Novel neutral hexacoordinate silicon(iv) complexes with two bidentate monoanionic benzamidinato ligands

Article abstract of DOI:10.1039/c0dt00391c

The novel neutral hexacoordinate bis(benzamidinato)silicon(iv) complexes 1-10 (SiN₄X₂ skeletons; X = F, Cl, Br, C, N, S, Se) were synthesised and characterised by elemental analyses, single-crystal X-ray diffraction (except for 2) an

Full text of DOI:10.1039/c0dt00391c

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HOT ARTICLE:
Novel neutral hexacoordinate silicon(IV) complexes with two bidentate monoanionic benzamidinato
ligands
Konstantin Junold, Christian Burschka, Rüdiger Bertermann and Reinhold Tacke
Dalton Trans., 2010, DOI: 10.1039/C0DT00391C
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PAPER
www.rsc.org/dalton | Dalton Transactions
Novel neutral hexacoordinate silicon(IV) complexes with two bidentate
monoanionic benzamidinato ligands†‡
Konstantin Junold, Christian Burschka, Ru¨diger Bertermann and Reinhold Tacke*
Received 29th April 2010, Accepted 23rd June 2010
DOI: 10.1039/c0dt00391c
The novel neutral hexacoordinate bis(benzamidinato)silicon(IV) complexes 1–10 (SiN4X2 skeletons;
X = F, Cl, Br, C, N, S, Se) were synthesised and characterised by elemental analyses, single-crystal X-ray
diffraction (except for 2) and NMR spectroscopy in the solid state and in solution. The dynamic
behavior of 1 (SiN4Cl2 skeleton) and 3 (SiN4F2) was additionally studied by variable-temperature
NMR experiments. Compounds 1 and 2 (SiN4Br2) were obtained by reaction of SiCl4 and SiBr4,
respectively, with two molar equivalents of the corresponding lithium amidinate. Compound 1 served as
the starting material in the syntheses of 3–10, in which the two chloro ligands of 1 were substituted by
two (pseudo)halogeno or one bidentate dianionic S,S, S,Se or Se,Se ligand. Compound 4 contains an
SiN4C2 skeleton and 5–7 contain an SiN6 skeleton. With the preparation of 8 (SiN4S2 skeleton), 9
(SiN4SSe) and 10 (SiN4Se2) it could be demonstrated that syntheses of hexacoordinate silicon(IV)
complexes with soft chalcogeno ligand atoms are indeed feasible. Compounds 9 and 10 are the first
hexacoordinate silicon(IV) complexes with Si–Se bonds.
Introduction
Amidinato ligands are well known in transition metal and main
group metal coordination chemistry, and the structural chemistry
of complexes containing such ligands has been studied extensively.
In contrast, only a few higher-coordinate silicon(IV) complexes
(mainly pentacoordinate monoamidinato complexes) are known
that contain this type of ligand.1 To the best of our knowledge,
compounds [PhC(NSiMe3)2]2SiCl21d (A) and [MeC(NiPr)2]2SiCl2
1b
(B) are the only hexacoordinate bisamidinatosilicon(IV) complexes
that have been reported in the literature (for selected reviews
dealing with higher-coordinate silicon compounds, see ref. 2).
Compound A was obtained from an unstable silylene by a
disproportionation reaction, whereas B was synthesised directly
by treatment of SiCl4 with Li[MeC(NiPr)2].
Scheme 1 Structures of the neutral hexacoordinate silicon(IV) complexes
investigated in this study.
In continuation of our systematic studies on higher-coordinate
silicon compounds (for recent publications, see ref. 3), we have
now succeeded in synthesising a series of novel neutral hexa-
coordinate bisamidinatosilicon(IV) complexes that contain two
bidentate monoanionic N,N¢-diisopropylbenzamidinato ligands
structurally characterised by single-crystal X-ray diffraction.
Furthermore, the dynamic behavior of 1 and 3 in solution was
studied by variable-temperature (VT) NMR experiments.
and (i) two monodentate monoanionic (pseudo)halogeno ligands
(F, Cl, Br, CN, N3, NCO, NCS) or (ii) one bidentate dianionic
benzene-1,2-dithiolato, 2-selenolatobenzenethiolato or benzene-
1,2-diselenolato ligand. We report here on the synthesis of
compounds 1–10 (Scheme 1; 8–10 were isolated as hemitoluene
solvates) and their NMR-spectroscopic characterisation in the
solid state and in solution. In addition, compounds 1, 3–7,
8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8 (C7H8 = toluene) were
The main focus of this study was the synthesis and struc-
tural characterisation of novel neutral hexacoordinate silicon(IV)
complexes with SiN4X2 skeletons (X = F, Cl, Br, C, N, S, Se).
In this context, compounds 5–7 (SiN6 skeletons), 8 (SiN4S2), 9
(SiN4SSe) and 10 (SiN4Se2) were of particular interest: To the best
of our knowledge, neutral hexacoordinate silicon(IV) complexes
with an SiN6 skeleton have not yet been reported, except for
a quite recently published phenanthroline adduct of Si(NCO)4,4
and hexacoordinate silicon(IV) complexes with SiN4S2, SiN4SSe
and SiN4Se2 skeletons were even totally unknown. Furthermore,
compounds 9 and 10 are the first hexacoordinate silicon(IV)
complexes with Si–Se bonds, whereas pentacoordinate silicon(IV)
complexes with Si–Se bonds have been reported quite recently.3d
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 Ju¨rgen Heck on the occasion of his 60th birthday.
‡ CCDC reference numbers 775531–775539. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00391c
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9401–9413 | 9401
©

CD2Cl2): d 23.0 (CH3), 23.59 (CH3), 23.62 (CH3), 23.9 (CH3),
47.0 (CH), 47.3 (CH), 127.1, 127.9, 128.9, 129.0, 130.3 and 130.9
(C6H5), 168.8 (NCN). 29Si NMR (59.6 MHz, CD2Cl2): d -171.0.
13C VACP/MAS NMR: d 22.2 (CH3), 23.3 (CH3), 25.1 (CH3),
45.4 (CH), 46.8 (CH), 125.1, 126.2 and 128.0–134.2 (C6H5),
168.1 (NCN). 15N VACP/MAS NMR: d -188.1, -208.5. 29Si
VACP/MAS NMR: d -170.4. Anal. Calcd for C26H38Cl2N4Si
(505.61): C, 61.76; H, 7.58; N, 11.08. Found: C, 61.5; H, 7.7; N,
11.1.
Experimental
General Procedures
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. 5.
Melting points were determined with a Bu¨chi Melting Point B-
540 apparatus using samples in sealed capillaries. The solution
1H, 13C, 19F, 29Si and 77Se NMR spectra were recorded at 23 ◦C
on a Bruker DRX-300 (1H, 300.1 MHz; 13C, 75.5 MHz; 29Si,
59.6 MHz; 77Se, 57.3 MHz), 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; 77Se, 95.4 MHz) using CD2Cl2
or C6D6 as the solvent. Chemical shifts (ppm) were determined
relative to internal CHDCl2 (1H, d 5.32; CD2Cl2), internal C6HD5
(1H, d 7.28; C6D6), internal CD2Cl2 (13C, d 53.8; CD2Cl2), internal
C6D6 (13C, d 128.0; C6D6), external CFCl3 (19F, d 0; CD2Cl2),
external tetramethylsilane (TMS) (29Si, d 0; CD2Cl2, C6D6) or
external Me2Se (5% w/w in C6D6) (77Se, d 0; CD2Cl2). Assignment
Dibromobis[N,N¢-diisopropylbenzamidinato(-)]silicon(IV) (2).
(i) Tetrabromosilane (911 mg, 2.62 mmol) was added dropwise
at 20 ◦C within 1 min to a stirred suspension of lithium N,N¢-
diisopropylbenzamidinate (1.10 g, 5.23 mmol) in diethyl ether
(30 ml) and the reaction mixture was stirred at this temperature for
24 h. The solvent was removed in vacuo, dichloromethane (30 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 (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 24 h. The resulting colorless 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: 611 mg (1.03 mmol, 39%).
of the 13C NMR data was supported by DEPT 135 and H,1H
1
1
and H,13C correlation experiments. Compounds 1 and 3 were
studied by VT NMR experiments. The thermocouple used with
the probe for these studies was calibrated for higher and lower
temperatures according to ref. 6 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, 29Si and
77Se VACP/MAS and 19F single-pulse MAS NMR spectra were
recorded at 22 ◦C on a Bruker DSX-400 NMR spectrometer with
bottom-layer rotors of ZrO2 (diameter, 7 mm (13C, 15N, 29Si, 77Se)
or 2.5 mm (19F)) containing ca. 200 mg (7 mm) or 20 mg (2.5 mm)
of sample (13C, 100.6 MHz; 15N, 40.6 MHz; 19F, 376.5 MHz; 29Si,
79.5 MHz; 77Se, 76.3 MHz; external standard, TMS (13C, 29Si; d
0), glycine (15N; d -342.0), CaF2 (19F; d -108.0) or Me2Se (77Se; d
0); spinning rate, 6–7 kHz (7 mm) or 33 kHz (2.5 mm); contact
time, 1 ms (13C), 3 ms (15N) or 5 ms (29Si, 77Se); 90◦ 1H transmitter
pulse length, 3.6 ms; repetition time, 4–5 s).
1
Mp: >193 C (dec.). H NMR (300.1 MHz, C6D6): d 1.29 (d,
3JHH = 6.8 Hz, 6 H, CH3), 1.38 (d, 3JHH = 6.8 Hz, 6 H, CH3), 1.47
(d, 3JHH = 6.8 Hz, 6 H, CH3), 1.64 (d, 3JHH = 6.8 Hz, 6 H, CH3),
3.62 (sept, 3JHH = 6.8 Hz, 2 H, CH), 4.63 (sept, 3JHH = 6.8 Hz, 2 H,
1
CH), 7.10–7.18 and 7.41–7.49 (m, 10 H, C6H5). 13C{ H} NMR
(75.5 MHz, C6D6): d 23.1 (CH3), 23.9 (CH3), 24.0 (CH3), 24.3
(CH3), 47.0 (CH), 47.5 (CH), 126.6, 128.1, 128.9, 129.4, 130.1 and
1
131.2 (C6H5), 168.3 (NCN). 29Si{ H} NMR (59.6 MHz, C6D6): d
-199.4. 13C VACP/MAS NMR: d 21.9 (CH3), 23.6 (CH3), 25.1
(CH3), 25.7 (CH3), 46.7 (CH), 47.4 (CH), 125.9, 128.1, 128.7,
129.5, 130.6 and 132.3 (C6H5), 168.3 (NCN). 15N VACP/MAS
NMR: d -191.3, -194.1, -209.8, -211.2. 29Si VACP/MAS NMR:
d -206. Anal. Calcd for C26H38Br2N4Si (594.51): C, 52.53; H, 6.44;
N, 9.42. Found: C, 52.8; H, 6.6; N, 9.5. (ii) Bromotrimethylsilane
(2.43 g, 15.9 mmol) was added in a single portion at 20 ◦C to
1 (801 mg, 1.58 mmol) and the resulting mixture was stirred at
this temperature for 18 h. The volatiles 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 24 h. The resulting colorless 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: 758 mg (1.28 mmol, 81%).
The analytical data of the product match with those obtained for
the product synthesised according to method (i).
Syntheses
Dichlorobis[N,N¢-diisopropylbenzamidinato(-)]silicon(IV) (1).
Tetrachlorosilane (1.00 g, 5.89 mmol) was added dropwise at
20 ◦C within 2 min to a stirred suspension of lithium N,N¢-
diisopropylbenzamidinate (2.48 g, 11.8 mmol) in diethyl ether
(80 ml) and the reaction mixture was stirred at this temperature for
17 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 (40 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 2 d. The resulting colorless 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: 2.01 g (3.98 mmol, 68%).
Difluorobis[N,N¢-diisopropylbenzamidinato(-)]silicon(IV) (3).
(i) Potassium fluoride (251 mg, 4.32 mmol) was added at 20 ◦C in
a single portion to a stirred suspension of 1 (788 mg, 1.56 mmol)
and 18-crown-6 (115 mg, 435 mmol) in acetonitrile (40 ml) and
the reaction mixture was stirred at this temperature for 48 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 toluene (15 ml). The resulting mixture was
heated until a clear solution was obtained, which was then cooled
◦
1
Mp: >265 C (dec.) H NMR (300.1 MHz, CD2Cl2): d 1.17 (d,
3JHH = 6.8 Hz, 6 H, CH3), 1.21 (d, 3JHH = 6.8 Hz, 6 H, CH3), 1.25
(d, 3JHH = 6.8 Hz, 6 H, CH3), 1.32 (d, 3JHH = 6.8 Hz, 6 H, CH3),
3
3
3.47 (sept, JHH = 6.8 Hz, 2 H, CH), 3.92 (sept, JHH = 6.8 Hz, 2
H, CH), 7.22–7.60 (m, 10 H, C6H5). 13C{ H} NMR (75.5 MHz,
1
9402 | Dalton Trans., 2010, 39, 9401–9413
This journal is
The Royal Society of Chemistry 2010
©

slowly to 20 ◦C and kept undisturbed at this temperature for 2 d.
The resulting colorless crystalline solid was isolated by filtration,
washed with n-pentane (2 ¥ 5 ml) and dried in vacuo (20 ◦C, 3 h,
Diazidobis[N,N¢-diisopropylbenzamidinato(-)]silicon(IV)
(5).
Azidotrimethylsilane (412 mg, 3.58 mmol) was added at 20 ◦C in
a single portion to a stirred suspension of 1 (722 mg, 1.43 mmol)
in diethyl ether (30 ml) and the reaction mixture was stirred at
this temperature for 19 h. The volatiles were removed in vacuo
and acetonitrile (25 ml) was added to the residue. The resulting
suspension was heated until a clear solution was obtained, which
then was 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 ¥ 5 ml) and dried
in vacuo (20 ◦C, 4 h, 0.01 mbar). Yield: 669 mg (1.29 mmol, 90%).
◦
1
0.01 mbar). Yield: 556 mg (1.18 mmol, 76%). Mp: 218 C. H
NMR (300.1 MHz, CD2Cl2): d 1.07–1.39 (br. m, 24 H, CH3),
1
3.30–3.50 (br. m, 4 H, CH), 7.19–7.66 (m, 10 H, C6H5). 13C{ H}
NMR (75.5 MHz, CD2Cl2): d 23.1 (CH3), 23.7 (CH3), 24.0
(CH3), 24.4 (CH3), 46.5 (CH), 46.8 (CH), 127.2, 128.2, 128.9,
1
128.9, 130.0 and 130.7 (C6H5), 169.7 (NCN). 19F{ H} NMR
1
(376.5 MHz, CD2Cl2): d -130.4. 29Si{ H} NMR (59.6 MHz,
1
CD2Cl2): d -161.6 (t, JSiF = 218 Hz). 13C VACP/MAS NMR:
◦
1
d 21.3 (CH3), 21.9 (CH3), 22.7 (CH3), 24.4 (CH3), 25.7 (CH3),
46.2 (CH), 47.3 (CH), 124.7, 125.9, 127.8–128.7, 129.9 and 131.1
(C6H5), 170.0 (NCN). 15N VACP/MAS NMR: d -191.1, -192.7,
-220.9. 19F MAS NMR: d -125.3, -128.1. 29Si VACP/MAS
NMR: d -161 (br. m). Anal. Calcd for C26H38F2N4Si (472.70):
C, 66.06; H, 8.10; N, 11.85. Found: C, 66.1; H, 8.4; N, 11.8. (ii)
Silver tetrafluoroborate (607 mg, 3.12 mmol) was added at 20 ◦C
in a single portion to a stirred solution of 1 (788 mg, 1.56 mmol)
and triethylamine (316 mg, 3.12 mmol) in tetrahydrofuran (30 ml)
and the reaction mixture was stirred at this temperature for 2 h.
The resulting precipitate was filtered off and discarded, and the
solvent of the filtrate was removed in vacuo, followed by the
addition of toluene (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 2 d. The
resulting colorless 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: 671 mg (1.42 mmol, 91%). The analytical
data of the product match with those obtained for the product
synthesised according to method (i).
Mp: >212 C (dec.). H NMR (300.1 MHz, CD2Cl2): d 1.18 (d,
3JHH = 6.8 Hz, 6 H, CH3), 1.21 (d, 3JHH = 6.8 Hz, 6 H, CH3), 1.27
(d, 3JHH = 6.8 Hz, 6 H, CH3), 1.35 (d, 3JHH = 6.8 Hz, 6 H, CH3),
3.48 (sept, 3JHH = 6.8 Hz, 2 H, CH), 3.54 (sept, 3JHH = 6.8 Hz, 2 H,
1
CH), 7.22–7.33 and 7.45–7.66 (m, 10 H, C6H5). 13C{ H} NMR
(75.5 MHz, CD2Cl2): d 23.0 (CH3), 23.0 (CH3), 23.4 (CH3), 23.9
(CH3), 46.9 (CH), 47.0 (CH), 126.9, 129.0, 129.3, 130.0, 130.4
1
and 130.4 (C6H5), 170.4 (NCN). 29Si{ H} NMR (59.6 MHz,
CD2Cl2): d -175.5. 13C VACP/MAS NMR: d 22.6 (CH3), 22.6
(CH3), 24.0 (CH3), 24.3 (CH3), 46.9 (CH), 126.6, 129.3, 130.0,
130.2, 130.3 and 131.4 (C6H5), 170.9 (NCN). 15N VACP/MAS
NMR: d -136.9 (SiNNN), -200.3 (NCN), -208.3 (SiNNN),
-219.2 (NCN), -297.9 (SiNNN). 29Si VACP/MAS NMR: d
-176.5. Anal. Calcd for C26H38N10Si (518.74): C, 60.20; H, 7.38;
N, 27.00. Found: C, 60.0; H, 7.4; N, 26.8.
Di(cyanato-N)bis[N,N¢-diisopropylbenzamidinato(-)]silicon(IV)
(6). Potassium cyanate (313 mg, 3.86 mmol) was added at 20 ◦C
in a single portion to a stirred suspension of 1 (886 mg, 1.75 mmol)
and 18-crown-6 (139 mg, 526 mmol) in acetonitrile (30 ml) and
the reaction mixture was stirred at this temperature for 2 d. The
solvent was removed in vacuo and toluene (30 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 (15 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 3 d.
The resulting colorless crystalline solid was isolated by filtration,
washed with n-pentane (2 ¥ 5 ml) and dried in vacuo (20 ◦C, 5 h,
Dicyanobis[N,N¢-diisopropylbenzamidinato(-)]silicon(IV) (4).
Cyanotrimethylsilane (303 mg, 3.05 mmol) was added at 20 ◦C in
a single portion to a stirred suspension of 1 (618 mg, 1.22 mmol)
in acetonitrile (30 ml) and the reaction mixture was stirred at
this temperature for 17 h. The volatiles were removed in vacuo
and acetonitrile (15 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 colorless 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: 525 mg (1.08 mmol, 89%).
◦
1
0.01 mbar). Yield: 844 mg (1.63 mmol, 93%). Mp: 181 C. H
NMR (300.1 MHz, CD2Cl2): d 1.18 (d, 3JHH = 6.8 Hz, 6 H, CH3),
3
3
1.20 (d, JHH = 6.8 Hz, 6 H, CH3), 1.25 (d, JHH = 6.8 Hz, 6 H,
CH3), 1.34 (d, 3JHH = 6.8 Hz, 6 H, CH3), 3.44 (sept, 3JHH = 6.8 Hz,
2 H, CH), 3.59 (sept, 3JHH = 6.8 Hz, 2 H, CH), 7.20–7.59 (m, 10
◦
1
Mp: >210 C (dec.). H NMR (300.1 MHz, CD2Cl2): d 1.23 (d,
3JHH = 6.8 Hz, 6 H, CH3), 1.25 (d, 3JHH = 6.8 Hz, 6 H, CH3), 1.33
(d, 3JHH = 6.8 Hz, 6 H, CH3), 1.46 (d, 3JHH = 6.8 Hz, 6 H, CH3),
1
H, C6H5). 13C{ H} NMR (75.5 MHz, CD2Cl2): d 22.7 (CH3),
23.5 (CH3), 23.8 (CH3), 23.9 (CH3), 46.9 (CH), 47.1 (CH), 117
(br., NCO), 126.9, 128.2, 129.1, 129.2, 130.2 and 130.4 (C6H5),
169.4 (NCN). 29Si NMR (59.6 MHz, CD2Cl2): d -192.3. 13C
VACP/MAS NMR: d 21.4 (CH3), 23.3 (CH3), 24.3 (CH3), 25.0
(CH3), 47.1 (CH), 48.2 (CH), 119 (br., NCO), 126.0, 127.0, 128.4,
128.7, 130.6 and 132.0 (C6H5), 169.7 (NCN). 15N VACP/MAS
NMR: d -191.3 (NCN), -217.2 (NCN), -315.5 (NCO). 29Si
VACP/MAS NMR: d -193.2. Anal. Calcd for C28H38N6O2Si
(518.73): C, 64.83; H, 7.38; N, 16.20. Found: C, 64.6; H, 7.3; N,
16.1.
3
3
3.45 (sept, JHH = 6.8 Hz, 2 H, CH), 3.83 (sept, JHH = 6.8 Hz, 2
H, CH), 7.19–7.65 (m, 10 H, C6H5). 13C{ H} NMR (75.5 MHz,
1
CD2Cl2): d 21.3 (CH3), 22.7 (CH3), 23.0 (CH3), 23.1 (CH3), 46.6
(CH), 46.7 (CH), 125.7, 126.3, 128.1, 128.3, 129.4 and 129.6
(C6H5), 142 (br., CN), 169.2 (NCN). 29Si{ H} NMR (59.6 MHz,
1
CD2Cl2): d -213.2. 13C VACP/MAS NMR: d 21.9 (CH3), 23.7
(CH3), 24.4 (CH3), 25.6 (CH3), 46.3 (CH), 47.5 (CH), 125.5,
127.3, 128.6, 128.8, 129.7 and 133.4 (C6H5), 139.2 (CN), 170.5
(NCN). 15N VACP/MAS NMR: d -105.0 (CN), -111.0 (CN),
-191.4 (NCN), -196.2 (NCN), -214.9 (NCN), -217.5 (NCN).
29Si VACP/MAS NMR: d -216.6. Anal. Calcd for C28H38N6Si
(486.74): C, 69.09; H, 7.87; N, 17.27. Found: C, 68.0; H, 7.9; N,
16.3.
Bis[N,N¢-diisopropylbenzamidinato(-)]di(thiocyanato-N)silicon-
(IV) (7). Ammonium thiocyanate (563 mg, 7.40 mmol) was
added at 20 ◦C in a single portion to a stirred suspension of
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9401–9413 | 9403
©

1 (1.70 g, 3.36 mmol) and 18-crown-6 (266 mg, 1.01 mmol) in
acetonitrile (50 ml) and the reaction mixture was stirred at this
temperature for 2 d. 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 (25 ml). The
resulting mixture was heated until a clear solution was obtained,
d -156.1. Anal. Calcd for C35.5H46N4S2Si (621.00): C, 68.66; H,
7.47; N, 9.02; S, 10.33. Found: C, 68.5; H, 7.6; N, 9.0; S, 10.2.
Bis[N,N¢-diisopropylbenzamidinato(-)][2-selenolatobenzenethi -
olato(2-)]silicon(IV)–Hemitoluene (9·0.5C7H8). Triethylamine
(585 mg, 5.78 mmol) and 2-selenylbenzenethiol3d (544 mg,
2.88 mmol) were added at 20 ◦C in single portions one after
another to a stirred solution of 1 (1.46 g, 2.89 mmol) in
tetrahydrofuran (40 ml) and the reaction mixture was stirred at
this temperature for 20 h. The resulting precipitate was filtered
off and discarded, and the solvent of the filtrate was removed
in vacuo, followed by the addition of toluene (12 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 colorless 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: 1.48 g (2.22 mmol, 77%).
◦
which was then cooled slowly to 20 C and kept undisturbed at
this temperature for 2 d. The resulting colorless 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: 1.47 g (2.67 mmol,
◦
1
79%). Mp: 163 C. H NMR (300.1 MHz, CD2Cl2): d 1.21 (d,
3JHH = 6.8 Hz, 6 H, CH3), 1.24 (d, 3JHH = 6.8 Hz, 6 H, CH3), 1.25
(d, 3JHH = 6.8 Hz, 6 H, CH3), 1.37 (d, 3JHH = 6.8 Hz, 6 H, CH3),
3
3
3.45 (sept, JHH = 6.8 Hz, 2 H, CH), 3.61 (sept, JHH = 6.8 Hz, 2
H, CH), 7.20–7.64 (m, 10 H, C6H5). 13C{ H} NMR (75.5 MHz,
1
CD2Cl2): d 22.4 (CH3), 23.4 (CH3), 23.8 (CH3), 23.9 (CH3), 47.2
(CH), 47.4 (CH), 126.7, 128.3, 129.1, 129.3, 129.4 and 130.8
(C6H5), 171.2 (NCN), NCS resonance signal not detected. 29Si
NMR (59.6 MHz, CD2Cl2): d -197.2. 13C VACP/MAS NMR: d =
18.9 (CH3), 21.4 (CH3), 23.0 (CH3), 23.6 (CH3), 24.4 (CH3), 25.2
(CH3), 25.3 (CH3), 26.2 (CH3), 46.5 (CH), 47.3 (CH), 47.5 (CH),
48.6 (CH), 126.8, 127.6, 128.8, 131, 132.3 and 133.7 (C6H5 and
NCS), 171.4 (NCN). 15N VACP/MAS NMR: d -192.3 (NCN),
-195.5 (NCN), -218.4 (NCN), -222.8 (NCN), -228.4 (NCS).
29Si VACP/MAS NMR: d -195.7. Anal. Calcd for C28H38N6S2Si
(550.87): C, 61.05; H, 6.95; N, 15.26; S, 11.64. Found: C, 60.8; H,
6.9; N, 15.0; S, 11.5.
1
3
Mp: 159 C. H NMR (500.1 MHz, CD2Cl2): d 1.03 (d, JHH
=
3
6.8 Hz, 3 H, CH3), 1.04 (d, JHH = 6.8 Hz, 3 H, CH3), 1.13 (d,
3JHH = 6.8 Hz, 3 H, CH3), 1.15 (d, 3JHH = 6.8 Hz, 3 H, CH3), 1.22
(d, 3JHH = 6.8 Hz, 6 H, CH3), 1.26 (d, 3JHH = 6.8 Hz, 3 H, CH3),
1.26 (d, JHH = 6.8 Hz, 3 H, CH3), 2.35 (s, 1.5 H, C6H5CH3),
3.47 (sept, JHH = 6.8 Hz, 1 H, CH), 3.49 (sept, JHH = 6.8 Hz, 1
3
3
3
3
3
H, CH), 4.05 (sept, JHH = 6.8 Hz, 1 H, CH), 4.15 (sept, JHH
=
6.8 Hz, 1 H, CH), 6.64–6.83 and 6.90–7.67 (m, 16.5 H, C6H5,
1
C6H4 and C6H5CH3). 13C{ H} NMR (125.8 MHz, CD2Cl2): d
21.5 (C6H5CH3), 23.2 (CH3), 23.3 (CH3), 23.8 (CH3), 23.9 (CH3),
24.0 (CH3), 24.1 (CH3), 24.4 (CH3), 24.6 (CH3), 46.9 (CH),
46.9 (CH), 47.0 (CH), 47.0 (CH), 122.3, 123.3, 125.6, 126.1,
127.3, 127.7, 128.1, 128.5, 128.7, 128.8, 128.9, 129.3, 129.4, 130.2,
131.8, 138.3, 138.7 and 144.5 (C6H5, C6H4 and C6H5CH3), 168.2
[Benzene-1,2-dithiolato(2-)]bis[N,N¢-diisopropylbenzamidinato-
(-)]silicon(IV)–Hemitoluene (8·0.5C7H8). Triethylamine (436 mg,
4.31 mmol) and benzene-1,2-dithiol (306 mg, 2.15 mmol) were
added at 20 ◦C in single portions one after another to a stirred
solution of 1 (1.09 g, 2.16 mmol) in tetrahydrofuran (40 ml) and
the reaction mixture was stirred at this temperature for 19 h. The
resulting precipitate was filtered off and discarded, and the solvent
of the filtrate was removed in vacuo, followed by the addition of
toluene (20 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
colorless crystalline solid was isolated by filtration, washed with
1
(NCN), 169.1 (NCN). 29Si{ H} NMR (99.4 MHz, CD2Cl2): d
1
-165.1 (1JSe,Si = 78 Hz). 77Se{ H} NMR (95.4 MHz, CD2Cl2): d
206.5. 13C VACP/MAS NMR: d 21.0 (C6H5CH3), 22.5 (CH3),
23.4–24.5 (CH3), 25.7 (CH3), 26.8 (CH3), 46.6 (CH), 121.9,
122.8, 123.6, 124.8, 126.6, 128.0, 128.9, 130.0, 131.2, 132.4, 136.7,
138.7, 139.9, 144.9 and 146.2 (C6H5, C6H4 and C6H5CH3), 167
(br., NCN), 168 (br., NCN). 15N VACP/MAS NMR: d -189.7,
-192.0, -192.7, -197.8, -200.9. 29Si VACP/MAS NMR: d -164.0.
77Se VACP/MAS NMR: d 182.1. Anal. Calcd for C35.5H46N4SSeSi
(667.89): C, 63.84; H, 6.94; N, 8.39; S, 4.80. Found: C, 63.8; H,
7.0; N, 8.4; S, 4.8.
◦
n-pentane (2 ¥ 5 ml) and dried in vacuo (20 C, 2 h, 0.01 mbar).
[Benzene-1,2-diselenolato(2-)]bis[N,N¢-diisopropylbenzamidin -
Yield: 735 mg (1.18 mmol, 55%). Mp: >160 ◦C (dec.). 1H NMR
ato(-)]silicon(IV)–Hemitoluene
(10·0.5C7H8). Triethylamine
3
(300.1 MHz, CD2Cl2): d 1.00 (d, JHH = 6.8 Hz, 6 H, CH3), 1.15
(354 mg, 3.50 mmol) and benzene-1,2-diselenol3d (413 mg,
1.75 mmol) were added at 20 ◦C in single portions one after
another to a stirred solution of 1 (885 mg, 1.75 mmol) in
tetrahydrofuran (30 ml) and the reaction mixture was stirred at
this temperature for 21 h. The resulting precipitate was filtered
off and discarded, and the solvent of the filtrate was removed
in vacuo, followed by the addition of toluene (30 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 colorless 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: 848 mg (1.19 mmol,
(d, 3JHH = 6.8 Hz, 6 H, CH3), 1.22 (d, 3JHH = 6.8 Hz, 6 H, CH3),
1.26 (d, 3JHH = 6.8 Hz, 6 H, CH3), 2.34 (s, 1.5 H, C6H5CH3), 3.49
3
3
(sept, JHH = 6.8 Hz, 2 H, CH), 3.97 (sept, JHH = 6.8 Hz, 2 H,
CH), 6.70–7.59 (m, 16.5 H, C6H5, C6H4 and C6H5CH3). 13C{ H}
1
NMR (75.5 MHz, CD2Cl2): d 21.5 (C6H5CH3), 23.3 (CH3), 23.8
(CH3), 23.9 (CH3), 24.3 (CH3), 46.9 (CH), 47.1 (CH), 122.2,
125.6, 126.2, 127.3, 128.0, 128.5, 128.8, 128.9, 129.3, 130.1, 131.7,
138.3 and 142.0 (C6H5, C6H4 and C6H5CH3), 168.6 (NCN).
29Si{ H} NMR (59.6 MHz, CD2Cl2): d -156.5. 13C VACP/MAS
1
NMR: d 21.6 (C6H5CH3), 23.3 (CH3), 23.7 (CH3), 25.3 (CH3),
27.1 (CH3), 46.7 (CH), 121.8, 123.9, 124.4, 125.3, 127.0, 127.6,
128.7, 130.2, 131.2, 132.3, 136.6, 142.1 and 143.0 (C6H5, C6H4
and C6H5CH3), 167.9 (NCN), 169.1 (NCN). 15N VACP/MAS
NMR: d -191.1, -192.3, -193.6, -198.6. 29Si VACP/MAS NMR:
◦
1
68%). Mp: >167 C (dec.). H NMR (300.1 MHz, CD2Cl2): d
3
3
1.06 (d, JHH = 6.8 Hz, 6 H, CH3), 1.16 (d, JHH = 6.8 Hz, 6 H,
CH3), 1.21 (d, JHH = 6.8 Hz, 6 H, CH3), 1.25 (d, JHH = 6.8 Hz,
3
3
9404 | Dalton Trans., 2010, 39, 9401–9413
This journal is The Royal Society of Chemistry 2010
©

3
6 H, CH3), 2.35 (s, 1.5 H, C6H5CH3), 3.46 (sept, JHH = 6.8 Hz,
3
2 H, CH), 4.23 (sept, JHH = 6.8 Hz, 2 H, CH), 6.70–6.80 and
1
7.11–7.59 (m, 16.5 H, C6H5, C6H4 and C6H5CH3). 13C{ H} NMR
(75.5 MHz, CD2Cl2): d 21.5 (C6H5CH3), 23.2 (CH3), 24.0 (CH3),
24.1 (CH3), 24.7 (CH3), 46.9 (CH), 46.9 (CH), 123.3, 125.6,
127.3, 127.8, 128.5, 128.7, 128.9, 129.2, 129.3, 130.2, 131.8, 138.3
1
and 141.9 (C6H5, C6H4 and C6H5CH3), 168.7 (NCN). 29Si{ H}
1
NMR (59.6 MHz, CD2Cl2): d -175.2. 77Se{ H} NMR (57.2 MHz,
CD2Cl2): d 258.3. 13C VACP/MAS NMR: d 20.7 (C6H5CH3),
23.2 (CH3), 23.8 (CH3), 24.4 (CH3), 25.6 (CH3), 26.7 (CH3),
45.6 (CH), 46.4 (CH), 122.9, 124.4, 126.4, 127.6, 128.2, 128.7,
129.9, 131.1, 132.3, 136.6, 141.9 and 143.3 (C6H5, C6H4 and
C6H5CH3), 167.9 (NCN), 169.3 (NCN). 15N VACP/MAS NMR:
d -190.8, -192.7, -199.4. 29Si VACP/MAS NMR: d -173.6. 77Se
VACP/MAS NMR: d 238.3. Anal. Calcd for C35.5H46N4Se2Si
(714.79): C, 59.65; H, 6.49; N, 7.84. Found: C, 59.8; H, 6.6; N, 7.8.
Crystal structure analyses
Suitable single crystals of 1 were obtained by slow partial
evaporation of the solvent of a saturated solution of 1 in toluene at
20 ◦C under reduced pressure (700 mbar). Suitable single crystals
of 3–7, 8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8 were obtained as
described in the experimental section dealing with the syntheses.
The crystals were mounted in inert oil (perfluoropolyalkyl ether,
ABCR) on a glass fiber and then transferred to the cold nitrogen
gas stream of the diffractometer (1 and 3: Bruker Nonius
KAPPA APEX II diffractometer, graphite-monochromated Mo-
Scheme 2 Syntheses of compounds 1 and 2.
˚
Ka radiation, l = 0.71073 A, Montel mirror; 4–7, 8·0.5C7H8,
9·0.5C7H8 and 10·0.5C7H8: Stoe IPDS diffractometer, graphite-
˚
monochromated Mo-Ka radiation, l = 0.71073 A). All structures
were solved by direct methods.7 The non-hydrogen atoms were
refined anisotropically.7 A riding model was employed in the
refinement of the CH hydrogen atoms. The crystallographic data
for the structures reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publication CCDC numbers 775531–775539. Copies of the data
can be obtained free of charge upon application to CCDC,
12 Union Road, Cambridge CB2 1EZ, U. K. [fax, (+44)-
1223/336033; e-mail, deposit@ccdc.cam.ac.uk].
Scheme 3 Syntheses of compound 3.
of the second method is the higher yield (91% vs. 76%) and the
much shorter reaction time (2 h vs. 72 h).
The dicyanosilicon(IV) complex 4 and the diazidosilicon(IV)
complex 5 were synthesised according to Scheme 4 by treatment
of the corresponding dichlorosilicon(IV) complex 1 with an excess
of cyanotrimethylsilane and azidotrimethylsilane, respectively
(yields: 4, 89%; 5, 90%). Acetonitrile and diethyl ether, respectively,
served as the solvent.
Results and discussion
Surprisingly, the synthetic method used for the preparation of
4 and 5 could not be applied to the synthesis of the analogous
di(cyanato-N)silicon(IV) complex 6 and its di(thiocyanato-N)
derivative 7. Treatment of 1 with (cyanato-N)trimethylsilane
and (thiocyanato-N)trimethylsilane, respectively, resulted in the
formation of complex product mixtures, from which 6 and 7 could
not be isolated. However, compounds 6 and 7 could be synthesised
according to Scheme 5 by treatment of 1 with 2 molar equivalents
of potassium cyanate and ammonium thiocyanate, respectively, in
the presence of 18-crown-6 (yields: 6, 93%; 7, 79%). Acetonitrile
served as the solvent.
The dichlorosilicon(IV) complex 1 served also as the precur-
sor for the synthesis of compounds 8–10 that contain sulfur
and/or selenium ligand atoms instead of the two chloro ligands.
Compounds 8–10 were synthesised according to Scheme 6 by
treatment of 1 with 1 molar equivalent of benzene-1,2-dithiol,
Syntheses
Compounds 1 and 2 were synthesised according to Scheme
2 by treatment of 2 molar equivalents of lithium N,N¢-
diisopropylbenzamidinate in diethyl ether with tetrachlorosilane
and tetrabromosilane, respectively (yields: 1, 68%; 2, 39%).
Compound 2 could also be synthesised by treatment of 1 with
2 molar equivalents of bromotrimethylsilane in the absence of any
solvent (yield 81%; Scheme 2).
The difluorosilicon(IV) complex 3 was synthesised according
to Scheme 3, starting from the corresponding dichlorosilicon(IV)
complex 1. Compound 3 was obtained by treatment of 1 either with
(i) 2 molar equivalents of potassium fluoride in the presence of 18-
crown-6 (yield 76%) or with (ii) 2 molar equivalents each of silver
tetrafluoroborate and triethylamine (yield 91%). Acetonitrile and
tetrahydrofuran, respectively, served as the solvent. The advantage
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9401–9413 | 9405
©

solvates 8·0.5C7H8 (yield 55%), 9·0.5C7H8 (77%) and 10·0.5C7H8
(68%), respectively.
Compounds 1–7, 8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8 were
isolated as colorless crystalline solids that show a remarkably high
thermal stability (see Experimental section). All compounds are
sensitive against water and ethanol, and the dibromosilicon(IV)
complex 2 in solution is also sensitive against light.
The identities of 1–7, 8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8
were established by elemental analyses (C, H, N, S), NMR-
spectroscopic studies in the solid state (13C, 15N, 19F, 29Si, 77Se) and
in solution (1H, 13C, 19F, 29Si, 77Se) and by crystal structure analyses
(except for 2). All attempts to grow suitable single crystals for a
crystal structure analysis of 2 failed.
Crystal structure analyses
Compounds 1, 3–7, 8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8 were
structurally characterised by single-crystal X-ray diffraction. The
crystal data and experimental parameters used for the crystal
structure analyses are given in Tables 1 and 2. For the hemitoluene
solvates 8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8, a disorder of
the toluene molecules was observed, which is also reflected
by the solid-state NMR data of these compounds (see section
Experimental). In addition, a disorder of the sulfur and selenium
atoms of 9·0.5C7H8 was observed. The molecular structures of 1
and 3–10 are shown in Fig. 1–Fig. 9; selected bond lengths and
angles are given in the respective figure legends.
Scheme 4 Syntheses of compounds 4 and 5.
Scheme 5 Syntheses of compounds 6 and 7.
Fig.
1 Molecular structure of 1 in the crystal (probability level
˚
of displacement ellipsoids 50%). Selected bond lengths [A] and
angles [◦]: Si–Cl(1) 2.2026(7), Si–Cl(2) 2.1846(7), Si–N(1) 1.8726(17),
Si–N(2) 1.8984(16), Si–N(3) 1.8680(17), Si–N(4) 1.9063(17), N(1)–C(1)
1.342(2), N(2)–C(1) 1.316(2), N(3)–C(14) 1.337(2), N(4)–C(14) 1.316(2);
Cl(1)–Si–Cl(2) 91.80(3), Cl(1)–Si–N(1) 97.75(5), Cl(1)–Si–N(2) 166.82(6),
Cl(1)–Si–N(3) 95.75(5), Cl(1)–Si–N(4) 90.61(5), Cl(2)–Si–N(1) 96.39(6),
Cl(2)–Si–N(2) 90.90(5), Cl(2)–Si–N(3) 98.16(6), Cl(2)–Si–N(4) 166.82(6),
N(1)–Si–N(2) 69.13(7), N(1)–Si–N(3) 159.78(7), N(1)–Si–N(4) 96.12(7),
N(2)–Si–N(3) 96.63(7), N(2)–Si–N(4) 89.69(7), N(3)–Si–N(4) 68.70(7),
Si–N(1)–C(1) 91.99(12), Si–N(2)–C(1) 91.69(12), Si–N(3)–C(14)
92.74(12), Si–N(4)–C(14) 91.71(12), N(1)–C(1)–N(2) 107.19(16),
N(3)–C(14)–N(4) 106.85(16).
Scheme 6 Syntheses of compounds 8–10.
2-selenylbenzenethiol3d and benzene-1,2-diselenol,3d respectively,
and 2 molar equivalents of triethylamine. In these syntheses
tetrahydrofuran served as the solvent. The products were isolated
after crystallisation from toluene as the respective hemitoluene
9406 | Dalton Trans., 2010, 39, 9401–9413
This journal is
The Royal Society of Chemistry 2010
©

Fig. 2 Molecular structure of 3 in the crystal (probability level of displace-
◦
˚
ment ellipsoids 50%). Selected bond lengths [A] and angles [ ]: Si–F(1)
1.6451(10), Si–F(2) 1.6529(19), Si–N(1) 1.8611(13), Si–N(2) 1.9647(13),
Si–N(3) 1.8571(14), Si–N(4) 1.9703(13), N(1)–C(1) 1.3380(18), N(2)–C(1)
1.318(2), N(3)–C(14) 1.3369(18), N(4)–C(14) 1.3189(19); F(1)–Si–F(2)
93.28(5), F(1)–Si–N(1) 95.71(5), F(1)–Si–N(2) 163.70(6), F(1)–Si–N(3)
97.09(5), F(1)–Si–N(4) 90.41(6), F(2)–Si–N(1) 96.44(6), F(2)–Si–N(2)
90.34(6), F(2)–Si–N(3) 94.95(5), F(2)–Si–N(4) 163.04(6), N(1)–Si–N(2)
68.08(6), N(1)–Si–N(3) 162.32(5), N(1)–Si–N(4) 99.66(6), N(2)–Si–N(3)
98.43(6), N(2)–Si–N(4) 90.73(5), N(3)–Si–N(4) 68.15(5), Si–N(1)–C(1)
93.85(9), Si–N(2)–C(1) 89.90(9), Si–N(3)–C(14) 94.02(9), Si–N(4)–C(14)
89.59(9), N(1)–C(1)–N(2) 107.58(13), N(3)–C(14)–N(4) 107.83(13).
Fig. 3 Molecular structure of 4 in the crystal (probability level of displace-
◦
˚
ment ellipsoids 50%). Selected bond lengths [A] and angles [ ]: Si–N(1)
1.8761(11), Si–N(2) 1.9046(11), Si–N(3) 1.8776(12), Si–N(4) 1.8930(11),
Si–C(29) 1.9440(13), Si–C(30) 1.9444(14), N(1)–C(1) 1.3465(15),
N(2)–C(1) 1.3245(17), N(3)–C(14) 1.3446(16), N(4)–C(14) 1.3234(17),
N(5)–C(29) 1.1467(17), N(6)–C(30) 1.1491(18); N(1)–Si–N(2) 69.17(5),
N(1)–Si–N(3) 162.07(5), N(1)–Si–N(4) 97.97(5), N(1)–Si–C(29) 98.77(5),
N(1)–Si–C(30) 93.92(5), N(2)–Si–N(3) 97.64(5), N(2)–Si–N(4) 91.69(5),
N(2)–Si–C(29) 167.94(6), N(2)–Si–C(30) 89.93(6), N(3)–Si–N(4) 69.52(5),
N(3)–Si–C(29) 94.22(5), N(3)–Si–C(30) 98.28(5), N(4)–Si–C(29) 90.38(6),
N(4)–Si–C(30) 167.79(5), C(29)–Si–C(30) 90.54(6), Si–N(1)–C(1) 92.22(8),
Si–N(2)–C(1) 91.67(7), Si–N(3)–C(14) 91.54(8), Si–N(4)–C(14) 91.54(8),
Si–C(29)–N(5) 177.23(13), Si–C(30)–N(6) 177.18(13), N(1)–C(1)–N(2)
106.93(10), N(3)–C(14)–N(4) 107.36(11).
Fig. 4 Molecular structure of 5 in the crystal (probability level of
◦
˚
displacement ellipsoids 50%). Selected bond lengths [A] and angles [ ]:
Si–N(1) 1.8784(15), Si–N(2) 1.9324(15), Si–N(3) 1.8720(16), Si–N(4)
1.9436(15), Si–N(5) 1.8507(16), Si–N(6) 1.8521(17), N(5)–N(7) 1.204(2),
N(6)–N(9) 1.204(2), N(7)–N(8) 1.141(2), N(9)–N(10) 1.145(2), N(1)–C(1)
1.345(2), N(2)–C(1) 1.322(2), N(3)–C(14) 1.339(2), N(4)–C(14) 1.324(2);
N(1)–Si–N(2) 68.76(6), N(1)–Si–N(3) 165.61(7), N(1)–Si–N(4) 101.46(7),
N(1)–Si–N(5) 92.70(7), N(1)–Si–N(6) 96.89(7), N(2)–Si–N(3) 100.49(7),
N(2)–Si–N(4) 91.49(6), N(2)–Si–N(5) 161.44(7), N(2)–Si–N(6) 92.90(7),
N(3)–Si–N(4) 68.42(6), N(3)–Si–N(5) 97.62(7), N(3)–Si–N(6) 93.10(7),
N(4)–Si–N(5) 91.38(7), N(4)–Si–N(6) 161.49(7), N(5)–Si–N(6) 90.15(9),
Si–N(5)–N(7) 124.99(14), Si–N(6)–N(9) 125.60(13), Si–N(1)–C(1)
Fig. 5 Molecular structure of 6 in the crystal (propability level of
displacement ellipsoids 50%). Selected bond lengths [A] and angles
˚
[◦]: Si–N(1) 1.8727(11), Si–N(2) 1.9461(12), Si–N(3) 1.8141(13),
O–C(14) 1.184(2), N(1)–C(1) 1.3353(17), N(2)–C(1) 1.3183(17),
N(3)–C(14) 1.152(2); N(1)–Si–N(1A) 163.78(8), N(1)–Si–N(2) 68.41(5),
N(1)–Si–N(2A) 99.79(5), N(1)–Si–N(3) 96.43(6), N(1)–Si–N(3A) 94.81(5),
N(2)–Si–N(2A) 90.93(7), N(2)–Si–N(3) 90.92(6), N(2)–Si–N(3A)
163.18(5), N(3)–Si–N(3A) 92.13(10), Si–N(3)–C(14) 152.66(13),
O–C(14)–N(3) 177.60(19), N(1)–C(1)–N(2) 108.05(11).
92.62(11),
Si–N(2)–C(1)
90.97(10),
Si–N(3)–C(14)
93.36(10),
Si–N(4)–C(14) 90.69(10), N(5)–N(7)–N(8) 176.4(2), N(6)–N(9)–N(10)
176.3(2), N(1)–C(1)–N(2) 107.57(13), N(3)–C(14)–N(4) 107.38(15).
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9401–9413 | 9407
©

Fig. 8 Molecular structure of 9 in the crystal of 9·0.5C7H8 (probability
level of displacement ellipsoids 50%; hydrogen atoms and the disorderd
˚
toluene molecules are omitted for clarity). Selected bond lengths [A]
and angles [◦]: Se(1)–Si 2.4064(19), S(2)–Si 2.231(7), Si–N(1) 1.8935(13),
Si–N(2) 1.9241(12), Si–N(3) 1.8991(13), Si–N(4) 1.9204(13), N(1)–C(1)
1.3334(19), N(2)–C(1) 1.3320(19), N(3)–C(14) 1.3359(19), N(4)–C(14)
1.3297(18); Se(1)–Si–S(2) 91.9(3), Se(1)–Si–N(1) 97.14(7), Se(1)–Si–N(2)
165.43(7), Se(1)–Si–N(3) 97.32(7), Se(1)–Si–N(4) 86.66(8), S(2)–Si–N(1)
97.1(3), S(2)–Si–N(2) 88.9(3), S(2)–Si–N(3) 98.0(3), S(2)–Si–N(4) 166.0(3),
N(1)–Si–N(2) 68.34(5), N(1)–Si–N(3) 158.67(6), N(1)–Si–N(4) 96.93(6),
N(2)–Si–N(3) 96.96(6), N(2)–Si–N(4) 95.96(6), N(3)–Si–N(4) 68.41(5),
N(1)–C(1)–N(2) 107.11(12), N(3)–C(14)–N(4) 107.31(12). Selected bond
Fig. 6 Molecular structure of 7 in the crystal (probability level of displace-
◦
˚
ment ellipsoids 50%). Selected bond lengths [A] and angles [ ]: Si–N(1)
1.8664(14), Si–N(2) 1.9279(14), Si–N(3) 1.8746(14), Si–N(4) 1.9930(14),
Si–N(5) 1.8338(15), Si–N(6) 1.8361(15), S(1)–C(27) 1.6023(19), S(2)–C(28)
1.6058(19), N(1)–C(1) 1.352(2), N(2)–C(1) 1.326(2), N(3)–C(14) 1.343(2),
N(4)–C(14) 1.327(2), N(5)–C(27) 1.171(2), N(6)–C(28) 1.174(2);
N(1)–Si–N(2) 69.39(6), N(1)–Si–N(3) 164.90(6), N(1)–Si–N(4) 99.54(6),
N(1)–Si–N(5) 95.38(6), N(1)–Si–N(6) 95.63(7), N(2)–Si–N(3) 100.61(6),
N(2)–Si–N(4) 92.15(6), N(2)–Si–N(5) 164.76(6), N(2)–Si–N(6) 90.33(6),
N(3)–Si–N(4) 68.82(6), N(3)–Si–N(5) 94.21(7), N(3)–Si–N(6) 95.72(6),
N(4)–Si–N(5) 89.89(6), N(4)–Si–N(6) 164.53(6), N(5)–Si–N(6) 91.72(7),
Si–N(5)–C(27) 159.35(14), Si–N(6)–C(28) 161.27(14), S(1)–C(27)–N(5)
178.39(17), S(2)–C(28)–N(6) 179.11(16), N(1)–C(1)–N(2) 107.55(14),
N(3)–C(14)–N(4) 107.39(14).
˚
lengths [A] of the second molecule (disorder: S(1)/Se(2) and Se(1)/S(2)
exchange): Se(2)–Si 2.419(4), S(2)–Si 2.231(7).
Fig. 7 Molecular structure of 8 in the crystal of 8·0.5C7H8 (probability
Fig. 9 Molecular structure of 10 in the crystal of 10·0.5C7H8 (probability
level of displacement ellipsoids 50%; hydrogen atoms and the disorderd
level of displacement ellipsoids 50%; hydrogen atoms and the disorderd
˚
˚
toluene molecules are omitted for clarity). Selected bond lengths [A]
toluene molecules are omitted for clarity). Selected bond lengths [A]
and angles [◦]: S(1)–Si 2.2558(6), S(2)–Si 2.2693(6), Si–N(1) 1.8869(13),
Si–N(2) 1.9239(13), Si–N(3) 1.8983(12), Si–N(4) 1.9261(12), N(1)–C(1)
1.3371(18), N(2)–C(1) 1.3314(18), N(3)–C(14) 1.3402(18), N(4)–C(14)
1.3266(18); S(1)–Si–S(2) 91.65(2), S(1)–Si–N(1) 96.98(4), S(1)–Si–N(2)
88.24(4), S(1)–Si–N(3) 98.21(4), S(1)–Si–N(4) 166.20(4), S(2)–Si–N(1)
97.54(4), S(2)–Si–N(2) 165.87(4), S(2)–Si–N(3) 97.52(4), S(2)–Si–N(4)
87.56(4), N(1)–Si–N(2) 68.47(5), N(1)–Si–N(3) 158.23(6), N(1)–Si–N(4)
96.78(5), N(2)–Si–N(3) 96.49(6), N(2)–Si–N(4) 95.87(6), N(3)–Si–N(4)
68.28(5), N(1)–C1–N(2) 106.93(13), N(3)–C(14)–N(4) 107.19(12).
and angles [◦]: Se(1)–Si 2.3989(8), Se(2)–Si 2.4142(7), Si–N(1) 1.8965(18),
Si–N(2) 1.9240(19), Si–N(3) 1.9022(18), Si–N(4) 1.9153(19), N(1)–C(1)
1.335(3), N(2)–C(1) 1.334(3), N(3)–C(14) 1.330(3), N(4)–C(14) 1.332(3);
Se(1)–Si–Se(2) 91.35(5), Se(1)–Si–N(1) 96.68(6), Se(1)–Si–N(2) 88.74(7),
Se(1)–Si–N(3) 98.17(6), Se(1)–Si–N(4) 166.16(6), Se(2)–Si–N(1) 97.56(6),
Se(2)–Si–N(2) 165.91(6), Se(2)–Si–N(3) 96.96(6), Se(2)–Si–N(4) 87.26(6),
N(1)–Si–N(2) 68.45(8), N(1)–Si–N(3) 158.92(8), N(1)–Si–N(4) 97.15(8),
N(2)–Si–N(3) 96.97(8), N(2)–Si–N(4) 95.94(9), N(3)–Si–N(4) 68.38(8),
N(1)–C(1)–N(2) 107.26(18), N(3)–C(14)–N(4) 107.38(18).
9408 | Dalton Trans., 2010, 39, 9401–9413
This journal is
The Royal Society of Chemistry 2010
©

Table 1 Crystallographic data for compounds 1 and 3–6
Compound
1
3
4
5
6
Empirical formula
Formula mass [g mol-1]
T [K]
C26H38Cl2N4Si
505.59
100(2)
0.71073
Monoclinic
P21/c (14)
9.5369(5)
17.8631(9)
16.0043(8)
90
94.067(2)
90
2719.6(2)
4
1.235
0.304
C26H38F2N4Si
472.69
100(2)
0.71073
Monoclinic
P21 (4)
8.1810(7)
16.4410(13)
9.7818(8)
90
102.801(4)
90
1282.99(18)
2
1.224
0.127
C28H38N6Si
486.73
183(2)
0.71073
Monoclinic
P21/c (14)
9.6880(19)
18.094(4)
16.310(3)
90
95.40(3)
90
2846.4(10)
4
1.136
0.109
C26H38N10Si
518.75
183(2)
C28H38N6O2Si
518.73
243(2)
0.71073
Monoclinic
P2/c (13)
10.2220(18)
8.1615(10)
18.248(3)
90
105.75(2)
90
1465.2(4)
2
1.176
0.114
˚
l (Mo-Ka) [A]
0.71073
Triclinic
Crystal system
¯
Space group (no.)
P1(2)
˚
a [A]
9.3457(13)
10.0135(16)
17.620(3)
97.257(18)
95.735(17)
115.332(16)
1456.5(4)
2
˚
b [A]
˚
c [A]
a [◦]
b [◦]
g [◦]
3
˚
V [A ]
Z
rc [g cm-1]
1.183
0.114
556
m [mm-1]
F(000)
1080
508
1048
556
Crystal dimensions [mm]
2q range [◦]
Index ranges
0.2 ¥ 0.1 ¥ 0.1
3.42–58.90
-13 £ h £ 13,
-24 £ k £ 24,
-21 £ l £ 22
20988
7501
0.0373
306
0
1.100
0.0287/2.9547
0.0457
0.1138
+0.453/-0.407
0.30 ¥ 0.18 ¥ 0.13
4.28–64.54
-12 £ h £ 11,
0 £ k £ 24,
0 £ l £ 14
66073
4629
0.0743
307
1
1.093
0.0422/0.1416
0.0318
0.0826
+0.328/-0.336
0.4 ¥ 0.2 ¥ 0.2
4.78–58.30
-13 £ h £ 13,
-24 £ k £ 24,
-22 £ l £ 22
37540
7599
0.0646
324
0
1.037
0.0573/0.1377
0.0411
0.1081
+0.298/-0.320
0.5 ¥ 0.3 ¥ 0.15
4.74–58.16
-12 £ h £ 11,
-13 £ k £ 13,
-24 £ l £ 24
16780
7508
0.0384
351
7
1.031
0.0733/0.6435
0.0530
0.1534
+0.465/-0.324
0.5 ¥ 0.4 ¥ 0.3
6.50–58.20
-13 £ h £ 13,
-11 £ k £ 11,
-24 £ l £ 24
20168
3869
0.0375
172
0
1.069
0.0678/0.2053
0.0454
0.1332
+0.295/-0.247
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)
Max./min. residual electron
-3
˚
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 = R ꢀFo| - |Fcꢀ/R |Fo|. d wR2 = {R [w(Fo - Fc2)2]/R [w(Fo2)2]}
.
2
0.5
The Si-coordination polyhedra of 1 and 3–10 are strongly
distorted octahedra, with maximum deviations from the ideal
90◦ and 180◦ angles ranging from 20.83(5)◦ to 21.92(6)◦ and
from 15.47(6)◦ to 21.77(6)◦, respectively (Table 3). These strong
distortions mainly result from the two highly strained four-
membered SiN2C rings formed by the silicon coordination center
and the bidentate amidinato ligands. The N–Si–N angles of
these rings range from 67.29(5)◦ to 69.52(5)◦. In all cases, the
(pseudo)halogeno ligands of 1–7 occupy cis positions, with X–Si–
X angles (X = F, Cl, C, N) of 90.15(9)◦ to 93.28(5)◦. Very similar
X–Si–X angles (X = S, Se) were also found for compounds 8–10
with their five-membered SiX2C2 rings.
the [Si(N3)6]2- dianion.8 The Si–N(azido) bond lengths of 5
˚
˚
(1.8507(16) A and 1.8521(17) A) are somewhat shorter than those
8
of the [Si(N3)6]2- dianion (1.866(1)–1.881(1) A). The N(5)–N(7)
˚
and N(6)–N(9) distances (Na–Nb) of the two azido ligands of
˚
5 amount to 1.204(2) A, and the N(7)–N(8) and N(9)–N(10)
˚
˚
distances (Nb–Ng ) are 1.141(2) A and 1.145(2) A, respectively.
These structural features are similar to those observed for the azido
ligands of the [Si(N3)6]2- dianion8 and might be best described in
terms of a dominance of the mesomeric structure Si–Na–Nb Ng
rather than Si–Na Nb Ng .
The Si–S and/or Si–Se bond lengths of 8–10 also deserve a
brief discussion because SiN4S2 (8), SiN4SSe (9) and SiN4Se2
skeletons (10) have not yet been described in the literature. The Si–
The Si–N(amidinato) bond lengths of 1 and 3–10 are in the range
˚
˚
1.8571(14)–1.9703(13) A (Table 4). The Si–N(amidinato) bonds of
S distances observed for 8 and 9 (2.231(7)–2.2693(6) A) are similar
9
˚
the two nitrogen atoms in trans positions are somewhat longer than
those of the two nitrogen atoms in cis positions, with maximum
to the sum of the covalent radii of silicon and sulfur (2.21 A),
˚
whereas the Si–Se bond lengths of 9 and 10 (2.3989(8)–2.419(4) A)
˚
˚
deviations ranging from 0.0275 A to 0.113 A. The N(amidinato)–
are slightly longer than the sum of the covalent radii of silicon and
9
˚
˚
C bond lengths of 1 and 3–10 amount to 1.316(2)–1.352(2) A,
selenium (2.34 A).
reflecting the presence of a conjugated system within the amidinato
ligands.
To the best of our knowledge, compound 5 is the first neutral
hexacoordinate silicon(IV) complex with azido ligands that could
be structurally characterised by single-crystal X-ray diffraction.
Therefore, its structural features can only be compared with
NMR studies
Compounds 1–7, 8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8 were
studied by NMR spectroscopy in the solid state (13C, 15N, 19F, 29Si,
77Se) and in solution (1H, 13C, 19F, 29Si, 77Se; solvent CD2Cl2 (1,
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9401–9413 | 9409
©

Table 2 Crystallographic data for compounds 7, 8·0.5C7H8, 9·0.5C7H8 and 10·0.5C7H8
Compound
7
8·0.5C7H8
9·0.5C7H8
10·0.5C7H8
Empirical formula
Formula mass [g mol-1]
T [K]
C28H38N6S2Si
550.85
173(2)
C35.5H46N4S2Si
620.97
173(2)
C35.5H46N4SSeSi
667.87
173(2)
C35.5H46N4Se2Si
714.77
173(2)
˚
l (Mo-Ka) [A]
0.71073
0.71073
0.71073
0.71073
Monoclinic
P21/n (14)
12.370(3)
20.230(4)
13.968(3)
90.15(3)
3495.5(12)
4
Crystal system
Monoclinic
P21/n (14)
12.6263(11)
15.6704(17)
15.3420(13)
91.051(11)
3035.0(5)
4
Monoclinic
P21/n (14)
12.2763(13)
20.044(2)
14.0228(19)
90.261(5)
3450.5(7)
4
Monoclinic
P21/n (14)
12.3497(10)
20.1217(18)
13.9760(12)
90.054(10)
3473.0(5)
4
Space group (no.)
˚
a [A]
˚
b [A]
˚
c [A]
b [◦]
3
˚
V [A ]
Z
rc [g cm-1]
1.206
0.242
1176
1.195
0.219
1332
1.277
1.206
1404
1.358
2.179
1476
m [mm-1]
F(000)
Crystal dimensions [mm]
2q range [◦]
Index ranges
0.5 ¥ 0.4 ¥ 0.2
5.20–58.22
-17 £ h £ 17,
-21 £ k £ 21,
-20 £ l £ 20
48274
7622
0.0573
342
0
1.056
0.0633/0.9262
0.0440
0.1231
+0.397/-0.499
0.3 ¥ 0.2 ¥ 0.2
4.86–58.40
-16 £ h £ 16,
-27 £ k £ 27,
-18 £ l £ 19
27226
9053
0.0391
412
4
1.035
0.0528/0.3140
0.0383
0.1001
+0.406/-0.385
0.5 ¥ 0.3 ¥ 0.2
4.84–58.28
-16 £ h £ 16,
-27 £ k £ 27,
-19 £ l £ 19
49552
9258
0.0424
419
6
1.074
0.0511/0.8953
0.0346
0.0921
+0.445/-0.367
0.3 ¥ 0.2 ¥ 0.2
4.84–58.28
-16 £ h £ 16,
-27 £ k £ 27,
-19 £ l £ 19
41663
9336
0.0509
371
4
1.019
0.0521/0.0000
0.0358
0.0888
+0.671/-0.748
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 = R ꢀFo| - |Fcꢀ/R |Fo|. d wR2 = {R [w(Fo - Fc2)2]/R [w(Fo2)2]}
.
2
0.5
3–10) or C6D6 (2)). The data obtained (see Experimental) confirm
the identities of the compounds studied.
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 hexacoordinate silicon(IV) complexes 1–10 also
exist in solution. This assumption is further supported by all the
other NMR data obtained. The isotropic 29Si chemical shifts of
1–10 vary from -216.6/-213.2 ppm (4, solid state/solution) to
-156.1/-156.5 ppm (8, 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 1–3 deserve a special discussion (Fig. 10). Notably, the
spectrum of 1 shows a relatively sharp resonance signal although
one would expect 29Si,35Cl and 29Si,37Cl couplings (in this context,
see ref. 3e). In contrast, the spectrum of 2 is characterised by a
broad resonance signal owing to 29Si,79Br and 29Si,81Br couplings,
and in the case of 3, 29Si,19F couplings lead to a complex resonance
signal (for a similar splitting pattern in the 29Si MAS NMR spectra
of other compounds with SiF2 moieties, see ref. 10).
While compounds 1, 2 and 4–10 show very well resolved
resonance signals in the 1H NMR spectra at 23 ◦C, the spectrum of
3 is characterised by broad signals. To analyse this phenomenon,
compounds 1 and 3 were additionally studied by VT NMR
experiments. Fig. 11–Fig. 13 show the temperature dependence of
the 1H NMR resonance signals of the isopropyl protons of 1 and
3. The 1H NMR spectra of the dichlorosilicon(IV) complex 1 show
two well resolved septets and four doublets in the temperature
Fig. 10 29Si VACP/MAS NMR spectra (urot = 7 kHz, T = 22 ◦C) of 1
(A), 2 (B) and 3 (C).
range 20–70 ◦C (Fig. 11). This is in accordance with the molecular
C2 symmetry of 1 in solution, which implies two equivalent
9410 | Dalton Trans., 2010, 39, 9401–9413
This journal is
The Royal Society of Chemistry 2010
©

1
Fig. 11 Temperature dependence of the H NMR resonance signals of
the isopropyl protons of 1 (solvent C6D6, 500.1 MHz).
1
Fig. 13 Temperature dependence of the H NMR resonance signals of
the isopropyl protons of 3 (solvent C6D6, 500.1 MHz). Top: Partial 1H
NMR spectra of the CH3CHCH3 protons upon heating from 23 ◦C to
◦
1
72 C (4J(1H,19F) couplings detected). Bottom: Partial H ◦NMR spectra
of the CH3CHCH3 protons upon heating from 23 ◦C to 72 C (5J(1H,19F)
couplings not detected). The temperature dependence of the 1H NMR
spectra is completely reversible upon cooling.
be explained by an exchange of the two nitrogen sites of the
amidinato ligands. Such kind of process was not observed for
the dichlorosilicon(IV) complex 1 on the NMR time scale. This
is in line with the longer Si–N bond lengths of 3 in the crystal
(see Table 4), which might be interpreted in terms of weaker Si–N
bonds compared with 1, leading to a decrease of configurational
stability of 3.
1
Fig. 12 Temperature dependence of the H NMR resonance signals of
the isopropyl protons of 3 (solvent CD2Cl2, 500.1 MHz). Top: Partial 1H
NMR spectra of the CH3CHCH3 protons upon cooling from 20 ◦C to
-20 ◦C. Bottom: Partial 1H NMR spectra of the CH3CHCH3 protons
upon cooling from 20 ◦C to -20 ◦C. The temperature dependence of the
1H NMR spectra is completely reversible upon heating.
As can be seen from the 13C NMR data of 1–10, the rotation
of the phenyl groups of all the compounds studied is hindered in
solution at 23 ◦C (see Experimental). This finding parallels with the
presence of separated resonance signals for the two diastereotopic
ortho protons. However, as shown by 1H NMR spectroscopic
measurements of 1 and 3 at 72 ◦C, this rotation is no longer
hindered and coalescence of the resonance signals of the two ortho
protons is observed. These two ortho protons show a crosspeak to
the methyl protons of the isopropyl groups in the 1H,1H NOESY
amidinato ligands with four diastereotopic methyl groups each. In
contrast, the 1H NMR resonance signals of the difluorosilicon(IV)
complex 3 are broadened in the temperature range -20 ◦C to
20 ◦C, indicating a dynamic process (Fig. 12). This process is
characterised by a loss of the diastereotopism of the methyl groups
of the difluorosilicon(IV) complex 3, leading finally to one doublet
for all eight methyl groups and one septet of triplets for all four
CH3CHCH3 protons at 72 ◦C (Fig. 13). This phenomenon could
◦
NMR spectrum (C6D6, 65 C), indicating the proximity of these
protons.
The hindered rotation of the phenyl groups at lower tempera-
tures was also observed by 13C NMR spectroscopic studies of the
difluorosilicon(IV) complex 3 (Fig. 14). At 20 ◦C, separated broad
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9401–9413 | 9411
©

1
Fig. 14 Temperature dependence of the 13C{ H} NMR resonance signals of the i-C (4J(13C,19F) couplings detected), o-C, m-C and p-C carbon atoms of
1
3 (solvent CD2Cl2, 125.8 MHz). The temperature dependence of the 13C{ H} NMR spectra is completely reversible upon heating.
Table 3 Maximum deviations of the X–Si–X angles (X = ligand atoms)
of 1 and 3–10 from the ideal 90◦ and 180◦ anglesa
Table 5 Comparison of the isotropic 29Si chemical shifts of 1–10 in the
solid state (T = 22 ◦C) and in solution (T = 23 ◦C)a
Compound
D 90◦
D 180◦
Skeleton
Compound
d
29Si (solid state)
d
29Si (solution)b
1
21.30(7)
21.92(6)
20.83(5)
21.58(6)
21.59(5)
21.18(6)
21.72(5)
21.66(5)
21.62(8)
20.22(7)
17.68(5)
17.93(5)
18.56(7)
16.82(5)
15.47(6)
21.77(6)
21.33(6)
21.08(8)
SiN4Cl2
SiN4F2
SiN4C2
SiN6
1
2
-170.4
-206
-171.0
-199.4
-161.6d
-213.2
-175.5
-192.3
-197.2
-156.5
-165.1e
-173.6
3
4
3
-161c
5
4
-216.6
-176.5
-193.2
-195.7
-156.1
-164.0
-175.2
6
SiN6
5
7
SiN6
6
8
SiN4S2
SiN4SSe
SiN4Se2
7
9
8
10
9
10
a Compounds 8–10 were studied as hemitoluene solvates.
a Compounds 8–10 were studied as hemitoluene solvates. b Solvent, CD2Cl2
(1, 3–10) or C6D6 (2). c Complex signal splitting due to strong dipolar
couplings within the 29Si19F2 unit.10 d Triplett, 1JSiF = 218 Hz. e 77Se satellites,
1JSiSe = 78 Hz.
resonance signals were observed for the two diastereotopic ortho
carbon atoms, whereas only one resonance signal was detected for
the two meta carbon atoms. Upon cooling to -20 ◦C, however, two
separated sharp resonance signals each were observed for both the
ortho and the meta carbon atoms.
Owing to its two different chalcogen ligand atoms in cis
position, compound 9 has C1 symmetry, whereas all the other
compounds studied have C2 symmetry. For this reason, the two
amidinato ligands of 9 are not equivalent as for 1–8 and 10. In
the case of compound 9 with its unsymmetric bidentate S,Se
ligand, the existence of two diastereomers should be possible,
analogously to the sulfur/selenium disorder in the crystal of
9·0.5C7H8 (see Crystal structure analyses). These diastereomers
differ in the positions of the sulfur and selenium atoms in the Si-
coordination polyhedron. However, except for some additional 13C
resonance signals of the aromatic groups, no NMR spectroscopic
differentiation between the two diastereomers at 23 ◦C was
possible.
a
˚
Table 4 Comparison of the Si–N(amidinatio) bond lengths [A] of 1 and 3–10
Compound
Si–N(1), Si–N(3)
Si–N(2), Si–N(4)
Dmax
Skeleton
1
1.8726(17), 1.8680(17)
1.8611(13), 1.8571(14)
1.8761(11), 1.8776(12)
1.8784(15), 1.8720(16)
1.8727(11)b
1.8664(14), 1.8746(14)
1.8869(13), 1.8983(12)
1.8935(13), 1.8991(13)
1.8965(18), 1.9022(18)
1.8984(16), 1.9063(17)
1.9647(13), 1.9703(13)
1.9046(11), 1.8930(11)
1.9324(15), 1.9436(15)
1.9461(12)c
1.9279(14), 1.9330(14)
1.9239(13), 1.9261(12)
1.9241(12), 1.9204(13)
1.9240(19), 1.9153(19)
0.0383
0.113
SiN4Cl2
SiN4F2
SiN4C2
SiN6
3
4
0.0285
0.0675
0.0734
0.0666
0.0392
0.0306
0.0275
5
6
SiN6
7
SiN6
8
SiN4S2
SiN4SSe
SiN4Se2
9
10
a Compounds 8–10 were studied as hemitoluene solvates. b Si–N(1) and Si–N(1A). c Si–N(2) and Si–N(2A).
9412 | Dalton Trans., 2010, 39, 9401–9413
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The Royal Society of Chemistry 2010
©

In this study, the bisamidinato ligand system has been demon-
strated to have a high synthetic potential for the chemistry of hex-
acoordinate silicon. Quite recently, we could show that this chem-
istry can be further developed. Starting from the new pentacoor-
dinate monoamidinatosilicon(IV) complex 11, the hexacoordinate
monoamidinatodichlorosilicon(IV) complex 13 could be synthe-
sised by treatment of 11 with 8-hydroxyquinoline/triethylamine,11
and compound 13 could then be further converted into the
derivatives 12 and 14–18 using an analogous synthetic strategy
as described in this article (Scheme 7).11
Scheme 7 Structures of the neutral pentacoordinate silicon(IV) complex
11 and the neutral hexacoordinate silicon(IV) complexes 12–18.
References
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Conclusion
With the synthesis of 1–10, a series of novel neutral hexacoordinate
bisamidinatosilicon(IV) complexes with SiN4F2, SiN4Cl2, SiN4Br2,
SiN4C2, SiN6, SiN4S2, SiN4SSe and SiN4Se2 skeletons has been
made available. Compounds 5–7 (SiN6 skeleton), 8 (SiN4S2), 9
(SiN4SSe) and 10 (SiN4Se2) are of particular interest: Except
for a phenanthroline adduct of Si(NCO)4, neutral hexacoordi-
nate silicon(IV) complexes with an SiN6 skeleton have not yet
been reported in the literature, and hexacoordinate silicon(IV)
complexes with SiN4S2, SiN4SSe and SiN4Se2 skeletons were
totally unknown. In addition, compounds 9 and 10 are the first
hexacoordinate silicon compounds with Si–Se bonds.
The dichlorosilicon(IV) complex 1 has been demonstrated
to be a versatile precursor for the synthesis of 2–10 and is
claimed to be also a suitable starting material for the synthesis
of further derivatives of 1 by replacement of the two chloro
ligands by other monodentate and bidentate ligands. Future
studies have to evaluate the synthetic potential of the related
(pseudo)halogenosilicon(IV) complexes 2–7.
The bisamidinatosilicon(IV) complexes 1–10 show a relatively
high thermal stability although they contain two highly strained
SiN2C rings. Compounds 1–10 exist in the solid state and
in solution. Their molecular structures are best described in
terms of distorted octahedral Si-coordination polyhedra, with
the (pseudo)halogeno ligands and the chalcogen ligand atoms,
respectively, in cis positions. The free rotation of the phenyl groups
of 1–10 is hindered at room temperature. However, upon heating
to ca. 70 ◦C free rotation was observed as shown by VT NMR
studies of 1 and 3. Compounds 1, 2 and 4–10 turned out to be
configurationally stable in solution on the NMR time scale. In
contrast to these compounds, the difluorosilicon(IV) complex 3
shows a dynamic behavior in solution, which could be explained
by an exchange of the two nitrogen sites of the amidinato ligands,
resulting in a loss of the diastereotopism of the isopropyl groups
of the amidinato ligands.
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9 Data taken from: Holleman-Wiberg, Lehrbuch der Anorganischen
Chemie, 102nd ed., Walter de Gruyter, Berlin, 2007, p. 138.
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11 K. Junold, C. Burschka and R. Tacke, unpublished results.
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9401–9413 | 9413
©