Diverse reactivity of an isolable dialkylsilylene toward imines

Article abstract of DOI:10.1039/c2dt32126b

The reactions of isolable dialkylsilylene 10 with various aldimines proceed smoothly at low temperatures to give diverse products depending on the substituents on the imine. The reactions of 10 with 4-XC₆H ₄CHNPh [X = H (11a), MeO (11b), and Cl (11c)] give the corresponding silaaziridines 12a-12c in high yields, which are thermally very stable and remain intact in the air and moisture for a long time. In contrast, the reactions of 10 with 4-F₃CC₆H₄CHNPh (11d) and 3,5-(F₃C)₂C₆H₃CHNPh (11e) having strong electron-withdrawing aryl substituents on imine carbon are accompanied by 1,2-trimethylsilyl migration rather unexpectedly to give silaazetidines 13d-13e incorporated into a bicyclo[3.2.0]heptane ring. The reaction of 10 with N-benzylbenzaldimine 11f affords the corresponding (dibenzylamino)silane 14f in a moderate yield. Molecular structures of 12a-12c, 13d-13e and 14f were determined by X-ray crystallography. All these reactions are proposed to occur via the initial formation of the corresponding imine silaylides, while the subsequent reactions leading to the final products are controlled by the electronic structure of the ylide depending on the substituents. N-Phenylbenzophenimine 11g does not react with 10. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c2dt32126b

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Diverse reactivity of an isolable dialkylsilylene toward
imines†
Cite this: Dalton Trans., 2013, 42, 1872
Weifeng Chen, Liliang Wang, Zhifang Li,* Aiqin Lin, Guoqiao Lai,* Xuqiong Xiao,
Yuan Deng and Mitsuo Kira*
The reactions of isolable dialkylsilylene 10 with various aldimines proceed smoothly at low temperatures
to give diverse products depending on the substituents on the imine. The reactions of 10 with
4-XC6H4CHvNPh [X = H (11a), MeO (11b), and Cl (11c)] give the corresponding silaaziridines 12a–12c in
high yields, which are thermally very stable and remain intact in the air and moisture for a long time. In
contrast, the reactions of 10 with 4-F3CC6H4CHvNPh (11d) and 3,5-(F3C)2C6H3CHvNPh (11e) having
strong electron-withdrawing aryl substituents on imine carbon are accompanied by 1,2-trimethylsilyl
migration rather unexpectedly to give silaazetidines 13d–13e incorporated into a bicyclo[3.2.0]heptane
ring. The reaction of 10 with N-benzylbenzaldimine 11f affords the corresponding (dibenzylamino)silane
14f in a moderate yield. Molecular structures of 12a–12c, 13d–13e and 14f were determined by X-ray
crystallography. All these reactions are proposed to occur via the initial formation of the corresponding
imine silaylides, while the subsequent reactions leading to the final products are controlled by the elec-
tronic structure of the ylide depending on the substituents. N-Phenylbenzophenimine 11g does not react
with 10.
Received 14th September 2012,
Accepted 7th November 2012
DOI: 10.1039/c2dt32126b
www.rsc.org/dalton
Introduction
Although the reactions of silylenes (silicon divalent com-
pounds)1,2 with carbon–oxygen double-bond compounds have
been extensively studied up to date,3 less attention has been
paid to the reactions of the silylenes with related carbon–nitro-
gen double bond compounds, imines. In 1993, Weidenbruch
and Piel reported the reaction of photochemically generated
dimesitylsilylene with N-aryl-1-(2-pyridyl)methanimines (aryl =
mesityl, 2,6-diisopropylphenyl) giving a mixture of 1 and 2
(Chart 1).4 Belzner et al. found that the reactions of a transient
silylene, bis[2-(dimethylaminomethyl)phenyl]silylene, with
N-phenylbenzophenimine and N-(2,6-dimethylphenyl)fluoreni-
mine gave the corresponding silaazacycles 3 and 4, respect-
ively.5 These 1 : 1 adducts 1–4 are usually considered to be
produced via the initial formation of the corresponding silay-
lides 5 followed by the cyclization to the corresponding sila-
aziridines 6,4,5 although neither 5 nor 6 has been detected
Chart 1
during these reactions. Similar 1 : 1 adducts were obtained by
Gehrhus et al. using the reaction of an isolable cyclic diamino-
silylene with imines.6 Recently, Nevárez and Woerpel have
reported that di-tert-butylsilylene generated from the corres-
ponding silacyclopropane in the presence of AgOTf as a cata-
lyst reacts with various ald- and ketimines affording the
corresponding silaaziridines in high yields.7 However, only a
limited number of these silaaziridines were isolated as pure
liquid or powder; most of them were characterized by solution
NMR spectroscopic studies or as their methanolysis products.
Very recently, Roesky et al. have reported that a base-stabilized
silylene reacts with PhCHvNPh to afford the corresponding
silaaziridine whose structure was determined by X-ray
crystallography.8
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of
Education, Hangzhou Normal University, Hangzhou, 310012, P. R. China.
E-mail: zhifanglee@hznu.edu.cn, mkira@m.tohoku.ac.jp
†Electronic supplementary information (ESI) available: X-ray analysis of 12c′ and
14f, crystal and refinement data for 12a–12c, 13d, 13e, and 14f. NMR spectra of
new compounds and the mechanism for the formation of 14f. CCDC 875388,
875347–875350, 875352. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt32126b
1872 | Dalton Trans., 2013, 42, 1872–1878
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suggests effective steric protection of the three-membered ring
by bulky substituents on the silylene moiety.
ð2Þ
Scheme 1
Silaaziridines 12a–12c were characterized by 1H, 13C, and
1
29Si NMR spectroscopic studies in CDCl3. Typically, in the H
NMR spectrum of 12a, a characteristic singlet signal due to the
benzylic proton appears at 3.71 ppm. Four resonances at 0.36,
0.32, 0.00 and −0.18 ppm correspond to protons of four
different SiMe3 groups, indicating that the environments of
the four SiMe3 groups are different from each other. In the 29Si
NMR spectrum of 12a, five resonances assignable to four
different SiMe3 and ring silicon nuclei are found at 3.9, 3.7,
3.5, 3.0, and −24.3 ppm. Similar spectral features are observed
for 12b and 12c. High-field shifted 29Si signals at around
−25 ppm are characteristic for the silaaziridine ring; ring 29Si
As the first silaaziridine whose structure was determined by
X-ray crystallography, silaaziridine 7 was synthesized by Brook
et al. via a different route using the reaction of a stable silene 8
with tert-butylisocyanide (eqn (1)).9
ð1Þ
The above reports have prompted us to investigate the reac-
tions of imines with isolable dialkylsilylene 1010 (Scheme 1),
which has been revealed to show remarkable reactivity towards
numerous organic and organometallic substrates including
ketones and alkenes.11 While the reactions of 10 with N-phenyl-
benzaldimines having electron-donating (4-MeO) or less elec-
tron-withdrawing substituents (4-H, 4-Cl) on the imine
C-phenyl ring afforded the corresponding silaaziridines 12 in
high yields, rather unexpectedly, the reactions of 10 with those
having strong electron-withdrawing substituents [4-CF3, 3,5-
(CF3)2] gave silaazetidines 13 exclusively (Scheme 1). The mole-
cular structures of these silaaziridines and silaazetidines were
determined by X-ray crystallography. The origin of the striking
diversity of the reactions is discussed. The results of the reac-
tions of 10 with N-benzylbenzaldimine and N-phenylbenzopheno-
imine are also reported.
t
resonances for Woerpel’s aziridines 6 (R = Bu, R1, R2 = Ph,
Alkyl, H, R3 = Ph, Bn) are reported to appear at around
−45 ppm.7
As shown in Fig. 1–3, silaaziridine structures of 12a–12c
were confirmed by the single-crystal X-ray diffraction study.13
Ring structures of 12a–12c are similar to each other but
slightly different from that of a base-stabilized silaaziridine
reported by Roesky et al.8 The Si–C and Si–N bond lengths of
their silaaziridine are 0.012 Å shorter and 0.02 Å longer than
those of 12a, probably due to the pentacoordinate nature of
the silicon atom of the former silaaziridine, while the differ-
ence in the C–Si–N bond angle is less than 1° between these
compounds. Comparison of the molecular structures between
Results and discussion
Reactions of 10 with ArCHvNPh (Ar = C6H5, 4-MeOC6H4, and
4-ClC6H4)
The reactions of silylene 10 with N-phenylbenzaldimines 11a–
11c having less electron-withdrawing substitutents at −30 °C
in hexane afforded the corresponding silaaziridines 12a–12c,
respectively, as single products in high yields (eqn (2)). Pure
aziridines 12a–12c were obtained in more than 80% yield as
colorless solids using flash chromatography or GPC. In con-
trast to air- and moisture-sensitive nature of silaaziridines syn- Fig. 1 ORTEP drawing of 12a. Hydrogen atoms are omitted for clarity. Thermal
thesized by Woerpel et al.7,12 and Brook et al.,9 12a–12c remain
intact more than one year at rt in the air. They are thermally
ellipsoids are shown at the 30% probability level. Selected bond lengths (Å) and
angles (°): N1–C1 = 1.488(3), N1–Si1 = 1.7113(17), C1–Si1 = 1.872(2), N1–C5 =
1.398(3), C1–C2 = 1.489(3), C3–Si1 = 1.885(2), C4–Si1 = 1.879(2); C1–N1–Si1 =
stable with high melting points and no decomposition was
71.24(10), N1–Si1–C1 = 48.80(8), N1–C1–Si1 = 59.95(10), C3–Si1–C4 = 101.53(9).
observed when a toluene solution of 12a was refluxed for 8 h.
Dihedral angles between two planes (°): 14.42 for C1–Si1–N1/N-aryl planes,
Unusually high thermal and chemical stability of 12a–12c 79.98 for C1–Si1–N1/C4–Si1–C3 planes, 82.74 for C-aryl/N-phenyl planes.
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bond lengths and wider bond angles are required around the
unsaturated carbon, because it is intrinsically sp2 hybridized.
Reactions of 10 with ArCHvNPh (Ar = 4-F3CC6H4 and 3,5-
(F3C)2C6H3)
When an imine with a strong electron-withdrawing substituent
on the C-phenyl ring is used for the reaction of silylene 10, an
unexpected bicyclic compound with a silaazetidine ring was
obtained exclusively, instead of the corresponding silaaziri-
dine. Thus, the reactions of 10 with N-phenylbenzaldimines
having trifluoromethyl substituents 11d and 11e gave 13d and
13e in 82 and 78% yields, respectively (eqn (3)).
Fig. 2 ORTEP drawing of 12b. Hydrogen atoms are omitted for clarity. Thermal
ellipsoids are shown at the 30% probability level. Selected bond lengths (Å) and
angles (°): Si1–N1 = 1.7134(18), Si1–C1 = 1.872(2), C1–N1 = 1.482(3), C1–C2 =
1.489(3), C5–N1 = 1.386(3), Si1–C3 = 1.878(2), Si1–C4 = 1.896(2); N1–Si1–C1 =
48.59(9), C1–N1–Si1 = 71.30(11), N1–C1–Si1 = 60.11(10), C3–Si1–C4 = 101.25(9).
Dihedral angles between two planes (°): 15.11 for C1–Si1–N1/N-aryl planes,
80.68 for C1–Si1–N1/C4–Si1–C3 planes, and 81.94 for C-aryl/N-phenyl planes.
ð3Þ
The structures of silaazetidines 13d and 13e were confirmed
by NMR spectroscopic studies and finally by X-ray crystallogra-
phy. In their 1H NMR spectra, the benzylic proton signal
appeared as a singlet at 5.39 and 5.42 ppm for 13d and 13e,
respectively; no signals due to the expected aziridine type com-
pounds were detected. As expected from the unsymmetrical
structures of 13d and 13e, five 29Si resonances were observed
at 41.2, 3.5, 2.9, −0.4, and −18.8 ppm for 13d and 42.0, 3.5,
3.02, −0.3, and −18.6 ppm for 13e. The lowest and highest
field 29Si signals that appeared at around 40 and −19 ppm are
assigned as the bridgehead silicon and the Me3Si silicon
bonded to the silicon, respectively.
Molecular structures of 13d and 13e determined by X-ray
crystallography are shown in Fig. 4 and 5, respectively, con-
firming their azasilabicyclo[3.2.0]heptane structure.13 The rela-
tive stereochemistry around the silaazetidine ring of 13d and
13e was determined as shown in eqn (3) by the X-ray structural
analysis. The four membered ring of 13d and 13e is not planar
but slightly folded with the C2–Si1–C1–N1 dihedral angle of
6.23 and 9.10°, respectively. The Si–C bridge bond length in
13d and 13e is a little longer than those of reported silaazeti-
dines,14 while other bond lengths in the ring are not much
different from each other.
Fig. 3 ORTEP drawing of 12c. One of the two crystallographically independent
molecules is shown. Another molecular structure of 12c (12c’) is shown in the
ESI.† Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at
the 30% probability level. Selected bond lengths (Å) and angles (°): Si1–N1 =
1.705(2), Si1–C1 = 1.878(3), C1–N1 = 1.489(3), C1–C2 = 1.483(4), C5–N1 =
1.395(3), Si1–C3 = 1.887(3), Si1–C4 = 1.874(3); N1–Si1–C1 = 48.80(11), C1–N1–
Si1 = 71.66(14), N1–C1–Si1 = 59.54(12), C4–Si1–C3 = 101.92(12). Dihedral
angles between two planes (°): 16.35 for C1–Si1–N1/N-aryl planes, 80.94 for
C1–Si1–N1/C4–Si1–C3 planes, and 81.51 for C-aryl/N-phenyl planes.
12a and Brook’s aziridine 79 would also be interesting because
the latter has an exocyclic methylene. The ring Si–C and C–N
bond lengths of 12a are slightly longer than those of 7 [1.830
(15) and 1.417(17) Å, respectively], while the ring Si–N bond
length of 12a is shorter than that of 7 [1.764(13) Å]. The N–Si–
C and C–N–Si bond angles of 12a are larger than those of 7
[46.4(5)° and 69.3(8)°], while the Si–C–N angle of 12a is
smaller than that of 7 [64.3(8)°]. The differences in bond
lengths and angles between 12a and 7 would be ascribed to
the difference in the hybridization of the ring carbons; shorter
Reactions of 10 with N-benzylbenzaldimine and
N-phenylbenzophenimine
During the reaction of 10 with N-benzylbenzaldimine 11f
under similar conditions to eqn (2) and (3) was obtained a
different type of product 14f in a moderate yield of 37% (eqn
(4)). The structure of 14f was confirmed by NMR spectroscopic
studies and X-ray crystallography (ESI†).13
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Fig. 4 ORTEP drawing of 13d. Hydrogen atoms are omitted for clarity. Thermal
ellipsoids are shown at the 30% probability level. Selected bond lengths (Å) and
angles (°): Si1–N1 = 1.7689(16), Si1–C2 = 1.937(2), C1–C2 = 1.595(3), C1–N1 =
1.478(2), Si1–Si2 = 2.3920(8), Si1–C4 = 1.895(2); N1–Si1–C2 = 78.44(8), C1–C2–
Si1 = 85.82(11), N1–C1–C2 = 99.55(14), C1–N1–Si1 = 95.85(11), C4–Si1–C2 =
99.38(9), C3–C2–Si1 = 101.23(13). Dihedral angles between two planes (°):
78.31 for C-aryl/N-phenyl planes, 6.23 for C1–Si1–N1/C1–Si1–C2 planes, and
6.21 for C2–N1–Si1/C2–N1–C1.
Fig. 5 ORTEP drawing of 13e. Hydrogen atoms are omitted for clarity. Thermal
ellipsoids are shown at the 30% probability level. Selected bond lengths (Å) and
angles (°): Si1–N1 = 1.771(2), Si1–C2 = 1.921(3), C1–C2 = 1.585(4), C1–N1 =
1.462(3), Si1–Si2 = 2.3778(13), Si1–C4 = 1.886(3); N1–Si1–C2 = 78.38(11), C1–
C2–Si1 = 85.69(17), N1–C1–C2 = 100.0(2), C1–N1–Si1 = 95.20(16), C4–Si1–C2 =
99.99(13), C3–C2–Si1 = 101.00(19). Dihedral angles between two planes (°):
76.13 for C-aryl/N-phenyl planes, 9.10 for C1–Si1–N1/C1–Si1–C2 planes, and
9.13 for C2–N1–Si1/C2–N1–C1.
substituents, and hence, the 4π-electrocyclic reactions giving
the corresponding silaaziridines 12a–12c would occur
preferentially.
ð4Þ
The reaction of an imine with silylene 10 is sensitive to the
bulkiness of the substituents on the imine. In contrast to the
reaction of 10 with benzophenone giving 1 : 1 adduct 15,3z no
reaction occurred between benzophenimine 11g and 10 even
at rt (eqn (5)).
ð6Þ
The reactions of silylene 10 with benzaldimines 11d and
11e having strong electron-withdrawing substituents are un-
usually accompanied by 1,2-trimethylsilyl migration of the sily-
lene moiety. The mechanism of the reactions is not fully
understood at present but a plausible mechanism is proposed
as follows: although the 1,2-silyl migration of 10 is a well-
known process at higher temperatures than 0 °C in solution, it
ð5Þ
Reaction mechanisms
As proposed in the previous reports,4,5 the reactions of a sily- does not occur appreciably at low temperatures such as
lene with an imine will proceed via the initial formation of the −30 °C.10,15 However, an imine silaylide formed between 10
corresponding imine silaylide 5 (Chart 1) followed by cycliza- and imine 11d or 11e may have preferred resonance form 16B,
tion or isomerization giving the corresponding 1 : 1 adducts. in which silylene silicon and imine carbon are positively and
This mechanism is applied to the reactions of 10 with negatively charged, respectively. Thus, the 1,2-silyl migration
N-phenyl benzaldimines 11a, 11b, and 11c, which bear hydro- from carbon to the neighboring cationic silicon center in the
gen-, an electron-donating methoxy-, and a weakly electron- ylide 16B is facilitated to afford 1,4-zwitterionic intermediate
withdrawing chloro-substituent at the 4-position of the 17. Intramolecular cyclization of 17 may give the correspond-
C-phenyl group, respectively (eqn (6)). Intermediary imine ing silaazetidine 13d or 13e (path a). As another route to the
silaylides may have two major resonance forms A and B, whose silaazetidines from 17, we may anticipate the elimination of
relative importance depends on the electronic nature of the imine 11d (or 11e) giving silaethene 18 and the imine (path b)
imine, by analogy with carbonyl silaylides formed by the followed by the [2 + 2] cycloaddition between them. To differ-
addition of silylenes to carbonyl compounds.3z Form B is less entiate between paths a and b, the reaction of imine 11d with
important for imines 11a–11c with less electron-withdrawing silaethene 1815 that was synthesized by thermal isomerization
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124.6, 118.34, 118.29, 43.5, 32.2, 30.6, 8.2, 5.2, 4.0, 2.8, 2.4, 2.2.
29Si NMR (80 MHz, CDCl3) δ 3.9, 3.7, 3.5, 3.0, −24.3; MS (70
eV, EI) m/z (%) 553 (M+, 100), 538 (M+ − 15, 45), 476 (55), 299
(64); HRMS m/z calcd for C29H51NSi5: 553.2868. Found:
553.2886.
12b: white solid (94 mg, 81%); mp 193–195 °C; 1H NMR
(400 MHz, CDCl3): δ 7.17–7.10 (m, 4H), 6.79–6.75 (m, 5H), 3.75
(s, 3H), 3.65 (s, 1H), 2.16–2.12 (m, 2H), 2.06–1.97 (m, 2H), 0.35
(s, 9H), 0.30 (s, 9H), −0.02 (s, 9H), −0.16 (s, 9H); 13C NMR
(100 MHz, CDCl3): δ 157.1, 146.6, 134.1, 128.5, 126.0, 118.3,
118.2, 113.8, 55.3, 42.8, 32.2, 30.6, 8.1, 5.1, 4.0, 2.8, 2.4, 2.1;
29Si NMR (80 MHz, CDCl3) δ 3.9, 3.7, 3.4, 2.9, −24.5; MS (ESI):
m/z 606 (M + Na)+; HRMS m/z calcd for C30H53NOSi5: 583.2974.
Found: 583.3055.
Scheme 2
12c: white solid (102 mg, 87%); mp 200–202 °C; 1H NMR
(400 MHz, CDCl3): δ 7.25–7.23 (m, 6H), 6.84–6.81 (m, 3H), 3.72
(s, 1H), 2.24–2.17 (m, 2H), 2.14–2.01 (m, 2H), 0.41 (s, 9H), 0.36
(s, 9H), 0.04 (s, 9H), −0.10 (s, 9H); 13C NMR (100 MHz, CDCl3):
δ 146.1, 141.0, 130.0, 128.6, 128.4, 126.5, 118.8, 118.3, 43.1,
32.2, 30.6, 8.3, 5.3, 4.1, 3.0, 2.5, 2.2; 29Si NMR (80 MHz, CDCl3)
δ 4.0, 3.7, 3.5, 3.1, −23.7; ESI-HRMS [M + H]+ calcd for
C29H51ClNSi5: 588.2556. Found: 588.2567.
of silylene 10 was investigated. Silaazetidine 13d was never
detected after the reaction at −30 °C for 6 h, though at reflux,
the reaction actually gave 13d; cycloadduct 13d was identified
by 29Si NMR spectroscopy and 1H NMR spectroscopy after puri-
fication. Path b should be eliminated by the above experiments
(Scheme 2).
Compound 14f is not a simple 1 : 1 adduct between 10 and
11f and for the formation are required two additional hydro-
gen atoms. The mechanism remains open but a plausible
mechanism is proposed in MSI.
13d: white solid (102 mg, 82%). mp 247–249 °C; 1H NMR
(400 MHz, CDCl3): δ 7.52 (d, J = 7.2 Hz, 2H), 7.35 (d, J = 7.8 Hz,
2H), 7.07 (t, J = 7.4 Hz, 2H), 6.67 (t, J = 7.2 Hz, 1H), 6.31 (d, J =
7.2 Hz, 2H), 5.39 (s, 1H), 2.06–2.04 (m, 2H), 1.65–1.54 (m, 1H),
1.48–1.40 (m, 1H), 0.28 (s, 9H), 0.25 (s, 9H), 0.24 (s, 9H), 0. 12
(s, 9H); 13C NMR (100 MHz, CDCl3): δ 147.6, 144.2, 128.5,
128.4, 127.6, 124.7, 124.3, 117.3, 115.0, 67.2, 32.5, 32.1, 29.7,
19.8, 3.6, 3.0, 2.0, 1.6; 19F NMR (376 MHz, CDCl3) δ −62.2; 29Si
NMR (80 MHz, CDCl3) δ 41.2, 3.5, 2.9, −0.4, −18.8; MS (70 eV,
EI) m/z (%) 621 (M+, 100), 548 (78), 456(45), 372(43); HRMS m/z
calcd for C30H50NF3Si5: 621.2742. Found: 621.2762.
Experimental section
All synthetic experiments were performed under argon or
nitrogen in a standard vacuum system unless otherwise noted.
1H (400 MHz), 13C (100 MHz), 29Si (80 MHz), and 19F NMR
(376 MHz) spectra were recorded with TMS as an internal stan-
13e: white solid (107 mg, 78%). mp 168–170 °C; 1H NMR
(400 MHz, CDCl3): δ 7.71 (s, 3H), 7.09 (t, J = 7.4 Hz, 2H), 6.70
(t, J = 7.2 Hz, 1H), 6.31 (d, J = 7.4 Hz, 2H), 5.41 (s, 1H),
2.11–2.07 (m, 1H), 1.97–1.89 (m, 1H), 1.56–1.44 (m, 2H), 0.30
(s, 9H), 0.27 (s, 9H), 0.26 (s, 9H), 0.14 (s, 9H); 13C NMR
(100 MHz, CDCl3): δ 147.1, 143.1, 131.0, 128.7, 127.6, 123.5,
120.4, 117.7, 114.8, 66.7, 32.5, 31.9, 29.8, 19.6, 3.6, 2.8, 2.0, 1.5;
19F NMR (376 MHz, CDCl3) δ −62.6; 29Si NMR (80 MHz, CDCl3)
δ 42.0, 3.5, 3.0, −0.3, −18.6; HRMS [M + H]+ calcd for
C31H50F6NSi5: 690.2694. Found: 690.2702.
dard on
a BRUKER AV-400 MHZ instrument. MS were
measured with a Trance 2000 DSQ mass spectrometer. High-
resolution MS were measured on a Thermo Scientific LTQ
Orbitrap XL spectrometer. Melting points are uncorrected. Sily-
lene 1010 and imines 11a–11f16 were prepared according to the
literature procedures. Silylene 10 and other air-sensitive
materials were handled in a MBraun glovebox. All products
were purified by flash chromatography or GPC (LC-9101, Japan
Analytical Industry Co. Ltd).
14f: white solid (43 mg, 37%). mp 121–123 °C; 1H NMR
(400 MHz, CDCl3): δ 7.21–7.19 (m, 6H), 7.10–7.08 (m, 4H), 5.54
General procedure for the reactions of 10 with 11
An excess amount of imine 11 (0.3 mmol) was added to a solu- (s, 1H), 4.04 (s, 4H), 2.12–2.05 (m, 2H), 2.02–1.95 (m, 2H), 0.25
tion of silylene 10 (75 mg, 0.2 mmol) in hexane at −30 °C. The (s, 18H), 0.20 (s, 18H); 13C NMR (100 MHz, CDCl3): δ 138.7,
reaction mixture was allowed to stir for 20 min at −30 °C. Then 129.0, 127.8, 126.6, 52.2, 32.4, 8.2, 4.0, 2.3; 29Si NMR (80 MHz,
the solvent was removed under vacuum. The product was iso- CDCl3) δ 15.5, 5.0, 1.7; MS (ESI): m/z 568 (M − H)+. HRMS
lated as a pure substance from the resulting residue by flash [M − H]+ calcd for C30H54NSi5: 568.3097. Found: 568.3075.
chromatography or GPC (toluene).
12a: white solid (95 mg, 86%); mp 151–153 °C; 1H NMR
(400 MHz, CDCl3): δ 7.22–7.14 (m, 6H), 7.08–7.06 (m, 1H),
Reaction of silaethene 18 with imine 11d
6.80–6.75 (m, 3H), 3.71 (s, 1H), 2.18–2.11 (m, 2H), 2.08–1.95 A solution of silylene 10 (150 mg, 0.4 mmol) in hexane (8 mL)
(m, 2H), 0.36 (s, 9H), 0.32 (s, 9H), 0.00 (s, 9H), −0.18 (s, 9H). was heated at 60 °C for 24 h in the dark. Hexane was evapo-
13C NMR (100 MHz, CDCl3): δ 146.5, 142.2, 128.5, 128.2, 125.1, rated and the residue was determined as silaethene 1810,15 by
1876 | Dalton Trans., 2013, 42, 1872–1878
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29Si NMR: 29Si NMR (80 MHz, C6D6) δ 137.0, 1.4, −9.4, −16.2. the corresponding (dibenzylamino)silane 14f in a moderate
Compound 18 was used directly without further purification. yield. All these reactions are proposed to occur via the initial
A solution of 18 (45 mg) obtained as above in hexane formation of the corresponding imine silaylides, while the sub-
(3 mL) was added to imine 11d (75 mg, 0.3 mmol) at −30 °C. sequent reactions leading to the final products are controlled
After stirring the hexane solution at −30 °C for 6 h, the reac- by the electronic structure of the ylide depending on the sub-
tion mixture was exposed to air. No silaazetidine was detected stituents. Ketimine 11g does not react with 10.
by TLC.
After refluxing a mixture of 18 (45 mg) and 11d (75 mg,
0.3 mmol) in hexane for 6 h, hexane was evaporated comple-
Acknowledgements
tely and the residue was purified by flash chromatography to
afford silaazetidine 13d as
a
major product. 1H NMR This work was supported by the National Natural Science
(400 MHz, CDCl3): δ 7.51 (d, J = 7.2 Hz, 2H), 7.35 (d, J = 7.8 Hz, Foundation of China (21101050, 21202031), Zhejiang Provin-
2H), 7.07 (t, J = 7.4 Hz, 2H), 6.67 (t, J = 7.2 Hz, 1H), 6.31 (d, J = cial Natural Science Foundation of China (Y4110297,
7.2 Hz, 2H), 5.39 (s, 1H), 2.06–2.04 (m, 2H), 1.65–1.55 (m, 1H), Y4090470), Scientific Research Fund of Zhejiang Provincial
1.48–1.40 (m, 1H), 0.29 (s, 9H), 0.25 (s, 9H), 0.24 (s, 9H), 0. 12 Education Department (Y200907742) and the Funds for Key
(s, 9H); 29Si NMR (80 MHz, CDCl3) δ 40.9, 3.5, 2.9, −0.6, −19.0. Innovation Team of Zhejiang Province (2009R50016).
Crystal structure determination
Notes and references
Single crystals of 12a–12c, 13d, 13e, and 14f suitable for X-ray
analysis were obtained by the recrystallization from CHCl3.
The X-ray diffraction data were collected on a Bruker Smart
Apex CCD diffractometer with graphite monochromated Mo-
Kα radiation (λ = 0.71073 Å) using the ω − 2θ scan mode. The
structure was solved by direct methods and refined on F2 by
full-matrix least-squares methods using SHELX-2000.17 All cal-
culations and molecular graphics were carried out on a com-
puter using the SHELX-2000 program package and Diamond.
The single crystal of compound 12c showed two crystallo-
graphically independent molecules in an asymmetric unit. In
molecules 12a and 13d–e, one Me3Si group in 12a, one CF3
group in 13d, and two CF3 groups in 13e are disordered over
two sites, respectively. Crystal and refinement data for 12a–
12c, 13d, 13e and 14 are described in the ESI. CCDC Nos.
875350 (12a), 875349 (12b), 875388 (12c), 875347 (13d), 875352
(13e), and 875348 (14f) contain the supplementary crystallo-
graphic data for this paper.
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Conclusions
In summary, isolable dialkylsilylene 10 reacts with various
aldimines smoothly at low temperatures to give diverse pro-
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1878 | Dalton Trans., 2013, 42, 1872–1878
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