Hetero-multimetallic tetrakis(SCS-pincer palladium)-(metallo)porphyrin hybrids. Tunable precatalysts in a Heck reaction

Article abstract of DOI:10.1021/om7005613

A series of meso-tetrakis(SCS-pincer PdCl)-(metallo)porphyrin hybrids have been synthesized using two distinct synthetic routes. Manganese and nickel were introduced into the porphyrin macrocycle prior to peripheral electrophilic palladation, whereas magnesium was introduced thereafter in light of its acid sensitivity. When these complexes were used as precatalysts in the Heck reaction between iodobenzene and styrene, different catalytic activities were observed for each hybrid complex. The catalytic activity increased for the metalloporphyrin series MnCl < 2H < Ni < Mg, which interestingly coincides with an increase of electron richness of the porphyrin ring. Control experiments on model compounds confirmed that an intramolecular effect rather than an intermolecular effect was responsible for this influence. We postulate that, in analogy with related NCN-pincer metal complexes, the electron density on the palladium atom in SCS-pincer palladium complexes is influenced by the electronic properties of the para-substituent, i.e., the metalloporphyrin in this case. This in turn influences the rate of palladium leaching and, hence, of catalysis.

Full text of DOI:10.1021/om7005613

534
Organometallics 2008, 27, 534–542
Hetero-multimetallic Tetrakis(SCS-pincer
palladium)-(Metallo)porphyrin Hybrids. Tunable Precatalysts in
a Heck Reaction
Bart M. J. M. Suijkerbuijk, Sara D. Herreras Martínez, Gerard van Koten, and
Robertus J. M. Klein Gebbink*
Chemical Biology & Organic Chemistry, Department of Chemistry, Faculty of Science, Utrecht UniVersity,
Padualaan 8, 3584 CH Utrecht, The Netherlands
ReceiVed June 8, 2007
A series of meso-tetrakis(SCS-pincer PdCl)-(metallo)porphyrin hybrids have been synthesized using
two distinct synthetic routes. Manganese and nickel were introduced into the porphyrin macrocycle prior
to peripheral electrophilic palladation, whereas magnesium was introduced thereafter in light of its acid
sensitivity. When these complexes were used as precatalysts in the Heck reaction between iodobenzene
and styrene, different catalytic activities were observed for each hybrid complex. The catalytic activity
increased for the metalloporphyrin series MnCl < 2H < Ni < Mg, which interestingly coincides with an
increase of electron richness of the porphyrin ring. Control experiments on model compounds confirmed
that an intramolecular effect rather than an intermolecular effect was responsible for this influence. We
postulate that, in analogy with related NCN-pincer metal complexes, the electron density on the palladium
atom in SCS-pincer palladium complexes is influenced by the electronic properties of the para-substituent,
i.e., the metalloporphyrin in this case. This in turn influences the rate of palladium leaching and, hence,
of catalysis.
Chart 1. General Formula of ECE-Pincer Metal Complexes
Introduction
ECE-pincer complexes of a multitude of transition metals
(Chart 1) have taken center stage as one of the most promising
classes of organometallic complexes, a fact that is largely
attributable to the impressive scope of their applications
combined with their facile synthesis.1–3 Another factor contrib-
uting to the popularity of these complexes is the ease with which
their reactivity can be modulated through modification of several
key features, viz., the metal M, the benzylic donor atoms E,
and the ligand(s) L. In this regard, especially the palladium(II)
complexes of the 2,6-bis[(phenylsulfido)methyl]phen-1-yl (SCS-
pincer) ligands have enjoyed widespread attention. Loeb,4,5
Reinhoudt,6–8 and Weck9–12 have explored their use for the
construction of supramolecular architectures, using the fourth
ligand position L for the attachment of functionalized Lewis
bases. Moreover, continuing research addresses their ability to
act as precatalysts for high-temperature palladium-catalyzed
organic transformations, particularly Heck reactions.13–20
For most of its applications, the para-substituent Z of SCS-
pincer palladium complexes has been utilized to immobilize this
moiety onto larger fragments, specifically for catalytic reuse.21–24
For these systems, the electronic influence exerted by the para-
substituent on the chelated palladium center has received little
attention, whereas the relationship between the electronic
properties of the pincer para-substituent Z and the electron
* r.j.m.kleingebbink@uu.nl, Phone: +31-30-2531889; Fax: +31-30-
2523615.
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3781.
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1792.
(4) Hall, J. R.; Loeb, S. J.; Shimizu, G. K. H.; Yap, G. P. A. Angew.
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1203–1213.
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2005, 347, 172–184.
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2230–2234.
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10.1021/om7005613 CCC: $40.75
2008 American Chemical Society
Publication on Web 02/01/2008

Tetrakis(SCS-pincer palladium)-(Metallo)porphyrin Hybrids
Organometallics, Vol. 27, No. 4, 2008 535
Chart 2. General Formula of Peripherally Metalated Pincer-Porphyrin Hybrids
2-
density on the metal (and thus its reactivity) has been well
established for similar pincer metal complexes.25–30
N4
coordination cavity.34–36 Virtually all metals can be
introduced in the porphyrin system using mild procedures, and
this provides a possible handle for remote, yet intramolecular,
control over the properties of the peripheral organometallic
groups. In other words, the free-base porphyrin can potentially
act as a modular para-substituent precursor.
In the investigations reported here, it was decided to focus
on meso-tetrakis(SCS-pincer Pd)-metalloporphyrin hybrids and
to investigate the effects of the (metallo)porphyrin on the
peripheral palladium moieties. In order to maximize the observ-
able effects, the porphyrin was metalated with metals ranging
from electropositive Mg(II) to electronegative Mn(III) to give
a novel class of heteromultimetallic pincer-porphyrin hybrids (Chart
2, right). The intramolecular effects were probed by applying these
complexes as catalyst precursors in the Heck reaction of iodoben-
zene with styrene, since it has been pointed out that different
palladacycles lead to different catalytic activities.37
We recently reported on the synthesis of a number of
peripherally metalated pincer-porphyrin hybrids (Chart 2, left)
and showed that the introduction of metal sites at the porphyrin’s
periphery has a substantial effect on the electronic absorption
spectrum and emission properties of the porphyrin core.31,32
Since the metalated pincer groups affect the physical charac-
teristics of the porphyrin core, we set out to investigate the
reciprocal effect, i.e., the influence of the porphyrin core on
the properties of the peripheral ECE-pincer metal groups. It was
found that in meso-(NCN-pincer PtCl)-(metallo)porphyrin
hybrids the electron density at the peripheral NCN-pincer Pt
centers depends on the electronic properties of the (metallo)por-
phyrin.32,33 Interestingly, the electronic properties of the por-
phyrin can be modified by complexation of a metal in the central
(21) Dijkstra, H. P.; Meijer, M. D.; Patel, J.; Kreiter, R.; van Klink,
G. P. M.; Lutz, M.; Spek, A. L.; Canty, A. J.; van Koten, G. Organometallics
2001, 20, 3159–3168.
Results
Synthesis and Characterization. All heteromultimetallic
target compounds were synthesized from the previously reported
meso-tetrakis(3,5-bis[(4-tert-butylphenylsul-
(22) Dijkstra, H. P.; Steenwinkel, P.; Grove, D. M.; Lutz, M.; Spek,
A. L.; van Koten, G. Angew. Chem., Int. Ed. 1999, 38, 2186–2187.
(23) Gimenez, R.; Swager, T. J. Mol. Catal. A: Chem. 2001, 166, 265–
273.
fido)methyl]phenyl)porphyrin 1(2H),31 which comprises four
SCS-pincer ligand groups connected to a porphyrin core via its
four meso-positions. The tert-butyl groups at the thiophenyl
substituents serve as solubilizing groups, since the parent
tetrakis(SCS-pincer)porphyrin is too insoluble for subsequent
reactions.31 Depending on the targeted meso-tetrakis(SCS-pincer
PdCl)-(metallo)porphyrin hybrid complex, two distinct meta-
lation strategies were employed (see Scheme 1). Route A
comprises metalation of the tetrapyrrolic macrocycle followed
by peripheral palladation of the SCS-pincer moieties, while in
route B the pincer ligands are metalated prior to the central
porphyrin ring.
(24) Bergbreiter, D. E.; Sung, S. D. AdV. Synth. Catal. 2006, 348, 1352–
1366.
(25) Dijkstra, H. P.; Slagt, M. Q.; McDonald, A.; Kruithof, C. A.; Kreiter,
R.; Mills, A. M.; Lutz, M.; Spek, A. L.; Klopper, W.; van Klink, G. P. M.;
van Koten, G. Eur. J. Inorg. Chem. 2003, 830–838.
(26) Slagt, M. Q.; Rodríguez, G.; Grutters, M. M. P.; Klein Gebbink,
R. J. M.; Klopper, W.; Jenneskens, L. W.; Lutz, M.; Spek, A. L.; van Koten,
G. Chem. Eur. J. 2004, 10, 1331–1344.
(27) Tromp, M.; van Bokhoven, J. A.; Slagt, M. Q.; Klein Gebbink,
R. J. M.; van Koten, G.; Ramaker, D. E.; Koningsberger, D. C. J. Am.
Chem. Soc. 2004, 126, 4090–4091.
(28) van de Kuil, L. A.; Luitjes, H.; Grove, D. M.; Zwikker, J. W.; van
der Linden, J. G. M.; Roelofsen, A. M.; Jenneskens, L. W.; Drenth, W.;
van Koten, G. Organometallics 1994, 13, 468–477.
(29) Aydin, J.; Selander, N.; Szabó, Tetrahedron Lett. 2007, 47, 8999–
9001.
(30) Fossey, J. S.; Richards, C. J. Organometallics 2004, 23, 367–373.
(31) Suijkerbuijk, B. M. J. M.; Lutz, M.; Spek, A. L.; van Koten, G.;
Klein Gebbink, R. J. M. Org. Lett. 2004, 6, 3023–3026.
(32) Suijkerbuijk, B. M. J. M.; Tooke, D. M.; Lutz, M.; Spek, A. L.;
van Koten, G.; Klein Gebbink, R. J. M. Manuscript in preparation.
(33) Suijkerbuijk, B. M. J. M.; Schamhart, D. J.; Kooijman, H.; Spek,
A. L.; van Koten, G.; Klein Gebbink, R. J. M. Manuscript in preparation.
(34) Dolphin, D. The Porphyrins; Academic Press, Inc.: New York,
1978.
(35) Smith, K. M., Porphyrins and Metalloporphyrins.; Elsevier Sci-
entific Publishing Company: Amsterdam, 1975.
(36) Liao, M.-S.; Scheiner, S. J. Chem. Phys. 2002, 117, 205–219.
(37) Phan, N. T. S.; Van Der Sluys, M.; Jones, C. W. AdV. Synth. Catal.
2006, 348, 609–679.

536 Organometallics, Vol. 27, No. 4, 2008
Suijkerbuijk et al.
Scheme 1. Synthetic Route towards meso-Tetrakis(SCS-pincer PdCl)-Metalloporphyrin Hybridsa
a
(i) for M ) MnCl: (a) Mn(OAc)2 · 4H2O, DMF, ∆; (b) NaCl, H2O/CH2Cl2; for M ) Ni: Ni(acac)2, toluene, ∆; (ii) (a) [Pd(NCMe)4](BF4)2,
MeCN/CH2Cl2, ∆; (b) LiCl, MeCN; (iii) MgBr2 · OEt2, Et3N, CH2Cl2.
Mn(III) and Ni(II) were readily introduced in the porphyrin
core of 1(2H) via reaction with Mn(OAc)2 · 4H2O and Ni(acac)2,
respectively, to give 1(MnCl) and 1(Ni) in good yields.
Although Mn(III) insertion is usually performed under aerobic
The resulting tetracationic species were converted into the
corresponding tetrachloride complexes with an excess of LiCl
to give 2(MnCl) and 2(Ni) in 86% and 89%, respectively.
For the synthesis of 2(Mg), however, this approach gave
problems since magnesium(II) porphyrins are highly unstable
toward acidic conditions.35 When an SCS-pincer ligand was
treated with [Pd(NCMe)4](BF4)2 in the presence of a mag-
nesium porphyrin (6(Mg), see Chart 3), the porphyrin was
quickly demetalated by HBF4 generated during the electro-
philic palladation. This precluded the use of route A for the
synthesis of multimetallic porphyrin 2(Mg), which was
therefore synthesized via route B.
conditions to oxidize the initially formed Mn(II) porphyrin,35
a
slightly modified procedure was used in this case. In light of
the substantial susceptibility of the sulfur atoms of 1(2H) toward
oxidation, a brief exposure to air (30 s) in the presence of NaCl
at room temperature was used instead after completion of the
Mn(II) insertion to successfully generate 1(MnCl) in 87% yield.
Porphyrin 1(Ni) was synthesized in 98% yield by reaction of
1(2H) with 20 equiv of Ni(acac)2 in boiling toluene.
Subsequently, the SCS-pincer ligand moieties of metal-
loporphyrins 1(MnCl) and 1(Ni) were selectively palladated
with [Pd(NCMe)4](BF4)2 in a mixture of CH2Cl2 and MeCN.6
Upon treatment of 1(2H) with 4 equiv of [Pd(NCMe)4](BF4)2
in a CH2Cl2/MeCN mixture, a fast color change from deep red
via brown to deep green was observed. The deep red color of

Tetrakis(SCS-pincer palladium)-(Metallo)porphyrin Hybrids
Organometallics, Vol. 27, No. 4, 2008 537
Chart 3. Structural Formulas of Model SCS-Pincer Palladium
Compound 5 and Reference Metalloporphyrins 6(M)
Figure 1. Comparison of the Soret and Q-band region of the
electronic spectra of 1(Ni) (gray) and 2(Ni) (black).
the free-base porphyrin was regenerated by addition of an excess
of Et3N, which indicated that the porphyrin dication, formed
by protonation of the free-base porphyrin by HBF4, which is
liberated during the electrophilic palladation reaction, was
responsible for the green color. The tetracationic SCS-pincer
palladium(II) porphyrin was subsequently treated with an excess
of LiCl in MeCN to give the desired complex 2(2H) in 93%
yield. The selectivity of this reaction for the peripheral SCS-
1
pincer ligand sites was confirmed by H NMR spectroscopy,
which showed similar ratios between the integrals corresponding
to the benzylic and pyrrolic protons, respectively, of 1(2H) (δ
) 4.30 (s) and -3.00 ppm, respectively) and 2(2H) (δ ) 4.83
(br) and -2.86 ppm, respectively; for an X-ray crystal structure
of 2(2H) see Supporting Information, Figure S1). It was
observed that after peripheral palladation, i.e., coordination of
the sulfur atoms to palladium, the compounds were stable toward
oxidation and could be stored under air for several months. Free-
base porphyrin 2(2H) was then reacted with MgBr2 · OEt2 in
the presence of Et3N38 to give 2(Mg) in 90% yield. Route B
could not be employed to synthesize 2(MnCl), since 2(2H) was
not stable under the rather forcing conditions of Mn(III) insertion
(refluxing DMF, vide supra). Divalent nickel could be inserted
into 2(2H) using Ni(OAc)2 in a mixed solvent system (MeOH/
CH2Cl2), but the isolated yields were generally low (∼60%).
For reasons of comparison, 2,6-bis[(4-tert-butylphenylsul-
fido)methyl]-1-chloridopalladio(II)benzene (5) and meso-tet-
rakis[3,5-bis(tert-butyl)phenyl]porphyrin (6(2H)) and its cor-
responding metal complexes (6(M); M ) Mg, MnCl, Ni) were
synthesized (Chart 3). All compounds were fully characterized
by means of 1H and 13C{1H} NMR spectroscopy, UV/vis
spectroscopy, mass spectrometry, and elemental analysis (see
Supporting Information).
UV/Vis Spectroscopy. The UV/vis spectra of 1(M) are
dominated by the features of the (metallo)porphyrin core, whose
molar absorption coefficients exceed those of the SCS-pincer ligand
moieties by 2 orders of magnitude. When 1(Ni) was treated with
[Pd(NCMe)4](BF4)2, a fast color change (orange to darker red) of
the reaction mixture occurred, which, over time, gradually returned
to the original color. After workup of the reaction, the Soret and
Q-band of 2(Ni) had shifted bathochromically by 6 nm with respect
to the parent 1(Ni), and the molar absorption coefficient ꢀ of each
band had increased (Figure 1).
Figure 2. Evolution of the normalized electronic spectra of the
reaction between 1(MnCl) and [Pd(NCMe)4](BF4)2.
Table 1. Positions of Peak Maxima of 1(M) and 2(M) in nm
Soret band
Soret band
M
(log ꢀ) 1(M)
(log ꢀ) 2(M)
2H
Mg
MnCl
Ni
420 (5.73)
n/a
479 (5.14)
417 (5.79)
426 (5.79)
433 (5.82)
481 (5.20)
422 (5.85)
(NCMe)4](BF4)2 a spectrum was recorded in which the Soret
band has shifted hypsochromically from 479 to 462 nm. During
the course of the reaction the Soret band gradually shifted
bathochromically to 481 nm for the product 2(MnCl).
These observations might be attributed to the electronic effects
exerted by the intermediates of the palladation reaction on the
porphyrin core. It is known that during an electrophilic
palladation of an ECE-pincer ligand (E ) NR2, SR, PR2)
a positively charged arenium ion is initially formed.39–41 In the
present meso-tetrakis(SCS-pincer)-(metallo)porphyrin hybrids,
this means that in total four arenium ions initially develop at
the meso-phenyl positions of the porphyrin. These render the
meso-groups relatively electron-poor, which in turn has an
electron-withdrawing effect on the porphyrin ring. This leads
to a reduction of the electron density on the latter and induces
a hypsochromic shift of the Soret band.42 As the reaction
(39) Canty, A. J.; van Koten, G. Acc. Chem. Res. 1995, 28, 406–413.
(40) Ryabov, A. D. Chem. ReV. 1990, 90, 403–424.
(41) Davies, D. L.; Donald, S. M. A.; Macgregor, S. A. J. Am. Chem.
Soc. 2005, 127, 13754–13755.
The spectral changes during palladation of 1(MnCl) are
shown in Figure 2. Five minutes after addition of [Pd-
(42) Foran, G. J.; Armstrong, R. S.; Crossley, M. J.; Lay, P. A. Inorg.
Chem. 1992, 31, 1463–1470.
(38) Lindsey, J. S.; Woodford, J. N. Inorg. Chem. 1995, 34, 1063–1069.

538 Organometallics, Vol. 27, No. 4, 2008
Suijkerbuijk et al.
gave 75% conversion, while the most active pincer-porphyrin
catalyst precursor 2(Mg) exhibited 56% conversion at the same
time. By that time the other pincer-porphyrin hybrids catalyst
precursors had converted considerably smaller amounts of
starting materials, with 2(MnCl) being the least active at 24%
conversion. A conversion of >95% was reached first by 5 (6
h) followed by 2(Mg) and 2(2H) (7 h and approximately 10 h,
respectively). After a relatively short induction period, the
reaction catalyzed by 2(Ni) had slowed down to give 90%
conversion after 14 h, requiring 25 h to reach full conversion.
The relatively electron-poor manganese(III) porphyrin 2(MnCl)
exhibited the least activity (92% conversion after 45 h).
Since possible differences between the catalytic behavior
among the tetrakis(SCS-pincer PdCl)-(metallo)porphyrin hy-
brids 2(M) might have originated from intermolecular processes
rather than intramolecular processes, we conducted some sys-
tematic catalytic studies on appropriate combinations of their
components, i.e., 4 equiv of 5 and 1 equiv of the respective model
(metallo)porphyrin 6(M). These experiments showed that all
mixtures of precatalysts led to virtually identical product yields
and kinetic traces (analogous to that of 5), and it was thus concluded
that intermolecular interactions between the palladacycles and
(metallo)porphyrins did not affect the catalytic behavior of the
systems. Control experiments with the metalloporphyrins 6(M)
furthermore showed that these (metallo)porphyrins did not exhibit
any reactivity in the same Heck reaction. These results indicate
that the differences in catalytic activity among the multimetallic
pincer-porphyrin hybrids 2(M) arise from intramolecular interac-
tions within the pincer-porphyrin hybrids and not from intermo-
lecular interactions between individual molecules.
As Figure 3 shows, the reactions catalyzed by precatalysts 5
and 2(M) all exhibit sigmoidal kinetics. As was recently shown
by the group of Weck,17 the sigmoidal curves observed from
SCS-pincer PdCl-catalyzed Heck reactions can be fitted to a
modified version of Finke’s model for transition metal nano-
cluster formation.45,46 In this model, a key notion is that the
rate of product formation will follow the kinetic model for metal-
particle formation. According to Finke’s model, the formation
of nanoparticles can be modeled using the combination of a
nucleation step (SCS-pincer PdCl f Pd(0), with rate constant
k1) and an autocatalytic surface growth step (Pd(0) + SCS-
pincer PdCl f 2 Pd(0), with rate constant k2). If the actual
stoichiometric catalytic cycle, i.e., Pd(0) + styrene + iodoben-
zene f Pd(0) + stilbene + HI, with rate constant k3, is then
assumed to be fast relative to k1 and k2, it follows that the
kinetics of the overall reaction are those of the first two steps.
The following expression (eq 1) is then obtained for the
concentration of SCS-pincer PdCl ([A]) in time:46
Figure 3. Plot of the conversion of starting materials to styrene
products vs time for reaction 1, catalyzed by 5 and several
tetrakis(SCS-pincer PdCl)-(metallo)porphyrin hybrids.
proceeds, H+ is eliminated from the meso-arenium groups to
form the meso-[3,5-bis([4-tert-butylphenylsulfido]methyl)-4-
palladium(II)]+ groups. After workup, the spectrum of 2(MnCl)
exhibited similar features compared to that of 1(MnCl), albeit
with small bathochromic shifts (Figure 2).
The Soret band wavelengths and molar absorption coefficients
of 1(M) and 2(M) are listed in Table 1. Important to note is
that the peak maxima of all compounds show a similar
bathochromic shift, with a concomitant increase of ꢀ. The
bathochromic shifts caused by palladation of the peripheral SCS-
pincer ligand groups might be attributed to the electron-releasing
nature of Pd when σ-bonded to an aryl fragment.26,43 The
palladium-induced higher electron density on the meso-aryl
groups of 2(M) may lead to a decreased HOMO–LUMO gap,
which results in a red-shift of the electronic absorption bands
of 2(M) compared to 1(M). A similar phenomenon was
observed for the structurally related meso-tetrakis(NCN-pincer
MX)-(metallo)porphyrin hybrids (MX ) PdBr, PtCl).32
Catalysis. With compounds 2(M) in hand, their behavior as
precatalysts for the Heck reaction between iodobenzene and
styrene was investigated (reaction 1). The catalytic experiments
were conducted in DMF at 119 °C with 1 equiv of iodobenzene,
1.5 equiv of styrene, 1.5 equiv of Et3N, and 0.2 mol % of the
Pd-catalyst, i.e., with 0.05 mol % of the respective pincer-
porphyrin hybrid 2(M). Each experiment was run three times
to ensure reproducibility of the results.
k1
+ [A]0
k2
For the pincer-porphyrin hybrids 2(M) different plots were
found for the conversion versus time (see Figure 3). All traces
showed a sigmoidal curve with an induction period, which is
consistent with the kinetic data obtained for other ECE-pincer
PdCl-catalyzed Heck reactions in the literature.10,15–17 The
parent SCS-pincer PdCl complex 5 was found to be the most
active with the shortest induction period. For the pincer-porphyrin
hybrids, the induction times increased in the order 2(Mg) <
2(Ni) < 2(2H) < 2(MnCl). Interestingly, this order coincides
with the order of decreasing HOMO energy of the metallo(por-
phyrin) macrocycle.44 After 240 min of reaction, complex 5
[A]t )
(1)
k1
e(k +k [A] )t
1
2
0
1 +
k2[A]
This formula then correlates with the iodobenzene (PhI)
concentration as [PhI]t ) 500[A]t since the total amount of Pd
precatalyst is 0.2 mol % ()500-1). Figure 4 shows the
concentration of iodobenzene in time for several precatalysts
(data points markers), while the solid lines represent the
calculated values of 500[A]t for each precatalyst according to
(45) Widegren, J. A.; Aiken, I. J. D.; Özkar, S.; Finke, R. G Chem.
Mater. 2001, 13, 312–324.
(43) Parshall, G. W. J. Am. Chem. Soc. 1974, 96 (8), 2360–2366.
(44) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic
Press, Inc.: New York, 1978; Vol. 3.
(46) Watzky, M. A.; Finke, R. G. J. Am. Chem. Soc. 1997, 119, 10382–
10400.

Tetrakis(SCS-pincer palladium)-(Metallo)porphyrin Hybrids
Organometallics, Vol. 27, No. 4, 2008 539
Figure 5. Evolution of the normalized Soret band area of 2(2H)
during reaction 1.
Figure 4. Graph representing the decrease in PhI concentration in
time (data points) and the fitted values for 500[A]t (black lines).
The data for 2(Ni) are not shown due to poor fit results.
Table 2. Fitted Kinetic Data for Reaction 1 According to Eq 1
k1 (×10-6 min-1
)
k2 (M-1 min-1
)
5
675 ( 60
638 ( 92
293 ( 30
238 ( 81
22.1 ( 0.9
16.7 ( 1.2
15.9 ( 0.6
13.5 ( 1.7
2(Mg)
2(2H)
2(MnCl)
eq 1. The fit results for 5, 2(Mg), 2(2H), and 2(MnCl) are
relatively accurate, which is a strong indication for the plausibil-
ity of the Finke model for the current systems.47 Only at longer
reaction times does the model not accurately fit the experimental
data. The fitted values for k1 and k2 are listed in Table 2. The
catalytic data of the nickel complex could not be fitted to the
model.
According to these values, the ease of generation of the
true catalysts from the pincer-porphyrin hybrids seems to
correlate to the electron density on the (metallo)porphyrin.
An increase in the electron-donating ability of the porphyrin
(2(MnCl) < 2(2H) < 2(Mg)) leads to an increase of both k1
and k2, which means that it enhances the rate of Pd(0)
formation as well as the rate of the autocatalytic reaction.
On the other hand, none of the 2(M) hybrids exceeds the
reactivity of parent compound 5.
UV/Vis during Catalysis. During the course of the Heck
reactions, the electronic spectra of the catalysis mixtures of
2(2H), 2(Mg), and 2(Ni) did not undergo substantial changes.
The intensity ratios between the Soret and Q-band(s) and their
appearance remained identical throughout the course of the
reaction, which indicates that demetalation of 2(Ni) and, more
notably, of 2(Mg) did not occur. However, it was noted that
the Soret bands of 2(2H), 2(Mg), and 2(Ni) gradually shifted
to shorter wavelengths by ∼6 nm (see Figure 5 for 2(2H)). In
fact, the wavelengths at which the Soret and Q-bands resided
at the end of the reactions coincide with those of the corre-
sponding 1(M) parent compounds, which corroborates leaching
of Pd from the SCS-pincer moieties.
Figure 6. Reaction of a sample taken from the 2(MnCl)-catalyzed
Heck reaction with air.
increased in intensity at the expense of the Soret band of
2(MnCl) at 481 nm. The new bands are similar to the absorption
bands observed for nitrogenous base adducts of Mn(II) tetra-
kis(aryl)porphyrins (∼440, 532, 575, 613 nm in THF).48,49 When
a sample in CH2Cl2, taken 60 min after initiation of the reaction,
was exposed to air, the 481 nm Mn(III) porphyrin band increased
again with clear isosbestic points, indicating a conversion from
one species into the other (Figure 6). As the Heck reaction
continued, the 445 nm band decreased again at the benefit of
broad bands between 500 and 750 nm, which could not be
compared to literature values for discrete manganese porphyrins.
Independent experiments on 6(MnCl) showed a similar behavior
of the electronic spectra under the catalytic conditions. Further
investigations showed that the sole addition of Et3N to a solution
of 6(MnCl) in DMF (119 °C) caused virtually identical spectral
changes. Hence, these spectral changes are not brought about
by the merger of the SCS-pincer PdCl groups with the
manganese tetraphenylporphyrin skeleton, but by a reduction
of the manganese porphyrin by Et3N.
During the Heck reaction catalyzed by the parent SCS-pincer
palladium(II) complex 5 the UV/vis spectra showed a new,
gradually increasing absorption band around 440 nm. The
position of this band agrees excellently with the data obtained
by Dupont et al. for their κ2-C,N-palladacycle and was attributed
The UV/vis spectrum of 2(MnCl) did, on the other hand,
show significant changes during the catalytic run. A Soret-type
band around 445 nm with Q-bands at 529, 577, and 620 nm
(48) Jones, R. D.; Summerville, D. A.; Basolo, F. J. Am. Chem. Soc.
1978, 100 (14), 4416–4424.
(47) Although the fits do closely resemble the experimental data, it
should be noted that this cannot be taken as conclusive proof for the stated
model of catalysis by palladium leaching, as was argued by Weck (ref 17).
(49) Reed, C. A.; Kouba, J. K.; Grimes, C. J.; Cheung, S. K. Inorg.
Chem. 1978, 17 (9), 2666–2670.

540 Organometallics, Vol. 27, No. 4, 2008
Suijkerbuijk et al.
to the formation of PdXn– species (X ) halide).50,51 The Soret
regions of 2(M) coincide with the diagnostic region for these
PdXn– salts and, therefore, prevented their possible observation.
The formation of Pd nanoparticles was, however, strongly
indicated by the considerable darkening of the reaction mixtures
and by very broad absorptions at longer wavelengths.
ties of the (metallo)porphyrin influence the peripheral Pd centers
in a similar manner. For the related NCN-pincer complexes of
Ni,28 Pd,25 and Pt26,27 and other pincer complexes29,30 it is
known that changes in the electronic parameters of their para-
substituents lead to changes in for example the redox potential28
or NMR chemical shift26 of the ligated metal center. For these
reasons, the Pd sites in the current systems are anticipated to
be influenced as well; that is, electronic variations on the
(metallo)porphyrin are passed on to the peripheral SCS-pincer
palladium centers. During the preparation of this article, an
interesting report by Osuka et al. appeared in which they used
metalloporphyrins in a similar way to modulate the catalytic
properties of a bis(2-pyridyl)pincer palladium complex in a Heck
reaction.59
Discussion
Palladacyclic compounds in general and ECE-pincer PdCl
complexes in particular have been widely applied as precatalysts
for Heck reactions. They are able to activate aryl chlorides and
show impressive turnover numbers without significant deposition
of palladium black.13,15–17,19,20,37,52–55 It was speculated that such
palladacycles exhibit exceedingly high activities due to their
ability to stabilize tetravalent palladium intermediates involved
in a Pd(II)/Pd(IV) catalytic mechanism.37,56 Recently, Bergbre-
iter,15 Weck and Jones,16,17 and Eberhard57 showed convincingly
that SCS- and PCP-pincer PdCl complexes are not the actual
catalysts for high-temperature palladium-catalyzed Heck reac-
tions between aryl halides and activated terminal olefins, but
rather are catalyst precursors. They showed that these pallada-
cyclic complexes slowly release Pd(0) particles that subsequently
take part in catalysis via a Pd(0)/Pd(II) mechanism. Although
these results have disproved the originally proposed Pd(II)/
Pd(IV) molecular mechanism,15–17,37,58 (ECE-type) pallada-
cycles are still being extensively used as precatalysts because
of the high turnover numbers (TON) that can be obtained.14–17
It was recently very convincingly put forward by De Vries that
the Pd(0)/Pd(II) mechanism is in fact operable in all high-
temperature Heck reactions.58
The tetrakis(SCS-pincer PdCl)-(metallo)porphyrin hybrid
systems described here also gradually eliminate Pd particles
when used in a Heck reaction. Evidence for this process was
provided by the putative formation of the parent 1(M) systems
from the peripherally palladated 2(M) species during the course
of the reaction, as observed by UV/vis spectroscopy.
The nature of the (metallo)porphyrin part within the
pincer-porphyrin hybrids 2(M) seems to have a considerable
effect on the rate of the Heck reaction between iodobenzene
and styrene. Combinations of 6(M) and 5 did not lead to altered
activities in the same reaction and, hence, the differences
between the performances of the pincer-porphyrin hybrids as
catalyst precursors originate from intramolecular effects. It was
also observed that the electronic properties of free-base,
magnesium(II), nickel(II), and zinc(II) porphyrins are passed
on to peripheral NCN-pincer Pt(II) centers.32,33 Although direct
means to probe the electron density at the palladium centers of
the 2(M) porphyrins were not employed, the similarities between
SCS- and NCN-pincer metal systems suggest that also in the
SCS-pincer Pd complexes discussed here the electronic proper-
Bergbreiter et al. recently showed that the kinetics of a similar
Heck reaction, catalyzed by 3,5-[(4-X-phenylsulfido)methyl]-
4-(pseudo)halidopalladio(II) acetanilides (X ) H, NMe2, NHC-
(O)Me, OMe, COOH), did not depend on the thiophenyl para-
substituent X. This can be rationalized by the fact that, during
the decomposition pathway, the sulfur atoms are displaced from
the palladium center by triethylamine, prior to the steps
culminating in palladium leaching.17 Weck, on the other hand,
mentioned that all reactions leading to palladium(0) formation
after decoordination of the sulfide groups are thermodynamically
downhill,16 which seems to contradict the finding of Bergbreiter
in that no correlation was found between the strength of the
Pd-S bond, which is expected to depend on X, and the catalytic
activity of the system. In the investigations presented here,
modification of an SCS-pincer PdCl moiety at the position para
with respect to the carbon-palladium bond was found to have
considerable effects on its catalytic properties in a Heck reaction.
It therefore seems that the strength of the Pd-C bond in SCS-
pincer Pd complexes does have an effect on the overall stability
of these complexes and, consequently, on their activity in Heck
catalysis, as opposed to the strength of the Pd-S bond.
On the basis of the calculated k values it seems that both k1
and k2 become larger as the metalloporphyrin becomes a better
electron donor. This indicates that the release of Pd from SCS-
pincer PdCl complexes and the following autocatalytic process
are both enhanced by an electron-rich para-substituent. It was
noted that for 2(MnCl) the fit of the experimental data to the
Finke model is poor at longer reaction times, which is probably
caused by secondary processes. In this regard it should be noted
that free-base, nickel(II), and magnesium(II) porphyrins are not
considered to be redox-active at the metal, whereas manga-
nese(III) porphyrins are susceptible to both reductive and
oxidative changes. The profound changes we observed in the
electronic spectra of the catalytic mixture of 2(MnCl) support
the assumption that several different manganese porphyrins are
present in the reaction mixture at any given moment. Therefore,
an exact description of the manganese porphyrin species
responsible for palladium leaching is not straightforward.
The parent SCS-pincer palladium complex 5 is the most active
compound among all investigated precatalysts. We have also
noted that the attachment of a free-base, nickel, or zinc porphyrin
to the para-position of a related NCN-pincer platinum complex
led to a higher platinum-centered electron density compared to
its para-H analogue.32 Although this might suggest that also in
5 the electron density on palladium is lower than in the free-
base, magnesium, and nickel complexes 2(2H), 2(Mg), and
2(Ni), this does not take into account that the leaching process
at one site in a pincer-porphyrin hybrid precatalyst may
(50) Consorti, C. S.; Flores, F. R.; Dupont, J. J. Am. Chem. Soc. 2005,
127, 12054–12065.
(51) Dupont, J.; Basso, N. R.; Meneghetti, M. R.; Konrath, R. A.;
Burrow, R.; Horner, M. Organometallics 1997, 16, 2386–2391.
(52) Soro, B.; Stoccoro, S.; Minghetti, G.; Zucca, A.; Cinellu, M. A.;
Manassero, M.; Gladiali, S. Inorg. Chim. Acta 2006, 359, 1879–1888.
(53) Takenaka, K.; Uozumi, Y. AdV. Synth. Catal. 2004, 346, 1693–
1696.
(54) Yoon, M. S.; Ryu, D.; Kim, J.; Ahn, K. H. Organometallics 2006,
25, 2409–2411.
(55) Ogo, S.; Takebe, Y.; Uehara, K.; Yamazaki, T.; Nakai, H.;
Watanabe, Y.; Fukuzumi, S. Organometallics 2006, 25, 331–338.
(56) Herrmann, W. A.; Böhm, V. P. W.; Reisinger, C.-P. J. Organomet.
Chem. 1999, 576, 23–41.
(57) Eberhard, M. R. Org. Lett. 2004, 6 (13), 2125–2128.
(58) de Vries, J. G. Dalton Trans. 2006, 421–429.
(59) Yamaguchi, S.; Katoh, T.; Shinokubo, H.; Osuka, A. J. Am. Chem.
Soc. 2007, 129, 6392–6393.

Tetrakis(SCS-pincer palladium)-(Metallo)porphyrin Hybrids
Organometallics, Vol. 27, No. 4, 2008 541
The brownish mixture was allowed to reach room temperature (RT)
and was evaporated to dryness in vacuo. The remaining solid was
dissolved in CHCl3 (35 mL), air was bubbled through the solution
for 30 s (in the dark), brine (35 mL) was added, and the biphasic
system was vigorously stirred for 5 min at room temperature. The
organic layer was separated, dried (MgSO4), filtered, and evaporated
to leave a green solid. The solid was purified by dry column
chromatography (basic alumina), eluting with CHCl3 and subse-
quently with 3% MeOH in CHCl3 to elute the desired product.
Finally, the compound was recrystallized from hexane at -30 °C.
Yield: 40.8 mg (87%). IR (cm-1): 3074, 2957, 2865, 1595, 1488,
1459, 1394, 1361, 1347, 1268, 1227, 1205, 1120, 1062, 1012, 946,
897, 819, 803, 742, 713. UV/vis [λmax (log ꢀ), CH2Cl2]: 376 (4.66),
402 (4.66), 422 (4.60), 479 (5.14), 540 (3.77), 585 (4.00), 620 (4.12)
nm. MALDI-TOF MS (DHB): m/z 2091.51 ([M - Cl]+), calcd
for C132H140MnN4S8: 2091.81; 1928.50 ([M - Cl - tert-
BuPhS · ]+), calcd for C122H127MnN4S7: 1928.78. Anal. Calcd for
influence the leaching of palladium at another SCS-pincer site
within the same molecule. In other words, the intramolecular
effects of palladium leaching may lead to an overall retardation
of the leaching process. Simultaneously, another factor of
importance in this regard may be the high local concentration
of Pd(0) around a molecule of 2(M) once it has leached a
palladium atom, which concomitantly affects the equilibria
leading to palladium leaching by the other metalated pincer sites.
Conclusions
A number of meso-tetrakis(SCS-pincer PdCl)-metalloporphyrin
hybrids have been synthesized in high yields using orthogonal
metalation procedures for either ligand site. Upon use of these
compounds in the Heck reaction of iodobenzene with styrene,
they show a marked difference in activity. The Mn(III) porphyrin
precatalyst exhibited the lowest activity while the Mg(II)
porphyrin precatalyst showed the highest activity. As these
observations are in line with the relative electron-donating
properties of the (metallo)porphyrin moieties, they show that
the nature of the porphyrin has a direct influence on the
(catalytic) properties of its peripheral Pd-moieties. Although this
proof-of-principle study did not lead to the development of
(pre)catalysts with increased activities compared to their SCS-
pincer PdCl congener, it does bear out the usefulness of
metalloporphyrins as catalyst-modulating substituents, which
was the objective of this study.
C132H140ClMnN4S8: C 74.45, H 6.63, N 2.63, S 12.05. Found: C
74.32, H 6.51, N 2.78, S 11.88.
[5,10,15,20-Tetrakis(3,5-bis[(4-tert-butylphenylsulfido)methyl]-
4-chloridopalladio(II)-phenyl)porphyrinato]manganese(III) Chlo-
ride (2(MnCl)). A green solution of 1(MnCl) (21.1 mg, 9.91 µmol)
in a CH2Cl2/MeCN mixture (8 mL/4 mL) was treated with a solution
of [Pd(NCMe)4](BF4)2 (17.6 mg, 39.8 µmol) in MeCN (4 mL),
whereupon the solution immediately turned dark orange. After 5 h
of stirring at room temperature, the mixture was heated to 45 °C
for 16 h. After cooling to room temperature, triethylamine (5 drops)
was added and the green solution was stirred for an additional hour
and evaporated to dryness. The green solid was then redissolved
in MeCN (60 mL) and treated with LiCl (excess) while stirring to
give a voluminous green precipitate. After 2 h, the precipitate was
isolated by centrifugation and partitioned between CH2Cl2 (20 mL)
and H2O (50 mL). The organic layer was isolated, dried (MgSO4),
filtered, and concentrated to 10 mL. Upon addition of pentane (80
mL), the product precipitated as a green solid, which was washed
with Et2O (80 mL) and redissolved in CH2Cl2 and filtered over a
plug of silica gel (eluent: 3% MeOH in CH2Cl2). The fast running,
first green band was collected, concentrated to 10 mL and Et2O
was added to precipitate the product as a green solid, which was
isolated by centrifugation and dried in vacuo. Yield: 23.0 mg (86%).
IR (cm-1): 3478 (br), 3049, 2959, 2867, 1593, 1488, 1460, 1397,
1363, 1346, 1268, 1204, 1116, 1081, 1062, 1011, 946, 904, 818,
804, 714. UV/vis [λmax (log ꢀ), CH2Cl2]: 338 (4.79), 381 (4.84),
407 (4.83), 424 (4.80), 481 (5.20), 531 (3.89), 588 (4.09), 624 (4.25)
nm. MALDI-TOF MS (9NA): m/z 2690.58 ([M]+), calcd for
Experimental Section
General Comments. All reactions were performed under a
nitrogen atmosphere using standard Schlenk techniques. All reac-
tions involving porphyrin compounds were shielded from ambient
light using aluminum foil. Et2O and THF were carefully dried and
distilled from sodium/benzophenone prior to use. CH2Cl2, MeCN,
N,N-dimethylformamide (DMF), N,N-diisopropylethylamine, and
triethylamine were distilled from CaH2. Iodobenzene and styrene
were distilled at low pressures prior to use and stored at -30 °C.
Just before use, all solvents were deoxygenated by bubbling a steady
stream of dry nitrogen through them while stirring vigorously for
at least 20 min. 1(2H) was obtained as described before,31 and
[Pd(NCMe)4](BF4)2 was synthesized from Pd(0) and NOBF4 in
MeCN according to a published procedure.60 Column chromatog-
raphy was performed using ACROS silica gel for column chro-
matography, 0.060–0.200 mm, pore diameter ca. 6 nm, or Merck
aluminum oxide 90 active basic (0.063–0.200 mm). 1H and 13C{1H}
NMR spectra were recorded at 300 and 75 MHz, respectively, on
a Varian 300 spectrometer operating at 298 K and were referenced
to the residual solvent signal. UV/vis spectra were recorded on a
Cary 50 scan UV–visible spectrophotometer. Chromatographic
analysis of the catalysis mixtures was carried out on a Perkin-Elmer
AutoSystem XL gas chromatograph. MALDI-TOF measurements
were performed on an Applied Biosystems Voyager-DE PRO
biospectrometry workstation with 2,5-dihydroxybenzoic acid (DHB)
or 9-nitroanthracene (9NA) or without matrix (LDI). ESI-MS
measurements were performed at the Biomolecular Mass Spec-
trometry Group, Bijvoet Centre for Biomolecular Research, Utrecht
University, The Netherlands. Elemental microanalyses were per-
formed by Dornis und Kolbe, Mikroanalytisches Laboratorium,
Müllheim a/d Ruhr, Germany.
C
C
132H136Cl5MnN4Pd4S8: 2690.26; 2656.00 ([M - Cl]+), calcd for
132H136Cl4MnN4Pd4S8: 2655.29; 2548.54 ([M - PdCl]+), calcd
for C132H136Cl4MnN4Pd3S8: 2548.38; 2406.58 ([M - 2(PdCl)]+),
calcd for C132H136Cl3MnN4Pd2S8: 2406.51; 2264.83 ([M -
3(PdCl)]+), calcd for C132H136Cl2MnN4PdS8: 2264.63; 2123.32 ([M
- 4(PdCl)]+), calcd for C132H136ClMnN4S8: 2122.76. Anal. Calcd
for C132H136Cl5MnN4Pd4S8: C 58.87, H 5.09, N 2.08, S 9.53. Found:
C 58.93, H 5.04, N 2.12, S 9.46.
[5,10,15,20-Tetrakis(3,5-bis[(4-tert-butylphenylsulfido)meth-
yl]phenyl)porphyrinato]nickel(II) (1(Ni)). To a dark red solution
of 1(2H) (150 mg, 73.5 µmol) in dry, degassed toluene (30 mL)
was added Ni(acac)2 (0.38 g, 1.47 mmol), and the mixture was
heated to reflux. The reaction progress was monitored by UV/vis
spectroscopy in dry CH2Cl2 and after 2 h, the lowest energy Q-band
(645 nm) of 1(2H) had disappeared. The volatiles were subsequently
evaporated in vacuo, and the resulting red solid was dissolved in
CH2Cl2 (30 mL) and washed with H2O (60 mL) and brine (60 mL).
The organic layer was dried (MgSO4), filtered, and concentrated
to 5 mL. EtOH (80 mL) was added, and after concentration of the
mixture to ∼30 mL, the red product was isolated by centrifugation
[5,10,15,20-Tetrakis(3,5-bis[(4-tert-butylphenylsulfido)meth-
yl]phenyl)porphyrinato]manganese(III) Chloride (1(MnCl)). To
a dark red solution of 1(2H) (45.0 mg, 22 µmol) in degassed, dry
DMF (5 mL) was added Mn(OAc)2 · 4H2O (200 mg, 816 µmol) at
once, and the solution was heated to reflux for 16 h under nitrogen.
1
and dried in vacuo. Yield: 151 mg (98%). H NMR (CDCl3): δ
(60) Yuan, J.-C.; Lu, S.-J. Organometallics 2001, 20, 2697–2703.
8.54 (s, 8H, ꢀH), 7.66 (s, 8H, ArH), 7.59 (s, 4H, ArH), 7.32 (d,

542 Organometallics, Vol. 27, No. 4, 2008
Suijkerbuijk et al.
3
3JHH ) 8.4 Hz, 16H, ArH), 7.24 (d, JHH ) 8.4 Hz, 16H, ArH),
eluted with CH2Cl2 (50 mL) and then with 5% MeOH in CH2Cl2
to elute the product as a purple-pink band. The volatiles were
removed, the residue was redissolved in CH2Cl2, and hexanes (40
mL) were added to induce precipitation of the product as a green
4.24 (s, 16H, CH2S), 1.13 (s, 72H, C(CH3)3) ppm. 13C{1H} NMR
(CDCl3): δ 150.2, 142.6, 141.0, 136.8, 133.1, 132.2, 131.1, 129.1,
126.1, 118.5, 39.9, 34.5, 31.2 ppm. UV/vis [λmax (log ꢀ), CH2Cl2]:
417 (5.43), 527 (4.30) nm. ESI-MS: m/z 2094.80 ([M + H]+), calcd
for C132H141N4NiS8: 2094.82. Anal. Calcd for C132H140N4NiS8: C
75.57, H 7.28, N 2.56, S 11.72. Found: C 75.64, H 7.28, N 2.51,
S 11.58.
1
solid. Yield: 29 mg (90%). H NMR (CDCl3/1% pyridine-d5): δ
8.87 (s, 8H, ꢀ-H), 7.94 (d, 3JHH ) 8.4 Hz, 16H, ArH), 7.80 (s, 8H,
ArH), 7.49 (d, 3JHH ) 8.4 Hz, 16H, ArH), 4.85 (br s, 16H, CH2S),
1.35 (s, 72H, C(CH3)3) ppm. 13C{1H} NMR (CDCl3/1% pyridine-
d5): δ 163.3, 153.8, 150.1, 147.6, 140.6, 132.0, 132.0, 129.4, 128.5,
127.0, 121.2, 53.8, 35.1, 31.4 ppm. UV/vis [λmax (log ꢀ), CH2Cl2]:
314 (4.62), 413 (4.79), 433 (5.82), 528 (3.75), 567 (4.35), 609 (4.27)
nm. MALDI-TOF MS (9NA): m/z 2726.36 ([M + Et3N]+), calcd
[5,10,15,20-Tetrakis(3,5-bis[(4-tert-butylphenylsulfido)methyl]-
4-chloridopalladio(II)phenyl)porphyrinato]nickel(II) (2(Ni)). Com-
pound 1(Ni) (134 mg, 64 µmol) was dissolved in dry CH2Cl2 (30
mL), and the bright red solution was diluted with MeCN (30 mL)
and stirred at room temperature. [(Pd(NCMe)4](BF4)4 (142 mg, 330
µmol) dissolved in MeCN (5 mL) was added, and the red solution
was stirred at reflux temperature overnight. All volatiles were
subsequently evaporated, and the resulting orange plaque was
dissolved in MeCN (30 mL). A large excess of LiCl was added,
and the resulting suspension was stirred for an additional hour. The
solids were isolated by means of centrifugation and stirred in a
biphasic system of CH2Cl2 (20 mL) and H2O (40 mL). After 30
min the organic layer was isolated, dried (MgSO4), and filtered.
The solution was concentrated to 10 mL, and hexanes (50 mL)
were added to induce precipitation of the product as an orange solid.
Yield: 152 mg (89%). 1H NMR (CDCl3): δ 8.73 (s, 8H, ꢀH), 7.91
for C138H151Cl4MgN5Pd4S8: 2725.46. Anal. Calcd for C132H136
-
Cl4MgN4Pd4S8: C 60.35, H 5.22, N 2.13, S 9.77. Found: C 60.26,
H 5.18, N 2.20, S 9.63.
General Procedure for the Heck Reaction. A flame-dried
Schlenk tube was charged with DMF (7.89 mL), pentadecane (550
µL, 2.00 mmol), freshly distilled iodobenzene (448 µL, 4.00 mmol),
styrene (687 µL, 6.00 mmol), and triethylamine (836 µL, 6.00
mmol), and the solution (total volume: 10.0 mL) was heated to
119 °C. In a separate vial, the respective precatalyst (2.00 µmol
2(M); 8.00 µmol [Pd] or a mixture of 8.00 µmol of 5 and 2.00
µmol of 6(M)) was weighed accurately, and the preheated substrate
solution was subsequently added at once via syringe (t ) 0). The
solution was immediately immersed in a preheated (119 °C)
carrousel reactor and magnetically stirred at 800 rpm under air.
The reactions were shielded from ambient light with aluminum foil.
Samples (∼30 µL) for substrate/product analysis were taken at
regular time intervals and diluted in a GC vial with Et2O (∼1.5
mL). Samples for UV/vis measurements (∼20 µL) were diluted in
a cuvette containing dry, deoxygenated CH2Cl2 (3.0 mL), and the
sample was immediately measured.
(d, 3JHH ) 8.4 Hz, 16H, ArH), 7.57 (s, 8H, ArH), 7.47 (d, 3JHH
)
8.4 Hz, 16H, ArH), 4.77 (br s, 16H, CH2S), 1.34 (s, 72H, C(CH3)3)
ppm. 13C{1H} NMR (CDCl3): δ 160.7, 153.6, 148.1, 142.8, 137.5,
132.2, 131.8, 129.0, 127.4, 127.0, 118.5, 53.0, 35.1, 31.4 ppm. UV/
vis [λmax (log ꢀ), CH2Cl2]: 422 (5.85), 531 (4.73) nm. MALDI-
TOF MS (9NA): m/z 2623.80 ([M
132H136Cl3N4NiPd4S8: 2623.32. Anal. Calcd for C132H136
Cl4N4NiPd4S8: C 59.58, H 5.15, N 2.11, Ni 2.21, S 9.64. Found: C
59.63, H 5.19, N 2.19, Ni 2.26, S 9.59.
-
Cl]+), calcd for
C
-
[5,10,15,20-Tetrakis(3,5-bis[(4-tert-butylphenylsulfido)meth-
yl]-4-chloridopalladio(II)phenyl)porphyrinato]magnesium(II)
(2(Mg)). Dry Et3N (68 µL, 490 µmol) was added to a stirred, dark
red solution of 2(2H) (32 mg, 12 µmol) in dry CH2Cl2 (4 mL).
After 5 min, MgBr2 · OEt2 (64 mg, 246 µmol) was added at once,
and the solution was stirred at room temperature. The progress of
the reaction was monitored by UV/vis spectroscopy, which showed
the disappearance of the lowest energy free-base porphyrin band
at 650 nm upon metalation with magnesium. After 1 h, all volatiles
were evaporated in vacuo. The residue was taken up in CH2Cl2 (5
mL) and filtered over a short pad of basic Al2O3, which was first
Acknowledgment. We thank The Netherlands Organisa-
tion for Scientific Research for a Jonge Chemici scholarship
(B.M.J.M.S. and R.J.M.K.G.) and for an Erasmus stipend
(S.D.H.M.).
Supporting Information Available: Experimental procedures
for the preparation of compounds 5 and 6(M) as well as a
reproduction of the X-ray crystal structure of 2(2H) are available
free of charge via the Internet at http://pubs.acs.org.
OM7005613