Changing the overall shape of heterodinuclear helicates via substitution of acylhydrazones by tosylhydrazones

Article abstract of DOI:10.1515/znb-2010-0313

Heterodinuclear helicate-type complexes are formed from acyl and tosyl hydrazone-substituted catechol ligands. Due to the different geometry of the carboxylate compared to the sulfonate unit, different overall structures are observed for the complexes. Th

Full text of DOI:10.1515/znb-2010-0313

Changing the Overall Shape of Heterodinuclear Helicates via Substitution
of Acylhydrazones by Tosylhydrazones
Markus Albrechta, Irene Latorrea, Yufeng Liua, and Roland Fro¨hlichb
a Institut fu¨r Organische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
b Organisch-chemisches Institut, Universita¨t Mu¨nster, Corrensstraße 40, 48149 Mu¨nster, Germany
Reprint requests to Prof. Markus Albrecht. E-mail: markus.albrecht@oc.rwth-aachen.de
Z. Naturforsch. 2010, 65b, 311 – 316; received November 11, 2009
Dedicated to Professor Rolf W. Saalfrank on the occasion of his 70th birthday, on recognition of his
outstanding contributions to the field of metallosupramolecular chemistry
Heterodinuclear helicate-type complexes are formed from acyl and tosyl hydrazone-substituted
catechol ligands. Due to the different geometry of the carboxylate compared to the sulfonate unit,
different overall structures are observed for the complexes. The acylate results in the formation of a
cylindrical triple-stranded system, while in the tosylate the pendant substituents fold back and form
a more condensed structure.
Key words: Self-assembly, Helicates, Heteronuclear, Catechol, Hydrazone
Introduction
Metallosupramolecular chemistry opens up an easy
entry to a family of complicated supramolecular ar-
chitectures by simple self-assembly processes. Well-
defined structures can be formed which possess special
structural features as well as properties [1]. In order
to introduce functionality, the concept can be used to
build up heteronuclear coordination compounds with
the ability for metal-metal communication. However,
this requires that different metals are bound selectively
at well defined positions [2].
A well investigated class of metallosupramolecular
complexes are the helicates [3 – 6]. They are defined as
coordination compounds in which two or more linear
ligand strands are wrapped around two or more metal
atoms to form a double- or triple-stranded helix [7]. A
special challenge is to design ligands capable of form-
ing sequential coordination compounds with different
metal ions located in distinct positions by connecting
two different ligands that are suited to coordinate dif-
ferent metals [8].
This concept was used by Piguet and Bu¨nzli [9] for
the formation of d-f heterodinuclear complexes (ligand
1) [10] and by us for the formation of a gallium(III)-
titanium(IV) complex (with ligand 2) [11]. Recently,
Hahn introduced the sequential catechol – benzene-
dithiol ligand 3 [12]. All the ligands 1 – 3 have the
Fig. 1.
and that they are only available by multistep syn-
thetic procedures [13, 14]. Therefore we introduced
the catechol-acylhydrazone 4 (Fig. 1), which is easily
available in large amounts and forms heterodinuclear
helicates with gallium(III) and lanthanum(III), for ex-
ample [15].
Based on these earlier results we now present the
disadvantage that their preparation is cumbersome, substitution of the benzoylhydrazone of 4 by tosylhy-
c
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312
M. Albrecht et al. · Heterodinuclear Helicates
drazone to obtain the new ligand 5. This changes the
overall structural features of heterodinuclear coordina-
tion compounds, introducing a new arrangement of the
pendant aromatic substitutents relative to the heterodi-
nuclear complex moiety.
Results and Discussion
The catechol-hydrazone ligands 4 and 5
The straightforward preparation of ligand 4 has al-
ready been described. Simple condensation of 2,3-
dihydroxybenzaldehyde with benzoylhydrazone af-
fords the ligand in high purity and very good yields
[15]. By analogy, the tosylhydrazone 5 was prepared
by reaction of 2,3-dihydroxybenzaldehyde with to-
syl hydrazine. The desired ligand 5 was obtained in
81 % yield after recrystallization from methanol/ ether
(Scheme 1).
Fig. 2. Molecular structure of ligand 4 · DMSO in the solid
state. The displacement ellipsoids are drawn at the 50 %
probability level.
The tosylhydrazone 5 was characterized by 1H
NMR spectroscopy in [D4]methanol showing a singlet
resonance for the CH=N proton at δ = 7.96 and two
doublets at δ = 7.79 and 7.39 with J = 8.7 Hz for the
aromatic tosyl protons. The catechol hydrogen atoms
lead to two resonances at δ = 6.82 (1H) and 6.72 (2H).
Finally, the methyl group is observed as a singlet at
δ = 2.39. Mass spectra and elemental analyses are also
consistent with the constitution of compound 5.
Crystals suitable for X-ray diffraction experiments
were obtained for the ligand 4. The structure shows the
Fig. 3. Molecular structure of 5 as calculated by force field
methods (SPARTAN O8).
An interesting intramolecular hydrogen bonding
pattern is observed in the crystal structure of 4. The hy-
conformation of 4 (Fig. 2) in the solid state. A close droxyl group in 2-position of the catechol binds to the
hydrazone =N- atom, and the OH group in 1-position
is binding to the O atom in 2-position [16]. The car-
bonyl oxygen atom of the acyl unit is oriented to the
“front” of the molecule forming the overall tridentate
site for metal coordination. In addition, one molecule
of DMSO cocrystallizes and becomes attached to the
hydrazone hydrogen atom of 4 by intermolecular hy-
drogen bonding.
to planar arrangement of the catechol, hydrazone and
phenyl groups is observed.
We were not able to obtain crystals of 5 suitable
for X-ray diffraction. However, simple modeling us-
ing the force field routine of SPARTAN O8 [17] re-
veals the major difference between the ligands 4 and
5 (see Fig. 3) associated with the different geome-
tries at the SO2 unit of 5 compared to the CO unit
of 4. While the latter is planar, the sulfur atom in 5
adopts a tetrahedral coordination geometry introduc-
ing a “kink” in the ligand and leading to a non-planar
structure. However, the tridentate O2catechol - C=N -
S=O pattern for the coordination of metal ions is still
Scheme 1. intact.
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M. Albrecht et al. · Heterodinuclear Helicates
313
Coordination studies and comparison of the structural
features of complexes of ligands 4 and 5
A thorough coordination study of the ligand 4 and
its bromo-substituted derivative has already been pub-
lished [15]. We now report the preparation of the
aluminum(III)/lanthanum(III) complex 6, which was
crystallized from DMF/methanol, and its molecular
structure in the crystalline state.
With ligand 5 we tried to prepare the neutral ti-
tanium(IV)/calcium(II) complex 7b and the cationic
titanium(IV)/lanthanum(III) complex 7c. Both co-
ordination compounds showed the expected NMR
spectra, and their ions were observed by ESI MS
Fig. 4. The heterodinuclear helicates 6 and 7a.
bonds to catecholate oxygen atoms are in the ranges
1.866(5)– 1.881(5) (oxygen atom in 3-position) and
+
(7b: MS ((+)-ESI): m/z = 1038.91 {L3TiCa+K} ,
˚
1.936(4)– 1.956(5) A (oxygen atom in 2-position),
MS ((–)-ESI): m/z = 999.25 {L3TiCa–H}−; 7c: MS
while corresponding titanium-oxygen separations of
1.949 – 19.960(5) (O3) and 1.954– 1.975(5) A (O2)
+
((+)-ESI): m/z = 2236.63 {[L3LaTi]2K} and 1123.50
˚
+
{L3LaTiNaH} ). However, no correct elemental anal-
are found. Hereby the bridging oxygen atoms in 2-
position show longer bonds due to their lower donor
character. The more highly coordinated metal atom
shows its longest bond to the central nitrogen atom
of the tridentate coordinating unit with the distances
ysis was obtained for those complexes. Finally we
succeeded to obtain the anionic heterodinuclear tita-
nium(IV)/potassium complex 7a, which could be fully
characterized. We were also able to obtain crystals
of 7a from methanol and could determine the crystal
structure by X-ray diffraction (Figs. 4 and 5).
˚
˚
2.742 – 2.918(6) A for 6 and 3.065– 3.191(5) A for
7a. Metal-to-oxygen distances are in the same range
for the catecholate and the acylate or tosylate oxy-
gen atoms with shorter bonds observed in 6 (La–O =
Fig. 5 shows the results of the crystallographic struc-
ture analyses of 6 and 7a (only the triple-stranded heli-
cate parts are shown). Fig. 5a reveals that the depro-
tonated ligand 4 adopts a very similar conformation
in the complex 6 as was observed in the solid-state
structure of the free ligand. Three of the ligands are
wrapped around the two metal atoms in a helical fash-
ion with aluminum binding to the three catechol units
giving it a coordination number of six. Lanthanum(III)
is coordinated to ten donor atoms with three triden-
tate O2catechol - C=N - S=O units of the ligands and
one DMF. Fig. 5b exhibits a view down the aluminum-
lanthanum axis revealing the helical arrangement of
the ligands.
The related heteronuclear coordination compound
7a adopts a very different, more compact structure. The
coordination pattern again shows the helical wrapping
around the metal ions. However, the tetrahedral coor-
dination geometry around the sulfur atom introduces a
break in the helical arrangement leading to a folding
back of the tosyl groups into the three grooves of the
triple helical complex moiety. This is nicely seen from
Fig. 5c (side view) and 5d (view down the Ti–K axis).
˚
2.476 – 2.658(4) A) in comparison to 7a (K–O =
˚
2.737 – 2.799(4) A).
Comparison of the two structures (6 and 7a) reveals
a very different overall geometry of the complexes.
The acyl hydrazones are planar leading to a linear ar-
rangement of the ligands and a cylinder-type structure
of the dinuclear compound. In the tosyl hydrazones the
folding of the ligand results in a more spherical shape
of the complex. This shows that simple substitution of
one connecting unit in the ligand results in differently
shaped metallosupramolecular objects.
Conclusion
We have presented two ligands 4 and 5, each hav-
ing one tridentate as well as one bidentate coordina-
tion site for metal ions. Therefore they are ideal for the
self-assembly of heterodinuclear helicates (6, 7a) in-
corporating either f- or heavy s-block cations. The two
ligands differ in the tridentate coordination site, with a
carbonyl versus a sulfonyl unit. Both are able to bind
to the metal cations, but result in coordination com-
Bond lengths between metal atoms and ligands are pounds with very different overall shapes. This is of
shorter in the aluminum/lanthanum (6) as compared course important for the development of structurally
to the titanium/potassium complex (7a). The Al-O different functional derivatives based on the hetero-
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314
(a)
M. Albrecht et al. · Heterodinuclear Helicates
(c)
(d)
(b)
Fig. 5. Molecular structures of the heterodinuclear helicates
6 (a, b) and 7a (c, d). The displacement ellipsoids are drawn
at the 50 % probability level.
dinuclear helicate core and differently arranged sub- 100 FTIR spectrometer and were measured in KBr (4000 –
650 cm−1) or neat. Elemental analyses were measured on a
stituents in side chains.
CHN-O-Rapid Vario EL from Heraeus, melting points on a
Bu¨chi B-540 melting point device.
Experimental Section
Commercially available reagents were used as received.
Data sets were collected on a Nonius KappaCCD diffrac-
The solvents were distilled and used without further purifi- tometer with Mo radiation and equipped with a rotating
cation. NMR spectra were taken on Varian Mercury 300 or anode generator. Programs used: data collection COLLECT
Inova 400, mass spectrometric data on Finnigan SSQ 7000 [18], data reduction DENZO-SMN [19], absorption correc-
and Thermo Deca XP instruments as EI (70 eV) or ESI. The tion SORTAV [20, 21] and DENZO [22], structure solution
infrared spectra were obtained on a PerkinElmer Spektrum SHELXS-97 [23], structure refinement SHELXL-97 [24].
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M. Albrecht et al. · Heterodinuclear Helicates
315
CCDC 755077–755079 contain the supplementary crys- 2846, 2112, 1601, 1559, 1456, 1376, 1255, 1216, 1049,
tallographic data for this paper. These data can be obtained 903, 869, 759, 739, 697, 657 cm−1. – MS ((–)-ESI): m/z =
free of charge via www.ccdc.cam.ac.uk/data request/cif.
535.87 [L2Al]−, 927.47 [L3LaAl–H]−. – MS ((+)-ESI):
m/z = 929.33 [L3LaAlH]+. – C42H30AlLaN6O9·2H2O:
calcd. C 52.29, H 3.55, N 8.71; found C 51.85, H 3.46,
N 8.62.
Ligand 4
For the preparation and characterization of 4, see refer-
ence [15].
X-Ray crystal structure analysis of 6: formula
(C14H10N2O3)3AlLa · 3 C3H7NO · CH3OH, Mr = 1179.94,
yellow crystal, 0.20 × 0.15 × 0.10 mm3, trigonal, space
X-Ray crystal structure analysis of 4: formula
C16H18N2O4S, Mr = 334.38, light-yellow crystal, 0.20 ×
0.20 × 0.05 mm3, monoclinic, space group P21/c (no. 14),
¯
˚
group R3 (no. 148), a = 41.1648(4), c = 21.8016(3) A, V =
3
31994.2(6) A , Z = 18, ρcalc = 1.10 g cm−3, µ = 0.7 mm−1
,
˚
˚
a = 10.9719(5), b = 15.3749(7), c = 9.9061(4) A, β =
◦
3
˚
empirical absorption correction (0.878 ≤ T ≤ 0.936), λ =
96.670(2) , V = 1659.77(13) A , Z = 4, ρcalc = 1.34 g
˚
cm−3, µ = 1.9 mm−1, empirical absorption correction
0.71073 A, T = 223(2) K, ω and ϕ scans, 63578 reflections
collected ( h, k, l), [(sinθ)/λ] = 0.62 A−1, 14407 inde-
˚
˚
(0.700 ≤ T ≤ 0.910), λ = 1.54178 A, T = 223(2) K, ω
pendent (Rint = 0.076) and 9647 observed reflections [I ≥
and ϕ scans, 12608 reflections collected ( h, k, l),
˚
2 σ(I)], 645 refined parameters, R = 0.071, wR2 =−03.243,
[(sinθ)/λ] = 0.60 A−1, 2947 independent (Rint = 0.047)
˚
max. / min. residual electron density 1.83 / −0.83 e A
.
and 2590 observed reflections [I ≥ 2 σ(I)], 215 refined
parameters, R = 0.041, wR2 = 0.114, max. / min. residual
Comment: Hydrogen atoms calculated and refined as
riding atoms; solvent molecules refined with geometrical
(SAME) restraints and one common isotropic thermal
parameter. The structure contains voids but the contents
could not be determined in a chemically meaningful way.
The use of the SQUEEZE routine in PLATON did not
improve the refinement.
electron density 0.26 / −0.28 e A−3. Comment: Hydrogen
˚
atoms at N9 from difference fourier map, others calculated
and refined as riding atoms.
Ligand 5
To a stirred solution of 4-methylbenzenesulfonylhydr-
azine (372.46 mg, 2 mmol, 2 equiv.) in MeOH (20 mL)
at r. t. a solution of 2,3-dihydroxy-benzaldehyde (276 mg,
2 mmol, 2 equiv.) in MeOH (20 mL) was added dropwise
within 4 min. The mixture was stirred for 72 h at r. t.. The
solvent was removed by rotary evaporation, and the product
was recrystallized twice from MeOH : Et2O (1 : 2). Ligand 5
was obtained as a dark-grey solid (495 mg, 1.62 mmol, 81 %
yield). M. p.: 187.3 ◦C. – 1H NMR (400 MHz, CD3OD): δ =
7.96 (s, 1H, CH=N), 7.79 (d, J = 8.7 Hz, 2H, CHTol), 7.39 (d,
J = 8.7 Hz, 2H, CHTol), 6.82 (dd, J = 7.2 Hz, J = 2.5 Hz, 1H,
CHCat), 6.72 (m, 2H, CHCat), 2.39 (s,3H,CH3). – IR (neat):
ν = 3485, 3218, 1615, 1593, 1475, 1367, 1318, 1281, 1200,
1159, 1062, 925, 816, 724, 663 cm−1. – MS (EI): m/z (%) =
306.1 (100) [M]+. – C14H14N2O4S: calcd. C 54.89, H 4.61,
N 9.14; found C 55.06 H 4.23 N 9.04.
Complex 7a
To a flask charged with a solution of 83 mg of 5
(0.27 mmol, 3 equiv.) in 10 mL of MeOH, a solution of
23.7 mg of TiO(acac)2 (0.09 mmol, 1 equiv.) and 12.5 mg
of K2CO3 (0.09 mmol, 1 equiv.) was added. The mixture
was stirred for 72 h, then the solvent was removed under
reduced pressure. The product was obtained as a dark-red
solid in quantitative yield (100 mg, 0.09 mmol). – 1H
NMR (400 MHz, [D6]DMSO): δ = 7.61 (s, 3H, CH=N),
7.64 (m, 12H, CH), 6.65 (d, J = 7.9, 6H, CH), 6.47 (m,
6H, CH), 2.12 (s, 9H, CH3). – IR (neat): ν = 3539, 3191,
3051, 2109, 1595, 1441, 1322, 1248, 1160, 1017, 921, 812,
737, 666 cm−1. – MS ((+)-ESI): m/z (%) = 1038.93 (100)
[L3TiK2H]+. – MS ((–)-ESI): m/z = 999.00 [L3TiK]−. –
C42H36K2N6O12S3Ti · H2O: calcd. C 47.72, H 3.62, N 7.95;
found C 47.91, H 4.19, N 7.83.
Complex 6
100 mg of 4 (0.39 mmol, 3 equiv.), 48.4 mg of
X-Ray crystal structure analysis of 7a: formula
LaCl3·7H2O (0.13 mmol, 1 equiv.), 17.4 mg of AlCl3 (C14H12N2O4S)3K2Ti · 5 CH3OH · H2O, Mr = 1217.27,
(0.13 mmol, 1 equiv.), and 54 mg of K2CO3 (0.39 mmol, orange crystal, 0.25 × 0.20 × 0.10 mm3, orthorhombic,
3 equiv.) were combined in a flask and dissolved in 10 mL space group Pna21 (no. 33), a = 26.0880(5), b = 11.7108(2),
3
˚
˚
of MeOH. The reaction mixture was heated to reflux for c = 18.8757(3) A, V = 5766.7(2) A , Z = 4, ρcalc = 1.40 g
5 min and then stirred at r. t. for 3 d. A yellow solid formed, cm−3, µ = 0.5 mm−1, empirical absorption correction
˚
which was filtered off and washed with Et2O. The product (0.891 ≤ T ≤ 0.954), λ = 0.71073 A, T = 223(2) K, ω and ϕ
was obtained as a yellow solid in 75 % yield (90 mg, scans, 26540 reflections collected ( h, k, l), [(sinθ)/λ] =
0.096 mmol). – 1H NMR (400 MHz, [D6]DMSO): δ = 0.66 A−1, 13753 independent (Rint = 0.053) and 10449
˚
8.52 (s, 3H, CH=N), 7.77 (d, J = 7.6 Hz, 6H, CHPh), observed reflections [I ≥ 2 σ(I)], 701 refined parameters,
7.54 (t, J = 7.6 Hz, 3H, CHPh), 7.24 (t, J = 7.6 Hz, 6H, R = 0.084, wR2 = 0.192, Flack parameter x = 0.−523 (5),
˚
CHPh), 6.37 (m, 9H, CHCat). – IR (neat): ν = 3190, 3058, max. / min. residual electron density 0.84 / −0.44 e A
.
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316
Comment: Structure refined as racemic twin. Hydro- Complex 7c
M. Albrecht et al. · Heterodinuclear Helicates
gen atoms calculated and refined as riding atoms; solvent
molecules refined with thermal restraints (ISOR). Hydrogen
atoms at the water molecule could not be located.
To a flask charged with a solution of 92 mg of 5
(0.3 mmol, 3 equiv.) in 5 mL of MeOH, a solution of 37 mg
of LaCl3·7H2O (0.1 mmol, 1 equiv.) in MeOH was added.
Also a solution of 26 mg of TiO(acac)2 (0.1 mmol, 1 equiv.)
and a solution of 41 mg of K2CO3 (0.3 mmol, 3 equiv.)
were added. The mixture was stirred for 72 h. The excess
of K2CO3 was filtered off, and the solvent was removed at
Complex 7b
To a flask charged with a solution of 92 mg of 5
(0.3 mmol, 3 equiv.) in 5 mL of MeOH, a solution of 16 mg
of CaAc2 (0.1 mmol, 1 equiv.) in MeOH as well as a solution
of 26 mg of TiO(acac)2 (0.1 mmol, 1 equiv.) and a solution of
40 mg of K2CO3 (0.3 mmol, 3 equiv.) were added. The mix-
ture was stirred for 72 h. The excess of K2CO3 was filtered
off, and the solvent was evaporated under reduced pressure.
The product was obtained as a light-brown solid (82 mg,
0.08 mmol, 82 % yield). – 1H NMR (400 MHz, CD3OD):
δ = 7.94 (s, 3H, CH=N), 7.33 (d, J = 7.7 Hz, 6H, CHTol),
7.10 (d, J = 7.7 Hz, 6H, CHTol), 6.52 (d, J = 7.5 Hz, 3H,
CHCat), 6.22 (t, J = 7.5 Hz, 3H, CHCat), 5.97 (d, J = 7.5 Hz,
3H, CHCat), 2.30 (s, 9H, CH3). – IR (neat): ν = 3377, 3191,
3053, 2321, 299, 1552, 1441, 1319, 1248, 1160, 1016, 737,
666 cm−1. – MS ((–)-ESI): m/z = 999.25 [L3TiCa–H]−. –
MS ((+)-ESI): m/z = 1038.91 [L3TiCaK]+.
◦
60 C in a vacuum. The product was obtained as an orange
1
solid (100 mg). – H NMR (400 MHz, CD3OD): δ = 7.63
(s, 3H, CH=N), 7.60 (d, J = 2.8 Hz, 6H, CHTol), 6.65 (d,
J = 7.8 Hz, 6H, CHTol), 6.46 (m, 9H, CHCat), 2.14 (s, 9H,
CH3). – MS ((+)-ESI): m/z (%) = 2236.63 (85) [L6La2Ti2K–
2H]+, 1123.50 (21) [L3LaTiNaH]+.
Acknowledgements
Support by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie is gratefully acknowledged.
Y. L. thanks the Chinese Scholarship Council (CSC) for fi-
nancial support.
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