Neutral pentacoordinate silicon(IV) complexes with a tridentate dianionic O,N,O or N,N,O ligand, an anionic PhX ligand (X = O, S, Se), and a phenyl group: Synthesis and structural characterization in the solid state and in solution

Article abstract of DOI:10.1002/zaac.201300523

A series of neutral pentacoordinate silicon(IV) complexes with a SiO ₃NC, SiO₂SNC, SiO₂SeNC, SiO₂N ₂C, SiOSN₂C, or SiOSeN₂C skeleton was synthesized and structurally characterized by multinuclear NMR spectroscopy in the solid state and in solution and by single-crystal X-ray diffraction. The compounds studied contain a tridentate dianionic O,N,O or N,N,O ligand, an anionic PhX ligand (X = O, S, Se), and a phenyl group. The structures, NMR spectroscopic parameters, and chemical properties of these silicon(IV) complexes were compared with those of related compounds that contain a tridentate dianionic S,N,O ligand instead of the O,N,O or N,N,O ligand. Copyright

Full text of DOI:10.1002/zaac.201300523

ARTICLE
DOI: 10.1002/zaac.201300523
Neutral Pentacoordinate Silicon(IV) Complexes with a Tridentate Dianionic
O,N,O or N,N,O Ligand, an Anionic PhX Ligand (X = O, S, Se), and a
Phenyl Group: Synthesis and Structural Characterization in the Solid State
and in Solution
Jörg Weiß,[a] Bastian Theis,[a] Johannes A. Baus,[a] Christian Burschka,[a]
Rüdiger Bertermann,[a] and Reinhold Tacke*[a]
Dedicated to Professor Werner Uhl on the Occasion of His 60th Birthday
Keywords: Chalcogens; Coordination chemistry; Pentacoordination; Silicon; Tridentate ligands
Abstract. A series of neutral pentacoordinate silicon(IV) complexes tridentate dianionic O,N,O or N,N,O ligand, an anionic PhX ligand
with
a
SiO3NC, SiO2SNC, SiO2SeNC, SiO2N2C, SiOSN2C, or
(X = O, S, Se), and a phenyl group. The structures, NMR spectroscopic
parameters, and chemical properties of these silicon(IV) complexes
were compared with those of related compounds that contain a triden-
SiOSeN2C skeleton was synthesized and structurally characterized by
multinuclear NMR spectroscopy in the solid state and in solution and
by single-crystal X-ray diffraction. The compounds studied contain a tate dianionic S,N,O ligand instead of the O,N,O or N,N,O ligand.
polyhedron; however, unlike 1a–g the oxygen and sulfur atoms
of the tridentate S,N,O ligand occupy the two axial positions.
Introduction
Recently, we have reported on the synthesis and characteri-
zation of the neutral pentacoordinate silicon(IV) complexes
1a–g.[1,2] These compounds contain a tridentate dianionic
S,N,O ligand, an (pseudo)halogeno ligand, and a phenyl group.
Formal replacement of the S,N,O ligand by an analogous
O,N,O or N,N,O ligand (formal S/O or S/NMe exchange) leads
to compounds 2a–g and 3a–g.[3,4] All these pentacoordinate
silicon(IV) complexes contain a distorted trigonal-bipyramidal
silicon coordination polyhedron, with the imino-nitrogen atom
of the tridentate ligand and the (pseudo)halogeno ligand in the
two axial positions.[5] Some of the respective S/O/NMe ana-
logues of the series 1–3 were found to differ significantly in
their chemical properties; i.e., replacement of the soft sulfur
ligand atom by a hard oxygen or nitrogen ligand atom strongly
affects the bonding characteristics at the silicon atom, which
could also be demonstrated by quantum-chemical studies.[4]
In context with our investigations on compounds 1a–g, we
have also synthesized and structurally characterized the related
neutral pentacoordinate silicon(IV) complexes 4b–d. Attempts
to prepare the oxygen analogue 4a failed; instead, the isomeric
tetracoordinate species 4aЈ was obtained.[6] Compounds 4b–d
contain a distorted trigonal-bipyramidal silicon coordination
In light of the different chemical properties observed for some
of the S/O/NMe analogues of series 1–3, we have now been
interested in the synthesis and characterization of the corre-
sponding O and NMe analogues of 4a–d, compounds 5a–d
and 6a–d, with a special focus on the comparison of the re-
spective S/O/NMe analogues (comparison between series
4–6). These studies were performed as part of our systematic
investigations on higher-coordinate silicon(IV) complexes.[7–9]
We report herein on the synthesis of compounds 5a–c and
6a–c and their structural characterization in the solid state
(crystal structure analyses and NMR spectroscopic studies) and
in solution (NMR spectroscopic studies) and the failed synthe-
sis of 5d and 6d.
* Prof. Dr. R. Tacke
Fax: +49-931-31-84609
E-Mail: r.tacke@uni-wuerzburg.de
[a] Institut für Anorganische Chemie
Universität Würzburg
Am Hubland
97074 Würzburg, Germany
300
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Neutral Pentacoordinate Silicon(IV) Complexes
Scheme 2. Synthesis of compounds 5b, 5c, 6b, and 6c.
Results and Discussion
yield). Compound 9 was obtained according to Scheme 3 by
reaction of N-methylbenzene-1,2-diamine with acetylacetone
(excess) in ethanol (73% yield).
Compounds 5a and 6a were synthesized according to
Scheme 1 by treatment of dichloro(phenoxy)phenylsilane (7)
with one molar equivalent of the O,N,O pre-ligand 8[10] or the
N,N,O pre-ligand 9 and two molar equivalents of triethyl-
amine. The syntheses were performed in tetrahydrofuran, and
the products were isolated after crystallization from aceto-
nitrile (yields: 5a 65% and 6a 68%).
Scheme 3. Synthesis of compounds 7 and 9.
Compounds 5a, 5b·CH3CN, 5c·CH3CN, 6a–c, and 9 were
isolated as crystalline solids, whereas 7 was obtained as a li-
quid. The identities of all these compounds were established
by elemental analyses (C, H, N, S) and multinuclear NMR
Scheme 1. Synthesis of compounds 5a and 6a.
Compounds 5b, 5c, 6b, and 6c were synthesized according spectroscopic studies in the solid state (15N, 29Si; except 7)
to Scheme 2 by reaction of the respective chlorosilicon(IV) and in solution (1H, 13C, 29Si, 77Se). In addition, compounds
complexes 2b and 3b with one molar equivalent of benz- 5a, 5b·CH3CN, 5c·CH3CN, and 6a–c were studied by crystal
enethiol or benzeneselenol and one molar equivalent of trieth- structure analyses.
ylamine. The syntheses were performed in tetrahydrofuran,
Compounds 5a, 5b·CH3CN, 5c·CH3CN, and 6a–c were
and the products were isolated after crystallization from aceto- structurally characterized by single-crystal X-ray diffraction.
nitrile (yields: 5b·CH3CN 54%, 5c·CH3CN 47%, 6b 72%, and The crystal data and experimental parameters used for the
6c 63%).
crystal structure analyses are given in Table 1. The molecular
All attempts to prepare the tellurium analogues 5d and 6d structures of 5a–c and 6a–c are shown in Figure 1, Figure 2,
analogously to the synthesis of 4d (treatment of 2b or 3b with Figure 3, Figure 4, Figure 5, and Figure 6, respectively. Se-
PhTeSiMe3) failed so far. Also, treatment of 2b or 3b with lected bond lengths and angles are given in the respective cap-
PhTeNa did not yield the target compounds 5d and 6d. The tions.
reasons for this are unclear.
The silicon coordination polyhedra of 5b and 5c (O,N,O)
Compound 7 was synthesized according to Scheme 3 by as well as 6b and 6c (N,N,O) are strongly distorted trigonal
treatment of trichloro(phenyl)silane with one molar equivalent bipyramids (Table 2), with the phenolato-oxygen or amido-
each of phenol and triethylamine in tetrahydrofuran (58% nitrogen atom and the enolato-oxygen atom in the two axial
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301

R. Tacke et al.
ARTICLE
Table 1. Crystallographic data for compounds 5a, 5b·CH3CN, 5c·CH3CN, and 6a–c.
5a
5b·CH3CN
5c·CH3CN
6a
6b
6c
Empirical formula
Mr
T /K
λ(Mo-Kα) /Å
Crystal system
Space group (no.)
a /Å
b /Å
C
23H21NO3Si
C25H24N2O2SSi
444.61
100(2)
0.71073
monoclinic
P21/c (14)
10.8288(3)
22.4627(5)
9.7599(2)
90
107.5170(10)
90
2263.95(9)
4
1.304
0.221
C25H24N2O2SeSi
491.51
193(2)
0.71073
monoclinic
P21/c (14)
11.0467(13)
22.488(4)
9.8776(11)
90
107.501(13)
90
2340.2(5)
4
1.395
1.680
C24H24N2O2Si
400.54
173(2)
C24H24N2OSSi
416.60
173(2)
0.71073
monoclinic
P21/c (14)
13.109(2)
10.9701(13)
14.690(2)
90
91.05(2)
90
2112.1(6)
4
1.310
0.228
C24H24N2OSeSi
463.50
173(2)
0.71073
monoclinic
P21/c (14)
13.195(3)
11.0155(15)
14.723(3)
90
90.36(2)
90
2139.8(7)
4
1.439
1.829
387.50
173(2)
0.71073
triclinic
0.71073
triclinic
¯
¯
P1 (2)
P1 (2)
10.297(3)
10.3614(19)
10.525(2)
106.55(2)
97.37(3)
111.39(3)
967.8(4)
2
7.7687(12)
11.560(2)
23.392(4)
100.18(2)
91.50(2)
95.28(2)
2056.9(6)
4
c /Å
α /°
β /°
γ /°
V /Å3
Z
ρcalcd. /g·cm–3
μ /mm–1
F(000)
1.330
0.146
408
1.293
0.137
848
936
1008
880
952
Crystal dimensions /mm 0.25ϫ0.2ϫ0.1
0.25ϫ0.15ϫ0.1
3.62–66.62
–16 Յ h Յ 16,
–34 Յ k Յ 34,
–15 Յ l Յ 14
142768
0.3ϫ0.3ϫ0.2
4.26–55.98
–14 Յ h Յ 14,
–29 Յ k Յ 29,
–12 Յ l Յ 12
30384
0.4ϫ0.4ϫ0.2
4.58–56.56
–10 Յ h Յ 10,
–14 Յ k Յ 15,
–31 Յ l Յ 31
20076
0.4ϫ0.2ϫ0.2
4.64–58.26
–17 Յ h Յ 17,
–15 Յ k Յ 14,
–20 Յ l Յ 19
29573
0.5ϫ0.4ϫ0.3
5.54–58.32
–18 Յ h Յ 18,
–14 Յ k Յ 14,
–20 Յ l Յ 20
23039
2 range /°
Index ranges
4.52–52.04
–12 Յ h Յ 12,
–12 Յ k Յ 12,
–12 Յ l Յ 12
7928
Reflns collected
Independent reflns
Rint
3568
0.0851
8680
0.0533
5552
0.0884
9452
0.0510
5608
0.0399
5683
0.0596
Restraints
0
255
0.848
0.0700/0.0000
0.0515
0
283
1.046
0.0518/0.8253
0.0340
0
283
0.947
0.0426/0.0000
0.0342
84
529
0.877
0.0485/0.0000
0.0404
0
265
1.066
0.0552/0.5987
0.0380
0
265
0.929
0.0545/0.0000
0.0347
Parameters
a)
S
b)
Weight parameters a/b
c)
R1 [I Ͼ 2σ(I)]
d)
wR2 (all data)
0.1363
0.0988
0.0822
0.1033
0.1031
0.0869
Max./min. residual elec- +0.327/–0.428
+0.600/–0.437
+0.542/–0.460
+0.350/–0.478
+0.370/–0.311
+0.608/–0.684
tron density /e·Å–3
2
2 2
2
2
a) S = {Σ[w(Fo – Fc ) ] / (n – p)}0.5; n = number of reflections; p = number of parameters. b) w–1 = σ2(Fo ) + (aP)2 + bP; P = [max(Fo ,0) +
2
2
2 2
2 2
2Fc ] / 3. c) R1 = ∑ ||Fo| – |Fc|| / Σ |Fo|. d) wR2 = {Σ [w(Fo – Fc ) ] / Σ [w(Fo ) ]}0.5
.
Figure 1. Molecular structure of 5a in the crystal (probability level of
Figure 2. Molecular structure of 5b in the crystal of 5b·CH3CN (prob-
displacement ellipsoids 50%). Selected bond lengths /Å and angles ability level of displacement ellipsoids 50%). Selected bond lengths
/°: Si–O1 1.680(2), Si–O2 1.679(2), Si–O3 1.687(2), Si–N 2.060(3), /Å and angles /°: Si–S 2.1694(3), Si–O1 1.7675(6), Si–O2 1.7668(6),
Si–C1 1.858(3); O1–Si–O2 132.59(13), O1–Si–O3 91.58(10), O1–Si–
N 87.77(10), O1–Si–C1 111.85(13), O2–Si–O3 87.43(11), O2–Si–N
81.72(10), O2–Si–C1 114.63(13), O3–Si–N 164.57(12), O3–Si–C1
102.32(12), N–Si–C1 92.20(12).
Si–N 1.8698(7), Si–C1 1.8838(8); S–Si–O1 93.71(2), S–Si–O2
83.29(2), S–Si–N 125.62(2), S–Si–C1 121.21(3), O1–Si–O2
170.13(3), O1–Si–N 89.12(3), O1–Si–C1 92.96(3), O2–Si–N 85.06(3),
O2–Si–C1 96.64(3), N–Si–C1 112.82(3).
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Neutral Pentacoordinate Silicon(IV) Complexes
Figure 3. Molecular structure of 5c in the crystal of 5c·CH3CN (prob-
ability level of displacement ellipsoids 50%). Selected bond lengths
/Å and angles /°: Si–Se 2.3097(7), Si–O1 1.7718(15), Si–O2
1.7699(15), Si–N 1.8738(17), Si–C1 1.893(2); Se–Si–O1 93.36(5), Se–
Si–O2 82.79(5), Se–Si–N 127.20(5), Se–Si–C1 120.44(6), O1–Si–O2
169.22(7), O1–Si–N 89.44(7), O1–Si–C1 93.60(8), O2–Si–N 84.96(7),
O2–Si–C1 97.03(8), N–Si–C1 111.95(8).
positions. The imino-nitrogen atom, the PhX ligand (X = S,
Se), and the phenyl group occupy the three equatorial posi-
tions. An analogous coordination mode was also observed for
the corresponding sulfur analogues 4b and 4c (S,N,O).[6] Quite
surprisingly, a totally different structure was observed for com-
pounds 5a (O,N,O) and 6a (N,N,O) with their PhO ligand. The
silicon coordination polyhedra of these two compounds are
also strongly distorted trigonal bipyramids (Table 2); however,
in these structures the two axial sites are occupied by the
imino-nitrogen atom of the tridentate O,N,O or N,N,O ligand
and the monodentate PhO ligand. I.e., replacement of the PhS
or PhSe ligand in 5b, 5c, 6b, and 6c (equatorial position) by a
PhO ligand (Ǟ 5a, 6a; axial position) changes the structure.
This phenomenon can be explained by the higher group elec-
tronegativity of the PhO ligand compared to the PhS and PhSe
ligands. This correlates with the structures of series 1–3, where
the strongly electron-withdrawing (pseudo)halogeno ligands
Figure 4. Molecular structures of the two crystallographically indepen-
dent molecules of 6a in the crystal (probability level of displacement
ellipsoids 50%). Selected bond lengths /Å and angles /° of molecule
A (top): Si1–O1 1.6999(15), Si1–O2 1.7181(14), Si1–N1 2.0637(16),
Si1–N2 1.7567(19), Si1–C1 1.8844(19); O1–Si1–O2 90.90(7), O1–
Si1–N1 87.77(7), O1–Si1–N2 127.36(8), O1–Si1–C1 111.50(9), O2–
Si1–N1 175.48(7), O2–Si1–N2 95.94(8), O2–Si1–C1 95.01(7), N1–
Si1–N2 81.48(7), N1–Si1–C1 89.50(7), N2–Si1–C1 119.70(9). Se-
also occupy an axial site.[1–4] The Berry distortions (transition lected bond lengths /Å and angles /° of molecule B (bottom): Si2–
trigonal bipyramid Ǟ square pyramid)[11] of 5a–c (O,N,O;
22.4–41.7%) are larger than those of the respective analogues
6a–c (N,N,O; 16.2–24.2%), and the Berry distortions of 4b
O21 1.6971(16), Si2–O22 1.7194(14), Si2–N21 2.0456(17), Si2–N22
1.7724(17), Si2–C31 1.877(2); O21–Si2–O22 90.53(7), O21–Si2–N21
87.84(7), O21–Si2–N22 127.29(8), O21–Si2–C31 114.48(8), O22–
Si2–N21 171.91(7), O22–Si2–N22 93.42(8), O22–Si2–C31 95.20(8),
and 4c (S,N,O) amount to 24.7–29.3%; i.e., the S/O/NMe ex-
change affects the degree of distortion of the trigonal-bipyram-
idal silicon coordination polyhedron.
N21–Si2–N22 81.32(7), N21–Si2–C31 92.68(8), N22–Si2–C31
117.42(9).
Contrary to the different degrees of distortion observed for
the respective S/O/NMe analogues (Table 2), replacement of
As can be seen from Table 4, the Si–N(imino) and Si–C
the tridentate S,N,O ligand of 4b and 4c by the analogous bond lengths of the respective S/O/NMe analogues 4b/5b/6b
O,N,O (Ǟ 5b, 5c) or N,N,O ligand (Ǟ 6b, 6c) only slightly and 4c/5c/6c are very similar, whereas the Si–O(enolato) bond
affects the Si–SPh and Si–SePh bond lengths (Table 3). In the distances of 6b/6c are slightly longer than those of 4b/4c and
case of the S,N,O and N,N,O ligand, these bond lengths are 5b/5c. However, the Si–O(enolato) and Si–N(imino) bond
almost identical, whereas for the O,N,O ligand a small shorten- lengths of 5a/6a (axial PhO ligand) differ significantly from
ing of the Si–SPh and Si–SePh bond distances was observed.
those of 4b/5b/6b and 4c/5c/6c (equatorial PhX ligand; X = S,
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R. Tacke et al.
ARTICLE
Table 2. Berry distortions /% and axial bond angles /° of compounds
4b·CH3CN, 4c·CH3CN, 5a, 5b·CH3CN, 5c·CH3CN, and 6a–c.
Compound (ligand)
Berry distortion
Axial bond angle
a)
a)
4b (S,N,O)
4c (S,N,O)
5a (O,N,O)
5b (O,N,O)
5c (O,N,O)
6a (N,N,O)
6b (N,N,O)
6c (N,N,O)
29.3
24.7
41.7
22.4
167.90(4)
168.68(3)
a)
a)
164.57(12)
170.13(3)
27.0
169.22(7)
20.4, 24.2
16.2
175.48(7), 171.91(7)
170.53(5)
18.8
169.76(8)
a) Data taken from Ref. [6].
Table 3. Comparison of the Si–X (X = OPh, SPh, SePh) bond lengths
/Å of compounds 4b·CH3CN, 4c·CH3CN, 5a, 5b·CH3CN, 5c·CH3CN,
and 6a–c.
Compound (ligand) Si–OPh
Si–SPh
Si–SePh
a)
a)
4b, 4c (S,N,O)
5a–c (O,N,O)
6a–c (N,N,O)
2.1881(6)
2.1694(3)
2.1860(6)
2.3201(3)
2.3097(7)
2.3313(7)
1.687(2)
1.7181(14),
1.7194(14)
Figure 5. Molecular structure of 6b in the crystal (probability level of
displacement ellipsoids 50%). Selected bond lengths /Å and angles
/°: Si–S 2.1860(6), Si–O 1.8470(10), Si–N1 1.8610(12), Si–N2
1.8115(12), Si–C1 1.8867(14); S–Si–O 79.23(4), S–Si–N1 122.42(4),
S–Si–N2 100.76(4), S–Si–C1 117.95(5), O–Si–N1 87.61(5), O–Si–N2
170.53(5), O–Si–C1 90.86(5), N1–Si–N2 84.43(5), N1–Si–C1
118.04(6), N2–Si–C1 97.40(6).
a) Data taken from Ref. [6].
ligands. The Si–C bond lengths of 4b/4c, 5a/5b/5c, and 6a/6b/
6c are very similar.
Compounds 5a, 5b·CH3CN, 5c·CH3CN, and 6a–c were
characterized by solid-state 15N, 29Si, and 77Se (5c·CH3CN and
6c) NMR spectroscopy (see Table 5 and Experimental Sec-
tion). The NMR spectroscopic data obtained are in accordance
with the experimentally established crystal structures. The iso-
tropic 29Si chemical shifts clearly indicate the presence of
pentacoordinate silicon atoms.
1
As shown by H, 13C, and 29Si NMR spectroscopic studies,
compounds 5a–c and 6a–c also exist in solution (solvent,
CD2Cl2; see Experimental Section). The stereochemistry of
these compounds in the solid state and in solution is very sim-
ilar. As shown by the X-ray diffraction studies, two different
types of structures exist in the crystal, depending on the type
of ligands (structures A and B; Figure 7). The isotropic 29Si
chemical shifts of 5a (PhO, O,N,O) and 6a (PhO, N,N,O) in
the solid state and in solution are very similar (Table 5), indi-
cating the presence of structure A both in the solid state and
in solution. The isotropic 29Si chemical shifts in solution for
5b (PhS, O,N,O), 6b (PhS, N,N,O), 5c (PhSe, O,N,O), and 6c
(PhSe, N,N,O) (Table 5) indicate that these compounds exist
Figure 6. Molecular structure of 6c in the crystal (probability level of
displacement ellipsoids 50%). Selected bond lengths /Å and angles
/°: Si–Se 2.3313(7), Si–O 1.8451(14), Si–N1 1.8652(18), Si–N2
1.8085(17), Si–C1 1.878(2); Se–Si–O 78.55(5), Se–Si–N1 123.44(6),
Se–Si–N2 100.65(6), Se–Si–C1 117.15(6), O–Si–N1 87.56(7), O–Si–
N2 169.76(8), O–Si–C1 91.02(8), N1–Si–N2 84.41(8), N1–Si–C1
117.66(8), N2–Si–C1 98.32(8).
Se). In the case of 5a/6a, a significant shortening of the Si–
O(enolato) and elongation of the Si–N(imino) bonds compared
to 4b/5b/6b and 4c/5c/6c was observed. This can be explained
Figure 7. Structures A and B discussed for compounds 4b, 4c, 5a–c,
by the different coordination modes of the respective tridentate and 6a–c.
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Neutral Pentacoordinate Silicon(IV) Complexes
Table 4. Comparison of the Si–O(enolato), Si–N(imino), and Si–C bond lengths /Å of 4b·CH3CN, 4c·CH3CN, 5a, 5b·CH3CN, 5c·CH3CN, and
6a–c.
Compound (ligand)
Si–O(enolato)
Si–N(imino)
Si–C
a)
a)
a)
a)
4b (S,N,O, SPh)
4c (S,N,O, SePh)
5a (O,N,O, OPh)
5b (O,N,O, SPh)
5c (O,N,O, SePh)
6a (N,N,O, OPh)
6b (N,N,O, SPh)
6c (N,N,O, SePh)
1.7676(10)
1.7644(8)
1.680(2)
1.7675(6)
1.8592(12)
1.8545(10)
2.060(3)
1.8698(7)
1.8738(17)
1.8782(16)
1.8757(12)
1.858(3)
1.8838(8)
1.893(2)
a)
a)
1.7718(15)
b)
b)
b)
1.6999(15), 1.6971(16)
1.8470(10)
2.0637(16), 2.0456(17)
1.8610(12)
1.8844(19), 1.877(2)
1.8867(14)
1.8451(14)
1.8652(18)
1.878(2)
a) Data taken from Ref. [6]. b) Data for two crystallographically independent molecules.
Table 5. Isotropic 15N (imino-nitrogen atom) and 29Si chemical shifts of compounds 4b·CH3CN, 4c·CH3CN, 5a, 5b·CH3CN, 5c·CH3CN, and
6a–c in the solid state (T = 22 °C) and 29Si chemical shifts of 4b, 4c, 5a–c, and 6a–c in solution (CD2Cl2, T = 23 °C).
Compound (ligand)
δ15N /ppm
δ29Si (solid state) /ppm
δ29Si (solution) /ppm
a)
a)
a)
4b (S,N,O, SPh)
4c (S,N,O, SePh)
5a (O,N,O, OPh)
5b (O,N,O, SPh)
5c (O,N,O, SePh)
6a (N,N,O, OPh)
6b (N,N,O, SPh)
6c (N,N,O, SePh)
–190.3
–186.4
–152.8
–204.5
–79.3
–82.6
–79.7
–82.7
a)
a)
a)
–109.5
–93.2
–93.9
–108.7
–88.3
–88.7
–107.5
–84.4
–84.2
–201.7
b)
b)
–156.5, –151.9
–205.8
–109.1, –106.1
–78.9
–78.5
–203.3
a) Data taken from Ref. [6]. b) Data for two crystallographically independent molecules.
as pentacoordinate silicon(IV) complexes in solution as well;
however, the shifts in the solid state and in solution differ by
about 5 ppm. The magnitude of this shift difference is not un-
usual and was already reported in one of our earlier publica-
tions and discussed extensively with support of computational
studies.[7e] In this context it is also interesting to note that the
solid-state 29Si chemical shifts of the two crystallographically
Scheme 4. Dynamic equilibrium between the pentacoordinate com-
plexes 4b (X = S) and 4c (X = Se) and the corresponding tetracoordi-
nate species 4bЈ and 4cЈ.
independent molecules of 6a, which have very similar struc-
tures, differ by 3.0 ppm (Table 5, Figure 4).
As shown by the NMR spectroscopic studies in solution,
there is another striking difference in the properties of the S/
O/NMe analogues 4a/5a/6a (PhO), 4b/5b/6b (PhS), and 4c/
5c/6c (PhSe). As already reported earlier, the pentacoordinate
Conclusions
With the synthesis of compounds 5a–c and 6a–c, a series
compound 4a (S,N,O, PhO) does not exist in the solid state and of novel neutral pentacoordinate silicon(IV) complexes with
in solution; instead, the tetracoordinate isomer 4aЈ (existing as an SiO3NC, SiO2SNC, SiO2SeNC, SiO2N2C, SiOSN2C, or
two diastereomers) was observed.[6] In addition, for the ana- SiOSeN2C skeleton was made available. These compounds
logues 4b (S,N,O, PhS) and 4c (S,N,O, PhSe) a dynamic equi- contain a tridentate dianionic O,N,O (series 5) or N,N,O ligand
librium between the pentacoordinate complexes and the corre- (series 6), an anionic PhX ligand (X = O, S, Se), and a phenyl
sponding tetracoordinate species 4bЈ and 4cЈ was detected in group. They represent analogues of the silicon(IV) complexes
solution (solvent, CD2Cl2; Scheme 4).[6] Interestingly, such 4a–c that contain a tridentate dianionic S,N,O ligand, with a
kind of equilibrium was not observed for the corresponding soft sulfur ligand atom instead of the hard oxygen (series 5)
analogues with an O,N,O or N,N,O ligand, compounds 5b, 5c, or nitrogen ligand atom (series 6). Comparison of the respec-
6b, and 6c. The same holds true for compounds 5a (O,N,O, tive S/O/NMe analogues of the series 4–6 revealed insight into
PhO) and 6a (N,N,O, PhO), the sulfur analogue of which (4a) the impact of the soft sulfur ligand atom on (i) the chemical
does not exist. These results can be explained in terms of a properties and (ii) the molecular structure.
more favored cleavage of the Si–S bond of compounds 4a, 4b,
The S/O/NMe analogues 4a/4b/4c with their PhO ligand
and 4c (S,N,O) compared to the cleavage of the stronger Si–O show striking differences in their chemical properties. The
bond of 5a, 5b, and 5c (O,N,O) and the stronger Si–N bond pentacoordinate silicon(IV) complex 4a (S,N,O) does not exist
of 6a, 6b, and 6c (N,N,O).
in the solid state and in solution; instead, the tetracoordinate
Z. Anorg. Allg. Chem. 2014, 300–309
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 305

R. Tacke et al.
ARTICLE
stirred suspension of 8 (970 mg, 5.07 mmol) in tetrahydrofuran
(40 mL), and the reaction mixture was stirred at 20 °C for 1 h. The
resulting solid was filtered off, washed with tetrahydrofuran (10 mL),
and discarded. The solvent of the filtrate (including the wash solution)
was removed in vacuo, and acetonitrile (10 mL) was added to the resi-
due. The solvent was removed in vacuo, acetonitrile (12 mL) was
added to the residue, and the resulting mixture was heated until a clear
solution was obtained, which was kept undisturbed at –20 °C for 16
h. The resulting precipitate was isolated by filtration, washed with n-
isomer 4aЈ was observed. In contrast, the pentacoordinate ana-
logues 5a (O,N,O) and 6a (N,N,O) are stable both in the solid
state and in solution and do not isomerize to the corresponding
tetracoordinate species. The S/O/NMe analogues 4b/5b/6b
(PhS) and 4c/5c/6c (PhSe) also exist in the solid state and in
solution; however, the pentacoordinate silicon(IV) complexes
4b and 4c (S,N,O) isomerize in a dynamic equilibrium upon
dissolution in organic solvents to give the tetracoordinate spe-
cies 4bЈ and 4cЈ. In contrast, compounds 5b and 5c (O,N,O)
pentane (10 mL), and dried in vacuo (0.01 mbar, 20 °C, 1 h) to give
1
as well as 6b and 6c (N,N,O) do not undergo such kind of 5a in 65% yield (1.28 g, 3.30 mmol) as a yellow crystalline solid. H
NMR (500.1 MHz, CD2Cl2): δ = 1.90 [d, 4J(1H,1H) = 0.3 Hz, 3 H,
isomerization, which can be explained by the stronger Si–O
and Si–N bonds compared to the weaker Si–S bond.
Both the different tridentate S,N,O, O,N,O, and N,N,O li-
gands and the different PhX ligands (X = O, S, Se) control the
structures of the pentacoordinate silicon(IV) complexes
studied. As shown by the X-ray diffraction studies, the silicon
coordination polyhedra of 5a and 6a are strongly distorted tri-
gonal bipyramids with the PhO ligand and the imino-nitrogen
atom of the tridentate O,N,O or N,N,O ligand in the two axial
CCH3], 2.50 (s, 3 H, CCH3), 5.69 [q, 4J(1H,1H) = 0.3 Hz, 1 H, CCHC],
6.75–6.79, 6.80–6.84, 6.88–6.92, 7.13–7.18, 7.22–7.25, 7.27–7.31, and
7.70–7.74 ppm (m, 14 H, C6H4, SiC6H5, OC6H5). 13C NMR
(125.8 MHz, CD2Cl2): δ = 24.0 (CCH3), 24.3 (CCH3), 104.6 (CCHC),
115.1, 118.7, 120.9, 121.0, 121.4 (2 C), 127.7 (2 C), 128.3, 129.1 (2
C), 129.7, 131.8, 135.9 (2 C), 138.4, 153.3, and 157.0 (C6H4, SiC6H5,
OC6H5), 171.1 [C(N)CH3], 179.9 ppm [C(O)CH3]. 29Si NMR
(99.4 MHz, CD2Cl2): δ = –108.7 ppm. 15N VACP/MAS NMR: δ =
–152.8 ppm. 29Si VACP/MAS NMR: δ = –109.5 ppm. C23H21NO3Si:
sites. Replacement of the strongly electron-withdrawing PhO calcd. C 71.29; H 5.46; N 3.61%; found: C 71.0; H 5.4; N 3.9%.
ligand by the less electronegative PhS or PhSe ligands changes
Synthesis of 5b·CH3CN: Triethylamine (305 mg, 3.01 mmol) and
benzenethiol (332 mg, 3.01 mmol) were added sequentially in single
portions at 20 °C to a stirred solution of 2b (994 mg, 3.01 mmol) in
tetrahydrofuran (20 mL), and the reaction mixture was stirred at 20 °C
the structures completely. The S/O/NMe analogues 4b/5b/6b
(PhS) and 4c/5c/6c (PhSe) have also distorted trigonal-bipy-
ramidal structures; however, in these structures the PhS and
PhSe ligands and the imino-nitrogen atom of the tridentate
for 1.5 h. The resulting solid was filtered off, washed with tetra-
O,N,O or N,N,O ligand occupy equatorial positions, together
hydrofuran (2ϫ5 mL), and discarded. The solvent of the filtrate (in-
with the phenyl group. Analysis of the Berry distortions of the
cluding the wash solutions) was removed in vacuo, and acetonitrile
S/O/NMe analogues 4b/5b/6b and 4c/5c/6c reveals that the
different tridentate S,N,O, O,N,O, and N,N,O ligands affect the
(1 mL) was added to the residue. The solvent was removed in vacuo,
acetonitrile (6 mL) was added to the residue, and the resulting mixture
degree of distortion, which can be explained by the different was heated until a clear solution was obtained, which was kept undis-
nature of the Si–S, Si–O, and Si–N bond. The 29Si NMR spec-
turbed at 20 °C for 2 h and then at –20 °C for a further 48 h. The
resulting precipitate was isolated by filtration, washed with n-pentane
(10 mL), and dried in vacuo (0.01 mbar, 20 °C, 10 min) to give
troscopic data of all the silicon(IV) complexes studied suggest
that the structures of these compounds in the solid state and in
solution are very similar.
5b·CH3CN in 54% yield (723 mg, 1.63 mmol) as an orange-colored
crystalline solid. 1H NMR (500.1 MHz, CD2Cl2): δ = 1.50 (s, 3 H,
CCH3), 1.97 (s, 3 H, NϵCCH3), 2.46 (s, 3 H, CCH3), 5.59 (s, 1 H,
CCHC), 6.73–6.80, 7.06–7.19, 7.27–7.37, and 7.72–7.77 ppm (m, 14
Experimental Section
H, C6H4, SiC6H5, SC6H5). 13C NMR (125.8 MHz, CD2Cl2): δ = 2.0
(NϵCCH3), 23.3 (CCH3), 24.3 (CCH3), 104.0 (CCHC), 116.9
(NϵCCH3), 115.0, 118.4, 121.2, 126.5, 127.8 (2 C), 128.3 (2 C),
128.4, 129.7, 131.2, 135.7 (2 C), 136.1, 136.3 (2 C), 139.5, and 154.7
(C6H4, SiC6H5, SC6H5), 172.7 [C(N)CH3], 182.5 ppm [C(O)CH3]. 29Si
NMR (99.4 MHz, CD2Cl2): δ = –88.3 ppm. 15N VACP/MAS NMR:
δ = –204.5 ppm.[12] 29Si VACP/MAS NMR: δ = –93.2 ppm.[12]
C25H24N2O2SSi: calcd. C 67.53; H 5.44; N 6.30; S 7.21%; found: C
66.9; H 5.3; N 5.9; S 6.9%.[13]
General Information: All syntheses were carried out under dry argon.
The organic solvents used were dried and purified according to stan-
dard procedures and stored under nitrogen. The solution-state 1H, 13C,
29Si, and 77Se NMR spectra were recorded at 23 °C with a Bruker
Avance 500 NMR spectrometer (1H, 500.1 MHz; 13C, 125.8 MHz;
29Si, 99.4 MHz; 77Se, 95.4 MHz). CD2Cl2 served as the solvent.
Chemical shifts (ppm) were determined relative to internal CHDCl2
(1H, δ = 5.32 ppm), internal CD2Cl2 (13C, δ = 53.8 ppm), external TMS
(29Si, δ = 0 ppm), or external Me2Se with 5% w/w C6D6 (77Se, δ =
0 ppm). Assignment of the 13C NMR spectroscopic data was supported
by DEPT 135 experiments and 13C,1H correlation experiments. Solid-
state 15N, 29Si, and 77Se VACP/MAS NMR spectra were recorded at
22 °C with a Bruker DSX-400 NMR spectrometer with bottom layer
rotors of ZrO2 (diameter, 4–7 mm) containing ca. 80–300 mg of sam-
ple [15N, 40.6 MHz; 29Si, 79.5 MHz; 77Se, 76.3 MHz; external stan-
dard, TMS (13C, 29Si; δ = 0 ppm), glycine (15N, δ = –342.0 ppm), or
Me2Se (77Se, δ = 0 ppm); spinning rate, 5–10 kHz; contact time, 1–2
ms (13C), 3 ms (15N), 3–5 ms (29Si), or 5 ms (77Se); 90° 1H transmitter
pulse length, 2.8 μs (4 mm), 3.6 μs (7 mm); repetition time, 4 s].
Synthesis of 5c·CH3CN: Triethylamine (283 mg, 2.80 mmol) and
benzeneselenol (440 mg, 2.80 mmol) were added sequentially in single
portions at 20 °C to a stirred solution of 2b (924 mg, 2.80 mmol) in
tetrahydrofuran (20 mL), and the reaction mixture was stirred at 20 °C
for 1 h. The resulting solid was filtered off, washed with tetra-
hydrofuran (2ϫ5 mL), and discarded. The solvent of the filtrate (in-
cluding the wash solutions) was removed in vacuo, and acetonitrile
(1 mL) was added to the residue. The solvent was removed in vacuo,
acetonitrile (5 mL) was added to the residue, and the resulting mixture
was heated until a clear solution was obtained, which was slowly co-
oled to 20 °C and kept undisturbed at 20 °C for 3 h and then at –20 °C
for a further 48 h. The resulting precipitate was isolated by filtration,
washed with n-pentane (10 mL), and dried in vacuo (0.01 mbar, 20 °C,
Synthesis of 5a: Triethylamine (1.03 g, 10.2 mmol) and 7 (1.36 g,
5.05 mmol) were added sequentially in single portions at 20 °C to a
306
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© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2014, 300–309

Neutral Pentacoordinate Silicon(IV) Complexes
10 min) to give 5c·CH3CN in 47% yield (647 mg, 1.32 mmol) as an (2 C), 128.2, 128.4, 129.0, 134.9 (2 C), 135.8 (2 C), 136.9, 140.7, and
orange-colored crystalline solid. 1H NMR (500.1 MHz, CD2Cl2):[14]
δ
148.2 (C6H4, SiC6H5, SC6H5), 171.4 [C(N)CH3], 181.9 ppm
= 1.50 (s, 3 H, CCH3), 1.97 (s, 3 H, NϵCCH3), 2.45 (s, 3 H, CCH3),
[C(O)CH3]. 29Si NMR (99.4 MHz, CD2Cl2): δ = –84.4 ppm. 15N
5.58 (s, 1 H, CCHC), 6.73–6.82, 7.06–7.23, 7.24–7.39, 7.46–7.52, and VACP/MAS NMR: δ = –290.1 (NCH3), –205.8 ppm (SiNCCH3). 29Si
7.70–7.76 ppm (m, 14 H, C6H4, SiC6H5, SeC6H5). 13C NMR VACP/MAS NMR: δ = –78.9 ppm. C24H24N2OSSi: calcd. C 69.19;
(125.8 MHz, CD2Cl2):[14] δ = 2.0 (NϵCCH3), 23.2 (CCH3), 24.4
(CCH3), 104.1 (CCHC), 116.9 (NϵCCH3), 115.0, 118.6, 121.2, 126.6,
127.8 (2 C), 128.4 (2 C), 129.8, 131.2, 132.5, 133.7, 136.1 (2 C), 137.0
(2 C), 139.7, and 154.7 (C6H4, SiC6H5, SeC6H5), 172.7 [C(N)CH3],
182.2 ppm [C(O)CH3]. 29Si NMR (99.4 MHz, CD2Cl2):[14] δ =
–88.7 ppm [77Se satellites, 1J(29Si,77Se) = 101 Hz]. 77Se NMR
H, 5.81; N, 6.72; S, 7.70%; found: C 69.1; H, 5.8; N, 6.8; S, 7.6%.
Synthesis of 6c: Triethylamine (544 mg, 5.38 mmol) and benzene-
selenol (844 mg, 5.37 mmol) were added sequentially in single por-
tions at 20 °C to a stirred solution of 3b (1.84 g, 5.37 mmol) in tetra-
hydrofuran (50 mL), and the reaction mixture was stirred at 20 °C for
2.5 h. The resulting solid was filtered off, washed with tetrahydrofuran
(10 mL), and discarded. The solvent of the filtrate (including the wash
solution) was removed in vacuo, and acetonitrile (10 mL) was added
to the residue. The solvent was removed in vacuo, acetonitrile (7 mL)
was added to the residue, and the reaction mixture was heated until a
clear solution was obtained, which was kept undisturbed at 20 °C for
16 h. The resulting precipitate was isolated by filtration, washed with
n-pentane (2ϫ9 mL), and dried in vacuo (0.01 mbar, 20 °C, 2 h) to
give 6c in 63% yield (1.56 g, 3.37 mmol) as a dark-red crystalline
solid. 1H NMR (500.1 MHz, CD2Cl2):[14] δ = 1.64 (s, 3 H, CCH3),
2.36 (s, 3 H, CCH3), 2.49 (s, 3 H, NCH3), 5.50 (s, 1 H, CCHC),
6.45–6.51, 6.58–6.64, 7.01–7.07, 7.10–7.17, 7.18–7.23, 7.25–7.31, and
7.47–7.56 ppm (m, 14 H, C6H4, SiC6H5, SeC6H5). 13C NMR
(125.8 MHz, CD2Cl2):[14] δ = 23.5 (CCH3), 24.4 (CCH3), 32.7
(NCH3), 104.9 (CCHC), 108.5, 114.4, 120.9, 126.3, 127.6 (2 C), 128.3
(2 C), 129.0, 129.7, 130.9, 133.7, 134.9 (2 C), 137.2 (2 C), 141.0, and
147.8 (C6H4, SiC6H5, SeC6H5), 171.1 [C(N)CH3], 181.1 ppm
[C(O)CH3]. 29Si NMR (99.4 MHz, CD2Cl2):[14] δ = –84.2 ppm [77Se
satellites, 1J(29Si,77Se) = 112 Hz]. 77Se NMR (95.4 MHz, CD2Cl2):[14]
δ = 140.0 ppm. 15N VACP/MAS NMR: δ = –287.3 (NCH3),
–203.3 ppm (SiNCCH3). 29Si VACP/MAS NMR: δ = –78.5 ppm (77Se
satellites not detected). 77Se VACP/MAS NMR: δ = 164.2 ppm.
C24H24N2OSeSi: calcd. C 62.19; H, 5.22; N, 6.04%; found: C 62.3;
H, 5.1; N, 6.1%.
(95.4 MHz, CD2Cl2):[14] δ = 131.1 ppm. 15N VACP/MAS NMR:[15]
δ
= –201.7 ppm (SiNCCH3); NϵCCH3 not detected. 29Si VACP/MAS
NMR: δ = –93.9 ppm [77Se satellites, 1J(29Si,77Se) = 109 Hz]. 77Se
VACP/MAS NMR: δ = 144.8 ppm. C25H24N2O2SeSi: calcd. C 61.09;
H, 4.92; N, 5.70%; found: C 60.8; H, 4.8; N, 5.1%.[13]
Synthesis of 6a: Triethylamine (1.21 g, 12.0 mmol) and 7 (1.61 g,
5.98 mmol) were added sequentially in single portions at 20 °C to a
stirred suspension of 9 (1.22 g, 5.97 mmol) in tetrahydrofuran (50 mL),
and the reaction mixture was stirred at 20 °C for 30 min. The resulting
solid was filtered off, washed with tetrahydrofuran (10 mL), and dis-
carded. The solvent of the filtrate (including the wash solution) was
removed in vacuo, acetonitrile (20 mL) was added to the solid residue,
and the resulting mixture was heated until a clear solution was ob-
tained, which was kept undisturbed at –20 °C for 20 h. The resulting
precipitate was isolated by filtration, washed with n-pentane (10 mL),
and dried in vacuo (0.01 mbar, 20 °C, 1 h) to give 6a in 68% yield
(1.63 g, 4.07 mmol) as
a
yellow crystalline solid. 1H NMR
4
(500.1 MHz, CD2Cl2): δ = 1.95 [d, J(1H,1H) = 0.6 Hz, 3 H, CCH3],
2.41 (s, 3 H, CCH3), 3.23 (s, 3 H, NCH3), 5.60 [q, 4J(1H,1H) = 0.6 Hz,
1 H, CCHC], 6.65–6.69, 6.72–6.76, 6.77–6.81, 6.83–6.87, 7.10–7.15,
7.17–7.22, and 7.25–7.29 ppm (m, 14 H, C6H4, SiC6H5, OC6H5). 13C
NMR (125.8 MHz, CD2Cl2): δ = 23.4 (CCH3), 24.6 (CCH3), 34.0
(NCH3), 105.8 (CCHC), 110.7, 115.9, 119.4, 120.6, 120.9 (2 C), 127.5
(2 C), 128.4, 128.7, 128.9 (2 C), 130.6, 133.3 (2 C), 140.5, 146.5, and
158.4 (C6H4, SiC6H5, OC6H5), 166.6 [C(N)CH3], 170.8 ppm
[C(O)CH3]. 29Si NMR (99.4 MHz, CD2Cl2): δ = –107.5 ppm. 15N
VACP/MAS NMR (data for two crystallographically independent mo-
lecules): δ = –305.8/–302.9 (NCH3), –156.5/–151.9 ppm (SiNCCH3).
29Si VACP/MAS NMR (data for two crystallographically independent
molecules): δ = –109.1/–106.1 ppm. C24H24N2O2Si: calcd. C 71.97; H,
6.04; N, 6.99%; found: C 72.0; H, 6.1; N, 7.0%.
Synthesis of 7: A solution of phenol (3.40 g, 36.1 mmol) in tetra-
hydrofuran (50 mL) was added dropwise at –20 °C within 1 h to a
stirred solution of freshly distilled trichloro(phenyl)silane (7.63 g,
36.1 mmol) and triethylamine (3.65 g, 36.1 mmol) in tetrahydrofuran
(50 mL). The resulting suspension was warmed to 20 °C and stirred
for 20 h. The solid residue was removed by filtration, washed with
tetrahydrofuran (20 mL), and discarded. The solvent of the filtrate (in-
cluding the wash solution) was removed in vacuo, diethyl ether
(100 mL) was added to the residue, and the resulting mixture was kept
undisturbed at –20 °C for 20 h. The resulting solid was removed by
filtration and discarded, the solvent of the filtrate was removed under
reduced pressure, and the residue was purified by distillation in vacuo
to give 7 in 58% yield (5.62 g, 20.9 mmol) as a colorless liquid. B.p.
107–111 °C/1 mbar. 1H NMR (500.1 MHz, CD2Cl2): δ = 7.11–7.17,
7.32–7.37, 7.51–7.56, 7.60–7.64, and 7.86–7.90 ppm (m, 10 H, C6H5,
OC6H5). 13C NMR (125.8 MHz, CD2Cl2): δ = 120.3 (2 C), 124.2,
128.9 (2 C), 130.1, 130.5, 132.9 (2 C), 134.1 (2 C), 152.3 ppm
(SiC6H5, OC6H5). 29Si NMR (99.4 MHz, CD2Cl2): δ = –26.2 ppm.
C12H10Cl2OSi: calcd. C 53.54; H, 3.74%; found: C 53.5; H, 3.7%.
Synthesis of 6b: Triethylamine (1.12 g, 11.1 mmol) and benzenethiol
(1.22 g, 11.1 mmol) were added sequentially at 20 °C to a stirred solu-
tion of 3b (3.79 g, 11.1 mmol) in tetrahydrofuran (50 mL), and the
reaction mixture was stirred at 20 °C for 2 h. The resulting solid was
filtered off, washed with tetrahydrofuran (10 mL), and discarded. The
solvent of the filtrate (including the wash solution) was removed in
vacuo, and acetonitrile (5 mL) was added to the residue. The solvent
was removed in vacuo, acetonitrile (60 mL) was added to the residue,
and the resulting mixture was heated until a clear solution was ob-
tained, which was kept undisturbed at 20 °C for 1 h and then at –20 °C
for a further 16 h. The resulting precipitate was isolated by filtration,
washed with n-pentane (2ϫ15 mL), and dried in vacuo (0.01 mbar,
20 °C, 3 h) to give 6b in 72% yield (3.34 g, 8.02 mmol) as a dark-red
crystalline solid. 1H NMR (500.1 MHz, CD2Cl2): δ = 1.58 (s, 3 H,
CCH3), 2.42 (s, 3 H, CCH3), 2.52 (s, 3 H, NCH3), 5.00 (s, 1 H,
CCHC), 6.46–6.50, 6.57–6.62, 7.04–7.05, 7.12–7.16, 7.17–7.20, 7.25–
7.33, 7.37–7.43, and 7.51–7.54 ppm (m, 14 H, C6H4, SiC6H5, SC6H5).
13C NMR (125.8 MHz, CD2Cl2): δ = 23.5 (CCH3), 24.4 (CCH3), 32.6
Synthesis of 8: This compound was synthesized according to Ref.[10]
.
Synthesis of 9: Acetylacetone (37.5 g, 375 mmol) was added in a sin-
gle portion at 20 °C to a stirred solution of freshly distilled N-methyl-
benzene-1,2-diamine (41.6 g, 341 mmol) in ethanol (200 mL), and the
reaction mixture was then stirred for 10 min, cooled to –20 °C, and
kept undisturbed at this temperature for 3 d. The resulting precipitate
(NCH3), 104.6 (CCHC), 108.2, 114.1, 120.9, 126.1, 127.6 (2 C), 128.1 was isolated by filtration, washed with n-pentane (2ϫ50 mL), and
Z. Anorg. Allg. Chem. 2014, 300–309
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de 307

R. Tacke et al.
ARTICLE
[8] For recent publications of other groups dealing with higher-coor-
dinate silicon(IV) complexes, see: a) S. Yakubovich, I. Kalikhman,
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dried in vacuo (0.01 mbar, 20 °C, 3 h) to give 9 in 73% yield (50.8 g,
249 mmol) as a yellow crystalline solid. 1H NMR (500.1 MHz,
4
CD2Cl2): δ = 1.78 [d, J(1H,1H) = 0.5 Hz, 3 H, CCH3], 2.04–2.06 (m,
3
3 H, CCH3), 2.82 [d, J(1H,1H) = 5.0 Hz, 3 H, NCH3], 4.05 [br. s, 1
H, N(CH3)H], 5.22–5.24 (m, 1 H, CCHC), 6.62–6.70, 6.93–6.99, and
7.12–7.21 (m, 4 H, C6H4), 11.8 ppm (br. s, 1 H, HNCCH3). 13C NMR
(125.8 MHz, CD2Cl2): δ = 19.3 (CCH3), 29.2 (CCH3), 30.5 (NCH3),
97.2 (CCHC), 110.6, 116.5, 124.4, 128.0, 128.6, and 145.9 (C6H4),
163.2 (NCCH3), 196.4 ppm (CO). 15N VACP/MAS NMR (data for
two crystallographically independent molecules): δ = –257.7/–252.1
(NCCH3), –323.9 ppm (2 N, NCH3). C12H16N2O: calcd. C 70.56; H,
7.89; N, 13.71%; found: C 70.5; H, 7.8; N, 13.7%.
Crystal Structure Analyses: Suitable single crystals of 5a,
5b·CH3CN, 5c·CH3CN, and 6a–c were mounted in inert oil (perfluo-
ropolyalkyl ether, ABCR) on a glass fiber and then transferred to the
cold nitrogen gas stream of the diffractometer [Stoe IPDS (5a,
5c·CH3CN, and 6a–c; graphite-monochromated Mo-Kα radiation, λ =
0.71073 Å) or Bruker Nonius KAPPA APEX II (5b·CH3CN; Montel
mirror, Mo-Kα radiation, λ = 0.71073 Å)]. All structures were solved
by direct methods (SHELXS-97[16]) and refined by full-matrix least-
squares methods on F2 for all unique reflections (SHELXL-97[16]).
SHELXLE was used as refinement GUI.[17] For the CH hydrogen
atoms, a riding model was employed.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the de-
pository numbers CCDC-966387 (5a), CCDC-966388 (5b·CH3CN),
CCDC-966389 (5c·CH3CN), CCDC-966390 (6a), CCDC-966391 (6b),
and CCDC-966392 (6c) (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
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© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2014, 300–309

Neutral Pentacoordinate Silicon(IV) Complexes
[14] As this compound decomposes in CD2Cl2 (PhSe/Cl exchange),
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[15] Compound 5c·CH3CN partially loses its acetonitrile under MAS
conditions.
Received: November 13, 2013
Published Online: December 16, 2013
Z. Anorg. Allg. Chem. 2014, 300–309
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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