Novel neutral hexacoordinate benzamidinatosilicon(iv) complexes with SiN3OF2, SiN3OCl2, SiN 3OBr2, SiN5O and SiN3O3 skeletons

Article abstract of DOI:10.1039/c1dt10898k

The neutral pentacoordinate monoamidinatosilicon(iv) complex 1 (SiN ₂Cl₃ skeleton) and the neutral hexacoordinate monoamidinatosilicon(iv) complexes 2-9 (SiN₃OF₂, SiN ₃OCl₂, SiN₃

Full text of DOI:10.1039/c1dt10898k

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PAPER
Novel neutral hexacoordinate benzamidinatosilicon(IV) complexes with
SiN3OF2, SiN3OCl2, SiN3OBr2, SiN5O and SiN3O3 skeletons†‡
Konstantin Junold, Christian Burschka, Ru¨diger Bertermann and Reinhold Tacke*
Received 12th May 2011, Accepted 28th June 2011
DOI: 10.1039/c1dt10898k
The neutral pentacoordinate monoamidinatosilicon(IV) complex 1 (SiN2Cl3 skeleton) and the neutral
hexacoordinate monoamidinatosilicon(IV) complexes 2–9 (SiN3OF2, SiN3OCl2, SiN3OBr2, SiN5O and
SiN3O3 skeletons) were synthesised and characterised by elemental analyses, single-crystal X-ray
diffraction (except for 1) and NMR spectroscopy in the solid state and in solution. Compounds 2–9
contain one bidentate monoanionic N,N¢-diisopropylbenzamidinato ligand, one bidentate
monoanionic ligand derived from 8-hydroxyquinoline and (i) two identical monoanionic ligands (F, Cl,
Br, N3, NCO, NCS, OSO2CF3) or (ii) one bidentate dianionic benzene-1,2-diolato ligand. The dynamic
behavior of 2–4 (SiN3OX2 skeleton; X = F, Cl, Br) and 9 (SiN3O3) in solution was studied by
multinuclear variable-temperature NMR experiments. Compound 1 was synthesised by reaction of
SiCl4 with the corresponding lithium amidinate, and compound 2 was obtained by reaction of 1 with
8-hydroxyquinoline and triethylamine. Compound 2 served as the starting material in the syntheses of
3–9, in which the two chloro ligands of 2 were substituted by two identical (pseudo)halogeno ligands,
two trifluoromethanesulfonato ligands or one benzene-1,2-diolato ligand. Compounds 3 and 4 contain
the novel SiN3OBr2 and SiN3OF2 skeletons, while compounds 5–7 are the first neutral hexacoordinate
silicon(IV) complexes with an SiN5O skeleton.
OSO2CF3) or (ii) one bidentate dianionic benzene-1,2-diolato
ligand. The novel neutral pentacoordinate monoamidinatosil-
icon(IV) complex 1 served as the precursor for the synthesis
of 2, which was then further converted into 3–9. We report
Introduction
In transition metal and main group metal chemistry, coordination
compounds with amidinato ligands have been studied exten-
sively. In contrast, the chemistry of silicon complexes containing
herein on the synthesis of compounds 1–9 (Scheme 1) and their
amidinato ligands is still a largely unexplored field. Only a few
higher-coordinate silicon(IV) compounds containing such ligands
are known1,2 (for selected reviews dealing with higher-coordinate
silicon compounds, see ref. 3). Very recently, we have reported
on a series of neutral hexacoordinate bis(amidinato)silicon(IV)
complexes with SiN4F2, SiN4Cl2, SiN4Br2, SiN6, SiN4C2, SiN4S2,
SiN4SeS and SiN4Se2 skeletons. In continuation of our systematic
studies on higher-coordinate silicon compounds (for recent publi-
cations, see ref. 2 and 4), we have now succeeded in synthesising a
series of novel neutral hexacoordinate monoamidinatosilicon(IV)
complexes, compounds 2–9. These silicon(IV) complexes con-
tain one bidentate monoanionic N,N¢-diisopropylbenzamidinato
ligand, one bidentate monoanionic ligand derived from 8-
hydroxyquinoline (in this context, see ref. 5) and (i) two identical
monodentate monoanionic ligands (F, Cl, Br, N3, NCO, NCS,
Universita¨t Wu¨rzburg, Institut fu¨r Anorganische Chemie, Am Hub-
land, D-97074, Wu¨rzburg, Germany. E-mail: r.tacke@uni-wuerzburg.de;
Fax: (+49)931-31-84609; Tel: (+49)931-31-85250
† Dedicated to Professor Ernst Mutschler on the occasion of his 80th
birthday.
‡ CCDC reference numbers 825851–825858 for 2–9. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/c1dt10898k
Scheme 1 Structures of the neutral higher-coordinate silicon(IV) com-
plexes investigated in this study.
9844 | Dalton Trans., 2011, 40, 9844–9857
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NMR-spectroscopic characterisation in the solid state and in solu-
tion. In addition, compounds 2–9 were structurally characterised
by single-crystal X-ray diffraction. Furthermore, the dynamic
behavior of 2–4 and 9 in solution was studied by multinuclear
variable-temperature (VT) NMR experiments.
The main focus of this study was the synthesis and structural
characterisation (including the dynamic behavior in solution)
of novel neutral hexacoordinate monoamidinatosilicon(IV) com-
plexes. In this context, compounds 3–7 were of particular interest
as, to the best of our knowledge, neutral hexacoordinate silicon(IV)
complexes with an SiN3OF2, SiN3OBr2 or SiN5O skeleton have
not yet been described in the literature. The synthesis of com-
pound 9, with its three different bidentate ligands, was also very
challenging (in this context, see also ref. 6).
suspension was heated until a clear solution was obtained, which
was then cooled slowly to -20 ◦C and kept undisturbed at this
temperature for 1 d. The resulting colorless crystalline solid was
isolated by filtration, washed with n-pentane (2 ¥ 20 ml) and
dried in vacuo (20 ◦◦C, 4 h, 0.01 mbar). Yield: 20.8 g (61.6 mmol,
1
77%). Mp: >150 C (dec.). H NMR (500.1 MHz, CD2Cl2): d
3
3
1.20 (d, J(1H,1H) = 6.8 Hz, 12 H, CH3), 3.65 (sept, J(1H,1H) =
6.8 Hz, 2 H, CH), 7.36–7.39 (m, 2 H, o-C6H5), 7.56–7.66 (m,
1
3 H, p- and m-C6H5). 13C{ H} NMR (125.8 MHz, CD2Cl2): d
22.9 (CH3), 47.5 (CH), 127.0 (i-C6H5), 127.4 (2 C) (o-C6H5),
1
129.6 (2 C) (m-C6H5), 131.8 (p-C6H5), 173.1 (NCN). 29Si{ H}
NMR (99.4 MHz, CD2Cl2): d -98.2. 13C VACP/MAS NMR: d
22.6 (2 C) (CH3), 23.9 (2 C) (CH3), 46.8 (CH), 48.4 (CH), 125.1
(C6H5), 126.4 (2 C) (C6H5), 129.4 (2 C) (C6H5), 133.1 (C6H5),
173.5 (NCN). 15N VACP/MAS NMR: d -230.6, -172.6. 29Si
VACP/MAS NMR: d -99.4. Anal. Calcd for C13H19Cl3N2Si
(337.75): C, 46.23; H, 5.67; N, 8.29. Found: C, 46.2; H, 5.7; N, 8.3.
Experimental
General procedures
Benzamidinatosilicon(IV) complex (2). Triethylamine (3.09 g,
30.5 mmol) and 8-hydroxyquinoline (4.43 g, 30.5 mmol) were
added at 20 ◦C in single portions one after another to a stirred
solution of 1 (10.3 g, 30.5 mmol) in tetrahydrofuran (150 ml),
and the reaction mixture was then stirred at this temperature
for 19 h. The resulting precipitate was filtered off, washed with
tetrahydrofuran (3 ¥ 20 ml) and discarded. The solvent of the
filtrate (including the wash solutions) was removed in vacuo,
followed by the addition of acetonitrile (100 ml). The resulting
mixture was heated until a clear solution was obtained, which
was then cooled slowly to -20 ◦C and kept undisturbed at this
temperature for 2 d. The resulting yellow crystalline solid was
isolated by filtration, washed with n-pentane (2 ¥ 10 ml) and dried
in vacuo (20 ◦C, 3 h, 0.01 mbar). Yield: 6.40 g (14.3 mmol, 47%).
Mp: >210 ◦C (dec.). 1H NMR (500.1 MHz, CD2Cl2): d -0.15 (d,
3J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.19 (d, 3J(1H,1H) = 6.8 Hz, 3 H,
CH3), 1.41 (d, 3J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.43 (d, 3J(1H,1H) =
All syntheses were carried out under dry argon. The or-
ganic solvents used were dried and purified according to stan-
dard procedures and stored under nitrogen. Lithium N,N¢-
diisopropylbenzamidinate was synthesised according to ref. 7.
Melting points were determined with a Bu¨chi Melting Point B-
540 apparatus using samples in sealed capillaries. The solution
1H, 13C, 19F and 29Si NMR spectra were recorded at 23 ◦C on
a Bruker Avance 400 (19F, 376.5 MHz) or a Bruker Avance 500
NMR spectrometer (1H, 500.1 MHz; 13C, 125.8 MHz; 29Si, 99.4
MHz) using CD2Cl2 as the solvent. The 19F,19F EXSY/NOESY
(mixing time, 800 ms; recycle delay, 2.0 s) and VT 19F NMR
spectra were recorded on a Bruker DRX 300 NMR spectrometer
(19F, 282.4 MHz). Chemical shifts (ppm) were determined relative
to internal CHDCl2 (1H, d 5.32), internal CD2Cl2 (13C, d 53.8),
external CFCl3 (19F, d 0) or external tetramethylsilane (TMS) (29Si,
d 0). Assignment of the 13C NMR data was supported by DEPT
3
6.8 Hz, 3 H, CH3), 3.21 (sept, J(1H,1H) = 6.8 Hz, 1 H, CH),
1
135 and H,13C correlation experiments. The thermocouple used
3
4.04 (sept, J(1H,1H) = 6.8 Hz, 1 H, CH), 7.24 (br. s, 1 H, o-
with the probe for the VT NMR studies was calibrated for higher
and lower temperatures according to ref. 8 using an 80% solution
of ethane-1,2-diol in [D6]DMSO and a 4% solution of MeOH in
[D4]MeOH containing a trace of HCl, respectively. Solid-state 13C,
15N and 29Si VACP/MAS NMR spectra were recorded at 22 ◦C on
a Bruker DSX-400 NMR spectrometer with bottom-layer rotors
of ZrO2 (diameter, 7 mm) containing ca. 200 mg of sample (13C,
100.6 MHz; 15N, 40.6 MHz; 29Si, 79.5 MHz; external standard,
TMS (13C, 29Si; d 0) or glycine (15N; d -342.0); spinning rate, 6–7
kHz; contact time, 1 ms (13C), 3 ms (15N) or 5 ms (29Si); 90◦ 1H
transmitter pulse length, 3.6 ms; repetition time, 4–5 s).
C6H5), 7.29 (dd, 3J(1H,1H) = 7.8 Hz, 4J(1H,1H) = 0.8 Hz, 1 H, H7,
C9H6NO), 7.36 (br. s, 1 H, o-C6H5), 7.41 (dd, 3J(1H,1H) = 8.2 Hz,
4J(1H,1H) = 0.8 Hz, 1 H, H5, C9H6NO), 7.49–7.58 (m, 3 H, m- and
3
3
p-C6H5), 7.68 (dd, J(1H,1H) = 8.2 Hz, J(1H,1H) = 7.8 Hz, 1 H,
H6, C9H6NO), 7.70 (dd, 3J(1H,1H) = 8.2 Hz, 3J(1H,1H) = 5.0 Hz,
1 H, H3, C9H6NO), 8.52 (dd, 3J(1H,1H) = 8.2 Hz, 4J(1H,1H) = 1.2
Hz, 1 H, H4, C9H6NO), 9.06 (dd, 3J(1H,1H) = 5.0 Hz, 4J(1H,1H) =
1
1.2 Hz, 1 H, H2, C9H6NO). 13C{ H} NMR (125.8 MHz, CD2Cl2):
d 21.9 (CH3), 22.2 (CH3), 23.61 (CH3), 23.65 (CH3), 46.9 (CH),
47.5 (CH), 112.5 (C7, C9H6NO), 115.6 (C5, C9H6NO), 122.9 (C3,
C9H6NO), 127.4 (br., 2 C) (o-C6H5), 128.95 (i-C6H5), 129.03 (C4a,
C9H6NO), 129.3 (br., 2 C) (m-C6H5), 130.9 (p-C6H5), 131.5 (C6,
C9H6NO), 135.7 (C8a, C9H6NO) 139.0 (C2, C9H6NO), 140.6
Syntheses
1
Benzamidinatosilicon(IV) complex (1). Tetrachlorosilane
(15.0 g, 88.3 mmol) was added dropwise at -78 ◦C within 2 min to
a stirred suspension of lithium N,N¢-diisopropylbenzamidinate
(16.8 g, 79.9 mmol) in diethyl ether (120 ml), and the stirred
reaction mixture was then allowed to warm up to 20 ◦C within 4
h. The solvent was removed in vacuo, dichloromethane (80 ml)
was added to the residue, and the remaining solid was filtered off
and discarded. The solvent of the filtrate was removed in vacuo,
and acetonitrile (50 ml) was added to the residue. The resulting
(C4, C9H6NO), 152.4 (C8, C9H6NO), 169.7 (NCN). 29Si{ H}
NMR (99.4 MHz, CD2Cl2): d -162.4. 13C VACP/MAS NMR:
d 21.1 (CH3), 23.1 (CH3), 24.6 (2 C) (CH3), 46.2 (CH), 48.7
(CH), 113.8, 118.1, 122.6, 124.7, 126.7, 128.7 (4 C), 130.2, 132.5,
135.4, 140.7, 141.1 and 151.4 (C6H5 and C9H6NO), 168.2 (NCN).
15N VACP/MAS NMR: d -209.0 (NCN), -186.8 (NCN), -129.3
(C9H6NO). 29Si VACP/MAS NMR: d -165.2 (br. s). Anal. Calcd
for C22H25Cl2N3OSi (446.45): C, 59.19; H, 5.64; N, 9.41. Found:
C, 58.9; H, 5.7; N, 9.5.
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3
1
C9H6NO), 170.7 (t, J(19F,13C) = 2.5 Hz, NCN). 19F{ H} NMR
Benzamidinatosilicon(IV) complex (3). Bromotrimethylsilane
(1.71 g, 11.2 mmol) was added at 20 C in a single portion to a
◦
(376.5 MHz, CD2Cl2): d -140.2 (br. s), -119.1 (br. s). 29Si{ H}
1
NMR (99.4 MHz, CD2Cl2): d -161.4 (t, 1J(29Si,19F) = 192 Hz). 13
C
stirred suspension of 2 (1.66 g, 3.72 mmol) in acetonitrile (30 ml),
and the reaction mixture was then stirred at this temperature
for 18 h. The volatile constituents were removed in vacuo, and
acetonitrile (50 ml) was added to the residue. The resulting
suspension was heated until a clear solution was obtained, which
was then cooled slowly to 20 ◦C and kept undisturbed at this
temperature for 4 d. The resulting yellow crystalline solid was
isolated by filtration, washed with n-pentane (2 ¥ 5 ml) and dried
in vacuo (20 ◦C, 43 h, 0.01 mbar). Yield: 817 mg (1.53 mmol,
VACP/MAS NMR: d 21.3 (CH3), 23.8 (CH3), 25.3 (2 C) (CH3),
45.1 (CH), 46.7 (CH), 112.3, 117.7, 122.7, 125.2, 127.8 (3 C), 129.2
(3 C), 132.7, 135.7, 138.7, 141.5 and 153.1 (C6H5 and C9H6NO),
167.8 (NCN). 15N VACP/MAS NMR: d -217.8 (NCN), -190.8
(NCN), -125.5 (C9H6NO). 29Si VACP/MAS NMR: d -170 to
-155 (m). Anal. Calcd for C22H25F2N3OSi (413.54): C, 63.90; H,
6.09; N, 10.16. Found: C, 63.9; H, 6.0; N, 10.2.
(ii) Silver tetrafluoroborate (631 mg, 3.24 mmol) was added
at 20 ◦C in a single portion to a stirred solution of 2 (724 mg,
1.62 mmol) and triethylamine (328 mg, 3.24 mmol) in tetrahydro-
furan (20 ml), and the reaction mixture was then stirred at this
temperature for 3 h. The resulting precipitate was filtered off and
discarded, and the solvent of the filtrate was removed in vacuo,
followed by the addition of acetonitrile (15 ml). The resulting
suspension was heated until a clear solution was obtained, which
was then cooled slowly to 20 ◦C and kept undisturbed at this
temperature for 1 d. The resulting yellow crystalline solid was
isolated by filtration, washed with n-pentane (2 ¥ 5 ml) and dried
in vacuo (20 ◦C, 5 h, 0.01 mbar). Yield: 476 mg (1.15 mmol, 71%).
The analytical data of the product match with those obtained for
the product synthesised according to method (i).
◦
1
41%). Mp: >180 C (dec.). H NMR (500.1 MHz, CD2Cl2): d
-0.15 (br. s, 3 H, CH3), 1.16–1.50 (m, 9 H, CH3), 3.3 (m, 1 H,
CH), 4.2 (m, 1 H, CH), 7.1–7.8 (m, 9 H, C6H5 and C9H6NO),
1
8.6 (m, 1 H, H4, C9H6NO), 9.1 (m, 1 H, H2, C9H6NO). 13C{ H}
NMR (125.8 MHz, CD2Cl2): d 22.1 (br., 2 C) (CH3), 23.4 (br.,
2 C) (CH3), 47.1 (CH), 47.2 (CH), 112.9 (C7, C9H6NO), 116.1
(C5, C9H6NO), 123.1 (C3, C9H6NO), 127.3 (br., 2 C) (o-C6H5),
129.1 (i-C6H5), 129.3 (br., 2 C) (m-C6H5), 130.2 (C4a, C9H6NO),
131.1 (p-C6H5), 131.6 (C6, C9H6NO), 135.5 (C8a, C9H6NO),
139.1 (C2, C9H6NO), 140.2 (C4, C9H6NO), 151.9 (br.) (C8,
1
C9H6NO), 170.0 (NCN). 29Si{ H} NMR (99.4 MHz, CD2Cl2):
d -190 (br. s). 13C VACP/MAS NMR: d 21.2 (CH3), 24.3 (CH3),
26.1 (CH3), 27.6 (CH3), 46.8 (CH), 48.9 (CH), 114.5, 115.6,
123.2, 126.6, 127.4 (2 C), 129.6, 130.4 (2 C), 131.4, 132.5, 134.7,
139.1, 140.7 and 150.1 (C6H5 and C9H6NO), 170.3 (NCN). 15N
VACP/MAS NMR: d -209.1 (NCN), -180.5 (NCN), -129.4
(C9H6NO). 29Si VACP/MAS NMR: d -200 to -160 (m). Anal.
Calcd for C22H25Br2N3OSi (535.35): C, 49.36; H, 4.71; N, 7.85.
Found: C, 49.7; H, 4.9; N, 7.9.
Benzamidinatosilicon(IV) complex (5). Azidotrimethylsilane
(1.03 g, 8.94 mmol) was added at 20 C in a single portion to a
◦
stirred suspension of 2 (1.59 mg, 3.56 mmol) in acetonitrile (30 ml),
and the reaction mixture was then stirred at this temperature
for 17 h. The volatile constituents were removed in vacuo, and
acetonitrile (30 ml) was added to the residue. The resulting
suspension was heated until a clear solution was obtained, which
was then cooled slowly to 20 ◦C and kept undisturbed at this
temperature for 1 d. The resulting yellow crystalline solid was
isolated by filtration, washed with n-pentane (2 ¥ 5 ml) and dried
in vacuo (20 ◦C, 4 h, 0.01 mbar). Yield: 1.53 g (3.33 mmol, 93%).
Mp: >190 ◦C (dec.). 1H NMR (500.1 MHz, CD2Cl2): d -0.19 (d,
3J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.18 (d, 3J(1H,1H) = 6.8 Hz, 3 H,
CH3), 1.39 (d, 3J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.45 (d, 3J(1H,1H) =
Benzamidinatosilicon(IV) complex (4). (i) Potassium fluoride
(195 mg, 3.36 mmol) was added at 20 ◦C in a single portion to a
stirred mixture of 2 (600 mg, 1.34 mmol), 18-crown-6 (150 mg,
567 mmol) and acetonitrile (20 ml), and the reaction mixture
was then stirred at this temperature for 72 h. The solvent was
removed in vacuo, and toluene (20 ml) was added to the residue.
The remaining solid was filtered off and discarded, and the solvent
of the filtrate was removed in vacuo, followed by the addition of
acetonitrile (5 ml). The resulting mixture was heated until a clear
solution was obtained, which was then cooled slowly to 20 ◦C
and kept undisturbed at this temperature for 1 d. The resulting
yellow crystalline solid was isolated by filtration, washed with n-
pentane (2 ¥ 5 ml) and dried in vacuo (20 ◦◦C, 3 h, 0.01 mbar).
6.8 Hz, 3 H, CH3), 3.24 (sept, J(1H,1H) = 6.8 Hz, 1 H, CH),
3
3.74 (sept, J(1H,1H) = 6.8 Hz, 1 H, CH), 7.2 (br. s, 2 H, o-
3
C6H5), 7.29 (dd, J(1H,1H) = 7.7 Hz, J(1H,1H) = 0.9 Hz, 1 H,
H7, C9H6NO), 7.41 (dd, 3J(1H,1H) = 8.4 Hz, 4J(1H,1H) = 0.9 Hz,
1 H, H5, C9H6NO), 7.51–7.60 (m, 3 H, p- and m-C6H5), 7.68 (dd,
3
4
1
1 H, J(1H,1H) = 8.4 Hz, J(1H,1H) = 7.7 Hz, H6, C9H6NO),
3
3
Yield: 237 mg (573 mmol, 43%). Mp: >210 C. H NMR (500.1
7.72 (dd, 1 H, 3J(1H,1H) = 8.4 Hz, 3J(1H,1H) = 5.0 Hz, H3,
MHz, CD2Cl2): d 1.19 (br. s, 12 H, CH3), 3.42 (br. s, 2 H, CH),
7.29 (dd, 3J(1H,1H) = 7.7 Hz, 4J(1H,1H) = 0.9 Hz, 1 H, H7,
C9H6NO), 8.54 (dd, J(1H,1H) = 8.4 Hz, J(1H,1H) = 1.2 Hz, 1
3
4
3
C9H6NO), 7.30 (br. s, 2 H, o-C6H5), 7.32 (dd, J(1H,1H) = 8.3
H, H4, C9H6NO), 9.00 (dd, J(1H,1H) = 5.0 Hz, J(1H,1H) = 1.2
3
4
4
Hz, J(1H,1H) = 0.9 Hz, 1 H, H5, C9H6NO), 7.50–7.57 (m, 3 H,
Hz, 1 H, H2, C9H6NO). 13C{ H} NMR (125.8 MHz, CD2Cl2):
1
m- and p-C6H5), 7.63 (dd, 3J(1H,1H) = 8.3 Hz, 3J(1H,1H) = 7.7 Hz,
d 21.8 (CH3), 22.2 (CH3), 22.8 (CH3), 23.5 (CH3), 46.4 (CH),
47.5 (CH), 112.2 (C7, C9H6NO), 115.5 (C5, C9H6NO), 122.7 (C3,
C9H6NO), 127.0 (br., 2 C) (o-C6H5), 127.9 (i-C6H5), 129.0 (C4a,
C9H6NO), 129.6 (br., 2 C) (m-C6H5), 131.0 (p-C6H5), 131.5 (C6,
C9H6NO), 136.5 (C8a, C9H6NO), 139.8 (C2, C9H6NO), 140.8
3
3
1 H, H6, C9H6NO), 7.66 (dd, J(1H,1H) = 8.3 Hz, J(1H,1H) =
5.1 Hz, 1 H, H3, C9H6NO), 8.45 (dd, 3J(1H,1H) = 8.3 Hz,
4J(1H,1H) = 1.3 Hz, 1 H, H4, C9H6NO), 9.10 (dd, J(1H,1H) =
3
5.1 Hz, J(1H,1H) = 1.3 Hz, 1 H, H2, C9H6NO). 13C{ H} NMR
(125.8 MHz, CD2Cl2): d 22.9 (4 C) (m, CH3), 46.5 (2 C) (m,
CH), 111.7 (C7, C9H6NO), 114.6 (C5, C9H6NO), 122.6 (C3,
4
1
(C4, C9H6NO), 153.0 (C8, C9H6NO), 171.2 (NCN). 29Si{ H}
1
NMR (99.4 MHz, CD2Cl2): d -167.5. 13C VACP/MAS NMR:
d 22.2 (3 C) (CH3), 24.1 (CH3), 45.2 (CH), 47.9 (CH), 111.0,
115.0, 121.7, 125.8, 128.9 (br., 4 C), 131.2 (2 C), 132.3, 135.4,
137.7, 141.2 and 152.3 (C6H5 and C9H6NO), 170.2 (NCN). 15N
VACP/MAS NMR: d -299.8 (SiNNN), -293.2 (SiNNN), -218.0
C9H6NO), 127.7 (br., 2 C) (o-C6H5), 128.7 (t, J(19F,13C) = 2.1
4
Hz, i-C6H5), 129.0 (C4a, C9H6NO), 130.5 (br., 3 C) (p- and m-
C6H5), 131.3 (C6, C9H6NO), 136.7 (C8a, C9H6NO), 139.9 (C2,
C9H6NO), 140.2 (C4, C9H6NO) 154.0 (t, 3J(19F,13C) = 2.6 Hz, C8,
9846 | Dalton Trans., 2011, 40, 9844–9857
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◦
(NCN), -208.5 (SiNNN), -204.5 (SiNNN), -187.2 (NCN), -133.0
(br., 2 N) (SiNNN), -130.4 (C9H6NO). 29Si VACP/MAS NMR: d
-169.4. Anal. Calcd for C22H25N9OSi (459.59): C, 57.50; H, 5.48;
N, 27.43. Found: C, 57.6; H, 5.6; N, 27.8.
682 mg (1.39 mmol, 79%). Mp: >170 C (dec.).1H NMR (500.1
MHz, CD2Cl2): d -0.15 (d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.18
3
(d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.43 (d, J(1H,1H) = 6.8 Hz,
3
3
3 H, CH3), 1.49 (d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 3.22 (sept,
3
3J(1H,1H) = 6.8 Hz, 1 H, CH), 3.82 (sept, J(1H,1H) = 6.8 Hz, 1
3
Benzamidinatosilicon(IV) complex (6). Potassium cyanate
(461 mg, 5.68 mmol) was added at 20 ◦C in a single portion
to a stirred mixture of 2 (1.26 g, 2.82 mmol), 18-crown-6 (225
mg, 851 mmol) and acetonitrile (50 ml), and the reaction mixture
was then stirred at this temperature for 19 h. The solvent was
removed in vacuo, and toluene (50 ml) was added to the residue.
The remaining solid was filtered off and discarded, and the solvent
of the filtrate was removed in vacuo, followed by the addition
of acetonitrile (10 ml). The resulting mixture was heated until
a clear solution was obtained, which was then cooled slowly to
20 ◦C and kept undisturbed at this temperature for 2 d. The
resulting yellow crystalline solid was isolated by filtration, washed
with n-pentane (2 ¥ 5 ml) and dried in vacuo (20 ◦◦C, 4 h, 0.01
mbar). Yield: 714 mg (1.55 mmol, 55%). Mp: >180 C (dec.). 1H
NMR (500.1 MHz, CD2Cl2): d -0.18 (br. d, 3J(1H,1H) = 6.8 Hz,
H, CH), 7.2 (br. s, 2 H, o-C6H5), 7.32 (dd, J(1H,1H) = 7.7 Hz,
3
4J(1H,1H) = 0.9 Hz, 1 H, H7, C9H6NO), 7.47 (dd, 3J(1H,1H) = 8.3
Hz, 4J(1H,1H) = 0.9 Hz, 1 H, H5, C9H6NO), 7.52–7.62 (m, 3 H, p-
and m-C6H5), 7.72 (dd, J(1H,1H) = 8.3 Hz, J(1H,1H) = 7.7 Hz,
3
3
1 H, H6, C9H6NO), 7.75 (dd, J(1H,1H) = 8.3 Hz, J(1H,1H) =
3
3
5.1 Hz, 1 H, H3, C9H6NO), 8.59 (dd, 3J(1H,1H) = 8.3 Hz,
4J(1H,1H) = 1.2 Hz, 1 H, H4, C9H6NO), 8.99 (dd, J(1H,1H) =
3
5.1 Hz, J(1H,1H) = 1.2 Hz, 1 H, H2, C9H6NO). 13C{ H} NMR
(125.8 MHz, CD2Cl2): d 21.9 (CH3), 22.0 (CH3), 23.45 (CH3),
23.46 (CH3), 46.8 (CH), 47.9 (CH), 112.9 (C7, C9H6NO), 116.1
(C5, C9H6NO), 123.0 (C3, C9H6NO), 127.9 (br., 2 C) (o-C6H5),
129.0 (i-C6H5), 129.4 (br., 2 C) (m-C6H5) 129.6 (C4a, C9H6NO),
130.0 (p-C6H5), 131.3 (C6, C9H6NO), 136.1 (C8a, C9H6NO), 139.8
(C2, C9H6NO), 141.4 (C4, C9H6NO), 151.9 (C8, C9H6NO), 171.9
4
1
(NCN), NCS resonance signals not detected. 29Si{ H} NMR
1
3
3 H, CH3), 1.15 (br. d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.39 (br.
(99.4 MHz, CD2Cl2): d -189.3 (quint, J(29Si,14N) = 20.5 Hz).
1
3
3
d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.45 (br. d, J(1H,1H) = 6.8
13C VACP/MAS NMR: d 21.9 (CH3), 24.5 (CH3), 25.6 (CH3),
26.4 (CH3), 45.4 (CH), 48.5 (CH), 113.9, 117.9, 122.8, 124.4,
126.5, 127.1, 130.1, 132.9, (2 C), 135.1 (3 C), 140.1 (2 C) and
151.1 (C6H5, C9H6NO and NCS), 172.4 (NCN). 15N VACP/MAS
NMR: d -234.1 (NCS), -231.3 (NCS), -218.6 (NCN), -195.3
(NCN), -130.6 (C9H6NO). 29Si VACP/MAS NMR: d -190.2.
Anal. Calcd for C24H25N5OS2Si (491.71): C, 58.62; H, 5.12; N,
14.24; S, 13.04. Found: C, 58.4; H, 5.1; N, 14.1; S, 13.1.
Hz, 3 H, CH3), 3.18 (br. sept, 3J(1H,1H) = 6.8 Hz, 1 H, CH), 3.77
(br. sept, J(1H,1H) = 6.8 Hz, 1 H, CH), 7.26 (dd, J(1H,1H) =
3
3
7.6 Hz, J(1H,1H) = 0.8 Hz, 1 H, H7, C9H6NO), 7.29 (br. s, 2
4
H, o-C6H5), 7.40 (dd, J(1H,1H) = 8.3 Hz, J(1H,1H) = 0.8 Hz, 1
3
4
H, H5, C9H6NO), 7.50–7.58 (m, 3 H, m- and p-C6H5), 7.67 (dd,
3
3J(1H,1H) = 8.3 Hz, J(1H,1H) = 5.0 Hz, 1 H, H3, C9H6NO),
7.68 (dd, 3J(1H,1H) = 8.3 Hz, 3J(1H,1H) = 7.6 Hz, 1 H, H6,
3
4
C9H6NO), 8.51 (dd, J(1H,1H) = 8.3 Hz, J(1H,1H) = 1.2 Hz, 1
H, H4, C9H6NO), 9.00 (br. dd, J(1H,1H) = 5.0 Hz, J(1H,1H)
3
4
Benzamidinatosilicon(IV) complex (8). Trifluoromethanesul-
fonatotrimethylsilane (800 mg, 3.60 mmol) was added at 20 ◦C in
a single portion to a stirred suspension of 2 (730 mg, 1.64 mmol)
in acetonitrile (30 ml), and the reaction mixture was stirred at
this temperature for 17 h. The volatile constituents were removed
in vacuo, and acetonitrile (5 ml) was added to the residue.
The resulting suspension was heated until a clear solution was
obtained, which was then cooled slowly to -20 ◦C and kept
undisturbed at this temperature for 1 d. The resulting yellow
crystalline solid was isolated by filtration, washed with n-pentane
(2 ¥ 5 ml) and dried in vacuo (20 ◦C, 4 h, 0.01 mbar). Yield:
not resolved, 1 H, H2, C9H6NO). 13C{ H} NMR (125.8 MHz,
1
CD2Cl2): d 22.1 (CH3), 22.2 (CH3), 23.6 (br., 2 C) (CH3), 46.6
(CH), 47.4 (CH), 112.3 (C7, C9H6NO), 115.3 (C5, C9H6NO),
119.6 (br.) (NCO), 120.9 (br.) (NCO), 122.7 (C3, C9H6NO), 127.1
(br.) (o-C6H5), 127.4 (br.) (o-C6H5), 128.3 (i-C6H5), 129.1 (C4a,
C9H6NO), 129.4 (br., 2 C) (m-C6H5), 130.9 (p-C6H5), 131.5 (C6,
C9H6NO), 136.2 (C8a, C9H6NO), 139.4(C2, C9H6NO), 140.4 (C4,
C9H6NO), 152.9 (C8, C9H6NO), 170.2 (NCN). 29Si{ H} NMR
1
(99.4 MHz, CD2Cl2): d -183.5 (br. s). 13C VACP/MAS NMR: d
21.2 (CH3), 23.2 (2 C) (CH3), 26.9 (CH3), 45.6 (CH), 48.3 (CH),
112.0, 114.3, 118.5, 122.1, 127.2 (3 C), 128.9, 129.6, 130.9 (2 C),
135.1, 137.7, 140.5 and 152.1 (C6H5 and C9H6NO), 170.9 (NCN),
NCO resonance signals not detected. 15N VACP/MAS NMR: d
-319.9 (NCO), -314.8 (NCO), -218.4 (NCN), -188.0 (NCN),
-127.3 (C9H6NO). 29Si VACP/MAS NMR: d -184.6. Anal. Calcd
for C24H25N5O3Si (459.58): C, 62.72; H, 5.48; N, 15.24. Found: C,
62.6; H, 5.5; N, 15.4.
◦
837 mg (1.24 mmol, 76%). Mp: >160 C (dec.).1H NMR (500.1
MHz, CD2Cl2): d -0.16 (d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 0.90
3
(d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 1.35 (d, J(1H,1H) = 6.8 Hz,
3
3
3 H, CH3), 1.41 (d, J(1H,1H) = 6.8 Hz, 3 H, CH3), 3.36 (sept,
3
3J(1H,1H) = 6.8 Hz, 1 H, CH), 3.82 (sept, J(1H,1H) = 6.8 Hz, 1
3
H, CH), 7.3 (br. s, 2 H, o-C6H5), 7.40 (dd, J(1H,1H) = 7.7 Hz,
3
4J(1H,1H) = 0.9 Hz, 1 H, H7, C9H6NO), 7.55 (dd, 3J(1H,1H) = 8.4
Hz, 4J(1H,1H) = 0.9 Hz, 1 H, H5, C9H6NO), 7.56–7.68 (m, 3 H, p-
Benzamidinatosilicon(IV) complex (7). Trimethyl(thiocyanato-
N)silane (509 mg, 3.88 mmol) was added at 20 ◦C in a single
portion to a stirred suspension of 2 (787 mg, 1.76 mmol) in
acetonitrile (25 ml), and the reaction mixture was then stirred
at this temperature for 18 h. The volatile constituents were
removed in vacuo, and acetonitrile (5 ml) was added to the
residue. The resulting suspension was heated until a clear solution
was obtained, which was then cooled slowly to 20 ◦C and kept
undisturbed at this temperature for 1 d. The resulting yellow
crystalline solid was isolated by filtration, washed with n-pentane
(2 ¥ 5 ml) and dried in vacuo (20 ◦C, 4 h, 0.01 mbar). Yield:
and m-C6H5), 7.79 (dd, J(1H,1H) = 8.4 Hz, J(1H,1H) = 7.7 Hz,
3
3
1 H, H6, C9H6NO), 7.87 (dd, J(1H,1H) = 8.4 Hz, J(1H,1H) =
3
3
5.1 Hz, 1 H, H3, C9H6NO), 8.72 (dd, 3J(1H,1H) = 8.4 Hz,
4J(1H,1H) = 1.2 Hz, 1 H, H4, C9H6NO), 9.13 (dd, J(1H,1H) =
3
5.1 Hz, J(1H,1H) = 1.2 Hz, 1 H, H2, C9H6NO). 13C{ H} NMR
(125.8 MHz, CD2Cl2): d 21.4 (CH3), 22.40 (CH3), 22.42 (CH3),
23.1 (CH3), 47.3 (CH), 48.4 (CH), 113.6 (C7, C9H6NO), 116.8 (C5,
C9H6NO), 123.3 (C3, C9H6NO), 127.4 (C4a, C9H6NO), 126.8 (br.,
2 C) (o-C6H5), 128.2 (br., 2 C) (m-C6H5), 128.7 (i-C6H5), 129.3 (br.)
(CF3), 130.1 (br.) (CF3), 130.3 (p-C6H5), 131.8 (C6, C9H6NO),
4
1
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136.6 (C8a, C9H6NO), 140.6(C2, C9H6NO), 142.9(C4, C9H6NO),
on a glass fiber and then transferred to the cold nitrogen gas
stream of the diffractometer (Stoe IPDS diffractometer, graphite-
1
151.2 (C8, C9H6NO), 174.8 (NCN).19F{ H} NMR (376.5 MHz,
CD2Cl2): d -78.53 (q, J(19F,19F) = 1.7 Hz, CF3), -78.31 (q,
monochromated Mo-Ka radiation, l = 0.71073 A). All structures
˚
1
J(19F,19F) = 1.7 Hz, CF3). 29Si{ H} NMR (99.4 MHz, CD2Cl2): d
were solved by direct methods.9 The non-hydrogen atoms were
refined anisotropically.9 A riding model was employed in the
refinement of the CH hydrogen atoms. The crystallographic data
for the structures are reported in the ESI.‡
-171.2. 13C VACP/MAS NMR (data for two crystallographically
independent molecules): d 20.6 (2 C) (CH3), 22.3 (4 C) (CH3), 23.2
(2 C) (CH3), 42.6 (br., 4 C) (CH), 112.2 (3 C), 117.9, 119.5, 123.7,
125.0, 126.3 (2 C), 127.1 (3 C), 128.8 (6 C), 129.9 (5 C), 131.7 (3 C),
136.7 (2 C), 142.1, 142.8, 144.5, 145.0, 150.8 and 151.3 (CF3, C6H5
and C9H6NO), 174.2 (NCN), 175.1 (NCN). 15N VACP/MAS
NMR (data for two crystallographically independent molecules):
d -208.8 (2 N) (NCN), -200.9 (NCN), -199.4 (NCN), -140.7
(C9H6NO), -140.1 (C9H6NO). 29Si VACP/MAS NMR (data for
two crystallographically independent molecules): d -171.0 (2 Si).
Anal. Calcd for C24H25F6N3O7S2Si (673.69): C, 42.79; H, 3.74; N,
6.24; S, 9.52. Found: C, 42.5; H, 3.8; N, 6.1; S, 9.6.
Results and discussion
Syntheses
The pentacoordinate trichlorosilicon(IV) complex 1 was synthe-
sised according to Scheme 2 by treatment of lithium N,N¢-
diisopropylbenzamidinate in diethyl ether with a small excess
of tetrachlorosilane (yield 77%). Treatment of 1 with one mo-
lar equivalent of each 8-hydroxyquinoline and triethylamine in
tetrahydrofuran afforded the hexacoordinate dichlorosilicon(IV)
complex 2 (Scheme 2; yield 47%).
Benzamidinatosilicon(IV) complex (9). Triethylamine (592 mg,
5.85 mmol) and benzene-1,2-diol (321 mg, 2.92 mmol) were added
at 20 ◦C in single portions one after another to a stirred solution
of 2 (1.30 g, 2.91 mmol) in tetrahydrofuran (35 ml), and the
reaction mixture was then stirred at this temperature for 16 h. The
resulting precipitate was filtered off and discarded, and the solvent
of the filtrate was removed in vacuo, followed by the addition of
acetonitrile (35 ml). The resulting mixture was heated until a clear
solution was obtained, which was then cooled slowly to 20 ◦C
and kept undisturbed at this temperature for 5 d. The resulting
yellow crystalline solid was isolated by filtration, washed with n-
pentane (2 ¥ 5 ml) and dried in vacuo (20 ◦C, 3 h, 0.01 mbar).
Yield: 971 mg (2.01 mmol, 69%). Mp: >180 ◦C (dec.). 1H NMR
(500.1 MHz, CD2Cl2): d -0.2 to 1.4 (m, 12 H, CH3), 3.24–3.54
(m, 2 H, CH), 6.54–6.69 (m, 4 H, C6H4O2), 7.13 (dd, 3J(1H,1H) =
4
7.7 Hz, J(1H,1H) = 0.9 Hz, 1 H, H7, C9H6NO), 7.25 (br. s, 2
3
4
H, o-C6H5), 7.30 (dd, J(1H,1H) = 8.4 Hz, J(1H,1H) = 0.9 Hz,
1 H, H5, C9H6NO) 7.40–7.57 (m, 3 H, p- and m-C6H5), 7.58–
3
7.65 (m, 2 H, H3 and H6, C9H6NO), 8.48 (dd, J(1H,1H) = 8.4
4
Hz, J(1H,1H) = 1.2 Hz, 1 H, H4, C9H6NO), 9.07 (br. dd, 1 H,
3J(1H,1H) and J(1H,1H) not resolved, H2, C9H6NO). 13C{ H}
NMR (125.8 MHz, CD2Cl2): d 22.6 (3 C) (CH3), 22.5 (1 C)
(CH3), 46.4 (2 C) (CH), 111.5 (C7, C9H6NO), 111.7 (br., 2 C)
(C6H4O2), 113.8 (br., 2 C) (C6H4O2), 118.4 (C5, C9H6NO), 122.5
(C3, C9H6NO), 127.6 (br., 2 C) (o-C6H5), 128.1 (br., 2 C) (C6H4O2),
128.9 (i-C6H5), 129.1 (C4a, C9H6NO), 129.2 (br., 2 C) (m-C6H5),
130.5 (p-C6H5), 131.6 (C6, C9H6NO), 136.7 (C8a, C9H6NO), 140.8
4
1
Scheme 2 Syntheses of compounds 1 and 2.
The hexacoordinate dibromosilicon(IV) complex 3 was pre-
pared according to Scheme 3 by treatment of the corresponding
dichlorosilicon(IV) complex 2 with an excess of bromotrimethylsi-
lane in acetonitrile (yield 41%).
(C4, C9H6NO), 142.4 (br.) (C2, C9H6NO) 150.9 (C8, C9H6NO),
1
170.9 (NCN). 29Si{ H} NMR (99.4 MHz, CD2Cl2): d -146.6. 13
C
VACP/MAS NMR: d 20.0 (CH3), 21.4 (CH3), 24.2 (CH3), 26.5
(CH3), 46.0 (br., 2 C) (CH), 109.3, 111.3 (3 C) 112.9, 118.2 (2 C),
122.6, 126.7 (2 C), 128.1, 129.1 (2 C), 130.3, 132.5, 137.1, 138.4,
142.9, 150.5, 152.8 and 154.6 (C6H5, C6H4O2 and C9H6NO), 172.6
(NCN). 15N VACP/MAS NMR: d -215.6 (NCN), -198.7 (NCN),
-129.3 (C9H6NO). 29Si VACP/MAS NMR: d -145.9. Anal. Calcd
for C28H29N3O3Si (483.64): C, 69.54; H, 6.04; N, 8.69. Found: C,
69.2; H, 5.9; N, 8.9.
Scheme 3 Synthesis of compound 3.
The hexacoordinate difluorosilicon(IV) complex 4 was synthe-
sised according to Scheme 4, starting from the corresponding
dichlorosilicon(IV) complex 2. Compound 4 was obtained by
treatment of 2 either with (i) two molar equivalents of potassium
fluoride in the presence of 18-crown-6 (yield 43%) or with (ii)
Crystal structure analyses
Suitable single crystals of 2–9 were obtained as described in the
synthetic procedures in the Experimental section. The crystals
were mounted in inert oil (perfluoropolyalkyl ether, ABCR)
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Scheme 6 Synthesis of compound 6.
ing to Scheme 7 resulted in the formation of the corresponding
bis(trifluoromethanesulfonato)silicon(IV) complex 8 (yield 76%).
Scheme 4 Syntheses of compound 4.
two molar equivalents each of silver tetrafluoroborate and triethy-
lamine (yield 71%). Acetonitrile and tetrahydrofuran, respectively,
served as the solvent. The advantage of the second method is the
higher yield (71% vs. 43%) and the much shorter reaction time
(3 h vs. 72 h).
The hexacoordinate diazidosilicon(IV) complex 5 and its
di(thiocyanato-N) analogue 7 were synthesised according to
Scheme 5 by treatment of the corresponding dichlorosili-
con(IV) complex 2 with an excess of azidotrimethylsilane
and trimethyl(thiocyanato-N)silane, respectively, in acetonitrile
(yields: 5, 93%; 7, 79%).
Scheme 7 Synthesis of compound 8.
Furthermore, it was possible to substitute the two monoanionic
chloro ligands of 2 by one dianionic bidentate benzene-1,2-diolato
ligand. Thus, treatment of the hexacoordinate dichlorosilicon(IV)
complex 2 with one molar equivalent of benzene-1,2-diol and
two molar equivalents of triethylamine in tetrahydrofuran ac-
cording to Scheme 8 afforded the corresponding (benzene-1,2-
diolato)silicon(IV) complex 9 (yield 69%).
Scheme 8 Synthesis of compound 9.
Compound 1 was isolated as a colorless crystalline solid,
whereas 2–9 were obtained as yellow crystalline solids. All
compounds are sensitive against water, and 2–9 are additionally
sensitive against light and have to be stored in the dark to prevent
slow decomposition.
Scheme 5 Syntheses of compounds 5 and 7.
The identities of 1–9 were established by elemental analyses (C,
H, N, S), NMR-spectroscopic studies in the solid state (13C, 15N,
29Si) and in solution (1H, 13C, 19F, 29Si) and by crystal structure
analyses (except for 1).
Surprisingly, the synthetic method used for the preparation
of 3, 5 and 7 could not be applied to the synthesis of the
analogous di(cyanato-N)silicon(IV) complex 6. After treatment of
2 with an excess of (cyanato-N)trimethylsilane only the starting
materials could bereisolated(identification of 2 and Me3SiNCO by
NMR spectroscopy). However, compound 6 could be synthesised
according to Scheme 6 by treatment of 2 with two molar
equivalents of potassium cyanate in the presence of 18-crown-6
(yield 55%). Acetonitrile served as the solvent.
The two chloro ligands of 2 could not only be substi-
tuted by (pseudo)halogeno ligands. Treatment of the hexa-
coordinate dichlorosilicon(IV) complex 2 with an excess of
trimethyl(trifluoromethanesulfonato)silane in acetonitrile accord-
Crystal structure analyses
Compounds 2–9 were structurally characterised by single-crystal
X-ray diffraction. The crystal data and the experimental parame-
ters used for the crystal structure analyses are given in Tables 1 and
2. The molecular structures of 2–9 are shown in Fig. 1–8; selected
bond lengths and angles are given in the respective figure legends.
The Si-coordination polyhedra of the hexacoordinate silicon(IV)
complexes 2–9 are distorted octahedra, with maximum deviations
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Table 1 Crystallographic data for compounds 2–5
Compound
2
3
4
5
Empirical formula
Formula mass/g mol-1
T/K
C22H25Cl2N3OSi
446.44
173(2)
0.71073
Monoclinic
P21/c (14)
15.6475(14)
9.7128(8)
15.3985(16)
90
107.087(11)
90
2237.0(4)
4
1.326
0.362
C22H25Br2N3OSi
535.36
173(2)
C22H25F2N3OSi
413.54
173(2)
0.71073
Monoclinic
P21/c (14)
14.657(2)
9.7605(8)
15.470(2)
90
110.049(16)
90
2079.0(4)
4
1.321
0.149
C22H25N9OSi
459.60
173(2)
˚
l(Mo-Ka)/A
0.71073
0.71073
Triclinic
Crystal system
Triclinic
¯
¯
Space group (no.)
P1 (2)
P1 (2)
˚
a/A
8.1749(16)
9.919(2)
14.424(3)
94.61(3)
102.42(3)
95.80(3)
1130.1(4)
2
9.3090(19)
9.898(2)
14.013(3)
109.12(3)
94.07(3)
98.48(3)
1196.8(4)
2
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
˚
V/A
Z
r
calcd/g cm-1
1.573
3.658
540
0.5 ¥ 0.2 ¥ 0.2
4.82–58.22
-11 £ h £ 11,
-13 £ k £ 13,
-19 £ l £ 19
16443
5566
0.0448
266
1.077
0.0722/0.5002
0.0381
0.1191
1.275
0.132
484
0.5 ¥ 0.5 ¥ 0.5
6.20–58.26
-11 £ h £ 12,
-13 £ k £ 13,
-19 £ l £ 19
13488
5854
0.0328
302
1.102
0.0544/0.4103
0.0401
0.1196
m/mm-1
F(000)
936
872
Crystal dimensions/mm
0.5 ¥ 0.4 ¥ 0.2
5.02–58.16
-21 £ h £ 21,
-13 £ k £ 13,
-21 £ l £ 21
31467
5956
0.0425
266
1.066
0.5 ¥ 0.4 ¥ 0.3
5.02–55.76
-19 £ h £ 19,
-12 £ k £ 12,
-19 £ l £ 19
15548
4918
0.0369
266
1.040
2q range/◦
Index ranges
Number of collected reflections
Number of independent reflections
Rint
Number of parameters
Sa
Weight parameters a/bb
0.0522/0.7972
0.0386
0.1029
0.0553/0.5034
0.0371
0.1025
c
R1 [I > 2s(I)]
d
wR2 (all data)
-3
˚
Max./min. residual electron density/e A
+0.372/-0.398
+0.644/-0.936
+0.307/-0.301
+0.412/-0.390
2
2
a S = {R[w(Fo - Fc2)2]/(n - p)}0.5; n = number of reflections; p = number of parameters. b w-1 = s (Fo2) + (aP)2 + bP, with P = [max(Fo2,0) + 2Fc2]/3.
c R1 = RꢀFo| - |Fcꢀ/R|Fo|. d wR2 = {R[w(Fo - Fc2)2]/R[w(Fo2)2]}
.
2
0.5
Fig. 1 Molecular structure of 2 in the crystal (probability level of
displacement ellipsoids 50%). Selected bond lengths [A] and angles
Fig.
2 Molecular structure of 3 in the crystal (probability level
˚
˚
of displacement ellipsoids 50%). Selected bond lengths [A] and
angles [◦]: Si–Br(1) 2.3750(10), Si–Br(2) 2.3703(12), Si–O 1.739(2),
Si–N(1) 1.899(3), Si–N(2) 1.861(2), Si–N(3) 1.987(3), N(1)–C(1) 1.327(4),
N(2)–C(1) 1.342(4); Br(1)–Si–Br(2) 92.42(5), Br(1)–Si–O 95.18(8),
Br(1)–Si–N(1) 164.78(8), Br(1)–Si–N(2) 95.85(8), Br(1)–Si–N(3) 87.44(8),
Br(2)–Si–O 90.58(9), Br(2)–Si–N(1) 92.59(10), Br(2)–Si–N(2) 93.85(9),
Br(2)–Si–N(3) 175.71(8), O–Si–N(1) 99.13(11), O–Si–N(2) 167.93(12),
O–Si–N(3) 85.17(11), N(1)–Si–N(2) 69.48(11), N(1)–Si–N(3) 88.62(12),
N(2)–Si–N(3) 90.43(11), Si–N(1)–C(1) 91.25(19), Si–N(2)–C(1) 92.46(18),
N(1)–C(1)–N(2) 106.8(2).
[◦]: Si–Cl(1) 2.1738(6), Si–Cl(2) 2.1977(5), Si–O 1.7411(12), Si–N(1)
1.9043(13), Si–N(2) 1.8840(13), Si–N(3) 2.0062(13), N(1)–C(1) 1.3233(19),
N(2)–C(1) 1.3384(19); Cl(1)–Si–Cl(2) 93.52(2), Cl(1)–Si–O 95.60(5),
Cl(1)–Si–N(1) 164.39(4), Cl(1)–Si–N(2) 95.47(4), Cl(1)–Si–N(3) 90.49(4),
Cl(2)–Si–O 89.04(4), Cl(2)–Si–N(1) 90.42(4), Cl(2)–Si–N(2) 94.76(4),
Cl(2)–Si–N(3) 173.05(4), O–Si–N(1) 99.57(6), O–Si–N(2) 168.06(6),
O–Si–N(3) 84.92(5), N(1)–Si–N(2) 69.14(6), N(1)–Si–N(3) 87.21(5),
N(2)–Si–N(3) 90.50(5), Si–N(1)–C(1) 91.29(9), Si–N(2)–C(1) 91.70(9),
N(1)–C(1)–N(2) 107.72(13).
from the ideal 90◦ and 180◦ angles ranging from 19.70(7)–
21.39(6)◦ and 15.22(8)–18.78(7)◦, respectively (Table 3). These
strong distortions mainly result from the highly strained four-
membered SiN2C ring formed by the amidinato ligand and the
silicon coordination centre, with N–Si–N angles ranging from
68.61(6)◦ to 70.30(7)◦. The two (pseudo)halogeno ligands of
9850 | Dalton Trans., 2011, 40, 9844–9857
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Table 2 Crystallographic data for compounds 6–9
Compound
6
7
8
9
Empirical formula
Formula mass/g mol-1
T/K
C24H25N5O3Si
459.58
173(2)
C24H25N5OS2Si
491.70
173(2)
0.71073
Monoclinic
P21/c (14)
11.5619(18)
13.4356(18)
16.906(3)
90
109.346(18)
90
2478.0(7)
4
1.318
0.290
C24H25F6N3O7S2Si
673.68
173(2)
0.71073
Orthorhombic
Pbca (61)
23.2733(16)
16.3163(10)
30.800(3)
90
C28H29N3O3Si
483.63
173(2)
0.71073
Monoclinic
P21/n (14)
10.9237(17)
18.318(2)
13.7567(19)
90
111.285(16)
90
2564.9(6)
4
1.252
0.126
˚
l(Mo-Ka)/A
0.71073
Crystal system
Triclinic
¯
Space group (no.)
P1 (2)
˚
a/A
8.4742(17)
10.239(2)
13.933(3)
94.55(3)
101.63(3)
95.44(3)
1172.8(4)
2
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
90
90
˚
V/A
11695.7(16)
16
1.530
0.309
5536
0.50 ¥ 0.25 ¥ 0.25
4.50–56.20
-30 £ h £ 30,
-21 £ h £ 21,
-40 £ h £ 40
148865
14160
0.0584
798
15
1.062
0.0610/5.5732
0.0439
0.1211
+0.666/–0.626
Z
r
calcd/g cm-1
1.301
0.136
484
0.5 ¥ 0.5 ¥ 0.4
6.00–58.18
-11 £ h £ 11,
-14 £ k £ 14,
-19 £ l £ 19
16905
5726
0.0348
302
0
1.087
0.0549/0.3588
0.0429
0.1236
+0.350/–0.400
m/mm-1
F(000)
1032
1024
Crystal dimensions/mm
0.5 ¥ 0.5 ¥ 0.2
4.84–58.20
-15 £ h £ 15,
-18 £ k £ 18,
-23 £ l £ 23
35139
6609
0.0457
302
0
1.052
0.0541/0.8993
0.0424
0.1159
+0.346/–0.410
0.5 ¥ 0.3 ¥ 0.1
5.46–55.76
-14 £ h £ 14,
-24 £ k £ 24,
-16 £ l £ 18
21567
6122
0.0801
320
0
0.945
0.0669/0.0000
0.0438
0.1159
+0.319/–0.281
2q range/◦
Index ranges
Number of collected reflections
Number of independent reflections
Rint
Number of parameters
Number of restraints
Sa
Weight parameters a/bb
c
R1 [I > 2s(I)]
d
wR2 (all data)
-3
˚
Max./min. residual electron density/e A
a S = {R[w(Fo - Fc2)2]/(n - p)}0.5; n = number of reflections; p = number of parameters. b w-1 = s (Fo2) + (aP)2 + bP, with P = [max(Fo2,0) + 2Fc2]/3.
2
2
c R1 = RꢀFo| - |Fcꢀ/R|Fo|. d wR2 = {R[w(Fo - Fc2)2]/R[w(Fo2)2]}
.
2
0.5
cis positions, with X–Si–X angles (X = F, Cl, Br, N, O) ranging
from 86.48(7)◦ to 93.90(5)◦. The nitrogen atoms of the bidentate
N,N ligand and N,O ligand of 2–9 show a fac arrangement, and
in all cases the nitrogen atom of the N,O ligand and one of the
(pseudo)halogeno/trifluoromethanesulfonato ligand atoms of 2–
8 (or one of the oxygen atoms of the benzene-1,2-diolato ligand
of 9) are found in trans position. Thus, the structures of the chiral
silicon(IV) complexes 2–9 (C1 symmetry) are characterised by the
same configuration. Both enantiomers of 2–9 are found in the
crystal.
The Si–O (oxygen atom of the N,O ligand) bond lengths of 2–9
˚
are in the range 1.7157(14)–1.7881(11) A (maximum difference ca.
˚
0.07 A) (Table 4). The Si–N(3) (nitrogen atom of the N,O ligand)
Fig. 3 Molecular structure of 4 in the crystal (probability level of
displacement ellipsoids 50%). Selected bond lengths [A] and angles
are significantly longer and show a higher degree of variation
(1.9556(16)–2.0834(12) A; maximum difference ca. 0.13 A) (Table
4). The Si–N(1) and Si–N(2) (N,N ligand) bond lengths are in the
range 1.8439(16)–1.9364(12) A (maximum difference ca. 0.09 A)
(Table 4). The differences in the bond lengths of the analogous
Si–O, Si–N(1), Si–N(2) and Si–N(3) bonds of 2–9 may be the
result of both substituent effects and crystal packing effects and
are therefore difficult to discuss.
˚
˚
˚
[◦]: Si–F(1) 1.5708(9), Si–F(2) 1.6880(9), Si–O 1.7881(11), Si–N(1)
1.8488(11), Si–N(2) 1.9364(12), Si–N(3) 2.0834(12), N(1)–C(1) 1.3536(18),
N(2)–C(1) 1.2823(16); F(1)–Si–F(2) 93.90(5), F(1)–Si–O 98.63(5),
F(1)–Si–N(1) 161.31(5), F(1)–Si–N(2) 93.70(5), F(1)–Si–N(3) 89.19(5),
F(2)–Si–O 86.86(5), F(2)–Si–N(1) 95.72(5), F(2)–Si–N(2) 99.07(5),
F(2)–Si–N(3) 174.25(5), O–Si–N(1) 97.87(5), O–Si–N(2) 165.94(5),
O–Si–N(3) 87.88(5), N(1)–Si–N(2) 68.97(5), N(1)–Si–N(3) 82.71(5),
N(2)–Si–N(3) 85.56(5), Si–N(1)–C(1) 91.72(8), Si–N(2)–C(1) 90.07(9),
N(1)–C(1)–N(2) 108.86(11).
˚
˚
NMR studies
2–7, the two trifluoromethanesulfonato ligands of 8 and the two
oxygen ligand atoms of the benzene-1,2-diolato ligand of 9 occupy
Compounds 1–9 were characterised by NMR spectroscopy in the
solid state (13C, 15N, 29Si) and in solution (1H, 13C, 19F, 29Si; solvent,
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Fig. 4 Molecular structure of 5 in the crystal (probability level of
displacement ellipsoids 50%). Selected bond lengths [A] and angles
Fig.
6
Molecular structure of
7
in the crystal (probability level
˚
˚
of displacement ellipsoids 50%). Selected bond lengths [A] and an-
gles [◦]: Si–O 1.7401(13), Si–N(1) 1.8901(13), Si–N(2) 1.8717(14),
Si–N(3) 2.0038(15), Si–N(4) 1.8256(14), Si–N(5) 1.8272(16), S(1)–C(23)
1.5999(17), S(2)–C(24) 1.6051(19), N(4)–C(23) 1.167(2), N(5)–C(24)
1.171(2), N(1)–C(1) 1.3243(19), N(2)–C(1) 1.3409(19); O–Si–N(1)
100.62(6), O–Si–N(2) 169.47(6), O–Si–N(3) 84.76(6), O–Si–N(4)
94.37(6), O–Si–N(5) 88.78(7), N(1)–Si–N(2) 69.47(6), N(1)–Si–N(3)
90.83(6), N(1)–Si–N(4) 164.64(6), N(1)–Si–N(5) 91.12(7), N(2)–Si–N(3)
91.68(6), N(2)–Si–N(4) 95.34(6), N(2)–Si–N(5) 94.81(7), N(3)–Si–N(4)
87.18(6), N(3)–Si–N(5) 173.50(7), N(4)–Si–N(5) 92.55(7), Si–N(4)–C(23)
173.87(14), N(4)–C(23)–S(1) 179.13(17), Si–N(5)–C(24) 162.69(15),
N(5)–C(24)–S(2) 179.61(18), Si–N(1)–C(1) 91.44(10), Si–N(2)–C(1)
91.73(9), N(1)–C(1)–N(2) 107.08(13).
[◦]: Si–O 1.7563(11), Si–N(1) 1.9126(12), Si–N(2) 1.8698(13), Si–N(3)
2.0037(15), Si–N(4) 1.8512(13), Si–N(5) 1.8465(15), N(4)–N(6) 1.2109(17),
N(5)–N(8) 1.2054(18), N(6)–N(7) 1.140(2), N(8)–N(9) 1.142(2), N(1)–C(1)
1.3206(17), N(2)–C(1) 1.3374(17); O–Si–N(1) 99.23(6), O–Si–N(2)
167.73(5), O–Si–N(3) 84.43(5), O–Si–N(4) 96.30(6), O–Si–N(5) 91.19(6),
Si–N(4)–N(6) 119.09(11), Si–N(5)–N(8) 123.28(10), N(1)–Si–N(2)
68.98(5), N(1)–Si–N(3) 87.53(6), N(1)–Si–N(4) 162.95(6), N(1)–Si–N(5)
93.70(7), N(2)–Si–N(3) 91.46(6), N(2)–Si–N(4) 95.02(6), N(2)–Si–N(5)
92.93(6), N(3)–Si–N(4) 87.01(6), N(3)–Si–N(5) 175.59(5), N(4)–Si–N(5)
92.96(6), Si–N(4)–N(6) 119.09(11), N(4)–N(6)–N(7) 176.72(17),
Si–N(5)–N(8) 123.28(10), N(5)–N(8)–N(9) 175.28(16), Si–N(1)–C(1)
91.09(8), Si–N(2)–C(1) 92.44(8), N(1)–C(1)–N(2) 107.40(11).
As can be seen from Table 5, the respective isotropic 29Si
chemical shifts in the solid state and in solution are very
similar, indicating that the penta- and hexacoordinate silicon(IV)
complexes 1–9 also exist in solution. This assumption is further
supported by all the other NMR data obtained. The isotropic
29Si chemical shifts of the hexacoordinate silicon(IV) complexes
2–9 vary from –145.9/–146.6 ppm (9, solid state/solution) to
–190.2/–189.3 ppm (7, solid state/solution), indicating a strong
dependence of the 29Si chemical shift on the different silicon-bound
ligands.
The 29Si VACP/MAS NMR spectra of the dihalogenosilicon(IV)
complexes 2–4 deserve a special discussion (Fig. 9; in this context,
see also ref. 2). Notably, the spectrum of 2 shows a relatively sharp
resonance signal although one would expect 29Si,35Cl and 29Si,37Cl
couplings (in this context, see ref. 4e). In contrast, the spectrum of 3
is characterised by a broad asymmetric “triplet” owing to dipolar
29Si,79Br and 29Si,81Br couplings,10 and in the case of 4, 29Si,19F
couplings lead to a complex resonance signal (for similar splitting
patterns in the 29Si MAS NMR spectra of other compounds with
SiF2 moieties, see ref. 2 and 11).
Due to the C1 symmetry of the hexacoordinate silicon(IV)
complexes 2–9, the four methyl groups of their amidinato ligand
are diastereotopic. Therefore, four doublets for these methyl
groups and two septets for the (CH3)2CH protons are observed
in the solution 1H NMR spectra at 23 ◦C (2, 5–8) or lower
temperatures (3, 4, 9) (Fig. 10). Quite remarkably, one of the four
doublets of 2–9 is found at ca. –0.15 ppm and is shifted by ca.
1.1–1.5 ppm to higher field compared to the other three doublets.
This can be explained by the influence of the diamagnetic ring
current of the aromatic ring system of the N,O ligand on one of
the four methyl groups. Indeed, as can be seen from the molecular
Fig.
5
Molecular structure of 6 in the crystal (probability level
˚
of displacement ellipsoids 50%). Selected bond lengths [A] and an-
gles [◦]: Si–O(1) 1.7594(13), Si–N(1) 1.9128(13), Si–N(2) 1.8789(15),
Si–N(3) 2.0114(14), Si–N(4) 1.8054(14), Si–N(5) 1.8136(15), O(2)–C(23)
1.1821(19), O(3)–C(24) 1.186(2), N(4)–C(23) 1.1712(19), N(5)–C(24)
1.152(2), N(1)–C(1) 1.319(2), N(2)–C(1) 1.3424(19); O(1)–Si–N1 96.52(6),
O(1)–Si–N(2) 164.30(6), O(1)–Si–N(3) 84.40(6), O(1)–Si–N(4) 95.71(7),
O(1)–Si–N(5) 91.27(7), Si–N(4)–C(23) 150.63(14), Si–N(5)–C(24)
158.70(15), O(2)–C(23)–N(4) 176.68(19), O(3)–C(24)–N(5) 177.9(2),
N(1)–Si–N(2) 68.98(6), N(1)–Si–N(3) 87.99(6), N(1)–Si–N(4) 166.42(7),
N(1)–Si–N(5) 92.82(7), N(2)–Si–N(3) 88.95(6), N(2)–Si–N(4) 98.18(7),
N(2)–Si–N(5) 95.32(7), N(3)–Si–N(4) 87.34(7), N(3)–Si–N(5) 175.66(7),
N(4)–Si–N(5) 92.79(7), Si–N(4)–C(23) 150.63(14), N(4)–C(23)–O(2)
176.68(19), Si–N(5)–C(24) 158.70(15), N(5)–C(24)–O(3) 177.9(2),
Si–N(1)–C(1) 91.32(10), Si–N(2)–C(1) 92.06(10), N(1)–C(1)–N(2)
107.61(13).
CD2Cl2). The NMR data obtained (see Experimental section)
confirm the identities of the compounds studied.
9852 | Dalton Trans., 2011, 40, 9844–9857
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Fig. 8 Molecular structure of 9 in the crystal (probability level of displace-
◦
˚
ment ellipsoids 50%). Selected bond lengths [A] and angles [ ]: Si–O(1)
1.7762(12), Si–O(2) 1.7520(12), Si–O(3) 1.7548(12), Si–N(1) 1.9026(13),
Si–N(2) 1.9144(13), Si–N(3) 1.9975(14), N(1)–C(1) 1.328(2), N(2)–C(1)
1.336(2); O(1)–Si–O(2) 97.50(6), O(1)–Si–O(3) 90.44(6), O(2)–Si–O(3)
91.18(6), O(1)–Si–N(1) 96.78(6), O(1)–Si–N(2) 164.21(6), O(1)–Si–N(3)
84.22(6), O(2)–Si–N(1) 164.95(6), O(2)–Si–N(2) 96.66(6), O(2)–Si–N(3)
85.18(5), O(3)–Si–N(1) 93.46(6), O(3)–Si–N(2) 96.21(6), O(3)–Si–N(3)
173.08(6), N(1)–Si–N(2) 68.61(6), N(1)–Si–N(3) 91.54(6), N(2)–Si–N(3)
90.06(6), Si–N(1)–C(1) 92.18(9), Si–N(2)–C(1) 91.41(9), N(1)–C(1)–N(2)
107.66(13).
Table 3 Maximum deviations of the X–Si–X angles (X = ligand atoms)
of 2–9 from the ideal 90◦ and 180◦ angles
Compound
D 90◦
D 180◦
Skeleton
2
20.86(6)
20.52(11)
21.03(5)
21.02(5)
21.02(6)
20.53(6)
19.70(7)
19.94(7)
21.39(6)
15.61(4)
15.22(8)
18.69(5)
17.05(6)
13.58(7)
15.36(6)
18.78(7)
16.29(7)
15.79(6)
SiN3OCl2
SiN3OBr2
SiN3OF2
SiN5O
3
4
5
6
SiN5O
7
SiN5O
8(A)
8(B)
9
SiN3O3
SiN3O3
SiN3O3
Fig. 7 Molecular structures of the two crystallographically independent
molecules of 8 in the crystal (probability level o◦f displacement ellipsoids
˚
50%). Selected bond lengths [A] and angles [ ] of molecule A (top):
˚
Table 4 Selected bond lengths [A] of 2–9
Si(1)–O(1) 1.7157(14), Si(1)–O(2) 1.7984(14), Si(1)–O(3) 1.8081(14),
Si(1)–N(1) 1.8666(17), Si(1)–N(2) 1.8439(16), Si(1)–N(3) 1.9622(17),
N(1)–C(1) 1.331(2), N(2)–C(1) 1.334(2); O(1)–Si(1)–O2 96.95(7),
O(1)–Si(1)–O(3) 88.24(7), O(2)–Si(1)–O(3) 87.11(7), O(1)–Si(1)–N(1)
101.83(7), O(1)–Si(1)–N(2) 172.11(8), O(1)–Si(1)–N(3) 86.00(7),
O(2)–Si(1)–N(1) 161.22(7), O(2)–Si(1)–N(2) 90.92(7), O(2)–Si(1)–N(3)
90.33(7), O(3)–Si(1)–N(1) 93.68(7), O(3)–Si(1)–N(2) 92.77(7),
O(3)–Si(1)–N(3) 173.38(7), N(1)–Si(1)–N(2) 70.30(7), N(1)–Si(1)–N(3)
90.71(7), N(2)–Si(1)–N(3) 93.38(7), Si(1)–N(1)–C(1) 91.09(12),
Si(1)–N(2)–C(1) 91.99(11), N(1)–C(1)–N(2) 106.61(16). Selected bond
Compound Si–O Si–N(1) Si–N(2)
Si–N(3)
Skeleton
2
1.7411(12) 1.9043(13) 1.8840(13) 2.0062(13) SiN3OCl2
1.739(2) 1.899(3) 1.861(2) 1.987(3) SiN3OBr2
3
4
1.7881(11) 1.8488(11) 1.9364(12) 2.0834(12) SiN3OF2
1.7563(11) 1.9126(12) 1.8698(13) 2.0037(15) SiN5O
1.7594(13) 1.9128(13) 1.8789(15) 2.0114(14) SiN5O
1.7401(13) 1.8901(13) 1.8717(14) 2.0038(15) SiN5O
1.7157(14)b 1.8666(17)c 1.8439(16)d 1.9622(17)e SiN3O3
1.7228(14)g 1.8493(16)h 1.8713(17)i 1.9556(16)j SiN3O3
1.7762(12) 1.9026(13) 1.9144(13) 1.9975(14) SiN3O3
5
6
7
8a
8f
9
◦
˚
lengths [A] and angles [ ] of molecule B (bottom): Si(2)–O(31) 1.7228(14),
Si(2)–O(32) 1.7872(14), Si(2)–O(33) 1.7945(14), Si(2)–N(31) 1.8493(16),
Si(2)–N(32) 1.8713(17), Si(2)–N(33) 1.9556(16), N(31)–C(31) 1.331(2),
N(32)–C(31) 1.329(2), O(31)–Si(2)–O(32) 97.70(7), O(31)–Si(2)–O(33)
88.88(7), O(32)–Si(2)–O(33) 86.48(7), O(31)–Si(2)–N(31) 98.51(7),
O(31)–Si(2)–N(32) 168.52(7), O(31)–Si(2)–N(33) 86.31(7), O(32)–Si(2)–
N(31) 163.71(7), O(32)–Si(2)–N(32) 93.70(7), O(32)–Si(2)–N(33) 88.45(7),
O(33)–Si(2)–N(31) 95.40(7), O(33)–Si(2)–N(32) 93.23(7), O(33)–Si(2)–
N(33) 172.49(7), N(31)–Si(2)–N(32) 70.06(7), N(31)–Si(2)–N(33)
91.02(7), N(32)–Si(2)–N(33) 92.62(7), Si(2)–N(31)–C(31) 92.02(11),
Si(2)–N(32)–C(31) 91.10(11), N(31)–C(31)–N(32) 106.82(16).
a Molecule A. b Si(1)–O(1). c Si(1)–N(1). d Si(1)–N(2). e Si(1)–N(3).
f Molecule B. g Si(2)–O(31). h Si(2)–N(31). i Si(2)–N(32). j Si(2) –N(33).
structures of 2–9 in the crystal (see Crystal structure analyses
section), one of the four methyl groups each is in proximity of the
aromatic ring system. This finding indicates that the structures of
2–9 in the solid state and in solution are similar.
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Table 5 Comparison of the 29Si chemical shifts [ppm] of 1–9 in the solid
state (T = 22 ◦C) and in solution (T = 23 ◦C)
Compound
d
29Si (solid state)
d
29Si (solution)a
1
2
3
4
5
6
7
8
9
-99.4
-98.2
-165.2
-162.4
-190
-200 to -160b
-170 to -155c
-169.4
-161.4d
-167.5
-183.5
-189.3e
-171.2
-146.6
-184.6
-190.2
-171.0
-145.9
a Solvent, CD2Cl2. b Complex signal splitting due to dipolar 29Si,79Br and
29Si,81Br couplings.9 c Complex signal splitting due to dipolar couplings
within the 29Si19F2 unit.2,11 d Triplet, 1J(29Si,19F) = 192 Hz. e Quintet,
1J(29Si,14N) = 20.5 Hz.
Coalescence of the four doublets and the two septets to one
broad signal each at 23 ◦C (4, 9) or above (3) could be explained by
a simultaneous exchange of the two nitrogen sites of the amidinato
ligand and the two binding sites of the N,O ligand, which breaks
the C1 symmetry of the complexes (Fig. 10). Upon cooling,
sharp resonance signals were observed for the difluorosilicon(IV)
complex 4 (Fig. 10).
Fig. 9 29Si VACP/MAS NMR spectra (urot = 7 kHz, T = 22 ◦C) of 2 (A),
3 (B) and 4 (C).
1
The solution H NMR spectra of 2–9 show broadened reso-
nance signals for the ortho and meta protons of the phenyl group
of the amidinato ligand at 23 ◦C. This can be explained by a not
completely hindered rotation of the phenyl group around the i-
C–CN2 bond, which is further supported by broadened resonance
signals for the ortho and meta carbon atoms in the 13C NMR
spectra. The temperature dependence of the 1H NMR resonance
signals is shown exemplarily for 4 in Fig. 10.
diastereomers. These results can be explained by configurational
instability of 9 in solution at room temperature resulting in a fast
exchange between the two diastereomers; at lower temperatures
this exchange becomes slower and both diastereomers can be
observed (Fig. 11).
The 29Si NMR spectrum of the difluorosilicon(IV) complex 4 in
◦
solution at 23 C shows a triplet (Fig. 12), indicating a dynamic
In addition to the above mentioned findings for compounds
process, which renders the two 1J(29Si,19F) cou◦pling constants
equal on the NMR time scale. However, at -50 C a doublet of
doublets is found, reflecting the presence of two slightly different
1J(29Si,19F) coupling constants (Fig. 12).
1
3, 4 and 9, the H and 13C NMR spectra of 3 and 9 also show
broadened resonance signals for the bidentate N,O ligand, for
the resonance signals of the silicon coordination centre, and in
the case of 9 for the bidentate O,O ligand. While the broadened
resonance signals of compound 3 just become sharp at lower
temperature (-60 ◦C), a complete second set of resonance signals
Analogously to the 29Si NMR spectrum, the 19F NMR spectrum
of 4 also shows a temperature dependence (Fig. 13). While at
◦
◦
23 C two very broad resonance signals are found, at -50 C an
AX system (2J(19F,19F) = 22.3 Hz) is observed, again reflecting the
non-equivalence of the two fluoro ligands.
1
is observed in the respective H, 13C and 29Si NMR spectra of 9
at this temperature (ratio, 1 : 4), indicating the presence of two
1
Fig. 10 Temperature dependence of the H NMR resonance signals of the CH3CHCH3 protons (right), the CH3CHCH3 protons (middle) and the
protons of the aromatic rings (left, partial spectra) of 4 (solvent, CD2Cl2; 500.1 MHz). The temperature dependence of the 1H NMR spectra is completely
reversible upon heating/cooling.
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Fig. 11 Temperature dependence of the 29Si NMR spectrum of 9 (solvent,
CD2Cl2; 99.4 MHz). The temperature dependence of the 29Si NMR
spectrum is completely reversible upon heating/cooling.
Fig. 13 Temperature dependence of the 19F NMR spectrum of 4 (solvent,
CD2Cl2; 282.4 MHz). For reasons of visibility, the spectrum at 23 ◦C has
been scaled up by a factor of 60. The temperature dependence of the 19
NMR spectrum is completely reversible upon heating/cooling.
F
Fig. 12 Temperature dependence of the 29Si NMR spectrum of 4 (solvent,
CD2Cl2; 99.4 MHz). The temperature dependence of the 29Si NMR
spectrum is completely reversible upon heating/cooling.
The 19F NMR spectrum of the bis(trifluoromethane-
sulfonato)silicon(IV) complex 8 shows two quartets at 23 ◦C
(J(19F,19F) = 1.7 Hz, Fig. 14). As 19F,19F NOESY NMR ex-
periments did not indicate interactions between the two trifluo-
romethyl groups, the 19F,19F coupling observed may result from
through-bond interactions (8J(19F,19F) coupling); however, it can-
not be excluded that through-space interactions are not monitored
by the NOE experiments. The 19F NMR spectrum shown in Fig. 14
does not suggest an exchange of the two trifluoromethylsulfonato
ligands at ambient temperature as observed for the two fluoro
ligands of 4 (see above), but 19F,19F EXSY NMR experiments with
8 at 23 ◦C indicate such kind of exchange process (Fig. 15). Cross
peaks between the two trifluoromethyl signals were observed at
Fig. 14 19F NMR spectrum of 8 at 23 ◦C (solvent, CD2Cl2; 376.5 MHz).
◦
◦
23 C, and at 60 C the extent of exchange increases, whereas at
-60 ◦C no cross peaks could be observed at all.
While the 29Si NMR spectrum of the di(cyanato-N)silicon(IV)
complex 6 in solution shows a relatively sharp singlet at 23 ◦C,
a well resolved quintet (1J(29Si,14N) couplings) is found for the
di(thiocyanato-N) analogue 7 (Fig. 16). Obviously, only the
nitrogen atoms of the two thiocyanato-N ligands seem to be
responsible for this signal splitting (in this context, see also ref.
12). These differences in the 29Si NMR spectra of the NCO/NCS
analogues 6 (singlet) and 7 (quintet, 1J(29Si,14N) coupling) are not
yet fully understood but it seems that in complex 6 the quadrupolar
relaxation of the 14N nuclei is the dominant relaxation process,
Fig. 15 19F,19F EXSY NMR spectrum of 8 at 23 ◦C (solvent, CD2Cl2;
282.4 MHz).
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hindered in solution at ambient temperature. In addition, the
NMR spectroscopic investigations (including VT and EXSY
experiments) revealed the existence of different exchange processes
in solution: (i) exchange of the two nitrogen sites of the N,N
ligand, (ii) exchange of the nitrogen and oxygen sites of the
N,O ligand (leading to diastereomeric species), and (iii) exchange
of the two monodentate ligands. The activation barriers of
these processes depend on the nature of the two monoden-
tate (pseudo)halogeno/trifluoromethanesulfonato ligand (or the
bidentate benzene-1,2-diolato ligand). The mechanism of these
exchange processes is unknown, and it is unclear as to whether or
not these processes are coupled with each other.
In conclusion, the amidinato ligand system has been demon-
strated to have a high synthetic potential for the chemistry of
penta- and hexacoordinate silicon, allowing the synthesis of novel
types of element combinations in the silicon coordination sphere
(in this context, see also ref. 2) and leading to novel types of static
and dynamic stereochemistry.
Fig. 16 29Si NMR spectra of 6 (left) and 7 (right) at 23 ◦C (solvent,
CD2Cl2; 99.4 MHz).
while in compound 7 the quadrupolar relaxation of the 14N
nuclei is less dominant due to a much smaller electric field
gradient, so that the 1J(29Si,14N) coupling becomes observable.
Conclusions
With the synthesis of compounds 2–9, a series of novel neu-
tral hexacoordinate monoamidinatosilicon(IV) complexes with
SiN3OF2, SiN3OCl2, SiN3OBr2, SiN5O and SiN3O3 skeletons
has been made available. Compounds 3 (SiN3OBr2 skeleton), 4
(SiN3OF2) and 5–7 (SiN5O) are of particular interest as neutral
hexacoordinate silicon(IV) complexes with such Si-coordination
polyhedra have not yet been reported in the literature. Compound
9 (SiN3O3 skeleton) shows also remarkable structural features:
this heteroleptic hexacoordinate silicon(IV) complex contains three
different bidentate ligands.
To the best of our knowledge, compound 1 (prepared from
tetrachlorosilane in a one-step synthesis) is the first neutral penta-
coordinate monoamidinatosilicon(IV) complex (SiN2Cl3 skeleton)
that has been used as a starting material for the synthesis of neutral
hexacoordinate silicon(IV) complexes. It has been demonstrated
that the dichlorosilicon(IV) complex 2 is a versatile precursor
for the synthesis of other neutral hexacoordinate silicon(IV)
complexes (compounds 3–9) by substitution of the two chloro
ligands by other mono- or bidentate ligands. In the targeted
three-step syntheses of 3–9 (SiCl4 → 1 → 2 → 3–9), the N,N¢-
diisopropylbenzamidinato ligand has been demonstrated to have
a high synthetic potential for the chemistry of hexacoordinate
silicon(IV) complexes.
Compounds 2–9 show a relatively high thermal stability al-
though they contain a highly strained four-membered SiN2C
ring, with N–Si–N angles in the range 68.61(6)◦ to 70.30(7)◦.
Compounds 2–9 exist both in the solid state and in solution.
Their molecular structures (C1 symmetry) are best described in
terms of distorted octahedral Si-coordination polyhedra, with the
two (pseudo)halogeno/trifluoromethanesulfonato ligands and the
benzene-1,2-diolato ligand atoms, respectively, in cis positions.
The nitrogen atoms of the bidentate N,N and N,O ligands of 2–9
adopt a fac arrangement, and the nitrogen atom of the N,O lig-
and and one of the (pseudo)halogeno/trifluoromethanesulfonato
ligands (or one of the oxygen atoms of the benzene-1,2-diolato
ligand) are found in trans positions; i.e., all compounds studied
show the same stereochemical features. According to NMR
spectroscopic studies, it is likely that the structures of 2–9 in the
solid state and in solution are very similar.
References
1 (a) H. W. Roesky, B. Meller, M. Noltemeyer, H.-G. Schmidt, U. Scholz
and G. M. Sheldrick, Chem. Ber., 1988, 121, 1403–1406; (b) H. H.
Karsch, P. A. Schlu¨ter and M. Reisky, Eur. J. Inorg. Chem., 1998, 433–
436; (c) C.-W. So, H. W. Roesky, J. Magull and R. B. Oswald, Angew.
Chem., Int. Ed., 2006, 45, 3948–3950; (d) C.-W. So, H. W. Roesky, P.
M. Gurubasavaraj, R. B. Oswald, M. T. Gamer, P. G. Jones and S.
Blaurock, J. Am. Chem. Soc., 2007, 129, 12049–12054; (e) L.-D. Lv,
J.-J. Li, W. Yang, C.-X. Ren and Y.-Q. Ding, Acta Crystallogr., Sect.
E: Struct. Rep. Online, 2008, 64, o870; (f) S. S. Sen, H. W. Roesky, D.
Stern, J. Henn and D. Stalke, J. Am. Chem. Soc., 2010, 132, 1123–1126.
2 K. Junold, C. Burschka, R. Bertermann and R. Tacke, Dalton Trans.,
2010, 39, 9401–9413.
3 Selected reviews dealing with higher-coordinate silicon(IV) compounds:
(a) R. R. Holmes, Chem. Rev., 1996, 96, 927–950; (b) V. Pestunovich,
S. Kirpichenko and M. Voronkov, in The Chemistry of Organic Silicon
Compounds, Vol. 2, Part 2 (ed., Z. Rappoport and Y. Apeloig), Wiley,
Chichester, 1998, pp. 1447–1537; (c) C. Chuit, R. J. P. Corriu and
C. Reye, in Chemistry of Hypervalent Compounds (ed., K.-y. Akiba),
Wiley-VCH, New York, 1999, pp. 81–146; (d) R. Tacke, M. Pu¨lm
and 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 and O. Seiler, in Silicon
Chemistry: From the Atom to Extended Systems (ed., P. Jutzi and U.
Schubert), Wiley-VCH, Weinheim, 2003, pp. 324–337; (g) D. Kost and
I. Kalikhman, Adv. Organomet. Chem., 2004, 5, 1–106; (h) D. Kost
and I. Kalikhman, Acc. Chem. Res., 2009, 42, 303–314; (i) E. P. A.
Couzijn, J. C. Slootweg, A. W. Ehlers and K. Lammertsma, Z. Anorg.
Allg. Chem., 2009, 635, 1273–1278.
4 (a) B. Theis, S. Metz, F. Back, C. Burschka and R. Tacke, Z. Anorg.
Allg. Chem., 2009, 635, 1306–1312; (b) S. Metz, C. Burschka and R.
Tacke, Chem.–Asian J., 2009, 4, 581–568; (c) S. Metz, C. Burschka and
R. Tacke, Organometallics, 2009, 28, 2311–2317; (d) B. Theis, S. Metz,
C. Burschka, R. Bertermann, S. Maisch and R. Tacke, Chem.–Eur.
J., 2009, 15, 7329–7338; (e) S. Metz, B. Theis, C. Burschka and R.
Tacke, Chem.–Eur. J., 2010, 16, 6844–6856; (f) S. Cota, M. Beyer, R.
Bertermann, C. Burschka, K. Go¨tz, M. Kaupp and R. Tacke, Chem.–
Eur. J., 2010, 16, 6582–6589.
5 Selected publications dealing with higher-coordinate silicon(IV) com-
plexes containing ligands derived from 8-hydroxyquinoline: (a) J.
Wagler, M. Schley, D. Gerlach, U. Bo¨hme, E. Brendler and G. Roewer,
Z. Naturforsch., 2005, 60b, 1054–1064; (b) M. G. Voronkov, O. M.
Trofimova, N. F. Chernov, A. I. Albanov, N. N. Chipanina and E. A.
Grebneva, Appl. Organomet. Chem., 2005, 19, 538–541; (c) J. Wagler,
D. Gerlach and G. Roewer, Chem. Heterocycl. Compd., 2006, 42, 1557–
1567; (d) E. Brendler, E. Wa¨chtler and J. Wagler, Organometallics, 2009,
28, 5459–5465.
As shown by NMR spectroscopic studies, the free rotation
of the phenyl group of 2–9 around the i-C–CN2 bond is
6 I. Kalikhman, V. Kingston, O. Girshberg and D. Kost, Organometallics,
2001, 20, 4713–4720.
9856 | Dalton Trans., 2011, 40, 9844–9857
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
7 J. Richter, J. Feiling, H.-G. Schmidt, M. Noltemeyer, W. Bru¨ser and F.
T. Edelmann, Z. Anorg. Allg. Chem., 2004, 630, 1269–1275.
8 S. Braun and S. Berger, 200 and More Basic NMR Experiments, VCH,
Weinheim, 2004, pp. 141–148.
dipolar coupling, which cannot be removed under MAS conditions. For
this reason, these resonance signals appear as broad asymmetric signals
with three maxima of inequal intensity. In this context, see: J. Bo¨hm,
D. Fenzke and H. Pfeifer, J. Magn. Res., 1983, 55, 197–204.
11 X. Helluy, R. Pietschnig and A. Sebald, Solid State Nucl. Magn. Reson.,
2003, 24, 286–300.
9 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2007,
64, 112–122.
10 The resonance signals for 29Si nuclei bound directly to a quadrupole
nucleus, such as 79Br or 81Br with a nuclear spin of I = 3/2, show residual
12 O. Seiler, C. Burschka, M. Fischer, M. Penka and R. Tacke, Inorg.
Chem., 2005, 44, 2337–2346.
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