Integrated palladium-catalyzed arylation of heavier groupa 14 hydrides

Article abstract of DOI:10.1002/chem.201001437

A convenient procedure has been developed for the preparation of Groupa 14 compounds by integrated palladium-catalyzed cross-coupling of aromatic iodides with the corresponding Groupa 14 hydrides in the presence of a base. The reaction conditions can be applied to the cross-coupling of tertiary, secondary, and primary Groupa 14 compounds. In most cases, the desired arylated products were obtained in synthetically useful yields. Even in the case of aryl iodides containing OH, NH₂, CN, or CO₂R groups, the reactions proceeded with good to high yields with tolerance of these reactive functional groups. A possible application of this method is the unique synthesis of a fungicidal diarylmethyl(1H-1,2,4-triazol-1-ylmethyl)silane derivative. A convenient procedure has been developed for the preparation of Groupa 14 compounds by integrated palladium-catalyzed cross-coupling of aromatic iodides with the corresponding Groupa 14 hydrides in the presence of a base (see picture). Application of this method in the synthesis of a fungicidal diarylmethyl(1H-1,2,4-triazol-1-yl-methyl)silane derivative is demonstrated. Copyright

Full text of DOI:10.1002/chem.201001437

FULL PAPER
DOI: 10.1002/chem.201001437
Integrated Palladium-Catalyzed Arylation of Heavier Group 14 Hydrides
Aldes Lesbani,[a, b] Hitoshi Kondo,[a] Yusuke Yabusaki,[a] Misaki Nakai,[a]
Yoshinori Yamanoi,*[a] and Hiroshi Nishihara*[a]
Abstract: A convenient procedure has
been developed for the preparation of
Group 14 compounds by integrated
palladium-catalyzed cross-coupling of
aromatic iodides with the correspond-
ing Group 14 hydrides in the presence
of a base. The reaction conditions can
be applied to the cross-coupling of ter-
tiary, secondary, and primary Group 14
compounds. In most cases, the desired
arylated products were obtained in syn-
thetically useful yields. Even in the
case of aryl iodides containing OH,
NH2, CN, or CO2R groups, the reac-
tions proceeded with good to high
yields with tolerance of these reactive
functional groups. A possible applica-
tion of this method is the unique syn-
thesis of a fungicidal diarylmethyl(1H-
1,2,4-triazol-1-ylmethyl)silane deriva-
tive.
Keywords: cross-coupling · germa-
nium
· homogeneous catalysis ·
palladium · silicon
Introduction
The transition-metal-catalyzed cross-coupling of organo-
metallics with organohalogen compounds is a powerful ap-
proach for connecting two molecules by carbon–carbon or
carbon–heteroatom bonds.[6] Transition-metal-catalyzed re-
actions of Si- or Ge-centered hydrides form the basis of a
number of important synthetic methodologies.[7] Recently,
the development of efficient methods for transition-metal-
catalyzed arylation of tertiary silanes has emerged as one of
the most powerful synthetic methods for accessing aryl si-
lanes. For example, pioneering coupling reactions of trial-
koxysilanes with aryl halides have been recently reported in-
dependently by Murata, Masuda et al.,[8] DeShong et al.,[9]
Denmark et al.,[10] Komuro et al.,[11] and Ito.[12] Although,
satisfactory results were obtained for the preparation of ar-
yltrialkoxysilanes, arylation of trialkylsilane[13] has met with
limited success due to the tendency to give a reduced prod-
uct (Scheme 1a).[14,15] Attention has also been paid to the
Compounds containing heavier Group 14 elements have at-
tracted considerable attention due to their widespread appli-
cations as intermediates for carbon–carbon bond forma-
tion,[1] as building blocks for the construction of novel mate-
rials,[2] and as biologically active pharmaceuticals or agro-
chemicals.[3] The conventional chemical routes to these com-
pounds
have predominantly
involved
nucleophilic
substitution with Grignard or organolithium reagents.[4,5]
These methods have limited applications because com-
pounds that contain functional groups sensitive to organo-
metallic reagents are only accessible in multiple steps. Con-
sequently, more general synthetically useful methods for the
preparation of functionalized Group 14 compounds remain
in great demand.
Pd-catalyzed arylation of trisACHTUNGTRNEUNG
(2-furyl)germane[16] or hydro-
[a] Dr. A. Lesbani, H. Kondo, Y. Yabusaki, Dr. M. Nakai,
Dr. Y. Yamanoi, Prof. Dr. H. Nishihara
Department of Chemistry, School of Science
The University of Tokyo
germatrane[8e] with aryl halides. Despite these significant ad-
vances, other examples of arylation of hydrogermanes with
aryl halides have not been described to date.
In the course of our research, we focused on the develop-
ment of a new methodology based on transition-metal-cata-
lyzed arylation using hydrosilanes.[17,18] We report herein a
detailed study in which we obtained Si- or Ge-containing
compounds by using the stepwise and integrated arylation
of primary, secondary, or tertiary Group 14 compounds in
the presence of a base, catalyzed by the commercially avail-
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
Fax : (+81)3-5841-8063
E-mail: yamanoi@chem.s.u-tokyo.ac.jp
nisihara@chem.s.u-tokyo.ac.jp
[b] Dr. A. Lesbani
Department of Chemistry, FMIPA
Sriwijaya University, JL Palembang Indralaya Km-32
Palembang, Sumatora Selatan 30662 (Indonesia)
able complex [PdACHTNUGTRENUNG(PtBu3)2] (Scheme 1b).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001437.
Chem. Eur. J. 2010, 16, 13519 – 13527
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
13519

DME at room temperature proved to be optimal for this re-
action.
Using the above-mentioned conditions, we investigated
the scope of palladium-catalyzed arylation of tertiary ger-
manes with various aryl iodides.[21] As summarized in
Table 1, the reactions proceeded in moderate to good yields.
The electronic properties of the aromatic ring had a large
impact on the arylation yield. Electron-deficient aryl iodides
gave lower yields than electron-rich aryl iodides. The reac-
tion proceeded smoothly to give the arylated germanes in
good yield even in the case of an ortho-substituted aryl
iodide, which did not effectively couple with tertiary silanes
in the presence of the palladium catalyst (Table 1, entries 3,
6, and 21).[18a] Heteroaryl iodides were also arylated with
good efficiencies (Table 1, entries 18, 30, and 32). Functional
groups, such as OH, NH2, and CN, on the aromatic ring of
the aryl iodides were tolerated under these conditions
(Table 1, entries 13–15). In all case, byproducts were due to
reduction (arenes), and no starting materials were observed
by GC-MS.
Scheme 1. a) Previous transition-metal-catalyzed reduction of aryl iodides
with hydrosilanes. b) Pd-catalyzed stepwise arylation of Group 14 hy-
drides with aryl iodides.
Results and Discussion
Arylation of secondary silanes and germanes: To probe the
generality of this catalytic arylation, we next examined the
reactions of various Group 14 dihydrides. Tertiary silanes
are commonly prepared by addition of organometallic re-
agents to secondary silanes. However, this method has limit-
ed application for compounds containing functional groups
sensitive to organometallic reagents.[22] Previously, we re-
ported that several aryl iodides and secondary silanes cou-
Arylation of tertiary germanes:[19,20] We recently developed
a facile protocol to synthesize functionalized silane com-
pounds by transition-metal-catalyzed arylation of tertiary si-
lanes.[18a–c] Encouraged by the preliminary results, we investi-
gated the arylation of a tertiary germane. Treatment of 4-io-
doanisole with triphenylgermane in the presence of [Pd-
ACHTUNGTRENNUNG(PtBu3)2] (5 mol%) and 1,4-diazabicycloACHTUNGTERN[NUGN 2.2.2]octane
(DABCO, 3.0 equiv) in DME at room temperature for 1 d
led to (4-methoxyphenyl)triphenylgermane (1) in 95% yield
(Table 1, entry 1). Small amounts of anisole were detected
under these conditions, as indicated by GC-MS analysis of
the crude reaction mixture. Although we screened several
pled in the presence of [PdACHTUNGETRN(NUG PtBu3)2] and Et3N to give the
corresponding tertiary silanes in good to high yields.[18d]
Having obtained satisfactory results in the above initial
studies, we proceeded to screen cross-coupling between a
broad range of aromatic iodides and secondary silanes or
reaction conditions, the [Pd
G
germanes. The scope and limitations of the [PdACHTGNUTERN(NUG PtBu3)2] cat-
Table 1. Arylation of tertiary germanes.[a]
Entry
Ar
R
Time [d]
Product
Yield [%]
Entry
Ar
R
Time [d]
Product
Yield [%]
1
2
3
4
5
6
7
8
4-MeOC6H4
3-MeOC6H4
2-MeOC6H4
4-Me2NC6H4
3-Me2NC6H4
2-Me2NC6H4
4-MeC6H4
4-EtC6H4
4-iPrC6H4
4-tBuC6H4
3,5-Me2C6H3
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
1
3
3
3
3
2
2
1
1
1
3
2
2
2
1
1
1
2
3
4
5
6
7
8
95
23
37
81
35
91
54
59
67
52
33
49
64
65
30
27
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
3-F3CC6H4
2-C4H3S
Ph
Ph
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
nBu
nBu
2
2
1
1
2
1
2
2
1
1
1
2
2
1
1
1
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
23
67
70
42
58
75
36
46
60
62
53
65
34
77
79
88
4-MeOC6H4
3-MeOC6H4
2-MeOC6H4
3-Me2NC6H4
Ph
4-MeC6H4
4-EtC6H4
4-iPrC6H4
4-tBuC6H4
3,5-Me2C6H3
3-F3CC6H4
2-C4H3S
9
9
10
11
12
13
14
15
16
10
11
12
13
14
15
16
4-HOC6H4
4-H2NC6H4
3-NCC6H4
4-F3CC6H4
4-MeOC6H4
2-C4H3S
[a] Reaction conditions: aryl iodide (0.5 mmol), tertiary germane (0.6 mmol), DABCO (1.5 mmol), [PdACHTUNRTGNEUNG(PtBu3)2] (0.025 mmol), DME (1.0 mL), RT.
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Pd-Catalyzed Arylation of Group 14 Hydrides
Table 2. Single arylation of Group 14 dihydrides.
FULL PAPER
Entry Ar
E
R1
R2
Time [d] Product Yield [%] Entry Ar
E
R1
R2
Time [d] Product Yield [%]
1[a]
3-MeOC6H4
2-MeC6H4
2,4-Me2C6H3 Si Ph
2-EtC6H4
2-iPrC6H4
2-tBuC6H4
2,6-Me2C6H3 Si Ph
4-iPrC6H4
4-tBuC6H4
3,5-Me2C6H3 Si Ph
4-Me2NC6H4 Si Ph
3-Me2NC6H4 Si Ph
4-H2NC6H4
3-NCC6H4
3-HOC6H4
4-MeOC6H4
3-MeOC6H4
4-MeC6H4
Si Ph
Si Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
2
2
2
2
2
2
2
2
2
2
2
2
2
2
5
2
2
2
33
34
35
36
37
43
80
85
80
67
19[a]
20[a]
21[a]
22[a]
23[a]
24[a]
25[a]
26[a]
27[a]
28[d]
29[d]
30[d]
31[d]
32[d]
33[d]
34[d]
35[d]
36[d]
3-MeC6H4
2-PhC6H4
4-F3CC6H4
3-F3CC6H4
1-Np
Ph
2-PhC6H4
2-iPrC6H4
Si
Si
Si
Si
Si
Si
Si
Si
Ph
Ph
Ph
Ph
Ph
Ph
Et
Et
Me
Me
Me
Me
Me
Me
Et
2
2
2
2
2
2
2
2
2
4
4
4
3
4
6.5
3
1
1
49
50
51
52
53
54
55
56
45
95
47
30
37
77
51
76
2[a]
3[a]
4[a]
Si Ph
Si Ph
Si Ph
5[a]
6[a]
–
–
–
–
[e]
[e]
7[a]
[e]
[e]
8[a]
Si Ph
Si Ph
38
39
40
41
42
43
44
45
46
47
48
67
52
61
51
64
89
52
49
38
46
65
Et
9[a]
4-MeOC6H4 Si
tBu tBu
–
–
[e]
[e]
10[a]
11[a]
12[a]
13[a]
14[b]
15[c]
16[a]
17[a]
18[a]
4-MeOC6H3 Ge Ph
3-MeOC6H4 Ge Ph
2-MeOC6H4 Ge Ph
4-tBuC6H4
3-F3CC6H4
3-NCC6H4
1-C10H7
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Et
Et
57
58
59
60
61
62
63
64
57
60
22
49
37
62
52
63
Si Ph
Si Ph
Si 1-Np Ph
Si Ph
Si Ph
Si Ph
Ge Ph
Ge Ph
Ge Ph
Ge Ph
Ge Et
Ge Et
Ph
Me
Me
2-iPrC6H4
2-tBuC6H4
[f]
[f]
–
–
[a] Reaction conditions: aryl iodide (1.0 mmol), secondary silane (1.5 mmol), Et3N (2.0 mmol), [Pd
conditions: aryl iodide (1.0 mmol), secondary silane (3.0 mmol), Et3N (3.0 mmol), [Pd(PtBu3)2] (0.05 mmol), THF (1.0 mL), RT. [c] Reaction conditions:
aryl iodide (1.0 mmol), secondary silane (1.5 mmol), Et3N (2.0 mmol), [Pd(PtBu3)2] (0.05 mmol), THF (1.0 mL), 08C. [d] Reaction conditions: aryl iodide
(1.0 mmol), secondary germane (2.5 mmol), iPr2EtN (1.5 mmol), [Pd(PtBu3)2] (0.05 mmol), THF (1.0 mL), RT. [e] No arylsilane was obtained. [f] A trace
ACHTUNGTREN(UNNG PtBu3)2] (0.05 mmol), THF (1.0 mL), RT. [b] Reaction
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
amount of arylated product was observed by GC-MS analysis.
alyst system applied in these reactions are summarized in
Table 2. In general, all reactions were very clean, and the
corresponding tertiary silanes and germanes were obtained
in moderate to good yields. In all cases, small amounts of
the reduced products were detected by GC-MS, but these
could be separated during purification by column chroma-
tography. Doubly arylated side products were not obtained
in any mono-arylation reaction. The electronic effects of the
substituents on the aromatic ring did not significantly affect
the reaction. We found that the catalyst system tolerated re-
active functional groups, such as NH2 (Table 2, entry 13),
OH (Table 2, entry 15), and CN (Table 2, entries 14 and 33).
However, attempts to perform the arylation using 2-tert-bu-
Figure 1. Material balance for Table 2, entry 30, based on 2-iodoanisole.
tyliodobenzene
and
2,6-dimethyliodobenzene
failed
(Table 2, entries 6 and 7), which could be attributed to steric
hindrance in the substrates. On studying the influence of hy-
drosilanes and hydrogermanes on the arylation reaction, we
found that 1-NpPhSiH2,[23] PhMeSiH2, Et2SiH2, Ph2GeH2,
and Et2GeH2 gave the corresponding tertiary Group 14
compounds in moderate to good yields. In contrast, the use
of di-tert-butylsilane, which has a greater degree of steric
hindrance, hampered the arylation reaction (Table 2,
entry 27). Studies on material balance were performed for
Table 2, entry 30 as a model reaction. In the course of the
tion, the scope of double arylation was examined (Table 3).
A diverse array of aryl iodides were good substrates for this
transformation. The yields of the diarylated products were
generally poor to moderate, and the reaction tolerated the
presence of a variety of functional groups. Double arylation
is sensitive to the steric and electronic effects of functional
groups in the aryl iodide. Electron-withdrawing aryl sub-
stituents, such as the ethyl ester group (CO2Et) in the sub-
strate, led to an inferior yield (Table 3, entries 23 and 28).
Electron-rich aryl iodides with meta and para substituents
reacted well under optimized conditions, whereas ArI sub-
strates with sterically demanding ortho substitution did not
produce any diarylated product (Table 3, entry 6). Reaction
of 1-naphthylphenylsilane with 4-iodoanisole also gave only
the mono-arylated product; the diarylated product was pro-
catalytic reaction, monoACTHNURGTNEaNUG rylated product 59 (22%) and re-
duced product (77%) were produced with excellent material
balance (99%, Figure 1). No doubly arylated product was
observed.
Encouraged by these promising results, double arylation
of diphenylsilane was first attempted in the presence of an
excess of 4-iodoanisole. Following the success of this reac-
Chem. Eur. J. 2010, 16, 13519 – 13527
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Y. Yamanoi, H. Nishihara et al.
Table 3. Double arylation of secondary silanes and germanes.
Entry Ar
E
R1 R2 Time [d] Product Yield [%] Entry Ar
E
R1 R2
Time [d] Product Yield [%]
1[a]
4-Me2NC6H4 Si Ph Ph
4
4
4
4
4
4
4
4
4
4
4
4
4
4
65
66
67
68
69
57
30
32
32
29
15[a]
16[a]
17[a]
18[a]
19[a]
20[a]
21[a]
22[a]
23[a]
24[b]
25[b]
26[b]
27[b]
28[b]
3-Me2NC6H4
4-H2NC6H4
3-HOC6H4
Ph
2-C4H3S
3-C4H3S
3-EtO2CC6H4 Si
4-MeOC6H4 Si
3-EtO2CC6H4 Si
4-MeOC6H4
2-C4H3S
Si
Si
Si
Si
Si
Si
Et Et
Et Et
Et Et
Et Et
Et Et
Et Et
Et Et
Ph Me
Ph Me
4
4
4
4
4
4
4
4
4
2
2
1
2.5
2.5
78
79
80
81
82
83
84
85
86
87
88
89
90
91
51
40
52
53
81
77
23
72
29
41
49
50
51
26
2[a]
4-MeC6H4
4-EtC6H4
4-iPrC6H4
4-tBuC6H4
2-MeC6H4
Si Ph Ph
Si Ph Ph
Si Ph Ph
Si Ph Ph
Si Ph Ph
3[a]
4[a]
5[a]
6[a]
–
–
[c]
[c]
7[a]
3,5-Me2C6H3 Si Ph Ph
70
71
72
73
74
75
76
77
21
70
90
44
59
49
70
72
8[a]
2-C4H3S
Si Ph Ph
Si Et Et
Si Et Et
Si Et Et
Si Et Et
Si Et Et
9[a]
4-MeOC6H4
4-MeSC6H4
4-MeC6H4
3-MeC6H4
4-iPrC6H4
10[a]
11[a]
12[a]
13[a]
14[a]
Ge Ph Ph
Ge Ph Ph
Ge Et Et
Ge Et Et
4-MeOC6H4
2-C4H3S
3-EtO2CC6H4 Ge Et Et
4-Me2NC6H4 Si Et Et
[a] Reaction conditions: aryl iodide (1.5 mmol), secondary silane (0.5 mmol), Et3N (2.0 mmol), [PdCAHTUNGTRENNUNG
conditions: aryl iodide (1.5 mmol), secondary germane (0.5 mmol), iPr2EtN (1.5 mmol), [PdACHTUNGTRENNUNG
lated product.
duced only in trace amounts due to the steric hindrance of
the 1-naphthyl moiety. Double arylation was also successful
with heteroaromatic iodides (Table 3, entries 8, 19, and 20).
These compounds were investigated as possible precursors
for silanediols, which have been shown to be effective bio-
proceed smoothly to give the corresponding secondary ger-
manes in moderate to good yields (Table 4, entries 1–5). For
example, when 2-ethyliodobenzene was treated with one
Table 4. Single and double arylation of primary silanes and germanes.
ACHTUNGTRENNUNG
isosteres for hydrated carbonyl groups.[24] The mass balance
of Pd-catalyzed double arylation was determined for the re-
action of Table 3, entry 24. Careful workup and purification
gave 17% anisole (reduced product), 31% 4-iodoanisole
(starting material), and 41% 87 (doubly arylated product)
based on 4-iodoanisole (Figure 2).
Entry
Ar
E
R
Product
Yield [%]
1[a]
2[a]
3[a]
4[a]
5[a]
6[b]
7[b]
8[b]
9[b]
10[b]
11[b]
1-C10H7
Ge
Ge
Ge
Ge
Ge
Si
Si
Si
Si
Si
tBu
tBu
tBu
tBu
92
93
94
95
96
97
98
99
87
29
27
62
78
16
40
46
42
52
46
2-Me2NC6H4
2-MeC6H4
2-EtC6H4
2-biphenyl
2-MeC6H4
2-iPrC6H4
2-iPrC6H4
2-MeOC6H4
1-C10H7
tBu
nBu
nBu
cC5H9
cC5H9
nBu
tBu
100
101
102
2-MeOC6H4
Ge
[a] Reaction conditions: primary germane (1.0 mmol), aryl iodide
(1.0 mmol), DABCO (1.5 mmol), [Pd(PtBu3)2] (0.05 mmol), THF
(3.0 mL), RT, 3 d. [b] All reactions were carried out by using [Pd(PtBu3)2]
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
(0.05 mmol), DABCO (2.5 mmol), aryl iodide (2.0 mmol), primary silane
or germane (1.0 mmol) in THF (3 mL) at RT for 3 d.
Figure 2. Material balance for Table 3, entry 24, based on 4-iodoanisole.
equivalent of tert-butylgermane, mono-arylated product 95
was isolated (Table 4, entry 4). Careful workup and purifica-
tion gave 95 in 62% yield along with 21% recovered start-
ing material and 4% reduced product (87% overall mass
balance, Figure 3). The remainder is likely lost to polymeri-
zation of starting material and/or product, which is not un-
expected. No other products were observed. Unfortunately,
the singly arylated product was not observed at all by GC-
MS on the reaction mixture when other aryl iodides were
used as substrates.
Arylation of primary silanes and germanes: Continuing in-
terest in palladium-mediated arylation prompted us to ex-
plore the possibility of using primary Group 14 compounds
as coupling partners. We initially investigated the single aryl-
ACHTUNGTRENNUNGation of various primary silanes and germanes with aryl io-
dides. The reactions typically provided a complex mixture of
inseparable products, including doubly arylated products,
and only in the case of tert-butylgermane did the reaction
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Pd-Catalyzed Arylation of Group 14 Hydrides
FULL PAPER
Table 5. Triple arylation of various primary silanes and germanes.[a]
Entry
Ar
E
R
Product
Yield [%]
1
2
3
4
5
6
7
8
4-MeSC6H4
2-C4H3S
3-C4H3S
4-MeSC6H4
4-MeOC6H4
5-Me-2-C4H3S
4-MeOC6H4
4-MeOC6H4
2-C4H3S
2-C4H3S
3-C4H3S
2-C4H3S
3-C4H3S
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Ge
Ge
Ge
Ge
Ph
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
42
47
70
53
46
55
61
60
61
45
52
52
47
46
20
4-MeC6H4
4-MeC6H4
4-MeC6H4
cC5H9
cC5H9
nC4H9
nC4H9
nC8H17
nC18H37
nC18H37
tBu
Figure 3. Material balance for Table 4, entry 4, based on 2-iodoethylben-
zene.
9
10
11
12
13
14
15
Next, we focused on double arylation of primary silanes
and germanes with aryl iodides (Table 4, entries 6–11).
ortho-Substituted and electron-donating aryl iodides proved
to be excellent double arylating reagents towards primary si-
lanes and germanes. The effect of increased steric hindrance
was studied by using four kinds of ortho-substituted aryl io-
dides (Table 4, entries 6–9). Steric hindrance at the ortho po-
sition appeared to have significant influence. Aryl iodides
with substituents meta and para to the iodido group failed to
generate the desired products. DABCO was found to be the
most effective base for arylation. Due to the steric hin-
drance of the aryl iodides, no triply arylated product was ob-
served, in good agreement with previous work. The reaction
of n-butylsilane and 2-isopropyliodobenzene gave several
products, identified after careful workup and purification
(Figure 4). Polar impurities observed were likely produced
by slow oxidation of 98 during workup.
tBu
tBu
nBu
4-MeSC6H4
4-MeOC6H4
[a] All reactions were carried out with [PdACHTUNTGRNEUNG(PtBu3)2] (0.05 mmol),
DABCO (5.0 mmol), aryl iodide (4.0 mmol), primary silane or germane
(1.0 mmol) in 3 mL of THF at RT for 7 d.
even larger excesses of aryl iodide did not improve the
yields. Since triply arylated products did not provide satis-
factory yields, the reaction mixture was closely examined to
identify other components by using Table 5, entry 1 as a
model reaction. The biaryl compound and a considerable
amount of unidentified byproducts most likely arise from
decomposition of singly and doubly arylated silanes
(Figure 5).
We examined the possibility of triple arylation of primary
Group 14 compounds (Table 5). Triarylated products were
obtained in moderate to good yield when primary silanes or
germanes were treated with 4 equiv of aryl iodide in the
presence of the palladium catalyst and base. Employing
Figure 5. Material balance for Table 5, entry 1, based on 4-iodothioani-
sole.
Sequential arylation of Group 14 hydrides: Having estab-
lished the feasibility of one-pot multi-arylation of Group 14
hydrides, we turned our attention to one-pot sequential
double arylation with two different aryl iodides. Two aryl io-
dides, Ar1I and Ar2I, were cross-coupled with secondary si-
lanes or germanes to produce the arylated product in good
yields. Thus, a solution of Ar1I, secondary silane or germane,
organic base (Et3N or iPr2EtN), and a catalytic amount of
Figure 4. Material balance for Table 4, entry 7, based on 2-isopropyliodo-
benzene
[PdACTHNURTGNE(UGN PtBu3)2] in THF was stirred at room temperature for 2–
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Y. Yamanoi, H. Nishihara et al.
4 d to produce the mono-arylated product in situ. After con-
sumption of Ar1I was confirmed by thin-layer chromato-
graphic monitoring, Ar2I was added to the solution and the
mixture was stirred for several additional days to produce
the doubly arylated product.[25] The products and yields of
this stepwise process are summarized in Table 6. Various
Table 6. Stepwise arylation of primary and secondary Group 14 hydrides.
Entry R1 R2
E
Ar1
Ar2
Product Yield [%]
1[a]
Ph Ph Si 4-MeOC6H4 2-C4H3S
Ph Me Si 4-MeOC6H4 2-C4H3S
Ph Me Si 4-MeOC6H4 4-EtC6H4
Ph Me Si 4-MeOC6H4 4-iPrC6H4
Ph Me Si 4-MeOC6H4 4-tBuC6H4
Ph Me Si 4-MeOC6H4 4-MeSC6H4
Et Et Si 4-MeOC6H4 4-iPrC6H4
Et Et Si 4-MeOC6H4 4-EtC6H4
118
119
120
121
122
123
124
125
39
74
60
74
76
43
70
50
62
64
73
61
49
31
39
32
43
38
9
Figure 6. Material balance for Table 6, entry 15, based on 4-iodoanisole.
2[a]
3[a]
4[a]
Next, this stepwise arylation reaction was applied to pri-
mary Group 14 compounds to produce unsymmetrically sub-
stituted Group 14 compounds. After careful screening of the
substrates, we achieved sequential arylation only in the case
5[a]
6[a]
7[a]
8[a]
9[a]
Et Et Si 4-MeOC6H4 4-Me2NC6H4 126
Et Et Si 4-MeOC6H4 4-Bu2NC6H4 127
Et Et Si 4-MeOC6H4 2-C4H3S
of tert-butylgermane. 2-Iodo-N,N-dimethylaniline was
a
10[a]
11[a]
12[a]
13[a]
14[a]
15[b]
16[b]
17[b]
18[b]
19[b]
20[c]
21[c]
22[c]
23[c]
good second coupling partner. Although the yields were
moderate (Table 6, entries 20–23), a variety of functional
Groups were tolerated and afforded unsymmetrical tertiary
germanes, which are difficult to synthesize by classical meth-
ods. Material balance studies on the reaction of Table 6,
entry 23 showed that 42% of 2-iodotoluene was converted
to 137, 28% to germanol, and 9% to toluene (Figure 7). Ac-
cordingly, the moderate yield may be due to formation of
germanol by an oxidation process during workup.
128
129
Et Et Si 4-MeOC6H4 4-tBuC6H4
Et Et Si 2-C4H3S
Et Et Si 4-tBuC6H4
4-MeOC6H4 128
4-MeOC6H4 129
Ph Ph Ge 4-MeOC6H4 4-tBuC6H4
Ph Ph Ge 4-MeOC6H4 4-Me2NC6H4 131
Ph Ph Ge 4-MeOC6H4 2-Me2NC6H4 132
130
Ph Ph Ge 4-MeOC6H4 2-C4H3S
133
Ph Ph Ge 2-C4H3S
4-MeOC6H4 133
2-Me2NC6H4 134
2-Me2NC6H4 135
2-Me2NC6H4 136
2-Me2NC6H4 137
tBu
tBu
tBu
tBu
H
H
H
H
Ge 1-C10H7
63
40
48
42
Ge 2-biphenyl
Ge 2-EtC6H4
Ge 2-MeC6H4
[a] Reaction conditions: i) Ar1I (1.0 mmol), secondary silane (1.5 mmol),
Et3N (2.5 mmol), [PdACHTUNGTRENNUNG(PtBu3)2] (0.05 mmol), THF (4.0 mL), RT, 2 d;
ii) Ar2I (1.5 mmol), RT, additional 2–4 d. [b] Reaction conditions: i) Ar1I
(1.0 mmol), secondary germane (2.0 mmol), iPr2EtN (3.0 mmol), [Pd-
ACHTUNGTRENNUNG
(PtBu3)2] (0.05 mmol), THF (2.0 mL), RT, 2–4 d; ii) Ar2I (2.0 mmol), RT,
additional 3.5–6 d. [c] Reaction conditions: i) Ar1I (1.0 mmol), tert-butyl-
germane (1.0 mmol), DABCO (2.5 mmol), [PdACHTUNRTGENUNG(PtBu3)2] (0.05 mmol),
THF (3.0 mL), RT, 1 d; ii) Ar2I (1.0 mmol), RT, additional 3 d.
electronically and structurally diverse aryl iodides were suc-
cessfully used to produce the corresponding quaternary
Group 14 compounds. In particular, a smoother transforma-
tion was observed when 4-iodoanisole was used as the first
arylating agent, and doubly arylated compounds could be
obtained in moderate to good yields by using a second aryl-
Figure 7. Material balance for Table 6, entry 23, based on 2-iodotoluene.
A
Agrochemical synthesis: Despite the recent introduction of
novel antifungal agents with promising activity, invasive
fungal infections have become a major cause in the reduc-
tion, by nearly 20%, of food and crop yields.[26] Therefore,
there has been increasing interest in developing structural
variants of the newer fungicides. Derivatives of 1,2,4-triazole
play an important role in agriculture and medicine, and sili-
con-containing groups have been used in biological research
for some time.[3] Thus, the triazole-containing silane flusil-
sensitive to the electronic properties of the first arylating
agent. Thus, use of 2-iodothiophene or 1-tert-butyl-4-iodo-
benzene instead of 4-iodoanisole resulted in slightly lower
yields of the doubly arylated product (Table 6, entries 13,
14, and 19). Product distribution analysis of Table 6,
entry 15 is shown in Figure 6 as an example. Although an
excellent material balance was obtained, germanol was ob-
tained in 15% yield due to slow oxidation of tertiary ger-
mane during the purification.
azole
(bis(4-fluorophenyl)methyl(1H-1,2,4-triazol-1-ylme-
13524
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Chem. Eur. J. 2010, 16, 13519 – 13527

Pd-Catalyzed Arylation of Group 14 Hydrides
FULL PAPER
thyl)silane) has been widely used as an antifungal agent
against mildew and rusts of cereal grains, fruits, vegetables,
and ornamentals.[27] Prompted by the diverse activities of
1,2,4-triazole derivatives, we prepared 1-(silylmethyl)-1,2,4-
triazole derivatives as potential fungicidal agents by palladi-
um-catalyzed double arylation of secondary silanes.
According to the literature, flusilazole can be prepared by
two-step synthesis from dichloro(chloromethyl)methylsilane
by using organometallic reagents. Our interest focused on
the concise preparation of 1-(silylmethyl)triazole derivatives
by using palladium-catalyzed arylation as the key step
(Scheme 2). Methyl(chloromethyl)silane[28] was treated with
dibenzylideneacetone) system at room temperature.[33] If ox-
idative addition of the haloarene to Pd0 is the key step of
this reaction, the arylated silane should also be obtained at
room temperature in good yield if the aryl bromide is used
as a starting material.
On the basis of these observations, we propose a mecha-
nism for the process described here, initiated by oxidative
addition of Group 14 hydrides to Pd0 to generate the PdII in-
termediate H-Pd-ER3 (E=Si, Ge). A pathway through s-
bond metathesis[34] between the PdII species and the aryl
iodide then leads to an arylated compound through reduc-
tive elimination (Scheme 4a). A pathway that proceeds
through further oxidative addi-
tion, resulting in the formation
of a PdIV species,[35] cannot be
completely
excluded
(Scheme 4b). Finally, the palla-
dium(0) catalyst can be regen-
erated by the removal of HI
with the aid of a base.
Scheme 2. Synthesis of flusilazole from secondary silane.
4-fluoroiodobenzene in the presence of [PdACTHUNGTRNEUNG(PtBu3)2] and
iPr2EtN in THF to give the doubly arylated product 138 in
À
82% yield. Notably, the C Cl bond was unaffected by the
palladium-catalyzed double arylation. Compound 138 was
subjected to N-alkylation with the sodium salt of 1,2,4-tri-
ACHTUNGTRENNUNGazole to give flusilazole (139) in 70% yield. This procedure
is a simple, reproducible method for the preparation of ana-
lytically pure flusilazole analogues on the laboratory scale.
Mechanistic considerations: In a preliminary communica-
tion, we proposed a possible mechanism for the process de-
scribed herein, with initiation by oxidative addition of hy-
drosilane to Pd0 to generate a H-Pd-SiR3 PdII intermediate.
Oxidative addition of hydrosilane to a transition-metal com-
plex has been reported previously.[29–31] To clarify the reac-
tion mechanism of the palladium-catalyzed cross-coupling
reaction, the palladium complex [PdI
formed by oxidative addition of 2-iodotoluene to [Pd-
(PtBu3)2], was prepared according to a modified literature
ACHTUTGNNERNUG(PtBu3)CAHTUNGTRNEN(UGN 2-MeC6H4)],
ACHTUNGTRENNUNG
method.[32] Treatment of the isolated aryl palladium iodide
complex with Ph2SiH2 (1.0 equiv) and iPr2EtN (1.0 equiv) in
THF at RT for 6 h gave the reduced product (toluene) in
78% yield, as determined by GC-MS (Scheme 3). Fu et al.
reported that Suzuki coupling of aryl bromides can be ac-
Scheme 4. Plausible catalytic cycle for the arylation of Group 14 hydride
(E=Si or Ge; B=Base).
complished by using the [Pd2ACHTNUGTRENUNG(dba)3]/PtBu3 (dba=trans,trans-
Conclusion
We have demonstrated that arylated heavier Group 14 com-
pounds are easily prepared in a one-step procedure in mod-
erate to good yields, starting from commercially available
aryl halides and the corresponding Group 14 hydride. This
strategy differs from the classical preparation exemplified
by the reaction of Grignard or organolithium reagents with
Scheme 3. Reactions in equivalent ratio.
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13525

Y. Yamanoi, H. Nishihara et al.
2107, no. 21108002), and the Global COE Program for “Chemistry Inno-
vation through the Cooperation of Science and Engineering” from the
Ministry of Education, Culture, Sports, Science, and Technology, Japan.
a chlorosilane. Our methodology can be applied in the pres-
ence of a wide range of reactive functional groups on the
aryl halide to produce a variety of aromatic Group 14 com-
pounds. Pd-catalyzed decomposition or oxidation of inter-
mediates seems to be the primary cause of low yields of
triply arylated product. The secondary and tertiary
Group 14 products were slightly reactive with oxygen and/or
water at ambient temperature in the presence of catalyst.[36]
Workup and purification with silica gel resulted in the par-
tial formation of silanol, germanol, or other unidentified oli-
gomeric products. The reaction gave complex mixtures with-
out aryl iodides. In the presence of transition-metal com-
plexes, secondary or primary silanes generally underwent a
scrambling of the substituents together with dehydrogena-
tive silane coupling via silylene complexes.[37] Accordingly,
the formation of the oligomeric products described above
can be also explained by the decomposition of hydrosilane
with catalyst.
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The simplicity of the reaction procedure coupled with the
broad range of substrates renders this method particularly
attractive for the efficient preparation of biologically, medic-
inally, and photochemically interesting Group 14 com-
pounds.
Experimental Section
All experiments were carried out under an argon atmosphere in oven-
dried glassware. Unless otherwise noted, the Group 14 hydrides and aryl
halides were purchased from commercial sources and were used without
purification. See the Supporting Information for details of the characteri-
zation of individual compounds.
Typical procedure for the palladium-catalyzed stepwise arylation of sec-
ondary silanes (Table 6, entry 5): Methylphenylsilane (206 mL, 1.5 mmol),
4-iodoanisole (234 mg, 1.0 mmol), and triethylamine (0.35 mL, 2.5 mmol)
were added to a solution of [PdACHTNUGTRNEUNG(PtBu3)2] (25 mg, 0.05 mmol) in THF
À
[5] For the transition-metal-catalyzed Si C bond-forming reaction be-
(4.0 mL). After 2 d at RT, 1-tert-butyl-4-iodobenzene (266 mL, 1.5 mmol)
was added. After a further 4 d, the reaction mixture was quenched with
water, extracted three times with CH2Cl2, and dried over Na2SO4. The
solvent was evaporated under reduced pressure, and silica-gel column
chromatography produced doubly arylated product 122 (274 mg, 76%).
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J. Org. Chem. 2009, 74, 1415.
Typical procedure for the palladium-catalyzed stepwise arylation of pri-
mary germane (Table 6, entry 20): DABCO (280 mg, 2.5 mmol), 1-iodo-
naphthalene (146 mL, 1.0 mmol), and tert-butylgermane (137 mL,
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1.0 mmol) were added to a solution of [PdACTHNUTRGNEU(NG PtBu3)2] (25 mg, 0.05 mmol) in
THF (3.0 mL). After 0.5 d at RT, 2-iodo-N,N-dimethylaniline (250 mg,
1.0 mmol) was added. After a further 3 d, the reaction mixture was
quenched with water, extracted three times with CH2Cl2, and dried over
Na2SO4. The solvent was evaporated under reduced pressure, and silica-
gel column chromatography produced doubly arylated product 134
(238 mg, 63%).
Acknowledgements
We thank Kimiyo Saeki and Dr. Aiko Sakamoto of the Elemental Analy-
sis Center of the University of Tokyo for elemental analysis. We also
thank Takafumi Taira, Jun-ichi Sato, and Ikuse Nakamula for their tech-
nical assistance. A.L. thanks the Japan Society for the Promotion of Sci-
ence (JSPS) for a postdoctoral fellowship. This work was financially sup-
ported by Grant-in-Aids for Young Scientists (B) (no. 21750036), Scien-
tific Research on Innovative Areas “Coordination Programming” (area
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13526
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Pd-Catalyzed Arylation of Group 14 Hydrides
FULL PAPER
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[25] Because secondary silanes gradually degraded in the presence of the
palladium catalyst, a high yield of the stepwise arylated product was
obtained by using 1.5 equiv of Ar2I, although 2.0 equiv Ar2I was the-
oretically necessary.
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Received: May 24, 2010
Published online: October 28, 2010
Chem. Eur. J. 2010, 16, 13519 – 13527
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13527