Synthesis of a Dichlorosilaimine Coordinated by an N-Heterocyclic Carbene from ArN(SiMe3)SiHCl2

Article abstract of DOI:10.1002/cjoc.201600719

NHC-stabilized dichlorosilaimine ArN=Si(IiPr)Cl₂ (2) (Ar = 2,6-iPr₂C₆H₃, IiPr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) and disilane LSiHCl-SiCl₂L (L=ArNSiMe₃) (3) could be synthesized from the reaction of aminodichlorosilane ArN(SiMe₃)SiHCl₂ (1) with IiPr under different conditions. This represents the first route to the generation of donor-stabilized dichlorosilaimine from substituted chlorosilane in the presence of an NHC via dehydrosilylation.

Full text of DOI:10.1002/cjoc.201600719

COMMUNICATION
DOI: 10.1002/cjoc.201600719
Synthesis of a Dichlorosilaimine Coordinated by an
N-Heterocyclic Carbene from ArN(SiMe3)SiHCl2
Haiyan Cui,*,a Peng Teng,a Enbin Zhang,a Jiahao Lu,a Fan Zhang,a and Meng Wu*,b
a Jiangsu Key Laboratory of Pesticide Science, College of Sciences, Nanjing Agricultural University,
Nanjing, Jiangsu 210095, China
b State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences,
Nanjing, Jiangsu 210008, China
NHC-stabilized dichlorosilaimine ArN＝Si(IiPr)Cl2 (2) (Ar＝2,6-iPr2C6H3, IiPr＝1,3-diisopropyl-4,5-dimeth-
ylimidazol-2-ylidene) and disilane LSiHCl-SiCl2L (L＝ArNSiMe3) (3) could be synthesized from the reaction of
aminodichlorosilane ArN(SiMe3)SiHCl2 (1) with IiPr under different conditions. This represents the first route to
the generation of donor-stabilized dichlorosilaimine from substituted chlorosilane in the presence of an NHC via
dehydrosilylation.
Keywords silaimine, dehydrosilylation, silane, N-heterocyclic carbene
Introduction
HSiCl3.[11] Soon several silylenes have been isolated
with similar methods by other groups.[12] Inoue’s group
recently reported an NHC-stabilized silyliumylidene ion
by dehydrochlorination from chlorosilanes.[6d] Base-
stabilized 1-hydrosilaimine ArN＝SiH(NHC)N(SiMe3)-
Ar could also be isolated from reactions of a less hin-
dered N-heterocyclic carbene with substituted chlorosi-
lanes.[13] To the best of our knowledge, there is no ex-
ample of dichlorosilaimine which could be synthesized
via dehydrosilylation by NHCs from substituted chloro-
silanes.
Herein, we reported the synthesis of NHC-stabilized
dichlorosilaimine ArN＝Si(IiPr)Cl2 (2, Ar＝2,6-iPr2-
C6H3, IiPr ＝ 1,3-diisopropyl-4,5-dimethylimidazol-2-
ylidene) from the reaction of aminodichlorosilane
ArN(SiMe3)SiHCl2 (1) with an N-heterocyclic carbene
IiPr. This is the first route to the synthesis of donor-sta-
bilized dichlorosilaimine from substituted chlorosilane
in the presence of an NHC via direct dehydrosilylation.
In addition, we demonstrate that the reactions of 1 with
IiPr are significantly influenced by the reaction condi-
tions.
The chemistry of unsaturated silicon compounds
(silylenes and silicon multiple-bonding species) has
been of great interest to chemists throughout the last
decades owing to their significant roles in the develop-
ment of silicon chemistry.[1,2] Silaimines (R2Si＝NR),
silicon analogues of imines, are considered as one of the
most intriguing topics in organosilicon chemistry.[2-9]
＋
With highly polarized Siδ －Nδ double bond, sila-
imines are extremely reactive species. The first sila-
imines were reported independently by Wiberg[4a,4b] and
Klingebiel[4c] in 1980’s via salt elimination. Since then,
a fair number of silaimines were isolated from direct
reactions of silylenes towards organic azides[5,6b] and
carbodiimides.[6a,6b] In 2012, Inoue and his co-worker
isolated the zwitterionic silaimine from the reaction of
silylene with (C6F5)3B.[6c] Very recently, we reported the
N-heterocyclic carbene (NHC)-stabilized vinylsila-
imines[7] and dichlorosilaimine[8] through reactions of a
donor-stabilized silylene with alkynes and SiCl4, re-
spectively. Subsequently, controlled oxidation of an
NHC-stabilized phosphinosilylene Ar(SiMe3)NSi(NHC)-
PPh2 with dioxygen was reported to afford donor-stabi-
lized dioxysilaimine and oxysilaimine.[9] However, di-
rect access to silaimines is still restricted.
Experimental
All operations were carried out under an atmosphere
of dry argon or nitrogen by using modified Schlenck
line and glovebox techniques. All solvents were freshly
distilled from Na and degassed immediately prior to use.
The 1H, 13C and 29Si NMR spectroscopic data were rec-
orded on Bruker Mercury Plus 300, 400 and 600 MHz
Substituted chlorosilanes are important building
blocks in silicon chemistry. Cui’s group and Roesky’s
group reported a dehydrohalogenation route for the
generation of a series of silylenes by NHCs under very
mild conditions from substituted chlorosilanes[10] and
*
E-mail: haiyancui555@163.com, mwu@issas.ac.cn
Received October 26, 2016; accepted December 18, 2016; published online XXXX, 2017.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201600719 or from the author.
Chin. J. Chem. 2017, XX, 1—4
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1

Cui et al.
COMMUNICATION
NMR spectrometers. ArN(SiMe3)Si(IiPr)Cl (1)[13a] and
IiPr[15] were synthesized according to published proce-
dures.
(Scheme 1).
Scheme 1 Synthesis of 2 and 3
2: A solution of 1 (0.35 g, 1 mmol) in THF (5 mL)
was added slowly to a solution of IiPr (0.27 g, 1.5 mmol)
in THF (5 mL) at 78 ℃. The color of the solution
soon changed from colorless to yellow. The mixture was
allowed to warm to room temperature and stirred over-
night. After filtration and removal of solvents, the re-
maining residue was washed successively with hexane
(5 mL) and Et2O (10 mL) to afford white powder 2
(0.11 g, 24.2%). m.p. 197－199 ℃; 1H NMR (400
MHz, C6D6) δ: 0.95 [d, J＝7.0 Hz, 12H, CH(CH3)2],
1.34 (s, 6H, CCH3), 1.56 [d, J ＝ 6.8 Hz, 12H,
CH(CH3)2], 4.13 [m, 2H, Ar-CH(CH3)2], 6.62 [m, 2H,
N-CH(CH3)2], 7.09 (m, 1H, Ar-H), 7.39 (d, J＝7.5 Hz,
2H, Ar-H); 13C NMR (100.61 MHz, d8-THF) δ: 10.69
(＝CCH3), 21.08 [CH(CH3)2], 24.16 [CH(CH3)2], 28.47
[Ar-CH(CH3)2], 51.73 [NCH(CH3)2], 116.06, 122.01,
129.73, 139.90, 145.78 (Ar-C), 145.99 (NCN); 29Si
NMR (79.49 MHz, d8-THF) δ: 107.03.
3: A solution of 1 (0.35 g, 1 mmol) in Et2O (5 mL)
was added slowly to a solution of IiPr (0.18 g, 1 mmol)
in Et2O (5 mL) at room temperature. Soon a white sus-
pension formed. The mixture was allowed to stir for 1 h.
After filtration, the residue was washed with cold
CHCl3 (3 mL×2) to yield white power 3 (0.22 g,
66.7%). Sublimated at 219 ℃ ( 1 mbar); 1H NMR (400
MHz, C6D6) δ: 0.17 (s, 9H, Me3Si), 0.28 (s, 9H, Me3Si),
1.15－1.42 (m, 24H, Me2CH), 3.66 (m, 1H, CHMe2),
3.76 (m, 2H, CHMe2), 3.98 (m, 1H, CHMe2), 5.47 (s,
1H, Si－H), 7.05 (m, 6H, Ar－H); 13C NMR (100.61
MHz, C6D6) δ: 1.01, 2.36, 2.59, 23.88, 24.30, 24.35,
25.02, 25.24, 26.01, 26.67, 26.80, 27.34, 27.42, 28.07,
28.27, 29.70, 77.20, 124.13, 124.26, 124.36, 125.90,
126.00, 146.83, 147.58,162.35; 13C NMR (100.61 MHz,
CDCl3) δ: 1.64, 2.49, 2.70, 24.01, 24.41, 24.53, 25.17,
25.40, 26.15, 26.91, 27.01, 27.44, 27.52, 28.06, 28.22,
28.42, 30.53, 124.23, 124.39, 124.48, 126.00, 126.08,
138.63, 143.13, 146.87, 147.52, 147.66; 29Si NMR
(59.62 MHz, CDCl3) δ: 19.25.
a) 1 to IiPr (1∶1.5), THF, 78 ℃ to r.t., overnight; b) 1 to IiPr (1∶1),
Et2O, r.t., 1 h
Compound 2 is air and moisture sensitive, and it is
soluble in THF and insoluble in n-hexane. 2 has been
1
fully characterized by H, 13C and 29Si NMR spectra.
From the NMR spectra, 2 was identified as NHC-stabi-
lized dichlorosilaimine ArN＝SiCl2(IiPr), which was
first reported by our group from the reaction of silylene
A and SiCl4 in ca. 21% yield.[8]
The proton NMR spectrum of 2 indicates the disap-
pearance of the SiMe3 group and the presence of one Ar
ring and one IiPr group in the structure. The 13C NMR
resonance for the carbene carbon atom in 2 occurs at δ
145.99, similar to those found in the NHCSi donor-
acceptor complexes.[7-9,12-14] The 29Si spectrum in
d8-THF for the central silicon atom exhibits a singlet
signal at δ 107.03. The multinuclear NMR is in good
agreement with the values reported in the literature.[8]
In order to improve the yield of 2, various experi-
mental conditions (different solvents, temperatures,
stoichiometries and addition sequences) have been ex-
amined. In most cases, it was impossible to isolate pure
products even from repeated crystallizations from dif-
ferent solvents. Nevertheless, addition of a solution of 1
to one equivalent of IiPr in Et2O at room temperature
afforded disilane 3 as white powder in 66.7% yield after
workup (Scheme 1). 3 was previously reported from the
reaction of 1 and ItBu[16] [1,3-bis(tert-butyl)imidazol-2-
ylidene] in a molar ratio of 2∶1,[13a] but has not been
structurally characterized.
Results and Discussion
We have recently reported reactions of ArN(SiMe3)-
SiHCl2 1 with different NHCs.[13,14a] And the products
were influenced by steric hindrance of NHCs and reac-
tion conditions. Donor-stabilized silylene Ar(SiMe3)-
NSiCl(IiPr) (A) was synthesized from dropping ArN-
(SiMe3)SiHCl2 1 into two equivalents of IiPr[15] at
78 ℃ in THF.[14a] To examine the effects of reaction
condition on products, we changed the ratios of the re-
actants. It was found that dropping 1 into 1.5 equiv. of
IiPr in THF from low temperature to ambient tempera-
ture led to a complicated mixture. Analysis of the solu-
ble materials by proton NMR spectroscopy indicated the
formation of A and a different species 2 with a ratio of
1∶0.47. 2 was isolated as white powder in 24.2% yield
Compound 3 is air and moisture sensitive, and ex-
hibits high thermal stability in the solid state, as indi-
cated by its high melting point. 3 has been fully charac-
terized by multinuclear NMR and X-ray single-crystal
1
analysis. The H NMR spectrum of 3 exhibits a singlet
at δ 5.47 (1JSi-H＝247.15 Hz) for the Si－H proton, and
two singlet resonances at δ 0.17 and 0.28 for SiMe3.
Single crystals of 3 suitable for an X-ray diffraction
study were obtained from toluene at ambient tempera-
ture. The X-ray crystal structure analysis confirmed
compound 3 to be a disilane, consisting of two tetra-
coordinated silicon atoms attached respectively with one
2
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Chin. J. Chem. 2017, XX, 1—4

Synthesis of a Dichlorosilaimine Coordinated by an N-Heterocyclic Carbene
Ar(SiMe3)N ligand (Figure 1). The Si1－N1 (1.7170(17)
Å) bond length and Si3－N2 1.7157(17) bond length
were shorter than the average value of Si2－N1 and Si4
－N2 bond lengths (1.7762 Å), but in the range of Si－
N single bond. The Si1－Si3 bond length (2.3680(8) Å)
was comparable to the Si－Si single bond value report-
ed in the literatures (2.36－2.46 Å).[17] The four atoms
N1, Si1, Si3 and N2 were almost coplanar with the tor-
sion angle N1-Si1-Si3-N2 (172.98(9)°).
While the formation of 3, as with the previously report-
ed literature,[10] may involve the initial generation of the
transient silylene N [ArN(SiMe3)SiCl] via a dehydro-
chlorination reaction with IiPr, followed by insertion
into the Si－H or Si－Cl single bond of another mole-
cule of 1 (Scheme 2, path b).
Conclusions
In summary, we have shown that reaction of 1 with
IiPr yielded NHC-stabilized dichlorosilaimine 2 and
disilane 3 in different reaction conditions. This repre-
sents the first approach for the generation of donor-sta-
bilized dichlorosilaimine from substituted chlorosilane
via direct dehydrosilylation in the presence of an NHC.
Reactivity studies of chlorosilanes and compound 2 are
currently in progress.
Acknowledgement
Figure 1 Ortep drawing of 3 with ellipsoids given at the 50%
probability level. Carbon bound hydrogen atoms have been omit-
ted for clarity. Selected bond lengths (Å), angles (°) and torsion
angles (°): N1－C1 1.472(2), N1－Si1 1.7170(17), N1－Si2
1.7733(18), N2－C16 1.468(2), N2－Si3 1.7157(17), N2－Si4
1.7792(18), Si1－Si3 2.3680(8), Si1－H1a 1.41(3), Si1－Cl1
2.0887(8), Si3－Cl3 2.0614(9), Si3－Cl2 2.0753(8), C1-N1-Si1
116.47(13), C1-N1-Si2 115.47(12), Si1-N1-Si2 127.95(10),
C16-N2-Si3 118.57(13), C16-N2-Si4 117.80(12), Si3-N2-Si4
123.58(9), N1-Si1-Si3 117.41(6), N2-Si3-Si1 117.03(6), N1-Si1-
Si3-N2 172.98(9).
We are grateful to the National Natural Science
Foundation of China (Grant No. 21402094, 41401258),
the Natural Science Foundation of Jiangsu Province
(Grant No. BK20140678, BK20131044) and the Fun-
damental Research Funds for the Central Universities
(Grant No. KJQN201551).
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