Formation of a silicon-containing macrocycle with a pyridoxalimine Schiff base ligand

Article abstract of DOI:10.1107/S0108270108036238

The reaction of dichloro-diphenyl-silane with a polydentate Schiff base ligand derived from pyridoxal and 2-hydroxy-aniline yields the macrocyclic centrosymmetric silicon com-pound 9,27-dimethyl-3,3,21,21-tetra-phenyl-2,4,20, 22-tetra-oxa-8,13,26,31-tetra

Full text of DOI:10.1107/S0108270108036238

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
product with halogenosilanes. It was our initial goal to prepare
a pentacoordinate silicon complex like (II). Surprisingly, the
macrocyclic silicon compound (III) was obtained from the
reaction of (I) with Ph2SiCl2 in tetrahydrofuran in the
presence of NEt3 as a supporting base to remove the hydrogen
chloride which is formed during the reaction. The first hint of
the formation of a tetracoordinate silicon complex was found
in the 29Si NMR spectrum: compound (III) has a single
resonance signal at ꢁ32.8 p.p.m. The 1H and 13C NMR spectra
did not give further information apart from the presence of
the ligand system including one hydroxyl group.
ISSN 0108-2701
Formation of a silicon-containing
macrocycle with a pyridoxalimine
Schiff base ligand
Uwe Bohme,a* Betty Gunthera and Anke Schwarzerb
¨
¨
aInstitut fur Anorganische Chemie, Technische Universitat Bergakademie Freiberg,
¨
¨
Leipziger Strasse 29, 09596 Freiberg, Germany, and bTurmhofstrasse 20, 09599
Freiberg, Germany
Correspondence e-mail: uwe.boehme@chemie.tu-freiberg.de
Received 6 October 2008
Accepted 5 November 2008
Online 14 November 2008
The reaction of dichlorodiphenylsilane with a polydentate
Schiff base ligand derived from pyridoxal and 2-hydroxy-
aniline yields the macrocyclic centrosymmetric silicon com-
pound 9,27-dimethyl-3,3,21,21-tetraphenyl-2,4,20,22-tetraoxa-
8,13,26,31-tetraaza-3,21-disilapentacyclo[30.4.0.06,11.014,19.024,29]-
hexatrideca-1(32),6,8,10,12,14,16,18,24,26,28,30,33,35-tetradeca-
ene-10,28-diol chloroform tetrasolvate, C52H44N4O6Si2ꢀ4CHCl3.
The asymmetric unit contains half of the macrocycle and two
molecules of chloroform, with C—Hꢀ ꢀ ꢀO and C—Hꢀ ꢀ ꢀN
contacts binding the two guests to the host in the crystal
structure. This macrocyclic silicon compound represents a
promising host for molecular-recognition processes and for the
construction of nanostructures.
Crystallization of (III) from a chloroform solution over a
period of several weeks at 278 K yielded single crystals of the
title chloroform solvate, (III), which crystallizes in the triclinic
space group P1 with half of the macrocycle and two chloro-
form molecules in the asymmetric unit (Fig. 1). The macro-
cycle is thus generated by a crystallographic inversion centre
(Fig. 2). The Si atom is bound to two phenyl groups, to phenol
atom O3 and to the aliphatic O atom from the next ligand
molecule, thus forming a macrocycle (Fig. 2). The Si—O bonds
are short (Table 1), but in the range for comparable Si—O
Comment
Carbon-based macrocycles are used frequently as hosts for
¨
molecular-recognition processes (Weber & Vogtle, 1996). The
macrocycle provides the necessary preorganization of the host
for the inclusion process (Konig, Rodel, Bubenitschek, Jones
& Thondorf, 1995). The incorporation of other main group
elements into the macrocycles gives these compounds new
¨
¨
¨
¨
binding properties (Konig, Rodel, Bubenitschek & Jones,
1995). Earlier work has shown the coordinative ability of
silicon (Jung & Xia, 1988), phosphorous (Caminade &
Majoral, 1994) and tin (Blanda et al., 1989) as bridging atoms
in macrocycles. During our work on silicon complexes with
O,N,O0-tridentate ligands of Schiff base type, we used pyrid-
oxal as a component of the ligand system. The reaction of
pyridoxal hydrochloride with o-aminophenole in the presence
of sodium methanolate gives the polydentate ligand
5-hydroxymethyl-4-[(2-hydroxyphenyl)iminomethyl]-2-methyl-
pyridin-3-ol, (I) (see scheme). There are numerous potential
docking sites in the ligand molecule: the pyridine N atom, one
aliphatic and two phenolic hydroxyl groups, and the imino N
atom. The presence of diverse functional groups in (I) makes it
difficult to predict the molecular structure of the reaction
¨
¨
bonds (Wagler et al., 2005; Bohme et al., 2006; Bohme &
¨
¨
Gunther, 2007; Bohme & Foehn, 2007). The coordination
geometry around the Si atom is distorted tetrahedral, with
bond angles between 104.9 (1) and 117.1 (1)ꢂ (Table 1). The
O2Si(Ph)2 group is a common structural motif. Some macro-
cycles with a similar distorted tetrahedral coordination
environment at the Si atom have been described previously
´
´
(Cragg et al., 1991; Rezzonico et al., 1998; Gomez & Farfan,
1999). The rather large bond angles at oxygen (Table 1) are
explained by the ionic character of the Si—O bonds (Gillespie
& Johnson, 1997).
Two planes can be used to characterize the conformation of
the dianion of the ligand molecule, (II). In the corresponding
o630 # 2008 International Union of Crystallography
doi:10.1107/S0108270108036238
Acta Cryst. (2008). C64, o630–o632

organic compounds
Figure 2
The molecular structure of (III). Displacement ellipsoids are drawn at the
50% probability level. The dashed line indicates the intramolecular
hydrogen bond. Chloroform solvent molecules have been omitted.
[Symmetry code: (i) ꢁx + 1, ꢁy + 1, ꢁz.]
Figure 1
The asymmetric unit of (III), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as small spheres of arbitrary radii. The dashed line
indicates the intramolecular hydrogen bond.
fragment of the molecule of (III), the plane of the C9–C14
benzene ring makes an angle of 17.5 (2)ꢂ with the plane of the
pyridine ring (C1–C5/N1). Nearly planar with this latter ring is
the six-membered pseudo-ring (Fig. 1) consisting of atoms H1/
O1/C2/C3/C7/N2 [at an angle of 2.1 (1)ꢂ to the pyridine ring].
The planarity of the six-membered pseudo-ring is caused by a
strong intramolecular O—Hꢀ ꢀ ꢀN interaction (entry 1, Table 2).
The formation of hydrogen bonds between the imine N atom
and an ortho hydroxyl group is a feature which is often
¨
observed in Schiff bases with o-hydroxy groups (Hokelek et
al., 2004; Filarowski et al., 1999).
Figure 3
A partial packing diagram for (III), showing key intermolecular
interactions. H atoms not involved in the hydrogen bonds have been
omitted for clarity.
Two independent chloroform solvent molecules are incor-
porated into the crystal structure. Contacts with the disor-
dered Cl atoms of the C28-based solvate (Fig. 1) are not
considered important for crystal structure formation. The
nondisordered solvate shows only one very weak chlorine
(III) as a host molecule in supramolecular recognition
processes. Furthermore, the available OH, azomethine N and
pyridine N groups could be useful for the construction of
nanostructures via complexation with transition metals
(Leininger et al., 2000).
ꢂ
˚
contact (C22—H22ꢀ ꢀ ꢀCl1 = 2.90 A and 144 ) but is bound to
the guest via a C28—H28ꢀ ꢀ ꢀO1 intermolecular contact
(entry 3, Table 2). The other guest is connected to the host via
a C—Hꢀ ꢀ ꢀN contact (Fig. 3; entry 2, Table 2). One C8—
H8Aꢀ ꢀ ꢀꢀ contact between one of the aliphatic H atoms, H8A,
and the pyridine unit is localized with a hydrogen-to-centre
Experimental
ꢂ
5-Hydroxymethyl-4-[(2-hydroxyphenyl)iminomethyl]-2-methylpyri-
din-3-ol, (I), was prepared as follows. To pyridoxal hydrochloride
(4.06 g, 20 mmol) dissolved in methanol was added a solution of
sodium methanolate (1.08 g, 20 mmol) in methanol. A solution of o-
aminophenol (2.18 g, 20 mmol) in methanol was added dropwise. The
suspension was boiled at reflux temperature. The colour of the
solution became orange and a precipitate was formed. After 2 h, the
suspension was cooled to room temperature and the precipitate was
filtered off. The solid was washed with small amounts of water to
remove sodium chloride, followed by diethyl ether. Compound (I)
˚
distance of 2.94 A and a C8—H8Aꢀ ꢀ ꢀCg angle of 109 , where
Cg is the centre of the C1–C5/N1 ring at the symmetry position
(2 ꢁ x, 1 ꢁ y, ꢁz). This contact forms intermolecular chains of
the host molecule along the crystallographic a axis (not shown
in Fig. 3). These intermolecular contacts of weak to moderate
strength in the crystal structure of (III) indicate potential
coordination sites for interactions with other guest molecules.
Numerous potential bonding sites in the ligand system,
along with the cavity of the macrocycle, provide promise for
ꢃ
Acta Cryst. (2008). C64, o630–o632
Bohme et al. C52H44N4O6Si2ꢀ4CHCl3 o631
¨

organic compounds
was obtained as an orange solid (yield 4.13 g, 80%; m.p. 495 K). The
preparation of (III) was performed in Schlenk tubes under argon with
dry and air-free solvents. Compound (III) was prepared by the
reaction of triethylamine (1.7 ml, 1.21 g, 12.0 mmol) and dichloro-
diphenylsilane (1.22 g, 4.8 mmol) with (I) (1.25 g, 4.8 mmol) in dry
tetrahydrofuran at room temperature. A white precipitate of
triethylamine hydrochloride formed upon stirring the mixture for 6 d.
After this period, the triethylamine hydrochloride was filtered off and
washed with tetrahydrofuran. The solvent was removed in vacuo
from the resulting clear red solution. The remaining solid was
extracted with 1,2-dimethoxyethane. Addition of hexane, cooling to
278 K and filtration of this sample gave a red solid product (yield
1.48 g, 70.3%; m.p. 485 K). Single crystals of the title compound, (III),
were obtained by recrystallization from CHCl3. NMR data are
available in the archived CIF.
Table 2
Hydrogen-bond geometry (A, ).
ꢂ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
O1—H1ꢀ ꢀ ꢀN2
C27—H27ꢀ ꢀ ꢀN1
C28—H28ꢀ ꢀ ꢀO1
0.84
1.00
1.00
1.77
2.16
2.35
2.511 (3)
3.149 (4)
3.295 (4)
147
168
158
chloroform molecules (30 restraints with the SIMU command and 84
restraints with the ISOR command in SHELXL97). All C-bound H
atoms were positioned geometrically, with C—H = 0.95, 0.98, 0.99 or
˚
1.00 A for aryl, CH3, CH2 or tertiary C—H groups, respectively, and
refined in riding mode, with Uiso(H) = 1.5Ueq(C) for methyl or
1.2Ueq(C) for all other H atoms. The H atom bonded to atom O1 was
˚
positioned geometrically, with O—H = 0.84 A, and refined in riding
mode, with Uiso(H) = 1.5Ueq(O).
Crystal data
Data collection: SMART (Bruker, 2004); cell refinement: SMART;
data reduction: SAINT (Bruker, 2004); program(s) used to solve
structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine
structure: SHELXL97 (Sheldrick, 2008); molecular graphics:
ORTEP-3 (Farrugia, 1997) and XP in SHELXTL-Plus (Release 4.1;
Sheldrick, 2008); software used to prepare material for publication:
SHELXL97.
C52H44N4O6Si2ꢀ4CHCl3
ꢃ = 98.733 (1)ꢂ
V = 1525.91 (8) A
Z = 1
Mo Kꢁ radiation
ꢄ = 0.64 mmꢁ1
T = 153 (2) K
0.33 ꢄ 0.30 ꢄ 0.22 mm
3
˚
Mr = 1354.56
Triclinic, P1
˚
a = 9.8831 (3) A
b = 11.2094 (3) A
˚
c = 14.7584 (4) A
˚
ꢁ = 102.853 (2)ꢂ
ꢂ = 101.899 (1)ꢂ
Financial support for this work from the Fond der chemi-
schen Industrie is gratefully acknowledged.
Data collection
Bruker SMART CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
Tmin = 0.818, Tmax = 0.873
14146 measured reflections
6493 independent reflections
5116 reflections with I > 2ꢅ(I)
Rint = 0.019
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GA3110). Services for accessing these data are
described at the back of the journal.
Refinement
R[F2 > 2ꢅ(F2)] = 0.043
wR(F2) = 0.114
S = 1.07
6493 reflections
391 parameters
126 restraints
H-atom parameteꢁrs3 constrained
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Acta Cryst. (2008). C64, o630–o632
¨