Selective synthesis of monohydrosilanes by the reactions of organoytterbium iodides with dihydrosilanes

Article abstract of DOI:10.1039/a901434i

Monohydrosilanes can be prepared selectively in high yields from the reaction of various aryl and alkyl iodides with ytterbium metal followed by the reaction with dihydrosilanes.

Full text of DOI:10.1039/a901434i

Selective synthesis of monohydrosilanes by the reactions of organoytterbium
iodides with dihydrosilanes
Wu-Song Jin, Yoshikazu Makioka, Tsugio Kitamura and Yuzo Fujiwara*
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, 6-10-1 Hakozaki,
Higashiku, Fukuoka 812-8581, Japan. E-mail: yfujitcf@mbox.nc.kyushu-u.ac.jp
Received (in Cambridge, UK) 22nd February 1999, Accepted 12th April 1999
Monohydrosilanes can be prepared selectively in high yields
from the reaction of various aryl and alkyl iodides with
ytterbium metal followed by the reaction with dihydrosi-
lanes.
In similar reactions of Grignard reagents and organolithiums,
the former give monosubstituted silanes in low yields even
Table 1 Reaction of arylytterbium(ii) iodides with dihydrolsilane 2a and
a
2aA
Recently, lanthanoid complexes with the pentamethylcyclo-
pentadienyl ligand and its analogues have been reported to
catalyze the hydrosilylation reactions of alkenes and alkynes, as
well as cyclization/silylation and polymerization of silanes.1,2
Marks and coworkers and others reported that the reactions of
Cp*2LnCH(SiMe3)2 (Cp* = C5Me5, Ln = La, Nd, Sm) with
PhSiH3 gave CH2(SiMe3)2, while Cp*2YMe(THF) converted
PhSiH3 to PhMeSiH2.2 However, applications of lanthanoid
complexes to direct alkylation or arylation of silanes are still
limited. Evans et al. reported the synthesis of divalent
organolanthanoid s-complexes (RLnI) from organic iodides
and lanthanoid metals in THF.3 We have explored the chemistry
of RLnI and found some unique reactivity toward various
electrophiles.4 In our continuing study on the organolanthanoid
chemistry, we have found that the monohydrosilanes can be
prepared selectively from the reaction of excess divalent
organoytterbium s-complexes (RYbI) with dihydrosilanes
[eqn. (1)]. Here, we report these results.
RPhSiH2
2a: R = Me
2a′: R = Ph
Arl
+
Yb
ArRPhSiH
(2)
THF
room temp.
1
3
Entry Substrate Ar
Dihydrosilane t/h Product Yield(%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
1a
Ph
Ph
2a
2a
2aA
8
2
1
2
8
1
2
8
4
1
2
2
1
1
2
8
4
8
2
4
8
4
2
1
4
4
3a
3a
3aA
3b
3bA
3c
3cA
3d
3dA
3e
64c
> 99
99
97
96
> 99
95
93
78
99
> 99
> 99
> 99
> 99
98
—
92
80
> 99
89
> 99
> 99
> 99
97
1b
1c
1d
1e
1f
o-MeOC6H4 2a
2aA
m-MeOC6H4 2a
2aA
p-MeOC6H4 2a
2aA
o-MeC6H4
2a
2aA
3eA
3f
m-MeC6H4 2a
2aA
3fA
3g
3gA
3h
3i
3iA
3j
3jA
3k
3kA
3l
1g
p-MeC6H4
2a
2aA
2a
2a
2aA
2a
R′R′′SiH2
Rl
+
Yb
RYbl
R′R′′RSiH
(1)
THF
d
1h
1i
o-ClC6H4
m-ClC6H4
First, we studied the reaction of various arylytterbium s-
complexes (ArYbI) with dihydrosilanes [eqn. (2)] and results
are summarized in Table 1.
1j
p-ClC6H4
2aA
1k
1l
o-CF3C6H4 2a
As shown in entry 1 in Table 1, when the reaction was carried
out using an equimolar amount of iodobenzene 1a, Yb metal
and MePhSiH2 2a, the monosilane 3a was formed only in 64%
yield. However, when the ratio of 1a and Yb to 2a was doubled,
3a was obtained quantitatively (entry 2). Most of the substrates
1a–g and 1i–m (entries 2–15 and 17–26) reacted smoothly with
ytterbium metal to produce arylytterbium iodides, and succes-
sive treatment with dihydrosilanes gave selectively mono-
hydrosilanes 3a–g, 3aA–gA and 3i–mA in high yields. For o-
chloroiodobenzene 1h (entry 16), many by-products were
formed, and the isolation of the desired product 3h was
unsuccessful. Under the present conditions, arylytterbium
iodides displayed high reactivity toward not only methylphe-
nylsilane but also diphenylsilane. In addition, dimers of silanes
were not formed in this reaction.5
2aA
a-Naphthyl 2a
2aA
3lA
3m
3mA
1m
2-Thienyl
2a
2aA
> 99
> 99
a
b
See footnote † for reaction conditions. GC yield based on 2a and 2aA.
c
Yb:RI:MePhSiH2
d Complex mixture obtained.
= 1:1:1 and unreacted MePhSiH2 recovered.
Table 2 Reaction of alkylytterbium(ii) iodides with methylphenylsilane
2aa
2a
Rl
+
Yb
RPhSiMeH
(3)
THF
room temp.
1
3
On the other hand, different results were obtained in the
reaction of aliphatic iodides [eqn. (3)] as shown in Table 2.
Primary alkyl iodides such as 1-iodoethane, 1-iodoheptane and
isobutyl iodides (1n–p) proceeded smoothly to afford mono-
hydrosilanes 3n–p in high yields (entries 15–17). By contrast,
for bulky 1q, the yield of 3q was low (entry 4). In the reactions
of secondary and tertiary iodides 1r–t, the reaction proceeded
slowly to give small amounts of the monosilanes 3r–t. These
results indicate that steric factors of the substrates plays an
important role in the reaction. It seems curious that no reaction
occurs with a-methoxy-substituted 1u although Yb metal reacts
with 1u to form (MeOCH2)YbI (entry 8).
Entry
Substrate
R
t/h
Product Yield(%)b
1
2
3
4
5
6
7
8
1n
1o
1p
1q
1r
1s
Et
8
8
8
24
4
8
3n
3o
3p
3q
3r
3s
> 99
89
> 99
50
10c
n-C7H15
Bui
ButCH2
Pri
cC6H11
18
1t
1u
But
72
72
3t
3u
Trace
—
d
MeOCH2
a
b
See notes as to the other reaction conditions. GC yield based on 2a.
c Isolated yield. d Methylphenylsilane recovered.
Chem. Commun., 1999, 955–956
955

under refluxing conditions,6 while the latter afford tetra-
substituted silanes rather than monosubstituted silanes.7 By
contrast, the present reaction of organoytterbium iodides with
dihydrosilanes proceeds smoothly under mild conditions and
gives monosubstituted silanes exclusively. Thus this reaction
should be a useful method for the synthesis of mono-
hydrosilanes.
In conclusion, we have demonstrated that monohydrosilanes
can be prepared selectively and conveniently from the reaction
of dihydrosilanes with excess divalent organoytterbium s-
complexes under mild conditions.
The present work was supported in part by a Grant-in-Aid for
Scientific Research on Priority Areas No. 283, ‘Innovative
Synthetic Reaction’ from Monbusho. Y. M. gratefully acknowl-
edges the Japan Society for the Promotion of Science for its
financial support.
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Notes and references
† Typical reaction procedure: Yb metal (173 mg, 1.0 mmol) was placed in
a 50 ml Schlenk tube. Then, THF (4.0 ml) and p-iodoanisole (234 mg, 1.0
mmol) were successively added at 0 °C under argon and the mixture stirred
for 30 min at this temperature to give a red–brown solution of the ArYbI
complex. Then, methylphenylsilane (61 mg, 0.5 mmol) was added. The
mixture was then heated to room temperature and stirred for 4 h. Usual
workup followed by a silica gel column chromatography (n-hexane–
benzene) gave p-anisylmethylphenylsilane 3d in 79% (90 mg) yield. The
GC yields were determined using n-tetradecane, n-nonadecane and n-
eicosane for aromatic iodides, 1-iodonaphthalene and aliphatic ioidides,
respectively, as an internal standard. Yields are based on dihydrosilanes.
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Communication 9/01434I
956
Chem. Commun., 1999, 955–956