Synthesis and structural characterization of neutral hexacoordinate silicon(iv) complexes with SiO2N4 skeletons

Article abstract of DOI:10.1002/asia.200800405

A series of novel neutral hexacoordinate silicon(IV) complexes with SiO₂N₄ skeletons (compounds 4-8) was synthesized and structurally characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy (¹³C,

Full text of DOI:10.1002/asia.200800405

DOI: 10.1002/asia.200800405
Synthesis and Structural Characterization of Neutral Hexacoordinate
Silicon(IV) Complexes with SiO2N4 Skeletons
Stefan Metz, Christian Burschka, and Reinhold Tacke*[a]
Abstract: A series of novel neutral hexacoordinate silicon(IV) complexes with
SiO2N4 skeletons (compounds 4–8) was synthesized and structurally characterized
by single-crystal X-ray diffraction and solid-state NMR spectroscopy (13C, 15N,
29Si). The silicon(IV) complexes each contain two bidentate monoanionic O,N
Schiff base ligands and two cyanato-N or thiocyanato-N ligands. Compounds 4–8
Keywords: coordination chemistry ·
hexacoordination · N,O ligands ·
silicon · X-ray diffraction
were prepared from SiACHTNUTRGENNUG(NCO)4 or SiACHUTNGTREN(NGUN NCS)4, whereby the complex formation in-
volved some unexpected chemical transformations of the ligands.
Introduction
In a series of recent publications, we have reported on the
synthesis and structural characterization of the first penta-
[1]
ꢀ
coordinate silicon(IV) complexes with Si S bonds. Quite
recently, we have also demonstrated that hexacoordinate sil-
ꢀ
icon(IV) complexes with Si S bonds, such as compounds 1–
3, can be synthesized.[2] The neutral silicon(IV) complex 1
(SiS2O2N2 skeleton), with its two tridentate dianionic S,N,O
ligands, was obtained by treatment of tetra(cyanato-N)silane
with two molar equivalents of 1-(2-methyl-2,3-dihydroben-
zothiazol-2-yl)propan-2-one and four molar equivalents of
triethylamine. The derivatives 2 and 3 were obtained analo-
gously. To our great surprise, totally different products were
obtained when these syntheses were performed in the ab-
sence of triethylamine. Herein, we report on the synthesis
and structural characterization of the neutral hexacoordi-
nate silicon(IV) complexes 4–8. The studies reported in this
paper were performed in context with our systematic inves-
tigations on higher-coordinate silicon compounds (for recent
publications, see reference [3]; in this context, see also refer-
ences [4] and [5]). Preliminary results of the studies reported
here have already been presented elsewhere.[6]
[a] Dr. S. Metz, Dr. C. Burschka, Prof. Dr. R. Tacke
Institut fꢀr Anorganische Chemie
Universitꢁt Wꢀrzburg
Am Hubland, 97074 Wꢀrzburg (Germany)
Fax : (+49)931-888-4609
E-mail: r.tacke@mail.uni-wuerzburg.de
Chem. Asian J. 2009, 4, 581 – 586
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPERS
Results and Discussion
the (formal) hydrogen elimination, the bidentate mono-
AHCTUNGTREGaNNUN nionic 2-(benzothiazol-2-yl)phenolato ligand is formed.
Syntheses
The mechanism of this redox chemistry, which was not ob-
served in the presence of triethylamine,[2] is unclear.[8]
Treatment of tetra(cyanato-N)silane with 2-(2-methyl-1,3-
thiazolidin-2-yl)phenol resulted in another surprise: Again,
the expected product 2 (SiS2O2N2 skeleton) could not be ob-
tained. Instead, the silicon(IV) complex 6 (SiO2N4 skeleton)
was isolated. However, in contrast to the treatment of tet-
ra(cyanato-N)silane with 2-(2,3-dihydrobenzothiazol-2-yl)-
phenol (!4), the analogous treatment with 2-(2-methyl-1,3-
thiazolidin-2-yl)phenol (!6) did not involve hydrogen elim-
ination. Rather we observed the formation of a thiocarba-
mate group as part of the ligand system. This result might
be explained by the coordination of the ring-opened isomer
of 2-(2-methyl-1,3-thiazolidin-2-yl)phenol (in this context,
see reference [2]) as a bidentate monoanionic O,N ligand
and addition of the resulting HNCO to the free SH group.
Treatment of tetra(cyanato-N)silane with 2-(2-methyl-2,3-di-
hydrobenzothiazol-2-yl)phenol resulted in an analogous re-
action (formation of 7). However, when using tetra(thiocya-
nato-N)silane instead of tetra(cyanato-N)silane, compound 8
(with an SH group as part of the ligand system) was formed.
Obviously, the resulting HSCN does not react with the
ligand system, contrary to what is observed in the case of
HNCO.
Compounds 4–8 were synthesized according to Scheme 1,
starting from tetra(cyanato-N)silane or tetra(thiocyanato-
N)silane, and were isolated as crystalline solids (7 was ob-
The unexpected formation of compounds 6 and 7 suggest-
ed this chemistry could be useful as a method for the syn-
thesis of thiocarbamates. To test this approach, 6 was treated
with ethanol to generate the free ligand of 6, compound 9
(64% yield, Scheme 2). Demonstrating that the reaction se-
Scheme 1. Syntheses of compounds 4–8.
tained as the acetonitrile solvates 7·2CH3CN[7] (preparative
scale) and 7·4CH3CN (single crystals for X-ray diffraction
studies) (yields: 4, 48%; 5, 39%; 6, 71%; 7·2CH3CN, 32%;
8, 62%). In principle, all these yields could be improved by
reducing the volume of solvent used in the synthesis; howev-
er, this was only possible at the expense of crystal quality
owing to fast crystallization of the products. All attempts at
recrystallization failed owing to their poor solubility in
common organic solvents.
Treatment of 2-(2,3-dihydrobenzothiazol-2-yl)phenol with
tetra(cyanato-N)silane or tetra(thiocyanato-N)silane, in the
absence of triethylamine, did not result in the formation of
3 (SiS2O2N2 skeleton) as expected; instead, the silicon(IV)
complexes 4 and 5 (SiO2N4 skeletons) were isolated. From a
formal point of view, the formation of 4 (5) involves the
elimination of HNCO (HSCN) and hydrogen. As a result of
Scheme 2. Synthesis of compound 9.
quence Si
N
thesis of the thiocarbamate 9, starting from 2-(2-methyl-1,3-
thiazolidin-2-yl)phenol, future studies would be necessary to
evaluate the scope and applicability of this method.
Compounds 4–6, 7·2CH3CN, and 8 were characterized by
elemental analyses (C, H, N, S), solid-state VACP/MAS
NMR experiments (13C, 15N, 29Si), and single-crystal X-ray
diffraction studies (7 was structurally characterized as the
solvate 7·4CH3CN). Compound 9 was characterized by ele-
mental analysis (C, H, N, S) and solution NMR spectroscopy
(1H, 13C; solvent: [D6]DMSO).
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Chem. Asian J. 2009, 4, 581 – 586

Neutral Hexacoordinate Silicon(IV) Complexes with SiO2N4 Skeletons
Crystal Structure Analyses
The crystal data and the experimental parameters for the
crystal structure analyses of 4–6, 7·4CH3CN, and 8 are given
in Table 1. The molecular structures in the crystal are shown
in Figures 1–5; selected bond lengths and angles are given in
the respective figure legends.
The Si-coordination polyhedra of 4–6, 7·4CH3CN, and 8
are slightly distorted octahedra, with the two NCX (X = O,
S) ligands in trans positions. The two nitrogen atoms and the
two oxygen atoms of the two bidentate O,N ligands each
also occupy trans positions. The same stereochemistry has
also been observed experimentally for the related com-
pounds 10 and 11, and the five possible stereoisomers of the
Figure 1. Molecular structure of 4 in the crystal (probability level of dis-
placement ellipsoids 50%). Selected bond lengths [ꢃ] and angles [8]: Si-
O2 1.7324(12), Si-N1 1.8262(13), Si-N2 1.9668(14), N1-C1 1.1654(19), C1-
O1 1.1898(19); O2-Si-O2A 179.999(1), O2-Si-N1 88.51(6), O2-Si-N1A
91.49(6), O2-Si-N2 89.31(6), O2-Si-N2A 90.69(6), N1-Si-N1A 180.00(9),
N1-Si-N2 90.37(6), N1-Si-N2A 89.63(6), N2-Si-N2A 180.0, Si-N1-C1
158.77(13), N1-C1-O1 177.44(17).
model system 12 have been studied computationally.[3a]
Except for in the case of 5, the asymmetric units contain
ied are in the range 1.7046(10)–1.7324(12) ꢃ, and the Si N
ꢀ
ꢀ
(Si NCX; X = O, S) distances range from 1.950(2) ꢃ
ꢀ
half a molecule. The Si O distances of the compounds stud-
(1.8262(13) ꢃ) to 1.9680(12) ꢃ (1.8577(18) ꢃ). All these
Table 1. Crystallographic data for compounds 4–6, 7·4CH3CN, and 8.
4
5
6
7·4CH3CN
8
Empirical formula
Formula mass [gmolꢀ1
T [K]
C28H16N4O4S2Si
564.66
193(2)
C28H16N4O2S4Si
596.78
173(2)
C24H26N6O6S2Si
586.72
173(2)
C40H38N10O6S2Si
847.01
173(2)
C30H24N4O2S4Si
628.86
173(2)
]
l
G
0.71073
0.71073
monoclinic
C2/c (15)
15.2726(15)
12.9228(11)
13.8134(13)
90
104.745(11)
90
2636.5(4)
4
0.71073
monoclinic
C2/c (15)
14.529(3)
8.5317(17)
21.745(4)
90
101.58(3)
90
2640.5(9)
4
0.71073
0.71073
Crystal system
Space group (no.)
triclinic
triclinic
triclinic
¯
¯
¯
P1 (2)
P1 (2)
P1 (2)
a [ꢃ]
b [ꢃ]
c [ꢃ]
a [8]
b [8]
g [8]
V [ꢃ3]
Z
7.1874(14)
9.2835(19)
9.983(2)
74.20(3)
70.09(3)
75.58(3)
593.6(2)
1
7.3210(15)
10.779(2)
14.706(3)
73.05(3)
81.37(3)
72.82(3)
1058.0(4)
1
7.4107(11)
9.6940(14)
11.4629(17)
66.980(16)
74.052(17)
79.065(18)
725.59(18)
1
1calcd [gcmꢀ3
1.580
0.323
1.503
0.442
1.476
0.300
1.329
0.213
1.439
0.405
m [mmꢀ1
F000
290
1224
1224
442
326
Crystal dimensions [mm]
2q range [8]
Index ranges
0.5ꢄ0.3ꢄ0.2
4.62–54.58
ꢀ9ꢁhꢁ9
ꢀ11ꢁkꢁ11
ꢀ12ꢁlꢁ12
5406
0.5ꢄ0.5ꢄ0.4
5.52–56.08
ꢀ20ꢁhꢁ20
ꢀ17ꢁkꢁ16
ꢀ18ꢁlꢁ18
13734
0.5ꢄ0.3ꢄ0.1
5.56–56.00
ꢀ19ꢁhꢁ19
ꢀ11ꢁkꢁ11
ꢀ28ꢁlꢁ28
19646
0.5ꢄ0.5ꢄ0.4
5.60–56.06
ꢀ9ꢁhꢁ9
ꢀ14ꢁkꢁ14
ꢀ19ꢁlꢁ19
12766
0.4ꢄ0.4ꢄ0.3
4.58–56.16
ꢀ9ꢁhꢁ9
ꢀ12ꢁkꢁ12
ꢀ15ꢁlꢁ15
8461
No. of collected reflections
No. of independent reflections
2424
3147
3158
4715
3237
Rint
0.0411
0.0325
0.0546
0.0433
0.0467
No. of reflections used
2424
3147
3158
4715
3237
No. of parameters
178
1.053
0.0502/0.1661
0.0340
0.0909
180
1.055
0.0418/3.2876
0.0328
0.0885
179
1.097
0.0887/4.7061
0.0585
0.1747
277
1.063
0.0659/0.3049
0.0442
0.1231
191
1.038
0.0447/0.4871
0.0405
0.1056
S[a]
Weight parameters a/b[b]
R1[c] [I>2s(I)]
wR2[d] (all data)
Max./min. residual electron density [eꢃꢀ3
]
+0.276/ꢀ0.333
+0.509/ꢀ0.540
+1.355/ꢀ0.538
+0.341/ꢀ0.348
+0.292/ꢀ0.449
2
2
2
[a] S={S[w
U
(nꢀp)}0.5
;
ACTHNGUTRENNUG CAHTUNGTRENNUNG
n=no. of reflections; p=no. of parameters. [b] wꢀ1 =s2(Fo )+(aP)2+bP, with P=[max(Fo ,0)+2Fc2]/3.
2
2
[c] R1=SjjFo jꢀjFc jj/SjFo j. [d] wR2={S[w
U
(Fo )2]}0.5
ACHTUNGTERNNUNG .
Chem. Asian J. 2009, 4, 581 – 586
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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R. Tacke et al.
FULL PAPERS
Figure 4. Molecular structure of 7 in the crystal of 7·4CH3CN (probability
level of displacement ellipsoids 50%). Selected bond lengths [ꢃ] and
angles [8]: Si-O2 1.7220(12), Si-N1 1.8269(16), Si-N2 1.9606(14), N1-C1
1.172(2), C1-O1 1.191(2); O2-Si-O2A 180.0, O2-Si-N1 88.41(6), O2-Si-
N1A 91.59(6), O2-Si-N2 90.36(6), O2-Si-N2A 89.64(6), N1-Si-N1A
180.00(7), N1-Si-N2 88.93(6), N1-Si-N2A 91.07(6), N2-Si-N2A 180.00(5),
Si-N1-C1 159.33(13), N1-C1-O1 177.84(18).
Figure 2. Molecular structure of 5 in the crystal (probability level of dis-
placement ellipsoids 50%). Selected bond lengths [ꢃ] and angles [8]: Si-
O 1.7046(10), Si-N1 1.8577(18), Si-N2 1.8287(19), Si-N3 1.9680(12), N1-
C1 1.162(3), N2-C2 1.170(3), C1-S1 1.607(2), C2-S2 1.605(2); O-Si-OA
179.87(8), O-Si-N1 90.07(4), O-Si-N2 89.93(4), O-Si-N3 90.07(5), O-Si-
N3A 89.93(5), N1-Si-N2 180.0, N1-Si-N3 91.33(4), N1-Si-N3A 91.33(4),
N2-Si-N3 88.67(4), N2-Si-N3A 88.67(4), N3-Si-N3A 177.34(7), Si-N1-C1
180.0, Si-N2-C2 180.0, N1-C1-S1 180.0, N2-C2-S2 180.0.
Figure 3. Molecular structure of 6 in the crystal (probability level of dis-
placement ellipsoids 50%). Selected bond lengths [ꢃ] and angles [8]: Si-
O2 1.718(2), Si-N1 1.850(2), Si-N2 1.950(2), N1-C1 1.158(4), C1-O1
1.202(4); O2-Si-O2A 180.0, O2-Si-N1 88.74(10), O2-Si-N1A 91.26(10),
O2-Si-N2 90.83(10), O2-Si-N2A 89.17(9), N1-Si-N1A 180.00(15), N1-Si-
N2 89.63(10), N1-Si-N2A 90.36(10), N2-Si-N2A 179.999(1), Si-N1-C1
162.1(2), N1-C1-O1 178.1(3).
Figure 5. Molecular structure of 8 in the crystal (probability level of dis-
placement ellipsoids 50%). Selected bond lengths [ꢃ] and angles [8]: Si-
O 1.7096(15), Si-N1 1.8465(17), Si-N2 1.9519(16), N1-C1 1.174(3), C1-S1
1.606(2); O-Si-OA 180.0, O-Si-N1 88.13(8), O-Si-N1A 91.87(8), O-Si-N2
90.27(7), O-Si-N2A 89.73(7), N1-Si-N1A 180.0, N1-Si-N2 89.68(7), N1-Si-
N2A 90.32(7), N2-Si-N2A 179.999(1), Si-N1-C1 165.90(16), N1-C1-S1
178.8(2).
bond lengths are very similar to those found for structurally
related hexacoordinate silicon(IV) complexes with SiO2N4
skeletons.[3a] The trans-X-Si-X (X = O, S) angles fit almost
perfectly with the ideal 1808 angle (maximum deviation,
2.66(7)8), and the cis-X-Si-X (X = O, S) angles show a maxi-
mum deviation of 1.87(8)8 from the ideal 908 angle. The Si-
N-C(X) (X = O, N) angles range from 158.77(13)8 to 180.08,
and the N-C-X (X = O, N) angles range from 177.44(17)8 to
180.08.
Some structural features of compound 5 differ from those
observed for 4, 6, 7·4CH3CN, and 8. Noteworthy are the two
ꢀ
different Si N(CS) bond lengths (1.8287(19) and
1.8577(18) ꢃ) and the linear S-C-N-Si-N-C-S moiety of 5,[9]
as the Si-N-C(X) and N-C-X (X = O, S) angles of all the
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Neutral Hexacoordinate Silicon(IV) Complexes with SiO2N4 Skeletons
125.8 MHz) using [D6]DMSO as the solvent. Chemical shifts (ppm) were
determined relative to internal [D5]DMSO (1H, d=2.49 ppm) or
[D6]DMSO (13C, d=39.5 ppm). Assignment of the 13C NMR data was
supported by DEPT 135 and 13C,1H correlation experiments. Solid-state
13C, 15N, and 29Si VACP/MAS NMR spectra were recorded at 228C on a
Bruker DSX-400 NMR spectrometer with bottom-layer rotors of ZrO2
(diameter 7 mm) containing ca. 200–300 mg of sample (13C, 100.6 MHz;
15N, 40.6 MHz; 29Si, 79.5 MHz; external standard, TMS (13C, 29Si; d=
0 ppm) or glycine (15N, d=ꢀ342.0 ppm); spinning rate, 5–6 kHz; contact
time, 2 ms (13C), 3–5 ms (15N), or 5 ms (29Si); 908 1H transmitter pulse
other compounds studied differ from the 1808 angle (Si-N-
C(X), 158.77(13)–165.90(10)8; N-C-X, 177.44(17)–178.8(2)8).
NMR Studies
Compounds 4–6, 7·2CH3CN, and 8 were studied by solid-
state VACP/MAS NMR spectroscopy (13C, 15N, 29Si). The
isotropic 29Si chemical shifts obtained in these studies (4, d=
ꢀ201.9 ppm; 5, d=ꢀ204.0 ppm; 6, d=ꢀ206.1 ppm;
length, 3.6 ms; repetition time, 4 s). The precursors Si
ACHTUNGRTEN(NUNG NCO)4 and
7·2CH3CN, d=ꢀ205.7 ppm; 8, d=ꢀ207.1 ppm)[10] are very
similar and are in the same range as those found for struc-
turally related silicon(IV) complexes with SiO2N4 skeletons
that also contain two bidentate O,N Schiff base ligands and
two cyanato-N or thiocyanato-N ligands.[3a] Thus, the 29Si
NMR data obtained confirms the identities of 4–8. The
solid-state 13C and 15N NMR data are also compatible with
the structures determined by single-crystal X-ray diffraction.
Owing to the poor solubility of 4–6, 7·2CH3CN, and 8 in
common organic solvents, no solution-state NMR experi-
ments could be performed.
Si(NCS)4 were synthesized according to reference [12]. The ligands were
ACHTUNGTRENNUNG
synthesized according to reference [13]; for analytical data, see refer-
ence [2].
Silicon(IV) complex 4: Tetra(cyanato-N)silane (171 mg, 872 mmol) was
added in a single portion at 208C to a stirred solution of 2-(2,3-dihydro-
benzothiazol-2-yl)phenol (400 mg, 1.74 mmol) in acetonitrile (25 mL),
and the reaction mixture was then kept undisturbed at 208C for 2 days.
The resulting solid was isolated by filtration, washed with diethyl ether
(10 mL), and then dried in vacuo (0.01 mbar, 208C, 2 h) to give 4 in 48%
yield (235 mg, 416 mmol) as a yellow crystalline product; m.p. 224–2258C.
13C VACP/MAS NMR: d=117–127 (br signal with intensity maxima at
118.9, 121.1, and 124.6), 129.1, 134.9, 147.0, and 156.8 (SC6H4N,
OC6H4C), 172.6 ppm (C=N), NCO signal not detected; 15N VACP/MAS
NMR: d=ꢀ316.5 (NCO), ꢀ142.6 ppm (C=N); 29Si VACP/MAS NMR:
d=ꢀ201.9 ppm; elemental analysis (%) calcd for C28H16N4O4S2Si
(564.68): C 59.56, H 2.86, N 9.92, S 11.36; found: C 59.6, H 3.1, N 10.1,
S 11.4.
Conclusions
Silicon(IV) complex 5: Tetra(thiocyanato-N)silane (350 mg, 1.34 mmol)
was added in a single portion at 208C to a stirred solution of 2-(2,3-dihy-
drobenzothiazol-2-yl)phenol (616 mg, 2.69 mmol) in THF (60 mL), and
the reaction mixture was then stirred at 208C for 5 min. The undissolved
solid was filtered off and discarded, and the filtrate was kept undisturbed
at 208C for 2 days. The resulting solid was isolated by filtration, washed
with diethyl ether (10 mL), and then dried in vacuo (0.01 mbar, 208C,
2 h) to give 5 in 39% yield (315 mg, 528 mmol) as a yellow crystalline
product; m.p.>2508C (decomp.). 13C VACP/MAS NMR: d=117.5,
120.3, 122.3 (2C), 124.1, 128.3 (3C), 132.3, 139.6, 146.9, and 155.2
(SC6H4N, OC6H4C), 173.5 ppm (C=N), NCS signal not detected; 15N
VACP/MAS NMR: no signals detected; 29Si VACP/MAS NMR: d=
ꢀ204.0 ppm; elemental analysis (%) calcd for C28H16N4O2S4Si (596.81):
C 56.35, H 2.70, N 9.39, S 21.49; found: C 56.4, H 2.9, N 9.3, S 21.4.
With the synthesis of compounds 4–6, 7·2CH3CN, and 8, a
series of novel neutral hexacoordinate silicon(IV) complexes
with SiO2N4 skeletons has been made accessible. All com-
pounds contain two bidentate monoanionic O,N Schiff base
ligands and two monodentate monoanionic cyanato-N or
thiocyanato-N ligands. The formation of 4–8 was totally un-
expected and is still not fully understood: When performing
the syntheses in the presence of triethylamine, the expected
neutral hexacoordinate silicon(IV) complexes with SiS2O2N2
skeletons are formed (compounds 1–3),[2] whereas in the ab-
sence of triethylamine, the sulfur atoms do not act as ligand
atoms, that is, the ligands used for the syntheses do not
behave as tridentate dianionic S,N,O ligands.[11] Instead, in
the course of the formation of 4–7, the ligands undergo fur-
ther reactions (4 and 5, formal hydrogen elimination; 6 and
7, formal addition of HNCO) and behave as bidentate mon-
oanionic O,N ligands. In the case of 8, the ligand undergoes
no additional transformations and behaves as a bidentate
monoanionic O,N ligand as well. Future studies to analyze
the course of the reactions that lead to the formation of 4–8
in more detail are necessary. Furthermore, the synthetic po-
tential of the ligand transformations (which has been dem-
onstrated exemplarily by the synthesis of 9) has to be evalu-
ated.
Silicon(IV) complex 6: Tetra(cyanato-N)silane (202 mg, 1.03 mmol) was
added in a single portion at 208C to a stirred solution of 2-(2-methyl-1,3-
thiazolidin-2-yl)phenol (400 mg, 2.05 mmol) in a mixture of acetonitrile
(20 mL) and THF (10 mL), and the reaction mixture was then kept un-
disturbed at 208C for 4 days. The resulting solid was isolated by filtration,
washed with diethyl ether (10 mL), and then dried in vacuo (0.01 mbar,
208C, 2 h) to give 6 in 71% yield (430 mg, 733 mmol) as a pale yellow
crystalline product; m.p.>1758C (decomp.). 13C VACP/MAS NMR: d=
19.7 (CH3), 27.6 (NCH2CH2S), 53.1 (NCH2CH2S), 118.9, 120.5 (2C),
128.2, 136.7, and 158.9 (OC6H4C), 172.7 (C(O)NH2 or C=N), 176.5 ppm
(C(O)NH2 or C=N), NCO signal not detected; 15N VACP/MAS NMR:
d=ꢀ315.3 (NCO), ꢀ273.0 (C(O)NH2), ꢀ141.6 ppm (C=N); 29Si VACP/
MAS NMR: d=ꢀ206.1 ppm; elemental analysis (%) calcd for
C24H26N6O6S2Si (586.72): C 49.13, H 4.47, N 14.32, S 10.93; found: C 49.3,
H 4.6, N 14.3, S 10.9.
Silicon(IV) complex 7·2CH3CN: Tetra(cyanato-N)silane (202 mg,
1.03 mmol) was added in a single portion at 208C to a stirred solution of
2-(2-methyl-2,3-dihydrobenzothiazol-2-yl)phenol (501 mg, 2.06 mmol) in
acetonitrile (12 mL), and the reaction mixture was then kept undisturbed
at 208C for 4 days. The resulting solid was isolated by filtration, washed
with diethyl ether (10 mL), and then dried in vacuo (0.01 mbar, 208C,
2 h) to give 7·2CH3CN in 32% yield (255 mg, 333 mmol) as a colorless
crystalline product; m.p. 152–1538C. 13C VACP/MAS NMR: d=2.7
(CH3CN), 21.6 (CH3), 119.4, 121.4 (2C), 128.6 (3C), 132.0 (2C), 137.1,
138.4, 150.2, and 160.2 (SC6H4N, OC6H4C), 166.9 (C(O)NH2 or C=N),
181.1 ppm (C(O)NH2 or C=N), CH3CN and NCO signals not detected;
Experimental Section
General procedures: All syntheses were carried out under dry nitrogen.
The organic solvents used were dried and purified according to standard
procedures and stored under nitrogen. Melting points were determined
with a Bꢀchi Melting Point B-540 apparatus using samples in sealed ca-
pillaries. The 1H and 13C solution NMR spectra were recorded at 238C
on
a
Bruker Avance 500 NMR spectrometer (1H, 500.1 MHz; 13C,
Chem. Asian J. 2009, 4, 581 – 586
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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585

R. Tacke et al.
FULL PAPERS
15N VACP/MAS NMR: d=ꢀ315.4 (NCO), ꢀ275 (br, C(O)NH2),
ꢀ132.0 ppm (C=N), CH3CN signal not detected; 29Si VACP/MAS NMR:
d=ꢀ205.7 ppm; elemental analysis (%) calcd for C36H32N8O6S2Si
(764.92): C 56.53, H 4.22, N 14.65, S 8.38; found: C 56.3, H 4.2, N 14.4,
S 8.4.
Angew. Chem. Int. Ed. 2007, 46, 7006–7009; h) G. Gonzꢅlez-Garcꢆa,
J. A. Gutiꢇrrez, S. Cota, S. Metz, R. Bertermann, C. Burschka, R.
Tacke, Z. Anorg. Allg. Chem. 2008, 634, 1281–1286; i) B. Theis, C.
Burschka, R. Tacke, Chem. Eur. J. 2008, 14, 4618–4630; j) R. Haga,
C. Burschka, R. Tacke, Organometallics 2008, 27, 4395–4400; k) S.
Metz, C. Burschka, R. Tacke, Organometallics 2008, 27, 6032–6034.
[4] Selected reviews dealing with higher-coordinate silicon compounds:
a) R. R. Holmes, Chem. Rev. 1996, 96, 927–950; b) V. Pestunovich,
S. Kirpichenko, M. Voronkov in The Chemistry of Organic Silicon
Compounds, Vol. 2, Part 2 (Eds.: Z. Rappoport, Y. Apeloig), Wiley,
Chichester, 1998, pp. 1447–1537; c) C. Chuit, R. J. P. Corriu, C.
Reye in Chemistry of Hypervalent Compounds (Ed.: K.-y. Akiba),
Wiley-VCH, New York, 1999, pp. 81–146; d) R. Tacke, M. Pꢀlm, B.
Wagner, Adv. Organomet. Chem. 1999, 44, 221–273; e) M. A.
Brook, Silicon in Organic, Organometallic, and Polymer Chemistry,
Wiley, New York, 2000, pp. 97–114; f) R. Tacke, O. Seiler in Silicon
Chemistry: From the Atom to Extended Systems (Eds.: P. Jutzi, U.
Schubert), Wiley-VCH, Weinheim, Germany, 2003, pp. 324–337;
g) D. Kost, I. Kalikhman, Adv. Organomet. Chem. 2004, 50, 1–106.
[5] Selected recent publications dealing with higher-coordinate silicon
compounds: a) D. Gerlach, E. Brendler, T. Heine, J. Wagler, Orga-
nometallics 2007, 26, 234–240; b) U. Bçhme, B. Gꢀnther, Inorg.
Chem. Commun. 2007, 10, 482–484; c) Y. Liu, S. A. Steiner III,
C. W. Spahn, I. A. Guzei, I. S. Toulokhonova, R. West, Organometal-
lics 2007, 26, 1306–1307; d) J. Wagler, Organometallics 2007, 26,
155–159; e) J. Wagler, D. Gerlach, G. Roewer, Inorg. Chim. Acta
2007, 360, 1935–1942; f) J. Wagler, A. F. Hill, Organometallics 2007,
26, 3630–3632; g) M. Spiniello, J. M. White, Organometallics 2008,
27, 994–999; h) V. V. Negrebetsky, P. G. Taylor, E. P. Kramarova,
A. G. Shipov, S. A. Pogozhikh, Y. E. Ovchinnikov, A. A. Korlyukov,
A. Bowden, A. R. Bassindale, Y. I. Kaukov, J. Organomet. Chem.
2008, 693, 1309–1320; i) E. Kertsnus-Banchik, I. Kalikhman, B. Gos-
tevskii, Z. Deutsch, M. Botoshansky, D. Kost, Organometallics 2008,
27, 5285–5294.
Silicon(IV) complex 8: Tetra(thiocyanato-N)silane (300 mg, 1.15 mmol)
was added in a single portion at 208C to a stirred solution of 2-(2-
methyl-2,3-dihydrobenzothiazol-2-yl)phenol (561 mg, 2.31 mmol) in ace-
tonitrile (60 mL), and the reaction mixture was then stirred for 5 min.
The undissolved solid was filtered off and discarded, and the filtrate was
kept undisturbed at 208C for 3 days. The resulting solid was isolated by
filtration, washed with diethyl ether (10 mL), and then dried in vacuo
(0.01 mbar, 208C, 2 h) to give 8 in 62% yield (450 mg, 716 mmol) as a
yellow crystalline product; m.p.>1408C (decomp.). 13C VACP/MAS
NMR: d=21.4 (CH3), 120.1 (2 C), 122.6, 126.3, 129.6 (2C), 131.2 (3C),
140.7, 145.0, and 159.4 (SC6H4N, OC6H4C), 180.6 ppm (C=N), NCS signal
not detected; 15N VACP/MAS NMR: d=ꢀ139.0 ppm (C=N), NCS signal
not detected; 29Si VACP/MAS NMR: d=ꢀ207.1 ppm; elemental analysis
(%) calcd for C30H24N4O2S4Si (628.90): C 57.30, H 3.85, N 8.91, S 20.40;
found: C 57.4, H 3.9, N 8.8, S 20.2.
9: A suspension of 6 (400 mg, 682 mmol) in a mixture of THF (5 mL) and
ethanol (5 mL) was stirred at 208C for 3 h. The solvent was removed
under reduced pressure, and the remaining solid was dissolved in boiling
ethanol (9 mL). The resulting hot mixture was filtered, and the filtrate
was kept undisturbed at ꢀ208C for 24 h. The resulting solid was isolated
by filtration and dried in vacuo (0.01 mbar, 208C, 2 h) to give 10 in 64%
yield (209 mg, 877 mmol) as a yellow crystalline product; m.p. 143–1458C.
1H NMR ([D6]DMSO): d=2.34 (s, 3H, CH3), 3.08 (t, 3J
2H, SCH2CH2N), 3.71 (t, 3J
(H,H)=6.6 Hz, 2H, SCH2CH2N), 6.75–6.79
ACHTUNGTREN(NUNG H,H)=6.6 Hz,
AHCTUNGTRENNUNG
(m, 2H, H-4/H-6, OC6H4C), 7.24–7.29 (m, 1H, H-5, OC6H4C), 7.63–7.66
(m, 1H, H-3, OC6H4C), 7.4–7.8 (brm, 2H, NH2), 15.91 ppm (s, 1H, OH);
13C NMR ([D6]DMSO): d=14.7 (CH3), 29.7 (SCH2CH2N), 49.2
(SCH2CH2N), 117.0 and 117.8 (C-4/C-6, OC6H4C), 119.1 (C-2, OC6H4C),
128.8 (C-3, OC6H4C), 132.3 (C-5, OC6H4C), 162.9 (C-1, OC6H4C), 166.6
(C=N or C(O)NH2), 172.9 ppm (C=N or C(O)NH2); elemental analysis
(%) calcd for C11H14N2O2S (238.31): C 55.44, H 5.92, N 11.76, S 13.46;
found: C 54.7, H 5.9, N 11.8, S 13.4.
[6] S. Metz, C. Burschka, R. Tacke, The 14th International Symposium
on Organosilicon Chemistry/3rd European Organosilicon Days,
Wꢀrzburg, Germany, July 31–August 5, 2005, Book of Abstracts,
Abstract P 159, p. 202.
Crystal structure analyses: Suitable single crystals of 4–6, 7·4CH3CN, and
8 were isolated directly from the respective reaction mixtures. The crys-
tals were mounted in inert oil (perfluoropolyalkyl ether, ABCR) on a
glass fiber and then transferred to the cold nitrogen gas stream of the dif-
fractometer (Stoe IPDS; graphite-monochromated MoKa radiation, l=
0.71073 ꢃ). All structures were solved by direct methods.[14] The non-hy-
drogen atoms were refined anisotropically.[15] A riding model was em-
ployed in the refinement of the CH hydrogen atoms. CCDC 713792 (4),
713793 (5), 713794 (6), 713795 (7·4CH3CN), and 713796 (8) contain the
supplementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
[7] The composition of this solvate is based on the elemental analysis.
[8] The synthesis of 5 was also performed in dichloromethane leading
to a similar yield and indicating that the formation of the oxidized
product does not depend on the solvent.
[9] Only in the case of 5, the S-C-N-Si-N-C-S moiety lies on a crystallo-
graphic twofold axis. As can be seen from the thermal parameters,
the N1-C1-S1 moiety could be slightly disordered, which conse-
quently would result in a deviation of the Si-N1-C1 angle from 1808.
[10] Owing to 29Si,14N coupling, the 29Si VACP/MAS NMR spectra of 4–
6, 7·2CH3CN, and 8 are characterized by broad and slightly struc-
tured signals.
[11] One could speculate that the SH sulfur atom of the ring-opened
form of the reagents can only coordinate to the silicon center in the
presence of triethylamine; in the absence of the amine, the SH
group may exist as it is or undergo further reactions. However, there
is no experimental evidence for this assumption.
[12] R. G. Neville, J. J. McGee in Inorganic Syntheses, Vol. VIII (Ed.:
H. F. Holtzclaw, Jr.), McGraw-Hill, New York, 1966, pp. 23–31.
[13] a) R. V. Singh, J. P. Tandon, Synth. React. Inorg. Met.-Org. Chem.
1981, 11, 109–131; b) S. V. Singh, R. V. Singh, Synth. React. Inorg.
Met.-Org. Chem. 1987, 17, 947–960.
[1] D. Troegel, C. Burschka, S. Riedel, M. Kaupp, R. Tacke, Angew.
Chem. 2007, 119, 7131–7135; Angew. Chem. Int. Ed. 2007, 46, 7001–
7005, and references therein.
[2] S. Metz, C. Burschka, R. Tacke, Eur. J. Inorg. Chem. 2008, 4433–
4439.
[3] Recent publications dealing with higher-coordinate silicon com-
pounds: a) O. Seiler, C. Burschka, M. Fischer, M. Penka, R. Tacke,
Inorg. Chem. 2005, 44, 2337–2346; b) O. Seiler, C. Burschka, S.
Metz, M. Penka, R. Tacke, Chem. Eur. J. 2005, 11, 7379–7386; c) R.
Tacke, R. Bertermann, C. Burschka, S. Dragota, Angew. Chem.
2005, 117, 5426–5429; Angew. Chem. Int. Ed. 2005, 44, 5292–5295;
d) X. Kꢁstele, P. Klꢀfers, R. Tacke, Angew. Chem. 2006, 118, 3286–
3288; Angew. Chem. Int. Ed. 2006, 45, 3212–3214; e) O. Seiler, C.
Burschka, K. Gçtz, M. Kaupp, S. Metz, R. Tacke, Z. Anorg. Allg.
Chem. 2007, 633, 2667–2670; f) O. Seiler, C. Burschka, T. Fenske, D.
Troegel, R. Tacke, Inorg. Chem. 2007, 46, 5419–5424; g) S. Metz, C.
Burschka, D. Platte, R. Tacke, Angew. Chem. 2007, 119, 7136–7139;
[14] a) G. M. Sheldrick, SHELXS-97, University of Gçttingen, Gçttingen
(Germany), 1997; b) G. M. Sheldrick, Acta Crystallogr. Sect. A 1990,
46, 467–473.
[15] G. M. Sheldrick, SHELXL-97, University of Gçttingen, Gçttingen
(Germany), 1997.
Received: October 23, 2008
Revised: December 10, 2008
Published online: February 2, 2009
586
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ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 581 – 586