Isolation, Characterization, and Reaction of Activated Iodosylbenzene Monomer Hydroxy(phenyl)iodonium Ion with Hypervalent Bonding: Supramolecular Complex PhI+OH·18-Crown-6 with Secondary I...O Interactions

Article abstract of DOI:10.1021/ja0377899

The isolation, characterization, and reaction of the active species hydroxy(phenyl)iodonium ion with hypervalent bonding are reported. Reaction of iodosylbenzene with HBF₄-Me₂O in the presence of equimolar 18-crown-6 in dichloromethane afforded the hydroxy-λ³-iodane complex PhI(OH)BF₄·18-crown-6 as stable yellow prisms. X-ray structure analysis indicated that both the close contacts between the iodine(III) and the three adjacent oxygen atoms of 18-crown-6, and the hydrogen bonding OH...O(crown ether) will be responsible for the increased stability of the complex as compared to the uncomplexed PhI(OH)BF₄. The crown ether complex is highly reactive and serves as a versatile oxidant even in water: thus, the complex undergoes oxidative transformations of a variety of functional groups such as olefins, alkynes, enones, silyl enol ethers, sulfides, and phenols under mild conditions. Copyright

Full text of DOI:10.1021/ja0377899

Published on Web 10/03/2003
Isolation, Characterization, and Reaction of Activated Iodosylbenzene
Monomer Hydroxy(phenyl)iodonium Ion with Hypervalent Bonding:
Supramolecular Complex PhI+OH‚18-Crown-6 with Secondary I‚‚‚O
Interactions
Masahito Ochiai,*,† Kazunori Miyamoto,† Motoo Shiro,‡ Tomoyuki Ozawa,§ and Kentaro Yamaguchi§
Faculty of Pharmaceutical Sciences, UniVersity of Tokushima, 1-78 Shomachi, Tokushima 770-8505, Japan,
Rigaku Corporation, 3-9-12 Matsubara, Akishima, Tokyo 196-8666, Japan, and Chemical Analysis Center,
Chiba UniVersity, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
Received August 6, 2003; E-mail: mochiai@ph.tokushima-u.ac.jp
Iodosylbenzene (ISB), a versatile oxygen-atom transfer agent in
organic and biomimetic syntheses,1 is a polymer bridged by
secondary I‚‚‚O hypervalent interactions2 and hence is essentially
insoluble in all nonreactive organic solvents.3 In most of the
oxidations with ISB, addition of Brφnsted or Lewis acids is required
to increase the activity through its depolymerization or their
coordination to its oxygen atom.1 For instance, HBF4- or TfOH-
catalyzed reactions using ISB are believed to involve as a reactive
species the generation of the protonated hydroxy(phenyl)iodonium
ion PhI+OH that undergoes a variety of oxidative transformations
under mild conditions,4,5 while intermediacy of the zwitterionic
species 2 is proposed for the BF3-Et2O-catalyzed oxidations.6
Extensive spectroscopic studies by Richter, Koser, and co-workers
suggested that in an acidic aqueous solution ISB mostly exists as
hydroxy(phenyl)iodonium ion 1 (S ) H2O), ligated with at least
one water molecule at an apical site of the iodine(III) atom.7,8
Detailed structures of these reactive species in the solid state as
well as in solution, however, are virtually unknown, because their
isolation appears to be very difficult because of the lack of thermal
stability. In fact, the electrophilic hydroxy-λ3-iodane 1 (S ) BF4-),
generated from ISB by the reaction with HBF4-Me2O at -50 to 0
°C in dichloromethane, decomposes at room temperature within a
few minutes to give a black tar.5 Herein, we report the isolation
and characterization of the protonated ISB monomer 1 [S ) 18-
crown-6 (18C6)], stabilized by the coordination of 18C6 through
secondary I‚‚‚O bonding.9 The crystalline crown ether complex is
stable at ambient temperature, but reactive enough to effect
oxidations of a variety of functional groups under mild conditions.
Most importantly, the complexation with 18C6 dramatically
increased the stability of 1: thus, no decomposition of 1‚BF4
(S ) 18C6) was detected when it was left standing under ambient
conditions over 10 days. In solution, however, it gradually
decomposes at room temperature with half-life times (t1/2) of 6 h
in CD2Cl2 and 25 h in CD3CN. It should be noted that the complex
is more stable in water (t1/2 ) 5 days).
-
The 1H NMR spectrum of the complex in CD3CN showed simply
a sharp methylene singlet (δ 3.64 ppm) and a set of signals assigned
to the monosubstituted phenyl group [δ 8.26 (o), 7.81 (p), and 7.67
(m) ppm]. A broad exchangeable singlet with D2O at δ 8.01 ppm
indicates the presence of a hydroxy group, which was further
supported by the characteristic IR absorptions at 3533 and 2471
cm-1 10
The observed downfield shift (0.13 ppm) of a methylene
.
singlet in 1‚BF4- (S ) 18C6) as compared to that of 18C6 suggests
the complex formation between 1 (S ) BF4-) and 18C6 in solution.
The 13C resonance of 18C6 at δ 71.2 ppm is shifted to higher field
(δ 70.7 ppm) in the complex.
Firm evidence for the association in solution is obtained by mass
spectroscopy.9 Cold-spray ionization (CSI) MS for 1‚BF4 (S )
-
18C6) taken in positive mode in MeCN at -20 °C revealed the
most prominent peak of the molecular ion [PhIOH‚18C6]+ at m/z
485. Interestingly, in MeOH, a base peak corresponding to
[PhIOMe‚18C6]+ at m/z 499 was observed in addition to the
remarkable molecular ion peak, indicating the intervention of a
facile ligand exchange of the hydroxy group on the iodine(III) by
the solvent MeOH.11
Single crystals for X-ray analysis were obtained by recrystalli-
zation from acetone-hexane at -30 °C.12 Figure 1 reveals a
protonated iodosylbenzene structure with a single I(1)-O(1) bond,
which is slightly shorter than that predicted (1.99 Å) for covalent
radii but comparable to the reported values for [hydroxy(tosyloxy)-
iodo]benzene13 and cyclic hydroxy-λ3-iodanes.3b Including a close
contact between I(1) and a crown ether oxygen O(2) through
-
secondary bonding, the geometry around the iodine in 1‚BF4
(S ) 18C6) is T-shaped with a near-linear O(1)-I(1)‚‚‚O(2) triad
(171.7°). The close contact, in addition to the other weak I(1)‚‚‚
O(3) and I(1)‚‚‚O(4) bonding, will be responsible for increasing
the stability of the complex.
Strong intramolecular hydrogen bonding H(1O)‚‚‚O(5) (1.92 Å)
of the hydroxy ligand on the iodine(III) will also lead to the
enhanced thermal stability. The presumed highly acidic nature of
H(1O) will be responsible for the pronounced hydrogen bonding.14
The versatility of the supramolecular complex as an oxidizing
agent is noteworthy, and the reactions shown in Scheme 1 illustrate
the broad range of the utility. All of the reactions proceed smoothly
without further activation of the complex by adding an external
When the reaction of ISB with HBF4-Me2O was carried out in
the presence of equimolar 18C6 in dichloromethane at -78 to 0
°C, the complex 1‚BF4 (S ) 18C6) was obtained quantitatively
as a yellow powder after repeated decantation with hexane and
diethyl ether at -60 to -40 °C. The complex is soluble in MeCN,
MeOH, water, DMSO, and dichloromethane, but not in less polar
solvents (chloroform, benzene, diethyl ether, and ethyl acetate).
-
† University of Tokushima.
‡ Rigaku Corporation.
§ Chiba University.
9
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J. AM. CHEM. SOC. 2003, 125, 13006-13007
10.1021/ja0377899 CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
Chalcone and styrene afforded the rearranged acetals 6 and 7 in
MeOH, respectively, as reported by Moriarty.4 Oxidation of indene
in acetic acid in the presence of a small amount of acetic anhydride
gave the trans-diacetate 8 with 90% stereoselectivity, while the
reaction in dichloromethane-acetic acid, followed by acetylation
of the resulting vicinal diol monoacetate, produced selectively the
cis-diacetate 8 in 68% yield.15 Reaction of the silyl enol ether 11
in MeCN-water afforded the R-hydroxy ketone 9, while under
solvent-free conditions 1,4-diphenylbutane-1,4-dione was produced
in 74% yield.16 Phenyl-λ3-iodanation of 1-decyne catalyzed by HgO
afforded a 1:1 alkynyl-λ3-iodane‚18C6 complex 10 directly.17
In conclusion, we have synthesized the hydroxy-λ3-iodane
complex, coordinated by a neutral molecule, as stable crystals. The
λ3-iodane complex serves as a versatile oxidant.
Supporting Information Available: Experimental procedures,
compound characterization data for 3-10, CSI-MS (PDF), and X-ray
crystallographic data in CIF format for 1‚BF4 (S ) 18C6). This
-
Figure 1. ORTEP drawing of the complex 1‚BF4 (S ) 18C6). Selected
-
bond lengths (Å) and angles (deg): I(1)-C(1) 2.103(3), I(1)-O(1) 1.937-
(2), O(1)-H(1O) 0.71(4), I(1)‚‚‚O(2) 2.598(2), I(1)‚‚‚O(3) 2.910(2),
I(1)‚‚‚O(4) 3.137(2), O(1)-I(1)-C(1) 91.85(9).
material is available free of charge via the Internet at http://pubs.acs.org.
References
Scheme 1a
(1) (a) Varvoglis, A. The Organic Chemistry of Polycoordinated Iodine;
VCH: New York, 1992. (b) Zhdankin, V. V.; Stang, P. J. Chem. ReV.
2002, 102, 2523.
(2) Carmalt, C. J.; Crossley, J. G.; Knight, J. G.; Lightfoot, P.; Martin, A.;
Muldowney, M. P.; Norman, N. C.; Orpen, A. G. J. Chem. Soc., Chem.
Commun. 1994, 2367.
(3) Recently, a soluble monomeric ISB was elegantly synthesized by replacing
the intermolecular interactions with intramolecular I‚‚‚O contacts. See:
(a) Macikenas, D.; Skrzypczak-Jankun, E.; Protasiewicz, J. D. J. Am.
Chem. Soc. 1999, 121, 7164. (b) Macikenas, D.; Skrzypczak-Jankun, E.;
Protasiewicz, J. D. Angew. Chem., Int. Ed. 2000, 39, 2007.
(4) (a) Moriarty, R. M.; Khosrowshahi, J. S.; Prakash, O. Tetrahedron Lett.
1985, 26, 2961. (b) Kitamura, T.; Furuki, R.; Taniguchi, H.; Stang, P. J.
Tetrahedron 1992, 48, 7149.
(5) (a) Zhdankin, V. V.; Tykwinski, R.; Caple, R.; Berglund, B.; Koz’min,
A. S.; Zefirov, N. S. Tetrahedron Lett. 1988, 29, 3703. (b) Zhdankin, V.
V.; Mullikin, M.; Tykwinski, R.; Berglund, B.; Caple, R.; Zefirov, N. S.;
Koz’min, A. S. J. Org. Chem. 1989, 54, 2605.
(6) Ochiai, M. In Topics in Current Chemistry; Wirth, T., Ed.; Springer:
Berlin, 2003; Vol. 224, p 5.
(7) Richter, H. W.; Cherry, B. R.; Zook, T. D.; Koser, G. F. J. Am. Chem.
Soc. 1997, 119, 9614.
(8) The iodonium ion 1 (S ) H2O) was also assumed to be a primary
monomeric species, when [hydroxy(tosyloxy)iodo]benzene was dissolved
in water. See ref 7.
(9) (a) Ochiai, M.; Suefuji, T.; Miyamoto, K.; Tada, N.; Goto, S.; Shiro, M.;
Sakamoto, S.; Yamaguchi, K. J. Am. Chem. Soc. 2003, 125, 769. (b)
Ochiai, M.; Miyamoto, K.; Suefuji, T.; Sakamoto, S.; Yamaguchi, K.;
Shiro, M. Angew. Chem., Int. Ed. 2003, 42, 2191.
(10) The stretching vibration of a OH ligand on iodine(III) involved in strong
hydrogen bonding appears at 2400-2450 cm-1. See: (a) Baker, G. P.;
Mann, F. G.; Sheppard, M. N.; Tetlow, A. J. J. Chem. Soc. 1965, 3721.
(b) Moss, R. A.; Vijayaraghavan, S.; Emge, T. J. Chem. Commun. 1998,
1559. (c) Moss, R. A.; Wilk, B.; Krogh-Jespersen, K.; Blair, J. T.;
Westbrook, J. D. J. Am. Chem. Soc. 1989, 111, 250.
a Conditions: (a) 1-naphthol, H2O, 0 °C to room temperature (3 h), 67%;
(b) 2,4,6-trimethylphenol, H2O, 0 °C to room temperature (3 h), 92%; (c)
thioanisole, H2O, room temperature (3 h), 98%; (d) (E)-PhC(O)CHdCHPh,
MeOH, room temperature (18 h), 72%; (e) styrene, MeOH, 0 °C (1.5 h)
then room temperature (11 h), 73%; (f) indene, Ac2O, AcOH, 16 °C (1 h),
89% (trans-8); (g) (i) indene, CH2Cl2-AcOH (2.5:1), -20 °C (1.5 h), (ii)
Ac2O, pyridine, room temperature (2 days), 68% (cis-8); (h) PhC(OTMS)d
CH2 (11), MeCN-H2O (3:1), 0 °C (1 h), 73%; (i) 1-decyne, HgO, CH2Cl2,
room temperature (3 h), 56%.
(11) The ligand exchange with MeOH is further supported by the detection of
both ion peaks [PhIOH]+ and [PhIOMe]+. For a ligand exchange on
iodine(III), see ref 6.
(12) Crystallographic data for PhI(OH)BF4‚18C6: C18H30BF4IO7, M ) 572.14,
T ) 93 K, triclinic space group P-1 (No. 2), a ) 9.409(2) Å, b ) 11.449-
(3) Å, c ) 13.198(3) Å, â ) 112.33(2)°, V ) 1142.9(5) Å3, Z ) 2, Dc )
1.662 g cm-3, µ (Mo KR) ) 14.70 cm-1. 11 705 reflections were collected;
6428 were unique. R ) 0.050, Rw ) 0.083.
(13) Koser, G. F.; Wettach, R. H. J. Org. Chem. 1976, 41, 3609.
(14) The pKa value for the hydroxy ligand in 1‚BF4- (S ) 18C6) is estimated
to be around 5, because of the low basicity of 18C6. See ref 7.
(15) (a) Zhdankin, V. V.; Tykwinski, R.; Berglund, B.; Mullikin, M.; Caple,
R.; Zefirov, N. S.; Koz’min, A. S. J. Org. Chem. 1989, 54, 2609. (b)
Sengupta, S.; Mondal, S. Tetrahedron Lett. 1999, 40, 3469.
(16) Moriarty, R. M.; Prakash, O. Org. React. 1999, 54, 273.
(17) Yoshida, M.; Nishimura, N.; Hara, S. Chem. Commun. 2002, 1014.
acid catalyst, which indicates that the highly electrophilic nature
of Zhdankin’s hydroxy-λ3-iodane 1 (S ) BF4-) is maintained in
our crown ether complex. It is noted that the complex functions as
an efficient oxidizing agent even in water, because of both the
moderate solubility and the excellent stability in water. Thus,
oxidation of phenols, 1-naphthol and 2,4,6-trimethylphenol, with
-
1‚BF4 (S ) 18C6) in water at 0 °C afforded naphthoquinone (3)
and p-quinol 4, respectively, in good yields.1 Thioanisole gave a
98% yield of the sulfoxide 5 in water at room temperature with no
evidence for formation of methyl phenyl sulfone.
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