Reactions of diaryliodonium trifluoromethanesulfonates with low-valent ytterbium and samarium reagents

Article abstract of DOI:10.1016/S0022-328X(00)00402-2

The reduction of diaryliodonium trifluoromethanesulfonates with low-valent ytterbium and samarium reagents has been studied. In the reaction of diphenyliodonium trifluoromethanesulfonate with two equimolar amounts of metallic ytterbium, benzene is formed

Full text of DOI:10.1016/S0022-328X(00)00402-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 611 (2000) 509–513
Reactions of diaryliodonium trifluoromethanesulfonates with
low-valent ytterbium and samarium reagents
Yoshikazu Makioka, Yuzo Fujiwara, Tsugio Kitamura *
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu Uni6ersity, Hakozaki, Fukuoka 812-8581, Japan
Received 28 February 2000; accepted 26 March 2000
Abstract
The reduction of diaryliodonium trifluoromethanesulfonates with low-valent ytterbium and samarium reagents has been
studied. In the reaction of diphenyliodonium trifluoromethanesulfonate with two equimolar amounts of metallic ytterbium,
benzene is formed almost quantitatively. On the other hand, iodobenzene is produced together with benzene in the reaction with
divalent YbI or SmI . The intermediates generated in situ by the reaction of arylphenyliodonium trifluoromethanesulfonates and
2
2
metallic ytterbium are trapped with methylphenylsilane to afford diphenylmethylsilane and arylmethylphenylsilanes. With respect
to the substituent effect on the aromatic ring of the arylphenyliodonium salts, electron-donating groups favor the formation of
arylmethylphenylsilanes rather than diphenylmethylsilane, whereas electron-withdrawing groups induce the favorable production
of diphenylmethylsilane. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Hypervalent iodine compound; Diaryliodonium salt; Low-valent lanthanoid; Ytterbium; Reduction; Hydrosilane
1
. Introduction
naturally arouse our interest. Herein we wish to report
on the chemical behavior of diaryliodonium trifl-
uoromethanesulfonates with low-valent lanthanoid
reductants.
Hypervalent iodine compounds have become of great
interest in recent years owing to their biological and
chemical uniqueness [1]. Among them, diaryliodonium
salts can be regarded as precursors of aryl carbocations
and utilized in the reactions coupling with various
nucleophiles. Diaryliodonium salts exhibit another as-
pect of an electron acceptor, and the photochemical [2]
and electrochemical [3] reductions of diaryliodonium
salts have been well documented. However, much less
has been reported on the reactions of diaryliodonium
salts with low-valent metallic reductants [4]. In particu-
lar, to the best of our knowledge no publications have
dealt with lanthanoid induced reductions of diaryliodo-
nium salts in spite of their strong reducing power [5].
We have established synthetic reactions induced by
lanthanoid metals and revealed their unique reactivity
of organolanthanoid(II) iodides to hydrosilanes and
carbonyl compounds [6]. Thus, the combination of
those oxidants and low-valent lanthanoid reductants
2. Results and discussion
The reaction of diphenyliodonium trifluoromethane-
sulfonate (1a) (0.50 mmol) with zerovalent Yb (40
mesh, 1.0 mmol) in THF at 0°C for 1 h gave 0.99 mmol
(199%) of benzene. However, either iodobenzene or
phenyl trifluoromethanesulfonate was not produced.
When a similar reaction was carried out in the presence
of methylphenylsilane (2.0 mmol) for 12 h, diphenyl-
methylsilane (2a) (0.35 mmol, 70%) was produced
(
70%) together with benzene (0.55 mmol, 110%) (Eq.
(
1)). On the other hand, the reaction of 1a with Yb at
0
°C for 1 h, followed by treating with cyclohexanone
(
1.0 mmol) afforded 1-phenylcyclohexanol (3) (0.32
mmol) in 65% yield. These results are the evidence
supporting that phenylytterbium species whose phenyl
moiety is anionic are in situ formed by the electron
transfer from low-valent ytterbium to 1a.
*
Corresponding author. Tel.: +81-92-6423549; fax: +81-92-
6
515606.
E-mail address: tkitatcf@mbox.nc.kyushu-u.ac.jp (T. Kitamura).
0
022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00402-2

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10
Y. Makioka et al. / Journal of Organometallic Chemistry 611 (2000) 509–513
+
−
Ph2I
OTf+Yb+PhMeSiH ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁPh MeSiH
of Ph MeSiH (2a) could be observed when MePhSiH
2
2
2
2
1
a
THF, 0°C, 3 h 2a (70%)
was present in those two reactions. Instead, the reaction
of 1a with YbI or SmI in the presence of cyclohexa-
none afforded the alcohol 4 in 58 and 85%, respectively
Eq. (2)).
PhI+ PhH
+ (
0%)
(1)
(110%)
2
2
Other lanthanoid reducing agents were also tested for
the reaction of the diaryliodonium salt 1a. Using ze-
rovalent samarium in lieu of ytterbium resulted in no
(
(2)
reaction. In the case of YbI [7], a divalent ytterbium,
2
which acts as a one-electron reductant in various trans-
formations of organic functional groups [8,9], benzene
and iodobenzene were produced in 99 and 79% yields,
respectively. SmI [7] also reduced 1a to give benzene
2
As Ph MeSiH (2a) was formed in the reaction of 1a
2
(
94%) and iodobenzene (92%). However, no formation
with excess Yb in the presence of MePhSiH , the effect
2
of the amounts of Yb on the product distribution was
investigated (Table 1). As mentioned above, 2a was
obtained together with benzene when two equivalents
of Yb were treated with 1a, but no iodobenzene could
be detected on GC (Entry 1). On the contrary, iodoben-
zene was produced in 34% yield in the reaction with an
equimolar amount of Yb (Entry 3). Table 1 indicates
that decreasing the amount of Yb causes the decrease in
the yield of 2a and the increase of iodobenzene. How-
ever, production of benzene seems to be independent on
the variation of the amount of Yb. A similar phe-
nomenon was observed in the trapping experiment with
a ketone. The reaction of 1a with one equivalent of Yb,
followed by trapping with cyclohexanone gave 4 and
iodobenzene in 38 and 38% yields, respectively.
Table 1
Influence of the amounts of Yb on the product distribution in the
reaction of diphenyliodonium trifluoromethanesulfonate (1a) with Yb
and PhMeSiH2
Entry
Yb (equivalent to 1a)
Yields (%) a
Ph MeSiH
PhI
PhH
2
1
2
3
4
2.0
1.0
0.66
0.33
70
30
18
7
0
34
48
66
110
126
122
100
a
GC yields.
Table 2
Next, the reaction of arylphenyliodonium salts 1a–d
Reaction of arylphenyliodonium trifluoromethanesulfonates 1 with
Yb in the presence of PhMeSiH2
with Yb in the presence of MePhSiH were performed
2
in order to investigate the relationship between the
substituent of 1 and the selectivity of the products. The
results are summarized in Table 2. In all reactions,
neither iodobenzene nor aryl iodides could be detected
on GC. In the reaction of phenyl(p-tolyl)iodonium- (1b)
+
−
Yields (%) a
Entry
ArPhI OTf, Ar
Ph MeSiH
ArPhMeSiH
2
a
1
2
3
4
5
6
Ph (1a)
70 (2a)
24 (2a)
14 (2a)
31 (2a)
12 (2a)
28 (2a)
p-MeC H4 (1b)
42 (2b)
21 (2c)
6
and
p-anisylphenyliodonium
trifluoromethanesul-
p-MeOC H4 (1c)
6
fonates (1c), which have electron donating groups on
the aromatic rings, p-tolyl- and p-anisyl-substituted
monohydrosilanes 2b and 2c were predominantly pro-
duced (Entries 2 and 3). On the other hand, 2a was
afforded in superior yield compared with (p-
ClC H )PhMeSiH (2d), which contains an electron-
p-ClC H4 (1d)
15 (2d)
6
b
2,4,6-Me C H (1e)
2,4,6- Pr C H (1f)
3
6
2
i
c
3
6
2
a
GC yields.
2
2
b
c
,4,6-Me C H I was formed in 59% yield.
3 6 2
i
6
4
,4,6- Pr C H I was formed in 28% yield.
3 6 2
withdrawing
group
(Entry
4).
Although
mesitylphenyliodonium- and phenyl(2,4,6-triisopropyl-
phenyl)iodonium salts 1e and 1f reacted with metallic
ytterbium, only 2a was produced in 12 and 28% yields,
respectively, as the silylated products (Entries 5 and 6).
In addition, iodomesitylene (59%) and 1-iodo-2,4,6-tri-
isopropylbenzene (28%) were formed.
Table 3
Reduction of ArPhIOTf 1 with ytterbium (0.33 equivalents)
Entry
Iodonium salt, Ar
Yields (%)a
PhH
ArH
PhI
ArI
To investigate the pathway for the formation of
monohydrosilanes 2, the reductions of 1a–d with a 0.33
equivalents of Yb were examined (Table 3). In these
reactions, PhH, ArH, PhI, and ArI were produced.
With respect to the production of PhH and ArH, the
yields of ArH were less than those of PhH in the
reaction of 1b and 1c (Entries 2 and 3), whereas
1
2
3
4
5
6
Ph (1a)
80
47
59
21
67
28
–
76
27
21
58
17
47
–
p-MeC H4 (1b)
29
26
65
21
60
50
59
19
68
37
6
p-MeOC H4 (1c)
6
p-ClC H4 (1d)
6
2,4,6-Me C H (1e)
3
6
2
i
2,4,6- Pr C H (1f)
3
6
2
a
GC yields.

Y. Makioka et al. / Journal of Organometallic Chemistry 611 (2000) 509–513
511
In summary, we first investigated the chemical behav-
ior of diaryliodonium trifluoromethanesulfonates to-
wards low-valent lanthanoids and revealed that two
kinds of reduction occur stepwise. Synthetic application
of diaryliodonium salt/lanthanoid reagents is currently
under way.
3
. Experimental
3.1. Measurements and materials
Melting points were determined with a Yanaco melt-
1
13
ing point apparatus and are uncorrected. H- and C-
NMR spectra were recorded on a JEOL JNM-AL300
spectrometer, and chemical shifts were expressed in l
ppm downfield from tetramethylsilane. IR spectra were
recorded on a HORIBA FT-200 IR spectrophotometer.
Analytical GC evaluations of product mixtures were
performed on a Shimadzu GC-9A flame ionization
chromatograph. Elemental analyses were performed by
the Service of the Elementary Analysis of Organic
Compounds, Graduate School of Science, Kyushu
University.
All reactions were performed under argon. THF was
distilled from sodium/benzophenone. Ytterbium (40
mesh) was washed with THF and dried under vacuum.
Arylphenyliodonium trifluoromethanesulfonates [12]
and lanthanoid(II) iodides [7] were prepared according
to the literature method. Other materials were commer-
cially available and used without further purification.
Scheme 1.
chlorobenzene was predominantly formed in the reac-
tion of 1d (Entry 4). In contrast, an opposite tendency
was observed for the yield of PhI and ArI; the reactions
of 1b and 1c gave ArI in better yields than PhI (Entries
and 3), whereas the reaction of 1d produced more
yield of PhI than that of 4-chloroiodobenzene (Entry
). Formation of ArH and PhI was superior in the
reduction of sterically hindered 1f (Entry 6). The
PhI:ArI ratios are in good agreement with the reported
data of the electrochemical one-electron reduction of
arylphenyliodonium bromides at mercury cathodes [3a]
and the CrCl -induced reductive coupling of
arylphenyliodonium tetrafluoroborates and benzalde-
hydes [4].
The first stage of the reactions of 1 with metallic
ytterbium should be the one-electron transfer from
zero- or divalent ytterbium to 1 to generate [9-I-2]
2
4
2
’
3.2. General procedure for the reduction of
arylphenyliodonium trifluoromethanesulfonates with
ytterbium in the presence of phenylmethylsilane
arylphenyliodanyl radicals [3,4], leading to Ar and PhI
or to Ph and ArI (Scheme 1). Since the alcohol 4 was
produced from the reduction of 1a with LnI (Ln=Sm
’
2
or Yb) [10], phenyl and aryl radicals should abstract a
hydrogen atom from THF to give benzene and ArH
together with a trihydrofuryl radical. However, the fate
of the trihydrofuryl radical, which is formed in the
reaction of 1 with lanthanoid reductants in the absence
of cyclohexanone, is still unknown. The further one-
electron reduction of phenyl or aryl radicals with diva-
lent ytterbium species to give phenyl and aryl anions
can be neglected because 2a was not formed from the
reaction of 1a with YbI or SmI .
On the other hand, no reaction occurred when
iodobenzene was treated with divalent YbI2 [7]. In
addition, the predominant formation of the more elec-
tron donating arylmethylphenylsilanes (Table 2) is
closely related to the preferential production of ArI
contains electron donating groups (Table 3) affects. It is
reasonable to consider that the second stage is the
two-electron transfer from zerovalent ytterbium to aryl
iodides to generate phenyl- and arylytterbium iodides
An arylphenyliodonium trifluoromethanesulfonate 1
0.50 mmol) was added into a 30 ml Schlenk tube
(
containing ytterbium (173 mg, 1.0 mmol), THF (3 ml)
and methylphenylsilane (244 mg, 2.0 mmol) at 0°C. The
mixture was stirred for 3 h at 0°C, followed by addition
of 0.1 ml of water. After n-eicosane as an internal
standard was added to the resulting mixture, the mix-
ture was analyzed by GC to qualify and quantify the
products. Separation of the products was performed by
2
2
column chromatography on SiO , using n-hexane as an
2
eluent.
Diphenylmethylsilane (2a): colorless liquid. IR (neat)
−
1
1
2121.3, 1261.2 cm
; H-NMR (CDCl ): l 0.62 (d,
3
J=4.0 Hz, 3H), 4.94 (q, J=4.0 Hz, 1H), 7.32–7.39 (m,
13
6H), 7.53–7.58 (m, 4H); C-NMR (CDCl ): l −5.0,
3
127.9, 129.5, 134.8, 135.3. These spectra are in good
agreement with those of the authentic sample commer-
cially available.
[
11], which undergo phenylation or arylation of
Methyl(4-methylphenyl)phenylsilane (2b): colorless
−
1
1
methylphenylsilane to give 2a–d [6a].
liquid. IR (neat) 2119.4, 1249.5 cm
;
H-NMR

5
12
Y. Makioka et al. / Journal of Organometallic Chemistry 611 (2000) 509–513
(
CDCl ): l 0.60 (d, J=3.6 Hz, 3H), 2.35 (s, 3H), 4.92
3.4. Reaction of diphenyliodonium
3
(
q, J=3.6 Hz, 1H), 7.19 (d, J=7.5 Hz, 2H), 7.34–7.36
trifluoromethanesulfonate (1a) with YbI or SmI and
cyclohexanone
2
2
(
m, 3H), 7.45 (d, J=3.6 Hz, 2H), 7.54–7.56 (m, 2H);
1
3
C-NMR (CDCl ): l −4.9, 21.5, 127.9, 128.8, 129.4,
3
1
31.6, 134.8, 134.9, 135.6, 139.5. Anal. Calc. for
A solution of samarium iodide (0.1 M in THF, 5.0
ml) or ytterbium iodide (0.04 M in THF, 12.5 ml) was
added into a Schlenk tube containing diphenyliodo-
nium trifluoromethanesulfonate (1a) (53.9 mg, 0.125
mmol) and cyclohexanone (98.1 mg, 1.0 mmol) at room
temperature. The resulting mixture was treated with 0.1
C H Si: C, 79.18; H, 7.59. Found: C, 79.30; H, 7.63%.
1
4
16
(
4-Methoxyphenyl)methylphenylsilane (2c): colorless
−
1
1
liquid. IR (neat) 2834.8, 2117.5, 1249.6 cm
NMR (CDCl ): l 0.59 (d, J=4.0 Hz, 3H), 3.81 (s, 3H),
; H-
3
4
7
.92 (q, J=4.0 Hz, 1H), 6.92 (d, J=8.6 Hz, 2H),
.35–7.37 (m, 2H), 7.47 (d, J=8.6 Hz, 2H), 7.53–7.56
ml of H O, and insoluble materials were removed by
2
1
3
(m, 3H); C-NMR (CDCl ): l −4.8, 55.0, 113.8,
3
short-column (SiO , ether). Yields of the products were
2
126.0, 127.9, 129.4, 134.8, 135.8, 136.3, 160.8. Anal.
quantified by gas chromatography using n-eicosane as
an internal standard. A similar workup to Section 3.3
afforded 1-(oxacyclopent-2-yl)cyclohexanol (4) as color-
Calc. for C H OSi: C, 73.63; H, 7.06. Found: C,
1
4
16
73.76; H, 7.24%.
(
4-Chlorophenyl)methylphenylsilane (2d): colorless
−1
1
less liquid. IR (neat) 3469.3, 1068.4 cm ; H-NMR
−
1
1
liquid. IR (neat) 2125.2, 1253.5 cm
;
H-NMR
(
1
CDCl ): l 1.21–1.93 (m, 15H), 3.68 (t, J=7.5 Hz,
3
(CDCl ): l 0.61 (d, J=3.6 Hz, 3H), 4.92 (q, J=3.6 Hz,
13
3
H), 3.78–3.85 (m, 2H); C-NMR (CDCl ): l 21.5,
3
13
1H), 7.32–7.54 (m, 9H); C-NMR (CDCl ): l −5.1,
3
2
1.6, 25.2, 25.8, 26.2, 32.8, 35.8, 68.6, 71.7, 85.3. Anal.
128.1, 128.2, 129.7, 133.7, 134.7, 135.9, 136.2. Anal.
Calc. for C H O : C, 70.55; H, 10.66. Found: C,
10
18
2
Calc. for C H ClSi: C, 67.08; H, 5.63. Found: C,
1
3
13
7
0.77; H, 10.8%.
66.82; H, 5.66%.
Iodomesitylene [14]: colorless needles; m.p. 29.8–
0.8°C (Lit. [14] 30–31°C). IR (neat) 2921.6, 1457.9,
3
1
2
2
−
1
1
Acknowledgements
004.7, 846.6 cm ; H-NMR (CDCl ): l 2.22 (s, 3H),
3
13
.42 (s, 6H), 6.87 (s, 2H); C-NMR (CDCl ): l 20.6,
3
This work was supported by a Grant-in-Aid for
Scientific Research on Priority Areas (A), The Chem-
istry of Inter-element Linkage (No. 11120242) from
Ministry of Education, Science, Sports and Culture,
Japan.
9.5, 104.2, 127.9, 137.2, 141.7.
1
-Iodo-2,4,6-triisopropylbenzene [14]: colorless oil.
−
1 1
IR (neat) 2960.2, 1461.8, 998.9, 873.6 cm ; H-NMR
CDCl ): l 1.24 (d, J=6.9 Hz, 12H), 1.25 (d, J=6.9
(
3
Hz, 6H), 2.87 (sep, J=6.9 Hz, 1H), 3.39 (sep, J=6.9
13
Hz, 2H), 6.95 (s, 2H); C-NMR (CDCl ) l 23.4, 24.0,
3
33.9, 39.2, 105.6, 122.0, 148.8, 150.7.
References
3
.3. Reaction of diphenyliodonium
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1
1
[
13] 62–63°C). IR (KBr) 3347.8 cm
;
H-NMR
[
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7
2
1
.21–7.25 (m, 1H), 7.31–7.37 (m, 2H), 7.49–7.52 (m,
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6
3 (1998) 7114.
1
3
3
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[
(
[
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