Probing the radialene-character in triplesalophen ligands by spectroscopic and structural analysis

Article abstract of DOI:10.1021/jo202273s

The triplesalen ligand system based on three salen-like coordination environments bridged by a common phloroglucinol ring has been designed and successfully applied for the rational synthesis of single-molecule magnets from two trinuclear triplesalen comp

Full text of DOI:10.1021/jo202273s

Article
pubs.acs.org/joc
Probing the Radialene-Character in Triplesalophen Ligands by
Spectroscopic and Structural Analysis
Carl-Georg Freiherr von Richthofen, Anja Stammler, Hartmut Bogge, and Thorsten Glaser*
̈
Lehrstuhl fur Anorganische Chemie I, Fakultat fur Chemie, Universitat Bielefeld, Universitatsstr. 25, D-33615 Bielefeld, Germany
̈
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: The triplesalen ligand system based on three
salen-like coordination environments bridged by a common
phloroglucinol ring has been designed and successfully applied
for the rational synthesis of single-molecule magnets from two
trinuclear triplesalen complexes and one hexacyanometallate by
supramolecular recognition. In order to optimize this system
with respect to magnetic anisotropy, the triplesalophen ligand
system has been identified, which should allow for the synthesis
of nonanuclear complexes composed of two trinuclear triple-
salophen complexes and three connecting units. Herein, the
convergent synthesis of the triplesalophen ligand system is
described, which differs fom the divergent strategy for the
triplesalen ligand system. The molecular and elecrtronic structures of the triplesalophen ligands H6baronR (R = Me, Cl, Br) have
been established by single-crystal X-ray diffraction, NMR, FTIR, and UV−vis spectroscopies. These complementary methods
allowed the assignment of the central compartment not to be in the O-protonated tautomer but in the N-protonated tautomer with
the prevalence of a keto-enamine resonance description, which resembles a heteroradialene. Furthermore, the comparison with the
mononucleating unsymmetrical salophen reference ligand H2carlCl and with compounds from the literature provides unique
signatures for the appearance of the heteroradialene motif not only in NMR spectra and structural parameters but also in IR and
UV−vis spectra. These signatures form the basis for the interpretation and understanding of the electronic structures of transition
metal complexes with the triplesalophen ligand system.
[MnIII6CrIII]3+,31 [MnIII6FeIII]3+,32 and [MnIII6CoIII]3+ with
33
INTRODUCTION
■
[MnIII6CrIII]3+ being a single-molecule magnet.
We have designed the triplesalen ligand system1−3 (Scheme 1)
to meet two necessary (but not sufficient) requirements for the
rational design of single-molecule magnets (SMMs): (1) a high
Although [MnIII6CrIII]3+ exhibits a high spin ground state of
S = 21/2, a magnetic anisotropy of the spin ground state, and a
molecular C3 symmetry, the single-molecule magnet properties
(anisotropy barrier and blocking temperature) are not better
than the first reported SMM [Mn12O12(O2CCH3)16(OH2)4],
Mn12.34−36 Lately, some strategies have been successful in
increasing the blocking temperature in the family of Mn6
(= [Mn6O2(saoR)6(O2CR′)2(solv)n]; with H2sao = salicylaldox-
ime) complexes37−42 and in Dy243 and Tb244 (= [K(18-crown-6)-
(THF)2][{[(Me3Si)2N]2(THF)Ln}2(μ-η2:η2-N2)]; with Ln =
Dy, Tb). We have analyzed the magnetic properties of
[MnIII6CrIII]3+ in detail and identified several optimization stra-
tegies.3 One reason for the low blocking temperature is the too
small magnetic anisotropy of the total spin ground state St. The
main component of the magnetic anisotropy of the total spin
ground state arises from the projection of the single-site an-
isotropies onto the total spin ground state, while dipolar and
anisotropic interactions yield mainly only minor contribu-
tions.25,45 In the heptanuclear complexes [Mt6Mc]n+ the single-
site anisotropy tensors of the MnIII ions (which coincides with
spin ground state St and (2) a strong magnetic anisotropy DS .
t
We have chosen the phloroglucinol bridging unit X (Scheme 1)
to transmit ferromagnetic interactions in trinuclear com-
plexes4−10 by the spin-polarization mechanism.11−24 We have
chosen a salen-like coordination environment because the salen
ligand Y (Scheme 1) should establish a pronounced magnetic
anisotropy by its strong ligand field in the basal plane.25−27
A
well-studied example is the Jacobson catalyst [(salen′)MnIIICl]
(with H2salen′ = (R,R)-N,N′-bis(3,5-di-tert-butylsalicylidene)-
1,2-cyclohexanediamine), which is a MnIII (S = 2) species with
a strong magnetic anisotropy parametrized by a zero-field
splitting parameter D = −2.5 cm−1.28−30 Severe ligand foldings
have been observed in the complexes of the ligand H6talent‑Bu
2
(= 2,4,6-tris{1-[2-(3,5-di-tert-butylsalicylaldimino)-2-methyl-
propylimino]-ethyl}-1,3,5-trihydroxybenzene) resulting in over-
all bowl-shaped molecular structures (Scheme 1, bottom
left).2,6 We have taken advantage of this ligand folding by
using the trinuclear complexes [(talent‑Bu ){M (solv)n}3] to
act as molecular building blocks with hexacyanometallates
[Mc(CN)6]3− for the formation of heptanuclear complexes
t
m+
2
Received: November 9, 2011
Published: January 5, 2012
[Mt Mc ]n + (= [{(talent ‑ B u )M }2 {M (CN)6 }]n + ):
t
c
2
6
3
© 2012 American Chemical Society
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almost cancellation of the local magnetic anisotropies by the
projection onto the total spin ground state. A collinear arrange-
ment of the MnIII anisotropy tensors would maximize the
projection of the local anisotropies onto the total spin ground
state. Thus, an improvement for our system would be an almost
planar trinuclear building block (Scheme 1, bottom right)
compared to the bowl-shaped triplesalen building block (Scheme
1, bottom left).2,6 Therefore, the triplesalophen ligand system
with a completely sp2-hybridized and therefore almost planar
backbone (Scheme 1) appeared to us as a natural choice for a
rational improvement of our system. Trinuclear triplesalophen
complexes should thus allow the construction of nonanuclear
complexes [Mt6Mc3]n+ with all local anisotropies tensors
arranged collinear for maximizing the total magnetic anisotropy
instead of the almost cancellation of the local anisotropy tensors
in the bowl-shaped heptanuclear complexes [Mt6Mc]n+ with
triplesalen complexes.
Scheme 1
Herein, we present the efficient synthesis of the triplesalo-
phen ligands H6baronR (R = Me, Cl, Br; Scheme 2). We have
recently communicated the synthesis of H6baronBr and its
trinuclear NiII complex [(baronBr)Ni{Ni(py)2}2], which ex-
hibits ferromagnetic interactions between the octahedrally
coordinated NiII ions.46 The specific requirements of the phe-
nylenediamine backbone prevented the application of the
established divergent synthesis of the triplesalen ligands. Thus,
a convergent synthesis was established. Additionally, the
characterization of H6baronR in the solid state by high resolu-
tion single-crystal X-ray diffraction and in solution by extensive
NMR spectroscopy allows a detailed description of the tauto-
meric and electronic structure of H6baronR. In contrast to
simple salophen ligands, the triplesalophen ligands H6baronR
the Jahn−Teller axis indicated by the thick bars in Scheme 1,
bottom) are not collinear with the molecular C3 axis but form
angles of 36−41° (Scheme 1, bottom left). This results in an
Scheme 2
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prevail in the N-protonated tautomer in the central backbone
with a radialene-like resonance structure (“heteroradialene”) being
more important than an aromatic benzene resonance structure.
The combined application of the complementary methods
NMR spectroscopy, single-crystal X-ray diffraction, FTIR, and
UV−vis spectroscopies allowed us to identify prominent signa-
tures of the central heteroradialene in extended phloroglucinol
ligands in all four methods. These signatures will allow us the
assignment of the electronic structure of the central phlorog-
lucinol backbone in the transition metal complexes with the
triplesalophen ligand system.
Scheme 3
RESULTS
■
Synthesis. The syntheses of symmetrical salen ligands are
easily achieved by one-pot Schiff-base condensations of one
diamine and two identical aldehyde or ketone derivatives. In
contrast, the preparation of asymmetrical salen ligands is more
challenging and requires a stepwise protocol. In the first step,
the isolation of a monocondensed diamine derivative, a so-
called half-unit, is necessary.47−56 The reaction of the remaining
amine function of this intermediate with an other aldehyde or
ketone derivative would lead to the desired unsymmetrical
salen ligand. As imine condensations are equilibrium reactions,
the back reaction reforms the first used aldehyde or ketone and
the diamine so that a mixture of compounds can be formed.
Thus, it is important to consider that an aldimine is usually
easy to prepare but not very stable. Ketimines require harsher
conditions for the preparation but are usually more stable than
aldimines.57 Therefore, in the first step of the reaction sequence
for an unsymmetrical salen ligand, the more stable ketimine
half-unit should be synthesized, which reacts with an aldehyde
in the second step.
from the reaction solutions as bright yellow solids. As a reference
for the comparison of the electronic and structural properties
of the unsymmetrical trinucleating triplesalophen ligands with
that of an analogous unsymmetrical mononucleating salophen
ligand, we also synthesized the ligand H2carlCl (Scheme 2). Mass
spectrometry and elemental analysis confirmed the successful
synthesis of all compounds.
Taking these considerations into account, we were able to
prepare the triplesalen ligand system in a divergent synthesis.1,2
As the isolation of the parent salen half-unit is not feasible,48 we
made use of an observation of Elias and co-workers to isolate
the ketimine triplesalen half-unit A (Scheme 3).58 The sterically
more crowded amine function of 1,2-diamino-2-methylpropane
reacts only with aldehydes but not with ketones.
Crystal and Molecular Structures. Crystals of H2carlCl
suitable for single-crystal X-ray diffraction were obtained by
slow diffusion of pentane into a solution of H2carlCl in toluene.
Selected interatomic distances are summarized in Table 1. The
molecular structure of H2carlCl (Figure 1) shows that the ben-
zene ring of the phenylenediamine backbone and the phenol
ring of the aldimine compartment are almost coplanar (torsion
angle C11−N11−C13−C14 = 7.4°), whereas the phenol ring
of the ketimine compartment is rotated along N12−C18
resulting in a C17−C18−N12−C19 torsion angle of 64.5°. The
benzene ring of the ketimine moiety is almost perpendicular to
the phenol ring (C192−C191−C19−C102 torsion angle of
113.4°). The mean values of the C−C bond lengths (Table 2)
of the phenol ring of the aldimine and ketimine compartment
differ not significantly (1.39 and 1.40 Å, respectively). The
same holds true for the C−O bond length (1.36 and 1.35 Å,
respectively), and both CN bond lengths are 1.29 Å. However,
the Car−Cimine bond length of the aldimine (1.45 Å) is slightly
shorter than for the ketimine (1.48 Å).
Beside this half-unit A we were also able to synthesize the
chiral half-unit B of the H6chand ligand system by using the
chiral trans-1,2-cyclohexanediamine.59,60 The isolation of half-
unit B based on the symmetrical cyclohexanediamine is in accord
with the isolation of an analogous salen half-unit49−51 and may
be attributed to the less strong reactivity of cyclohexanediamine.
Analogously, we tried to synthesize the triplesalophen ligand
system in a divergent synthesis. However, many efforts to syn-
thesize an analogous triplesalophen half-unit C (Scheme 3) with
the symmetric 1,2-phenylenediamine resulted only in impure
solids. Reactions of these solids with salicylaldehyde resulted in
the sublimation of the pure symmetrical salophen ligand. There-
fore, we tried a convergent approach for the triplesalophen ligand
system rather than the established divergent approach for the
triplesalen ligand system. This requires a ketimine salophen half-
unit and the trialdehyde of phloroglucinol.
Sinn and co-workers established the synthesis of the ketimine
salophen half-unit 1Cl (Scheme 2) using 5-chloro-2-hydroxy-
benzophenone and 1,2-phenylenediamine in the presence of
piperidine and triethylorthoformate in ethanol.61 Thus, we
synthesized in the first step the ketimine half-units 1R by a
modified procedure of 1Cl and reacted these in a second Schiff-
base condensation with trialdehyde 262 in tetrahydrofuran
(Scheme 2). The ligands H6baronR (R = Me, Cl, Br) precipitate
Crystals of H6baronR·C5H12 suitable for single-crystal X-ray
diffraction could be obtained for all three triplesalophen ligands
by slow diffusion of pentane into a solution of the respective
ligand in toluene. All three ligands crystallize in the trigonal
space group P3. Interestingly, H baronMe·1.5CH Cl obtained
̅
6
2
2
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Table 1. Selected Interatomic Distances [Å] for H6baronR·C5H12, H6baronMe·1.5CH2Cl2, and H2carlCl
H6baronMe·C5H12
H6baronMe·1.5CH2Cl2
H6baronCl·C5H12
H6baronBr·C5H12
H2carlCl
C(1)−C(2)
1.459(3)
1.458(3)
1.458(3)
1.380(3)
1.322(3)
1.401(3)
1.294(3)
1.420(3)
1.253(3)
1.349(2)
1.394(3)
1.402(3)
1.379(3)
1.383(4)
1.391(3)
1.385(3)
1.472(3)
1.493(3)
1.379(3)
1.411(3)
1.398(3)
1.383(3)
1.389(3)
1.376(3)
1.374(4)
1.383(4)
1.389(4)
1.372(6)
1.352(6)
1.390(4)
1.451(3)
1.456(3)
1.456(3)
1.385(3)
1.322(2)
1.404(2)
1.292(2)
1.424(2)
1.258(2)
1.353(2)
1.388(3)
1.404(3)
1.389(3)
1.384(3)
1.387(3)
1.385(3)
1.467(3)
1.493(2)
1.380(3)
1.411(3)
1.403(3)
1.372(3)
1.393(3)
1.374(3)
1.381(3)
1.389(3)
1.388(3)
1.380(4)
1.384(4)
1.378(3)
1.450(3)
1.464(3)
1.464(3)
1.382(3)
1.323(3)
1.399(3)
1.292(3)
1.423(3)
1.255(3)
1.345(2)
1.395(3)
1.403(3)
1.382(3)
1.383(4)
1.395(3)
1.380(3)
1.473(3)
1.496(3)
1.389(3)
1.415(3)
1.404(3)
1.373(3)
1.386(3)
1.377(3)
1.370(4)
1.386(4)
1.392(4)
1.362(6)
1.349(6)
1.392(4)
1.457(3)
1.459(3)
1.459(3)
1.382(3)
1.324(3)
1.403(3)
1.290(3)
1.424(3)
1.254(3)
1.345(3)
1.388(3)
1.408(3)
1.387(3)
1.379(4)
1.391(4)
1.378(3)
1.472(3)
1.495(3)
1.385(4)
1.413(3)
1.405(3)
1.373(3)
1.382(4)
1.377(4)
1.372(4)
1.384(4)
1.396(5)
1.361(6)
1.351(6)
1.395(5)
1.411(2)
a
a
C(1)−C(2) #1
C(2)−C(1) #2
C(2)−C(11)
N(11)−C(11)
N(11)−C(13)
N(12)−C(19)
N(12)−C(18)
O(11)−C(1)
1.445(2)
1.286(2)
1.412(2)
1.293(2)
1.423(2)
1.355(2)
1.347(2)
1.399(2)
1.402(2)
1.381(2)
1.384(2)
1.384(2)
1.394(2)
1.476(2)
1.496(2)
1.397(2)
1.418(2)
1.409(2)
1.378(2)
1.390(2)
1.380(2)
1.390(2)
1.392(2)
1.389(2)
1.382(2)
1.389(2)
1.391(2)
1.394(2)
1.405(2)
1.380(2)
1.392(2)
1.383(2)
O(12)−C(101)
C(13)−C(14)
C(13)−C(18)
C(14)−C(15)
C(15)−C(16)
C(16)−C(17)
C(17)−C(18)
C(19)−C(102)
C(19)−C(191)
C(101)−C(106)
C(101)−C(102)
C(102)−C(103)
C(103)−C(104)
C(104)−C(105)
C(105)−C(106)
C(191)−C(196)
C(191)−C(192)
C(192)−C(193)
C(193)−C(194)
C(194)−C(195)
C(195)−C(196)
C(1)−C(6)
C(2)−C(3)
C(3)−C(4)
C(4)−C(5)
C(5)−C(6)
a
Symmetry transformations used to generate equivalent atoms: #1, −y, x − y − 1, z; #2, −x + y + 1, −x, z.
by evaporation of a dichloromethane solution crystallizes in the
same space group. Selected interatomic distances are summarized
in Table 1. As the molecules are almost isostructural, the molecular
structure of H6baronMe in crystals of H6baronMe·C5H12is shown
exemplary in Figure 2. Thermal ellipsoid plots for all structures are
provided as Figures S5−S8 in the Supporting Information.
The asymmetric units of H6baronR·C5H12 consist of one-
third of the ligand and one-third of a pentane molecule of cryst-
allization, while that of H6baronMe·1.5CH2Cl2 bears also one-
third of the ligand but two disordered dichloromethane molecules
of crystallization with 1/6 and 1/3 occupancy.
3.59 Å (C2−Cl5) and 3.64 Å (C1−Cl3) (sum of van der Waals
radii of a carbon and a chlorine atom 3.50 Å). In contrast to the
pentane solvate, in H6baronMe·1.5CH2Cl2 an additional dichlo-
romethane molecule is encapsulated by six phenol rings related
by a 3 axis (Figure 3c,d). This solvent encapsulation results in
2D double-layers with the hydroxyl groups pointing outside
(Figure 3e).
In all four molecular structures the central phloroglucinol
ring and the phenylenediamine backbone are almost coplanar,
which is an evidence for a strong conjugation. This coplanarity
is lost at N12 by rotation along N12−C18 resulting in C17−
C18−N12−C19 torsion angles of the terminal ketimine
The ligand molecules in crystals of H6baronR·C5H12 are bowl-
shaped with the bottom built up by the phloroglucinol backbone
and the wall by the three ketimine compartments (Figure 2b). Three
other ligand molecules are acting as a kind of cover (Figure 3a) with
their phenylenediamine backbones. A disordered pentane molecule
is encapsulated in this closed bowl. The shortest distance between
the ligand and the encapsulated solvent is 3.70 Å (C2−C2P) (sum
of the van der Waals radii of two carbon atoms 3.40 Å).
moieties in H6 baronM e·C5 H1 2
, ,
H6 baronC l·C5 H1 2
H6baronBr·C5H12, and H6baronMe·1.5CH2Cl2 of 81.2°, 78.0°,
80.9°, and 83.3°, respectively. Additionally, the terminal
benzene ring is almost perpendicular to the terminal phenol
ring by C192−C191−C19−C102 torsion angles of 94.6°,
102.2°, 97.7°, and 94.1° in H6baronMe·C5H12, H6baronCl·C5H12,
H6baronBr·C5H12, and H6baronMe·1.5CH2Cl2, respectively.
Significant differences become apparent by comparing struc-
tural parameters of the central and the terminal moiety of the
triplesalophen ligands (Table 2). The mean value of the central
C−O bond length (1.26 Å) is shorter than the terminal C−O
In the case of H6baronMe·1.5CH2Cl2 disordered dichloro-
methane is encapsulated by the same arrangement as described
of H6baronR·C5H12 (Figure 3b). The shortest distances bet-
ween the ligand and the encapsulated dichloromethane are
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Figure 1. Molecular structure of H2carlCl with the numbering scheme
used (a) drawn perpendicular to the benzene ring of the phenyl-
enediamine backbone and (b) drawn parallel to the central benzene
ring of the aldimine moiety. Hydrogen atoms are omitted for clarity
with the exception of H11 and H12.
bond length (1.35 Å). The same effect can be detected for the
central and terminal Car−Cimine bond length (1.38 and 1.47 Å,
respectively). On the other hand, the mean bond lengths of the
central Car−Car bond (central, 1.46 Å; terminal, 1.39 Å) and the
CN bond (central, 1.32 Å; terminal, 1.29 Å) are elongated
compared to the respective terminal bonds. This tremendous
effect is accompanied by a change of the protonation: whereas in
the terminal phenol-imine units the phenol oxygen atoms are
protonated, the “imine” nitrogen atoms are protonated in the
central compartments (Figure 2).
Electronic Absorption Spectroscopy. The electronic
absorption spectra of the salophen half-units 1R (Figure 4a)
display two broad absorption features at 26700 and 28900 cm−1
and higher energy absorption above 35000 cm−1 (maximum at:
37300 cm−1 for R = Me; 38500 cm−1 for R = Cl; 38000 cm−1 for
R = Br). The electronic absorption spectrum of H2carlCl (Figure 4a)
exhibits absorption maxima in the same energy range (29100 and
38400 cm−1) but with increased intensity compared to the salophen
half-units. The spectra of H6baronR (R = Me, Cl, Br; Figure 4b)
exhibit even stronger absorption features in this energy range
Figure 2. Molecular structure of H6baronMe in crystals of H6baronMe·C5H12
with the numbering scheme used (a) drawn perpendicular to the central
benzene ring of the phloroglucinol backbone and (b) drawn parallel to the
central benzene ring of the phloroglucinol backbone. Hydrogen atoms are
omitted for clarity with the exception of H11B and H12A.
around 30000 and 37000 cm−1 and a new very intensive low-energy
feature at ∼23000 cm−1.
ANALYSIS AND DISCUSSION
■
Tautomerism and Resonance in Triplesalophen
Ligands Analyzed in Solution by NMR and in the Solid
State by Single-Crystal X-ray Diffraction. The triplesalen
ligand system has been designed in order to enforce ferro-
magnetic couplings between three paramagnetic transition
metal ions by the spin-polarization mechanism due to the
m-phenylene arrangement.11−21 Magnetic studies on CuII and
3
(VIVO)3 triplesalen complexes5−7 revealed that the exchange
coupling is indeed ferromagnetic but only weakly, whereas the
Table 2. Comparison of Structural Parameters in Triplesalophen Ligands [Å]
C−Ocent
C−Oterm
CNcent
CNterm
Car−Cimine
Car−Cimine
Car−Car
Car−Car
term
cent
term
cent
H2carlCl
1.36
1.25
1.26
1.26
1.25
1.27
1.26
1.35
1.35
1.35
1.35
1.35
1.36
1.29
1.32
1.32
1.32
1.32
1.31
1.33
1.29
1.29
1.29
1.29
1.29
1.28
1.45
1.38
1.39
1.38
1.38
1.43
1.38
1.48
1.47
1.47
1.47
1.47
1.39
1.46
1.45
1.46
1.46
1.45
1.45
1.40
1.39
1.39
1.39
1.39
H6baronMe·C5H12
H6baronMe·1.5CH2Cl2
H6baronCl·C5H12
H6baronBr·C5H12
H6chandrac60
other heteroradialenes found in CSD62−67
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Figure 4. (a) Electronic absorption spectra of H2salen, H2carlCl, and
the salophen half-units 1R (R = Me, Cl, Br), all measured in CH2Cl2.
(b) Electronic absorption spectra of the ligands H6baronR (R = Me, Cl,
Br), H2carlCl, H3felden, H3felddien, and H6talen, all measured in
CH2Cl2. Note different y-scalings in the two figures.
diffraction and in solution by NMR spectroscopy of this series
of triplesalophen ligands in combination with the unsym-
metrical mononucleating salophen reference ligand H2carlCl
makes it possible to obtain more insight into this tautomerism-
resonance senario.
The molecular structure of the mononucleating H2carlCl
reference exhibits no significant differences compared to known
salophen ligands.77,78 The C−O, CN, and the mean benzene
Car−Car bond lengths (Table 2) matches the values found in the
literature (1.35, 1.29, and 1.40 Å, respectively).77,78 The high-
resolution single-crystal X-ray diffraction data for H2carlCl allows
the location of the acidic hydrogen atoms to be bound to the
phenolic oxygen atoms O11 and O12 (Figure 1).
Figure 3. Illustration of the solvent encapsulation in (a)
H6baronMe·C5H12 and (b) H6baronMe·1.5CH2Cl2. Part of the crystal
structure of (c) H6baronMe·C5H12 and (d) H6baronMe·1.5CH2Cl2
showing the ligand in ball-and-stick representation and the solvent
in the space-filling representation. (e) Illustration of the bilayer
structure in crystals of H6baronMe·C5H12 as a representative of all
ligands showing the hydrophobic (A) and hydrophilic (B) compart-
ments.
1
The H NMR spectrum of H2carlCl reveals two singlets at
coupling is even slightly antiferromagnetic in MnIII com-
3
plexes59,68 and slightly antiferromagnetic to uncoupled in FeIII
14.12 ppm for O12H and at 12.94 ppm for O11H typical for
salophen ligands.78−80 The singlets at 8.38 ppm are also typical
for imine groups.
3
complexes.60 This observation is contrary to the stronger ferro-
magnetic interactions observed in the related N,N′,N′′-1,3,5-
benzenetriyltris(oxamato) complexes.69,70 Recently, we identified a
possible reason for this unexpected magnetic behavior in our tri-
plesalen complexes by NMR studies on the related phloroglu-
cinol-based ligands H3felden9 and H3felddien10 (Scheme 4) based
on the work of MacLachlan62,71 and others on tris(N-salicylid-
enaniline)s.63,65,67,72−76 These studies reveal that the central phlo-
roglucinol backbone is not in the expected O-protonated tau-
tomeric form but in the N-protonated tautomeric form (Scheme 5).
Furthermore, this tautomer must be considered as a resonance
hybrid of the neutral keto-enamine resonance structure IV with
some contribution of the ionic phenolate-iminium resonance
structure III (Scheme 5). The prevalence of the resonance
structure IV in the ligands H3felden9 and H3felddien10 indicates
the loss of the aromatic π system so that a π spin-polarization
mechanism cannot be active. The combined analysis of solid-
state molecular structures established by single-crystal X-ray
Further evidence for the O-protonated tautomer in both
compartments is provided by 13C NMR spectroscopy. The 13
C
NMR spectrum of H2carlCl exhibits resonances at 161.3 ppm
for C1 and at 161.4 ppm for C101 typical for salophen ligands
(161 ppm)80 and for enol-imines (160.9 ppm).81 Claramunt
et al. remarked that the 13C resonance varies from ∼151 ppm
for an enol-imine to ∼180 ppm for a pure keto-enamine tau-
tomer,82 making the 13C resonance a powerful parameter to
discern the relative tautomeric population. The 13C NMR spectrum
exhibits also resonances for the aldimine C11 (162.6 ppm) and the
ketimine C19 (173.9 ppm) at typical chemical shifts.79−81 Thus,
X-ray diffraction and NMR spectroscopy demonstrate that in
H2carlCl the aldimine and ketimine moieties are in the enol-imine
form in the solid state and in solution.
Contrarily, the analysis of the molecular structure of
H6baronR (R = Me, Cl, Br) in crystals of H6baronR·C5H12
and H6baronMe·1.5CH2Cl2 reveal that the acidic protons of the
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Scheme 4
Scheme 5
central aldimine moieties are not bond to O12 but bond to
N11 (Figure 2). This different tautomerism scenario is cor-
roborated by 1H NMR spectroscopy. While the O12H
resonance (13.85 ppm for R = Me; 14.02 ppm for R = Cl;
14.08 ppm for R = Br) is a singlet as in H2carlCl, the N11H
resonance is a doublet (J = 13 Hz; 13.49 ppm for R = Me,
proton C11H, which appears also as a doublet (J = 13 Hz; 8.65
ppm for R = Me; 8.54 ppm for R = Cl; 8.56 ppm for R = Br).
This splitting pattern has already been observed for the N-
protonated ligands H3felden9 and H3felddien10 as well as for
tris(N-salicylideneaniline)s62,71 and was proposed for the pure
N-protonated tautomer.83 These results demonstrate that the
acidic protons are bond to O12 and N11 in solution as well.
1
1
13.52 ppm for R = Cl, and 13.54 ppm for R = Br). 2D H, H
COSY NMR experiments prove coupling with the “imine”
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Additionally, several structural and NMR spectroscopic
features makes it possible to analyze the relative contributions
of the resonance structures III and IV for the central phloro-
glucinol backbone. The C−O bond distances differ tremen-
dously for the terminal C−O bonds (1.35 Å) and the central
C−O bonds (1.25−1.26 Å). Comparison to H2carlCl (1.35−
1.36 Å) clearly establishes an usual enol-imine compartment for
the terminal units. However, the central C−O bond length of
1.25−1.26 Å indicates severe double-bond character demon-
strated by the comparison to the bond length of phenol D
(1.39 Å)84 and of triketone E (1.21 Å)85 (Scheme 4).
exocyclic C−C double bonds is reminiscent to [6]radialenes.
Radialenes are cross-conjugated alicyclic hydrocarbons com-
prised of sp2-hydridized ring carbon atoms and show as many
exocyclic double bonds as possible.92−95 Already in the first
report on a radialene96 and in a quantum-chemical study published
shortly thereafter aiming to reproduce the electronic absorption
spectrum,97 it was concluded that [6]radialenes are not planar but
should exhibit a deformed chair conformation of cyclohexane. This
interpretation was later confirmed by several structural analyses of
substituted [6]radialenes.98−103 Based on structural and theoretical
considerations, the cross-conjugated [6]radialenes are considered
as nonaromatic alicycles.92,93,97,104
It must be noted that the structural properties of these
[6]radialene exhibit significant differences to the triplesalophen
ligands. Besides the planar central framework of the triple-
salophen ligands as compared to the nonplanar framework of
[6]radialenes mostly described as a chair conformation, the C−
C distances in the ring of [6]radialenes are longer (1.49−1.50
vs 1.45−1.46 Å in H6baronR) and the exocyclic double-bonds
are shorter (1.32−1.34 vs 1.38−1.39 Å in H6baronR) Addi-
tionally, the 13C chemical shifts of the endocyclic carbon
atoms are higher than that of the exocyclic ones (136.8 and
122.6 ppm, respectively) contrary to those of the triplesalophen
ligands.105
The Car−Car bond lengths of the terminal phenols of 1.39 Å
are in accord to those of H2carlCl (1.39−1.40 Å) and are typical
values for Car−Car bond distances in benzene rings (1.38 Å).86
On the other hand, the central phloroglucinol unit has Car−Car
bond distances of 1.45−1.46 Å, which also confirms a strong
contribution of resonance structure IV. This is further
confirmed by the short Car−Cimine central bond length of 1.38−
1.39 Å, which indicates a strong double-bond character com-
pared to those of the terminal compartment (1.47 Å) and that
of H2carlCl (1.48 Å). This effect is less strong in the bond
length of the “imine” bond, which is only slightly longer for the
central compartment (1.32 Å) as compared to the terminal
compartment and H2carlCl (1.29 Å).
It might be questioned that the elongation of the mean Car−
Car bond length of the central compartment of H6baronR could
be a result of the 6-fold substitution of the benzene ring. How-
ever, the 6-fold substituted phloroglucinol derivative D bearing
saturated substituents in 2,4,6-positions (Scheme 4) exhibits a
mean C−C bond length of 1.37 Å84 typical for phenols (1.38 Å).86
Also the sterically highly crowded substituents in 2,4,6-triacetyl-
1,3,5-tris(dimethylthiocarbamoylthio)benzene87 leading to a mean
Car−Car bond length of 1.40 Å clearly demonstrate that six bulky
substituents do not necessarily induce elongated bond lengths in
the benzene ring.
These differences indicate that our ligands and other tris-
(N-salicylideneaniline)s cannot exclusively be formulated by re-
sonance structure IV but also exhibit some contributions of III
(Scheme 5). As a zwitterionic resonance structure III is energe-
tically not accessible in [6]radialenes, the push−pull effect of the
electron-withdrawing oxygen atoms and electron-donating nitro-
gen atoms stabilize this resonance structure III in our ligands. In
this respect, compounds that are comprised of the structural
motifs found in our ligands and in tris(N-salicylideneaniline)s62−67
as well as in H91 may be considered as heteroradialenes93 in order
to avoid misunderstandings with regards to structural and spectro-
scopic properties of [6]radialenes.
Recently, two [6]radialene derivatives have been reported, in
which two neighboring exocyclic carbon atoms are connected
either by a common sulfur or selenium bridge.106 The molecular
structures exhibit planar geometries and C−C bond distances of
1.45−1.46 Å in the ring and 1.36−1.37 Å for the exocyclic bonds.
Thus, these two [6]radialenes with constraints induced by the five-
membered rings deviate from the nonconstrained [6]radialenes as
much as the triplesalophen ligands do. Interestingly, DFT calcula-
tions provide nucleus-independent chemical shifts (NICS) close to
zero for the central ring. This is interpreted by the authors, that
the ring can be considered to be practically nonaromatic. Further-
more, the authors compare the situation to that of benzene in a
pure sigma state that does not include any contribution from π
orbitals.106
This interpretation is corroborated by analysis of the 13C
resonances: the values of the terminal C101 (160.0 ppm for R
= Me; 160.9 ppm for R = Cl; 161.4 ppm for R = Br) fit well
with that of H2carlCl (161.4 ppm), while the central C1 exhibits
a chemical shift at lower field (185.2 ppm, 185.1 ppm, and
185.0 ppm for H6baronMe, H6baronCl, and H6baronBr,
respectively). Comparing these values to values of related
compounds (157.6 ppm for D, 202.2 ppm for E, 197.1 ppm for
F,88 and 200.6 and 196.8 ppm for G89) strongly corroborates
that the central compartment of H6baronR possess strong
contributions of resonance structure IV (Scheme 5).
The terminal ketimine carbon atoms C19 exhibit 13C che-
mical shifts (177.1 ppm for R = Me; 176.3 ppm for R = Cl;
176.2 ppm for R = Br) corresponding to that of H2carlCl
(176.3 ppm). Contrarily, the central aldimine 13C resonance of
C11 (148.2 ppm for R = Me; Cl, Br) are shifted to higher field
relative to that of H2carlCl (162.6 ppm). This shift is consistent
with the formulation as keto-enamines (F 150.5 ppm88 and G
151.0 ppm89). This assignment is also corroborated by the 13C
chemical shift of C2 (107.3 ppm for R = Me; Cl, Br) with is
much closer to that of F (104.5 ppm) and G (110.1 ppm) than
to that of H2carlCl (119.4 ppm).
Some of these structural (Table 2) and NMR spectroscopic
properties have been reported for tris(N-salicylidenaniline)s,62−67,90
H,91 H6chandrac,60 H3felden,9 and H3felddien10 and support
the formulation of the central backbone of H6baronR to have
a strong contribution of resonance structure IV (Scheme 5).
This formulation comprised of a six-membered ring with six
Infrared Spectroscopy. Whereas the FTIR spectra of
H6baronR (R = Me, Cl, Br) exhibit no significant bands for the
OH and NH stretches in the 3100−2200 cm−1 region, 4 pro-
minent bands between 1700 and 1400 cm−1 (Figure 5) are present,
which do not correspond to the known salophen vibrations. In
order to identify the IR signatures of the central heteroradialene
backbone, the bands caused by the terminal ketimine compart-
ments of H6baronR have to be identified.
Acetophenone exhibits a CO stretch at 1692 cm−1. Intro-
duction of a o-hydroxy group results in a low-energy shift to
1648 cm−1. The same trend is observed in benzo-
phenone I, where the CO stretch at 1664 cm−1 is shifted
to 1624−1630 cm−1 in the respective 2-hydroxybenzophenones
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with 2-enamine substituents have been reported to exhibit two
different CO stretches (1665 and 1600 cm−1 for G112 and
1670 and 1605 cm−1 for L113). The vibration at higher energy
was assigned to the CO group not involved in hydrogen
bonding and the low energy vibration to the CO group
involved in hydrogen bonding. Additionally, for L a band
at 1585 cm−1 was assigned to a mixed ν(CC)/δ(N−H)
mode,113 which appears in G at 1590 cm−1.112
These comparisons indicate that the 1611 cm−1 mode in
heteroradialenes has a strong CO character and the 1552 cm−1
mode has a strong CC character. It should be stressed that
conflicting reports for assignment of the keto-enamines
appeared in the literature. Dabrowski and Daboriwska per-
formed intensive IR studies on simple keto-enamines M, con-
ferring the nomenclature for vibrations of amides on vinylogene
keto-enamines.114 The energetically highest IR band at ∼1650 cm−1
was assigned to a vibrational mode comprised mainly of a
CO stretch (“amide-vinyloge-band I”, AVI). The band at
∼1550 cm−1 (AVII) was assigned to a complicated normal
mode, comprised of vibrations of the whole structure with pro-
nounced N−H and C−N contributions. The third band at
about 1455 cm−1 (AVIII) was assigned to a normal mode
involving the whole system without providing specific assign-
ments.
Figure 5. FTIR spectra of ligands H6baronR (R = Me, Cl, Br), H2carlCl,
H3felden, and H3felddien in the range of 1700−1400 cm−1.
used as starting materials for 1R. The low-energy shift by
introduction of an o-hydroxy group reflects the CO bond
order reduction induced by the hydrogen bond. This can be
described by a zwitterionic protonated keto-enolate resonance
structure in VB theory (Scheme 6).
A different assignment was suggested later for the IR spectra
of several isomers of keto-enamines like N based on DFT
calculations.115 The band at higher frequency was assigned to a
vibrational mode mainly of CC character rather than of
CO character. This assignment was supported by reports on
the heteroradialene H for which the band at 1565 cm−1 was also
assigned to the CO stretch.91
Scheme 6
In summary, the three bands at 1611, 1553, and 1443 cm−1
seem to be characteristic for the heteroradialene structural
motif. Due to the conflicting reports we refrain from a definite
assignment at the moment. We are currently performing a
comprehensive DFT study to gain more insight into these
vibrational modes.
Formation of the phenylimine of benzophenone and 1R leads
to a further low energy shift for the resulting CN bond to
1616 cm−1 in imine K107 and ∼1590 cm−1 in 1R. Thus the
vibration at 1591 cm−1 in H2carlCl and at ∼1580 cm−1 in H6baronR
may be assigned to the terminal ketimine CN stretch.
Electronic Absorption Spectroscopy. The ligand
H2salen has a strong absorption at 31600 cm−1 with ε ≈
7.9 × 103 M−1 cm−1 (Figure 4a),2 which has been assigned to
π → π* transitions involving the imine group.116−118 A higher
energy band around 39100 cm−1 originates from π → π*
transitions associated with the phenolic chromophor.116−118
The observed red shift and increased intensities of the imine
π → π* bands of H2carlCl (29100 cm−1, ε ≈ 17.9 × 103 M−1
cm−1, Figure 4a) compared to H2salen can be attributed to the
larger π delocalization over the whole ligand caused by the
substitution of the ethylene bridge in H2salen by a phenylene
bridge in H2carlCl.118
Benzaldehyde exhibits the CO stretch at 1700 cm−1, which
shifts to 1665 cm−1 by incorporation of a o-hydroxy group in
salicylaldehyde. Reaction with 1,2-phenylendiamine results in
the formation of H2salophen with a CN stretch at 1616
cm−1.108−110 Thus, the band at 1614 cm−1 in H2carlCl is
assigned to the aldimine CN stretch.
The bands at 1611 and 1553 cm−1 in the FTIR spectra of the
triplesalophen ligands H6baronR are also present in FTIR
spectra (Figure 5) of H3felden (1611 and 1545 cm−1)9 and
H3felddien (1611 and 1547 cm−1).10 The band at 1443 cm−1 is
slightly shifted to lower frequencies compared to H3felden
(1460 cm−1) and H3felddien (1462 cm−1). These three bands
at 1611, 1533, and 1443 cm−1 might be characteristic for the
heteroradialene structural motif. Interestingly, the salophen
ligand H2carlCl and the triplesalophen ligands H6baronR exhibit
a vibration at about the same frequency (1614 and 1611 cm−1,
respectively) which is of different origin. This vibration is as-
signed to the aldimine of H2carlCl, which is absent in H6baronR.
The comparison to the IR spectra of related molecules seems
to be helpful. The IR spectrum of the α,β-unsaturated
cyclohexanone F (Scheme 4) exhibits vibrations at 1650 and
1551 cm−1, which have been assigned to the CO and the
CC stretches, respectively.111 The 1,3-diketones G and L
By going from the mononucleating salophen ligand H2carlCl
to the trinucleating triplesalophen ligand H6baronR (Figure 4b),
the π → π* transition of H2carlCl seems to split into two strong
bands around 23000 and 30000 cm−1 with intensities of ∼7 ×
104 and ∼5 × 104 M−1 cm−1, respectively. A similar trend has
been observed by going from the mononucleating salen ligand
to the trinucleating triplesalen ligand (see H2salen in Figure 4a
and H6talen in Figure 4b). As these strong absorptions in
H6talen also appear in H3felden and H3felddien (Figure 4b),
they have been assigned to the heteroradialene backbone in
these extended phloroglucinol ligands.9,10
Again, the extension of the π system from triplesalen to
triplesalophen ligands shifts these strong absorptions from 28800
and 32400 cm−1 to 23000 and 30000 cm−1 with increased intensity
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2-[(2-Aminophenylimino)phenylmethyl]-4-methylphenol
(1Me). 5-Methyl-2-hydroxybenzophenone (3.00 g, 14.13 mmol) and
1,2-phenylenediamine (1.56, 14.43 mmol, 1.02 equiv) were suspended
in ethanol (10 mL). This suspension was stirred at 40 °C until an
orange solution has formed. Piperidine (1.50 mL, 15.18 mmol, 1.07
equiv) and triethylorthoformate (3.00 mL, 18.06 mmol, 1.28 equiv)
were added. The reaction mixture was heated at reflux for 3 h.
While cooling to room temperature orange needles were formed. The
precipitate was collected by filtration, washed with ethanol (20 mL),
and dried in vacuum. Yield: 1.98 g (46%). Mp 195−197 °C. 1H NMR
(500.05 MHz, CDCl3) δ 14.20 (s, 1H; O12H), 7.35 (m, 3H; C193−
C195H), 7.21 (m, 3H; C105H, C192H, C196H), 7.01 (d, 1H;
C106H), 6.89 (d, 1H; C103H), 6.84 (dt, 1H; C15H), 6.69 (dd, 1H;
C14H), 6.42 (dt, 1H; C16H), 6.28 (dd, 1H; C17H), 3.85 (s, 2H;
N11H2), 2.18 (s, 3H; C120H3). 13C NMR (125.75 MHz, CDCl3) δ
175.1 (C19), 160.1 (C101), 139.2 (C13), 134.3 (C191), 134.2
(C105), 134.0 (C18), 132.1 (C103), 129.1 (C194), 128.3 (C192,
C196), 128.1 (C193, C195), 127.1 (C104), 125.6 (C15), 121.8 (C17),
119.6 (C102), 117.9 (C16), 117.6 (C106), 115.1 (C14), 20.5 (C120).
IR (KBr) ν 3458 m, 3366s, 1626 m, 1597s, 1562 m, 1493 m, 1400w,
1335 m, 1292 m, 1240 m, 1132 m, 827 m, 746s, 712 m cm−1. ESI-MS
(CHCl3/MeOH) m/z 303.1 [M + H]+, 325.0 [M + Na]+, 626.7 [2M
+ Na]+, 927.5 [3M + Na]+. Anal. Calcd for C20H18N2O: C, 79.44; H,
6.00; N, 9.26. Found: C, 79.32; H, 6.00; N, 9.09.
as has been observed by going from salen to salophen ligands.
Absorption bands at similar energies with similar intensities are
reported for other tris(N-salicylidenaniline) derivatives.66
The absorption features above 36000 cm−1 are present in all
ligands that exhibit terminal enol-imine chromophores as well
as in H2salen, H2carlCl and 1R but are absent in the spectra of
H3felddien and H3felden consistent with the assignment of
these transitions to the terminal enol-imine chromophores.
CONCLUSIONS
■
1. The triplesalophen ligand system has been synthesized in
a convergent approach by reaction the trialdehyde of
phloroglucinol with salophen ketimine half-units in con-
trast to the divergent approach of the triplesalen ligand
system by reaction of the triplesalen ketimine half-unit
with aldehydes.
2. The use of the complementary methods X-ray
diffraction, NMR, IR, and UV−vis spectroscopies affords
signatures of the central heteroradialene in extended
phloroglucinol ligands not only for NMR spectroscopies
but also for structural parameters and IR and UV−vis
spectroscopies:
2-[(2-Aminophenylimino)phenylmethyl]-4-chlorophenol
(1Cl). 5-Chloro-2-hydroxybenzophenone (2.00 g, 8.60 mmol) and 1,2-
phenylenediamine (0.96 g, 8.88 mmol, 1.03 equiv) were suspended in
ethanol (7.5 mL). This suspension was stirred at 40 °C until an orange
solution has formed. Piperidine (0.90 mL, 9.10 mmol, 1.06 equiv) and
triethylorthoformate (1.70 mL, 10.23 mmol, 1.20 equiv) were added.
The reaction mixture was heated at reflux for 3 h. While cooling to
room temperature orange needles were formed. The precipitate was
collected by filtration, washed with ethanol (10 mL), and dried in
NMR: doublet for enamine proton at ∼13.5 ppm;
doublet for “imine” proton at ∼8.6 ppm; 13C C
O at ∼185 ppm compared to ∼161 ppm for C−O
in enol-imines; 13C “imine” at ∼148 ppm com-
pared to ∼162 ppm in enol-imines.
RSA: d(CO) ∼1.25−1.26 Å compared to 1.39 Å
in phenol D; d(Car−Cimine) ∼1.38−1.39 Å
compared to 1.47 Å in H2carlCl; d(Car−Car)
∼1.45−1.46 Å compared to 1.38 Å in benzene.
IR: three intense bands at 1611, 1553, and
1443 cm−1 with the band at 1443 cm−1 differing
slightly to 1460 cm−1 in H3felden and 1462 cm−1 in
H3felddien.
vacuum. Yield: 1.69 g (61%). Mp 194−196 °C [lit.61 192 °C]. H
1
NMR (500.05 MHz, CDCl3) δ 14.46 (s, 1H; O12H), 7.36 (m, 3H;
C193H-C195H), 7.32 (dd, 1H; C105H), 7.19 (dd, 2H; C192H,
C196H), 7.07 (d, 1H; C103H), 7.03 (d, 1H; C106H), 6.85 (dt, 1H;
C15H), 6.69 (dd, 1H; C14H), 6.42 (dt, 1H; C16H), 6.26 (dd, 1H;
C17H), 3.84 (s, 2H; N11H2). 13C NMR (125.75 MHz, CDCl3) δ
174.1 (C19), 161.0 (C101), 139.3 (C13), 133.5 (C191), 133.4 (C18),
133.1 (C105), 131.2 (C103), 129.5 (C194), 128.2 (C192, C196),
128.4 (C193, C195), 126.1 (C15), 122.8 (C104), 121.8 (C17), 120.9
(C102), 119.5 (C106), 118.0 (C16), 115.3 (C14). IR (KBr) ν 3458 m,
3368s, 1622 m, 1591s, 1557 m, 1489 m, 1392w, 1329 m, 1281 m, 1236
m, 1134 m, 927 m, 829 m, 743s, 704 m cm−1. ESI-MS (CHCl3/
MeOH) m/z 323.1 [M + H]+, 345.1 [M + Na]+, 666.3 [2M + Na]+.
Anal. Calcd for C19H15N2OCl: C, 70.70; H, 4.68; N, 8.68. Found: C,
70.67; H, 4.79; N, 8.64.
UV−vis: intense bands at 23000 cm−1 (ε = ∼7 ×
104 M−1 cm−1) and 30000 cm−1 (ε = ∼5 × 104 M−1
cm−1) that are even more intense and red-shifted
compared to the triplesalen ligand system at
29000 cm−1 (ε = ∼4.2 × 104 M−1 cm−1) and
34000 cm−1 (ε = ∼3.9 × 104 M−1 cm−1) demon-
strating the participation of the phenylenediamine
backbone in the delocalized π system.
2-[(2-Aminophenylimino)phenylmethyl]-4-bromophenol
(1Br). 5-Bromo-2-hydroxybenzophenone (2.77 g, 10.00 mmol) and
1,2-phenylenediamine (1.15 g, 10.00 mmol, 1.00 equiv) were suspended
in ethanol (6.0 mL). The suspension was stirred at 40 °C until an orange
solution has formed. Piperidine (1.00 mL, 10.00 mmol, 1.00 equiv) and
triethylorthoformate (2.00 mL, 12.40 mol, 1.20 equiv) were added. The
reaction mixture was heated at reflux for 3 h. While cooling to room
temperature orange needles were formed. The precipitate was collected
by filtration, washed with ethanol (8 mL), and dried in vacuum. Yield:
2.28 g (62%). Mp 191−192 °C. 1H NMR (500.05 MHz, CDCl3) δ 14.48
(s, 1H; O12H), 7.45 (dd, 1H; C105H), 7.37 (m, 3H; C193H-C195H),
7.20 (d, 1H; C103H), 7.18 (m, 2H; C192H, C196H), 6.97 (d, 1H;
C106H), 6.85 (dt, 1H; C15H), 6.70 (dt, 1H; C14H), 6.42 (dt, 1H;
C16H), 6.26 (dd, 1H; C17H), 3.88 (s, 2H; N11H2). 13C NMR (125.75
MHz, CDCl3) δ 174.2 (C19), 161.6 (C101), 139.3 (C13), 136.1 (C105),
134.3 (C103), 133.6 (C191), 133.5 (C18), 129.7 (C194), 128.6 (C193,
C195), 128.4 (C192, C196), 126.3 (C15), 122.0 (C17), 121.6 (C102);
120.1 (C106), 118.3 (C16), 115.5 (C14), 109.9 (C104). IR (KBr) ν
3458 m, 3368s, 1624 m, 1589s, 1555 m, 1491 m, 1478 m, 1385w,
1329 m, 1287 m, 1238 m, 1134 m, 970 m, 827 m, 743s, 702 m cm−1.
ESI-MS (CHCl3/MeOH) m/z 369.0 [M + H]+, 389.0 [M + Na]+. Anal.
3. Extended phloroglucinol ligands are in the N-protonated
tautomeric form, in which the keto-enamine resonance
structure IV has strong contributions. However, in these
heteroradialenes are also some contributions of the ionic
resonance structure III in contrast to [6]radialenes.
EXPERIMENTAL SECTION
■
Preparations of Compounds. Solvents and starting materials
were of the highest commercially available purity and used as received
except for ethanol and tetrahydrofuran, which were dried over CaH2
and distilled under an argon atmosphere before use. All reactions were
performed using standard Schlenk-conditions except for the synthesis
of H2carlCl. 2,4,6-Triformylphloroglucinol (2) was synthesized by a
literature procedure.62 The synthesis of 1Cl and H2carlCl were
performed by using modified literature procedures.61 H6baronBr has
been communicated recently.46 The assignments of the NMR reson-
ances in all products were supported by 2D COSY, HMBC, and
HMQC spectroscopy and the numbering was done according to the
numbering scheme in Figures 1 and 2.
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Article
Table 3. Crystallographic Data for H6baronR·C5H12, H6baronMe·1.5CH2Cl2, and H2carlCl
compound
H6baronMe·C5H12
H6baronMe·1.5CH2Cl2
H6baronCl·C5H12
H6baronBr·C5H12
H2carlCl
chem formula
fw (g mol−1)
T (K)
C69H54N6O6·C5H12
1135.33
C69H54N6O6·1.5CH2Cl2
1190.57
C66H45N6O5Cl3·C5H12
1196.58
C66H45N6O5Br3·C5H12
1329.96
C26H19N2O2
426.88
173(2)
100(2)
173(2)
173(2)
100(2)
space group
a (Å)
P3
P3
P3
P3
P1
17.9054(8)
17.9054(8)
11.0374(7)
90.00
17.6734(6)
17.6734(6)
11.0022(4)
90.00
17.9406(6)
17.9406(6)
10.8992(5)
90.00
18.0254(6)
18.0254(6)
11.0413(5)
90.00
8.8280(2)
9.8280(2)
12.6380(3)
87.0450(12)
70.9630(13)
87.2910(14)
2383.6(3)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
90.00
90.00
90.00
90.00
120.00
120.00
120.00
120.00
3064.5(3)
2
2976.12(18)
2
3038.1(2)
2
3106.9(2)
2
Z
−3
ρcalc (g cm )
1.230
1.329
1.308
1.422
1.370
−1
λ (Å); μ (Mo Kα, mm )
crystal size (mm)
0.71073, 0.079
0.40 × 0.26 × 0.14
15295; 24.99
3556 (Rint = 0.0277)
2697
0.71073; 0.215
0.20 × 0.15 × 0.03
20868; 24.99
3483 (Rint = 0.0301)
2552
0.71073; 0.211
0.46 × 0.40 × 0.20
16462; 26.00
3967 (Rint = 0.0253)
3196
0.71073; 2.006
0.34 × 0.30 × 0.12
18384; 26.97
4465 (Rint = 0.0257)
3570
0.71073; 0.211
0.32 × 0.30 × 0.28
7073; 25.00
3626 (Rint = 0.0139)
3424
coll reflns; 2θmax
unique reflns
obs reflns (I > 2σ(I))
data/restraints/parameters
3556/3/257
1.024
3483/0/311
1.026
3967/3/256
0.969
4465/2/256
1.026
288
a
goodness-of-fit on F2
1.017
b
c
R1 ; wR2 (I > 2σ(I))
0.0557; 0.1572
0.0424; 0.0986
0.0532; 0.1456
0.0365; 0.0912
0.0302; 0.0788
max/min residuals (e Å−3)
0.989 and −0.204
0.277 and −0.300
0.850 and −0.255
0.667 and −0.380
2
0.208 and −0.227
a
b
c
GooF = [∑w(Fo2 − Fc2)2]/(n − p)]1/2 R1 = ∑||Fo| − |Fc||/∑|Fo| wR2 = [∑[w(Fo2 − Fc2)2]/∑[w(Fo )2]]1/2, in which w = 1/[σ2(Fo ) + (aP)2 +
2
bP], P = (Fo +2Fc2)/3
2
Calcd for C19H15N2OBr: C, 62.14; H, 4.12; N, 7.63. Found: C, 62.14; H,
4.29; N, 7.49.
C120H3). 13C NMR (125.75 MHz, C2D2Cl4) δ 185.2 (C1), 177.1
(C19), 160.0 (C101), 148.2 (C11), 138.1 (C18), 134.8 (C105), 133.7
(C191), 132.7 (C103), 131.5 (C13), 129.2 (C194), 129.3 (C193,
C195), 128.3 (C192, C196), 127.5 (C104), 125.5 (C15), 125.0 (C16),
122.9 (C17), 119.4 (C102), 117.8 (C106), 115.1 (C14), 107.3 (C2).
IR (KBr) ν 1611s, 1582s, 1553s, 1443 m, 1294 m, 1263 m, 1234 m,
750w, 704w cm−1. MALDI-TOF-MS (DHB) m/z: 1063.5 [M + H]+,
1085.5 [M + Na]+. Anal. Calcd for C69H54N6O6 (H6baronMe): C,
77.95; H, 5.12; N, 7.90. Found: C, 77.91; H, 5.45; N, 7.70.
2,4,6-Tris{[2-((5-chloro-2-hydroxyphenyl)phenylmethyl-
imino)-phenylimino]-methyl}-1,3,5-trihydroxybenzene
(H6baronCl). Compounds 2 (0.065 g, 0.31 mmol) and 1Cl (0.58 g,
1.81 mmol, 6.00 equiv) were dissolved in tetrahydrofuran (18 mL).
The resulting orange solution was stirred at room temperature for 3 d,
during which a yellow precipitate was formed. It was collected by
filtration, washed with methanol (10 mL), and dried in vacuum.
H6baronCl was isolated as a bright yellow solid. Yield: 0.34 g (98%).
Mp 243−245 °C (decomp). 1H NMR (600.13 MHz; C2D2Cl4) δ
14.02 (s, 3H; O12H), 13.52 (d, 3H; 3J = 13 Hz, N11H), 8.54 (d, 3H; 3
J = 13 Hz, C11H), 7.43 (dd, 3H; C105H), 7.32 (m, 9H; C193H-
C195H), 7.17 (d, 3H; C106H), 7.14 (m, 9H; C14H), 6.98 (m, 3H;
C15H), 6.87 (t, 3H; C16H), 6.56 (d, 3H; C17H). 13C NMR (125.75
MHz, C2D2Cl4) δ 185.1 (C1), 176.3 (C19), 160.9 (C101), 148.2
(C11), 137.5 (C18), 133.6 (C105), 132.9 (C191), 131.6 (C103),
131.1 (C13), 129.7 (C194), 128.4 (C193, C195), 128.0 (C192,
C196), 125.9 (C15), 125.0 (C16), 122.8 (C17), 122.7 (C104), 120.6
(C102), 119.5 (C106), 115.1 (C14), 107.3 (C2). IR (KBr) ν 1611s,
1578s, 1553s, 1443 m, 1294 m, 1265 m, 1234 m, 700w cm−1. MALDI-
TOF-MS (DHB) m/z: 1124.9 [M + H]+, 1146.9 [M + Na]+. Anal.
Calcd for C70H54Cl3N6O7.5 (H6baronCl·THF·0.5H2O): C, 69.74; H,
4.52; N, 6.97. Found: C, 69.75; H, 4.38; N, 7.03.
N-Phenyl-N-(2-hydroxy-5-chlorophenyl)-N′-(2-hydroxy-
phenyl)-1,2-phenylenediamine (H2carlCl). To a hot suspension of
1Cl (1.05 g, 3.25 mmol) in methanol (10 mL) were added salicy-
laldehyde (0.35 mL, 3.35 mmol, 1.03 equiv) and piperidine (0.5 mL,
5.06 mmol, 1.56 equiv). The resulting yellow suspension was heated
at reflux for 0.5 h. After cooling to room temperature, the yellow
precipitate was collected by filtration, washed with methanol (20 mL),
and recrystellized from toluene/pentane. Yield: 0.86 g (60%). Mp
213−214 °C. 1H NMR (600.13 MHz, CDCl3) δ 14.12 (s, 1H; O12H),
12.94 (s, 1H; O11H), 8.38 (s, 1H; C11H), 7.37 (dt, 1H; C5H), 7.32
(m, 2H; C3H, C105H), 7.29 (m, 1H; C194H), 7.22 (t, 2H; C193H,
C195H), 7.07 (m, 6H; C14H-C16H, C106H, C192H, C196H), 7.03
(d, 1H; C103H), 6.98 (d, 1H; C6H), 6.92 (t, 1H; C4H), 6.80 (m, 1H;
C17H). 13C NMR (125.75 MHz, CDCl3) δ 173.9 (C19), 162.6 (C11),
161.4 (C101), 161.3 (C1), 141.6 (C18), 139.7 (C13), 133.9 (C191),
133.4 (C5), 132.3 (C3), 131.4 (C103), 129.4 (C194), 128.4 (C192,
C196), 128.2 (C193, C195), 127.1 (C16), 126.0 (C15), 123.1 (C17),
122.7 (C104), 119.8 (C106), 119.4 (C2), 119.1 (C6), 118.5 (C14),
117.6 (C4). IR (KBr) ν 1614s, 1607s, 1564s, 1477 m, 1331 m, 1284 m,
1238 m, 758 m, 702 m cm−1. ESI-MS (CHCl3/MeOH) m/z 427.2
[M + H]+, 449.2 [M + Na]+, 874.6 [2M + Na]+. Anal. Calcd for
C26H19N2O2Cl: C, 73.15; H, 4.49; N, 6.56. Found: C, 73.29; H,
4.38; N, 6.59.
2,4,6-Tris{[2-((5-methyl-2-hydroxyphenyl)phenylmethyl-
imino)-phenylimino]-methyl}-1,3,5-trihydroxybenzene
(H6baronMe). Compounds 2 (0.21 g, 1.00 mmol) and 1Me (1.81 g,
5.99 mmol, 5.99 equiv) were dissolved in tetrahydrofuran (60 mL).
The resulting orange solution was stirred at room temperature for 3 d,
during which a yellow precipitate formed. It was collected by filtration,
washed with methanol (30 mL), and dried in vacuum. H6baronMe was
isolated as a bright yellow solid. Yield: 0.98 g (93%). Mp 246−248 °C
(decomp). 1H NMR (500.25 MHz; C2D2Cl4) δ 13.85 (s, 3H; O12H),
2,4,6-Tris{[2-((5-bromo-2-hydroxyphenyl)phenylmethyl-
imino)-phenylimino]-methyl}-1,3,5-trihydroxybenzene
(H6baronBr). Compounds 2 (0.10 g, 0.48 mmol) and 1Br (1.01 g,
2.78 mmol, 5.8 equiv) were dissolved in tetrahydrofuran (30 mL). The
resulting orange solution was stirred at room temperature for 3 d,
during which a yellow precipitate was formed. It was collected by
filtration, washed with methanol (10 mL), and dried in vacuum.
3
3
13.49 (d, 3H; J = 13 Hz, N11H), 8.65 (d, 3H; J = 13 Hz, C11H),
7.32 (m, 15H; C14H, C105H, C193H-C195H), 7.15 (d, 3H; C106H),
7.12 (dd, 6H; C192H, C196H), 7.05 (dd, 3H; C15H), 6.99 (d, 3H;
C103H), 6.87 (dd, 3H; C16H), 6.50 (d, 3H; C17H), 2.23 (s, 9H;
1445
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The Journal of Organic Chemistry
Article
H6baronBr was isolated as a bright yellow solid. Yield: 0.58 g (92%).
Mp 235−238 °C (decomp). 1H NMR (500.25 MHz; C2D2Cl4) δ
14.08 (s, 3H; O12H), 13.54 (d, 3H; 3J = 13 Hz N11H), 8.56 (d, 3H; 3
J = 13 Hz, C11H), 7.58 (dd, 3H; C105H), 7.33 (m, 9H; C193H-
C195H), 7.28 (d, 3H; C103H), 7.23 (d, 3H; C14H), 7.06 (dd, 3H;
C15H), 6.89 (dd, 3H; C16H), 6.55 (d, 3H; C17H). 13C NMR (125.75
MHz, C2D2Cl4) δ 185.0 (C1), 176.2 (C19), 161.4 (C101), 148.2
(C11), 137.4 (C18), 136.3 (C105), 134.6 (C103), 132.8 (C191),
131.2 (C13), 129.7 (C194), 128.4 (C193, C195), 128.0 (C192,
C196), 126.0 (C15), 125.0 (C16), 122.7 (C17), 121.3 (C102), 120.0
(C106), 115.1 (C14), 109.9 (C104), 107.3 (C2). IR (KBr) ν 1611s,
1578s, 1553s, 1493w, 1443 m, 1331w, 1290 m, 1265 m, 1234 m, 750w
cm−1. MALDI-TOF-MS (DHB) m/z: 1258.5 [M]+, 1281.5 [M + Na]+,
1298.0 [M + K]+ . Anal. Calcd for C7 2 H5 7 N6 O7 . 5 Br3
(H6baronBr·1.5THF): C, 63.31; H, 4.21; N, 6.15. Found: C, 63.65;
H, 4.34; N, 6.36.
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X-ray Crystallography. Yellow single crystals of H6baronR·C5H12
(R = Me, Cl, Br) and H6baronMe·1.5CH2Cl2 and red single crystals of
H2carlCl were removed from the mother liquor, coated with oil,
and immediately cooled to 183(2) K (100(2) K for H2carlCl and
H6baronMe·1.5CH2Cl2) on a diffractometer (sealed tube, Mo Kα
radiation (λ = 0.71073 Å), graphite monochromator). An empirical
absorption correction using equivalent reflections was performed with
the program SADABS 2.10 (2008/1 for H6baronMe·1.5CH2Cl2).119
The structures were solved with the program SHELXS-97120 and
refined using SHELXL-97.120 The crystal lattice of H6baronR·C5H12
contains one pentane molecule per formula unit, which is disordered
around a 3-fold crystallographic axis. No hydrogen atoms could be
localized at the pentane molecules. The crystal lattice of
H6baronMe·1.5CH2Cl2 contains one disordered dichloromethane mole-
cule on a crystallographic 3 axis and one disordered dichloromethane
molecule on a crystallographic 3 axis. The carbon atom of the latter
and all hydrogen atoms of the dichloromethane molecules could not
be localized. All other hydrogen atoms were refined in calculated posi-
tions except the N−H and O−H hydrogen atoms for H2carlCl and
H6baronMe·1.5CH2Cl2, which could be localized from a difference Fourier
map and refined without restraints. Crystal data and further details
concerning the crystal structure determination are found in Table 3.
Other Physical Measurements. Infrared spectra (400−4000 cm−1)
of solid samples were recorded on a FTIR spectrometer as KBr disks.
UV−vis−NIR absorption spectra of solutions were measured in the
range 200−1200 nm at ambient temperatures. 1H and 13C NMR
spectra were measured on a 500 MHz or a 600 MHz spectrometer
using the solvent as an internal standard.
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ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra of H6baronR (R = Me, Cl, Br).
Thermal ellipsoid plots and crystallographic data (CIF format)
of the ligands. This material is available free of charge via the
Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: thorsten.glaser@uni-bielefeld.de.
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ACKNOWLEDGMENTS
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