First X-ray structures of ethylene bridged neutral dimeric hexacoordinate silicon complexes with tetradentate salen-type ligands

Article abstract of DOI:10.1515/znb-2005-0702

Syntheses and structures of two novel "doubledecker" silicon complexes [R-Si(o-O-p-OMe-C₆H₃-C(Ph)=N-(CH ₂)₂-N=C(Ph)-C₆H₃-p-OMe-o-O)-CH ₂-]₂ (R = Ph, p-tBu-C₆

Full text of DOI:10.1515/znb-2005-0702

First X-Ray Structures of Ethylene Bridged Neutral Dimeric Hexa-
coordinate Silicon Complexes with Tetradentate Salen-Type Ligands
J o¨ rg Wagler and Gerhard Roewer
Institut f u¨ r Anorganische Chemie, Technische Universit a¨ t Bergakademie Freiberg, Leipziger Str. 29,
D-09596 Freiberg, Germany
Reprint requests to Prof. Dr. Gerhard Roewer. Fax: (+49) 3731 39 4058.
E-mail: gerhard.roewer@chemie.tu-freiberg.de
Z. Naturforsch. 60b, 709 – 714 (2005); received February 24, 2005
Syntheses and structures of two novel “doubledecker” silicon complexes [R-Si(o-O-p-OMe-C H -
6
3
C(Ph)=N-(CH ) -N=C(Ph)-C H -p-OMe-o-O)-CH -] (R = Ph, p-tBu-C H -O) with the silicon
2
2
6
3
2
2
6
4
atoms hexacoordinated by two salen-type tetradentate ꢀONNOꢁ-chelating ligands are described. Hy-
drogen bonding between the halves of the bridged complexes as well as with chloroform solvate
molecules determines the conformation. Compared with analogous mononuclear silicon complexes
these ”doubledeckers” show bathochromically shifted Vis-absorption.
Key words: Doubledecker, Hexacoordinate, Hypercoordination, Schiff Base, Silicon
Introduction
Dinuclear hypercoordinate silicon complexes
should provide representative molecules to study
interactions between the linked coordination spheres.
1
,2-bis(trichlorosilyl)ethane and 1,2-bis(phenyldi-
chlorosilyl)ethane are suitable starting materials
to synthesize model complexes. Up to now, four
complexes with pentacoordinate [1 – 3] and only two
with hexacoordinate [3, 4] Si atoms with a C -spacer
2
between the central Si atoms were characterized by Scheme 1.
X-ray structure analysis. Those involving hexacoor-
dinate silicon atoms (Scheme 1) offer quite flexible
coordination spheres due to their mono- and bidentate
ligands. Realizing the cis-orientation of the mon-
odentate substituents should give rise to less sterical
repulsion between the two halves of the complex.
Results and Discussion
Tetradentate chelating ligands of 2-iminomethyl-
phenol type proved to be suitable for complex-
ation of silanes leading to hexacoordinate silicon
complexes with two trans-situated monodentate sub-
stituents [5, 6]. Reaction of the trimethylsilyl deriva-
tive of 1 with 1,2-bis(trichlorosilyl)ethane affords the
silicon complex 2 exhibiting two pentacoordinate sil-
iconium moieties [7]. This dinuclear building block
was employed to synthesize 3 by addition of p-tert-
Scheme 2.
butylphenol and elimination of HCl by triethylamine
(Scheme 2).
0
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J. Wagler – G. Roewer · Ethylene Bridged Neutral Dimeric Hexacoordinate Silicon Complexes
Fig. 1. Molecular structure of 3 (ORTEP plot with 50% prob-
ability ellipsoids, hydrogen atoms and chloroform molecules
omitted for clarity. The molecule is situated on a crystallo-
graphically imposed inversion centre.) Selected bond lengths
Fig. 2. One half of molecule 3 (hydrogen atoms omitted for
clarity, centroid Z placed into the p-tert-butylphenolate ring).
˚
◦
A] and angles [ ]: Si1-C41 1.947(2), Si1-N1 1.929(2),
[
Si1-N2 1.942(2), Si1-O1 1.762(2), Si1-O2 1.745(2), Si1-
O5 1.799(2), C41-C41* 1.553(4), O5-Si1-C41 173.8(1), Si1-
C41-C41* 123.2(2).
◦
C41-C41* [123.2(2) ] is remarkably large with respect
1
3
to a tetracoordinate carbon atom. The C NMR spec-
tra of 3 confirm this deformation since C41 produces
The ionic state of 2 and its good solubility in chloro- a signal at 33.8 ppm, significantly downfield-shifted
3
form allowed the stoichiometric conversion of this hy- with regard to data of sp -hybridized Si-bound CH
2
pervalent silicon complex with p-tert-butylphenol into groups. However, this wide bond angle is not the
3
in solution. Single crystals of 3 were grown from its result of the repulsion between the two chelating
chloroform solution. 3*6CHCl crystallizes in the tri- ligands: Even in 1-SiPhEt [6] the corresponding angle
3
¯
◦
clinic space group P1 with one molecule of 3 in the is 123 at the Si-linked CH group. Therefore, we can
2
unit cell. The two complex moieties are symmetrically conclude that the repulsive interaction between the
arranged in the molecule (Fig. 1). The centre of the salen-type ligands and the carbon atom in β-position
ethylene spacer (C41-C41*-bond)is situated on a crys- is determining the distance between the two silicon
tallographically imposed inversion centre.
atoms. Referring to the other ethylene bridged silicon
complexes [1 – 4], 3 has the largest angle at a spacer
carbon atom found in such dinuclear compounds.
The coordination of the silicon atoms is nearly
◦
octahedral (O5-Si1-C41: 173.8(1) ; O2-Si1-N1:
1
◦
◦
74.55(8) ; O1-Si1-N2: 174.75(8) ) with the two
Besides these structural features, complex 3 shows
monodentate substituents (p-tert-butylphenolate and interesting external bonding between the units in the
crystal. The asymmetric unit contains three chloro-
form molecules with their positively polarized hydro-
gen atoms oriented towards electron rich sites (Fig. 2).
One chloroform molecule forms bifurcated hydro-
alkyl groups) in axial positions. Surprisingly, the Si-C
˚
bond [Si1-C41: 1.947(2) A] as well as the C-C bond
˚
of the ethylene spacer [C41-C41*: 1.553(4) A] are not
elongated significantly. The bond lenghts are identical
with those found in the analogous mononuclear com- gen bonding with the chelating ligand’s donor atoms
˚
plex 1-SiPhEt [6]. The planes of the two tetradentate O1 and O2 (distances H-O1 and H-O2: 2.535 A each).
ligand moieties are arranged anti-parallel without any The H atom of the second chloroform molecule points
discernible repulsive interactions. The bond angle Si1- to the aromatic ring of the p-tert-butylphenolate lig-
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J. Wagler – G. Roewer · Ethylene Bridged Neutral Dimeric Hexacoordinate Silicon Complexes
711
Scheme 3.
Fig. 3. Part of the molecule of 3 (most hydrogen atoms and
chloroform molecules omitted for clarity). The shortest in-
tramolecular hydrogen contacts are depicted by arrows.
˚
and (distances H-C33 and H-Z: 2.496 A each). The
Fig. 4. Molecular structure of 1,2-bis(phenyldichlorosil-
yl)ethane (ORTEP plot with 50% probability ellipsoids). The
molecule is situated on a crystallographically imposed in-
third CHCl molecule is twofold disordered, but the
3
H atom clearly points to one of the salen-type ligand’s
˚
two methoxy substituents (distance H-O4: 2.446 A).
◦
˚
version centre. Selected bond lengths [A] and angles [ ]:
Between the aromatic systems of molecule 3 sev- Si1-C1 1.853(1), Si1-C2 1.851(1), Si1-Cl1 2.0552(5), Si1-
Cl2 2.0546(4), C1-C1* 1.539(2), C1-Si1-C2 114.46(5), Cl1-
Si1-Cl2 108.26(2), Si1-C1-C1* 113.1(1).
eral intramolecular hydrogen contacts are established
(Fig. 3).
These contacts between the two parallel tetradentate
˚
ligand moieties are in the range of 2.85– 3.18 A, al-
lowing the conclusion that the interactions are attrac-
tive. In mononuclear hexacoordinatesilicon complexes
with ligand 1 the plane of the salen-ligand’s phenyl
substituent is perpendicular to the chelating plane and
this conformation is also found in 3.
According to an alternative route [6], the reaction
of a dinuclear diorganodichlorosilane with ligand 1
yields the dinuclear diorganosilane 4 with hexacoor-
dinate silicon atoms, which is also a “doubledecker”
(Scheme 3). The X-ray structures of the educt and the
product have been determined (Figs 4 and 5). (Suitable
single crystals of complex 4 were grown from tetra-
chloroethane.)
Fig. 5. Molecular structure of 4 (ORTEP plot with 50%
probability ellipsoids, hydrogen atoms and tetrachloroethane
molecules omitted for clarity. The molecule is situated
1
,2-bis(phenyldichlorosilyl)ethane crystallizes in
¯
the hexagonal space group R3 with 9 molecules in the
unit cell. The torsion angle Si1-C1-C1*-Si1* (180 ) on a crystallographically imposed inversion centre.) Se-
◦
˚
◦
lected bond lengths [A] and angles [ ]: Si1-C31 1.987(2),
Si1-C37 1.946(2), Si1-N1 1.982(2), Si1-N2 1.994(2), Si1-
O1 1.779(2), Si1-O2 1.776(2), C37-C37* 1.527(5), C31-Si1-
C37 176.2(1), Si1-C37-C37* 122.4(2).
indicates the staggered conformation of the molecule.
The midpoint of the C1-C1* bond is located on an in-
version centre, therefore maximum separation of the
two bulky phenyl groups is achieved.
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J. Wagler – G. Roewer · Ethylene Bridged Neutral Dimeric Hexacoordinate Silicon Complexes
Fig. 6. Vis spectra of 1-SiPhMe (0.01 mol/l), 1-SiPhEt
(0.01 mol/l) and 4 (0.005 mol/l) in chloroform (d = 0.50 cm).
Compound 4 crystallizes in the monoclinic space
group P2 /c with 2 molecules in the unit cell. Analo- Scheme 4.
1
gous to 3, the ethylene spacer of 4 is also positioned on
salts and bifunctional phenols, should be explored.
Investigations of the formation and spectroscopic as
well as electronic properties of electronically coupled
a crystallographically imposed point of symmetry. The
angle Si1-C37-C37* of the ethylene bridge is similar
◦
◦
to that in compound 3 [122.4(2) in 4, 123.2(2) in 3],
while the angle at the ethylene spacers’ carbon atoms
in the precursor with tetracoordinate silicon atoms is
“
double-” and “multidecker”-silicon complexes with
salen-type ligands seem to be a promising route to a
better understanding of special electronic effects in hy-
percoordinate silicon complexes.
◦
about 113 . Due to the repulsion between the salen-
type ligands and the phenyl groups’ ortho-hydrogen
atoms, the planes of the chelating ligand moieties in
In general, “doubledecker” silicon complexes with
short spacers and aromatic ligands represent inter-
esting model compounds for exploring π-π interac-
tions between the ligand spheres (“molecular metals”).
Up to now, only one of them – a bis(phthalocyanin-
ato)tetrasiloxane with two O-bridged hexacoordinate
silicon atoms and parallel arrangement of the macro-
cyclic ligand moieties – has been structurally charac-
terized [8]. We expect that di- and oligonuclear hex-
acoordinate silicon complexes with salen-type ligands
will provide further examples.
4
are not parallel.
Compound 4 is a suitable starting point to study the
UV/Vis-spectroscopic behavior of such “doubledeck-
ers”. A comparison with the data of related mononu-
clear complexes 1-SiPhMe and 1-SiPhEt [6] is pre-
sented in Fig. 6.
Compounds 4, 1-SiPhMe and 1-SiPhEt exhibit no
distinct absorption bands in the Vis region but there is
a remarkable bathochromic shift of a long wave shoul-
der [λ(1-SiPhMe) < λ(1-SiPhEt) ꢂ λ(4)]. Replace-
ment of the methyl group in 1-SiPhMe by the more
electron-donatingethyl group gives rise only to a slight
bathochromic shift of this absorption shoulder. This ef-
fect may either be due to the enhanced +I-effect of the
ethyl group or the rehybridization of the alkyl-C-atom
Experimental Section
All reagents were commercially available. All manipula-
tions were carried out under an inert atmosphere of dry ar-
gon. Triethylamine was distilled from calcium hydride and
˚
◦
3
stored over molecular sieve 3 A. Chloroform (stabilized with
(
123 at the sp -hybridized carbon atom!). The change
˚
amylene) was dried over molecular sieve 3 A. NMR spectra
in the absorption behavior between 1-SiPhEt and 4,
however, is much more striking. It may be concluded
that in 4 the two salen-type ligand moieties interact
electronically which causes a narrow HOMO-LUMO-
gap and a bathochromic shift of the Vis absorption.
were recorded on a BRUKER DPX 400 instrument (CDCl3
solutions with TMS as internal standard). Elemental analy-
ses were carried out on a Foss Heraeus CHN-O-Rapid. Vis
spectra were recorded on a SPECORD S100 UV/vis spec-
trometer.
3
: Triethylamine (1.0 g, 9.9 mmol) and p-tert-butyl-
Conclusions
phenol (0.42 g, 2.8 mmol) were added to a stirred solu-
tion of 2 [7] (1.55 g, 1.40 mmol) in chloroform (10 ml)
Based on the present results, the synthesis of “mul-
tidecker” coordination polymers with salen type lig- at ambient temperature to give a clear yellow solution.
ands (Scheme 4), starting from bifunctional siliconium This mixture was stored at ambient temperature for 3 h
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J. Wagler – G. Roewer · Ethylene Bridged Neutral Dimeric Hexacoordinate Silicon Complexes
713
Table 1. Data of crystal structure determination and refinement of (3∗6CHCl ), (1,2-bis(phenyldichlorosilyl)ethane) and
3
(
4∗4C H Cl ).
2
2
4
Compound
3*6CHCl3
1,2-Bis(phenyldichlorosilyl)ethane
4*4C2H2Cl4
Empirical formula
T (K)
C88H88N4O10Si2Cl18
198(2)
triclinic, P1
12.799(1)
13.013(1)
14.5970(9)
85.932(6)
80.336(7)
C14H14Si2Cl4
203(2)
hexagonal, R3
19.4330(9)
19.4330
11.9611(16)
90
C82H74N4O8Si2Cl16
93(2)
¯
¯
Crystal system, space group
monoclinic, P21/c
11.7529(8)
19.3081(14)
19.2624(14)
90
107.462(4)
90
4169.7(5), 2
1.487, 0.614
1916
˚
a (A)
˚
b (A)
˚
c (A)
◦
α ( )
◦
β ( )
90
120
◦
γ ( )
77.622(7)
˚
3
V (A ), Z
2339.4(3), 1
1.459, 0.611
1058
50 0. 58×0.22×0.10
3911.8(6), 9
1.453, 0.806
1746
60 0. 35×0.23×0.15
−27 ≤ h ≤ 27,
−27 ≤ k ≤ 26,
−16 ≤ l ≤ 16
39674, 0.0263
2545, 91
R1 = 0.0256,
wR2 = 0.0735
R1 = 0.0301,
wR2 = 0.0753
0.475 and −0.454
ρcalc (g cm 3), µ (mm−1
−
)
F(000)
3
Crystal size (mm )
θmax ( )
Index ranges
50 0. 25×0.10×0.10
◦
2
−15 ≤ h ≤ 15,
−13 ≤ h ≤ 13,
−22 ≤ k ≤ 22,
−22 ≤ l ≤ 22
56351, 0.0419
7332, 589
R1 = 0.0390,
wR2 = 0.1030
R1 = 0.0573,
wR2 = 0.1106
0.729 and −0.669
−
−
15 ≤ k ≤ 15,
17 ≤ l ≤ 17
Reflections collected, Rint
Independent reflections, parameters
Final R indices [I > 2σ(I)]
72985, 0.0978
8215, 582
R1 = 0.0394,
wR2 = 0.0824
R1 = 0.0713,
wR2 = 0.0901
0.332, −0.311
R Indices (all data)
˚
−3
)
Largest diff. peak and hole (eA
to yield yellow crystals of 3. The product was filtered off, crude solid product was recrystallized from pentane. Yield:
washed with chloroform (10 ml) and dried in vacuum. Yield: 2,60 g (6.84 mmol, 56%) nearly colorless crystals, m.p.
◦
.10 g (1.02 mmol, 73%) yellow crystals of 3*6CHCl . 62 C. – H NMR (400 MHz, CDCl ): δ = 1.46 (s, 4H,
3 3
1
2
◦
1
13
m.p. 153 C (sealed capillary, not corrected). – H NMR Si-CH -), 7.40 – 7.75 (mm, 10H, ar). – C NMR (101 MHz,
2
(
1
-
400 MHz, CDCl ): δ = 0.87 (s, 4H, Si-CH -), 1.19 (s, CDCl ): δ = 12.5 (Si-CH -), 128.5, 131.4, 131.9, 133.5 (o-,
3 2 3 2
8H, -C(CH ) ), 3.27 (m, 8H, N-CH CH -N), 3.74 (s, 12H, i-, p-, m- ar). – Si-NMR (79 MHz, CDCl ): δ = 18.9.
3 3 2 2 3
2
9
3
4
OCH ), 6.00 (dd, 4H, ar, J = 8.8 Hz, J = 2.4 Hz), – C H Si Cl (380.23): calcd. C 44.22, H 3.71; found
3 HH HH 14 14 2 4
3
4
6
2
.36 (d, 4H, ar, JHH = 8.8 Hz), 6.43 (d, 4H, ar, JHH
.4 Hz), 6.62 (d, 4H, ar, JHH = 8.8 Hz), 6.72 (d, 4H,
=
C 43.91, H 3.74.
3
4: In 22 ml of chloroform, 1 (6.08 g, 12.7 mmol) and tri-
ar, JHH = 7.6 Hz), 6.9 – 7.5 (mm, 20H, ar). – 13C NMR ethylamine (3,00 g, 29,7 mmol) were stirred at room tem-
3
(
101 MHz, CDCl ): δ = 30.5 ((CH ) C-), 31.7 ((CH ) C-), perature and a solution of 1,2-bis(phenyldichlorosilyl)ethane
3 3 3 3 3
3.8 (Si-CH -), 48.7 (N-CH CH -N), 55.3 (-OCH ), 103.9, (2.41 g, 6.34 mmol) in 10 ml of chloroform was added drop-
3
1
1
1
2 2 2 3
05.6, 114.5, 120.9, 124.9, 126.3, 127.2, 128.5, 128.7, 128.8, wise. Within 3 d the chloroform solvate of 4 (4∗2CHCl )
3
34.2, 135.4, 139.8 (aromatic C-H, C-C), 157.9, 165.0, crystallized from the resulting orange solution. It was sepa-
65.3 (aromatic C-O), 169.0 (C=N). – 29Si NMR (79 MHz, rated by filtration, washed with 5 ml of a chloroform/hexane
CDCl ): δ = −172.3, (79 MHz, CP/MAS): δ = −170.8. (4 : 1) and 10 ml of a chloroform/hexane mixture (2 : 3),
3
iso
–
C H N O Si Cl (2055.90): calcd. C 51.41, H 4.31, and briefly dried in vacuum. (Upon drying the crystals eas-
88 88 4 10 2 18
N 2.73; found C 52.44, H 4.53, N 2.73.
ily collapse losing chloroform.) Yield: 8.10 g (5.65 mmol,
1
,2-Bis(phenyldichlorosilyl)ethane: The synthesis of this 89%) orange powder of 4*2CHCl (approximate stoichio-
3
1
silane was already described in [9], but due to the bad yield metry) H NMR (400 MHz, CDCl ): δ = 1.22 (s, 4H, Si-
48.5%) of this literature method, it was carried out in a sol- CH -CH -Si), 2.88 (m, 8H, N-CH CH -N), 3.62 (s, 12H,
vent (Me SiCl). – To trimethylchlorosilane (5 ml) a solution -OCH ), 5,95 (dd, 4H, ar, J = 8.8 Hz, J = 2.4 Hz),
of H PtCl *6H O (50 mg) in 5 drops of isopropanol was 6.27 (d, 4H, ar, JHH = 2.4 Hz), 6.42 (d, 4H, ar, JHH
3
(
2 2 2 2
3
4
3
3
HH
HH
4
3
=
2
6
2
1
3
added and stirred for 10 min. Then, phenylvinyldichlorosi- 8.8 Hz), 6.9 – 7.8 (mm, 30H, ar). – C NMR (101 MHz,
lane (3,00 g, 12,3 mmol) and phenyldichlorosilane (2,50 g, CDCl ): δ = 30.9 (Si-CH -); 48.5 (N-CH CH -N), 55.0
3
2
2
2
1
4,1 mmol) were added and the mixture was stirred un- (-OCH ), 104.0, 105.3, 115.1, 124.7, 126.3, 126.6, 127.1,
3
der reflux for 15 min. After cooling to room temperature 127.3, 128.8 (2×), 128.9, 132.5, 134.2, 135.6, 165.1, 165.4,
2
9
the volatiles were removed under reduced pressure and the 166.1 (ar), 169.5 (C=N). – Si NMR (79 MHz, CDCl ): δ =
3
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J. Wagler – G. Roewer · Ethylene Bridged Neutral Dimeric Hexacoordinate Silicon Complexes
−
167.6. – C H N O Si Cl (1434.30): calcd. C 63.64, atoms were placed in idealized positions and refined isotrop-
7
6
68
4
8
2
6
H 4.78, N 3.91; found C 61.78, H 4.73, N 3.85.
ically. Selected data of structure determination and re-
4
*4C H Cl was obtained by recrystallization from finement are presented in Table 1. Crystallographic data
2
2
4
tetrachloroethane. – C H N O Si Cl (1866.83): calcd. (excluding structure factors) for the structures reported
82
74
4
8
2
16
C 52.76, H 4.00, N 3.00; found C 54.15, H 4.28, N 3.11. in this paper have been deposited with the Cambridge
The systematically higher contents of C, H and N may orig- Crystallographic Centre as supplementary publication no.
inate from partial evaporation of tetrachloroethane from the CCDC-244226 (3*6CHCl ), CCDC-263779 (1,2-bis(phen-
(
3
crystals upon drying under vacuum prior to elemental analy- yldichlorosilyl)ethane) and CCDC-263780 (4*4C H Cl ).
2
2
4
sis.)
Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [Fax: (internat.) +44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk).
X-ray analyses
X-ray structure data were recorded on a Bruker-Nonius-
Kappa-CCD diffractometer (3*6CHCl ) and a Bruker-
Nonius-APEX2-CCD diffractometer [1,2-bis(phenyldichlo-
3
Acknowledgements
rosilyl)ethane and 4*4C H Cl ] with Mo-Kα -radiation (λ =
This work was financially supported by the German Sci-
.71073 nm) and semi-empirically corrected (SADABS). ence Foundation (DFG) and the German Chemical Industry
2
2
4
0
The structures were solved with direct methods (SHELXS- Fund. We kindly acknowledge X-ray analysis of 3*6CHCl3
7) and refined by least squares methods (refinement of by Sigrid Goutal, Institut f u¨ r Organische Chemie, Technische
9
F
2
against all reflections with SHELXL-97). All non- Universit a¨ t Dresden, Bergstr. 66, D-01069 Dresden (Ger-
hydrogen atoms were refined anisotropically. Hydrogen many).
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