pH-selective synthesis and structures of alkynyl, acyl, and ketonyl intermediates in anti-markovnikov and markovnikov hydrations of a terminal alkyne with a water-soluble iridium aqua complex in water

Article abstract of DOI:10.1021/ja0473541

Chemoselective synthesis and isolation of alkynyl [Cp*Ir ^III(bpy)CCPh]⁺ (2, Cp* = η⁵-C ₅Me₅, bpy = 2,2′-bipyridine), acyl [Cp*Ir ^III(bPy)C(O)CH₂Ph]⁺ (3), and ketonyl [Cp*Ir^III(bpy)CH₂C(O)Ph]⁺ (4) intermediates in anti-Markovnikov and Markovnikov hydration of phenylacetylene in water have been achieved by changing the pH of the solution of a water-soluble aqua complex [Cp*Ir^III(bpy)(H₂O)] ²⁺ (1) used as the same starting complex. The alkynyl complex [2]₂·SO₄ was synthesized at pH 8 in the reaction of 1·SO₄ with H₂O at 25 °C, and was isolated as a yellow powder of 2·X (X = CF₃SO₃ or PF ₆) by exchanging the counteranion at pH 8. The acyl complex [3] ₂·SO₄ was synthesized by changing the pH of the aqueous solution of [2]₂·SO₄ from 8 to 1 at 25°C, and was isolated as a red powder of 3·PF₆ by exchanging the counteranion at pH 1. The hydration of phenylacetylene with 1·SO₄ at pH 4 at 25°C gave a mixture of [4] ₂·SO₄ and [4]₂·SO₄. After the counteranion was exchanged from SO₄^2- to CF ₃SO₃^-, the ketonyl complex 4·CF ₃SO₃ was separated from the mixture of 2·CF ₃SO₃ and 4·CF₃SO₃ because of the difference in solubility at pH 4 in water. The structures of 2-4 were established by IR with ¹³C-labeled phenylacetylene (Ph ¹²C≡¹³CH), electrospray ionization mass spectrometry (ESI-MS), and NMR studies including ¹H, ¹³C, distortionless enhancement by polarization transfer (DEPT), and correlation spectroscopy (COSY) experiments. The structures of 2·PF₆ and 3·PF₆ were unequivocally determined by X-ray analysis. Protonation of 3 and 4 gave an aldehyde (phenylacetaldehyde) and a ketone (acetophenone), respectively. Mechanism of the pH-selective anti-Markovnikov vs Markovnikov hydration has been discussed based on the effect of pH on the formation of 2-4. The origins of the alkynyl, acyl, and ketonyl ligands of 2-4 were determined by isotopic labeling experiments with D₂O and H ₂¹⁸O.

Full text of DOI:10.1021/ja0473541

Published on Web 11/23/2004
pH-Selective Synthesis and Structures of Alkynyl, Acyl, and
Ketonyl Intermediates in Anti-Markovnikov and Markovnikov
Hydrations of a Terminal Alkyne with a Water-Soluble Iridium
Aqua Complex in Water
Seiji Ogo,*,† Keiji Uehara,† Tsutomu Abura,† Yoshihito Watanabe,‡ and
Shunichi Fukuzumi*,†
Contribution from the Department of Material and Life Science, Graduate School of
Engineering, Osaka UniVersity, PRESTO & CREST, Japan Science and Technology Agency
(JST), Suita, Osaka 565-0871, Japan, and Department of Chemistry, Graduate School of
Science, Nagoya UniVersity, Chikusa-ku, Nagoya 464-8602, Japan
Received May 6, 2004; Revised Manuscript Received August 18, 2004; E-mail: ogo@ap.chem.eng.osaka-u.ac.jp
Abstract: Chemoselective synthesis and isolation of alkynyl [Cp*IrIII(bpy)CCPh]+ (2, Cp* ) η5-C5Me5, bpy
) 2,2′-bipyridine), acyl [Cp*IrIII(bpy)C(O)CH2Ph]+ (3), and ketonyl [Cp*IrIII(bpy)CH2C(O)Ph]+ (4) intermediates
in anti-Markovnikov and Markovnikov hydration of phenylacetylene in water have been achieved by changing
the pH of the solution of a water-soluble aqua complex [Cp*IrIII(bpy)(H2O)]2+ (1) used as the same starting
complex. The alkynyl complex [2]2‚SO4 was synthesized at pH 8 in the reaction of 1‚SO4 with H2O at 25
°C, and was isolated as a yellow powder of 2‚X (X ) CF3SO3 or PF6) by exchanging the counteranion at
pH 8. The acyl complex [3]2‚SO4 was synthesized by changing the pH of the aqueous solution of [2]2‚SO4
from 8 to 1 at 25 °C, and was isolated as a red powder of 3‚PF6 by exchanging the counteranion at pH 1.
The hydration of phenylacetylene with 1‚SO4 at pH 4 at 25 °C gave a mixture of [2]2‚SO4 and [4]2‚SO4.
2-
After the counteranion was exchanged from SO4 to CF3SO3-, the ketonyl complex 4‚CF3SO3 was
separated from the mixture of 2‚CF3SO3 and 4‚CF3SO3 because of the difference in solubility at pH 4 in
water. The structures of 2-4 were established by IR with 13C-labeled phenylacetylene (Ph12Ct13CH),
electrospray ionization mass spectrometry (ESI-MS), and NMR studies including 1H, 13C, distortionless
enhancement by polarization transfer (DEPT), and correlation spectroscopy (COSY) experiments. The
structures of 2‚PF6 and 3‚PF6 were unequivocally determined by X-ray analysis. Protonation of 3 and 4
gave an aldehyde (phenylacetaldehyde) and a ketone (acetophenone), respectively. Mechanism of the
pH-selective anti-Markovnikov vs Markovnikov hydration has been discussed based on the effect of pH on
the formation of 2-4. The origins of the alkynyl, acyl, and ketonyl ligands of 2-4 were determined by
isotopic labeling experiments with D2O and H218O.
Introduction
Since Tokunaga and Wakatsuki reported on the first anti-
Markovnikov hydration of terminal alkynes into aldehydes
Organic synthesis catalyzed by transition metal complexes
in water is rapidly developing because the use of water as a
solvent, a reagent, and a ligand has many potential advantages
such as alleviation of environmental problems associated with
the use of organic solvents, simple isolation of organic products
by phase separation, and reaction-specific pH selectivity.1-7
(3) (a) Su¨ss-Fink, G.; Faure, M.; Ward, T. R. Angew. Chem., Int. Ed. 2002,
41, 99-101. (b) Cherioux, F.; Maisse-Francois, A.; Neels, A.; Stoeckli-
Evans, H.; Su¨ss-Fink, G. J. Chem. Soc., Dalton Trans. 2001, 14, 2184-
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Evans, H. New J. Chem. 1997, 21, 785-790. (d) Su¨ss-Fink, G.; Meister,
A.; Meister, G. Coord. Chem. ReV. 1995, 143, 97-111.
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Merbach, A. E.; Hedinger, R.; Hegetschweiler, K.; Alberto, R.; Prinz, U.;
Raabe, G.; Koelle, U.; Hall, S. Inorg. Chem. 2003, 42, 3516-3526. (b)
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U. Coord. Chem. ReV. 1994, 135/136, 623-650. (e) Koelle, U. New J.
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metallics 2004, 23, 3047-3052. (b) Ogo, S.; Uehara, K.; Abura, T.;
Fukuzumi, S. J. Am. Chem. Soc. 2004, 126, 3020-3021. (c) Hayashi, H.;
Ogo, S.; Abura, T.; Fukuzumi, S. J. Am. Chem. Soc. 2003, 125, 14266-
14267. (d) Abura, T.; Ogo, S.; Watanabe, Y.; Fukuzumi, S. J. Am. Chem.
Soc. 2003, 125, 4149-4154. (e) Ogo, S.; Nakai, H.; Watanabe, Y. J. Am.
Chem. Soc. 2002, 124, 597-601. (f) Ogo, S.; Abura, T.; Watanabe, Y.
Organometallics 2002, 21, 2964-2969.
† Osaka University, PRESTO & CREST, JST.
‡ Nagoya University.
(1) (a) Joo´, F. In Catalysis by Metal Complexes; Aqueous Organometallic
Catalysis 23; James, B. R., van Leeuwen, P. W. N. M., Series Eds.; Kluwer
Academic Publishers: Dordrecht, 2001; p 300, and references therein. (b)
Joo´, F. Acc. Chem. Res. 2002, 35, 738-745. (c) Joo´, F.; Kova´cs, J.; Be´nyei,
A. C.; Nadasdi, L.; Laurenczy, G. Chem. Eur. J. 2001, 7, 193-199. (d)
Laurenczy, G.; Joo´, F.; Nadasdi, L. Inorg. Chem. 2000, 39, 5083-5088.
(e) Joo´, F.; Kova´cs, J.; Katho´, AÄ .; Be´nyei, A. C.; Decuir, T.; Darensbourg,
D. J. Inorg. Synth. 1998, 32, 1-45. (f) Joo´, F.; Kova´cs, J.; Be´nyei, A. C.;
Katho´, AÄ . Angew. Chem., Int. Ed. 1998, 37, 969-970.
(2) (a) Cornils, B.; Herrmann, W. A. Aqueous-Phase Organometallic Cataly-
sis: Concept and Applications, 2nd & rev. ed.; Wiley-VCH: Weinheim,
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9
16520
J. AM. CHEM. SOC. 2004, 126, 16520-16527
10.1021/ja0473541 CCC: $27.50 © 2004 American Chemical Society

Anti-Markovnikov and Markovnikov Hydration of Alkyne
A R T I C L E S
catalyzed by a ruthenium complex in organic solvents (vide
infra),8 a variety of transition metal complexes have been
investigated as catalysts for the anti-Markovnikov hydration in
organic solvents.9-12
(bpy)CH2C(O)Ph]+ (4) in the Markovnikov hydration of a
terminal alkyne (phenylacetylene) by using the same water-
soluble aqua complex [Cp*IrIII(bpy)(H2O)]2+ (1) as a starting
complex in water. The structures of 2-4 were established by
IR with 13C-labeled phenylacetylene (Ph12Ct13CH), electrospray
ionization mass spectrometry (ESI-MS), and 1H and 13C NMR
studies, which were assisted by the use of distortionless
enhancement by polarization transfer (DEPT) and correlation
spectroscopy (COSY) techniques. The structures of 2 and 3 were
definitely determined by X-ray analysis. The isolation of 2-4
allowed us to investigate their reactivity toward H2O.
Experimental Section
Materials and Methods. All experiments were carried out under
an Ar atmosphere by using standard Schlenck techniques and a
glovebox. The aqua complex [Cp*IrIII(bpy)(H2O)]SO4 (1‚SO4) was
prepared by the method described in the literature.17 All chemicals
(highest purity available) were purchased from Aldrich Chemicals Co.
and used without further purification. The manipulations in acidic media
were carried out with plasticware and glassware (without metals). D2O
(99.9% D) and 40% NaOD/D2O (99% D) were purchased from
Cambridge Isotope Laboratories. H218O (96.5% 18O), 65% DNO3/D2O
(99% D), and 13C-labeled phenylacetylene (Ph12Ct13CH, 99% 13C) were
purchased from Isotec Inc. Purification of water (18.2 MΩ cm) was
performed with a Milli-Q system (Millipore; Milli-RO 5 plus and
Milli-Q plus). The spectra of 1H and 13C NMR, DEPT-135, and H-H
and C-H COSY were recorded on JEOL-JNM-AL300 and JEOL-JNM-
ECP400 spectrometers at 25 °C. IR spectra of solid samples were
recorded on a Thermo Nicolet NEXUS 870 FT-IR instrument using 2
cm-1 standard resolution at ambient temperature, and infrared spectra
of aqueous solutions were obtained by an ASI ReactIR 1000 spectro-
photometer under an Ar atmosphere. ESI-MS data were collected on
an API 365 triple quadrupole mass spectrometer (PE-Sciex) in positive
detection mode, equipped with an ion spray interface. The sprayer was
held at a potential of +5.0 kV, and compressed N2 was employed to
assist liquid nebulization. The orifice potential was maintained at +20
V. A Nissin magnetic stirrer (Model SW-R800) was used.
Onishi and co-workers have shown the chemoselective
isolation of acyl complexes (as an intermediate of anti-
Markovnikov hydration) and ketonyl complexes (as an inter-
mediate of Markovnikov hydration) in organic solvents by
changing the substituent groups (R) in the hydrated alkynyl
complexes as follows.13
Anti-Markovnikov hydration of terminal alkynes (such as
propargylic alcohols) catalyzed by ruthenium complexes in
aqueous media has recently been investigated.14-16 However,
chemoselective synthesis and isolation of the intermediates in
the transition metal catalyzed anti-Markovnikov and Markovni-
kov hydration of terminal alkynes in water rather than in organic
solvents have yet to be achieved.
We report herein the first example of pH-selective synthesis
and isolation of an alkynyl intermediate [Cp*IrIII(bpy)CCPh]+
(2, Cp* ) η5-C5Me5, bpy ) 2,2′-bipyridine) and an acyl
intermediate [Cp*IrIII(bpy)C(O)CH2Ph]+ (3) in the anti-Mar-
kovnikov hydration as well as a ketonyl intermediate [Cp*IrIII-
pH Adjustment. In a pH range of 1-9, pH values of the solutions
were determined by a pH meter (TOA, HM-18E) equipped with a pH
combination electrode (TOA, GS-5015C). The pH of the solution was
adjusted by using 1 M HNO3/H2O (pH 1-3), 0.1 M CH3COOH/CH3-
COONa (pH 4-6), and 0.2 M Na2HPO4/NaH2PO4 (pH 7-9) solutions.
During the reaction, a stainless steel micro pH probe (IQ Scientific
Instruments, Inc., PH15-SS) was dipped in the reaction mixture at 70
°C under an Ar atmosphere, and the pH of the solution was monitored
by a pH meter (IQ Scientific Instruments, Inc., IQ200). It was confirmed
that the pH of the solution does not change during the course of the
reactions under the conditions of this study. To determine the exact
(6) Li, C.-J.; Chan, T.-H. In Organic Reactions in Aqueous Media; John Wiley
& Sons: New York, 1997; p 199 and references therein.
(7) Auge´, J.; Beletskaya, I. P.; Cheprakov, A. V.; Fringuelli, F.; Gajewski, J.
J.; Garner, P. P.; Grieco, P. A.; Kobayashi, S.; Lubineau, A.; Parker, D.
T.; Piermatti, O.; Pizzo, F.; Queneau, Y. In Organic Synthesis in Water;
Grieco, P. A., Ed.:, Thomson Science: London, 1998; p 310 and references
therein.
1
pH values, the H NMR experiments were performed by dissolving
the samples in HNO3/H2O in an NMR tube (diameter ) 5.0 mm) with
a sealed capillary tube (diameter ) 1.5 mm) containing 3-(trimethyl-
silyl)propionic-2,2,3,3-d4 acid sodium salt (TSP, 500 mM, as the
reference with the methyl proton resonance set at 0.00 ppm) dissolved
in D2O (for deuterium lock). Values of pD were corrected by adding
0.4 to the observed values.18
[Cp*IrIII(bpy)CCPh]X (2‚X, Where X ) CF3SO3 or PF6). A
reaction of [Cp*IrIII(bpy)(OH2)]SO4 (1‚SO4, 30 mg, 50 µmol) with
phenylacetylene (25.5 mg, 250 µmol) in H2O (30 mL) at pH 8 at 25
°C for 10 min provides a yellow solution of [2]2‚SO4. To the solution
was added CF3SO3Na (17.2 mg, 100 µmol) or NH4PF6 (16.3 mg, 100
µmol) at pH 8 in water (3 mL), and the mixture was stirred for 1 min
(8) Tokunaga, M.; Wakatsuki, Y. Angew. Chem., Int. Ed. 1998, 37, 2867-
2869.
(9) Beller, M.; Seayad, J.; Tillack, A.; Jiao, H. Angew. Chem., Int. Ed. 2004,
43, 3368-3398.
(10) Alonso, F.; Beletskaya, I. P.; Yus, M. Chem. ReV. 2004, 104, 3079-3159.
(11) (a) Suzuki, T.; Tokunaga, M.; Wakatsuki, Y. Org. Lett. 2001, 3, 735-
737. (b) Tokunaga, M.; Suzuki, T.; Koga, N.; Fukushima, T.; Horiuchi,
A.; Wakatsuki, Y. J. Am. Chem. Soc. 2001, 123, 11917-11924.
(12) Grotjahn, D. B.; Incarvito, C. D.; Rheingold, A. L. Angew. Chem., Int. Ed.
2001, 40, 3884-3886.
(13) (a) Arikawa, Y.; Nishimura, Y.; Kawano, H.; Onishi, M. Organometallics
2003, 22, 3354-3356. (b) Arikawa, Y.; Nishimura, Y.; Ikeda, K.; Onishi,
M. J. Am. Chem. Soc. 2004, 126, 3706-3707.
(14) Suzuki, T.; Tokunaga, M.; Wakatsuki, Y. Tetrahedron Lett. 2002, 43, 7531-
7533.
(15) Alvarez, P.; Bassetti, M.; Gimeno, J.; Mancini, G. Tetrahedron Lett. 2001,
42, 8647-8470.
(16) Alessandro, N. D.; Deo, M. D.; Bonetti, M.; Tonucci, L.; Morvillo, A.;
Bressan, M. Eur. J. Inorg. Chem. 2004, 810-817.
(17) Ogo, S.; Makihara, N.; Kaneko, Y.; Watanabe, Y. Organometallics 2001,
20, 4903-4910.
(18) (a) Glasoe, P. K.; Long, F. A. J. Phys. Chem. 1960, 64, 188-190. (b)
Mikkelsen, K.; Nielsen, S. O. J. Phys. Chem. 1960, 64, 632-637.
9
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A R T I C L E S
Ogo et al.
to afford a yellow powder of 2‚CF3SO3 or 2‚PF6, which was collected
by filtration, washed with water, and dried in vacuo (yield of 2‚CF3-
SO3: 88% based on 1‚SO4; yield of 2‚PF6: 84% based on 1‚SO4). 1H
NMR of 2‚CF3SO3 (300 MHz, in CDCl3, reference to TMS, 25 °C):
δ 1.80 (s, 15H), 6.97 (d, 2H), 7.04 (m, 3H), 7.65 (t, 2H), 8.20 (t, 2H),
8.69 (d, 2H), 8.75 (d, 2H). 13C NMR of 2‚CF3SO3 (in CDCl3, reference
to TMS, 25 °C): δ 8.76 {s; η5-C5(CH3)5}, 87.33 {s; CtC}, 91.63 {s;
η5-C5(CH3)5}, 99.70 {s; CtC}, 125.28 {s; CH of bpy}, 125.75 {s;
CH of Ph}, 127.08 {s; CH of Ph}, 127.82 {s; CH of Ph}, 128.10 {s;
CH of Ph}, 131.71 {s; CH of Ph}, 139.98 {s; CH of bpy}, 151.03 {s;
CH of bpy}, 155.71 {s; CH of bpy}. Anal. Calcd for C29H28N2F3Ir1O3S1
(2‚CF3SO3): C, 47.47; H, 3.85; N, 3.82. Found: C, 47.18; H, 3.77; N,
3.81.
Figure 1. pH-dependent formation ratio of 2-4 on the reaction of 1 with
phenylacetylene in H2O at 70 °C after 10 min.
[Cp*IrIII(bpy)C(O)CH2Ph]PF6 (3‚PF6). Method A: The alkynyl
complex [2]2‚SO4 was prepared by the reaction of 1‚SO4 (30 mg, 50
µmol) with phenylacetylene (25.5 mg, 250 µmol) in H2O (30 mL) at
pH 8 at 25 °C for 10 min. The pH of the aqueous solution of [2]2‚SO4
was changed from 8 to 1 at 25 °C. To the solution was added NH4PF6
(16.3 mg, 100 µmol) in H2O (3 mL) to provide a red powder of 3‚PF6,
which was collected by filtration (yield: 78% based on 1‚SO4).
Method B: Phenylacetylene (51.0 mg, 50 mmol) was added to 0.1
M HNO3/H2O solution (20 mL) of 1‚SO4 (60 mg, 0.1 mmol). After
the solution was stirred at 70 °C for 10 min, the color of the solution
turned to red. To the solution was added NH4PF6 (16.3 mg, 0.1 mmol)
in H2O (3 mL) to form a red powder of 3‚PF6 {yield: 86% based on
1
1‚SO4}. H NMR (300 MHz, in CDCl3, reference to TMS, 25 °C): δ
1.64 (s, 15H), 3.44 (s, 2H), 6.43 (d, 2H), 6.93 (m, 3H), 7.72 (t, 2H),
8.07 (t, 2H), 8.23 (d, 2H), 8.88 (d, 2H). 13C NMR (in CDCl3, reference
to TMS, 25 °C): δ 8.36 {s; η5-C5(CH3)5}, 63.53 {s; C(O)CH2}, 92.64
{s; η5-C5(CH3)5}, 124.01 {s; CH of bpy}, 126.29 {s; CH of Ph}, 128.23
{s; CH of Ph}, 128.26 {s; CH of bpy}, 128.41 {s; CH of Ph}, 128.41
{s; CH of Ph}, 133.07 {s; CH of Ph}, 139.26 {s; CH of bpy}, 151.38
{s; CH of bpy}, 155.55 {s; CH of bpy}, 222.0.67 {s; C(O)CH2}. Anal.
Calcd for C28H30N2F6Ir1O1P1‚0.5H2O: C, 44.44; H, 4.12; N, 3.70.
Found: C, 44.44; H, 4.01.; N, 3.81.
Figure 2. 1H NMR spectrum of 2‚CF3SO3 in CDCl3 at 25 °C. TMS,
reference with the methyl proton resonance set at 0.00 ppm.
Data Center as Supplementary Publication Nos. CCDC-237677 and
237678, respectively. Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
{fax: (+44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk}. Mea-
surements were made on a Rigaku/MSC Mercury CCD diffractometer
with graphite monochromated Mo KR radiation (λ ) 0.7107 Å). Data
were collected and processed using the CrystalClear program (Rigaku).
All calculations were performed using the teXsan crystallographic
software package of Molecular Structure Corporation.
[Cp*IrIII(bpy)CH2C(O)Ph]CF3SO3 (4‚CF3SO3). The reaction of 1‚
SO4 (0.35 mmol) with phenylacetylene (1.75 mmol) in H2O (30 mL)
at pH 4 (0.1 M CH3COOH/CH3COONa buffer) at 25 °C for 10 min
gave a mixture of [2]2‚SO4 and [4]2‚SO4. To the solution was added
CF3SO3Na (3.5 mmol) in H2O (3 mL) at pH 4 to give the powder of
2‚CF3SO3, which was removed by filtration. The solution was extracted
with CHCl3. Upon evaporation of CHCl3, a brown powder was obtained.
The powder was recrystallized from MeOH/diethyl ether to provide a
very hygroscopic brown powder of 4‚CF3SO3 (yield: 29% based on
1
Results and Discussion
1‚SO4). H NMR (300 MHz, in CDCl3, reference to TMS, 25 °C): δ
1.66 (s, 15H), 3.06 (s, 2H), 7.00 (m, 5H), 7.43 (t, 2H), 7.97 (t, 2H),
8.30 (d, 2H), 8.40 (d, 2H). 13C NMR (in CDCl3, reference to TMS, 25
°C): δ 8.20 {s; η5-C5(CH3)5}, 15.0.75 {s; CH2C(O)}, 90.18 {s; η5-C5-
(CH3)5}, 124.41 {s; CH of bpy}, 126.50 {s; CH of Ph}, 127.73 {s; CH
of bpy}, 128.02 {s; CH of Ph}, 131.74 {s; CH of Ph}, 138.80 {s; CH
of bpy}, 139.05 {s; C of Ph}, 150.64 {s; CH of bpy}, 154.98 {s; C of
bpy}, 202.06 {s; C(O)CH2}. The ketonyl complex 4‚CF3SO3 is very
hygroscopic.
Typical Procedure for the Hydration of Phenylacetylene with
the Aqua Complex 1. The pH of the solution of 1‚SO4 (2.4 mg, 3.93
mmol) in H2O (0.5 mL) was adjusted by using HNO3/H2O, CH3COOH/
CH3COONa, Na2HPO4/NaH2PO4, and NaHCO3/NaOH. Ten equivalents
of phenylacetylene (4.0 mg, 39.3 mmol) was added to the solution.
The mixture was vigorously stirred (1000 rpm, Nissin magnetic stirrer
Model SW-R700) for 10 min at 70 °C. After it was cooled to 0 °C, a
counteranion salt was added to the resulting mixture. It was extracted
by CDCl3. The ratio of complexes 1-4 in the CDCl3 solution has been
determined by 1H NMR. It was confirmed that no reaction occurred in
the absence of complexes 1 (as blank experiments).
pH-Selective Synthesis and Structure of the Alkynyl
Complex 2. The water-soluble aqua complex 1‚SO4 reacts with
phenylacetylene in H2O at 25 °C for 10 min to give the water-
soluble alkynyl complex [2]2‚SO4. The formation of [2]2‚SO4
is pH-dependent as shown in Figure 1 (filled circles). The
alkynyl complex 2 was isolated as a yellow powder of 2‚CF3-
SO3 by addition of CF3SO3Na to the solution of [2]2‚SO4 at
pH 8 at 25 °C. The structure of 2‚CF3SO3 was established by
NMR (1H and 13C NMR, DEPT-135, and H-H and C-H
1
COSY), IR, and ESI-MS. Figure 2 shows H NMR spectrum
of 2‚CF3SO3 in CDCl3. The signal at 1.80 ppm corresponds to
the Cp* protons {C5(CH3)5} of 2‚CF3SO3. 13C NMR (S1),
DEPT-135 (S2), H-H COSY (S3), and C-H COSY (S4)
spectra of 2‚CF3SO3 are shown in the Supporting Information.
In an IR spectrum in the 1400-2600 cm-1 region as a KBr
disk of 2‚CF3SO3 (Figure 3a), a prominent peak at 2114 cm-1
was assigned to ν(CtC) that shifts to 2081 cm-1 by isotopic
substitution of a carbon atom in the alkynyl ligand (Ir-13Ct
12CPh, Figure 3b). The shift value (33 cm-1) agrees well with
X-ray Crystallographic Analysis. Crystallographic data for 2‚PF6
and 3‚PF6 have been deposited with the Cambridge Crystallographic
9
16522 J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004

Anti-Markovnikov and Markovnikov Hydration of Alkyne
A R T I C L E S
Figure 3. (a) IR spectrum of 2‚CF3SO3 as a KBr disk. (b) IR spectrum of
13C-labeled 2‚CF3SO3 {[Cp*IrIII(bpy)(13CCPh)](CF3SO3)} as a KBr disk.
Figure 5. 1H NMR spectrum of 3‚PF6 (a) and D-labeled 3‚PF6 (b) in CDCl3
at 25 °C. TMS, reference with the methyl proton resonance set at 0.00
ppm; †, CHCl3.
Figure 4. (a) Positive-ion ESI mass spectrum of 2‚CF3SO3 in H2O. (b)
Signal at m/z 585.2 for [2]+. Red circles, calculated isotopic distribution
for [2]+.
that expected by Hooke’s law calculation for a pure CtC
stretching mode. A positive-ion ESI mass spectrum of 2‚CF3-
SO3 in H2O is shown in Figure 4a. The prominent signal at m/z
585.2 {relative intensity (I) ) 100% in the range of m/z 400-
800} has a characteristic distribution of isotopomers (Figure
4b) that matches well with the calculated isotopic distribution
(red circles) for [2]+.
pH-Selective Synthesis and Structure of the Acyl Complex
3. The water-soluble acyl complex [3]2‚SO4 was synthesized
by changing the pH of the solution of the alkynyl complex [2]2‚
SO4 in H2O from 8 to 1 at 25 °C as shown in Figure 1 (open
circle). The acyl complex 3 was isolated as a red powder of
3‚PF6 by addition of NH4PF6 to the solution of [3]2‚SO4 at pH
Figure 6. (a) IR spectrum of 3‚PF6 as a KBr disk. (b) IR spectrum of
13C-labeled 3‚PF6 {[Cp*IrIII(bpy)(13C(O)CH2Ph)](CF3SO3)} as a KBr disk.
1. The structure of 3‚PF6 was determined by NMR (1H and 13
C
NMR, DEPT-135, and H-H and C-H COSY), IR, and ESI-
MS. Figure 5 shows the 1H NMR spectrum of 3‚PF6 in CDCl3.
The signal of the Cp* protons of 3 was observed at 1.64 ppm.
13C NMR (S5), DEPT-135 (S6), H-H COSY (S7), and C-H
COSY (S8) spectra of 3‚PF6 are shown in the Supporting
Information. Figure 6a shows an IR spectrum in the 1400-
1800 cm-1 region as a KBr disk of 3‚PF6. The peaks at 1632
and 1644 cm-1 shifted to 1593 and 1605 cm-1 by isotopic
substitution of 12C for 13C in the CdO group (Figure 6b). A
positive-ion ESI mass spectrum of [3]2‚SO4 in H2O shows a
prominent signal at m/z 603.2 (I ) 100% in the range of m/z
400-800, Figure 7a), which has a characteristic distribution of
isotopomers (Figure 7b) that matches well with the calculated
isotopic distribution (red circles) for [3]+.
It is known that acyl complexes can arrive from vinylidene
species.19 It has also been proposed that anti-Markovnikov
hydration of alkynes proceeds through vinylidene inter-
mediates.20-25 However, such vinylidene species were not
observed in our hydration system with the Ir complexes in water.
(19) Bianchini, C.; Casares, J. A.; Peruzzini, M.; Romerosa, A.; Zanobini, F. J.
Am. Chem. Soc. 1996, 118, 4585-4594.
(20) Bianchini, C.; Peruzzini, M.; Zanobini, F.; Lopez, C.; de los Rios, I.;
Romerosa, A. Chem. Commun. 1999, 443-444.
(21) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Pe´rez-Carren˜o, E.; Garc´ıa-Granda,
S. Organometallics 1999, 18, 2821-2832.
(22) Baya, M.; Crochet, P.; Esteruelas, M. A.; Lo´pes, A. M.; Modrego, J.; On˜ate,
E. Organometallics, 2001, 20, 4291-4294.
(23) del R´ıo, I.; Gossage, R. A.; Hannu, M. S.; Lutz, M.; Spek, A. L.; van
Koten, G. Organometallics 1999, 18, 1097-1105.
(24) Katayama, H.; Wada, C.; Taniguchi, K.; Ozawa, F. Organometallics 2002,
21, 3285-3291.
9
J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004 16523

A R T I C L E S
Ogo et al.
Figure 7. (a) Positive-ion ESI mass spectrum of [3]2‚SO4 in H2O. (b) The
signal at m/z 603.2 corresponds to 3. Red circles, calculated isotopic
distribution for [3]+. (c) Positive-ion ESI-MS spectrum of 18O-labeled 3.
Red circles, calculated isotopic distribution for [18O-labeled 3]+.
pH-Selective Synthesis and Structure of the Ketonyl
Complex 4. The reaction of 1‚SO4 with phenylacetylene in H2O
at pH 4 at 25 °C for 10 min gave a mixture of [2]2‚SO4 and
[4]2‚SO4 as shown in Figure 1 (filled squares). To the solution
was added CF3SO3Na in H2O at pH 4 to give the powder of
2‚CF3SO3, which was removed by filtration. The solution was
extracted with CHCl3. Upon evaporation of CHCl3, a brown
powder was obtained. After recrystallization (MeOH/diethyl
ether), we isolated a very hygroscopic brown powder of 4‚CF3-
SO3. The structure of 4‚CF3SO3 was determined by NMR (1H
and 13C NMR, DEPT-135, and H-H and C-H COSY), IR,
and ESI-MS. Figure 8 shows the 1H NMR spectrum of 4‚CF3-
SO3 in CDCl3. The signal at 1.66 ppm corresponds to the Cp*
protons of 4‚CF3SO3. 13C NMR (S9), DEPT-135 (S10), H-H
COSY (S11), and C-H COSY (S12) spectra of 4‚CF3SO3 are
shown in the Supporting Information. Figure 9 shows an IR
spectrum in the 1200-2000 cm-1 region as a KBr disk of 4‚
CF3SO3. A positive-ion ESI mass spectrum of 4‚CF3SO3 in CH3-
Cl shows a prominent signal at m/z 603.2 (I ) 100% in the
range of m/z 400-800, Figure S13), which coincides with the
signal observed in the ESI mass spectrum of the acyl complex
[3]+ as shown in Figure 7a.
1
Figure 8. (a) H NMR spectrum of 4‚CF3SO3 in CDCl3 at 25 °C. TMS,
reference with the methyl proton resonance set at 0.00 ppm; †, CHCl3. (b)
1H NMR spectrum of D-labeled 4‚CF3SO3 in CDCl3 at 25 °C. (c) 2H NMR
spectrum of D-labeled 4‚CF3SO3 in CHCl3. ‡, CDCl3
Crystal Structure of the Alkynyl Complex 2. Yellow
crystals of 2‚PF6 used for the X-ray analysis were obtained from
MeOH/diethyl ether. Crystal data, data collection parameters,
and structure refinement for 2‚PF6 are listed in Table 1. Selected
bond lengths and angles for 2‚PF6 are listed in Table 2. An
ORTEP drawing of 2 is shown in Figure 10. Complex 2 adopts
a distorted octahedral coordination that is surrounded by one
Cp*, one bpy, and one alkynyl ligand. The Ir1-C1 bond length
of 2 is 2.006(9) Å, which is very close to the metal-C bond
length observed in [Cp*Ru(CCH)(PEt3)2H]BPh4 {2.034(4)
Å},25a [Ru(CCH)(cym)(phen)]BAr′4 (cym ) η6-4-methyliso-
propylbenzene, phen ) 1,10-phenanthroline, Ar′ ) 3,5-bis-
(25) (a) Bustelo, E.; Carbo´, J. J.; Lledo´s, A.; Mereiter, K.; Puerta, M. C.; Valerga,
P. J. Am. Chem. Soc. 2003, 125, 3311-3321. (b) Aneetha, H.; Jime´nez-
Tenorio, M.; Puerta, M. C.; Valerga, P.; Mereiter, K. Organometallics 2003,
22, 2001-2013. (c) Tenorio, M. A. J.; Tenorio, M. J.; Puerta, M. C.;
Valerga, P. Organometallics 2000, 19, 1333-1342. (d) Bustelo, E.;
Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. Organometallics 1999,
18, 950-951. (e) de los R´ıos, I.; Tenorio, M. J.; Puerta, M. C.; Valerga, P.
J. Am. Chem. Soc. 1997, 119, 6529-6538.
Figure 9. IR spectrum of 4‚CF3SO3 as a KBr disk.
(trifluoromethyl)phenyl) {2.022(9) Å},26 and [Cp*Ir(CCCMe3)-
(Pro)(phen)] (Pro ) L-prolinate) {2.012(8) Å}27 within the error
limits. The C1-C2 bond length of 1 is 1.21(1) Å, which is
9
16524 J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004

Anti-Markovnikov and Markovnikov Hydration of Alkyne
A R T I C L E S
Table 1. Summary of Crystal Data, Data Collection Parameters,
and Structure Refinement for {[Cp*IrIII(bpy)CCPh](PF6)} 2‚PF6 and
{[Cp*IrIII(bpy)C(O)CH2Ph](PF6)} 3‚PF6
compound
empirical formula
fw
2‚PF6
C28H28F6IrN2P
729.73
3‚PF6
C28H30F6IrN2OP
747.74
cryst color
cryst dimen (mm)
cryst syst
a (Å)
b (Å)
c (Å)
yellow
orange
0.20 × 0.12 × 0.12 0.20 × 0.18 × 0.15
monoclinic
13.158(1)
13.577(1)
16.160(2)
88.936(6)
2886.2(5)
P21/c (14)
4
monoclinic
14.873(5)
12.882(4)
29.567(10)
95.768(4)
5635(3)
P21/c (14)
8
â (deg)
V (Å3)
space group (No.)
Z
D
calc (g cm-3
)
1.679
1.762
F000
1424
4.752
0.7107
-50.0
55
numerical
2928
4.872
µ(Mo KR) (cm-1
radiation (λ, Å)
temp (°C)
)
0.7107
-100.0
55
numerical
12891
703
0.076
0.098
0.045
0.92
2θmax (deg)
abs corr method
Figure 10. ORTEP drawing of 2. The counteranion (PF6) is omitted for
clarity.
no. of reflns obsd (all, 2θ < 54.97°) 6586
no. of params
343
Table 3. Selected Bond Lengths (l/Å) and Angles (φ/deg) for
3‚PF6
Ra
0.107
0.155
0.056
1.04
0.004
4.52
b
Rw
R1c
Ir1-C1
2.037(8)
2.080(5)
1.229(9)
2.253(7)
2.179(7)
2.171(7)
1.45(1)
Ir1-N1
2.067(6)
1.54(1)
1.52(1)
2.259(7)
2.192(7)
1.38(1)
1.43(1)
1.44(1)
goodness of fit indicator, Sd
max shift/error in final cycle
max peak in final diff map (e Å-3
Ir1-N2
C1-C2
0.002
5.36
-3.41
C1-O1
C2-C3
)
)
Ir1-C19
Ir1-C21
Ir1-C23
C19-C23
C21-C22
Ir1-C20
Ir1-C22
C19-C20
C20-C21
C22-C23
min peak in final diff map (e Å-3
-3.69
2
2
2
2
a R ) ∑(Fo2 - Fc )/∑Fo . b Rw ) [∑w(Fo2 - Fc )2/∑w(Fo )2]1/2
.
c R1 )
2
∑||Fo | - |Fc||/∑|Fo| for I > 2.0σ(I) data. d Goodness of fit indicator, S )
[Sw(|Fo| - |Fc|)2/(No - Nv)]1/2 (No ) number of observations, Nv ) number
of variables).
1.43(1)
Ir1-C1-C2
123.4(6)
111.3(6)
82.6(2)
35.6(3)
37.5(3)
38.5(2)
Ir1-C1-O1
C1-Ir1-N1
N1-Ir1-N2
C19-Ir1-C23
C21-Ir1-C22
119.6(6)
91.9(3)
77.4(2)
38.3(3)
38.3(2)
C1-C2-C3
C1-Ir1-N2
C19-Ir1-C20
C20-Ir1-C21
C22-Ir1-C23
Table 2. Selected Bond Lengths (l/Å) and Angles (φ/deg) for
2‚PF6
Ir1-C1
2.006(9)
2.095(8)
1.49(1)
2.19(1)
2.17(1)
1.44(2)
1.40(2)
1.40(1)
Ir1-N1
2.089(8)
1.21(1)
2.22(1)
2.15(1)
2.19(1)
1.42(1)
1.41(1)
Ir1-N2
C1-C2
C2-C3
Ir1-C19
Ir1-C21
Ir1-C23
C19-C23
C21-C22
Ir1-C20
Ir1-C22
C19-C20
C20-C21
C22-C23
Ir1-C1-C2
C1-Ir1-N1
N1-Ir1-N2
C19-Ir1-C23
C21-Ir1-C22
174.3(9)
91.3(3)
76.4(3)
37.7(4)
38.1(4)
C1-C2-C3
178(1)
87.6(4)
38.1(4)
37.6(4)
37.4(4)
C1-Ir1-N2
C19-Ir1-C20
C20-Ir1-C21
C22-Ir1-C23
close to a carbon-carbon triple bond {1.20(2) Å} of an alkynyl
complex which was determined previously by X-ray analysis.28
Crystal Structure of the Acyl Complex 3. Orange crystals
of 3‚PF6 obtained from CHCl3/diethyl ether were used for the
X-ray analysis. Crystal data, data collection parameters, and
structure refinement for 3‚PF6 are listed in Table 1. Selected
bond lengths and angles for 3‚PF6 are listed in Table 3. As
depicted in Figure 11, complex 3 adopts a distorted octahedral
coordination that is surrounded by one Cp*, one bidentate bpy,
and one acyl ligand. The Ir1-C1 bond length of 3 is 2.037(8)
Å, which is very close to the Ru-C bond length observed in
[Ru(C(O)CH3)(cym)(phen)]BAr′4 {2.08(1) Å}.26 The distances
between the Ir atom and carbons of the Cp* ring of complex 3
Figure 11. ORTEP drawing of 3. The counteranion (PF6) is omitted for
clarity.
in the solid state are not equivalent; the distances of Ir1-C19
and Ir1-C20 {2.253(7) and 2.259(7) Å, respectively} trans to
the acyl ligand are longer than those of Ir1-C21, Ir1-C22,
and Ir1-C23 {2.179(7), 2.192(7), and 2.171(7) Å, respectively}
trans to the bpy ligand. This indicates that the acyl ligand has
a greater trans influence than the bpy ligand.
Reactivity of the Isolated Acyl Complex 3 and Ketonyl
Complex 4 in Acidic Media. Although the isolated acyl
complex 3‚PF6 was acid-stable above pH 0 (1 M HNO3/H2O),
it drastically reacted with 4 M HNO3/H2O (pH -0.6, 2.0 mL)
(26) Mene´ndez, C.; Morales, D.; Pe´rez, J.; Riera, V.; Miguel, D. Organometallics
2001, 20, 2775-2781.
(27) Carmona, D.; Vega, C.; Lahoz, F. J.; Atencio, R.; Oro, L. A.; Lamata, M.
P.; Viguri, F.; Jose´, E. S. Organometallics 2000, 19, 2273-2280.
(28) Manna, J.; John, K. D.; Hopkins, M. D. AdV. Organomet. Chem. 1995, 38,
79-154.
9
J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004 16525

A R T I C L E S
Ogo et al.
Table 4. Yield of Phenylacetaldehyde (A) and Acetophenone (K)a
0 equiv phenylacetylene (noncatalytic reaction with 3 or 4)
100 equiv phenylacetylene (catalytic reaction with 1)
pH 0. 6 pH 1
pH
−0. 6
pH 1
−
aqua complex 1
acyl complex 3
ketonyl complex 4
A
K
TON: 0.1
TON: 2
A
K
TON: 0
TON: 3
A
K
A
K
yield: 28%
yield: 0%
yield: 0%
yield: 100%
A
K
A
K
yield: 0%
yield: 0%
yield: 0%
yield: 100%
a The reactions were carried out at 70 °C for 10 min.
Scheme 1
Figure 12. (a) pH-dependent TON for formation of acetophenone from
reaction of 1‚SO4 (2.62 µmol) with phenylacetylene (262 µmol) in water
(1 mL) at 70 °C for 10 min. (b) Time course of the TONs of the hydration
of phenylacetylene from the reaction of 1‚SO4 (2.62 µmol) with phen-
ylacetylene (262 µmol) in water (1 mL) at pH 1 at 70 °C.
70 °C for 10 min to provide acetophenone (yield: 100% based
on 4‚CF3SO3). It was confirmed that no reaction occurred in
the absence of complex 1 or 4 (as blank experiments).
Isotopic Labeling Experiments. To establish the origin of
the acyl ligand in 3, the reaction of 1‚SO4 with phenylacetylene
at 70 °C for 10 min to yield phenylacetaldehyde (A in Table 4,
yield: 28% based on 3‚PF6), accompanied by regeneration of
1. The formation of 1 was confirmed by 1H NMR. The isolated
ketonyl complex 4‚CF3SO3 quantitatively reacted with H2O at
pH 1.0 in H2O at 70 °C for 10 min to provide acetophenone (K
in Table 4, yield: 100% based on 4‚CF3SO3). It was confirmed
that no isomerization of the acyl complex 3 into the ketonyl
complex 4 occurred at pH 1 or pH -0.6.
Catalytic Anti-Markovnikov and Markovnikov Hydra-
tions of Phenylacetylene with the Aqua Complex 1 in Acidic
Media. Under catalytic conditions, the aqua complex 1 reacted
with phenylacetylene (100 equiv) at pH 1 or pH -0.6 in H2O
at 70 °C for 10 min to give phenylacetaldehyde (anti-Mar-
kovnikov) and acetophenone (Markovnikov), as shown in Table
4. The turnover numbers (TON ) the number of moles of
acetophenone formed per mole of 1) of the catalytic reaction
of 1‚SO4 with 100 equiv of phenylacetylene at pH 1 in H2O at
70 °C for 10 min is pH-dependent, as shown in Figure 12a.
The rate of hydration shows a maximum around pH 1. Figure
12b illustrates the time course of the hydration of phenylacety-
lene with 1‚SO4 at pH 1 at 70 °C. The isolated ketonyl complex
4‚CF3SO3 quantitatively reacted with H2O at pH 1.0 in H2O at
1
was carried out at pD 1.4 in D2O at 70 °C. The results of H
NMR showed that the signal (observed at 3.44 ppm in Figure
5a) of the methylene protons of 3‚PF6 was disappeared in the
1H NMR spectrum (Figure 5b); i.e., the D atoms derived from
D2O were incorporated into the acyl ligand of 3‚PF6. The
reaction of 1‚SO4 with phenylacetylene was also carried out at
pH 1 in H218O at 70 °C. The results of ESI-MS (Figure 7c)
showed that the 18O atom from H218O was incorporated into
the acyl ligand of 3‚SO4.
Deuterium-labeled 4 was prepared by a reaction of 1‚SO4
with phenylacetylene in D2O at pD 4.4 at 0 °C for 10 min.29
The results of 1H NMR indicate that one of the methyl protons
of the ketonyl ligand is derived from the terminal proton of
phenylacetylene without H/D exchange at 25 °C (Figure 8b).
2
The results of H NMR show that the signal derived from the
(29) The isotopic labeling experiments were carried out at 0 °C to avoid the
back-reaction of 2 with protons.
9
16526 J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004

Anti-Markovnikov and Markovnikov Hydration of Alkyne
A R T I C L E S
D-labeled methylene protons of 4‚CF3SO3 is observed at 3.06
(anti-Markovnikov vs Markovnikov) results from only the
change in pH, the regioselectivity originates from different
attacking species (H+ or OH-) depending on pH as shown in
Scheme 1.
ppm (Figure 8c).
1
ESI-MS, H NMR, and GC-MS experiments using D2O or
H218O indicate that two of the methyl protons and one oxygen
atom of acetophenone are derived from D2O or H218O,
respectively.
In conclusion, we have succeeded in pH-selective isolation
of an alkynyl intermediate [Cp*IrIII(bpy)CCPh]+ (2) and an acyl
intermediate [Cp*IrIII(bpy)C(O)CH2Ph]+ (3) in the anti-Mar-
kovnikov hydration as well as a ketonyl intermediate [Cp*IrIII-
(bpy)CH2C(O)Ph]+ (4) in the Markovnikov hydration of a
terminal alkyne (phenylacetylene) by starting from the same
water-soluble aqua complex [Cp*IrIII(bpy)(H2O)]2+ (1). The
present study has provided valuable insight into the regiose-
lective and catalytic hydration of a terminal alkyne.
Mechanism of the pH-Selective anti-Markovnikov vs
Markovnikov Hydration. As shown in Figure 1, the formation
of 2-4 from the reaction of 1‚SO4 with phenylacetylene in H2O
at 70 °C for 10 min is pH-dependent. Scheme 1 summarizes
the effect of pH on the formation of 2-4. First, the reaction of
the aqua complex 1 with phenylacetylene may produce a
[M-phenylacetylene]2+ species (M ) Cp*IrIIIbpy) such as a
π-complex (Scheme 1). Deprotonation of the [M-phenylacety-
lene]2+ species occurs efficiently to give the alkynyl complex
2 around pH 8 (right-hand cycle in Scheme 1), in competition
with nucleophilic attack of OH- to the [M-phenylacetylene]2+
species to form the ketonyl complex 4 in a pH range of about
2-6 (left-hand cycle). Isotopic labeling experiments at 25 °C
(vide supra) clearly indicate that the ketonyl ligand of 4 is
derived from the terminal proton of phenylacetylene. At pH
1-2, the protonation of 2 may occur, followed by nucleophilic
attack of OH-, leading to the formation of the acyl complex 3
(right-hand cycle). The protonation of 3 and 4 gives phenyl-
acetaldehyde (anti-Markovnikov hydration) and acetophenone
(Markovnikov hydration), respectively. Since the regioselectivity
Acknowledgment. This work was supported by grants in aid
(15036242, 15350033, 16205020, and 16655022) from the
Ministry of Education, Culture, Sports, Science, and Technol-
ogy, Japan. We thank Professor K. Isobe (Kanazawa University)
and emeritus Professor A. Nakamura (Osaka University) for
valuable discussions.
Supporting Information Available: Figures S1-S13, show-
ing spectra for 2-4, and crystallographic data (CIF) for 2‚PF6
and 3‚PF6. This material is available free of charge via the
Internet at http://pubs.acs.org.
JA0473541
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J. AM. CHEM. SOC. VOL. 126, NO. 50, 2004 16527