Selective Double Hydrosilylation of Nitriles Catalyzed by an Iron Complex Containing Indium Trihalide

Article abstract of DOI:10.1002/cctc.201600940

Selective double hydrosilylation was achieved by using tertiary and secondary silanes with an excess amount of an organonitrile (RC≡N; R=alkyl, aryl) in the presence of a catalytic amount of triirondodecacarbonyl [Fe₃(CO)₁₂] and indium trichloride (InCl₃). This reaction was also catalyzed by an iron complex containing indium trihalide [Fe(MeCN)₆][Fe(CO)₄(InX₃)₂], prepared by the reaction of Fe₃(CO)₁₂ with InX₃ (X=Cl, Br, I). This is a novel report of the combination of a transition-metal complex and an indium source in organic synthesis.

Full text of DOI:10.1002/cctc.201600940

DOI: 10.1002/cctc.201600940
Communications
Selective Double Hydrosilylation of Nitriles Catalyzed by
an Iron Complex Containing Indium Trihalide
Masaki Ito, Masumi Itazaki, and Hiroshi Nakazawa*[a]
Selective double hydrosilylation was achieved by using tertiary
and secondary silanes with an excess amount of an organo-
nitrile (RCꢀN; R=alkyl, aryl) in the presence of a catalytic
amount of triirondodecacarbonyl [Fe3(CO)12] and indium tri-
chloride (InCl3). This reaction was also catalyzed by an iron
selective hydrosilylation of conjugated nitriles.[8] Unfortunately,
the catalyst was moisture sensitive and expensive.
Most catalytic reactions for the hydrosilylation of nitriles re-
quire an excess amount of the hydrosilane to afford the disilyl-
amine selectively. Herein, we report a new catalytic system for
the selective double hydrosilylation of nitriles by using an iron-
based catalyst without an excess amount of the hydrosilane.
Acetonitrile (4.0 mmol), Me2PhSiH (0.80 mmol), Fe3(CO)12
(0.027 mmol), and InCl3 (0.080 mmol) were charged into
a sealed glass tube under a dry nitrogen atmosphere, and the
solution was heated at 808C for 24 h (Scheme 2). After removal
complex
containing
indium
trihalide
[Fe(MeCN)6]-
[Fe(CO)4(InX3)2], prepared by the reaction of Fe3(CO)12 with InX3
(X=Cl, Br, I). This is a novel report of the combination of a
transition-metal complex and an indium source in organic
synthesis.
The transformation of organonitriles into other organic com-
pounds catalyzed by a transition-metal complex has been re-
ported, including CÀCN bond cleavage[1] and the hydrosilyla-
tion of CꢀN bonds.[2] We previously reported the synthesis of
silyl cyanides through CÀCN bond activation of organonitriles
by an iron catalyst.[3]
Scheme 2. Double hydrosilylation of acetonitrile promoted by Fe3(CO)12 with
InCl3.
Among these reactions, the hydrosilylation of a CꢀN bond is
one of the most atom-efficient reactions, because the reaction
theoretically produces no byproducts. In the reaction of RCꢀN
with hydrosilanes R’3SiH, the expected products are silyl imines
(RHC=NSiR’3) and disilylamines [RH2C-N(SiR’3)2], which are
formed by single[4a–d] and double[4e–k] hydrosilylation, respec-
tively (Scheme 1). These N-silylated compounds are highly
of volatile materials under reduced pressure, the disilylamine
MeCH2-N(SiMe2Ph)2 was obtained in 78% yield by extraction
with n-hexane and drying in vacuo (Table 1, entry 1). Unexpect-
edly, double hydrosilylation had occurred selectively, even if an
excess amount of the nitrile over the hydrosilane was used.
The 1H NMR spectrum of the reaction mixture revealed that
the silyl imine was not formed. A deuterium-labeling experi-
ment by using CD3CN in place of CH3CN afforded CD3CH2-
N(SiMe2Ph)2 in 73% yield. To the best of our knowledge, there
Scheme 1. Hydrosilylation of nitriles.
Table 1. Catalytic double hydrosilylation of acetonitrile with Me2PhSiH.[a]
useful precursors of nitrogen-containing organic compounds[5]
and silicon-containing polymers.[6] Moreover, the hydrosilyla-
tion of a CꢀN bond is an effective method to reduce nitriles.[7]
Only a few examples of double hydrosilylation catalyzed by
a transition-metal complex have been reported.[4e–k] In addition,
the catalytic hydrosilylation of nitriles without a transition-
metal catalyst has been reported; in 2015, Chang’s group re-
ported that B(C6F5)3 exhibited catalytic activity for the chemo-
Entry
Catalyst (mol%)[b]
Yield[c] [%]
1
2
3
4
5
6
7
8[d]
9[e]
10
11
Fe3(CO)12 (3.3)+InCl3 (10)
Fe3(CO)12 (3.3)
InCl3 (10)
[Fe(MeCN)6][(CO)4Fe(InCl3)2] (5)
[Fe(MeCN)6][(CO)4Fe(InBr3)2] (5)
[Fe(MeCN)6][(CO)4Fe(InI3)2] (5)
[Fe(MeCN)6][(CO)4Fe(InCl3)2] (1)
[Fe(MeCN)6][(CO)4Fe(InCl3)2] (5)
[Fe(MeCN)6][(CO)4Fe(InCl3)2] (5)
[Fe(MeCN)6][PF6]2 (5)
78
0
0
85
56
21
trace
trace
0
0
35
[a] M. Ito, Dr. M. Itazaki, Prof. Dr. H. Nakazawa
Department of Chemistry, Graduate School of Science
Osaka City University
Sumiyoshi-ku, Osaka 558-8585 (Japan)
E-mail: nakazawa@sci.osaka-cu.ac.jp
[PPN]2[(CO)4Fe(InCl3)2] (5)
[a] Me2PhSiH/acetonitrile=0.8:4.0 mmol. [b] Based on [Me2PhSiH].
[c] Yield of isolated product. [d] In THF (0.5 mL). [e] At room temperature.
Supporting Information for this article can be found under:
http://dx.doi.org/10.1002/cctc.201600940.
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are no previous reports of an iron complex combined with an
indium source used in organic synthesis.[9]
part of the catalyst (Table 2, entry 2). The hydrosilylation was
strongly influenced by steric effects of the substituent on the
nitrile carbon atom; the yield decreased upon using iPrCN
(Table 2, entry 4), and no reaction was observed upon using
tBuCN (Table 2, entry 5). Yields from tolunitrile decreased in the
order p-tolunitrile>m-tolunitrile>o-tolunitrile, presumably be-
cause of the increasing steric hindrance around the nitrile
group (Table 2, entries 7–9). Benzonitrile and p-tolunitrile gave
the corresponding disilylamines in similar yields (Table 2, en-
tries 6 and 7). 4-PyCN (py=pyridyl) was also converted into
the corresponding disilylamine, although the yield was low
(Table 2, entry 10). Nitriles containing electron-withdrawing
substituents and NC(CH2)4CN did not undergo hydrosilylation
(Table 2, entries 11–13). Reactions were observed for the
double hydrosilylation of Me2FcSiH with p-TolCN and MePhSiH2
with MeCN, which gave the corresponding disilylamines in
yields of 43 and 76%, respectively (Table 2, entries 14 and 15).
All disilylamines obtained were characterized by 1H NMR,
13C{1H} NMR, 29Si{1H} NMR, GC–MS, and elemental analyses (see
the Supporting Information).
Upon using either Fe3(CO)12 or InCl3 separately for the
double hydrosilylation of acetonitrile with Me2PhSiH, no cata-
lytic activity was found (Table 1, entries 2 and 3). The
[Fe(MeCN)6][Fe(CO)4(InX3)2] complexes prepared from Fe3(CO)12
and InX3[10,11] did, however, exhibit catalytic activity (Table 1, en-
tries 4–6), and [Fe(MeCN)6][Fe(CO)4(InCl3)2] showed the highest
activity among them. If the amount of [Fe(MeCN)6][Fe(-
CO)4(InCl3)2] was reduced from 5 to 1 mol% or if THF was used
as the solvent, the yield was greatly diminished (Table 1, en-
tries 7 and 8). Further, the reaction did not proceed at room
temperature (Table 1, entry 9). Upon using [Fe(MeCN)6][PF6]2 as
the catalyst, hydrosilylation was not observed (Table 1,
entry 10), but the reaction proceeded if [PPN]2[Fe(CO)4(InCl3)2]
was used (Table 1, entry 11). It was, therefore, concluded that
the anionic part of [Fe(MeCN)6][(CO)4Fe(InCl3)2] acted as the
catalyst in the double hydrosilylation reaction. The different ac-
tivities of the iron–indium complexes in entries 4 and 11
(Table 1) may result from the different degrees of stabilization
by the cation.
To obtain insight into the mechanism of the [Fe(MeCN)6][Fe-
(CO)4(InCl3)2] system, we examined two reactions. First, we per-
formed the reaction by using InCl3 as an additive in excess
amount [Eq. (1)] and found that no hydrosilylation occurred.
We, therefore, concluded that the dissociation of InCl3 was
important in our system.
To explore the scope of the double hydrosilylation reactions
catalyzed by [Fe(MeCN)6][Fe(CO)4(InCl3)2], several combinations
of nitriles and hydrosilanes were examined (Table 2). Reactions
were observed for the double hydrosilylation of Me2PhSiH with
RCꢀN, for which R=Me, Et, iBu, iPr, Ph, p-Tol, m-Tol, or
o-Tol (Table 2, entries 1–4, 6–9). In the case of propane nitrile
(EtCN), the main product was EtCH2N(SiMe2Ph)2, with
MeCH2N(SiMe2Ph)2 as a byproduct (2% yield, as determined by
NMR spectroscopy). The byproduct is believed to have formed
from MeCN, owing to EtCN/MeCN exchange on the cationic
We suspected that InCl3 eliminated from the catalyst precur-
sor reacted with hydrosilane to give indium hydride HInCl2, as
reported by Baba and co-workers.[12] Moreover, they reported
that HInX2 acted as a radical.[13] We examined our reaction
system in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO) as a radical scavenger and found that the formation
of the disilylamine was suppressed [Eq. (2)]. We, therefore, con-
cluded that HInCl2 was involved in the reaction pathway.
Table 2. Double hydrosilylation of various nitriles with hydrosilanes
catalyzed by an iron–indium complex.[a]
Entry RCꢀN
R’3SiH
RCH2N(SiR’3)2
Yield[b] [%]
1
2
3
4
MeCN
EtCN
iBuCN
iPrCN
Me2PhSiH MeCH2N(SiMe2Ph)2 (1)
Me2PhSiH EtCH2N(SiMe2Ph)2(2)
Me2PhSiH iBuCH2N(SiMe2Ph)2(3)
Me2PhSiH iPrCH2N(SiMe2Ph)2(4)
85
65[c]
75
66
–
5
tBuCN
Me2PhSiH
–
6
7
8
9
10
11
12
13
14
15
PhCN
Me2PhSiH PhCH2N(SiMe2Ph)2 (5)
Me2PhSiH (p-Tol)CH2N(SiMe2Ph)2(6)
Me2PhSiH (m-Tol)CH2N(SiMe2Ph)2(7) 49
Me2PhSiH (o-Tol)CH2N(SiMe2Ph)2(8)
Me2PhSiH (4-Py)CH2N(SiMe2Ph)2(9)
54
55
(p-Tol)CN
(m-Tol)CN
(o-Tol)CN
(4-Py)CN
CCl3CN
(C6F5)CN
NC(CH2)4CN Me2PhSiH
(p-Tol)CN
MeCN
41
21
–
–
–
On the basis of the observations mentioned above, we ten-
tatively propose a catalytic cycle, as depicted in Scheme 3.
First, one indium ligand in [Fe(CO)4(InCl3)2]2À dissociates and
monoindium–iron species A is generated. Then, the released
indium trichloride reacts with hydrosilane to give indium hy-
dride and chlorosilane. One of the CO ligands in A is replaced
by the nitrile used to give B. Then, B reacts with indium hy-
dride to form indyl imine complex C. Intermediate C reacts
with hydrosilane to give silyl imine iron complex D, which
reacts further to give indylsilylamine complex E. Finally, E
Me2PhSiH
Me2PhSiH
–
–
–
Me2FcSiH (p-Tol)CH2N(SiMe2Fc)2(10) 43
MePhSiH2 MeCH2N(SiMePhH)2(11) 76
[a] See the Supporting Information for details of the reaction conditions.
[b] Yield of isolated product. [c] The relatively low reaction yield of
EtCH2N(SiMe2Ph)2 was caused by difficulties associated with removing the
MeCH2N(SiMe2Ph)2 byproduct produced in this reaction by distillation
because of similar boiling points.
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Keywords: hydrosilylation · indium · iron · nitriles · silanes
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Scheme 3. Proposed catalytic cycle for the formation of a disilylamine in the
reaction of nitriles with hydrosilanes promoted by [Fe(MeCN)6][Fe(CO)4-
(InCl3)2].
reacts with hydrosilane and then the nitrile used to produce
disilylamine and HInCl2 with regeneration of B. We think that
the silyl imine in D does not dissociate readily from the iron
center and/or that D is extremely reactive toward HInCl2;
therefore, selective disilylamine formation is eventually
achieved.
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double hydrosilylation of organonitriles promoted by a combi-
nation of triirondodecacarbonyl [Fe3(CO)12] with indium tri-
chloride (InCl3). The iron–indium [Fe(MeCN)6][Fe(CO)4(InX3)2]
complex also showed catalytic activity. In our reaction system,
only the double hydrosilylation product was obtained and no
single hydrosilylation product was produced. Our catalytic
system was applicable to various nitriles and hydrosilanes.
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Experimental Section
General procedure for synthesis of disilylamine derivatives
The nitrile (4.0 mmol) was treated with a tertiary (or secondary)
silane (0.80 mmol) in the presence of [Fe(CH3CN)6][(CO)4Fe(InCl3)2]
(36.5 mg, 0.040 mmol) at 808C under a nitrogen atmosphere for
24 h. After all volatile materials were removed under reduced pres-
sure, the residue was extracted with n-hexane (3ꢁ2 mL), and the
filtrate was dried in vacuo to give the corresponding disilylamine.
The purified product (see Table 2) was obtained by distillation by
using a Kugelrohr.
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Acknowledgements
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um indane complexes, fac-[Ru(NCMe)3(CO)2(InX3)] (X=Cl, Br). M. Itazaki,
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This work was supported by a Challenging Exploratory Research
Grant (No. 15K13662), a Grant-in-Aid for Science Research Japan
(C) (No. 16K05728 and 25410073), a Grant-in-Aid for Scientific Re-
search on Innovative Area “Stimuli-responsive Chemical Species
for the Creation of Function Molecules (No. 2408)”(JSPSKAKENHI
Grant Number JP15H00957) from the Ministry of Education, Cul-
ture, Sports, Science and Technology (MEXT), Japan, and the Sa-
sakawa Scientific Research Grant from The Japan Science Society.
Received: August 1, 2016
Published online on && &&, 0000
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M. Ito, M. Itazaki, H. Nakazawa*
My cup of tea! Selective double hydro-
silylation is achieved by using tertiary
and secondary silanes with an excess
amount of an organonitrile (RCꢀN;
R=alkyl, aryl) in the presence of a cata-
lytic amount of triirondodecacarbonyl
[Fe3(CO)12] and indium trichloride (InCl3).
This reaction is also catalyzed by an iron
complex containing indium trihalide
[Fe(MeCN)6][Fe(CO)4(InX3)2], prepared by
the reaction of Fe3(CO)12 with InX3
(X=Cl, Br, I).
&& – &&
Selective Double Hydrosilylation of
Nitriles Catalyzed by an Iron Complex
Containing Indium Trihalide
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