DOI: 10.1002/chem.201502746
Communication
&
CÀH Bond Activation
Synthesis of Silaphenalenes by Ruthenium-Catalyzed Annulation
between 1-Naphthylsilanes and Internal Alkynes through CÀH
Bond Cleavage
Yuichiro Tokoro,* Kengo Sugita, and Shin-ichi Fukuzawa*[a]
Abstract: Ruthenium-catalyzed annulation of 1-naphthyl-
silanes with internal alkynes afforded silaphenalenes
through cleavage of the CÀH bond at the 8-position of
the naphthalene. [RuH2(CO){P(p-FC6H4)3}3] efficiently cata-
lyzed the reaction. The use of 1-naphthyldiphenylsilane as
a substrate resulted in a better yield of the annulation
product compared to the use of silanes with alkyl groups
on the silicon atom. Internal alkynes with both aryl and
alkyl groups were tolerated in this reaction.
Table 1. Scope of ruthenium catalyst in ruthenium-catalyzed silaphena-
lene synthesis.[a]
[Ru]
Solvent
Yield [%][b]
1
2
3
4
5
[RuH2(CO){P(p-FC6H4)3}3]
[RuH2(CO)(PPh3)3]
[RuHCl(CO)(PPh3)3]
[RuHCl(CO)(PCy3)2]
[RuCl2(PPh3)3]
toluene
toluene
toluene
toluene
64
59
55
46
1
Unsaturated organosilanes, such as siloles[1] and vinylsilanes,[2]
show unique optical and electronic properties derived from
the interactions between the CÀSi s* and C=C p* bonds. The
interaction usually lowers the LUMO level, which leads to n-
type semiconducting behavior. Conventionally, unsaturated or-
ganosilanes have been prepared by transition-metal-catalyzed
hydrosilylation of alkynes[3] or nucleophilic substitution using
highly reactive aryl metals compounds containing lithium or
magnesium.[4] Recently, transition-metal-catalyzed cyclization
through CÀH activation has become a powerful method for
constructing five-membered rings containing silicon.[5,6]
The CÀH activation method was also applied to annulation
between arenes with directing groups and unsaturated sub-
strates, such as alkynes.[7] The directing groups often contain
nitrogen and oxygen, which can bind with the transition metal
center, and the annulation reaction is suitable for the synthesis
of N- or O-heterocycles. A similar approach may be considered
in the synthesis of silicon-containing rings from silanes and al-
kynes, because hydrosilyl groups can be regarded as directing
groups.[6,8] However, hydrosilylation in the presence of silanes
and alkynes is usually catalyzed by transition metals.[3] Herein,
we report the synthesis of silaphenalenes by ruthenium-cata-
lyzed annulation between 1-naphthylsilanes and internal al-
kynes.
toluene
6
7
[RuH2(PPh3)4]
[RuHCl(PPh3)3]
toluene
toluene
toluene
toluene
toluene
1,4-dioxane
tAmOH
18
9
8[c]
9[d]
10[e]
11[e]
12[e]
13[e]
[RuH2(CO){P(p-FC6H4)3}3]
[RuH2(CO)(PPh3)3]
[RuH2(CO){P(p-FC6H4)3}3]
[RuH2(CO){P(p-FC6H4)3}3]
[RuH2(CO){P(p-FC6H4)3}3]
[RuH2(CO){P(p-FC6H4)3}3]
41
23
43
41
41
27
1,2-dichloroethane
[a] Compound 1a (0.50 mmol), 2a (1.0 mmol), [Ru] (0.010 mmol), toluene
(1.0 mL). [b] Determined by GC versus dodecane as internal standard.
[c] Tris(4-fluorophenyl)phosphine (0.020 mmol) was added. [d] Xantphos
(0.010 mol) was added; [e] 1008C.
Based on literature reports of g-selective CÀH bond cleavage
by hydrosilyl directing groups, (1-naphthyl)dimethylsilane (1a)
was selected as a substrate to activate the CÀH bond at the 8-
position (Table 1).[9] Annulation between the silane and diphe-
nylacetylene (2a) proceeded in the presence of toluene and
a catalytic amount (2.0 mol%) of [RuH2(CO){P(p-FC6H4)3}3],[10] af-
fording a silaphenalene (3aa) in moderate yield (entry 1,
64%).[10] The analogue of [RuH2(CO){P(p-FC6H4)3}3] with triphe-
nylphosphine slightly decreased the catalytic activity (entry 2).
Diphenylethenes were detected by GC-MS, indicating that the
alkyne acted as a hydrogen acceptor. Furthermore, GC-MS
analysis suggested the generation of some isomers of alkenyl-
silanes through hydrosilylation. While a similar chlorohydrido
complex was also effective for annulation (entry 3, 55%), the
use of tricyclohexylphosphine, which is more electron-rich
than triphenylphosphine, slightly reduced the yield of the sila-
phenalene (entry 4, 46%). Complexes without a carbonyl
ligand showed low catalytic activity (entries 5–7), suggesting
that the carbonyl ligand played a crucial role in the annulation
reaction. Adding extra phosphines (entries 8 and 9) and lower-
[a] Dr. Y. Tokoro, K. Sugita, Prof. Dr. S.-i. Fukuzawa
Department of Applied Chemistry
Institute of Science and Engineering, Chuo University
1-13-27 Kasuga, Bunkyo-ku, Tokyo, 112-8551 (Japan)
Supporting information for this article is available on the WWW under
Chem. Eur. J. 2015, 21, 13229 – 13232
13229
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim