadening of all resonances.
For example, the terminal n-butyl CH3 in 4 shows a width
of 1.48 Hz, which increases to about 4 Hz in the case of
the nanoparticles. A similar resonance broadening can be
observed for all the molecule protons with a various degree
of broadening; noteworthy is that the CH2 signal of the
Figure 5. XPS Au 4f spectrum of AuNPs-4.
ethyl group widens from 4.5 to 70.5 Hz; the meso proton
singlet is the most affected, thereby increasing its width
from 1.5 to about 130 Hz. This significant increase in the
half-height width, which corresponds to a much longer cor-
relation time relative to that of the isolated molecule and
thus to a lower mobility, strongly suggests the formation of
an interaction between complex 4 molecules in AuNPs-4.[32]
Since the greater half-height width variation is observed for
the resonance of the meso protons, and by considering that
their chemical shift is also the most affected by the interac-
tion with Au, it could be hypothesized that complex 4 stabi-
lizes the nanoparticles through the porphyrinic rings yet
still retains a degree of mobility for the n-butyl and phenyl
moieties.
X-ray photoelectron spectroscopy measurements were
also performed on the porphyrin-stabilized gold nanopar-
ticles AuNPs-4; data were acquired at C 1s, N 1s, P 2p, Pd
3d, Zn 2p and Au 4f core-energy levels and compared to the
data acquired on pristine complex 4, as shown in Table 2.
The C 1s, N 1s, Pd 3d, Zn 2p and P 2p EB values ob-
served for the AuNPs-4 sample are quite close to those mea-
sured for complex 4, thus showing that the interaction with
gold nanoclusters does not affect the chemical structure of
the Zn–porphyrin complex.
Conclusion
Protected gold nanoparticles have been prepared with a
porphyrin-bridged di-bis(tributylphosphane)palladium–di-
phenylacetylide dinuclear complex 4 as stabilizing agent.
The analogous oligomer with 3–5 repeat units (5) has also
been prepared and spectroscopically characterized. The
gold nanoparticles surrounded by the porphyrin complex
(AuNPs-4) show a spherical shape with mean diameter of
about 5 nm, observed by TEM analysis. The optical charac-
terizations allowed us to assess the plasmon resonance at
500 nm and the absorption features of the porphyrin-based
complex at about 440 and 620 nm; also, no quenching ef-
fects in the emission features centred at 572 nm with a
shoulder at 325 nm have been observed. NMR spec-
troscopy, XPS and elemental analyses suggest the unusual
assembly of about 120 densely packed physisorbed por-
phyrin-based complex molecules tilted on the Au core, with
no evidence of covalent bonds between the porphyrin and
the gold nanoparticles. This study suggests promising appli-
cations of gold–porphyrin hybrids in an unconventional as-
sembly for the development of future optoelectronic de-
vices.
The Au 4f spectrum is reported in Figure 5; by following
a curve-fitting procedure, two contributions to the two
spin–orbit components are detected. The Au 4f7/2 compo-
nent of the peak at lower EB values (83.69 eV) is due to
Experimental Section
metallic gold; the second Au 4f7/2 component at EB
=
84.98 eV can been associated to the Au atoms that interact
Materials: Deionized water was obtained from a Millipore Milli-Q
with the organometallic molecule. XPS data support a phy- water purification system. Hydrogen tetrachloroaurate(III) trihydr-
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A Porphyrin-Bridged Pd Dimer Complex Stabilizes Gold Nanoparticles
ate (Aldrich, 99.9+%), tetraoctylammonium bromide (Aldrich,
400.13 MHz for the proton in CDCl3 with TMS as chemical-shift
98%), sodium borohydride (Aldrich, 99%), sodium sulfate anhy- reference. Monodimensional proton spectra were acquired at a
drous (Carlo Erba), Celite 545 filter agent (Aldrich) and florisil
were used as received. All solvents (Aldrich, reagent grade) were
dried with Na2SO4 before use. Argon was passed through the reac-
tion solvents to deoxygenate the reaction systems, the reactions
were further performed under an argon atmosphere by using stan-
dard labware.
temperature of 298 K by employing the sequence present in the
spectrometer routines with a spectral width of 15 ppm, 64000 data
points, an acquisition time of 5.5 s, a repetition time of 5 s and 16
scans. Bidimensional COSY experiments[40] were recorded at 298 K
by employing the sequence present in the spectrometer routines.
Bidimensional homonuclear proton NOESY[41,42] experiments were
acquired with several mixing times (150, 200, 250 and 500 ms) at
298 K by employing the sequences present in the spectrometer rou-
tines. All homonuclear bidimensional spectra were acquired with a
spectral width of 15 ppm in both dimensions, a matrix of 2kϫ512
data points for both the direct and the indirect dimensions, a repeti-
tion delay of 2 s and 64 scans. All spectra were processed with
Bruker Topspin 1.3 software.
2,8,12,18-Tetraethyl-5,15-diethynyl-3,7,13,17-tetramethyl-
porphyrinatozinc(II) (1; ZnDEP) was synthesized according to a
literature report[33] from 3,7,13,17-tetraethyl-2,8,12,18-tetramethyl-
10,20-bis(trimethylsilylethynyl)pophyrin (ZnDEPSi) (1a)[34] and
precursor dichloride and monochloro acetylide PdII complexes {i.e.
trans-[Pd(PBu3)2Cl2] (2) and trans-[Pd(PBu3)2(CϵC–C6H5)Cl] (3)}
obtained by means of already published methods.[35,36] Spectral
data are reported in the Supporting Information.
General Procedures: The Pd–ZnDEP binuclear complex 4 and the
polynuclear compound 5 have been synthesized by condensation
of 1 with trans-[Pd(PBu3)2Cl2] or trans-[Pd(PBu3)2(CϵC–C6H5)Cl],
respectively, by a procedure modified from that reported for the
synthesis of multinuclear Pt analogous compounds (method a);[43]
compound 4 was obtained with a “one-pot” method as well
(method b). The reaction scheme and the chemical structures are
reported in Scheme 1.
Methods: FTIR spectra were recorded as films deposited from
CHCl3 solutions by using ZSM-5 cells with a Bruker Vertex 70
Fourier transform spectrometer. 1H and 31P NMR spectra were
recorded with a Bruker AC 300P spectrometer at 300 and
121 MHz, respectively, in CDCl3; the chemical shifts (ppm) were
1
referenced to TMS for H NMR spectra by assigning the residual
1H impurity signal in the solvent at δ = 7.24 ppm (CDCl3). 31P
NMR spectroscopic chemical shifts are relative to H3PO4 (85%).
UV/Vis spectra were recorded with a Varian Cary 100 instrument.
Photoluminescence spectra were performed with a Perkin–Elmer
LS 50 fluorescence spectrometer. All optical measurements were
performed at room temperature in CHCl3. Elemental analyses were
provided by the Servizio di Microanalisi of the Department of
Chemistry with an EA 1110 CHNS-O instrument. Number-average
Synthesis of Porphyrin-Bridged Di-bis(tributylphosphane)palladium
Diphenylacetylide (4): Method a: In a 150-mL three-necked flask,
[Pd(PBu3)2(CϵC–C6H5)Cl] (3, 123 mg, 0.197 mmol) was dissolved
in a mixture of solvents [30 mL of NHEt2/CHCl3 (2:1 v/v), pre-
viously degassed with argon flux for 30 min]. CuI (2 mg) was added
at T = 25 °C to the thoroughly stirred mixture. A solution (30 mL)
of ZnDEP (1, 46.7 mg, 0.079 mmol) in NHEt2/CHCl3 (2:1 v/v) was
then added dropwise to the previous mixture over 45 min in the
dark. The reaction course was monitored by UV/Vis spectroscopy
until a strong absorption band at 452 nm was detected after 3 h.
The reaction was interrupted by immersing the flask in an ice/salt
bath, and the mixture was dried in vacuo to obtain a solid crude
product. The crude mixture was washed thoroughly with water
three times to eliminate the ammonium salt side product, and the
organic phase was concentrated to small volume with a rotavapor
and dried with anhydrous Na2SO4. MeOH was added to this small
volume (about 5 mL) and left at T = 4 °C to yield the purified
molecular weight (Mn), weight-average molecular weight (Mw) and
[37]
dispersity a = Mw/Mn
were determined by gel permeation
chromatography (GPC) on a PL-gel column that contained a
highly cross-linked spherical polystyrene/divinylbenzene matrix
packed with 10 micron particles with a pore size of 100 Å. CHCl3
(HPLC grade) was used as eluent and pumped at a flow rate of
0.8 mLmin–1 by a binary LC pump through an injection loop with
a volume of 24 μL. Monodisperse polystyrene standards were used
for calibration, and the samples detected with a UV detector. Mass
spectra were acquired with a Bruker MicroToF mass spectrometer.
For transmission electron microscopy (TEM) observations and the
diffraction contrast imaging, a FEI TECNAI G2 F30 Supertwin
field-emission gun scanning transmission electron microscope
(FEG STEM) operating at 300 kV and with a point-to-point reso-
lution of 0.205 nm was used. The TEM specimens were prepared
by depositing a few drops of the diluted solutions on carbon-coated
TEM grids to be directly observed in the instrument. XPS analysis
was performed with an instrument of our own design and construc-
tion. It consisted of a preparation and an analysis UHV chamber
equipped with a 150-mm mean radius hemispherical electron ana-
lyzer with a four-element lens system with a 16-channel detector,
thus giving a total instrumental resolution of 1.0 eV as measured
at the Ag 3d5/2 core level. Mg-Kα non-monochromatized X-ray ra-
diation (hν = 1253.6 eV) was used for acquiring core-level spectra
of all samples (C 1s, N 1s, P 2p, Pd 3d, Zn 2p and Au 4f). The
spectra were energy referenced to the C 1s signal of aromatic C
atoms with a binding energy EB = 284.70 eV. Atomic ratios were
calculated from peak intensities by using Scofield’s cross-section
values and calculated λ factors.[38] Curve-fitting analysis of the C
1s, N 1s, P 2p, Pd 3d, Zn 2p and Au 4f spectra was performed by
using Voigt profiles as fitting functions after subtraction of a Shir-
ley-type background.[39] All NMR spectra were carried out with a
Bruker Avance 400 spectrometer operating at a frequency of
1
product (4). Yield: 36 mg (0.020 mmol, 25%). H NMR (CDCl3):
δ = 0.76 (t, J = 7.15 Hz, PCH2CH2CH2CH3), 1.22 (m, J = 7.15,
7.50 Hz, PCH2CH2CH2CH3), 1.56 (m,
J = 7.50, 4.40 Hz,
PCH2CH2CH2CH3), 1.71 (t, J = 7.75 Hz, CH2CH3), 1.95 (m,
PCH2CH2CH2CH3), 3.70 (s, CH3), 3.89 (q, J = 7.75 Hz, CH2CH3),
7.16 (d, 2 H, para-phenyl), 7.27 (d, 4 H, ortho-phenyl), 7.37 (t, 4
H, meta-phenyl), 9.72 (s, meso-2 H) ppm. 31P NMR (CDCl3): δ =
10.86 ppm. UV/Vis (CHCl3): λmax = 277, 452, 588, 620 nm. FTIR
(nujol): ν = 2079 [ν(CϵC)], 1597 [ν(C=C), arom.], 1208 [ν(C–H),
˜
pyrrole], 845 [ν(C–N), pyrrole] cm–1. C100H152P4N4Pd2Zn: calcd. C
66.27, H 8.45, N 3.09; found C 64.80, H 8.04, N 3.38. MS: m/z =
1812.4 (molecular peak).
Method b: In a three-necked flask, 3,7,13,17-tetraethyl-2,8,12,18-
tetramethyl-10,20-bis(trimethylsilylethynyl)pophyrin
(DEPSI;
35.8 mg, 0.053 mmol) was dissolved in THF (10 mL) with tetrabu-
tylammonuim bromide (100 μL) whilst stirring in the dark at T =
25 °C for 1 h. In another three- necked vessel, a solution made from
[Pd(PBu3)2(CϵC–C6H5)Cl] (69.1 mg, 1.11 mmol) and CuI (1 mg)
dissolved in an NHEt2/CHCl3 mixture (20 mL, 1:1 v/v) was pre-
pared. After 1 h, NHEt2 (10 mL) was poured into the first reaction
flask, and, while increasing the pressure of argon, this reaction mix-
ture was added dropwise into the second one over 3.5 h. Also in
Eur. J. Inorg. Chem. 2011, 4906–4913
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4911

I. Fratoddi et al.
FULL PAPER
this case, the reaction course was monitored by UV/Vis spec-
troscopy until a strong absorption band at 452 nm was detected.
The resulting reaction solution was handled as reported for method
a. The final small-volume organic solution was purified by elution
with THF on a short column for chromatography (florisil). The
eluted material was further purified by crystallization (THF/
MeOH), and pure complex 4 was obtained. Yield: 29.6 mg
(0.017 mmol, 32%). The elemental analysis and spectroscopic char-
acterizations are consistent with those reported in method a.
to thank Prof. Marco Rossi and Dr. Roberto Matassa for helpful
comments and discussion of the TEM analysis.
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re-suspended in methanol, washed with acetonitrile and hexane,
recovered from dichloromethane and dried for 3 d under vacuum.
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452 nm). UV/Vis (CHCl3): λmax = 436, 500, 590, 620 nm. FTIR
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sented.
Acknowledgments
The authors gratefully acknowledge the financial support to this
research by Progetti Ateneo Sapienza 2009 (C26A09AS5R), At-
eneo Federato AST 2008 (26F09MA27) and the MAE-Ministero
dellЈUniversità e della Ricerca (MIUR), Progetti di Ricerca Scien-
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Received: March 30, 2011
Published Online: September 14, 2011
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