Hexacoordinate silicon(IV) complexes containing thiocyanato-N ligands - Syntheses, structural characterization, and computational studies

Article abstract of DOI:10.1002/zaac.200300097

The hexacoordinate silicon(IV) complexes [NEt₄] ₂-[Si(NCS)₆] (2), [K(18-crown-6)]₂[Si(NCS) ₆]·2CH₃CN (3·2CH₃CN), and cis-[(acac)₂Si(NCS)₂] (cis-4; acac = ac

Full text of DOI:10.1002/zaac.200300097

Hexacoordinate Silicon(IV) Complexes Containing Thiocyanato-N Ligands ؊
Syntheses, Structural Characterization, and Computational Studies
Oliver Seiler, Rüdiger Bertermann, Nele Buggisch, Christian Burschka, Martin Penka, David Tebbe, and
Reinhold Tacke*
Würzburg, Institut für Anorganische Chemie der Bayerischen Julius-Maximilians-Universität
Received April 2nd, 2003.
Dedicated to Professor Heinrich Nöth on the Occasion of his 75th Birthday
Abstract. The hexacoordinate silicon(IV) complexes [NEt
Si(NCS) ] (2), [K(18-crown-6)] [Si(NCS) ]·2CH CN (3·2CH CN),
and cis-[(acac) Si(NCS) ] (cis-4; acac ϭ acetylacetonato-O,O) were
synthesized, starting from Si(NCS) (1). Compounds 1, 2,
·2CH CN, and cis-4 were structurally characterized in the solid
4
]
2
-
experimental investigations were complemented by computational
2
Ϫ
[
6
2
6
3
3
6
studies (RI-MP2 geometry optimizations of 1, [Si(NCS) ] , cis-4,
2
9
2
2
and trans-4; calculations of the Si NMR chemical shifts using the
4
optimized structures).
3
3
13
15
29
state ( C, N (cis-4 only), and Si MAS NMR; crystal structure
Keywords: Coordination chemistry; Hexacoordinate silicon; Sili-
con; Solid-state NMR spectroscopy; Thiocyanato-N ligand
analyses) and in solution ( H, 13C, and Si NMR; cis-4 only). The
1
29
Hexakoordinierte Silicium(IV)-Komplexe mit Thiocyanato-N-Liganden ؊ Synthesen,
strukturelle Charakterisierung und theoretische Untersuchungen
1
Inhaltsübersicht. Die hexakoordinierten Silicium(IV)-Komplexe
NEt [Si(NCS) (2), [K(18-Krone-6)] [Si(NCS) ]·2CH CN
3·2CH CN) und cis-[(acac) Si(NCS) ] (cis-4; acac ϭ Acetylaceton-
ato-O,O) wurden ausgehend von Si(NCS) (1) synthetisiert. Die
Verbindungen 1, 2, 3·2CH CN und cis-4 wurden im festen Zustand
sen) und in Lösung ( H-, 13C- und 29Si-NMR; nur cis-4) strukturell
charakterisiert. Die experimentellen Untersuchungen wurden
durch theoretische Studien ergänzt (RI-MP2-Geometrieoptimie-
[
(
4
]
2
6
]
2
6
3
3
2
2
2
Ϫ
4
rungen von 1, [Si(NCS)
Si-NMR-chemischen Verschiebungen für die geometrieoptimier-
6
]
, cis-4 und trans-4; Berechnungen der
2
9
3
13
15
29
(
C-, N- (nur cis-4) und Si-MAS-NMR; Kristallstrukturanaly-
ten Strukturen).
Introduction
already been synthesized by an alternative method (starting
material: (RO) Si(NCS) (R ϭ Et, n-Pr) [4]), but its stereo-
2
2
6
chemistry has been studied only by solution NMR spec-
troscopy. We report here on the syntheses of compounds 1,
Compared to the chemistry of dianionic λ Si-silicates with
SiO skeletons [1], the chemistry of dianionic hexacoordi-
6
2
, 3·2CH CN, and cis-4 and their structural characteri-
nate silicon(IV) complexes with SiN frameworks is signifi-
3
6
13
zation in the solid state (single-crystal X-ray diffraction;
C
cantly less explored [2]. Compound 2 represents the first
example of this particular formula type that has been struc-
turally characterized by single-crystal X-ray diffraction [2b].
As the quality of this structure analysis is poor and no
NMR data of the Si(NCS)6 dianion have been reported,
compound 2 was resynthesized and studied by single-crystal
X-ray diffraction and solid-state NMR spectroscopy. In ad-
dition, the related potassium-18-crown-6 salt 3 and the neu-
tral silicon(IV) complex cis-4 (SiO N skeleton) were syn-
15
29
(except for 1), N (cis-4 only), and Si MAS NMR) and
1
13
29
in solution ( H, C, and Si NMR; cis-4 only). These ex-
perimental studies were complemented by computational
investigations. The studies presented in this paper were car-
ried out as part of our systematic investigations on higher-
2
Ϫ
4
2
thesized and structurally characterized. In all cases, the sil-
ane 1 [3] served as the starting material. Compound 4 has
*
Prof. Dr. Reinhold Tacke
Institut für Anorganische Chemie
Universität Würzburg
Am Hubland
D-97074 Würzburg, Germany
E-mail: r.tacke@mail.uni-wuerzburg.de
Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411
DOI: 10.1002/zaac.200300097
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1403

O. Seiler, R. Bertermann, N. Buggisch, C. Burschka, M. Penka, D. Tebbe, R. Tacke
coordinate silicon compounds (for recent publications, see
The crystal data and the experimental parameters used for
these studies are given in Table 1; selected interatomic dis-
tances and angles are listed in Table 2. The structures of
the respective molecules (1, cis-4) and dianions (2,
ref. [5]; for reviews dealing with higher-coordinate silicon
compounds, see refs. [1] and [6]). Preliminary results of the
studies reported here have already been presented else-
where [7].
3·2CH CN) in the crystal are shown in Figures 1Ϫ4.
3
The silane 1 crystallizes in the space group I4 /a, with
1
˚
SiϪN distances in the range 1.6745(14)Ϫ1.6831(15) A. The
Results and Discussion
Si-coordination polyhedron is an almost ideal tetrahedron,
with NϪSiϪN angles in the range 108.81(7)Ϫ109.94(7)°.
The SiϪNϪC angles amount to 174.54(15)Ϫ177.12(15)°.
Syntheses
Compounds 1Ϫ4 were synthesized according to Scheme 1.
Tetra(thiocyanato-N)silane (1) [3] was obtained by reaction
of tetrachlorosilane with four molar equivalents of am-
monium thiocyanate. Tetraethylammonium hexa(thiocyan-
ato-N)silicate (2) [2b] was synthesized by treatment of 1
with two molar equivalents each of tetraethylammonium
chloride and potassium thiocyanate. The related potassium-
Compounds 2 [8] and 3·2CH CN crystallize in the space
3
groups P4 /m and Fdd2, respectively. The Si-coordination
2
polyhedra of the [Si(NCS)6]2 dianions are almost ideal oc-
Ϫ
tahedra, with NϪSiϪN angles in the ranges
8
9.15(10)Ϫ90.74(7)° and 179.37(12)Ϫ180.0°. The SiϪN dis-
˚
tances amount to 1.8167(15)Ϫ1.8369(17) A; they are signif-
icantly longer than those observed for 1. The SiϪNϪC
angles are in the range 159.01(16)Ϫ180.0°.
18-crown-6 salt 3 was obtained by reaction of 1 with two
molar equivalents each of potassium thiocyanate and 18-
crown-6 and was isolated as the acetonitrile solvate
The asymmetric unit of 3 contains half an [Si(NCS)6]2
Ϫ
dianion and one potassium cation that is coordinated by an
3
·2CH CN. The neutral complex cis-bis[acetylacetonato-
3
18-crown-6 molecule. In addition, there is one acetonitrile
O,O]di(thiocyanato-N)silicon(IV) (cis-4) was synthesized by
treatment of 1 with two molar equivalents of acetylacetone.
Compounds 1, 2, 3·2CH CN, and cis-4 were isolated as
crystalline solids (yield: 1, 65 %; 2, 71 %; 3·2CH CN, 80 %;
cis-4, 77 %). Their identities were established by elemental
molecule completing the coordination sphere of the potass-
ium cation (Figure 5).
The neutral complex cis-4 crystallizes in the space group
3
3
P2 /c,
with
SiϪO
distances
in
the
range
1
˚
.7716(13)Ϫ1.7843(13) A and SiϪN distances of
1
1
analyses, NMR studies, and crystal structure analyses.
˚
˚
.8093(17) A and 1.8145(16) A. The Si-coordination poly-
hedron is a slightly distorted octahedron, with NϪSiϪN,
NϪSiϪO, and OϪSiϪO angles in the ranges
Crystal Structure Analyses
8
7.13(6)Ϫ94.05(6)°
and
177.00(7)Ϫ178.69(6)°.
The
The crystal structures of compounds 1, 2, 3·2CH CN, and
cis-4 were determined by single-crystal X-ray diffraction.
3
SiϪNϪC angles amount to 167.43(16)° and 173.01(16)°.
Comparison of the bonding situation in the NCS groups
of compound 1 (tetracoordination) and compounds 2,
3
·2CH CN, and cis-4 (hexacoordination) reveals significant
3
differences. As can be seen from Table 2, the NϪC distances
of 1 are longer than those of the hexacoordinate silicon
complexes, whereas the CϪS distances of 1 are shorter than
those of 2, 3·2CH CN, and cis-4.
3
NMR Studies
Compounds 1, 2, 3·2CH CN, and cis-4 were characterized
3
by solid-state 29Si NMR spectroscopy (1: single pulse MAS
NMR; 2, 3·2CH CN, and cis-4: VACP/MAS NMR). Com-
3
pounds 2, 3·2CH CN, and cis-4 were also studied by solid-
3
state 13C VACP/MAS NMR experiments, and cis-4 was ad-
15
ditionally characterized by N VACP/MAS NMR spec-
troscopy. All the NMR experiments were performed at
2
2 °C. The isotropic 29Si chemical shift of the tetracoordi-
nate silicon compound 1 (δ ϭ Ϫ143.2) and of the hexacoor-
dinate silicon compounds 2 (δ ϭ Ϫ256.5), 3·2CH CN (δ ϭ
3
Ϫ253.0), and cis-4 (δ ϭ Ϫ210.2) indicate that the thio-
cyanato-N ligand causes a significant high-field shift of the
2
9
29
Si resonance. As shown in Figure 6, all solid-state Si
NMR spectra are characterized by splitted resonance sig-
1
14 29
Scheme 1
nals due to J( N, Si) couplings.
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 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411

Hexacoordinate Silicon(IV) Complexes Containing Thiocyanato-N Ligands
3
Table 1 Crystal data and experimental parameters for the crystal structure analyses of 1, 2, 3·2CH CN, and cis-4
Compound
1
2
3·2CH
3
CN
cis-4
Empirical formula
Formula mass/g mol
Collection T/K
λ(MoKα)/A
Crystal system
C
260.41
173(2)
0.71073
tetragonal
4
N
4
S
4
Si
C
637.07
173(2)
0.71073
tetragonal
P4 /m (84)
10.3565(15)
10.3565(15)
15.369(3)
90
22
H
40
N
8
S
6
Si
C
34
H
54
K
2
N
8
O
12
S
6
Si
12 14 2 4 2
C H N O S Si
342.46
173(2)
Ϫ1
1065.50
173(2)
0.71073
orthorhombic
Fdd2 (43)
25.814(5)
29.830(6)
13.842(3)
90
˚
0.71073
monoclinic
P2 /c (14)
Space group (no.)
I4
1
/a (88)
2
1
˚
a/A
15.0280(13)
15.0280(13)
18.634(2)
90
4208.3(7)
16
14.463(2)
8.2446(8)
13.785(2)
98.205(18)
1626.9(4)
4
˚
b/A
˚
c/A
β/°
˚
3
V/A
1648.5(5)
2
1.283
10659(4)
8
1.328
Z
Ϫ3
D(calcd)/g cm
µ/mm
1.644
0.974
1.398
0.415
Ϫ1
0.478
0.493
F(000)
Crystal dimensions/mm
2080
676
4464
0.8 x 0.8 x 0.6
4.18Ϫ49.44
Ϫ30 Յ h Յ 30,
Ϫ35 Յ k Յ 35,
Ϫ16 Յ l Յ 16
32792
712
0.5 x 0.5 x 0.5
5.42Ϫ52.76
Ϫ18 Յ h Յ 18,
Ϫ18 Յ k Յ 18,
Ϫ23 Յ l Յ 23
23370
0.5 x 0.4 x 0.3
4.74Ϫ49.42
Ϫ12 Յ h Յ 12,
Ϫ12 Յ k Յ 12,
Ϫ18 Յ l Յ 18
13766
0.5 x 0.3 x 0.2
5.70Ϫ54.00
Ϫ18 Յ h Յ 18,
Ϫ10 Յ k Յ 10,
Ϫ17 Յ l Յ 17
16747
2
θ Range/°
Index ranges
Collected reflections
Independent reflections
2148
0.0771
1467
0.0430
4536
0.0513
3514
0.0624
R
int
Reflections used
Parameters
2148
118
0
1.034
0.0386/2.4795
0.0284
0.0779
ϩ0.181/Ϫ0.266
1467
98
0
1.013
0.0393/0.1215
0.0262
0.0671
ϩ0.171/Ϫ0.143
4536
286
1
1.032
0.0375/3.0440
0.0228
0.0578
ϩ0.142/Ϫ0.128
0.01(3)
3514
194
0
1.077
0.0658/0.9351
0.0455
0.1259
ϩ0.905/Ϫ0.717
Restraints
a)
S
b)
Weight parameters a/b
c)
R1 [I > 2σ(I)]
d)
wR2 (all data)
˚
Ϫ3
Max./min. residual electron density/e A
Absolute structure parameter
a)
2
2
2 2
0.5
S ϭ {Σ[w(F
o
Ϫ F
) ϩ (aP) ϩ bP, with P ϭ [max(F
ʈ/ΣΗF Η.
c
) ]/(n Ϫ p)} ; n ϭ no. of reflections; p ϭ no. of parameters.
b) Ϫ1
2
2
2
2
w
ϭ σ (F
o
o
c
,0) ϩ 2F ]/3.
c)
R1 ϭ ΣʈF
o
Η Ϫ ΗF
wR2 ϭ {Σ[w(F
c
2
o
d)
2 2
2)2]}0.5.
Ϫ F ) ]/Σ[w(F
o c o
Compound cis-4 was also studied by H, 13C, and 29Si
1
observed by H, 13C, and 29Si NMR spectroscopy. The ki-
1
1
1
NMR experiments in solution (CDCl , 22 °C) [9]. The H
and C NMR spectra of a freshly prepared solution are
compatible with the cis-structure. The C and Si chemical
shifts of cis-4 are very similar to the respective isotropic
chemical shifts in the solid-state NMR spectra. Upon dis-
netics of this process were studied by H NMR spec-
troscopy. As shown in Figure 7, after a period of 20 hours
an equilibrium cis/trans ratio of 1.5:1 was observed. This
3
1
3
1
3
29
solution of cis-4 in CDCl , a cis/trans isomerization was
3
Fig. 1 Molecular structure of 1 in the crystal (probability level of
Fig. 2 Structure of the dianion in the crystal of 2 (probability
displacement ellipsoids 50 %).
level of displacement ellipsoids 50 %).
Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411
zaac.wiley-vch.de
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1405

O. Seiler, R. Bertermann, N. Buggisch, C. Burschka, M. Penka, D. Tebbe, R. Tacke
˚
3
Table 2 Selected interatomic distances/A and angles/° for 1, 2, 3·2CH CN, and cis-4
1
2
3·2CH
3
CN
cis-4
SiϪN1
SiϪN2
SiϪN3
SiϪN4
N1ϪC1
N2ϪC2
N3ϪC3
N4ϪC4
C1ϪS1
C2ϪS2
C3ϪS3
C4ϪS4
N1ϪSiϪN2
N1ϪSiϪN3
N1ϪSiϪN4
N2ϪSiϪN3
N2ϪSiϪN4
N3ϪSiϪN4
SiϪN1ϪC1
SiϪN2ϪC2
SiϪN3ϪC3
SiϪN4ϪC4
N1ϪC1ϪS1
N2ϪC2ϪS2
N3ϪC3ϪS3
N4ϪC4ϪS4
1.6831(15)
1.6788(14)
1.6779(14)
1.6745(14)
1.182(2)
1.183(2)
1.185(2)
SiϪN1
SiϪN2
SiϪN3
N1ϪC1
N2ϪC2
N3ϪC3
C1ϪS1
C2ϪS2
1.823(2)
1.822(2)
1.832(2)
1.166(3)
1.167(3)
1.166(3)
1.593(3)
1.600(3)
1.602(3)
SiϪN1
SiϪN2
SiϪN3
N1ϪC1
N2ϪC2
N3ϪC3
C1ϪS1
C2ϪS2
C3ϪS3
N1ϪSiϪN1A
N1ϪSiϪN2
N1ϪSiϪN2A
N1ϪSiϪN3
N1ϪSiϪN3A
N1AϪSiϪN2
N1AϪSiϪN2A
N1AϪSiϪN3
N1AϪSiϪN3A
N2ϪSiϪN2A
N2ϪSiϪN3
N2ϪSiϪN3A
N2AϪSiϪN3
N2AϪSiϪN3A
N3ϪSiϪN3A
SiϪN1ϪC1
SiϪN2ϪC2
SiϪN3ϪC3
N1ϪC1ϪS1
N2ϪC2ϪS2
N3ϪC3ϪS3
1.8369(17)
1.8294(17)
1.8167(15)
1.165(2)
1.170(2)
1.162(2)
1.6057(19)
1.597(2)
1.594(2)
89.15(10)
90.74(7)
179.61(6)
90.40(7)
90.05(7)
179.61(8)
90.74(7)
90.05(7)
90.40(7)
89.36(11)
89.57(7)
89.97(7)
89.97(7)
89.57(7)
SiϪO1
SiϪO2
SiϪO3
SiϪO4
SiϪN1
SiϪN2
N1ϪC1
N2ϪC2
1.7816(14)
1.7716(13)
1.7843(13)
1.7729(13)
1.8093(17)
1.8145(16)
1.167(3)
1.168(2)
1.601(2)
1.6022(19)
93.30(6)
88.82(6)
87.28(6)
87.13(6)
178.69(6)
94.05(6)
177.54(7)
89.99(7)
88.96(7)
90.18(7)
90.34(7)
177.00(7)
90.47(7)
1.183(2)
1.5592(17)
1.5573(16)
1.5576(16)
1.5556(16)
C3ϪS3
C1ϪS1
C2ϪS2
N1ϪSiϪN1A
N1ϪSiϪN2
N1ϪSiϪN2A
N1ϪSiϪN3
N1ϪSiϪN3A
N1AϪSiϪN2
N1AϪSiϪN2A
N1AϪSiϪN3
N1AϪSiϪN3A
N2ϪSiϪN2A
N2ϪSiϪN3
N2ϪSiϪN3A
N2AϪSiϪN3
N2AϪSiϪN3A
N3ϪSiϪN3A
SiϪN1ϪC1
SiϪN2ϪC2
SiϪN3ϪC3
N1ϪC1ϪS1
N2ϪC2ϪS2
N3ϪC3ϪS3
180.0
89.41(9)
90.59(9)
90.0
O1ϪSiϪO2
O1ϪSiϪO3
O1ϪSiϪO4
O2ϪSiϪO3
O2ϪSiϪO4
O3ϪSiϪO4
O1ϪSiϪN1
O1ϪSiϪN2
O2ϪSiϪN1
O2ϪSiϪN2
O3ϪSiϪN1
O3ϪSiϪN2
O4ϪSiϪN1
O4ϪSiϪN2
N1ϪSiϪN2
SiϪN1ϪC1
SiϪN2ϪC2
N1ϪC1ϪS1
N2ϪC2ϪS2
109.64(7)
108.81(7)
109.42(7)
109.34(7)
109.94(7)
109.67(7)
174.74(15)
174.54(15)
176.22(14)
177.12(15)
179.77(18)
179.15(16)
179.17(16)
178.98(16)
90.0
90.59(9)
89.41(9)
90.0
90.0
180.0
90.0
90.0
90.0
90.0
180.0
179.37(12)
171.34(15)
160.34(15)
159.01(16)
179.62(16)
177.58(17)
177.30(17)
88.64(7)
90.97(8)
167.43(16)
173.01(16)
178.34(18)
178.71(17)
170.2(2)
173.40(19)
180.0
178.8(2)
178.5(2)
180.0
1
J( C, N) ϭ 24.9 Hz; Figure 9) were observed in the 13C
13 14
isomerization was also described in ref. [4]; however, some
of our NMR data differ significantly from those reported
in ref. [4]. One of the most striking differences concerns the
NMR spectrum of the cis/trans mixture (ref. [4]: one signal
for both isomers at δ ϭ 133.5).
2
9
Si NMR data of the cis/trans mixture (this study: cis-4:
δ ϭ Ϫ208.7; trans-4: δ ϭ Ϫ208.2 (Figure 8); ref. [4]: δ ϭ
Ϫ199.3 and Ϫ214.0). Furthermore, separated resonance
signals for the NCS groups of both isomers (cis-4: δ ϭ
Computational Studies
Geometry optimizations for 1, [Si(NCS)6]2Ϫ, cis-4, and
trans-4 were performed at the RI-MP2 level [10] using a
1
13 14
133.0, J( C, N) ϭ 26.3 Hz; trans-4: δ ϭ 134.7;
Fig. 3 Structure of the dianion in the crystal of 3·2CH
3
CN
Fig. 4 Molecular structure of cis-4 in the crystal (probability level
(probability level of displacement ellipsoids 50 %).
of displacement ellipsoids 50 %).
1406
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411

Hexacoordinate Silicon(IV) Complexes Containing Thiocyanato-N Ligands
Fig. 5 Interaction of the [K(18-crown-6)] cations with the
2Ϫ
[Si(NCS)
6
]
3
dianion and the CH CN molecules in the crystal of
3
·2CH CN.
3
1
29
Fig. 8 Partial H, Si COSY NMR spectrum of a mixture of cis-
1
4
and trans-4 in CDCl
3
at 22 °C
,
showing the correlating H signals
2
9
(CH groups) and Si signals of cis-4 and trans-4.
3
Fig. 6 Solid-state 29Si MAS NMR spectra of 1 (a), 2 (b),
·2CH CN (c), and cis-4 (d) showing the splittings due to the
J( N, Si) couplings.
Fig. 9 Partial 13C NMR spectrum of a mixture of cis-4 and trans-
in CDCl at 22 °C showing the NCS resonance signals of cis-4
higher field) and trans-4 (lower field) as tripletts due to the
3
3
4
3
,
1
14 29
(
1
13 14
J( C, N) couplings.
TZP basis set [11] and a TZVP auxiliary basis for the fit of
the charge density [12]. The calculations were performed
starting from Td symmetry (1), Oh symmetry
Ϫ
[Si(NCS)]62 ), C symmetry (cis-4), or C symmetry (trans-
(
2
i
4) using the TURBOMOLE program system [13]. The
structures of the respective calculated minima are shown in
Figures 10Ϫ13, with selected calculated distances and
angles in the respective figure captions. As can be seen from
Figures 10Ϫ12, the calculated and experimentally estab-
lished structures are in reasonable agreement [14]. The ex-
perimental SiϪNϪC angles vary from 180° (symmetry axis
in the case of 2) to 159.01(16)° (SiϪN3ϪC3 for
3
·2CH CN). As shown by additional computational studies
3
2Ϫ
of the [Si(NCS)6] dianion (geometry optimization for CS
symmetry; Figure 14), this variability of the SiϪNϪC angle
can be explained by intermolecular interactions in the crys-
tal: when all six SiϪNϪC angles are artificially bent to 160°
(the resulting structure does not represent a local mini-
Fig. 7 Kinetics of the cis/trans isomerization of 4, starting from a
Ϫ1
3
solution of cis-4 in CDCl (25 mg mL ). The kinetics were moni-
1
tored at 22 °C by H NMR spectroscopy, using the methyl reso-
nance signals of cis-4 and trans-4 as the probe. After a period of
Ϫ1
20 h, an equilibrium cis/trans ratio of 1.5 : 1 was observed.
mum), an energy increase of only 8.8 kJ mol arises which
Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411
zaac.wiley-vch.de
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1407

O. Seiler, R. Bertermann, N. Buggisch, C. Burschka, M. Penka, D. Tebbe, R. Tacke
Fig. 10 Calculated structure of 1 (T
lengths/A and angles/°:
d
symmetry); selected bond
˚
SiϪN 1.698, NϪC 1.204, CϪS 1.569, NϪSiϪN 109.5, SiϪNϪC 180.0,
2
9
NϪCϪS 180.0. Calculated Si NMR shift for this structure: δ ϭ Ϫ141.
Fig. 12 Calculated structure of cis-4 (C
lengths/A and angles/°:
2
symmetry); selected bond
˚
SiϪO1 1.822, SiϪO2 1.802, SiϪN 1.800, NϪC 1.197, CϪS 1.593,
O1ϪSiϪO2 91.4, O1ϪSiϪO1A 86.3, O1ϪSiϪO2A 86.4, O1ϪSiϪN 176.3,
O1ϪSiϪNA 90.2, O2ϪSiϪO2A 176.9, O2ϪSiϪN 89.6, O2ϪSiϪNA 92.5,
2
9
NϪSiϪNA 93.3, SiϪNϪC 150.7, NϪCϪS 179.2. Calculated Si NMR shift
for this structure: δ ϭ Ϫ199.
Fig. 11 Calculated structure of the [Si(NCS)
metry); selected bond lengths/A and angles/°:
6
]2Ϫ dianion (O
h
sym-
˚
SiϪN 1.833, NϪC 1.187, CϪS 1.613, NϪSiϪN 90.0/180.0, SiϪNϪC 180.0,
2
9
NϪCϪS 180.0. Calculated Si NMR shift for this structure: δ ϭ Ϫ251.
can be easily compensated by packing effects in the crystal.
2
9
The isotropic Si chemical shifts determined experimen-
tally for 1, 2, 3·2CH CN, cis-4, and trans-4 were also accu-
3
Fig. 13 Calculated structure of trans-4 (C
bond lengths/A and angles/°:
SiϪO1 1.804, SiϪO2 1.801, SiϪN 1.815, NϪC 1.198, CϪS 1.594,
O1ϪSiϪO2 93.3, O1ϪSiϪO1A 180.0, O1ϪSiϪO2A 86.7, O1ϪSiϪN 90.3,
O1ϪSiϪNA 89.7, O2ϪSiϪO2A 180.0, O2ϪSiϪN 90.4, O2ϪSiϪNA 89.6,
NϪSiϪNA 180.0, SiϪNϪC 150.0, NϪCϪS 179.2. Calculated Si NMR
shift for this structure: δ ϭ Ϫ201.
i
symmetry); selected
rately reproduced by quantum-chemical calculations (see
captions of Figures 10Ϫ13). These studies were carried out
at the HF/TZP level.
˚
The calculated relative energies of the cis- and trans-iso-
2
9
Ϫ1
mers of 4 differ only by 1.8 kJ mol , the cis-isomer being
energetically more stable than the trans-isomer. The molar
equilibrium ratio determined by NMR spectroscopy (cis/
Experimental Section
trans ratio in CDCl at 22 °C ca. 1.5:1) is in good agreement
3
with the calculated energy difference between cis-4 and
trans-4.
General Procedures. All syntheses were carried out under dry nitro-
gen. The organic solvents used were dried and purified according
1408
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411

Hexacoordinate Silicon(IV) Complexes Containing Thiocyanato-N Ligands
hydrofuran (20 mL) was heated under reflux for 3 h. After the mix-
ture was cooled to 20 °C, the precipitate was filtered off and dis-
carded, and the filtrate was concentrated to ca. 5 mL and then kept
at Ϫ20 °C for 24 h. The resulting precipitate was isolated by fil-
tration, washed with n-pentane (10 mL), and dried in vacuo
(
0.01 mbar, 20 °C, 2 h) to give 1.30 g (yield: 71 %) of a colorless
crystalline product. Mp. 76 °C
C
22
H
40
N
8
S
6
Si (637.1 g molϪ1
Analyses: C 41.6 (calc. 41.48); H 6.3 (6.33); N 17.8 (17.59); S 29.9
30.20) %.
)
(
13C
27.3Ϫ131.5 (NCS) [15]. Ϫ Si VACP/MAS NMR: δ ϭ Ϫ256.5.
2 3 2 3
VACP/MAS NMR: δ ϭ 8.7 (NCH CH ), 52.5 (NCH CH ),
2
9
1
Potassium-18-crown-6 Hexa(thiocyanato-N)silicate-Diacetonitrile
3). A mixture of 1 (938 mg, 3.60 mmol), potassium thiocyanate
700 mg, 7.20 mmol), 18-crown-6 (1.90 g, 7.19 mmol), and aceto-
(
(
nitrile (20 mL) was heated under reflux for 3 h. After the mixture
was cooled to 20 °C, the precipitate was filtered off and discarded,
and the filtrate was kept at Ϫ20 °C for 24 h. The resulting precipi-
tate was isolated by filtration, washed with n-pentane (10 mL), and
dried in vacuo (0.01 mbar, 20 °C, 2 h) to give 3.08 g (yield 80 %) of
a colorless crystalline product. Mp. 232 °C (dec.)
Fig. 14 Calculated structure of the “bentЉ [Si(NCS)
6
]2Ϫ dianion
˚
(C
s
symmetry); selected bond lengths/A and angles/°:
SiϪN 1.836Ϫ1.844, NϪC 1.188Ϫ1.190, CϪS 1.610Ϫ1.614, NϪSiϪN
8
9.3Ϫ90.7/178.6Ϫ179.9, SiϪNϪC 160.0, NϪCϪS 177.5Ϫ177.9. Calculated
Si NMR shift for this structure: δ ϭ Ϫ246.
2
9
C
34
H
54
K
2
N
8
O
12
S
6
Si (1065.5 g molϪ1
Analyses: C 38.5 (calc. 38.33); H 5.0 (5.11); N 10.4 (10.52); S 17.9
18.06) %.
)
(
to standard procedures and stored under nitrogen. Melting points
were determined with a Büchi Melting Point B-540 apparatus using
samples in sealed capillaries. The H, C, and Si solution NMR
13C VACP/MAS NMR: δ ϭ 2.1 (CH
3
2 3
CN), 71.2 (OCH C), 117.3 (CH CN),
29
1
13
29
1
26.7 (NCS), 131.1 (NCS), 132.1 (NCS) [15]. Ϫ Si VACP/MAS NMR:
spectra were recorded at 22 °C on a Bruker DRX-300 NMR spec-
δ ϭ Ϫ253.0.
1
13
29
trometer ( H, 300.1 MHz; C, 75.5 MHz; Si, 59.6 MHz) using
CDCl as the solvent. Chemical shifts (ppm) were determined rela-
tive to internal CHCl
7.00), or external TMS ( Si, δ ϭ 0). Assignment of the C NMR
data was supported by DEPT 135 experiments. Assignment of the
3
cis-Bis[acetylacetonato-O,O]di(thiocyanato-N)silicon(IV) (cis-4).
Acetylacetone (1.37 g, 13.7 mmol) was added at 20 °C to a stirred
solution of 1 (1.79 g, 6.87 mmol) in tetrahydrofuran (20 mL). After
the mixture was stirred at 20 °C for 1 h, n-pentane (20 mL) was
added, and the resulting mixture was kept undisturbed at 20 °C for
2 days. The resulting precipitate was isolated by filtration, washed
with n-pentane (10 mL), and dried in vacuo (0.01 mbar, 20 °C, 2 h)
to give 1.82 g (yield 77 %) of a colorless crystalline product. Mp.
180 °C (dec.)
1
13
3
3
( H, δ ϭ 7.24), internal CDCl ( C, δ ϭ
2
9
13
7
2
9
1
29
Si NMR data of cis-4 and trans-4 was supported by H, Si
COSY experiments. Solid-state 13C, N, and Si VACP/MAS
15
29
NMR spectra were recorded at 22 °C on a Bruker DSX-400 NMR
spectrometer with bottom layer rotors of ZrO (diameter 7 mm)
2
1
3
15
containing ca. 300 mg of sample ( C, 100.6 MHz; N, 40.6 MHz;
29
13
29
Si, 79.5 MHz; external standard, TMS ( C, Si; δ ϭ 0) or glycine
N, δ ϭ Ϫ342.0); spinning rate, 5Ϫ7 kHz; contact time, 1Ϫ8 ms
(1
(
5
3
C
12
H
14
N
2
O
4
S
2
Si (342.5)
1
15
29
1
C), 3 ms ( N), or 5Ϫ8 ms ( Si); 90° H transmitter pulse length,
Analyses: C 42.1 (calc. 42.09); H 4.2 (4.12); N 8.2 (8.18); S 18.4
3
.6 µs; repetition time, 4 s). Solid-state 29Si single-pulse MAS NMR
(
18.73) %.
spectra were recorded at 22 °C on a Bruker DSX-400 NMR spec-
trometer with bottom layer rotors of ZrO (diameter 7 mm) con-
taining ca. 300 mg of sample (79.5 MHz; external standard, TMS
1
2
H NMR (CDCl ): δ ϭ 2.10 (s, 6 H, CH ), 2.24 (s, 6 H, CH ), 5.86 (s, 2 H,
3
3
3
1
3
CH). Ϫ C NMR (CDCl
3
): δ ϭ 25.7 (CH
3
), 25.9 (CH
3
), 102.89 (CH), 133.0
(t, J(13C,14N) ϭ 26.3 Hz , NCS), 191.9 (CO), 193.1 (CO). Ϫ Si NMR
1
29
29
(δ ϭ 0); spinning rate, 5 kHz; Si transmitter pulse length, 4 µs;
13
(
2
(
CDCl
7.3 (CH
CO), 194.3 (CO), 194.9 (CO). Ϫ N VACP/MAS NMR: δ ϭ Ϫ233.5 and
3
): δ ϭ Ϫ208.7. Ϫ C VACP/MAS NMR: δ ϭ 26.3 (CH
3 3
), 27.1 (CH ),
repetition time, 120 s).
3
), 103.2 (CH), 106.0 (CH), 131.4 (NCS), 132.8 (NCS) [15], 193.0
1
5
Tetra(thiocyanato-N)silane (1). The synthesis of 1 was carried out
analogously to ref. [3] by reaction of tetrachlorosilane (8.37 g,
2
9
1
14 29
Ϫ230.8. Ϫ Si VACP/MAS NMR: δ ϭ Ϫ210.2 (quint., J( N, Si) ϭ 29.3
and 32.4 Hz ).
49.3 mmol) with ammonium thiocyanate (15.0 g, 197 mmol), using
1
Solution NMR data of trans-4: H NMR (CDCl
3
): δ ϭ 2.21 (s, 12 H, CH
3
),
toluene instead of benzene as the solvent. Yield: 8.32 g (65 %) of a
colorless crystalline solid. Mp. 145 °C.
Si (260.4 g molϪ1
C N S )
4 4 4
13
5
.86 (s, 2 H, CH). Ϫ C NMR (CDCl
3
): δ ϭ 25.8 (CH ), 102.93 (CH),
3
1
13 14
29
134.7 (t, J( C, N) ϭ 24.9 Hz , NCS), 192.8 (CO). Ϫ Si NMR (CDCl3):
δ ϭ Ϫ208.2.
Analyses: C 18.8 (calc. 18.45); N 21.1 (21.51) %.
29Si MAS NMR: δ ϭ Ϫ143.2.
Single-Crystal X-Ray Diffraction Studies. A suitable single crystal
of 1 was obtained directly from the reaction mixture. Suitable single
Tetraethylammonium Hexa(thiocyanato-N)silicate (2). A mixture
of 1 (750 mg, 2.88 mmol), tetraethylammonium chloride (954 mg,
crystals of 2, 3·2CH
crystallization from THF at Ϫ20 °C; 3·2CH
from acetonitrile (cooling of a saturated solution from 20 °C to
3
CN, and cis-4 were obtained as follows: 2,
3
CN, crystallization
5.76 mmol), potassium thiocyanate (560 mg, 5.76 mmol), and tetra-
Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411
zaac.wiley-vch.de
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1409

O. Seiler, R. Bertermann, N. Buggisch, C. Burschka, M. Penka, D. Tebbe, R. Tacke
Ϫ20 °C); cis-4, crystallization from THF/n-pentane (1:1 (v:v)) at
0 °C. The crystals were mounted in inert oil (perfluoroalkyl ether,
ABCR) on a glass fiber and then transferred to the cold nitrogen
[5] Recent publications dealing with compounds of higher-coordi-
nate silicon: (a) R. Tacke, M. Penka, F. Popp, I. Richter, Eur.
J. Inorg. Chem. 2002, 1025. (b) A. Biller, C. Burschka, M.
Penka, R. Tacke, Inorg. Chem. 2002, 41, 3901. (c) I. Richter,
M. Penka, R. Tacke, Inorg. Chem. 2002, 41, 3950. (d) I.
Richter, M. Penka, R. Tacke, Organometallics 2002, 21, 3050.
(e) O. Seiler, C. Burschka, M. Penka, R. Tacke, Z. Anorg. Allg.
Chem. 2002, 628, 2427. (f) O. Seiler, C. Burschka, M. Penka,
R. Tacke, Silicon Chemistry, in press. (g) R. Tacke, R. Berterm-
ann, A. Biller, C. Burschka, M. Penka, Can. J. Chem., submit-
ted. (h) R. Bertermann, A. Biller, M. Kaupp, M. Penka, O.
Seiler, R. Tacke, Organometallics, submitted.
2
gas stream of the diffractometer (Stoe IPDS diffractometer; graph-
˚
ite-monochromated MoK
α
radiation, λ ϭ 0.71073 A). The struc-
3
tures were solved by direct methods (1, ref. [16a]; 2, 3·2CH CN,
and cis-4, ref. [16b]). The non-hydrogen atoms were refined aniso-
tropically [17]. A riding model was employed in the refinement of
the CH hydrogen atoms. Crystallographic data (excluding structure
factors) for the structures reported in this paper have been de-
posited with the Cambridge Crystallographic Data Centre as sup-
plementary publication nos. CCDC-206855 (1), CCDC-206856 (2),
CCDC-206857 (3·2CH
the data can be obtained free of charge on application to CCDC,
3
CN), and CCDC-206858 (cis-4). Copies of
[6] Selected reviews dealing with compounds of higher-coordinate
silicon: (a) S. N. Tandura, M. G. Voronkov, N. V. Alekseev,
Top. Curr. Chem. 1986, 131, 99. (b) W. S. Sheldrick, in: The
Chemistry of Organic Silicon Compounds, Part 1, S. Patai, Z.
Rappoport (eds.), Wiley, Chichester, U.K., 1989, pp. 227Ϫ303.
12 Union Road, Cambridge CB2 1EZ, UK (fax: (ϩ44) 1223/
336033; e-mail: deposit@ccdc.cam.ac.uk).
(
c) A. R. Bassindale, P. G. Taylor, in: The Chemistry of Organic
Computational Studies. RI-MP2 [10] geometry optimizations of 1,
2Ϫ
Silicon Compounds, Part 1, S. Patai, Z. Rappoport (eds.),
Wiley, Chichester, U.K., 1989, pp. 839Ϫ892. (d) R. J. P. Corriu,
J. C. Young, in: The Chemistry of Organic Silicon Compounds,
Part 2, S. Patai, Z. Rappoport (eds.), Wiley, Chichester, U.K.,
1989, pp. 1241Ϫ1288. (e) R. R. Holmes, Chem. Rev. 1990, 90,
[Si(NCS)
6
]
, cis-4, and trans-4 were carried out at the TZP level
(with a TZVP auxiliary basis for the fit of the charge density)
[11,12] using the TURBOMOLE program system [13]. The calcu-
lations were performed starting from the following symmetries: T
d
2Ϫ
2Ϫ
(
(
(
1), O
h 6 s 6 2 i
([Si(NCS) ] ), C (“bent” [Si(NCS) ] ), C (cis-4), and C
1
7. (f) C. Chuit, R. J. P. Corriu, C. Reye, J. C. Young, Chem.
trans-4). The optimized structures were characterized as minima
the “bent” [Si(NCS)
2Ϫ
Rev. 1993, 93, 1371. (g) R. Tacke, J. Becht, A. Lopez-Mras, J.
Sperlich, J. Organomet. Chem. 1993, 446, 1. (h) J. G. Verkade,
Coord. Chem. Rev. 1994, 137, 233. (i) R. Tacke, O. Dannappel,
in: Tailor-made Silicon-Oxygen Compounds Ϫ From Molecules
to Materials, R. Corriu, P. Jutzi (eds.), Vieweg, Braunschweig-
Wiesbaden, Germany, 1996, pp. 75Ϫ86. (j) E. Lukevics, O. A.
Pudova, Chem. Heterocycl. Compd. (Engl. Transl.) 1996, 32,
6
]
dianion is not a minimum because the
SiϪNϪC angles were fixed during the optimization) on the poten-
tial energy surfaces by harmonic vibrational frequency analysis.
The calculations of the 29Si NMR chemical shifts for the optimized
2Ϫ
6
structures of 1, [Si(NCS) ] , cis-4, and trans-4 were carried out at
the HF/TZP level using the module mpshift implemented in TUR-
BOMOLE. Computed absolute shieldings (σ) were converted to
relative shifts (δ) using the shielding of TMS (399.4 ppm), com-
puted at the same theoretical level. The reported energy differences
include the MP2 and zero-point vibrational energies obtained by
HF calculations.
1
381. (k) R. R. Holmes, Chem. Rev. 1996, 96, 927. (l) D. Kost,
I. Kalikhman, in: The Chemistry of Organic Silicon Com-
pounds, Vol. 2, Part 2, Z. Rappoport, Y. Apeloig (eds.), Wiley,
Chichester, U.K., 1998, pp. 1339Ϫ1445. (m) V. Pestunovich, S.
Kirpichenko, M. Voronkov, in: The Chemistry of Organic Sili-
con Compounds, Vol. 2, Part 2, Z. Rappoport, Y. Apeloig
Acknowledgment. We thank the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie for financial support.
(
eds.), Wiley, Chichester, U.K., 1998, pp. 1447Ϫ1537. (n) C.
Chuit, R. J. P Corriu, C. Reye, in: Chemistry of Hypervalent
Compounds, K. Akiba (ed.), Wiley-VCH, New York, 1999, pp.
81Ϫ146. (o) R. Tacke, M. Pülm, B. Wagner, Adv. Organomet.
Chem. 1999, 44, 221. (p) M. A. Brook, Silicon in Organic, Or-
ganometallic, and Polymer Chemistry, Wiley, New York, 2000,
pp. 97Ϫ114.
References and Notes
[1] Recent review dealing with penta- and hexacoordinate sili-
con(IV) complexes with SiO and SiO skeletons: R. Tacke,
5
6
[7] O. Seiler, N. Buggisch, M. Penka, R. Tacke, XIII International
Symposium on Organosilicon Chemistry Ϫ 35th Organosilicon
Symposium, Guanajuato, Mexico, August 25Ϫ30, 2002, Ab-
stracts Book, Abstract P2-45, p. 161.
O. Seiler, in: Silicon Chemistry: From Molecules to Extended
Systems, P. Jutzi, U. Schubert (eds.), Wiley-VCH, Weinheim,
in press.
[
2] Publications dealing with hexacoordinate silicon(IV) com-
[8] The quality of the crystal structure analysis described in this
paper is significantly better than that reported in ref. [2b].
[9] Attempts to obtain solution NMR spectra of 1 and the
6
plexes with SiN skeletons: (a) E. Bär, W. P. Fehlhammer, D.
K. Breitinger, J. Mink, Inorg. Chim. Acta 1984, 82, L17. (b)
W. Heininger, R. Stucka, G. Nagorsen, Z. Naturforsch. 1986,
2
Ϫ
[Si(NCS)
6
]
3
dianion of 2 and 3·2CH CN were unsuccessful.
4
1b, 702. (c) W. Heininger, K. Polborn, G. Nagorsen, Z. Na-
[10] (a) F. Weigend, M. Häser, Theor. Chem. Acc. 1997, 97, 331.
(b) F. Weigend, M. Häser, H. Patzelt, R. Ahlrichs, Chem. Phys.
Lett. 1998, 294, 143.
[11] A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97,
2571.
turforsch. 1988, 43b, 857. (d) M. Fritz, D. Rieger, E. Bär, G.
Beck, J. Fuchs, G. Holzmann, W. P. Fehlhammer, Inorg. Chim
Acta 1992, 198Ϫ200, 513. (e) A. C. Filippou, P. Portius, G.
Schnakenburg, J. Am. Chem. Soc. 2002, 124, 12396.
[
[
3] Synthesis of 1: R. G. Neville, J. J. McGee, in: Inorganic Syn-
theses, Vol. VIII, H. F. Holtzclaw, Jr. (ed.), McGraw-Hill, New
York, 1966, pp. 27Ϫ31.
4] Alternative synthesis and solution NMR studies of 4: S. P.
Narula, R. Shankar, B. Kaur, S. Soni, Polyhedron 1991, 10,
[12] A. Schäfer, C. Huber, R. Ahlrichs, J. Chem. Phys. 1994, 100,
5829.
[13] Program system TURBOMOLE: R. Ahlrichs, M. Bär, M.
Häser, H. Horn, C. Kölmel, Chem. Phys. Lett. 1989, 162, 165.
[14] A perfect agreement between the calculated and experimen-
2
Ϫ
2463.
tally established structures of 1, [Si(NCS)
6
] , and cis-4 cannot
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Hexacoordinate Silicon(IV) Complexes Containing Thiocyanato-N Ligands
be expected since the latter are influenced by intermolecular
interactions in the crystal.
Bari, Bari, Italy, 1997. A. Altomare, G. Cascarano, G. Giacov-
azzo, A. Guagliardi, M. C. Burla, G. Polidori, M. Camalli, J.
Appl. Cryst. 1994, 27, 435. (b) G. M. Sheldrick, SHELXS-97,
University of Göttingen, Göttingen, Germany, 1997. G. M.
Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467.
1
13 14
[
15] The expected splittings due to the J( C, N) coupling of the
NCS carbon atoms were only poorly resolved because of the
low signal to noise ratio of the respective signals and the large
chemical shift anisotropy (CSA) of the NCS carbon atoms.
16] (a) A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi,
M. C. Burla, G. Polidori, M. Camalli, SIR97, University of
[17] G. M. Sheldrick, SHELXL-97, University of Göttingen,
Göttingen, Germany, 1997.
[
Z. Anorg. Allg. Chem. 2003, 629, 1403Ϫ1411
zaac.wiley-vch.de
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1411