N-heterocyclic carbene stabilized dichlorosilaimine IPr·Cl 2Si=NR

Article abstract of DOI:10.1021/om100737v

N-Heterocyclic carbene stabilized dichlorosilaimine IPr·Cl ₂Si=N(Diip) (2) has been synthesized by the reaction of dichlorosilylene IPr·SiCl₂ (1) with bis(2,6-diisopropylphenyl) carbodiimide (IPr =:C[N(2,6-i-Pr₂-C₆H₃)CH] ₂, Diip = 2,6-i-Pr₂-C₆H₃). Reaction of 1 with terphenyl azides also affords dichlorosilaimines IPr·Cl ₂Si=N(2,6-Diip₂-C₆H₃) (3) and IPr·Cl₂Si=N(2,6-Triip₂-C₆H₃) (4) (Triip = 2,4,6-i-Pr₃-C₆H₂). Compounds 2-4 are stable under an inert atmosphere and were characterized by elemental analysis and NMR spectroscopic studies. The molecular structures of 2-4 were determined by single-crystal X-ray analysis.

Full text of DOI:10.1021/om100737v

Organometallics 2010, 29, 6329–6333 6329
DOI: 10.1021/om100737v
N-Heterocyclic Carbene Stabilized Dichlorosilaimine IPr Cl2SidNR
3
Rajendra S. Ghadwal,† Herbert W. Roesky,*,† Carola Schulzke,‡ and Markus Granitzka†
†
€
Institut fu€r Anorganische Chemie der Universitat Gottingen, Tammannstrasse 4, D 37077 Gottingen,
€
€
Germany, and ‡School of Chemistry, Trinity College Dublin, Dublin 2, Ireland
Received July 27, 2010
N-Heterocyclic carbene stabilized dichlorosilaimine IPr Cl2SidN(Diip) (2) has been synthesized
3
by the reaction of dichlorosilylene IPr SiCl2 (1) with bis(2,6-diisopropylphenyl)carbodiimide (IPr =
:C[N(2,6-i-Pr2-C6H3)CH]2, Diip = 2,6-i-Pr2-C6H3). Reaction of 1 with terphenyl azides also affords
dichlorosilaimines IPr Cl2SidN(2,6-Diip2-C6H3) (3) and IPr Cl2SidN(2,6-Triip2-C6H3) (4) (Triip =
3
3
3
2,4,6-i-Pr3-C6H2). Compounds 2-4 are stable under an inert atmosphere and were characterized by
elemental analysis and NMR spectroscopic studies. The molecular structures of 2-4 were deter-
mined by single-crystal X-ray analysis.
Introduction
reacts with another molecule of organic azide to form azido-
silane or silaterazoline.3,4
Silylenes are key intermediates in numerous thermal and
photochemical reactions1 of organosilicon compounds.
Silylene chemistry has been in focus over the last two decades.2
After the isolation of room-temperature-stable silylenes their
reactivity toward a wide range of unsaturated organic and
organometallic substrates has been examined,3,4 which is
diverse and dependent on the substituents on the silicon atom
and the nature of the substrates. Reactions of N-heterocyclic
silylenes (NHSis) with organic azides are reported that show
significant difference in their reactivity. Although a THF
adduct of a silaimine was reported by West3 et al. by the
reaction of a NHSi with a bulky azide, most of the reactions of
NHSis with organic azides resulted in the formation of either
azidosilane3,4 or silatetrazolines.3,4 On the basis of this, the
involvement of initial formation of an unstable silaimine as an
intermediate in these reactions was proposed, which further
The search for the formation of multiply bonded silicon
compounds5 has been attracting attention throughout the
last decades and is still one of the most interesting topics for
silicon chemists. Dialkylsilaimines are compounds with a
silicon-nitrogen double bond, which were first isolated
independently by Wiberg6 and Klingebiel7 in 1986 by ther-
mal salt elimination through multistep reactions.
Moreover, direct methods for silaimine synthesis are still
scarce, and there is no reported example of a dihalosilaimine
because of the unavailability of suitable starting materials.
Gaseous dihalosilylenes, SiX2 (X = F or Cl), have been
known for many years;8 however at room temperature they
condense to polymeric (SiX2)n or disproportionate to Si and
SiX4. There are a number of theoretical investigations9
reporting the reactivity of silylenes. However, the only available
experimental evidence10 involves SiCl2, which was generated
*To whom correspondence should be addressed. E-mail: hroesky@
gwdg.de.
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r
2010 American Chemical Society
Published on Web 11/15/2010
pubs.acs.org/Organometallics

6330 Organometallics, Vol. 29, No. 23, 2010
Ghadwal et al.
Scheme 1
in situ and trapped by reagents to form Si(IV) compounds. Very
recently, we generated and stabilized SiCl2 by N-heterocyclic
carbene (NHC) and isolated IPr SiCl2 (1) at room tem-
3
perature.11 Reaction of 1 with 1-azidoadamantane yielded a
functionalized NHC12 via the formation of unstable dichloro-
silaimine as an intermediate. Silaimines contain polarized SidN
bonds, and the presence of an alkyl or aryl group on the nitrogen
atom plays a very important role in their stabilization. In view of
the above results, we expected the reaction of 1 with aryl azides
to lead to NHC-stabilized dichlorosilaimines. Furthermore, no
reaction of stable silylene with a carbodiimide has appeared so
far. Herein, we report on the synthesis and characterization of
dichlorosilaimines IPr Cl2SidN(Diip) (2), IPr Cl2SidN(2,6-
3
3
Diip2-C6H3) (3), and IPr Cl2SidN(2,6-Triip2-C6H3) (4) (IPr =
3
:C[N(2,6-i-Pr2-C6H3)CH]2, Diip = 2,6-i-Pr2-C6H3, Triip =
2,4,6-i-Pr3-C6H2) by reacting 1 with bis(2,6-diisopropylphe-
nyl)carbodiimide or terphenyl azides. Silaimines 2-4 should
serve as suitable precursors for the preparation of differently
substituted silaimines and silanitriles or silaisonitriles, which are
currently under investigation.
Figure 1. Molecular structure of 2. Anisotropic displacement
parameters are depicted at the 50% probability level. The
toluene solvent molecule and H atoms are omitted for clarity.
˚
Selected bond distances (A) and angles (deg): Si(1)-Cl(1)
Results and Discussion
2.0717(18), Si(1)-Cl(2) 2.095(2), Si(1)-C(1) 1.917(5), Si(1)-N(3)
1.563(4), N(3)-C(28) 1.366(6); Cl(1)-Si(1)-Cl(2) 100.10(8),
Cl(1)-Si(1)-C(1) 106.36(16), Cl(2)-Si(1)-C(1) 99.77(16),
Cl(1)-Si(1)-N(3) 116.51(18), Cl(2)-Si(1)-N(3) 122.69(17),
C(1)-Si(1)-N(3) 109.2(2).
Reaction of IPr SiCl2 (1) with bis(2,6-diisopropylphenyl)-
3
carbodiimide (Scheme 1) affords NHC-stabilized dichlorosi-
laimine IPr Cl2SidN(Diip) (2). 1 reacts with an equimolar
3
amount of 2,6-Diip2-C6H3N3 or 2,6-Triip2-C6H3N3 with clean
formation of dichlorosilaimines IPr Cl2SidN(2,6-Diip2-C6H3)
(3) and IPr Cl2SidN(2,6-Triip2-C6H3) (4), respectively.
3
spectra of 2-4 show resonances for the IPr ligand coordi-
nated to the silicon atom along with the resonances due to the
aryl group attached to the imine nitrogen atom. 29Si NMR
resonances for 2, 3, and 4 appear at δ -107.07, -99.95,
and -99.70 ppm, respectively, which are shifted upfield with
respect to 1 (δ 18 ppm)11 due to higher coordinate silicon atoms
and are consistent with Si(IV) compounds.13
3
Dichlorosilaimines 2-4 are yellow crystalline compounds
that are stable under an inert atmosphere and soluble in
common organic solvents. 2-4 were characterized by single-
1
crystal X-ray diffraction, elemental analyses, and H, 13C,
and 29Si NMR spectroscopic studies. 1H and 13C NMR
(11) Ghadwal, R. S.; Roesky, H. W.; Merkel, S.; Henn, J.; Stalke, D.
Angew. Chem., Int. Ed. 2009, 48, 5683–5686. Angew. Chem. 2009, 121,
5793-5796.
(12) Ghadwal, R. S.; Roesky, H. W.; Granitzka, M.; Stalke, D. J. Am.
Chem. Soc. 2010, 132, 10018–10020.
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Kratzert, D.; Merkel, S.; Stalke, D. Angew. Chem., Int. Ed. 2010, 49,
3952–3955. Angew. Chem. 2010, 122, 4044-4047.

Article
Organometallics, Vol. 29, No. 23, 2010 6331
Figure 3. Molecular structure of 4. Anisotropic displacement
parameters are depicted at the 50% probability level. The second
molecule, toluene solvent molecules, and H atoms are omitted for
Figure 2. Molecular structure of 3. Anisotropic displacement
parameters are depicted at the 50% probability level. H atoms
˚
are omitted for clarity. Selected bond distances (A) and angles
(deg): Si(1)-Cl(1) 2.0649(10), Si(1)-Cl(2) 2.0653(10), Si(1)-C(1)
1.953(2), Si(1)-N(3) 1.588(2), N(3)-C(28) 1.376(3); Cl(1)-
Si(1)-Cl(2) 102.08(4), Cl(1)-Si(1)-C(1) 103.25(8), Cl(2)-Si(1)-
C(1) 99.33(8), Cl(1)-Si(1)-N(3) 114.18(8), Cl(2)-Si(1)-N(3)
122.17(8), C(1)-Si(1)-N(3) 113.26(10).
˚
clarity. Selected bond distances (A) and angles (deg): Si(1)-Cl(1)
2.0612(9), Si(1)-Cl(2) 2.0668(9), Si(1)-C(1) 1.938(2), Si(1)-N(3)
1.594(2), N(3)-C(28) 1.376(3); Cl(1)-Si(1)-Cl(2) 101.59(4),
Cl(1)-Si(1)-C(1) 104.67(8), Cl(2)-Si(1)-C(1) 98.12(7), Cl(1)-
Si(1)-N(3) 114.46(8), Cl(2)-Si(1)-N(3) 124.76(8), C(1)-Si(1)-
N(3) 110.57(10).
(i) NHC-stabilized dichlorosilylene 1 reacts with bis(2,6-diiso-
propylphenyl)carbodiimide in a unexpected way to afford
dichlorosilaimine 2. The reaction of a stable silylene with
carbodiimide is reported for the first time. (ii) NHC-stabi-
lized dichlorosilaimines 3 and 4 have been prepared by the
reaction of 1 with terphenyl azides. The availability of easily
replaceable and reducible chlorine atoms in compounds 2-4
on the silicon atom makes them interesting starting materials
for preparing a variety of silicon compounds, which are
presently under further investigation.
Single-Crystal X-ray Structures. The molecular structures
of compounds 2, 3, and 4 were established by single-crystal
X-ray crystallography and are shown in Figures 1-3. Silai-
mines 2-4 were obtained as yellow crystals, containing
toluene molecules in the lattice. Crystallographic data for
2-4 are summarized in Table 1. The molecular structure of 2
is shown in Figure 1. Compound 2 crystallizes in the mono-
clinic space group P21/c. The silicon atom in 2 exhibits a
distorted tetrahedral geometry. Two coordination sites of
the silicon atom are occupied by the two chlorine atoms, the
third one is occupied by the C atom of the NHC, and the
fourth site is occupied by one N atom of the imine moiety.
Silaimine 3 crystallizes in the monoclinic space group C2/
c, whereas 4 crystallizes in the triclinic space group P1 with
two molecules in the asymmetric unit. The silicon atom in
each of 3 and 4 is four-coordinate, and the sum of the bond
angles around silicon exhibits a distorted tetrahedral geometry
(Figures 2 and 3). The NHC ligand, the Cl atoms, and imine N
atom in 3 and 4 are arranged in a similar fashion to those in 2.
Experimental Section
General Procedures. All reactions and manipulations were
performed under an inert atmosphere using standard Schlenk
line techniques or a glovebox. The solvents used were purified by
MBraun solvent purification system MB SPS-800. The N-het-
erocyclic carbene, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-yli-
dene (IPr),15 and IPr SiCl2 (1)11 were prepared by literature
3
methods. Bis(2,6-diisopropylphenyl)phenyl azide and bis(2,4,6-
triisopropylphenyl)phenyl azide were prepared according to
reported methods.16 C6D6 was dried over Na metal and distilled
under nitrogen prior to use. 1H, 13C, and 29Si NMR spectra were
recorded using Bruker Avance DPX 200 or Bruker Avance
DRX 500 spectrometers. Tetramethylsilane (TMS) was used
as an internal (1H and 13C NMR) or an external (29Si NMR)
reference. Elemental analyses were obtained from the Analytical
Laboratory of the Institute of Inorganic Chemistry at the
˚
The SidN bond lengths for 2-4 (av 1.565(4) A) are consistent
with those reported3,6 for silaimine THF adducts. The SirC
˚
˚
bond distances for 2(1.917(5) A), 3(1.953(2) A), and4(1.938(2)
˚
A) are only marginally shorter than that of 1 (1.985(4) A). The
˚
˚
average Si-Cl bond length (2.0708(18) A) in 2-4 is noticeably
shorter than that of 1 (2.1664(16) A) and in agreement with that
˚
of four-coordinate14 silicon in IPr SiCl2 B(C6F5)3.
€
University of Gottingen. Melting points were measured in
sealed capillary tubes under nitrogen.
3
3
Synthesis of IPr Cl2SidN(Diip) (2). To a mixture of 1 (1.03 g,
2.11 mmol) and bis(2,6-diisopropylphenyl)carbodiimide (0.77 g,
3
Conclusion
In this article we presented two methods for the prepara-
tion of dichlorosilaimines stabilized by a NHC ligand.
(15) Jafarpour, L.; Stevens, E. D.; Nolan, S. P. J. Organomet. Chem.
2000, 606, 49–54.
(16) (a) Twamley, B.; Hwang, C. S.; Hardman, N. J.; Power, P. P.
J. Organomet. Chem. 2000, 609, 152–160. (b) Gavenonis, J.; Tilley, T. D.
Organometallics 2004, 23, 31–43.
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Eur. J. 2010, 16, 85–88.

6332 Organometallics, Vol. 29, No. 23, 2010
Table 1. Crystallographic Data and Structure Refinement for Compounds 2-4
Ghadwal et al.
2 C6H5CH3
3
3
4 0.75C6H5CH3
3
formula
CCDC no.
fw
C46H61Cl2N3Si
746183
754.97
C57H73Cl2N3Si
780073
899.17
C273H364Cl8N12Si4
780074
4209.72
cryst size/mm
cryst syst
space group
0.50 Â 0.20 Â 0.05
monoclinic
P21/c
18.146(4)
13.126(3)
18.957(4)
90
104.39(3)
90
4373.3(15)
1.147
0.17 Â 0.10 Â 0.08
monoclinic
C2/c
18.674(3)
14.193(2)
38.194(6)
90
93.331(2)
90
10105(3)
1.182
0.30 Â 0.25 Â 0.10
triclinic
P1
13.0796(16)
˚
a/A
˚
b/A
˚
21.796(3) A
˚
c/A
22.043(3)
90.581(2)
92.462(2)
100.942(2)
6163.0(13)
1.134
R/deg
β/deg
γ/deg
3
˚
V/A
Dcalcd/g cm-3
Z
4
0.210
1.16 to 26.00
26 102/8478
8
0.192
2.45 to 24.71
92 428/8602
4
0.167
1.31 to 24.71°.
75 367/21023
abs coeff/mm-1
θ range/deg
reflns collected/
indep reflns
[R(int) = 0.1307]
0.9868 and 0.9238
[R(int) = 0.0922]
0.7452 and 0.6190
[R(int) = 0.0617]
0.9874 and 0.7649
max. and min.
transmn
final R indices
[I > 2σ(I)]
R indices
(all data)
largest diff peak
˚
and hole/e A
R1 = 0.0893,
wR2 = 0.1727
R1 = 0.1721,
wR2 = 0.2054
0.608 and -0.458
R1 = 0.0475,
wR2 = 0.1026
R1 = 0.0758,
wR2 = 0.1163
0.933 and -0.464
R1 = 0.0480,
wR2 = 0.1124
R1 = 0.0817,
wR2 = 0.1285
0.711 and -0.367
3
2.12 mmol) was added precooled toluene (60 mL) at -78 °C. The
yellow reaction mixture was brought to room temperature and
turned red after 2 h. After overnight stirring, all volatiles were
removed under vacuum to obtain a pale yellow solid. The byproduct
2,6-diisopropylphenyl isonitrile was extracted with n-hexane (2 Â 30
mL) and characterized by NMR spectroscopy. The residue was
dissolved in 20 mL of toluene and stored at -35 °C for 2 days.
Yellow crystals of 2 were obtained (0.89 g, 63%). Mp: 170 (dec) °C.
Anal. Calcd (%) for C39H53Cl2N3Si (M = 662.85): C, 70.67; H,
to that of 3, by reaction of 1 (0.79 g, 1.62 mmol) and bis(2,4,6-
triisopropylphenyl)phenyl azide (0.85 g, 1.62 mmol) to yield yellow
crystals of 4 (1.17 g, 73%). Mp: 235-236 (dec) °C. Anal. Calcd (%)
for C63H85Cl2N3Si (M = 983.36): C, 76.95; H, 8.71; N, 4.27. Found
(%): C, 76.75; H, 8.78; N, 4.18. 1H NMR (200.13 MHz, C6D6, 298
K): δ0.76 (d, J=6.80Hz,12H,CHMe2),1.12(d,J=6.60Hz, 12H,
CHMe2), 1.26 (d, J = 6.80 Hz, 24H, CHMe2), 1.38 (d,
J = 6.80 Hz, 12H, CHMe2), 2.46 (m, J = 6.80 Hz, 4H,
CHMe2), 2.92 (m, 2H, CHMe2), 3.37 (m, J = 6.80 Hz, 4H,
CHMe2), 6.03 (s, 2H, NCH), 6.66 (t, J = 7.00 Hz, 1H, p-C6H3)
6.95-7.10 (m, 12H, C6H3) ppm. 13C{1H} NMR (125.76 MHz,
C6D6, 298 K): δ 23.48, 24.61, 26.34 (CH(CH3)2), 30.17, 30.67,
34.87 (CH(CH3)2), 120.90 (NCH), 125.63, 125.77 (m-C6H3),
129.27, 131.10, 133.27, 132.31 (p-C6H3), 134.92 (o-C6H3),
142.71, 145.51, 146.24, 147,87 (ipso-C6H3) ppm. 29Si NMR
(99.36 MHz, C6D6, 298 K): δ -99.70 ppm.
1
8.06; N, 6.34. Found (%): C, 70.56; H, 8.10; N, 6.25. H NMR
(200.13 MHz, C6D6, 298 K): δ 0.92 (d, J = 6.87 Hz, 12H, CHMe2),
1.31 (dd, J = 6.99 Hz, 24H, CHMe2), 2.79 (m, 4H, CHMe2), 3.21
(m, 2H, CHMe2), 6.23 (s, 2H, NCH), 7.00-7.27 (m, 9H, C6H3)
ppm. 13C{1H} NMR (125.76 MHz, C6D6, 298 K): δ 22.73, 23.35,
(CH(CH3)2), 25.35, 25.64 (CH(CH3)2), 28.74, 29.50 (CH(CH3)2),
123.42 (NCH), 124.36, 125.40 (m-C6H3), 131.60, (p-C6H3), 134.26
(o-C6H3), 145.45, 146.25 (ipso-C6H3) ppm. 29Si NMR (99.36 MHz,
C6D6, 298 K): δ -107.07 ppm.
X-ray Structure Determination of Compounds 2-4. A suitable
crystal of 2 was mounted on a glass fiber, and data were collected on
an IPDS II Stoe image-plate diffractometer (graphite-monochro-
Synthesis of IPr Cl2SidN(2,6-Diip2-C6H3) (3). To a 100 mL
3
˚
mated Mo KR radiation, λ = 0.71073 A) at 133(2) K. The data were
Schlenk flask containing 1 (0.56 g, 1.15 mmol) and bis(2,6-
diisopropylphenyl)phenyl azide (0.51 g, 1.16 mmol) was added
toluene (50 mL), and the resulting yellow solution was stirred for
5 h and then concentrated to 10 mL. Storing the solution at 4 °C
for 2 days afforded yellow crystals of 3 (0.71 g, 69%). Mp: 235
(dec) °C. Anal. Calcd (%) for C57H73Cl2N3Si (M = 899.23): C,
76.14; H, 8.18; N, 4.67. Found (%): C, 76.09; H, 8.24; N, 4.15.
1H NMR (200.13 MHz, C6D6, 298 K): δ 0.72 (d, J = 6.60 Hz,
12H, CHMe2), 1.10 (d, J = 6.20 Hz, 12H, CHMe2), 1.21 (dd,
J = 6.22 Hz, 24H, CHMe2), 2.42 (m, 2H, CHMe2), 2.85 (m, 2H,
CHMe2), 3.34 (m, 4H, CHMe2), 6.02 (s, 2H, NCH), 6.69 (t,
J = 6.80 Hz, 1H, p-C6H3) 6.92-7.27 (m, 14H, C6H3) ppm.
13C{1H} NMR (125.76 MHz, C6D6, 298 K): δ 22.98, 23.14,
23.37 (CH(CH3)2), 24.15, 24.25, 25.59, 25.82 (CH(CH3)2),
29.83, 30.24, 30.38, 30.56, 30.72 (CH(CH3)2), 122.66 (NCH),
124.22, 125.42 (m-C6H3), 130.20, 130.63, 132.80, 132.89
(p-C6H3), 134.48 (o-C6H3), 144.50, 145.04, 147.01, 147.66
(ipso-C6H3) ppm. 29Si NMR (99.36 MHz, C6D6, 298 K):
δ -99.95 ppm.
integrated with X-area and absorption corrected by X-red32. The
data for 3 and 4 were collected from shock-cooled crystals at 100(2)
K17 and were measured on a Bruker TXS-Mo rotating anode with
Helios mirror optics and an APEX II detector with a D8 goniometer.
The diffractometer was equipped with a low-temperature device17
˚
and used Mo KR radiation, λ = 0.71073 A. The data of 3 and 4 were
integrated with SAINT18 and an empirical absorption correction
(SADABS) was applied.19 The structures were solved by direct
methods (SHELXS-97) and refined by full-matrix least-squares
methods against F2 (SHELXL-97).20 All non-hydrogenatoms were
refined with anisotropic displacement parameters. The hydrogen
atoms were refined isotropically on calculated positions using a
riding model with their Uiso values constrained to equal 1.5 times
the Ueq of their pivot atoms for terminal sp3 carbon atoms and 1.2
times for all other carbon atoms. Disordered moieties were
(17) (a) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615–619.
(b) Stalke, D. Chem. Soc. Rev. 1998, 27, 171–178.
(18) SAINT v7.68A; Bruker AXS Inc.: Madison, WI, USA, 2009.
Synthesis of IPr Cl2SidN(2,6-Triip2-C6H3) (4). Compound 4
€
(19) Sheldrick, G. M. SADABS 2008/2; Gottingen, 2008.
3
was synthesized, adopting a similar method for the preparation
(20) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.

Article
Organometallics, Vol. 29, No. 23, 2010 6333
refined using bond length restraints and isotropic displacement
parameter restraints. Due to the very low diffraction of the crystal
of 2 and data collection time of one week, ice formed around the
crystal and was frequently removed. But still, this had an impact
on the R-values (in particular the internal R-value), which are
comparatively high.
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft is greatly acknowledged.
Supporting Information Available: Crystallographic data for
complexes 2-4 as CIF files. This material is available free of
charge via the Internet at http://pubs.acs.org.