Pd(0)-catalyzed carbene insertion into Si-Si and Sn-Sn bonds

Article abstract of DOI:10.1021/jacs.5b09135

The first Pd(0)-catalyzed carbene insertion into Si-Si and Sn-Sn bonds has been realized by using N-tosylhydrazones as the carbene precursors. Geminal bis(silane) and geminal bis(stannane) derivatives were obtained in good to excellent yields under mild conditions. Migratory insertion of Pd carbene is supposed to be the key step for the reaction.

Full text of DOI:10.1021/jacs.5b09135

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Communication
Pd(0)-Catalyzed Carbene Insertion into Si-Si and Sn-Sn Bonds
Zhenxing Liu, Haochen Tan, Tianren Fu, Ying Xia, Di Qiu, Yan Zhang, and Jianbo Wang
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b09135 • Publication Date (Web): 24 Sep 2015
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Zhenxing Liu, Haochen Tan,† Tianren Fu,† Ying Xia, Di Qiu, Yan Zhang, Jianbo Wang*
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Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular
Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China
Supporting Information Placeholder
Scheme 1. Catalytic Carbene Insertion into  bonds
ABSTRACT: The first Pd(0)-catalyzed carbene inser-
tion into Si-Si and Sn-Sn bonds have been realized by
using N-tosylhydrazones as the carbene precursors.
Geminal bis(silane) and geminal bis(stannane) deriva-
tives were obtained in good to excellent yields under
mild conditions. Migratory insertion of Pd carbene is
supposed to be the key step for the reaction.
Catalytic carbene insertions into bonds are attractive
transformations for their versatility and high efficiency.1
Up to date, X-H (X = C, N, O, etc.) insertions are the
most popular and have become one of the carbene’s
symbolic reactions. Typically, transition-metal catalysts
such as rhodium and copper complexes are used to en-
sure reactivity and selectivity.2 Mechanistically, the in-
sertion reactions are initiated by the formation of metal
carbene species, then followed by two possible pathways.
For non-polar bonds (C-H, Si-H bonds), the reaction
to alkynes and alkenes, mostly with nickel, palladium
goes through concerted mechanism; while for the polar
and platinum as the catalysts.5 A recent example is by
bonds (O-H, N-H bond), the reaction proceeds through
Spencer, Navarro and co-workers who have synthesized
ylide formation and subsequent 1,2-proton migration
a novel NHC-bearing palladium complex, which could
(Scheme 1a).3 This type of carbene insertion reactions
efficiently catalyze Si-Si bonds addition to internal al-
have been extensively studied and have found wide ap-
kynes using unactivated Me3SiSiMe3.6 The last step has
plications in organic synthesis. However, examples of
carbene insertion into other type of σ bonds are limited.
Recently, we have proposed a formal C-H insertion pro-
cess which follows stepwise mechanism: C-H bond meta-
lation, carbene formation, migratory insertion and the
protonation (Scheme 1b). We have conceived that such a
process that involves metal carbene migratory insertion
may be applied to other types of σ bonds. In this context
we have recently achieved a Rh(I)-catalyzed formal C-C
bond insertion.4 Herein we report the Pd(0)-catalyzed
carbene insertion into Si-Si and Sn-Sn bonds based on
the same mechanistic paradigm.
Scheme 2. Hypothetical Catalytic Cycle for Si-Si
Bond Insertion
The hypothetical carbene insertion into Si-Si bond is
shown in Scheme 2. The reaction starts with oxidative
addition of Si-Si bond to transition-metal catalyst [M],
followed by metal carbene formation, silyl migratory
insertion, and finally reductive elimination of C-Si bond
to afford the insertion product. Amongst the four steps of
this catalytic cycle, the first and last steps have been
known in transition-metal catalyzed Si-Si bond additions
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also been reported in transition-metal catalyzed hydrosi-
species.10,11 Screening of the catalysts with nickel, palla-
dium and platinum revealed that only
lylation of alkenes.7 Metal carbene formation and the
subsequent migratory insertion have been supposed as
the key steps in many transition-metal catalyzed cross-
coupling reactions. The migratory inserted moieties have
been demonstrated to include aryl, alkenyl, alkynyl, ben-
zyl, etc.8 However, the metal carbene formation by a
metal-silyl complex (B to C) and the subsequent silyl
migratory insertion (C to D) are unprecedented in cata-
lytic reactions.9
Pd(dba)2/P(OCH2)3CEt system could afford the expected
product in 10% NMR yield (entries 1-4).12 The failure of
other catalysts might be attributed to the difficulty in the
metal carbene forming step (entries 1-3),13 while in the
case of entry 4 the low efficiency might be due to the in-
ert nature of the Si-Si bonds. To tune the reactivity of Si-
Si bond, we have switched Me3SiSiMe3 to
PhMe2SiSiMe2Ph and FMe2SiSiMe2F (entries 5-6). This
could indeed improve the yields of insertion products
(entries 5, 6). It was observed that the concentration sig-
nificantly affected the reaction (entries 7-9). The reaction
worked better under lower concentration, in which there
were fewer side products due to the reactions of carbene
species (entries 8-9). With concentration of 0.025 M and
slightly increased catalyst loading the yield of product
was improved to 90% (1H NMR). The product was isolat-
ed by bulb-to-bulb distillation in 81% yield (entry 10).
Finally, control experiments indicated that with
Rh2(OAc)4 as the catalyst or in the absence of catalyst the
reaction did not give the product 3c (entries 11 and 12).
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With the hypothesis in mind, we started to examine
the reaction with N-tosylhydrazone derived from 4-
biphenylcarboxaldehyde and Me3SiSiMe3 as the sub-
strates (Table 1). N-Tosylhydrazones have been recently
widely used as the precursors for the in-situ generation
of non-stabilized diazo compounds in transition-metal
catalyzed cross-coupling reactions involving carbene
Table 1. Optimization of Transition-Metal-Catalyzed
Carbene Si-Si Insertiona
Next, we proceeded to explore the scope of the reac-
tion under the optimized reaction conditions. As shown
in Scheme 3, a series of N-tosylhydrazones could be em-
ployed as substrates in the reaction, affording the corre-
sponding geminal bis(silane) derivatives 5a-ab efficient-
ly. For mono-substituted aromatic aldehyde derived N-
tosylhydrazones, the substrates bearing substituents in
para-, meta-, and ortho-position with different electron-
ic properties all proceeded well in the reaction (5a-e, j-
g). Notably, Bpin could be tolerated under current condi-
tions (5f). The reactions with the N-tosylhydrazones
bearing two substituents on the aromatic rings also pro-
ceeded well to give the corresponding products in excel-
lent yields (5k-m).
entry [M]( mol%)/ligand (mol%) 2, X conc. (M) 3, %b
1
NiCl2(PPh3)2 (2)
Pt(PPh3)4 (2)
2a, Me 0.1
2a, Me 0.1
2a, Me 0.1
3a, 0
3a, 0
3a, 0
2
3
Pd(OAc)2 (2)/
tOctNC (30)
4
Pd(dba)2 (2)/
P(OCH2)3CEt (4)
Pd(dba)2 (2)/
P(OCH2)3CEt (4)
Pd(dba)2 (2)/
P(OCH2)3CEt (4)
Pd(dba)2 (2)/
P(OCH2)3CEt (4)
Pd(dba)2 (2)/
P(OCH2)3CEt (4)
Pd(dba)2 (2)/
P(OCH2)3CEt (4)
Pd(dba)2 (2)/
P(OCH2)3CEt (8)
Rh2(OAc)4 (2)
none
2a, Me 0.1
2b, Ph 0.1
3a, 10
3b, 30
3c, 50
3c, 40
5
Likewise, the reaction with N-tosylhydrazones derived
from fused polycyclic or heterocyclic aromatic aldehydes
could afford the corresponding geminal bis(silane) prod-
ucts in moderate yields (5n-v). The reaction also worked
well with N-tosylhydrazones derived from unsaturated
aldehydes (5w-z). Finally, for N-tosylhydrazones derived
from aromatic ketones, the yields were slightly dimin-
ished, presumably due to steric effect (5aa-ab).
6
2c, F
2c, F
2c, F
2c, F
2c, F
0.1
0.2
7
8
9
0.05 3c, 69
0.03 3c, 75
Encouraged by the successful carbene Si-Si bond in-
sertion, we proceed to explore the same strategy for oth-
er similar type of bonds. Sn-Sn bonds have been ap-
plied in transition-metal catalyzed addition to unsaturat-
ed organic molecules as Si-Si bonds.14 Accordingly, we
conceived that carbene insertion into Sn-Sn bonds might
also be realized under similar conditions and this indeed
proved to be the case. As shown in Scheme 4, for a series
of N-tosylhydrazones the Pd(0)-catalyzed reaction with
hexamethyldistannane (Me3SnSnMe3, 2d) afforded the
corresponding geminal bis(stannane) derivatives 6a-w
in moderate to excellent yields. It is worth mentioning
that the N-tosylhydrazones derived from alkyl aldehydes
are also excellent substrates for the Sn-Sn bonds inser-
tion, while the corresponding Si-Si insertion reaction
10
0.025 3c, 90
(81)c
11
2c, F
2c, F
0.025 3c, 0
0.025 3c, 0
12
aThe reaction was carried out with N-tosylhydrazone 1 (0.10
mmol), XMe2SiSiMe2X 2 (0.20 mmol) and LiOtBu (0.30
mmol) in the presence of catalyst in toluene at 60 oC for 12 h.
1
bThe yields were determined by H NMR with mesitylene as
the internal standard. cThe yield in parentheses refers to
isolated yield. tOctNC: 1,1,3,3-tetramethylbutyl isocyanide.
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Scheme 3. Scope of Pd(0)-Catalyzed Carbene Inser-
failed to afford the desired products. The structure of 6s
was confirmed by X-ray crystallography.
tion into Si-Si Bondsa,b
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Scheme 4. Scope of Pd(0)-Catalyzed Carbene Inser-
tion into Sn-Sn Bondsa,b
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aThe reaction was carried out with N-tosylhydrazones 4
(0.10 mmol), Me3SnSnMe3 2d (0.15 mmol) and LiOtBu
(0.30 mmol) in the presence of Pd(dba)2 (4
o
mol%)/P(OCH2)3CEt (8 mol%) in 1.0 mL toluene at 80 C
b
c
for 12 h. All the yields refer to isolated product. The reac-
tion was carried out with bis-N-tosylhydrazones (0.10
mmol), Me3SnSnMe3 (0.30 mmol) and LiOtBu (0.60 mmol)
in the presence of Pd(dba)2 (8 mol%)/P(OCH2)3CEt (16
mol%) in 2.0 mL toluene at 80 oC for 12 h.
aThe reaction was carried out with N-tosylhydrazones 4
(0.10 mmol), FMe2SiSiMe2F 2c (0.20 mmol) and LiOtBu
(0.30 mmol) in the presence of Pd(dba)2 (4
o
mol%)/P(OCH2)3CEt (8 mol%) in 4.0 mL toluene at 60 C
b
c
for 12 h. All the yields refer to isolated yield. The yield re-
fers to a 0.5 mmol scale reaction.
To further assess the applicability of the Pd(0)-
catalyzed carbene Si-Si and Sn-Sn bond insertion, the
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L.; Morton, D. Chem. Soc. Rev. 2011, 40, 1857-1869. (c)
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the corresponding N-tosylhydrazone and then was sub-
jected to the Pd(0)-catalyzed reaction. The Si-Si inser-
tion and Sn-Sn insertion products were obtained in 73%
and 62% yields, respectively (eq. 1).
Doyle, M. P.; Ratnikov, M.; Liu, Y. Org. Biomol. Chem.
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(1)
In conclusion, we have developed the first Pd(0)-
catalyzed carbene insertion into Si-Si and Sn-Sn bonds.15
The study further demonstrates the generality of carbene
migratory insertion/reductive elimination sequence as a
novel strategy to achievebond insertion, which may
open new possibilities in carbene chemistry. Besides, the
mild conditions, wide substrate scope and high efficiency
of the current reactions make them attractive methods to
access geminal bis(silane) and geminal bis(stannane)
derivatives.16
Supporting Information. Experimental procedure,
1
characterization data, copies of H and 13C NMR spectra, X-
ray crystallographic data for 6s. This material is available
free of charge via the Internet at http://pubs.acs.org.
Corresponding Author
wangjb@pku.edu.cn
†HT and TF contributed equally to this work.
(11) We also attempted the reaction with methyl phenyldiazo-
acetate, however, the reaction failed to give the insertion
product under the current conditions.
The project is supported by the National Basic Research
Program of China (973 Program, No. 2012CB821600) and
the Natural Science Foundation of China (Grant 21472004,
21332002).
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(13) For Ni(II) and Pt(0) catalysts, the metal carbene formation
might be problematic, while for Pd(II)/isocyanide system,
isocyanide may react with N-tosylhydrazones. For the use
of these catalysts in Si-Si bond activation, see: (a) Oki-
noshima, H.; Yamamoto, K.; Kumada, M. J. Am. Chem.
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Coord. Chem. Rev. 2008, 252, 545-555. (b) Davies, H. M.
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(15) The related B-B bond insertions are known, for a recent
example, see: Cuenca, A. B.; Cid, J.; García-López, D.; Car-
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