Synthesis of tetrahedral shape-persistent tetranuclear metal-salphens

Article abstract of DOI:10.1002/ejoc.201100745

The synthesis of two novel tetrakis(salicylaldehydes) based on a rigid tetraphenylmethane core is presented. These salicylaldehydes were used as precursors for the construction of three-dimensional multimetallic salphens, as exemplified by the synthesis of rigid and shape-persistent tetranuclearzinc-, nickel- and palladium-salphens with defined geometries and distances between the metal sites. The UV/Vis measurements of the tetranuclear metal complexes are presented. A series of tetranuclear metal-salphens (metal = Zn, Ni, Pd) with rigid defined three-dimensional geometries have been synthesized from readily accessible tetrakis(salicylaldehyde) precursors.

Full text of DOI:10.1002/ejoc.201100745

FULL PAPER
DOI: 10.1002/ejoc.201100745
Synthesis of Tetrahedral Shape-Persistent Tetranuclear Metal–salphens
Michael Mastalerz*[a] and Iris M. Oppel[b]
Keywords: Synthesis design / Zinc / Nickel / Palladium / UV/Vis spectroscopy / N,O ligands
The synthesis of two novel tetrakis(salicylaldehydes) based
on a rigid tetraphenylmethane core is presented. These salic-
ylaldehydes were used as precursors for the construction of
three-dimensional multimetallic salphens, as exemplified by
the synthesis of rigid and shape-persistent tetranuclear
zinc–, nickel– and palladium–salphens with defined geo-
metries and distances between the metal sites. The UV/Vis
measurements of the tetranuclear metal complexes are pre-
sented.
more (catalytically active) metal centers in a predefined
three-dimensional geometry.[12] The majority of investigated
oligometallic salphen systems contain two metal centers,
either with the same metal species (homodimetallic)[12,13] or,
rarely, with two different metals (heterodimetallic).[14] Most
of the previously mentioned macrocyclic[3] systems contain
three salphen pockets. In addition, Glaser and co-workers
introduced planar compounds with three metal–salphen
units, the magnetic properties of which were investigated
as well as the cooperative effects in catalytic reactions.[15]
MacLachlan and co-workers described the first three-di-
mensional trinuclear nickel–salphens based on triptycenes,
having high surface areas in the solid state.[16] With the ex-
ception of polymeric systems,[17] discrete compounds con-
taining more than three salphen pockets, which are coval-
ently connected to each other, are to the best of our knowl-
edge very rare, and only two examples have recently been
described in the literature.[18] One example is that of
MacLachlan and co-workers,[18a] who synthesized two dif-
ferent kinds of salphen pockets in a stepwise manner, first
by the (irreversible) formation of ketimine bonds and sec-
ondly by the reversible formation of aldimine bonds. How-
ever, no metal ion incorporation into the salphen pockets
has been described to date. Very recently, Kleij and co-
workers described the cooperative self-assembly of tetranu-
clear salphen macrocycles containing either four zinc or
four palladium centers.[18b] In almost all of the compounds
mentioned above, the salphen pockets are arranged in a
planar 2D structure. Therefore, we envisaged the synthesis
of tetrahedral tetrakis(salicylaldehydes) that will serve as
precursors for the synthesis of 3D multinuclear salphen
compounds, dendrimers, or even extended polymeric struc-
tures with different properties in comparison with the “flat”
systems. For this purpose we chose the well-known tetra-
phenylmethane[19] as a core unit, which has previously been
demonstrated to serve as an ideal subunit in the construc-
tion of rigid tetraaromatic compounds, which are ideal for
studying homoconjugation or energy-transfer mecha-
Introduction
The Schiff base condensation reaction[1] is a versatile and
powerful synthetic tool due to the fact that the formation
of imines is a reversible process. Furthermore, the reversibil-
ity of the reaction allows the system to eventually reach
the thermodynamically most stable product. Therefore, the
Schiff base condensation reaction is one of the most investi-
gated reactions used in dynamic covalent chemistry or sys-
tems chemistry.[2] It is widely exploited to synthesize shape-
persistent macrocycles,[3] cage compounds,[4] or helicates[5]
from relatively simple molecules in a single step and usually
in high yields. Even sophisticated molecules such as borro-
mean rings are readily accessible in high yields in one step
through a combination of imine bond formation and metal
complexation.[6]
Of the numerous Schiff bases, tetradentate salens or sal-
phens, derived from salicylaldehydes and diamines, are
known for their extraordinary ability to complex a large
variety of metal ions. These metal complexes are excellent
catalysts for a wide range of transformations, in particular,
for enantioselective reactions[7] or for the fixation of CO2
as cyclic carbonates or polymeric lactones.[8,9] In addition
to their application as homogeneous catalysts, metal–
salphens also serve as a construction motif for the forma-
tion of supramolecular assemblies or novel functional mate-
rials.[10] It is known that the cooperative effects of two or
more metal–salphen sites play an important role in several
catalytic reactions.[11] Therefore, efforts have been made to
synthesize molecular structures with multiple salphen/salen
binding pockets, offering the possibility of placing two or
[a] Organic Chemistry II & Advanced Materials, Ulm University,
Albert-Einstein-Allee 11, 89081 Ulm, Germany
Fax: +49-731-50-22840
E-mail: michael.mastalerz@uni-ulm.de
[b] Institute of Inorganic Chemistry, RWTH Aachen,
Landoltweg 1, 52074 Aachen, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100745.
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M. Mastalerz, I. M. Oppel
FULL PAPER
nisms.[20] Furthermore, this core unit has been exploited as oxyphenylboronic acid, which gave 85% yield of the corre-
a molecular precursor for the synthesis of discrete poly- sponding tetrakis(biphenylyl)methane 5.[26] Formylation
phenylene dendrimers.[21]
and subsequent BBr3-promoted cleavage of the methyl
Herein we present the synthesis of the first tetrahedral groups finally gave the tetrakis(salicylaldehyde) 7 in high
tetrakis(salicylaldehydes) 4 and 7, which have been used for yield (83% over two steps).
the construction of three-dimensional tetranuclear metal–
salphens. In addition, the photophysical properties of the
various tetranuclear metal–salphens are discussed.
Before using the tetraaldehydes 4 and 7 in Schiff base
condensation reactions with 10,[27] monoaldehyde 9 was
synthesized from tritylphenol (8) as a model compound to
optimize the reaction conditions for the preparation of un-
symmetrical salphen–metal complexes 11a–c, which can be
viewed structurally as components of the final products
13a–c, respectively (Scheme 2). Therefore, half-imine 10 was
treated with aldehyde 9 and metal acetate in methanol at
Results and Discussion
Synthesis and Characterization
The tetrakis(salicylaldehydes) 4 and 7 were synthesized room temperature[28,29] to yield zinc–salphen 11a as a
by starting with tetrakis(p-bromophenyl)methane (1), which bright-yellow solid, nickel–salphen 11b as a brownish-red
is easily accessible by bromination of tetraphenylmeth- solid, and palladium–salphen 11c as an orange solid in 88,
ane.[22] To obtain the smaller salicylaldehyde 4, 1 was first 82, and 58% yields, respectively. In contrast to a literature
converted into the tetramethoxylated compound 2 in 57% procedure,[29] in which the salicylaldehyde was used in ex-
yield by a copper-mediated cross-coupling reaction with so- cess to obtain a higher conversion of the unsymmetrical
dium methoxide in a solvent mixture of dimethylformamide zinc–salphen, we had to use half-imine 10 in excess: 10 is
(DMF) and methanol (Scheme 1).[23] The next step was the very soluble in the reaction solvent, whereas salicylaldehyde
Duff formylation of
2 with hexamethylenetetraamine 9 is not. Therefore, the excess of 10 can easily be removed
(HMTA) in anhydrous trifluoroacetic acid, which gave tet- by washing the crude product several times with methanol.
raaldehyde 3 in 80% yield.[24] Subsequent demethylation The conversion to unsymmetrical zinc–salphen 11a is very
with BBr3 in dry dichloromethane provided the tetrakis- clean, the 1H NMR spectrum of the crude product showing
(salicylaldehyde) 4 almost quantitatively.[25] This reaction exclusively the signals of the desired product. Instead, in
sequence (first the Duff formylation, then the deprotection) the reaction of 9 and 10 in the presence of nickel(II) or
is preferred, because it is known that para-substituted meth- palladium(II) acetate, the 1H NMR spectra of the crude
oxylated arenes give the mono-ortho-formylated products products revealed the formation of substantial amounts of
exclusively, whereas the more reactive phenols can further the symmetrical metal–salphens 12b and 12c, which could
react to the ortho-diformylated salicyldialdehydes, leading be removed by crystallization from CH2Cl2/MeOH, leading
to a complex mixture of products, which is difficult to sepa- to a lower yield (58%) of the unsymmetrical palladium–
rate.[24] The homologue tetrakis(salicylaldehyde) 7 with ad- salphen 11c. Zinc–salphen 11a forms stable dimers (11a)2 in
ditional 1,4-phenylene units was synthesized by a four-fold the gas phase, which were detected by MALDI-TOF mass
Suzuki–Miyaura reaction of tetrabromide 1 with p-meth- spectrometry; in the mass spectrum a peak at m/z = 1465
Scheme 1. Synthesis of tetrakis(salicylaldehydes) 4 and 7 starting from tetrakis(4-bromophenyl)methane (1).
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Tetrahedral Shape-Persistent Tetranuclear Metal-salphens
can be observed in addition to the peak at m/z = 732 for
the monomer 11a (see the Supporting Information).[30]
Such aggregate formation was not observed for the corre-
sponding nickel– and palladium–salphens 11b and 11c un-
der similar conditions.
Figure 1. Crystal structure of 11a. The dimer of the asymmetric
unit is depicted along a nondefined crystallographic axis. Gray: car-
bon; blue: nitrogen; red: oxygen; yellow: zinc. The (ZnO)2 cluster
is depicted as a ball-and-stick-model. Hydrogen atoms have been
omitted for clarity.
Scheme 2. Synthesis of unsymmetrical metal–salphens 11a–c.
attributed to a relatively strongly bound network by forma-
tion of (Zn–O)2 dimer subunits (see above). In the 1H NMR
By slow vapor diffusion of methanol into a solution of spectrum, two peaks can be clearly assigned to the imine
11a in DMF, we were able to grow single crystals suitable protons, the two singlets at δ = 8.92 and 8.73 ppm, which
for X-ray diffraction (Figure 1):[30,31] 11a crystallizes as di- are comparable to the imine proton signals of the model
¯
mers in the triclinic space group P1. The analysis shows compound 11a (δ = 8.93 and 8.74 ppm). In the FTIR spec-
that the salphen backbones are bent out of plane. The Zn– trum, the characteristic stretching band of the C=N bond
N distances are 2.105(2) and 2.066(2) Å, and the distances appears at 1614 cm–1, which again is comparable to that of
1
for the intramolecular Zn–O bonds are 2.051(1) and the model compound 11a (1614 cm–1). In neither the H
1.954(1) Å. The formation of dimers is favored by a second NMR spectrum nor the IR spectrum can signals of residual
type of intermolecular Zn–O bond [d = 2.053(1) Å]. The O2 formyl groups be detected, which suggests complete trans-
and Zn1 atoms form a parallelogram with Zn–O–Zn angles formation of all four salicylaldehyde subunits of the precur-
of 96.2 and 83.5°. The similar lengths of the inter- and in- sor 4. However, in the MALDI-TOF mass spectrum of 13a
tramolecular Zn–O bonds suggest a relatively strong inter- a number of fragment peaks can be detected in addition to
action in the dimer. The zinc dimers are themselves ar- the molecular peak, which gives a hint of the instability of
ranged in a linear fashion, mainly through intermolecular the tetranuclear zinc complex under the ionization condi-
π–π interactions between the imine groups and the adjacent tions. This is in agreement with earlier findings by Kleij and
aromatic ring (d = 3.26 Å) and CH–π interactions of the co-workers, who demonstrated that zinc–salphens can be
hydrogen atoms located in the meta-positions with respect selectively decomposed in a directing fashion.[32]
to the imine bonds and the aromatic planes of the trityl
In contrast to the synthesis of zinc complex 13a, the reac-
subunits of adjacent molecules (d = 2.86 Å). Furthermore, tion of 4 and 10 with nickel(II) acetate in methanol did not
the linear arrangements are connected by intermolecular yield the tetranuclear nickel–salphen 13b exclusively. In-
CH–π interactions between the tert-butyl hydrogen atoms stead, incomplete reactions were observed, resulting in two-
and the aromatic rings of the trityl subunit [d(H–C) = and three-fold reacted intermediates that are difficult to
3.00 Å] and π–π interactions between the aromatic rings of separate from the desired product 13b. DMF was shown
trityl subunits (d = 3.31 Å).
to be the solvent of choice. For a high conversion of 4 to
We tested the conditions elaborated for the model com- tetranuclear 13b, an excess (8 equiv.) of half-imine 10 was
pounds for the synthesis of tetranuclear metal–salphens required to force the four-fold reaction to completion. By-
using tetrakis(salicylaldehyde) 4, half-imine 10, and metal products were removed by washing the crude product with
acetate as the reactants (see Scheme 3). Tetranuclear zinc– DMF to give pure 13b as a wine-red solid in 70% yield.
salphen 13a can be synthesized in 73% yield from methanol As for the corresponding zinc complexes 13a and 11a, the
under similar conditions as model compound 11a (Fig- similarity of the characteristic peaks of nickel complexes
1
1
ure 1). The structure of 13a was confirmed by H NMR, 13b and 11b in the H NMR and IR spectra is clear: The
IR, HRMS, and UV/Vis spectroscopy (see the Supporting protons of the imine bonds resonate at δ = 8.81 and
Information). Zinc complex 13a is poorly soluble in most 8.77 ppm for compound 13b and are comparable to the sig-
common organic solvents except for polar, coordinating sol- nals at δ = 8.79 and 8.73 ppm for compound 11b. The IR
vents such as DMF and DMSO, which probably can be stretching of the imine bonds can be assigned to the strong
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conversion of all four salicylic aldehyde units. In the 1H
NMR spectrum of 14, the two characteristic singlets at δ =
8.82 and 8.98 ppm have been assigned to the imine protons.
The MALDI-TOF mass spectrum shows a base peak at m/z
= 2251, as expected.
Scheme 3. Synthesis of tetrahedral tetranuclear metal–salphens
13a–c. For the exact reaction conditions, see the Experimental Sec-
tion.
bands at 1616 and 1614 cm–1 for 13b and 11b, respectively.
The structure of 13b was further confirmed by an intense
base peak at m/z = 1950 in the MALDI-TOF mass spec-
trum. The isotopic pattern exactly fits the one calculated
for the structure of 13b (see the Supporting Information).
Tetranuclear palladium–salphen 13c was synthesized by
using DMF as solvent. Similarly to the model compound
11c, the tetrakis(salphen) 13c had to be isolated by several
recrystallization steps (for details see the Experimental Sec-
tion), giving the compound as a bright-orange solid in 61%
Scheme 4. Synthesis of the larger tetranickel–salphen 14.
1
yield. The H NMR spectrum of 13c shows characteristic
In an initial experiment we tested whether all four zinc
peaks at δ = 9.15 and 9.06 ppm, which have been assigned cations in 13a can be exchanged by nickel ions and there-
to the protons of the imine bonds and, again, are compar- fore can be a potential precursor for the templated synthesis
able to the shifts of the imine protons of model compound of other tetranuclear tetrahedral metal–salphens that are
11c in [D6]DMSO (δ = 9.14 and 9.03 ppm). The MALDI- difficult to access by the direct route depicted in
TOF mass spectrum shows a base peak at m/z = 2141 with Scheme 3.[33] Therefore, the tetranuclear zinc complex 13a
an isotopic pattern as expected for C113H116N8O8Pd4.
was dissolved in DMF, which resulted in a yellow solution,
Because the tetranuclear nickel–salphen 13b was less dif- and an excess of nickel(II) acetate tetrahydrate was added.
ficult to isolate, purify, and characterize than the corre- The reaction mixture immediately turned deep red, and a
sponding zinc– and palladium–salphens 13a and 13c, we precipitate was formed. The wine-red precipitate was col-
decided to test similar reaction conditions with elongated lected by filtration and washed with small portions of
tetrakis(salicylaldehyde) 7 as reactant for the synthesis of DMF. The 1H NMR, MALDI-TOF mass, and FTIR spec-
the corresponding nickel–salphen congener 14 (Scheme 4), tra of this product are identical to those observed for 13b
1
which we were able to isolate in 36% yield. The H NMR synthesized according to Scheme 3, which demonstrates
and FTIR spectra (see the Supporting Information) show that the zinc complex 13a serves as an efficient precursor
no peaks corresponding to aldehyde moieties, revealing full for transmetalation reactions.
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Tetrahedral Shape-Persistent Tetranuclear Metal-salphens
UV/Vis Spectroscopy
the ligand (MLCT band).[36] Furthermore, a relatively
sharp maximum appears at λmax = 387 and 389 nm, respec-
tively, which derives from π–π* transitions in the ligands.[36]
The palladium complexes 11c and 13c show broad
MLCT bands at λmax = 486 and 490 nm, respectively (Fig-
ure 4). Furthermore, in both spectra a shoulder appears at
387 and 383 nm, as well as three sharp overlapping peaks
at λmax = 363, 346, and 323 nm for 11c and at λmax = 363,
349, and 319 nm for 13c.[37]
Depending on the nature of the metal, metal–salphen
complexes are brightly colored (zinc: yellow; nickel: deep
red; palladium: orange) and are used, for example, as op-
tical sensors for the detection of explosives[34] or as the
active material in organic light-emitting devices
(OLEDs).[35] Therefore, we studied the metal–salphens by
UV/Vis spectroscopic methods.
The UV/Vis absorption spectrum of tetranuclear zinc
complex 13a has a similar shape to that of the model com-
pound 11a and shows a maximum at λmax = 415 nm with a
shoulder at around 460 nm, which is comparable to results
previously reported for similar zinc compounds (Fig-
ure 2).[34]
Figure 4. Comparison of the UV/Vis spectra of palladium–salphen
complexes 11c (solid line) and 13c (dashed line) in DMF (c =
10–5 m). The spectra are normalized for better comparison.
The adsorption maxima of the tetranuclear complexes
13a–c are only slightly bathochromically shifted in compari-
son with the model compounds 11a–c.
Figure 2. Comparison of the UV/Vis absorption spectra of the
zinc–salphens 11a (solid line) and 13a (dashed line) in DMF as
solvent (c = 10–5 m). The spectra are normalized.
Similarly to the zinc complexes, the UV/Vis spectra of all
three nickel–salphens have nearly the same adsorption
bands (Figure 3). Complexes 11b and 13b each show a
broad peak at λmax = 496 nm with an onset at around
650 nm, which can be assigned to a CT from the metal to
Conclusions
Two novel, rigid tetrahedral tetrakis(salicylaldehydes)
have been synthesized. These salicylaldehydes are versatile
building blocks for the synthesis of three-dimensional oli-
gonuclear rigid metal–salphens with defined distances be-
tween the metal centers.[38] This was demonstrated by the
full conversion of 4 and 7 into the corresponding tetranu-
clear zinc–salphen 13a, the tetranuclear nickel–salphens 13b
and 14, and palladium–salphen 13c. These are, to the best
of our knowledge, the first examples of discrete tetranuclear
metal–salphen complexes with three-dimensional geome-
tries. Currently, we are investigating the scope of the syn-
thetic procedures to prepare tetranuclear metal–salphen
complexes with various redox-active metal ions (e.g., Cu2+
,
Co2+, or Pt2+) for detailed investigation of their electro-
chemical and optical properties to gain an insight into the
intramolecular interactions of the distinct metal centers. In
addition, we have employed 4 and 7 as rigid building blocks
for the synthesis of novel extended three-dimensional poly-
meric metal–salphen/salen materials.[39] The results will be
presented in due course.
Figure 3. Comparison of the UV/Vis spectra of nickel–salphen
complexes 11b (solid line), 13b (dashed line), and 14 (dotted line)
in CH2Cl2 (c = 10–5 m). The spectra are normalized for better com-
parison.
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OCH2]+, 335, 334. C29H28O4·H2O (458.55): C 75.96, H 6.59; found
C 76.06, H 6.18.
Experimental Section
General: NMR spectra were recorded with a Bruker AMX 500 (1H
NMR: 500 MHz; 13C NMR: 125 MHz) or Avance 400 (1H NMR:
400 MHz; 13C NMR: 100 MHz) spectrometer at 298 K, unless
otherwise mentioned. Chemical shifts (δ) are given in ppm and were
calibrated with residual non-deuteriated solvent peaks (CDCl3: δH
5,5Ј,5ЈЈ,5ЈЈЈ-Methanetetrayltetrakis(2-methoxybenzaldehyde)
(3):
Tetrakis(4-methoxyphenyl)methane (2; 80 mg, 0.18 mmol) and
HMTA (500 mg, 3.57 mmol) were dissolved in trifluoroacetic acid
(4.5 mL), and the mixture was heated at 100 °C for 18 h. The
orange-colored reaction mixture was cooled to room temperature
and poured into 0.5 n hydrochloric acid (30 mL) and dichlorometh-
ane (25 mL) and stirred at room temperature for 4 h. The layers
were separated, the aqueous layer was extracted with dichlorometh-
ane (2ϫ25 mL), and the combined organic layers were washed
with water (2ϫ25 mL), saturated NaHCO3 (25 mL), and brine
(25 mL), and dried with Na2SO4. The solvent was removed in a
rotary evaporator to give 100 mg of an off-white solid. Column
chromatography (SiO2, ethyl acetate/petroleum ether, 3:1) and sub-
sequent drying under high vacuum gave 80 mg (80%) of 3 as a
colorless solid. M.p. 294–296 °C (dec.). 1H NMR (400 MHz,
CDCl3): δ = 10.40 (s, 4 H, ArCHO), 7.62 (d, J = 2.4 Hz, 4 H), 7.30
(dd, J = 8.8, J = 2.8 Hz, 4 H), 6.92 (d, J = 9.2 Hz, 4 H) 3.92 (s, 12
H, OCH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 189.53 (d,
CHO), 160.40 (s, ArC-OMe), 138.64, 138.23, 129.11, 123.86,
= 7.26 ppm, δC = 77.0 ppm; [D8]THF: δH = 3.58 ppm, δC
=
67.7 ppm; [D6]DMSO: δH = 2.50 ppm) as internal standards. EI
and CI mass spectrometry was performed with a Finnigan MAT
SSQ-7000 or a Varian Saturn 2000 GC–MS instrument. MALDI-
TOF mass spectra were recorded with a Bruker Daltonics Reflex
III spectrometer by using dithranol or DCTB {trans-2-[3-(4-tert-
butylphenyl)-2-methyl-2-propenylidene]malononitrile} as matrix.
UV/Vis absorption spectroscopy was performed with a Perkin–El-
mer Lambda 19 spectrometer by using Merck Uvasol grade sol-
vents. IR spectra were recorded as KBr pellets with a Perkin–Elmer
FTIR Spectrum 2000 spectrometer. Melting points were measured
with a Büchi B-545 apparatus. Elemental analyses were performed
with an Elementar Vario EL instrument (Ulm University). Plastic
sheets precoated with silica gel (Merck Si60 F254) were used for
thin-layer chromatography. Glass columns packed with Merck Sil-
ica 60 (mesh 40–60 μm) were used for flash-chromatographic puri-
fication. Solvents were purchased at ProLabo and distilled prior to
use. If necessary, solvents were dried in advance by applying com-
mon procedures.[40] All reagents were purchased from commercial
sources and used without further purification: Sodium methoxide
(Merck, for synthesis), copper(I) bromide (Acros Organics, 98%),
hexamethylenetetraamine (Fluka, 99%), trifluoroacetic acid (Sol-
vay Fluorochemicals GmbH), boron tribromide (Merck, for syn-
thesis), [Pd2dba3] (Alfa Aesar), HP(tBu)3BF4 (Aldrich, 97%), 4-
methoxyphenylboronic acid (Alfa Aesar, 97%+), nickel(II) acetate
tetrahydrate (Acros Organics, p.a.). Tetrabromide 1[22] and half-
imine 10[27] were synthesized as described previously.
111.75, 61.99 (s, Ar C), 55.78 (q, OCH ) ppm. IR (KBr pellet): ν
˜
4
3
= 3011 (w), 2948 (w), 2875 (w), 2761 (w), 1679 (s), 1604 (s), 1577
(w), 1493 (s), 1461 (w), 1446 (w), 1417 (w), 1392 (m), 1283 (s), 1256
(s), 1202 (w), 1181 (m), 1113 (m), 1016 (m), 919 (w), 834 (w), 809
(w), 731 (vw), 650 (w), 626 (w), 562 (vw), 510 (w) cm–1. MS (CI):
m/z (%) = 582 (7), 581 (20) [M + C2H5]+, 580 (8), 554 [M + H]+,
553 (100) [M]+, 552 (14), 417 (5), 89 (52), 61 (37). C33H28O8
(552.57): C 71.73, H 5.11; found C 71.60, H 5.16.
5,5Ј,5ЈЈ,5ЈЈЈ-Methanetetrayltetrakis(2-hydroxybenzaldehyde)
(4):
Boron tribromide (1.5 mL, 19 mmol) was added dropwise to a solu-
tion of 3 (282 mg, 0.5 mmol) in dry dichloromethane (100 mL) co-
oled to 0 °C under argon. The reaction mixture immediately turned
orange. The mixture was allowed to warm up to room temperature
and stirred for 12 h. The mixture was cooled again to 0 °C, water
(100 mL) was slowly added, and again the mixture was stirred at
room temperature for 4 h. The layers were separated and the or-
ganic layer washed with 1 n hydrochloric acid (2ϫ100 mL), water
(100 mL), and brine (100 mL), and dried with Na2SO4. Dichloro-
methane was removed under reduced pressure to give a red solid.
Purification by column chromatography (SiO2, dichloromethane)
gave, after drying, 236 mg (95%) of 4 as a colorless solid. M.p.
Synthetic Procedures
Tetrakis(4-methoxyphenyl)methane (2): In a screw-capped vial tetra-
bromide
1 (1.92 g, 3 mmol) and sodium methoxide (6.92 g,
128 mmol) were suspended in a mixture of anhydrous methanol
(8.5 mL) and anhydrous DMF (20 mL). The mixture was heated
to 110 °C (complete dissolution occurs), and CuBr (1.98 g,
13.7 mmol) was added in one portion. The reaction mixture turned
bluish-gray. After 2–2.5 h, the reaction mixture was allowed to cool
to room temperature, and 2 n hydrochloric acid (150 mL) and
dichloromethane (150 mL) were added. The aqueous layer was ex-
tracted with dichloromethane (2ϫ100 mL), and the combined or-
ganic extracts were washed with 2 n hydrochloric acid
(2ϫ100 mL), water (3ϫ100 mL), and brine (200 mL), and the
mixture was dried with sodium sulfate. After removing the solvents
by rotary evaporation, the remaining residue was treated with
methanol (10 mL), sonicated, and the off-white precipitate col-
lected with a Büchner funnel. Washing with methanol (3ϫ10 mL)
and drying in vacuo gave 1.04 g of an off-white solid. Column
chromatography (SiO2, light petroleum ether/dichloromethane, 1:1)
gave, after drying in vacuo, 760 mg (57%) of compound 2 as a
1
280–282 °C. H NMR (400 MHz, [D6]DMSO): δ = 10.81 (br. s, 4
H, ArOH), 10.21 (s, 4 H, ArCHO), 7.37 (d, J = 2.2 Hz, 4 H), 7.12
(dd, J = 8.7, J = 2.2 Hz, 4 H), 6.96 (d, J = 8.7 Hz, 4 H) ppm. 13C
NMR (100 MHz, [D6]DMSO): δ = 190.81 (d, ArCHO), 159.37 (s,
ArC-OH), 138.93, 136.64, 128.64, 121.27, 117.26, 61.20 (s, Ar4C),
54.86 ppm. IR (KBr pellet): ν = 3435 (br., m), 2853 (w), 1659 (s),
˜
1621 (m), 1586 (m), 1482 (s), 1375 (w), 1324 (w), 1284 (s), 1236
(m), 1207 (s), 1147 (w), 902 (m), 866 (w), 830 (w), 775 (w), 746 (w),
695 (w), 687 (w), 628 (w), 615 (w), 458 (w) cm–1. MS (CI): m/z (%)
= 526 (7), 525 (20) [M + C2H5]+, 499 (7), 498 (34), 497 (100) [M +
H]+, 496 (17), 375 (9), 139(18), 102 (5), 89 (37), 87 (10), 85 (14), 74
(5), 61 (33). C29H20O8·0.5CH2Cl2 (538.93): C 65.74, H 3.93; found
C 65.99, H 4.00.
1
colorless powder. M.p. 246–248 °C. H NMR (400 MHz, CDCl3):
δ = 7.07 (d, J = 8.8 Hz, 8 H, ArH), 6.77 (d, J = 8.8 Hz, 8 H, ArH),
3.79 (s, 12 H, OCH3) ppm. 13C NMR (100 MHz, CDCl3): δ =
157.39 (s, ArC-OMe), 139.75, 132.00, 112.58, 62.21 (s, Ar4C), 55.19
Tetrakis(4Ј-methoxy-1,1Ј-biphenyl-4-yl)methane
(5):[41]
Tetra-
bromide 1 (756 mg, 1.18 mmol) and 4-methoxyphenylboronic acid
(788 mg, 5.18 mmol) were suspended in THF (30 mL). An aqueous
potassium carbonate solution (2 n, 30 mL), [Pd2dba3]·CHCl3
(q, OCH ) ppm. IR (KBr pellet): ν = 3020 (w), 2949 (w), 2930 (w),
˜
3
2904 (w), 2835 (w), 1605 (m), 1575 (s), 1507 (s), 1466 (m), 1457
(m), 1442 (m), 1294 (m), 1250 (s), 1180 (s), 1117 (m), 1032 (s), 1011 (120 mg, 0.12 mmol, 5 mol-%), and HP(tBu)3BF4 (120 mg,
(w), 942 (vw), 908 (vw), 823 (s), 811 (m), 785 (w), 732 (w), 637 (w), 0.41 mmol) were added. The reaction mixture was heated at 75 °C
582 (s), 528 (w) cm–1. MS (EI): m/z = 441 [M + H]+, 440, 410 [M –
for 18 h. After cooling the reaction mixture to room temperature,
5976
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5971–5980

Tetrahedral Shape-Persistent Tetranuclear Metal-salphens
THF (ca. 200 mL) was added until complete dissolution of the or-
ganic material. The layers were separated, the organic layer was
washed with water (2ϫ100 mL) and brine (100 mL), and dried
with Na2SO4. After removing the solvent by rotary evaporation, a
brownish-green solid remained. Column chromatography (dichlo-
romethane/light petroleum ether, 1:3) gave 5 as a pale-yellow solid.
The solid was suspended in methanol (5 mL), collected by suction
filtration, and washed with methanol (3ϫ5 mL) and light petro-
leum ether (3ϫ5 mL). After drying in vacuo, 760 mg (86%) of 5
remained as colorless solid. M.p. 318–320 °C. 1H NMR (400 MHz,
[D8]THF): δ = 7.55 (d, J = 8.8 Hz, 8 H), 7.51 (d, J = 8.4 Hz, 8 H,
ArH), 7.37 (d, J = 8.4 Hz, 8 H, ArH), 6.95 (d, J = 8.8 Hz, 8 H,
322 °C. 1H NMR (400 MHz, [D6]DMSO): δ = 10.83 (br. s, 4 H,
ArOH), 10.30 (s, 4 H, ArCHO), 7.94 (d, J = 2.4 Hz, 4 H), 7.86
(dd, J = 8.4, J = 2.4 Hz, 4 H), 7.63 (d, J = 8.4 Hz, 8 H), 7.34 (d,
J = 8.4 Hz, 8 H), 7.09 (d, J = 8.8 Hz, 4 H) ppm. 13C NMR
(100 MHz, [D6]DMSO): δ = 191.42 (d, ArCHO), 160.11 (s, ArC-
OH), 145.06, 136.42, 134.33, 130.89, 130.72, 126.79, 125.48, 122.35,
117.87, 63.51 (s, Ar C) ppm. IR (KBr pellet): ν = 3202 (w), 3029
˜
4
(w), 2845 (w), 1681 (m), 1655 (s), 1620 (m), 1589 (m), 1477 (s),
1402 (w), 1370 (w), 1323 (w), 1296 (m), 1271 (m), 1223 (m), 1176
(m), 1127 (w), 1015 (w), 960 (w), 907 (m), 819 (s), 770 (w), 757 (m),
739 (w), 695 (w), 679 (w), 587 (w), 531 (m), 468 (m) cm–1. MS
(MALDI-TOF, DCTB): m/z
= 828 [M +
28]+, 800 [M]+.
ArH), 3.79 (s, 12 H, OMe) ppm. 13C NMR (100 MHz, [D8]THF): C53H36O8·3H2O (854.27): C 74.46, H 4.95; found C 74.70, H 4.76.
δ = 160.73 (s, ArC-OMe), 146.58 (s), 139.57 (s), 134.10 (s), 132.62
8 (340 mg,
2-Hydroxy-5-tritylbenzaldehyde (9): Tetrakis(biaryl)
(d), 128.79 (d), 126.61 (d), 115.25 (d), 65.27 (s, Ar4C), 55.71 (q,
1.00 mmol) and HMTA (190 mg, 1.3 mmol) were suspended in
TFA (2 mL). The reaction mixture was heated at 100 °C for 2 h.
After cooling the reaction mixture to room temperature, the vis-
cous oil was poured into 1 n hydrochloric acid (15 mL) and dichlo-
romethane (15 mL) and stirred at room temperature for 1 h. The
layers were separated, and the organic layer was washed with water
(2ϫ10 mL) and brine (10 mL), and dried with Na2SO4. The sol-
vents were removed by rotary evaporation, and the remaining solid
was purified by column chromatography (SiO2, dichloromethane/
petroleum ether, 1:1). After drying in vacuo, 291 mg (79%) of sal-
icylaldehyde 9 remained as a colorless powder. M.p. 184–186 °C.
1H NMR (400 MHz, CDCl3): δ = 11.02 (s, 1 H, Ar-OH), 9.72 (s,
1 H, ArCHO), 7.43 (d, J = 2.4 Hz, 1 H, Ar-2-H), 7.35 (dd, J = 8.8,
2.2 Hz, 1 H, Ar-4-H), 7.18–7.30 (m, 15 H, ArЈ-H), 6.90 (d, J =
8.8 Hz, 1 H, Ar-3-H) ppm. 13C NMR (100 MHz, CDCl3): δ = 196.8
(d, ArCHO), 160.1 (s, ArC-OH), 146.2, 140.7, 138.7, 134.8, 131.0,
127.8, 126.3, 119.6, 116.9, 64.2 (s, Ar3-C-ArЈ) ppm. IR (KBr pellet):
OCH ) ppm. IR (KBr pellet): ν = 3029 (m), 3000 (m), 2957 (m),
˜
3
2906 (m), 2835 (m), 1607 (s), 1580 (m), 1561 (w), 1522 (s), 1494
(vs), 1463 (s), 1441 (s), 1424 (w), 1399 (w), 1289 (s), 1249 (vs), 1210
(m), 1178 (vs), 1111 (w), 1041 (s), 1024 (m), 1014 (m), 1001 (m),
817 (vs), 751 (m), 720 (w), 702 (m), 632 (w), 588 (w), 559 (w), 525
(s) cm–1. MS (MALDI-TOF, DCTB): m/z (%) = 744 [M]+.
C53H44O4 (744.32): C 85.46, H 5.95; found C 85.49, H 5.95.
4Ј,4ЈЈЈ,4ЈЈЈЈЈ,4ЈЈЈЈЈЈЈ-Methanetetrayltetrakis(4Ј-methoxy-1,1Ј-biphen-
yl-3Ј-carbaldehyde) (6): Tetrakis(biaryl) 5 (750 mg, 1.01 mmol) and
HMTA (2.8 g, 20 mmol) were suspended in TFA (25 mL). The re-
action mixture was heated at reflux for 18 h. After cooling the reac-
tion mixture to room temperature, the viscous oil was poured into
1 n hydrochloric acid (150 mL), and the mixture was stirred over-
night. The precipitate was collected by suction filtration to give
840 mg of a yellow solid. After separation by column chromatog-
raphy (SiO2, THF) 6 was obtained as a pale-yellow powder. The
powder was washed several times with n-pentane and dried in
vacuo to give 740 mg (85%) of 6 as an off-white solid. M.p. 296–
300 °C. 1H NMR (500 MHz, [D6]DMSO, 373 K): δ = 10.41 (s, 4
H, ArCHO), 7.96 (“d”, J = 5.0 Hz, 8 H, ArH, two interpenetrating
signals), 7.63 (d, J = 8.0 Hz, 8 H, ArH), 7.39 (d, J = 8.0 Hz, 8 H,
ArH), 7.31 (d, J = 9.0 Hz, 4 H, ArH), 3.91 (s, 12 H, OMe) ppm.
13C NMR (125 MHz, [D6]DMSO, 373 K): δ = 188.21 (d, ArCHO),
160.32 (s, ArC-OMe), 144.66 (s), 135.82 (s), 133.25 (d), 131.52 (s),
130.34 (d), 125.10 (d), 124.89 (d), 124.23 (s), 112.97 (d), 63.13 (s,
ν = 3087 (w), 3052 (w), 3030 (w), 2846 (w), 1659 (s), 1617 (m),
˜
1588 (m), 1478 (s), 1443 (w), 1375 (w), 1350 (m), 1325 (m), 1289
(s), 1236 (m), 1201 (s), 1170 (m), 1130 (m), 1082 (m), 1035 (m),
1010 (w), 1001 (w), 964 (w), 838 (m), 750 (s), 729 (w), 702 (s), 674
(m), 645 (m), 633 (m), 607 (m) cm–1. MS (CI): m/z (%) = 393 (27)
[M + C2H5]+, 366 (32) [M + H]+, 365 (100) [M]+, 364 (26), 288 (9),
287 (47), 243 (9). C26H20O2 (364.44): C 85.69, H 5.69; found C
85.86, H 5.69.
Zinc–salphen 11a: Aldehyde 9 (72 mg, 0.20 mmol) and half-imine
10 (104 mg, 0.32 mmol) were suspended in methanol (10 mL) in
a screw-capped vial. A solution of zinc acetate dihydrate (72 mg,
0.33 mmol) in methanol (2 mL) was added and the reaction mix-
ture stirred at room temperature for 40 h. The yellow precipitate
was collected by suction filtration, washed with methanol
(3ϫ4 mL), and dried in vacuo to give 130 mg (88%) of 11a as
yellow solid. M.p. Ͼ400 °C. 1H NMR (400 MHz, [D6]-
DMSO): δ = 8.93 (s, 1 H, ArCH=N), 8.74 (s, 1 H, ArЈCH=N),
7.83 (d, J = 7.9 Hz, 2 H, ArЈ-6-H), 7.53–7.02 (m, 21 H, Ar-H), 6.92
(d, J = 8.9 Hz, 1 H, ArЈ-4-H), 6.59 (d, J = 8.9 Hz, 1 H, ArЈ-3-H),
1.46 [s, 9 H, C(CH3)3], 1.27 [s, 9 H, C(CH3)3] ppm. 13C NMR
(101 MHz, [D6]DMSO): δ = 170.63, 170.29, 163.50, 162.53, 146.96,
140.64, 139.97, 139.31, 137.41, 136.38, 133.28, 130.43, 129.64,
127.71, 127.14, 126.54, 125.79, 122.90, 118.17, 118.08, 116.82,
116.76, 116.37, 63.53, 35.20, 33.57, 31.37, 29.62 ppm. IR (KBr pel-
Ar C), 55.61 (q, OCH ) ppm. IR (KBr pellet): ν = 3031 (w), 2940
˜
4
3
(w), 2862 (w), 1680 (s), 1607 (s), 1580 (w), 1487 (s), 1462 (w), 1442
(w), 1425 (w), 1389 (w), 1305 (vw), 1271 (s), 1247 (m), 1181 (m),
1122 (m), 1049 (w), 1016 (m), 904 (m), 812 (s), 752 (vw), 701 (w),
650 (w), 519 (w) cm–1. MS (MALDI-TOF, DCTB): m/z = 879 [M
+ Na]+, 856 [M]+, 744. C57H44O8·2H2O (892.33): C 76.67, H 5.42;
found C 76.70, H 5.19.
4Ј,4ЈЈЈ,4ЈЈЈЈЈ,4ЈЈЈЈЈЈЈ-Methanetetrayltetrakis(4Ј-hydroxy-1,1Ј-biphen-
yl-3Ј-carbaldehyde) (7): Boron tribromide (1.2 mL, 15 mmol) was
added dropwise to a solution of 6 (500 mg, 0.60 mmol) in dry
dichloromethane (100 mL) at 0 °C under argon. The reaction mix-
ture immediately turned red. The mixture was allowed to warm to
room temperature and stirred for 3 h. The mixture was cooled
again to 0 °C, water (100 mL) was slowly added, and again the
mixture was stirred at room temperature for 30 min. The layers
were separated, and the organic layer was washed with 1 n hydro-
chloric acid (2ϫ100 mL), water (100 mL), and brine (100 mL), and
dried with Na2SO4. Dichloromethane was removed in vacuo and
the remaining solid diluted in THF and filtered through a plug of
silica. After evaporation of the THF, a light-orange solid remained.
The solid was suspended in THF (6 mL), collected with a Büchner
let): ν = 3056 (w), 2957 (m), 1614 (s), 1582 (m), 1526 (m), 1469
˜
(m), 1425 (w), 1384 (m), 1360 (w), 1294 (w), 1254 (w), 1194 (w),
1163 (m), 1109 (w), 1036 (w), 972 (w), 923 (w), 835 (w), 793 (w),
748 (m), 702 (m), 625 (w) cm–1. MS (MALDI-TOF, DCTB): m/z
= 732.7 [M]+, 1565.8 [2 M]+. C47H44N2O2Zn (734.24): C 76.88, H
6.04, N 3.82; found C 76.96, H 5.94, N 4.13.
funnel, and washed with n-pentane (3ϫ10 mL) to give, after drying Nickel–salphen 11b: Aldehyde 9 (76 mg, 0.21 mmol) and half-imine
in vacuo, 7 as a pale-yellow solid. Yield: 447 mg (97%). M.p. 318– 10 (116 mg, 0.35 mmol) were suspended in methanol (6 mL) in a
Eur. J. Org. Chem. 2011, 5971–5980
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5977

M. Mastalerz, I. M. Oppel
FULL PAPER
screw-capped vial. A solution of nickel acetate tetrahydrate (78 mg,
0.27 mmol) in methanol (6 mL) was added and the reaction mix-
ture stirred at room temperature for 46 h. The red precipitate was
collected by suction filtration, washed with methanol (3ϫ4 mL),
and dried in vacuo to give a red solid (160 mg). The solid was
redissolved in dichloromethane (20 mL), and overlayered with
methanol (60 mL). After complete diffusion of the methanol into
the dichloromethane layer, the red precipitate was collected by suc-
tion filtration and dried in vacuo to give 126 mg (82%) of 11b as
H), 7.31–7.21 (m, 20 H, Ar-H), 7.10 (d, J = 9.1 Hz, 4 H, ArЈЈ-H),
6.63 (d, J = 9.0 Hz 4 H, ArЈЈ-H), 1.48 [s, 36 H, C(CH3)3], 1.28 [s,
36 H, C(CH ) ] ppm. IR (KBr pellet): ν = 2955 (m), 2905 (m),
˜
3 3
2863 (w), 1614 (s), 1581 (s), 1525 (s), 1467 (m), 1424 (m), 1384 (w),
1253 (w), 1194 (m), 1163 (m), 792 (w), 750 (w) cm–1. MS (MALDI-
TOF, DCTB): m/z = 1976 [M]+.[5] HRMS (MALDI-TOF, DCTB):
+
calcd. for C113H116N8O8Zn4 1975.60376; found 1975.61156.
Tetranuclear Nickel–salphen 13b:[42] Salicylaldehyde
4 (50 mg,
0.10 mmol), half-imine 10 (260 mg, 0.80 mmol), and nickel acetate
tetrahydrate (260 mg, 0.92 mmol) were suspended in dry DMF
(8 mL), and the mixture was stirred at room temperature. After
40 h, a red precipitate was collected by suction filtration, washed
with dry DMF (5ϫ3 mL), and dried in vacuo (5.1ϫ10–1 bar,
100 °C) for 5 h to give 138 mg (70%) of 13b as a wine-red solid.
M.p. Ͼ400 °C. 1H NMR (400 MHz, [D6]DMSO): δ = 8.81 (s, 4 H,
ArCH=N), 8.77 (s, 4 H, ArЈCH=N), 8.23 (d, J = 8.2 Hz, 4 H, ArЈ-
H), 8.12 (d, J = 8.4 Hz, 4 H, ArЈ-H), 7.47 (d, J = 1.5 Hz, 4 H, Ar-
H), 7.42 (d, J = 1.4 Hz, 4 H, Ar-H), 7.32 (d, J = 1.7 Hz, 4 H, Ar-
H), 7.29 (t, J = 7.5 Hz, 4 H, ArЈЈ-H), 7.23 (t, J = 7.5 Hz, 4 H, ArЈЈ-
H), 7.07 (d, J = 9.1 Hz, 4 H, ArЈЈ-H), 6.80 (d, J = 9.0 Hz 4 H,
ArЈЈ-H), 1.39 [s, 36 H, C(CH3)3], 1.28 [s, 36 H, C(CH3)3] ppm. IR
1
a red solid. M.p. Ͼ400 °C. H NMR (400 MHz, CDCl3): δ = 8.19
(s, 1 H, ArCH=N), 8.08 (s, 1 H, ArЈCH=N), 7.69 (d, J = 7.7 Hz,
1 H, ArЈ-6-H), 7.62 (d, J = 7.9 Hz, 1 H, ArЈ-6-H), 7.38 (d, J =
2.3 Hz, 1 H, Ar-H), 7.26–7.15 (m, 21 H), 7.08 (d, J = 2.3 Hz, 1 H,
Ar-H), 7.02 (dd, J = 9.1, 2.4 Hz, 1 H, Ar-H), 6.92 (d, J = 9.1 Hz,
1 H, Ar-H), 1.44 [s, 9 H, C(CH3)3], 1.30 [s, 9 H, C(CH3)3] ppm. 13
C
NMR (101 MHz, [D6]DMSO): δ = 166.26, 164.84, 153.75, 153.56,
146.61, 143.08, 142.66, 140.98, 139.84, 137.01, 133.74, 133.00,
131.11, 130.50, 127.56, 126.88, 126.46, 126.00, 121.16, 119.23,
118.54, 114.70, 114.46, 63.92, 35.59, 34.02, 31.22, 29.38 ppm. IR
(KBr pellet): ν = 3055 (w), 3028 (w), 2957 (m), 2904 (w), 2867 (w),
˜
1616 (s), 1602 (m), 1576 (m), 1523 (m), 1489 (m), 1461 (m), 1425
(w), 1384 (m), 1358 (w), 1335 (w), 1266 (w), 1246 (w), 1198 (w),
1181 (m), 1129 (w), 1110 (w), 1083 (w), 1035 (w), 969 (w), 941 (w),
891 (w), 867 (w), 832 (w), 787 (w), 745 (m), 702 (m), 645 (w), 633
(w), 555 (m), 538 (w) cm–1. MS (MALDI-TOF, DCTB): m/z =
726.0 [M]+. C47H44N2NiO2·0.5CH2Cl2 (770.03): C 74.09, H 5.89,
N 3.64; found C 73.81, H 5.86, N 3.70.
(KBr pellet): ν = 2955 (m), 2905 (m), 2867 (w), 1614 (s), 1575 (s),
˜
1520 (s), 1487 (m), 1460 (m), 1425 (m), 1382 (w), 1358 (m), 1336
(w), 1245 (w), 1196 (s), 1182 (s), 1128 (w), 1110 (w), 1044 (w), 942
(w), 920 (w), 892 (w), 862 (w), 842 (w), 803 (w), 787 (w), 742 (m),
712 (w), 638 (w), 552 (w), 536 (w) cm–1. MS (MALDI-TOF,
DCTB): m/z = 1946.2 [M]+. C113H116N8Ni4O8·2H2O (1984.98): C
68.37, H 6.09, N 5.65; found C 68.34, H 5.89, N 5.66.
Palladium–salphen 11c: Aldehyde 9 (72 mg, 0.20 mmol) and half-
imine 10 (110 mg, 0.34 mmol) were suspended in methanol (6 mL)
in a screw-capped vial. A solution of palladium acetate (74 mg,
0.33 mmol) in methanol (6 mL) was added and the reaction mix-
ture stirred at room temperature for 40 h. The orange-brown pre-
cipitate was collected by suction filtration, washed with methanol
(3ϫ4 mL), and dried in vacuo to give 133 mg of an orange-brown
solid. The solid was redissolved in dichloromethane (20 mL) and
covered with methanol (60 mL). After complete diffusion of the
methanol into the dichloromethane layer, a bright-orange precipi-
tate was formed. The precipitate was collected by suction filtration
and dried in vacuo to give 90 mg (58%) of 11c as an orange solid.
M.p. Ͼ400 °C. 1H NMR (400 MHz, CDCl3): δ = 8.50 (s, 1 H,
ArCH=N), 8.34 (s, 1 H, ArЈCH=N), 7.87 (d, J = 7.9 Hz, 1 H, ArЈ-
H), 7.79 (d, J = 7.8 Hz, 1 H, ArЈ-H), 7.52 (d, J = 2.0 Hz, 1 H, Ar-
H), 7.30–7.08 (m, 21 H, Ar-H), 1.53 [s, 9 H, C(CH3)3], 1.33 [s, 9 H,
C(CH3)3] ppm. 13C NMR (126 MHz, CDCl3): δ = 170.03, 167.30,
146.59, 143.88, 141.38, 140.73, 136.81, 135.05, 131.77, 131.72,
131.15, 130.51, 130.47, 128.27, 128.21, 127.60, 127.45, 127.00,
126.94, 126.05, 121.91, 119.87, 119.22, 115.70, 115.39, 63.94, 36.00,
Tetranuclear Palladium–salphen 13c:[42] Salicylaldehyde 4 (50 mg,
0.10 mmol), half-imine 10 (260 mg, 0.80 mmol), and palladium
acetate (203 mg, 0.90 mmol) were suspended in dry DMF (6 mL),
and the mixture was stirred at room temperature. After 60 h, an
orange-colored precipitate was collected by suction filtration,
washed with dry DMF (4ϫ4 mL), and dried in a stream of air
to give 300 mg of an orange-colored solid. Recrystallization from
CH2Cl2/MeOH and then from DMF gave, after drying in vacuo
(5.1ϫ10–1 bar, 100 °C) for 5 h, 130 mg (61%) of 13c as bright-
1
orange solid. M.p. Ͼ400 °C. H NMR (400 MHz, [D6]DMSO): δ
= 9.15 (s, 4 H, ArCH=N), 9.06 (s, 4 H, ArЈCH=N), 8.40 (d, J =
8.7 Hz, 4 H, ArЈ-H), 8.33 (d, J = 8.5 Hz, 4 H, ArЈ-H), 7.65 (d, J =
2.0 Hz, 4 H, Ar-H), 7.57 (d, J = 2.0 Hz, 4 H, Ar-H), 7.47 (d, J =
2.0 Hz, 4 H, Ar-H), 7.39 (t, J = 7.7 Hz, 4 H, ArЈЈ-H), 7.33 (t, J =
7.8 Hz, 4 H, ArЈЈ-H), 7.25 (m, 4 H, ArЈЈ-H), 7.00 (d, J = 9.1 Hz 4
H, ArЈЈ-H), 1.48 [s, 36 H, C(CH3)3], 1.31 [s, 36 H, C(CH3)3] ppm.
IR (KBr pellet): ν = 2955 (m), 2905 (m), 2867 (w), 1605 (s), 1576
˜
(s), 1516 (s), 1487 (m), 1456 (m), 1417 (m), 1385 (w), 1330 (w),
1245 (w), 1192 (s), 1172 (s), 1091 (w), 785 (w), 748 (m), 535 (w)
cm–1. MS (MALDI-TOF, DCTB): m/z = 2142 [M]+. HRMS (ESI)
calcd. for C113H116N8O8Pd4 + H+ 2141.51848; found 2141.51866.
34.02, 31.24, 29.71 ppm. IR (KBr pellet): ν = 3056 (w), 2957 (m),
˜
1604 (s), 1577 (s), 1513 (s), 1485 (m), 1451 (m), 1385 (m), 1360 (w),
1331 (m), 1244 (w), 1191 (w), 1173 (m), 1132 (w), 1107 (w), 1036
(w), 970 (w), 940 (w), 890 (w), 832 (w), 786 (w), 746 (m), 702 (m),
646 (w), 634 (w), 554 (w), 536 (w) cm–1. MS (MALDI-TOF,
DCTB): m/z = 773.9 [M]+. C47H44N2O2Pd·0.5H2O (793.29): C
71.98, H 5.78, N 3.57; found C 71.69, H 5.45, N 4.00.
Tetranuclear Nickel–salphen 14:[42] Salicylaldehyde
7 (80 mg,
0.10 mmol), half-imine 10 (260 mg, 0.80 mmol), and nickel acetate
tetrahydrate (260 mg, 0.92 mmol) were suspended in dry DMF
(8 mL), and the mixture was stirred at room temperature for 48 h.
After 40 h, a red precipitate was collected by suction filtration and
washed with dry DMF (5ϫ3 mL). After one night, a second frac-
Tetranuclear Zinc–salphen 13a:[42] Salicylaldehyde
0.10 mmol), half-imine 10 (156 mg, 0.48 mmol), and zinc acetate
4 (50 mg,
dihydrate (260 mg, 1.2 mmol) were suspended in dry MeOH tion of 14 precipitated from the mother liquor, which was collected
(6 mL), and the mixture was stirred at room temperature. After
50 h, a yellow precipitate was collected by suction filtration, washed
with dry MeOH (3ϫ3 mL), and dried in vacuo (5.1ϫ10–1 bar,
by filtration. The combined fractions were dried in vacuo
(5.1ϫ10–1 bar, 140 °C) for 10 h to give 80 mg (36%) of 14 as a
wine-red solid. M.p. Ͼ400 °C. 1H NMR (400 MHz, [D6]DMSO,
100 °C) for 5 h to give 156 mg (73%) of 13a as an orange solid. 375 K): δ = 8.89 (s, 4 H, ArCH=N), 8.72 (s, 4 H, ArCH=N), 8.12
M.p. Ͼ400 °C. 1H NMR (400 MHz, [D6]DMSO): δ = 8.92 (s, 4 H, (m, ArH, 4 H), 8.08 (m, 4 H, ArH), 7.98 (d, J = 2.3 Hz, 4 H, ArH),
ArCH=N), 8.73 (s, 4 H, ArЈCH=N), 7.82 (d, J = 8.0 Hz, 8 H, ArЈ-
5978
7.71 (dd, J = 9.0, 2.5 Hz, 4 H, ArH), 7.64 (d, J = 8.6 Hz, 8 H,
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5971–5980

Tetrahedral Shape-Persistent Tetranuclear Metal-salphens
M. M. Belmonte, J. Benet-Buchholz, A. W. Kleij, Chem. Com-
mun. 2010, 46, 4580–4582.
S. I. Vagin, R. Reichardt, S. Klaus, B. Rieger, J. Am. Chem.
ArH), 7.42 (m, 12 H, ArH), 7.38 (d, J = 2.4 Hz, 4 H, ArH), 7.32
(m, ArH, 8 H), 6.92 (d, J = 8.9 Hz, 4 H, ArH), 1.41 [s, 36 H,
[9]
C(CH ) ], 1.29 [s, 36 H, C(CH ) ] ppm. IR (KBr pellet): ν = 2955
˜
3 3
3 3
Soc. 2010, 132, 14367–14369.
(m), 2905 (m), 2867 (w), 1617 (s), 1601 (s), 1575 (s), 1524 (s), 1506
(m), 1488 (m), 1459 (m), 1425 (m), 1384 (w), 1357 (m), 1336 (w),
1245 (w), 1194 (s), 1179 (s), 1163 (w), 1014 (w), 940 (w), 816 (w),
787 (w), 742 (m), 554 (w), 539 (w) cm–1. MS (MALDI-TOF,
DCTB): m/z = 2251.4 [M]+. C137H132N8Ni4O8·2H2O (2289.37): C
71.87, H 5.99, N 4.89; found C 71.88, H 5.80, N 4.87.
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Fonds der Chemischen Industrie are gratefully acknowledged for
financial support as well as Solvay Fluor GmbH for the donation
of chemicals.
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5979

M. Mastalerz, I. M. Oppel
FULL PAPER
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1957.4(1) Å3, Z = 1, Dcalcd. = 1.246 gcm–3, μ = 0.667 mm–1,
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for 11a: T = 110(2) K, C94H88N4O4Zn2, M = 1468.42, triclinic
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¯
space group P1, a = 9.3987(3), b = 11.4260(5), c = 19.0400(7)
Received: May 27, 2011
Å, α = 97.225(3), β = 98.220(3), γ = 101.553(3)°, V =
Published Online: July 25, 2011
5980
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5971–5980