1,4-Dehydrogenation with a Two-Coordinate Cyclic (Alkyl)(amino)silylene

Article abstract of DOI:10.1002/chem.201901407

Cyclic (alkyl)(amino)silylene (CAASi) 1 has been found to successfully dehydrogenate 1,4-dihydroaromatic compounds containing various substituents to afford the corresponding aromatic compounds. The observed high substrate generality proves 1 to be a potential 1,4-dehydrogenation reagent for organic compounds. For the reaction with 9,10-dimethyl-9,10-dihydroanthracene, silylene 1 activated not only benzylic C?H bonds but also aromatic C?H bonds to yield a silaacenaphthene derivative, which is an unprecedented reaction of silylenes. The results of the experimental and computational study of the reaction of CAASi 1 with 9,10-dihydroanthracene and 1,4-cyclohexadiene are consistent with the notion that 1,4-dehydrogenation with CAASi 1 proceeds mainly through a stepwise hydrogen-abstraction mechanism.

Full text of DOI:10.1002/chem.201901407

A Journal of
Accepted Article
Title: 1,4-Dehydrogenation with a Two-Coordinate Cyclic (Alkyl)
(amino)silylene
Authors: Taichi Koike, Tomoyuki Kosai, and Takeaki Iwamoto
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10.1002/chem.201901407
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1,4-Dehydrogenation with a Two-Coordinate Cyclic
(Alkyl)(amino)silylene
Taichi Koike, Tomoyuki Kosai, and Takeaki Iwamoto*[a]
Abstract: Cyclic (alkyl)(amino)silylene (CAASi) 1 successfully
dehydrogenated 1,4-dihydroaromatic compounds with various
substituents affording the corresponding aromatic compounds.
The high substrate generality proved 1 to be a potential 1,4-
dehydrogenation reagent for organic compounds. For the reaction
with 9,10-dimethyl-9,10-dihydroanthracene, 1 activated not only
benzylic C–H bonds but also aromatic C–H bonds to yield a
silaacenaphthene derivative, which is an unprecedented reaction
of silylenes. Experimental and computational results for the
reaction with 9,10-dihydroanthracene and 1,4-cyclohexadiene are
consistent with the notion that 1,4-dehydrogenation with CAASi 1
proceeds mainly via a stepwise hydrogen abstraction.
cleave the C=C bond in benzene to yield a bis(silylene) adduct
D.[4a] Our group also reported similar C=C bond cleavage of
benzene derivatives using
a isolable dialkylsilylene upon
irradiation.[4b] Driess et al. found that cyclic diaminosilylene E
activates the N–H bond of ammonia to yield triaminosilane F.[5]
Recently, Aldridge et al. have reported the activation of
dihydrogen with acyclic (amino)(boryl)silylene G
to yield
dihydridosilane H.[6] These results clearly indicate that judicious
design of the substituents on the divalent silicon atom enables the
activation of numerous organic molecules. However, application
of silylenes as reagents for molecular transformation reactions
other than silylation is scarce, due to the high tendency of
silylenes to undergo cycloaddition or insertion reactions.[1]
tBu
Introduction
Si
1.
tBu
A
Chemistry of silylenes (R2Si), heavier element analogues of
carbenes have shown tremendous development in the last few
decades.[1a-c] Although silylenes are generally known as low-
coordinate reactive intermediates in silicon chemistry, taming
their high reactivity through bulky substituents and/or electron-
donor groups bonded to the divalent silicon atom has enabled the
isolation of various stable silylenes. Recently, isolable silylenes
have emerged as effective ligands for transition metal complexes
or as starting materials of novel silicon compounds (R2Si=X; X =
SiR2, CNR, NR, O, S, Se, Te, etc.).[2]
Furthermore, owing to the intrinsic Lewis basicity (lone pair
electrons) and Lewis acidity (vacant 3p orbital) on the divalent
silicon atom, a number of small-molecule activation with either
transient or isolable silylenes have been reported up to date. Such
discoveries have brought attention to the application of silylenes
as potential reagents for transformation of organic molecules in
organic chemistry.[1d-f] For example, Woerpel et al. took
advantage of the nature of silylenes to undergo reversible [1+2]
cycloaddition with alkenes in the transfer reaction of di-tert-
butylsilylene generated from its cyclohexene adduct A to various
alkenes affording the corresponding silacyclopropanes B.[3]
Okazaki and Tokitoh reported that two molecules of transient
tBu
Si
AgOTf, toluene
2. TMEDA
R
tBu
R
B
Mes
Si
Mes
Tbt
Mes
Si Si
Mes
Tbt
C
Tbt
Si
Mes
∆
Si
Tbt
Tbt
D
Dip
Dip
N
SiH2
Dip
Dip
N
Si
N
Dip
Me3Si
Dip
Me3Si
Dip
N
H2
N
Si
H
NH3
toluene
Si
D6
C6
N
N
B
B
NH2
N
Dip
N
N
Dip
Dip
G
H
F
E
Chart 1. Examples of transformation reactions of organic molecules as well as
small molecule activation reactions with silylenes (Mes: 2,4,6-trimethylphenyl,
Dip: 2,6-diisopropylphenyl, Tbt: 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl).
Recently, we successfully synthesized the thermally stable
cyclic (alkyl)(amino)silylene (CAASi) 1, which is stable at
temperatures up to 150 °C, and found that 1 underwent
dehydrogenation of 1,4-cyclohexadiene (CHD) and 9,10-
dihydroanthracene (DHA) to yield the corresponding aromatic
compounds along with dihydrogenated CAASi (2) (Scheme 1).[7]
This was the first intermolecular benzylic and allylic C–H bond
activation with an isolable silylene.[8] Similar benzylic and allylic
C–H bond activation with N,N’-diamidocarbenes have been
reported for CHD and 9,10-dihydrophenanthrene by Bielawski's
group.[9] By far, main group element compounds applicable as
dehydrogenation reagents are limited, and such reagents with
wide substrate generality should be crucial for improving cost-
silylene
Tbt(Mes)Si
(C,
Tbt
=
2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl, Mes = 2,4,6-trimethylphenyl)
[a]
T. Koike, Dr. T. Kosai, Prof. Dr. T. Iwamoto
Department of Chemistry, Graduate School of Science,
Tohoku University, Aoba-ku, Sendai 980-8578 (Japan)
E-mail: takeaki.iwamoto@tohoku.ac.jp
Homepage: http://www.ssoc.chem.tohoku.ac.jp/en_index.html
Supporting information for this article and the ORCID identification
number(s) for the author(s) of this article can be found under:
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Table 1. Dehydrogenation of CHD and DHA derivatives with CAASi 1.
efficiency and to broaden the option of reagents accessible for
synthesizing olefinic/aromatic molecules.
R
R
R
H
Me
3Si SiMe3
R
2Si
(1.0 eq)
+
R
2SiH2
°
D
C6
C
+
6,150
SiH2
N
(sealed tube)[a]
heptane,
H
4
R
5
°
150 C (sealed tube)
Ad
(77%)
2
Me
3Si SiMe3
2
(70%)
Product Yield[b]
Si
N
Substrate
Product
time
16 h
5
2
Ad
1
CAASi
+
2
Si )
81% 82%
(R2
16
16
heptane,
°
150 C (sealed tube)
4a
5a
(35%)
(39%)
O
O
37 h
42 h
16 h
72% 71%
53% 54%
83% 87%
Me
3Si SiMe3
t-Bu
t-Bu
H
4b
4c
5b
5c
Si
+
N
Ad
(22%)
3
Scheme 1. Dehydrogenation of CHD and DHA with CAASi 1 (Ad = 1-
adamantyl). The yields were determined by 1H NMR spectroscopy.
4d
5d
R1
R1
Herein, we report the successful dehydrogenation of a series of
1,4-dihydroaromatic compounds with CAASi 1. We also
examined the mechanistic details of the reaction by experimental
and computational studies. These results indicate that 1 could be
a 1,4-dehydrogenation reagent complementary to commonly
used reagents represented by 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ) and chloranils[10f,11] that have contributed to
the synthesis of numerous polycyclic aromatic hydrocarbons
(PAHs).[11h-j]
R
R
= R 2= Me
= R 2= Me
R1
R1
20 h
72 h
30%[c] 63%[c]
22% 49%
2
4e
2
5e
= Et, R = Me
= Et, R = Me
R1
R1
2
2
4f
5f
= i-Pr, R = Me
= i-Pr, R = Me
0%[d] 24%[d]
R1
R1
100 days
16 h
2
2
4g
5g
Bu
Bu
COOMe
COOMe
COOMe
COOMe
21%[e] 21%[e]
Bu
Bu
4h
5h
Results and Discussion
[a] All reactions were conducted in a sealed tube heated at 150 °C. [b] Yiel-
(Sc-
ds were calculated from 1H NMR spectroscopy. [c] Silaacenapthene
heme 2) was observed as the major byproduct in 13% yield. [d] CAASi
6
1
re-
All 1,4-dehydrogenation reactions with CAASi 1 were conducted
at 150 °C in [D6]benzene placed in a sealed tube because
reactions at lower temperature just elongate the completion of
reaction (e.g. DHA: 240 h at 60 °C; 15 h at 150°C). CAASi 1
successfully dehydrogenated numerous CHD derivatives 4a-4h
(Table 1). Similar to the reaction with parent CHD, reaction with
1-heptadecyl substituted CHD (4a) provided heptadecylbenzene
(5a) and dihydrogenated CAASi (2) with no sign of formation of
C–H insertion product such as 3. The reaction with 4b, which has
an electron-donating methoxy group and a t-butyl moiety also
gave the corresponding anisole 5b in good yield without formation
of any conspicuous byproducts. The reaction with a CHD that has
a fused five-membered ring (4c) gave 5c with no sign of indene
according to 1H NMR spectroscopy. Reaction with 1,4-
dihydronaphthalene (4d) afforded naphthalene (5d) and 2 in high
yields. Compared to the reaction with DHA, C–H inserted product
mained with unidentified byproducts. [e] Signs of unidentified byproducts w-
ere observed.
The reaction with 9,10-dialkylanthracenes 4e and 4f
successfully yielded the corresponding anthracenes 5e, 5f, and
dihydridosilane 2, however, with large discrepancies in yields
between the resulting anthracene derivatives and 2.[12-13] While
the yields of 2 for 4e and 4f were 63% and 49% respectively,
anthracenes were only half of those numbers: 30% and 22%,
respectively. Actually, in the reaction with 4e, silaacenaphthene
6[14] (Scheme 2) was generated in 13% yield as a major byproduct.
As reaction with 1 and 9,10-dimethylanthracene (5e) yielded 6 as
a major product together with formation of 2 (Scheme 2), 1 should
dehydrogenate 4e to provide 5e and undergo further
dehydrogenation of 5e to yield 6. This reaction is an
unprecedented simultaneous activation of benzylic and aryl C–H
bond with an isolable silylene. The reaction with isopropyl-
substituted DHA 4g proceeded very slowly to yield 2, however,
with no sign of formation of the corresponding anthracene 5g.[15]
1
was not observed by H NMR or mass spectroscopy. This is in
good agreement with the previous result that allyl C–H inserted
product of CHD is not observed as well.
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CAASi 1 remained even after 100 days of heating, implying that
the benzyl hydrogen adjacent to the secondary carbon atom might
be too sterically crowded for 1 to approach. Reaction with DHA
Previously, Oestreich et al. reported the reaction of 1,4-
cyclohexadienyl-substituted hydridosilane in the presence of a
catalytic amount of B(C6F5)3 to afford SiH4 and benzene.[17] In this
reaction, the borane abstracts the hydride at the 4-position in the
cyclohexa-1,4-dienyl moiety and generates the benzene-
coordinated silylium ion as an intermediate. Subsequently, the
silylium ion is converted into hydridosilane by abstracting the
hydride of -HB(C6F5)3. As 1 has a vacant 3p orbital that can work
as a Lewis acid, 1 might as well behave the same manner as
B(C6F5)3 towards 3. However, the reaction of 3 in the presence of
1 for 16 h (150 °C, [D6]benzene, sealed tube) did not yield
anthracene or 2, indicating that 3 is not an intermediate in 1,4-
dehydrogenation of DHA.
with
a carbonyl moiety (4h) afforded the corresponding
anthracene 5h and 2 in relatively low yields (21% and 21%)
probably due to the numerous reaction sites such as ester groups
available in 4h.[16]
Me
3Si
Me
3Si
(0.5 eq)
Si
N
5e
+
1
2
°
Ad
D
C6
C
6,150
(sealed tube),
20 h
Consequently, 1,4-dehydrogenation was assumed to proceed
via direct dehydrogenation of DHA by CAASi 1. Initially, whether
hydrogens other than the benzyl site are abstracted was clarified.
Reaction with 9,9,10,10-tetradeuterated-9,10-dihydroanthracene
(DHA-d4) and 1 yielded anthracene-d2 (19%), 2-d2 (23%), and 3-
d4 (56%) as the major products with only trace sign of 2 and 2-d1,
as well as no sign of anthracene or anthracene-d1 judging from
high-resolution mass and NMR spectroscopy (Figures S21-S22,
S42-S44).[18] Therefore, 1,4-dehydrogenation should proceed
simply via abstraction of benzyl hydrogens (Scheme 4). Then,
crossover experiment was conducted to identify whether
dehydrogenation proceeds via concerted or stepwise pathway.
Reaction of 1 with an almost equimolar amount of DHA (0.49 eq)
and DHA-d4 (0.53 eq) afforded a mixture of anthracene (5%),
anthracene-d1 (trace), anthracene-d2 (11%), dihydridosilanes 2
(12%), 2-d1 (6%), 2-d2 (4%), 3 (18%), 3-d1, 3-d2 3-d3, and 3-d4 (3-
d1-4 : 36% in total),[18] which were identified as follows. Anthracene
and anthracene-d2, which were also obtained by the reaction of 1
with 1.0 eq of DHA[7] or DHA-d4 (Figures S21-S22), were identified
by 1H NMR spectroscopy (Figure S29). In addition to the 1H NMR
signals due to anthracene and anthracene-d2, a quartet-like
multiplet signal at around δ = 7.84-7.87 ppm (coupling constant =
3.2 Hz, 4H) which is assignable to the protons at the 1,4,5,8-
position and a singlet signal at 8.21 ppm (1H) which is assignable
to the proton at the 9-position, were observed (Figure S29)
suggesting the formation of anthracene-d1. Dihydridosilane 2 and
its deuterated counterparts were identified by multinuclear NMR
spectroscopy (Figures S29-S30) and high-resolution mass
spectrometry (Figures S45-S50) as well as comparison of 1H
NMR spectrum with those observed during the reaction of 1 with
1.0 eq of DHA[7] or DHA-d4 (Figures S21-S22) and with those of
authentic sample of 2-d1 prepared alternatively (Figures S23,
S28). Moreover, the formation of C–H inserted products 3-d1-4
was suggested by 1H NMR integrals of the benzyl protons (Figure
S29) and high-resolution mass spectroscopy (Figures S45-S50).
Formation of silanes 3-d1-3 implies that hydrogen and deuterium
atoms at the benzyl positions are scrambling in the course of
reaction. Thus, the C–H inserted products are more likely to be
formed by a recombination of the hydridosilyl radical and 9,10-
dihydro-9-anthryl radical intermediates after H–D scrambling
rather than by a concerted pathway. This is in good agreement
with the formation of the H–D scrambled monodeuteriosilane 2-
d1. Overall results indicate that dehydrogenation of DHA by 1
(23%)
6
(33%)
Scheme 2. Reaction of CAASi 1 with 9,10-dimethylanthracene (5e) (Ad = 1-
adamantyl). The yields were determined by 1H NMR spectroscopy.
To clarify the generality of the dehydrogenation reaction,
reactions of 1,2-dihydroaromatic compounds with
conducted. Although we carried out the reaction of 1,2-
dihydronaphthalene (7) and tetralin (8) under the same conditions
as 4d (150 °C, [D6]benzene, sealed tube), no reaction proceeded.
1 were
7
8
Chart 2. Substrates for attempted dehydrogenation with 1.
Despite the success of dehydrogenation for 1,4-
dihydroaromatic hydrocarbons with CAASi 1, the reaction with
9,10-dihydroacridine, a heterocyclic hydroaromatic compound
provided N–H insertion product 9 as the sole product in 91% yield
rather than the corresponding aromatic compound, acridine
(Scheme 3). Product 9 was characterized by multinuclear NMR
spectroscopy and X-ray crystallographic analysis. Silylenes are
known to insert into N–H bonds in ambient temperatures[1,5] and
1 likely to have followed the precedented reactivity of silylenes in
prior to dehydrogenation.
H
R
2Si
R
N
2Si
(1.0 eq)
°
D
C6
C
6, 150
N
H
(sealed tube), 1h
9
(91%)
Scheme 3. Reaction of 9,10-dihydroacridine with CAASi 1. The yield of 9 was
determined by 1H NMR spectroscopy.
Mechanism for the 1,4-dehydrogenation of 1 was investigated.
Initially, we assumed that a C–H inserted product such as 3 is the
intermediate of the reaction, because formation of
concomitant to 1,4-dehydrogenation in the reaction with DHA.[7]
3 is
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mainly proceeds via a stepwise pathway and more likely through
a radical intermediate.
We further examined the reaction routes theoretically using
density functional theory (DFT) calculations on the (U)B3PW91-
D3/6-31+G(d) level of theory for the reactions with CHD or DHA
(Scheme 5) to discuss thoroughly with the experimental results.
The results of the calculations were consistent with the
experimental investigations. The reaction of 1 and cyclohexa-1,4-
diene [V(CHD)] to form dihydridosilane 2 and benzene [Z(CHD)]
is predicted to be considerably exergonic (ΔG (298.15 K) =
−150.9 kJ/mol) at 298.15 K. The hydrogen abstraction of CAASi
1 from V(CHD) to form the corresponding silyl radical INT1 and
cyclohexadienyl radical [W(CHD)] is calculated to be moderately
endergonic (ΔG = 96.0 kJ/mol). Conversely, the ionic pathway
could be ruled out as the formation of the corresponding silyl
cation INT2 and cyclohexadienyl anion [X(CHD)] after the proton
abstraction was found to be largely endergonic (ΔG = +398.1
kJ/mol), as well as the formation of silyl anion INT3 and
cyclohexadienyl cation [Y(CHD)] which is much more endergonic
D
D
D
D
D
D
R
2Si
(1.0 eq)
+
+
R2SiD2
D
°
D
C6D6
C
,
150
D
(sealed tube), 16 h
D
(23%)
2-d2
3-d4
(56%)
(19%)
R2Si
H
H
H
H
D
D
+
E1
D
D
(0.49 eq)
(0.53 eq)
R2SiE1E2
+
°
C6D6
C
,
150
E2
(sealed tube), 16 h
E
(ΔG
=
+459.6 kJ/mol).[19] The reaction of
and anthracene
1 with 9,10-
1=E2
1=E2
=H: 12%
2
E
=H: 5%
E1=H, E2=D: trace
1=E2
1 E1=H, E2=D: 6%
1=E2
2-d
2-d
dihydroanthracene [V(DHA)] providing
2
E
=D: 11%
2 E
=D: 4%
[Z(DHA)] is also predicted to be moderately exergonic (ΔG = -55.5
kJ/mol) and similar radical pathway through the formation of INT1
and 10-hydro-9-anthryl radical [W(DHA)] was calculated to be
more favorable compared to the corresponding ionic pathways
(Scheme 5). It should be noted that formation of the C–H insertion
product U(DHA) (= 3) (ΔG = -73.1 kJ/mol) is slightly more
exergonic compared to formation of 2 and anthracene [Z(DHA)]
(ΔG = −55.5 kJ/mol),[20] while formation of 2 and benzene
[Z(CHD)] (ΔG = -150.9 kJ/mol) is substantially more exergonic
compared to the formation of C–H insertion product U(CHD) (ΔG
= −79.4 kJ/mol). The larger exergonicity for the formation of 2 and
benzene [Z(CHD)] should be due to the formation of the aromatic
ring and may be responsible for the selective formation of 2 and
benzene.
E1
R
2Si
E2
+
E3
E4
E
1=E2=E3=E4
=H: 18%
3
3-d1
3-d2
3-d3
3-d4
36% in total
Scheme 4. Reactions of 1 with deuterated DHA (E = H or D). The yields were
determined by 1H NMR spectroscopy.
Entrapment of intermediates was attempted to identify whether
the reaction proceeds via radical or ionic intermediate. However,
we were not able to obtain distinct evidence of the intermediate
by using radical scavengers due to the high reactivity of 1 itself.
For example, reaction of 1 with TEMPO gave a complex mixture
and reaction with di-tert-butyl peroxide and phenol gave O–O
inserted product 10 and O–H inserted product 11, respectively
(Chart 3). Furthermore, we have measured EPR spectrum during
the reaction of 1 with DHA in heptadecane at 150 °C, however,
no significant EPR signals were observed. This implies that no
paramagnetic species with a long lifespan exists in situ. These
experimental results alone could not confirm whether the
stepwise 1,4-dehydrogenation proceeds via ionic or radical
pathway.
H
H
C
N
+
SiH
Me
3Si SiMe3
C
N
INT1
96.0 kJ/mol (CHD)
W
=
N
109.8 kJ/mol (DHA)
Ad
H
H
C
N
C
C
N
+
+
+
SiH
SiH2
Si
N
2
Z
1
V
INT2
X
0.0 kJ/mol (CHD)
0.0 kJ/mol (DHA)
-150.9 kJ/mol (CHD)
-55.5 kJ/mol (DHA)
398.1 kJ/mol (CHD)
352.8 kJ/mol (DHA)
H
H
C
N
+
Me
Me
3Si SiMe3
OtBu
3Si SiMe3
OPh
SiH
C
N
H
Si
Si
Si
= CHD or DHA
INT3
Y
H
OtBu
N
N
U
459.6 kJ/mol (CHD)
448.5 kJ/mol (DHA)
Ad
Ad
-79.4 kJ/mol (CHD)
-73.1 kJ/mol (DHA)
10
11
Scheme 5. Free energy change (298.15 K) during hydrogen abstraction from
CHD or DHA by 1 calculated at the (U)B3PW91-D3/6-31+G(d) level of theory
(Solvent = heptane).
Chart 3. Products for the reaction of 1 with radical scavengers (Ad = 1-
adamantyl).
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(alkyl)(amino)silylene (CAASi), 1],[7] 1-heptadecylcyclohexa-1,4-diene,[23]
Although the competition of a concerted hydrogen abstraction
or more complicated route could not be ruled out,[21] the
experimental and calculation results are consistent with the notion
that 1,4-dehydrogenation is likely to proceed via a stepwise
hydrogen abstraction rather than a proton/hydride abstraction.
1-(tert-butyl)-4-methoxycyclohexa-1,4-diene,[23]
2,3,4,7-tetrahydro-1H-
indene,[23] 9,10-dimethyl-9,10-dihydroanthracene,[24] 9-ethyl-10-methyl-
9,10-dihydroanthracene,[24]
9-isopropyl-10-methyl-9,10-
dihydroanthracene,[24] and 1,4-dibutyl-2,3-bis(methoxycarbonyl)-9,10-
dihydroanthracene[25] were prepared according to the published
procedures. H2 gas was prepared by a YMC hydrogen generator YH-500
and preserved in a YMC MH canister YMH-60LP prior to use.
Conclusion
General Procedure for Dehydrogenation of CHD and DHA Derivatives
with 1.
In conclusion, the scope and limitation of 1,4-
dehydrogenation of CHD and DHA derivatives were explored and
the observed vast generality of the reaction proved that CAASi 1
possesses the potential of regioselective hydrogen abstraction in
the (double) allyl or benzyl site to form the corresponding aromatic
hydrocarbons. Unexpected simultaneous activation of benzyl C–
H bond and aromatic C–H bond was observed for the reaction
with 9,10-dimethylanthracene to yield silaacenaphthene 6.
Moreover, careful investigation of the mechanism is consistent
with the notion that dehydrogenation with 1 proceeds mainly via a
stepwise hydrogen abstraction. However, the competition of a
concerted hydrogen abstraction is not ruled out. The
investigations in this study should pave new avenue for CAASis
as a synthetic tool for aromatic compounds. Investigation of
reaction conditions for activating more inert C–H bonds are further
explored and should be reported in the near future.
All dehydrogenation reactions were carried out in a flame-sealed tube
unless otherwise noted. In a sealed tube, a mixture of 1 and CHD or DHA
derivative (1.0 eq) in [D6]benzene (0.45 mL) was placed. Heating the
sealed tube at 150 ºC gave the corresponding aromatic compound and
dihydridosilane 2. The yields of the products were determined using
ferrocene or 1,3,5-tri-tert-butylbenzene as an internal standard. Formation
of the aromatic compound and 2 was confirmed by the comparison of the
NMR spectra with those of the authentic samples. For details of the
reaction with each substrate, see Supporting Information.
Reaction of 1 with 9,10-dimethylanthracene (5e)
In a sealed tube, a mixture of 1 (23 mg, 0.063 mmol) and 9,10-
dimethylanthracene (6.7 mg, 0.0324 mmol) in [D6]benzene (0.45 mL) was
placed. Heating the mixture at 150 ºC for 20 h gave dihydridosilane 2 and
silaacenaphthene 6 in 33% and 23% yields, respectively. Yields were
determined by 1H NMR spectrum using ferrocene as an internal standard.
Formation of 2 and 6 were confirmed by the comparison of the NMR
spectra with those of the authentic samples. Isolation of 6: In a sealed tube,
a mixture of 1 (99 mg, 0.27 mmol) and 9,10-dimethylanthracene (29 mg,
0.14 mmol) in heptane (1.0 mL) was placed. The mixture was heated at
150 ºC for 18 hours. After the mixture was cooled to room temperature,
the mixture was concentrated and dissolved in toluene (2.0 mL). After
separation with HPLC (eluent: toluene), the resulting yellow oil was
recrystallized from hexane at –30 ºC to afford yellow crystals. Washing the
crystals with hexane (0.2 mL) three times afforded analytically pure 6 (7.6
mg, 0.013 mmol) in 5% yield. 6: yellow powder; m.p. 162°C
(decomposition); 1H NMR (500 MHz, [D6]benzene, 24 °C, TMS) δ = –0.16
(s, 9H, SiMe3), 0.42 (s, 9H, SiMe3), 1.23 (brs, 6H, Ad), 1.66 (brs, 3H, Ad),
Experimental Section
General Procedures
All reactions treating air-sensitive compounds were carried out under
argon or nitrogen atmosphere using a high-vacuum line, standard Schlenk
techniques, or a glovebox, as well as dry and oxygen-free solvents. The
1H, 13C{1H}, and 29Si{1H} NMR spectra were recorded on a Bruker Avance
III 500 FT NMR spectrometer. The 1H and 13C NMR chemical shifts were
referenced to residual 1H and 13C of the solvents; [D6]benzene (1H δ 7.16
and 13C δ 128.0).[22] The 29Si NMR chemical shifts were relative to Me4Si
in ppm. Sampling of air-sensitive compounds was carried out using a VAC
NEXUS 100027 type glovebox. Mass spectra were recorded on a JEOL
JMS-Q1050 spectrometer or a Bruker Daltonics SolariX 9.4T spectrometer.
X-ray analysis was carried out using a Bruker AXS APEXII CCD
diffractometer. Recycling preparative HPLC using dry toluene as an eluent
was performed at 5.0 mL/min rate using a Japan Analytical Industry Co.,
LC-9201 equipped with an JAIGEL-H column (Japan Analytical Industry
Co., φ 20 mm × 600 mm).
2
3
1.72-1.81 (m, 6H, Ad), 2.22-2.27 (dd, J(H,H) = 13 Hz, J(H,H) = 4.0 Hz,
1H, CHH), 2.44-2.48 (m, 1H, CHH), 2.73 (s, 3H, CH3), 2.99-3.04 (m, 1H,
CHH), 3.10 (d, 2J(H,H) = 28 Hz, 1H, CHH), 3.14 (d, 2J(H,H) = 28 Hz, 1H,
CHH), 3.22-3.26 (m, 1H, CHH), 7.36-7.41 (m, 2H, ArH), 7.49 (dd, 3J(H,H)
3
= 8.8 Hz, 3J(H,H) = 6.3Hz, 1H, ArH), 7.92 (d, J(H,H) = 6.2 Hz,1H, ArH),
3
3
8.11 (d, J(H,H) = 8.8 Hz, 1H, ArH), 8.15 (d, J(H,H) = 8.2 Hz, 1H, ArH),
8.41 (d, 3J(H,H) = 8.4 Hz, 1H, ArH); 13C{1H} NMR (125 MHz, [D6]benzene,
25 °C, TMS) δ = 1.2 (CH3), 2.9 (CH3), 9.0 (C), 13.6 (CH3), 19.1 (CH2), 30.1
(CH), 30.8 (CH2), 36.9 (CH2), 43.6 (CH2), 44.4 (CH2), 53.2 (C), 125.0 (CH),
125.3 (CH), 125.8 (CH), 126.0 (CH), 126.1 (CH), 126.5 (CH), 128.7 (C),
129.5 (C), 130.9 (C), 131.3 (C), 132.3 (CH), 135.8 (C), 140.1 (C), 144.1
(C); 29Si{1H} NMR (99 MHz, [D6]benzene, 24 °C, TMS) δ = 1.7 (SiMe3), 3.0
(SiMe3), 10.9 (alkyl)(amino)Si); HRMS (APCI): m/z: calcd for C35H49NSi3,
567.3167 [M+]; found, 567.3167; elemental analysis calcd (%) for
C35H49NSi3: C, 74.01; H, 8.70; N, 2.47%. found: C, 74.28; H, 8.77; N,
2.49%.
Materials
Dry and degassed benzene, hexane, and THF were prepared using a VAC
103991 solvent purifier. Acetone, acetonitrile, and [D6]benzene were
degassed and dried by molecular sieves MS 4A. Heptane was distilled
over lithium aluminium hydride and degassed prior to use. Boron
tribromide in hexane solution, 1,4-cyclohexadiene, 9,10-dihydroacridine,
Reaction of 1 with 9,10-Dihydroacridine
9,10-dihydroanthracene,
1,4-dihydronaphthalene,
9,10-
dimethylanthracene, di-tert-butyl peroxide, ethanol, ferrocene, 10% Pd/C,
phenol, sodium borodeuteride, and 1,3,5-tri-tert-butylbenzene were
commercially available and used without further purification. N-(1-
Adamantyl)-3,3-bis(trimethylsilyl)-1-aza-2-silacyclopentane-2,2-diyl [cyclic
In a sealed tube, a mixture of 1 (12 mg, 0.033 mmol) and 9,10-
dihydroacridine (6.0 mg, 0.033 mmol) in [D6]benzene (0.45 mL) was
placed. Heating the mixture at 150 ºC for 1 hour gave diaminosilane 9 in
This article is protected by copyright. All rights reserved.

10.1002/chem.201901407
Chemistry - A European Journal
FULL PAPER
91% yield as a sole product. Yield of 9 was determined by 1H NMR
spectrum using ferrocene as an internal standard. Formation of 9 was
confirmed by the comparison of the NMR spectra with that of the authentic
sample. Isolation of 9: In a sealed tube, a mixture of 1 (50 mg, 0.14 mmol)
and 9,10-dihydroacridine (25 mg, 0.14 mmol) in heptane (0.40 mL) was
placed. The mixture was heated at 150 ºC for 1 hour. After the volatile was
removed in vacuo, recrystallization from hexane/toluene (10/1) solution at
–30 ºC gave colorless crystals of 9 (45 mg, 0.083 mmol) in 60 % yield. 9:
colorless crystals; m.p. 164-166 °C; 1H NMR (500 MHz, [D6]benzene, 24
ºC, TMS) δ = 0.21 (s, 9H, SiMe3), 0.34 (s, 9H, SiMe3), 1.35 (d, 2J(H,H) =
51.7 (C); 29Si{1H} NMR (99 MHz, [D6] benzene, 23 °C, TMS) δ = –26.3 (t,
1J(Si,D) = 31.5 Hz, SiHD), 3.8 (SiMe3); HRMS (APCI): m/z: calcd for
C19H38DNSi3, 366.2448 [M+]; found, 366.2447; elemental analysis calcd
(%) for C19H38DNSi3: C, 62.22; H, 10.99; N, 3.82%. found: C, 61.84; H,
10.80; N, 3.72%.
Reaction of 1 with DHA-d4
In a sealed tube, a mixture of 1 (65 mg, 0.18 mmol) and DHA-d4 (33 mg,
0.18 mmol) in [D6]benzene (0.45 mL) was placed. The mixture was heated
at 150 ºC for 16 hours. Anthracene-d2, dihydridosilane 2-d2, and
benzylsilane 3-d4 were obtained in 19%, 23%, and 56% yields respectively
(Figure S21). Yields were determined by 1H NMR spectrum using
ferrocene as an internal standard. Formation of 2-d2, anthracene-d2, and
3-d4 were confirmed by the comparison of the NMR spectra with those
observed in the reaction of 1 with DHA and HRMS (APCI) spectra of the
reaction mixture. HRMS (APCI): m/z: calcd for C19H37D2NSi3, 367.2510
[M+]; found, 367.2510. calcd for C33H45D4NSi3 548.3497 [M++H]; found,
548.3498. 2-d2: 29Si{1H} NMR (99 MHz, [D6]benzene, 25 ºC, TMS) δ = 3.8
(SiMe3), –26.5 (q, 1J(Si,D) = 30.7 Hz, SiD2). 3-d4: 29Si{1H} NMR (99 MHz,
2
2
12 Hz, 3H, Ad), 1.43 (d, J(H,H) = 12 Hz, 3H, Ad), 1.52 (d, J(H,H) = 12
2
Hz, 3H, Ad), 1.69 (d, J(H,H) = 12 Hz, 3H, Ad), 1.79 (brs, 3H, Ad), 2.12-
2.16 (m, 1H, CHH), 2.43-2.44 (m, 1H, CHH), 2.88-2.91 (m,1H, CHH), 3.10
(t, 3J (H,H) = 8.7 Hz, 1H, CHH), 3.64 (d, 2J(H,H) = 17 Hz, 1H, CHH), 3.86
(d, 2J(H,H) = 17 Hz, 1H, CHH), 5.58 (s with satellites (29Si), 1J(H,Si) = 232
Hz, 1H, SiH), 6.92-6.96 (m, 2H, ArH), 7.02-7.05 (m, 2H, ArH), 7.09-7.12
(m, 1H, ArH), 7.13-7.16 (m, 1H, ArH), 7.19-7.21 (m, 1H, ArH), 7.23-7.25
(m, 1H, ArH); 13C{1H} NMR (126 MHz, [D6]benzene, 24 ºC, TMS) δ = 1.7
(CH3), 2.1 (CH3), 7.7 (C), 29.5 (CH2), 30.2 (CH), 33.8 (CH2), 37.0 (CH2),
42.3 (CH2), 42.6 (CH2), 52.9 (C), 120.4 (CH), 122.3 (CH), 122.5 (CH),
122.9 (CH), 125.6 (CH), 126.3 (CH), 128.3 (CH), 128.4 (CH), 128.6 (C),
128.7 (C), 143.1 (C), 144.1 (C); 29Si{1H} NMR (99 MHz, [D6]benzene, 24
ºC, TMS) δ = –13.6 ((alkyl)(amino)Si), 2.4 (SiMe3), 4.5 (SiMe3); MS (EI, 70
eV): m/z (%): 544 (100) [M+], 529 (18) [M+–Me]; elemental analysis calcd
(%) for C32H48N2Si3: C, 70.52; H, 8.88; N, 5.14%. found: C, 70.63; H, 8.90;
N, 5.42%.
1
[D6]benzene, 25 ºC, TMS) δ = 4.3 (SiMe3), 2.2 (SiMe3), 1.8 (t, J(Si,D) =
32.7 Hz, (alkyl)(amino)DSi).
Crossover Experiment for the Reaction of Silylene 1 with DHA
In a sealed tube, a mixture of 1 (100 mg, 0.27 mmol), DHA (24 mg, 0.13
mmol), and DHA-d4 (28 mg, 0.15 mmol) in [D6]benzene (0.45 mL) was
placed. Heating the mixture at 150 ºC for 16 hours gave a mixture of
anthracene (5%), anthracene-d1 (trace), anthracene-d2 (11%),
dihydridosilanes 2 (12%), 2-d1 (6%), 2-d2 (4%), benzylsilanes 3 (18%), and
3-d1-4 (36% in total) (Figure S29). Formation of the products was confirmed
by the comparison with the NMR spectra of the reaction of 1 with DHA,
reaction of 1 with DHA-d4, pure 2-d1, and HRMS (APCI) spectroscopy of
the reaction mixture. HRMS (APCI): m/z: calcd for C19H39NSi3 (2),
365.2385 [M+]; found, 365.2385; calcd for C19H38DNSi3 (2-d1), 366.2448
[M+]; found, 366.2447; calcd for C19H37D2NSi3(2-d2), 367.2510 [M+]; found,
367.2510; calcd for C33H49NSi3 (3), 544.3246 [M++H]; found, 544.3251;
calcd for C33H48D1NSi3 (3-d1), 545.3308 [M++H]; found, 545.3310; calcd for
C33H47D2NSi3 (3-d2), 546.3371 [M++H]; found, 546.3373; calcd for
C33H46D3NSi3 (3-d3), 547.3434 [M++H]; found, 547.3435; calcd for
Preparation of DHA-d4
DHA-d4 was synthesized by an optimized procedure of the method
reported earlier.[26] 9,10-Dihydroanthracene (180 mg, 1.00 mmol) and 10%
Pd/C (10 wt% of 9,10-Dihydroanthracene) in D2O/THF=1:2 (1.5 mL) were
stirred at room temperature in a sealed Schlenk tube (10 mL) filled with H2
gas. After 4 days, the mixture was diluted with THF (4.0 mL) and filtered
using a disposable PTFE filter (pore size: 0.45 μm) to remove the catalyst.
After removing the volatile in vacuo, the procedure mentioned above was
repeated two more times. Resulting colorless crystals were recrystallized
from ethanol at –30 ºC followed by Kugel-rohr distillation (60-90 ºC, 2.0
Pa), to give colorless crystals in 61% yield (9,10-Dihydroanthracene-d4:
98% D content). The D content was calculated using the integral ratio of
1H NMR spectrum. Formation of DHA-d4 was confirmed by the comparison
of the NMR spectra with those reported in the literature.[27]
C
33H45D4NSi3 (3-d4), 548.3497 [M++H]; found, 548.3498.
Reaction of 1 with di-tert-butyl peroxide
Synthesis of Dihydridosilane 2-d1
In a Schlenk flask (50 mL), a mixture of 1 (49 mg, 0.14 mmol) and di-tert-
butyl peroxide (22 mg, 0.15 mmol), in benzene (0.3 mL) was placed and
stirred for 10 min. at room temperature. After the volatile was removed in
vacuo, the resulting white solid was recrystallized from hexane at –30 ºC
to give di-tert-butoxysilane 10 (47 mg, 0.092 mmol) as colorless crystals in
67% yield. 10: colorless crystals; m.p. 161 °C; 1H NMR (500 MHz,
[D6]benzene, 25 °C, TMS) δ = 0.37 (s, 18H, SiMe3), 1.46 (s, 18H, tBu),
1.60-1.68 (m, 6H, Ad), 2.00-2.08 (m, 9H + 2H, Ad + CH2), 2.84 (t, 3J(H,H)
= 6.5 Hz, 2H, CH2); 13C{1H} NMR (125 MHz, [D6]benzene, 25 °C, TMS) δ
= 3.3 (CH3), 6.8 (C), 27.4 (CH2), 30.5 (CH), 32.7 (CH3), 37.4 (CH2), 42.1
(CH2), 43.3 (CH2), 53.2 (C), 74.2 (C); 29Si{1H} NMR (99 MHz, [D6] benzene,
25 °C, TMS) δ = –50.5 ((alkyl)(amino)Si), 2.2 (SiMe3); MS (EI, 70 eV): m/z
(%): 509 (100) [M+], 452 (62) [M+–tBu]; elemental analysis calcd (%) for
C27H55NO2Si3: C, 63.59; H, 10.87; N, 2.75%. found: C, 63.72; H, 10.94; N,
2.99%.
In a Schlenk flask (50 mL), BBr3 (1.0 M hexane solution, 0.14 mL, 0.15
mmol) was added to a mixture of dihydridosilane 2 (160 mg, 0.43 mmol) in
hexane (10 mL). The resulting mixture was stirred for 24 h at room
temperature. After the volatile was removed in vacuo, the resulting oil was
recrystallized from hexane at –30 ºC for
2
weeks to give
bromohydridosilane as colorless crystals. Without further purification, the
obtained bromohydridosilane (23 mg, 0.052 mmol) was added into a
mixture of NaBD4 (D content >95%) (8.0 mg, 0.19 mmol) and CH3CN (0.40
ml) placed in a screw top vial equipped with a magnetic stir bar and stirred
for 17 h. After removing the volatile in vacuo, the crude mixture was diluted
with hexane (3.0 mL) and filtered to remove insoluble materials.
Recrystallization from acetone at –30 ºC gave 2-d1 (13 mg, 0.034 mmol)
in 8% yield. 2-d1: colorless crystals; m.p. 69-71 °C; 1H NMR (500 MHz,
[D6]benzene, 22 °C, TMS) δ = 0.20 (s, 18H, SiMe3), 1.51-1.59 (m, 6H, Ad),
3
1.79-1.84 (m, 6H, Ad), 1.95 (brs, 3H, Ad), 2.00 (t, J(H,H) = 6.5 Hz, 2H,
3
2
CH2), 2.83 (t, J(H,H) = 6.5 Hz, 2H, CH2), 4.94 (t, J(H,D) = 3.2 Hz, 1H,
SiHD); 2H NMR (76.7 MHz, [D6]benzene, 22 ºC) δ = 4.95 (d, 2J(D,H) =3.3
Hz 1D, SiHD); 13C{1H} NMR (125 MHz, [D6]benzene, 23 °C, TMS) δ = 0.8
(CH3), 2.9 (C), 29.5 (CH2), 30.3 (CH), 37.1 (CH2), 43.2 (CH2), 44.2 (CH2),
Reaction of 1 with phenol
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10.1002/chem.201901407
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FULL PAPER
In a Schlenk flask (50 mL), a mixture of 1 (52 mg, 0.14 mmol) and phenol
(14 mg, 0.14 mmol) in benzene (0.3 mL) was placed and stirred for 10 min.
at room temperature. After the volatile was removed in vacuo, the resulting
white solid was recrystallized from hexane at –30 ºC to give phenoxysilane
11 (39 mg, 0.086 mmol) in 60% yield. 11: a white powder; m.p. 72 °C; 1H
NMR (500 MHz, [D6]benzene, 25 °C, TMS) δ = 0.25 (s, 9H, SiMe3), 0.28
(s, 9H, SiMe3), 1.44-1.51 (m, 6H, Ad), 1.73-1.81 (m, 6H, Ad), 1.88 (brs, 3H,
Ad), 2.00-2.06 (m, 1H, CHH), 2.14-2.19 (m, 1H, CHH), 2.85-2.90 (m, 1H,
CHH), 3.04-3.09 (m, 1H, CHH), 5.57 (s with satellites (29Si), 1J(H,Si) = 236
Hz, 1H, SiH), 6.83 (tt, 3J(H,H) = 7.2 Hz, 4J(H,H) = 1.2 Hz, 1H, ArH), 7.06-
7.09 (m, 2H, ArH), 7.10-7.15 (m, 2H, ArH); 13C{1H} NMR (125 MHz,
[D6]benzene, 25 °C, TMS) δ = 1.2 (CH3), 1.7 (CH3), 6.9 (C), 28.6 (CH2),
30.2 (CH), 37.0 (CH2), 43.1 (CH2), 43.7 (CH2), 51.9 (C), 120.1 (CH), 121.9
(CH), 130.0 (CH), 155.7 (C); 29Si{1H} NMR (99 MHz, [D6] benzene, 25 °C,
TMS) δ = –14.5 ((alkyl)(amino)Si), 3.0 (SiMe3), 3.1 (SiMe3); MS (EI, 70
eV): m/z (%): 457 (100) [M+], 442 (17) [M+–Me]; elemental analysis calcd
(%) for C25H43NOSi3: C, 65.58; H, 9.47; N, 3.06%. found: C, 65.43; H, 9.43;
N, 3.03%.
The authors declare no conflict of interest.
Keywords: aromatic compound • C–H activation •
dehydrogenation • main-group element • silylene
[1]
For comprehensive reviews on silylenes, see: a) P. P. Gaspar, R. West,
The Chemistry of Organic Silicon Compounds, Vol. 2, (Eds.: Z.
Rappoport, Y. Apeloig,), Wiley, Chichester, 1998, 2463-2568; b) Y.
Mizuhata, T. Sasamori, N. Tokitoh, Chem. Rev. 2009, 109, 3479-3511;
c) M. Asay, C. Jones, M. Driess, Chem. Rev. 2011, 111, 354-396. For
seminal studies on reaction of silylenes with small molecules, see also:
d) B. Blom, M. Driess, Struct. Bonding 2014, 156, 85-123; e) B. Blom, D.
Gallego, M. Driess, Inorg. Chem. Front. 2014, 1, 134-148; f) S. Inoue,
Discovering the Future of Molecular Sciences (Ed.: B. Pignataro), Wiley-
VCH, Weinheim, 2014, 243-273.
[2]
For studies on disilene (R2Si=SiR2) synthesis from silylenes, see: a) S.
Ishida, T. Iwamoto, C. Kabuto, M. Kira, Nature 2003, 421, 725-727; b) T.
Kosai, S. Ishida, T. Iwamoto, J. Am. Chem. Soc. 2017, 139, 99-102; c)
T. Kosai, S. Ishida, T. Iwamoto, Dalton Trans. 2017, 46, 11271-11281;
d) T. Kosai, T. Iwamoto, J. Am. Chem. Soc. 2017, 139, 18146-18149; e)
T. Kosai, T. Iwamoto, Chem. Eur. J. 2018, 24, 7774-7780. For studies on
silanone (R2Si=O) synthesis from silylenes, see: f) Y. Xiong, S. Yao, M.
Driess, J. Am. Chem. Soc. 2009, 131, 7562-7563; g) Y. Xiong, S. Yao,
R. Müller ,M. Kaupp, M. Driess, Nat. Chem. 2010, 2, 577-580; h) D.
Wendel, D. Reiter, A. Porzelt, P. J. Altmann, S. Inoue, B. Rieger, J. Am.
Chem. Soc. 2017, 139, 17193-17198; i) D. C. H. Do, A. V. Protchenko,
M. Á. Fuentes, J. Hicks, E. L. Kolychev, P. Vasko, S. Aldridge, Angew.
Chem. Int. Ed. 2018, 57, 13907-13911; Angew. Chem. 2018, 130,
14103-14107. For studies on silaimine (R2Si=NR) synthesis from
silylenes, see: j) M. Denk, R. Hayashi, R. West, J. Am. Chem. Soc. 1994,
116, 10813-10814; k) S. Inoue, K. Leszczyńska, Angew. Chem. Int. Ed.
2012, 51, 8589-8593; Angew. Chem. 2012, 124, 8717-8721; l) P. Samuel,
R. Azhakar, R. Ghadwal, S. Sen, H. Roesky, M. Granitzka, J. Matussek,
R. Herbst-Irmer, D. Stalke, Inorg. Chem. 2012, 51, 11049-11054; m) H.
Cui, C. Cu, Dalton Trans. 2015, 44, 20326-20329. For studies on
silaketenimine (R2Si=C=NR) synthesis from a silylene, see: n) T. Abe, T.
Iwamoto, C. Kabuto, M. Kira, J. Am. Chem. Soc. 2006, 128, 4228-4229.
For studies on R2Si=X compounds (X = S, Se, Te) synthesis from
silylenes, see: o) H. Suzuki, N. Tokitoh, R. Okazaki, S. Nagase, M. Goto,
J. Am. Chem. Soc. 1998, 120, 11096-11105; p) N. Tokitoh, T. Sadahiro,
K. Hatano, T. Sasaki, N. Takeada, R. Okazaki, Chem. Lett. 2002, 31, 34-
35; q) T. Iwamoto, K. Sato, S. Ishida, C. Kabuto, M. Kira, J. Am. Chem.
Soc. 2006, 128, 16914-16920; r) S. Kostina, W. Leigh, J. Am. Chem. Soc.
2011, 133, 4377-4388.
X-ray Analysis
Single crystals suitable for X-ray diffraction study were obtained by
recrystallization in an inert atmosphere from toluene/hexane (1:10) for 9 at
−30 °C. The single crystals for data collection coated by Apiezon® grease
mounted on the glass fiber and then transferred to the cold nitrogen gas
stream of the diffractometer. X-ray diffraction data were collected on a
Bruker AXS APEX II CCD diffractometer with graphite monochromated
Mo-Kα radiation. An empirical absorption correction based on the multiple
measurement of equivalent reflections was applied using the program
SADABS[28] and the structures were solved by direct methods and refined
by full-matrix least squares against F2 using all data (SHELXL-2014).[29]
Molecular structure was analyzed by Yadokari-XG software.[30]
Crystal data of 9 (100 K) (CCCDC-1903066): C32H48N2Si3; Fw 545.01;
triclinic; space group P-1 (#2), a = 10.7123(3) Å, b = 18.7257(5) Å, c =
20.1677(5) Å, α = 63.2270(10)°, β = 87.3810(10)°, γ = 89.6140(10)°, V =
3607.65(17) Å3, Z = 4, R1 = 0.0369 (I > 2σ(I)), wR2 = 0.0987 (all data),
GOF = 1.018.
Computational Study
All theoretical calculations were performed using Gaussian 09[31] and
GRRM14[32] programs. Geometry optimization and frequency analysis for
all compounds shown in Scheme 5 were performed at the (U)B3PW91-
D3/6-31+G(d) level of theory. The concerted reaction routes calculated at
the B3PW91-D3/6-31G(d) level of theory were summarized in the
Supporting Information. The atomic coordinates for the optimized structure
were summarized in the Supporting Information. Imaginary frequencies
were not found in any of the optimized structures.
[3]
[4]
For some studies on silylene transfer reactions, see: a) T. G. Driver, A.
K. Franz, K. A. Woerpel, J. Am. Chem. Soc. 2002, 124, 6524-6525; b) J.
Ćiraković, T. G. Driver, K. A. Woerpel, J. Am. Chem. Soc. 2002, 124,
9370-9371; c) T. G. Driver, K. A. Woerpel, J. Am. Chem. Soc. 2003, 125,
10659-10663.
a) H. Suzuki, N. Tokitoh, R. Okazaki, J. Am. Chem. Soc. 1994, 116,
11572-11573; b) M. Kira, S. Ishida, T. Iwamoto, C. Kabuto, J. Am. Chem.
Soc. 2002, 124, 3830-3831.
Acknowledgements
[5]
[6]
A. Jana, C. Schulzke, H. W. Roesky, J. Am. Chem. Soc. 2009, 131, 4600-
4601.
This work was supported by MEXT KAKENHI grant JP24109004 (T.I.)
(Grant-in-Aid for Scientific Research on Innovative Areas “Stimuli-
responsive Chemical Species”) and the JSPS KAKENHI grant
JP15K13634 (T.I.). The authors thank Prof. Yujiro Hayashi (Tohoku
University) for helpful advices for the synthesis of the deuterated substrate
and Prof. Martin Oestreich (Technische Universität Berlin) for helpful
discussion on the reaction mechanism.
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Conflict of Interest
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[13] 9,10-Dimethyl-DHA 4e (9-methyl-MDHA, cis: trans= 95:5), 9-ethyl-
MDHA 4f (cis: trans= 5:1), 9-isopropyl-MDHA 4g (cis: trans= 1:2) were
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[14] For spectral data of 6, see Experimental Section and Supporting
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[15] A complex mixture was obtained, which prohibited identification of
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[19] The first transition states connected to INT1-INT3 could not be identified
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should be enough to postulate that the reaction proceeds through INT1
and W.
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Entry for the Table of Contents
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Me3Si SiMe3
Me3Si SiMe3
Taichi Koike, Tomoyuki Kosai, Takeaki
Iwamoto*
H
• Stepwise Hydrogen Abstraction
• Neutral Condition
• High Substrate Generality
Si
N
SiH2
N
+
+
H
Page No. – Page No.
CAASi
1,4-Dehydrogenation with a Two-
Coordinate Cyclic
(Alkyl)(amino)silylene
A two-coordinate cyclic (alky)(amino)silylene (CAASi) undergoes regioselective 1,4-
dehydrogenation for numerous 1,4-cyclohexadiene and 9,10-dihydroanthracene
derivatives. Experimental and computational studies indicated that the reaction
proceeds mainly via a stepwise hydrogen abstraction.
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