Osmium(III) and osmium(V) complexes bearing a macrocyclic ligand: A simple and efficient catalytic system for cis-dihydroxylation of alkenes with hydrogen peroxide

Article abstract of DOI:10.1002/asia.201300329

A simple protocol that uses [Os^III(OH)(H₂O)(L-N ₄Me₂)](PF₆)₂ (1; L-N ₄Me₂=N,N′-dimethyl-2,11-diaza[3.3](2,6) pyridinophane) as a catalyst and H₂O₂ as a terminal oxidant for efficient cis-1,2-dihydroxylation of alkenes is presented. Unfunctionalized (or aliphatic) alkenes and alkenes/styrenes containing electron-withdrawing groups are selectively oxidized to the corresponding vicinal diols in good to excellent yields (46-99 %). In the catalytic reactions, the stoichiometry of alkene:H₂O₂ is 1:1, and thus the oxidant efficiency is very high. For the dihydroxylation of cyclohexene, the catalytic amount of 1 can be reduced to 0.01 mol % to achieve a very high turnover number of 5500. The active oxidant is identified as the Os ^V(O)(OH) species (2), which is formed via the hydroperoxide adduct, an Os^III(OOH) species. The active oxidant 2 is successfully isolated and crystallographically characterized. The wizard of Os: A simple protocol that uses [Os^III(OH)(H₂O)(L-N₄Me ₂)](PF₆)₂ (1) and H₂O₂ for efficient cis-1,2-dihydroxylation of alkenes is presented. Unfunctionalized (or aliphatic) alkenes and alkenes/styrenes containing electron-withdrawing groups were converted into the corresponding vicinal diols in good to excellent yields. It has been confirmed that the Os^V(O)(OH) species (2) is the active oxidant, which is formed via the hydroperoxide adduct A. Copyright

Full text of DOI:10.1002/asia.201300329

FULL PAPER
DOI: 10.1002/asia.201300329
Osmium ACHTUNGTRENNUNG( III) and Osmium(V) Complexes Bearing a Macrocyclic Ligand: A
Simple and Efficient Catalytic System for cis-Dihydroxylation of Alkenes
with Hydrogen Peroxide
[
a]
Hideki Sugimoto,* Kenji Ashikari, and Shinobu Itoh*
Abstract: A simple protocol that uses
corresponding vicinal diols in good to
excellent yields (46–99%). In the cata-
lytic reactions, the stoichiometry of al-
kene:H O is 1:1, and thus the oxidant
droxylation of cyclohexene, the catalyt-
ic amount of 1 can be reduced to
0.01 mol% to achieve a very high turn-
over number of 5500. The active oxi-
III
[Os (OH)
ACHTUNGTRENNUNG( H O) ACHTUNGTRENNUNG( L-N Me )] ACHUTGNTRENNUGN( PF ) (1;
2 4 2 6 2
L-N Me =N,N’-dimethyl-2,11-diaza-
4
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[3.3]
ACHTUNGTRENNUNG( 2,6)pyridinophane) as a catalyst
2
2
V
and H O as a terminal oxidant for effi-
efficiency is very high. For the dihy-
dant is identified as the Os (O)(OH)
2
2
cient cis-1,2-dihydroxylation of alkenes
is presented. Unfunctionalized (or ali-
phatic) alkenes and alkenes/styrenes
species (2), which is formed via the hy-
droperoxide adduct, an Os ACHTUNGTRENNUNG( OOH)
species. The active oxidant 2 is success-
fully isolated and crystallographically
characterized.
III
Keywords: alkenes · dihydroxyla-
tion · homogeneous catalysis · OꢀO
containing
electron-withdrawing
activation · osmium
groups are selectively oxidized to the
Introduction
NMO and flavin as co-catalysts and tetraethylammonium
acetate (TEAA) as an additive, making the system rather
complicated. Although K2 ACHTUNTGNERNUG[ Os O (OH) ] can be employed
2 4
[5]
VI
Catalytic cis-1,2-dihydroxylation of alkenes is an important
chemical transformation since it can be applied to the syn-
theses of biologically active natural products, pharmaceuti-
as a pre-catalyst for alkene cis-1,2-dihydroxylation, the
osmate is rapidly oxidized by the terminal oxidants to OsO4
[1]
[1]
cals, and fine chemicals. Osmium
A
H
U
G
E
N
N
(VIII) tetroxide (OsO ) is
as the active oxidant. Thus, the development of an efficient
4
a particularly useful oxidant for cis-1,2-dihydroxylation of
catalytic alkene cis-1,2-dihydroxylation by H O using
2
2
[6]
[1]
alkenes. However, OsO is quite toxic and volatile, making
a much simpler OsO -free catalyst is highly desired.
4
4
its handling and separation from the reaction solution trou-
One strategy for developing such catalytic system is based
on the use of osmium-free complexes with organic ligands.
Bioinspired non-heme iron, manganese, and ruthenium
ꢀ
1
blesome (LC =40 ppm, LD =0.01 gkg ). In order to
50
50
[7]
[8]
[9]
reduce the amount of OsO , terminal oxidants such as
4
K [Fe(CN) ] and N-methylmorpholine (NMO) are often
catalysts have been examined for alkene cis-1,2-dihydroxyla-
3
6
added, making the reaction catalytic with respect to
tion with H O . However, several drawbacks still remain in
2
2
[2,3]
OsO4.
Based on the concept of green or sustainable
these systems such as substrate limitation, low substrate and
oxidant conversion, low product selectivity, and require-
ments of co-catalysts and/or additives.
chemistry, however, the development of catalysts with high
[4]
atom efficiency and selectivity is important. In this regard,
hydrogen peroxide (H O ) is one of the most desirable oxi-
Recently, dioxo-osmium(VI) complexes that are capable
2
2
[10]
dants for cis-1,2-dihydroxylation of alkenes because it gives
00% atom efficiency when the four atoms (2H+2O) are
of reacting with alkenes were reported. This means that
VIII
1
osmium reagents of lower oxidation numbers than Os
incorporated into alkenes (C=C) to form 1,2-diols ((HO)Cꢀ
C(OH)). Bꢀckvall and co-workers reported an efficient
OsO -catalyzed cis-1,2-dihydroxylation of alkenes with H O
compounds can also be candidates as alternative oxidants.
We have succeeded in developing a very efficient method
for alkene cis-1,2-dihydroxylation with H O catalyzed by an
4
2
2
2
2
as the terminal oxidant. However, the reaction requires
osmium
ACHTUNGTRENNU(GN III)/osmium(V) redox center supported by a tripo-
[11]
dal tetradentate ligand, tris(2-pyridylmethyl)amine (tpa).
In this catalytic reaction, Os O(OH) species work as the
active oxidant, and just one equivalent of H O is enough to
give cis-diols selectively in high yields and with high oxidant
efficiency. Furthermore, it should be emphasized that our
catalytic system is based on the concept that “all osmium re-
V
[
a] Prof. Dr. H. Sugimoto, K. Ashikari, Prof. Dr. S. Itoh
Department of Material and Life Science
Graduate School of Engineering
2
2
Osaka University
2
-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-7933
E-mail: sugimoto@mls.eng.osaka-u.ac.jp
shinobu@mls.eng.osaka-u.ac.jp
agents are not equally toxic as OsO ”, as mentioned by Do-
nohoe et al.
4
[12]
For example, the osmium(VI) compound K2-
AHCTUNGTREG[NNUN OsO (OH) ] is not volatile and its LD is reduced by more
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300329.
2
4
50
ꢀ
1
than 200-fold (2.69 gkg ) when compared with OsO .
4
Chem. Asian J. 2013, 00, 0 – 0
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Hideki Sugimoto et al.
Macrocyclic polyamines are often employed as a support-
ing ligand of metal catalysts for alkene dihydroxyla-
plex was finally hydrolyzed at pH 4.0 to give the hydroxo-
aqua osmium(III) complex of tpa, 3. Thus, the yield of
1 from the dichloro derivative (66%) was much higher than
AHCTUNGTRENNUNG
[7d,e,8,9]
tion.
the iron
diaza[3.3]
Among the catalysts that have been reported,
(III) complex supported by N,N’-dimethyl-2,11-
(2,6)pyridinophane (L-N Me ) is an efficient cata-
III
[11]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
the total yield of 3 from [Os Cl ACHTNUGTNERNUG( tpa)]PF (41%), indicat-
2 6
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ing that the synthetic procedure of the hydroxo-aqua
osmium(III) complex of the macrocyclic ligand (L-N Me )
was much simpler than that of the tpa ligand system.
4
2
lyst for cis-1,2-dihydroxylation of various alkenes with po-
tassium peroxymonosulfate (Oxone), although the catalytic
reaction does not proceed at all when oxone is replaced
ACHTUNGTRENNUNG
4
2
In the IR spectrum of 1, a sharp band was observed at
[13]
ꢀ1
with H O . It has also been reported that the ligand forms
3586 cm , which was assigned to the n
A
H
U
G
R
N
U
G
2
2
stable metal complexes with several transition metal ions
and offers the metal centers two coordinative labile sites in
bration (Figure S1a, Supporting Information). In the crystal
structure of 1 (Figure 2), two independent molecules are
present in a unit cell. The selected bond lengths and angles
[14]
a cis-position. It should also be noted that no dinuclear-
or polynuclear-metal complexes bridged by oxo groups have
been reported with the L-N Me ligand. This property
4
2
would be desirable since the m-oxo dimer complex may be
one of the dead-end species in the catalytic alkene cis-dihy-
droxylation reaction. Although dioxo-osmium(V) and -(VI)
complexes with macrocyclic polyamines were synthesized,
VI
the osmium centers adopt a trans-Os O structure in these
complexes.
2
[15]
Taking advantage of the features of the L-
N Me ligand, we herein developed a more efficient catalytic
4
2
system for alkene cis-1,2-dihydroxylation with H O using
2
2
the osmium ACHTUNGTRENNUNG( III)/osmium(V) redox couple. The chemical
structures of the osmium complexes examined in this study
are given in Figure 1.
Figure 2. ORTEP drawing (thermal ellipsoids at the 50% probability
level) of the two independent crystal structures in a unit cell of 1. One
solvent acetone molecule, hydrogen atoms, and counter anions are omit-
ted for clarity.
are listed in Table 1 (more detailed data are provided in
Table S1 in the Supporting Information). In this structure,
each osmium atom is coordinated with the four nitrogen
atoms of L-N Me and two oxygen atoms, thereby adopting
4
2
Figure 1. Chemical structures of complexes 1, 2, and 3.
a distorted octahedron. The bond length of Os(1)ꢀO(1) of
2
.056(6) ꢂ is longer than that of Os(1)ꢀO(2), 2.023(6) ꢂ,
ꢀ
Results and Discussion
thus indicating that the O(1) and O(2) atoms are of OH
and H O ligands, respectively. With respect to the Os(2)
2
Synthesis and Characterization
atom, the shorter Os(2)ꢀO(3) bond (2.009(6) ꢂ) and the
The hydroxo-aqua-osmium
A
H
U
G
R
N
U
G
longer O(2)ꢀO(4) bond (2.080(6) ꢂ) similarly indicate that
4
2
ꢀ
1
, was synthesized in a yield of 66% by hydrolysis of
O(3) and O(4) atoms are of OH and H O ligands, respec-
2
III
[16]
[
Os Cl2
under refluxing conditions (see the Experimental Section).
In this reaction, an oxo-bridged diosmium(III) complex such
(L-N Me ) ] was not formed, as confirmed
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(L-N Me )]PF
in an aqueous solution at pH 10
tively. There are distinct hydrogen bonding interactions be-
4
2
6
tween the hydroxo and aqua ligands (HꢀO····HꢀOꢀH) of
A
H
U
G
R
N
U
G
the two complex cations, where the distance between O(2)
and O(3) atoms is 2.514(8) ꢂ and that between O(1) and
O(4) atoms is 2.484(8) ꢂ. Each oxygen atom also has a hy-
III
2+
as [Os
ACHTUNGTRENNUNG( m-O) ACHTUNGTRENNUNG
2 2
4
2 2
by monitoring the mass spectra of the reaction solution. The
elemental analysis and ESI mass spectral data of the isolat-
ed complex were consistent with the chemical formulation
of 1. On the other hand, in the case of the tpa (tpa=tris-(2-
pyridylmethyl)amine) ligand system reported previously, the
Table 1. Selected bond lengths (ꢂ) and angles (8) of 1.
Bond Lengths [ꢂ]
corresponding hydroxo-aqua-osmium
A
H
U
G
R
N
N
(III) complex could
Os(1)ꢀO(1)
2.023(6)
2.056(6)
2.132(9)
1.996(7)
2.115(8)
2.002(8)
Os(2)ꢀO(3)
Os(2)ꢀO(4)
Os(2)ꢀN(5)
Os(2)ꢀN(6)
Os(2)ꢀN(7)
Os(2)ꢀN(8)
2.009(6)
2.080(6)
2.113(9)
1.975(7)
2.105(9)
1.995(7)
Os(1)ꢀO(2)
not be directly obtained from the dichloride derivative by
[17]
III
+
Os(1)ꢀN(1)
alkaline hydrolysis.
Thus, [Os Cl AHCTUNGTERUNNNG( tpa)] was first con-
2
Os(1)ꢀN(2)
verted into an oxo-carboxylato-bridged diosmium ACHUTGTNNRENUNG( III) com-
Os(1)ꢀN(3)
[
18]
plex by the treatment with sodium butylate under reflux-
ing conditions, and then ligand substitution of the bridging
Os(1)ꢀN(4)
Bond Angles [8]
O(1)-Os(1)-O(2)
N(1)-Os(1)-N(3)
ꢀ
84.8(3)
156.3(3)
O(3)-Os(2)-O(4)
N(5)-Os(2)-N(7)
86.1(3)
156.1(3)
groups with OTf was carried out in neat HOTf at 1008C to
give the ditriflato-osmium ACHUTNGRENNUG( III) complex. The ditriflate com-
&
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Hideki Sugimoto et al.
drogen bonding interaction with a nearby acetone molecule;
the distances between the oxygen atom of aqua or hydroxo
ligand and that of acetone are 2.69(1)–2.82(1) ꢂ.
Table 2. Selected bond lengths (ꢂ) and angles (8) of one of the two inde-
pendent molecules of 2.
Bond Lengths [ꢂ]
The acid–base property of the coordinating hydroxo and
aqua ligands coupled with the electron-transfer reaction of
the osmium center of 1 was examined by cyclic voltammetry
Os(1)ꢀO(1)
1.921(4)
2.166(5)
2.149(5)
Os(1)ꢀO(2)
Os(1)ꢀN(2)
Os(1)ꢀN(4)
1.753(5)
2.088(5)
2.005(5)
Os(1)ꢀN(1)
Os(1)ꢀN(3)
Bond Angles [8]
O(1)-Os(1)-O(2)
(
CV) over the pH range of 1 to 12. As shown in Figure S2
106.43(19)
N(1)-Os(1)-N(3)
154.01(18)
in the Supporting Information, the cyclic voltammograms
measured at pH 2, 6, 8, and 10 exhibited multiple redox cou-
II
ples due to changes of the oxidation states from Os to
length (1.921(4) ꢂ) is longer than the Os(1)ꢀO(2) bond
VI
Os . The E1 values for these redox couples were plotted
length (1.753(5) ꢂ), indicating that O(1) and O(2) atoms
/2
ꢀ
2ꢀ
against pH to provide a Pourbaix diagram (see Figure S3,
Supporting Information). The dominant species were deter-
mined by comparing the slope of each line to the value cal-
can be assigned to the oxygen atoms of OH and O
groups, respectively. With respect to the Os(2) atom, the
longer Os(2)ꢀO(3) bond (1.880(5) ꢂ) and the shorter
Os(2)ꢀO(4) bond (1.769(5) ꢂ) indicate that O(3) and O(4)
0
culated from the Nernst equation: E =E1/2 ꢀ(0.059 m/n)
1
/2
0
ꢀ
2ꢀ
pH, where E1/2 is the half-wave potential at pH 0 and m is
the number of protons gained when n electrons are
atoms are of OH and O ligands, respectively. Notably,
the electronic repulsion between the oxo and hydroxo
groups makes the bite angles of O(1)-Os(1)-O(2)
(106.43(19)8) and O(3)-Os(2)-O(4) angle (105.5(3)8) in 2
larger as compared to those of (O(1)-Os(1)-O(2) (84.8(3)8)
and O(3)-Os(2)-O(4) angle (86.1(3)8)) in 1.
[19]
gained. The dominant species are abbreviated in the dia-
III
2+
gram. For example, [Os (OH)
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
and
(H O)
2
4
2
V
2+
III
[
Os O(OH)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(L-N Me )] are indicated as Os (OH)
A
H
U
G
R
N
U
G
4
2
2
V
and Os O(OH), respectively. The diagram clearly indicates
that the osmium complex can be varied from the di-aqua-os-
mium(II) complex to the di-oxo-osmium(VI) compound by
proton-coupled electron transfer (PCET) and that a single
Catalytic cis-1,2-Dihydroxylation of Alkenes
+
ꢀ
step of 2H /2e transfer process is involved in the conver-
At first, the catalytic performance of 1 in the oxidation of
III
V
sion between the Os /Os redox couple in the acidic region.
The oxo-hydroxo-osmium(V) complex 2 was synthesized
by the oxidation of 1 with 2 equivalents of cerium(IV) am-
monium nitrate (CAN), and was isolated in a yield of 47%
based on 1. The elemental analysis and ESI-MS data of the
isolated complex were consistent with the chemical formula-
tion of 2. In the IR spectrum of 2 (Figure S1b, Supporting
cyclohexene with H O as the terminal oxidant was exam-
2
2
ined under the experimental conditions employed for the
Os-tpa system (Table 3). An aqueous solution of H O2
2
(29%, 0.5 mmol) was added to a solution containing the
Table 3. cis-Dihydroxylation of cyclohexene with
osmium complexes.
H
2
O
2
catalyzed by
[
a]
ꢀ
1
Information), there is a sharp band at 3545 cm , which is
assigned to the n
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OꢀH) stretching vibration. In the crystal
structure of 2 (Figure 3), two crystallographically independ-
ent molecules exist in a unit cell. In this case, there is no
direct interaction between the two osmium complexes, as
[
e]
[f]
Entry
Catalyst [mol%]
Yield [%]
TON
Ref.
[
b]
1
2
3
4
5
1 (1.0)
1 (0.01)
3 (1.0)
3 (1.0)
3 (0.01)
99
55
99
70
25
99
5500
99
70
2500
This work
This work
[11]
[11]
This work
[
c]
ꢀ
counter anions PF6 are present near the oxo and hydroxo
[b,d]
[b]
groups (Figure S4, Supporting Information). Thus, only one
of the two osmium complexes is shown in Figure 3, and se-
lected bond lengths and angles are listed in Table 2 (more
detailed data are provided in Table S2 in the Supporting In-
formation). Each osmium atom is coordinated by the four
nitrogen atoms of L-N Me and two oxygen atoms, thereby
[
c]
[
a] Reaction conditions: cyclohexene (500 mmol) and catalyst were dis-
solved in H O/tBuOH (5.0 mL, 1:1 v/v) under N . H (500 mmol) was
2
2
2 2
O
added to the mixture by using a syringe pump over 4 h, and the resulting
solution was stirred for an additional 1 h. [b] At 708C. [c] At 508C.
4
2
[
d] The reaction was carried out in an acetate buffer/tBuOH mixed solu-
adopting a distorted octahedron. The Os(1)ꢀO(1) bond
tion. [e] GC yield based on the substrate. [f] Turnover number (=100ꢃ
mol ratio of cyclohexanediol/osmium cat.).
substrate (0.5 mmol) and 1 (1 mol%) in a mixed solvent of
H O/tBuOH (1:1 v/v, 5.0 mL) using a syringe pump over
2
a period of 4 hours at 708C, and the reaction was allowed to
proceed further for 1 hour. The products were analyzed by
comparing the gas chromatography (GC) retention times to
those of authentic samples, and the yields were determined
by using calibration curves. cis-1,2-Cyclohexanediol was ob-
tained in an excellent yield (>99%) together with a trace
amount of 2-hydroxy-cyclohexan-1-one (entry 1). We have
Figure 3. ORTEP drawing (thermal ellipsoids at the 50% probability
level) of a crystal structure of 2. Hydrogen atoms and counter anions are
omitted for clarity.
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Hideki Sugimoto et al.
III
reported that Os (OH)
A
H
U
G
R
N
U
G
2 2
Table 4. Catalytic cis-dihydroxylation of alkenes with H O catalyzed by
2
[
a]
1
.
ligand, tpa, similarly catalyzes 1,2-dihydroxylation of cyclo-
hexene (0.5 mmol) with H O (0.5 mmol) to give the 1,2-diol
[
b]
Entry
Alkene
1,2-Diol
Yield [%]
in a yield of 99% yield, but only in a buffer solution such as
CH COOH/CH COONa, KH PO /Na HPO , or Na CO /
1
> 99
3
3
2
4
2
4
2
3
NaHCO (entry 3). Without the buffer, the product yield de-
3
[11]
creased to 70% (entry 4). In the case of catalyst 1, on the
other hand, a high yield was attained without the buffer, as
mentioned above (entry 1). Thus, the catalytic system can be
simplified by using the macrocyclic tetradentate ligand L-
N Me . More importantly, when the catalytic amount of
2
3
4
70
46
53
4
2
1
was reduced from 1 mol% to 0.01 mol%, a much higher
turnover number (TON) of 5500 was accomplished, even at
a lower temperature of (508C, entry 2). With catalyst 3, on
the other hand, the TON was much lower (2500) under the
same experimental conditions (entry 5), demonstrating the
robustness of catalyst 1.
5
6
98
69
The catalytic activity of 1 was further examined in the cis-
dihydroxylation of various alkenes (Table 4). In the case of
octenes, the corresponding cis-1,2-diols were obtained in
good to excellent yields (entries 1–6), where the threo and
erythro derivatives were obtained selectively from the trans-
and cis-alkenes, respectively. Thus, the dihydroxylation ex-
7
52
83
86
62
[11]
hibits syn-selectivity as in the case of catalyst 3. The yield
of diols decreased from 1-octene to 2-octene and then fur-
ther to 3-octene and 4-octene (entries 1–4) due to the steric
repulsion between the ligand L-N Me and the alkyl sub-
8
4
2
stituent(s) on the substrates. The higher yield of cis-2,3-octa-
nediol (entry 2) than that of cis-4,5-octanediol (entry 4) con-
9
trasts with the product yields using OsO (18% cis-2,3-octa-
4
[20]
nediol vs. 34% cis-4,5-octanediol).
This result rules out
the possibility that OsO leached from 1 catalyzed the dihy-
10
4
droxylation of alkenes as the real oxidant. The lower reac-
tivity of trans-olefins (entries 2–4) as compared to that of
cis-alkenes (entries 5 and 6) can also be ascribed to the
aforementioned steric factors. The syn-selective dihydroxyla-
tion also proceeded in good to excellent yields in the oxida-
tion of a tri-substituted alkene (entry 7) as well as substrates
with electron-withdrawing substituents (entries 8–10).
Among the 10 samples listed in Table 4, the yields of two
diols were higher than those obtained in the Os-tpa system
[
a] Reaction conditions: the alkene (500 mmol) and catalyst (1 mol%)
were dissolved in H O/tBuOH (5.0 mL, 1:1 v/v) at 708C under N . H O
(500 mmol) was added to the mixture by using a syringe pump over 4 h,
and the resulting solution was stirred for an additional 1.0 h. [b] Yield
2
2
2
2
1
based on the substrate, as determined by H NMR spectroscopy.
troscopy as shown in Figure 4a. The absorption bands at 249
and 342 nm originating from 1 decreased with contaminant
increase of new bands around 250–300 nm (solid line!
dashed line) upon addition of H O . The final spectrum was
nearly identical with that of the isolated complex
[Os O(OH)
plex was also formed in the reaction of 1 and H O . The re-
action obeyed first-order kinetics in the presence of an
excess amount of H O (10 equiv, pseudo-first-order condi-
(
entries 1 and 5), whereas the product yields of four diols
were lower than those obtained in the Os-tpa system (en-
[11]
tries 2, 3, 7, and 8). The yields of the remaining four diols
2
2
[11]
were comparable to those in the Os-tpa system. In view
of product yields, these results suggest that 1 works as
a better catalyst for alkenes with a sterically less hindered
double bond, whereas 3 is a better catalyst for dihydroxyla-
tion of alkenes with a sterically hindered double bond.
V
ACHTUNGTRENNUN(G L-N Me )] AHCTUNGTERNUNGN( PF ) (2), indicating that this com-
4 2 6 2
2
2
2
2
tions), as shown in Figure 4b, and the pseudo-first-order
ꢀ
3
ꢀ1
rate constant was determined as 2.3ꢃ10 s . Further, the
Catalytic Mechanism
UV/Vis spectrum of a H O/tBuOH solution of 2 changed to
2
[11]
As previously reported for the osmium-tpa system,
the
that of 1 upon addition of styrene (1 equiv) at 308C (Fig-
ure S5, Supporting Information), and the corresponding diol
was obtained. The above results clearly demonstrate that 2
is the active oxidant in the cis-1,2-dihydroxylation.
oxo-hydroxo-osmium(V) complex 2 (see Figures 1 and 3)
may be the reactive species in the catalytic cis-dihydroxyla-
tion of alkenes with complex 1. To confirm this assumption,
the reaction of 1 with H O was monitored by UV/Vis spec-
2
2
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&
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Hideki Sugimoto et al.
a concerted manner to give
a
five-membered glycolate
adduct B, which is hydrolyzed
to give the corresponding 1,2-
diol and the starting material
1
. The selective formation of
the threo- and erythro-products
obtained from the trans- and
cis-alkenes, respectively, indi-
cates that the reaction strictly
proceeds via
a
concerted
Figure 4. a) UV/Vis spectrum of 1 (solid line) and its change to that of 2 (dashed line) by the reaction with
H O (10 equiv) in H O; [1]=1ꢃ10 m. b) First-order plot based on the increase of absorption at 275 nm.
2 2 2
mechanism (Scheme 1). The
syn addition may be [3+2]
type as proposed for the stoi-
chiometric cis-dihydroxylation
ꢀ
4
VI
To gain further insights into the mechanism of the catalyt-
of alkenes by
a
cis-Ru O compound, [Me tacn-
2
3
ic cis-dihydroxylation with complex 1, an isotope labeling
experiment was carried out using cyclohexene as the sub-
A
T
N
T
E
N
N
(CF SO )RuO ]ClO (Me tacn=N,N’,N’’-1,4,7-triazacyclono-
3
3
22]
2
4
3
[
nane).
1
6
16
strate and 1 equivalent of H O (29% in H O solution) in
2
2
2
18
18
16
labeled H2 O, in which the ratio of O: O is 2:98. The
product, 1,2-cyclohexanediol, consisted of 11% of
Conclusions
16
12
16 18
18
12
C H O , 62% of C H O O, and 27% of C H O . The
6
2
6
12
6
2
1
6
18
18
formation of labeled products C H O O and C H O2
We have herein presented a protocol that uses the hydroxo-
aqua-osmium(III) complex 1 supported by a cyclic tetraden-
tate ligand as a catalyst and environmentally friendly H O2
as a terminal oxidant for selective cis-dihydroxylation of al-
kenes. Several alkenes including electron-deficient alkenes
have been efficiently converted into the corresponding 1,2-
diols in a completely syn-selective manner. In the case of
catalytic dihydroxylation of cyclohexene, a high turnover
number of 5500 has been achieved, which is much higher
than that of 3 under the same reaction conditions, thereby
6
12
6
12
unambiguously demonstrated that oxygen atom(s) of solvent
water is incorporated in the active oxidant 2. The oxygen
atom exchange reaction may occur between the oxo/hy-
droxo ligand in 2 and water molecules as demonstrated in
ACHTUNGTRENNUNG
2
[21]
the iron/tpa system. It should be noted, however, that the
1
12
6
unlabeled product C H O was also generated in a relative-
6
2
ly high yield (11%) even in the presence of the large excess
1
8
16
18
of labeled water H2 O ( O: O=2:98). This can be ex-
plained, if the oxo-hydroxo-osmium(V) active oxidant 2 is
generated through a side-on type hydroperoxo-osmium
A
H
U
G
R
N
U
G
demonstrating the robustness of catalyst 1. The stable com-
III
intermediate A as indicated in Scheme 1 and if the oxygen-
exchange reaction is relatively slow as compared with the
reaction with the alkene substrate. The active species 2 gen-
erated from intermediate A reacts with the substrate in
plex [Os (OH) ACHTUNGTRENNUNG( OH ) AHCTUNGERTNNGNU( L-N Me )] CATHUNGTRNEGUNN( PF ) (1) has been easily
2 4 2 6 2
III
prepared by the hydrolytic reaction of [Os Cl ACHTUNGTRENNUNG( L-
2
V
N Me )]PF , and [Os (O)(OH) ACUTHTGNRENNUG(N L-N Me )] ACHTUNGTRENNUN(G PF ) (2) has
4 2 6 2
4
2
6
been isolated and characterized as the active oxidant in the
catalytic cycle. Further efforts to develop more efficient
osmium catalysts that exhibit higher turnover numbers and
higher turnover frequencies are in progress.
Experimental Section
General
Except for the ligand and the complexes, the reagents and solvents used
in this study were obtained commercially of the highest available grade.
III
2 4 2 6
The complex of [Os Cl ACHTUNGERTUNNNG( L-N Me )]PF was synthesized from the ligand
[
16]
III
and OsO
4
according to the literature. [Os (OH)
A
H
U
G
R
N
N
(H
2
O)
6 2
ACHTUNGTNRENUNG( tpa)] ACHTUNGTRENNUNG( PF ) was
[
11] 1
prepared by following the reported procedure.
H NMR spectra were
recorded at 400 MHz on a JEOL-ECP400 or a JEOL-ECS400 spectrome-
ter. FTIR spectra were recorded with a Jasco FT/IR-4100 intrument. Ele-
mental analysis was carried out with a Yanaco CHN-Corder MT-5 ele-
mental analyzer. ESI-mass spectra were measured with a Mariner ESI-
TOF mass spectrometer. Electrochemical measurements were performed
with a Hokuto Denko HZ-3000 or a HZ-7000 measurement system. A
set of a platinum working electrode, an SCE reference electrode, and
a platinum counter electrode was employed in these experiments.
Scheme 1. Proposed catalytic mechanism for alkene cis-1,2-dihydroxyla-
tion with 1.
Chem. Asian J. 2013, 00, 0 – 0
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Hideki Sugimoto et al.
47 76 24 8 9 2 4
C H F N O Os P C H F N O Os P
Synthesis and Characterization of Complexes
3 2
Table 5. Crystallographic data for 21·5 ACHTUNGTERNNUG( CH ) CO and 22.
III
III
Formula
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[Os (OH)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(H
2
O)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(L-N
4
Me
2
)]
A
T
N
T
N
U
G
6
)
2
(1). [Os Cl
2
A
H
U
G
R
N
N
4
Me
2
)]PF
6
(150.9 mg,
32 42 24
8
4
2
4
0
4
9
.224 mmol) was added to an aqueous solution of sodium hydroxide (
.0 mm, 280 mL), and the resulting red suspension was refluxed for
0 min. Subsequently, the solution was cooled to room temperature, and
FW
size [mm]
T [K]
1857.42
0.40ꢃ0.30ꢃ0.10
103
1562.99
0.40ꢃ0.10ꢃ0.10
103
acetic acid (64.1 mL) and ammonium hexafluorophosphate (365.1 mg,
.24 mmol) were added. Concentration of the solution under reduced
pressure to ca. 5 mL afforded 1 as orange microcrystals, which were col-
crystal system
space group
Z
a [ꢂ]
b [ꢂ]
monoclinic
P2 /n (no. 14)
1
4
orthorhombic
Pbca (no. 61)
8
17.7519(3)
13.4604(3)
40.3571(9)
90
2
lected by filtration and dried in vacuo. Yield, 115.0 mg (66%). UV/Vis
9.9417(8)
22.613(2)
30.141(3)
90
99.515(2)
90
6682.8(9)
40.146
9658
15064
0.0761
0.2003
0.934
ꢀ
1
ꢀ1
(
(
C
2
H O): lmax =249 nm (e=10296m cm ), 290 (5908), 342 (7932); FTIR
ꢀ
1
KBr): 3586 cm
v
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OꢀH), 843 v
A
T
N
T
N
U
G
c [ꢂ]
16
H
23
F
12
N
4
O
2
OsP : C 24.53, H 2.96, N 7.15%; found: C 24.75, H 3.22, N
2
a [deg]
b [deg]
g [deg]
2
+
+
+
7
.11; ESI-MS: m/z=494.1 {[M] -(H )} .
90
90
V
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[Os (O)(OH)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(L-N
4
Me
2
)]
A
H
U
G
R
N
U
G
6
)
2
(2). Complex 1 (8.8 mg, 0.011 mmol) was
3
dissolved in trifluoromethanesulfonic acid (30 mm, 500 mL), and the solu-
tion was cooled to ca. 58C with an ice bath, whereupon cerium(IV) am-
monium nitrate (2 equiv, 12.3 mg, 0.022 mmol) dissolved in a minimum
amount of water was added dropwise. The color of the solution immedi-
V [ꢂ ]
9643.2(4)
55.348
8504
11014
0.0476
ꢀ
1
m [cm
no. reflns (I>2sI
no. reflns (all data)
]
0
)
[
a]
ately changed from yellow to green. An excess amount of NH
4
PF
6
dis-
R
1
(I>2.0 sI)
[
b]
solved in a minimum amount of water was added to the solution, and the
resultant solution was kept standing in a refrigerator overnight to afford
wR
2
(all data)
0.1206
1.136
GOF
2
as green crystals precipitated from the solution, which were collected
2
2
2
2 2 1/2
[
a] R
1
=Sj jF
o
jꢀjF
c
j j/SjF
o
j. [b] wR
2
=[S(w
A
H
U
T
E
N
N
(F
o
ꢀF
c o
) )/Sw ACHTUNREGTNNUNG( F ) ] .
by filtration, washed with cold water, and dried in vacuo. Yield, 4.1 mg
ꢀ1
ꢀ1
(
47%). UV/Vis (H
FTIR (KBr): n˜ =3545 cm
elemental anal. calcd (%) for C16
.17; found: C 24.78, H 2.99, N 7.31; ESI-MS (acetone): m/z=246.6
2
O): lmax =246 nm (e=11797m cm ), 285 (8641);
ꢀ
1
v
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
ACHTUNGTRENUNNG( Os-OH);
2
H
21
F
12
N
4
O
2
2
least-squares on F . The hydrogen atoms were attached at idealized posi-
tions on carbon atoms and were not refined. All structures in the final
stages of refinement showed no movement in the atom positions. The cal-
7
2
+
2+
+
+
[
2
M] ; ESI-MS (H O): m/z=492.1 {[M] -(H )} .
culations were performed using the software CrystalStructure, version
Catalytic Dihydroxylation
[24]
3
.8.
Crystallographic parameters are summarized in Table 5.
III
CCDC 928810 (1) and CCDC 928811 (2) contain the supplementary crys-
tallographic data for this paper. The data can be obtained free of charge
from The Cambridge Crystallographic Data Center via www.ccdc.cam.
ac.uk/data_request/cif.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[Os (OH)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(H
2
O)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(L-N
4
Me
2
)]
A
H
U
G
R
N
U
G
6
)
2
(1) (3.92 mg, 5 mmol) in H
for 30 min to exclude O
strate (500 mmol) was then added to the solution, and the mixture was
heated to 708C. Subsequently, H (29%, 52.6 mL, 500 mmol) was slowly
introduced into the solution over the course of 4 h by using a syringe
pump to avoid overoxidation of the diol product with excess H and
decomposition of the remaining H . The resulting mixture was allowed
2
O/tBuOH
. The sub-
(
5.0 mL, 1:1 v/v) was bubbled with N
2
2
2
O
2
2
O
2
2
O
2
to stir for an additional 1 h. For product analysis of cyclohexene dihy-
droxylation, chlorobenzene (5.2 mL, 50 mmol) was added after the catalyt-
ic reaction to the mixture as an internal standard. The reaction mixture
Acknowledgements
This work was partly supported by a grant (Grant 23350027 to H. S.) for
Scientific Research (B) from the Japan Society for Promotion of Science
and a grant (No. 24109015, Stimuli-responsive Chemical Species to H. S.)
for Scientific Research on Innovative Areas from MEXT of Japan. S. I.
acknowledges financial support by a grant (No. 22105007, Molecular acti-
vation) for Scientific Research on Innovative Areas from MEXT of
Japan.
was then analyzed with
equipped with a packed column (PEG-20M, 25% Uniport B 60/80 SUS
mꢃ3 mm). The products were identified by the GC retention time
a Shimadzu GC-14B gas chromatograph
2
through comparison with authentic samples. The product yields were cal-
culated from a calibration curve of a plot of mole ratio (moles of organic
compound/moles of internal standard) versus area ratio (area of organic
compound/area of standard). For product analyses of dihydroxylation of
other alkenes, the organic products were extracted with Et
after the catalytic reaction. The combined organic layer was dried over
Na SO , and the solvent was removed by using a rotary evaporator. The
2
O (5ꢃ15 mL)
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4
1
1
products were identified by H NMR spectroscopy through comparison
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H NMR spectra, where an integral ratio of the protons was compared
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[
X-ray Crystallography
III
Single
21·5(CH
tained by slow diffusion of Et
crystals
of
2 4 2 6 2 3 2
2[Os (OH) ACHTNUGTRNNEG(U H O)L-N Me ] ACHTUNTGNUREN(G PF ) ·5(CH ) CO
(
3
)
2
CO) suitable for X-ray structural determination were ob-
O into an acetone solution of the complex.
Single crystals of 2[Os (O)(OH)l-N Me (PF (22) were obtained
through precipitation by adding NH PF to a solution containing 1 and
cerium(IV) ammonium nitrate (2 equiv). Each single crystal of
1·5(CH CO and 22 was mounted on a loop with mineral oil, and all
2
V
4
2
]
A
H
U
G
R
N
U
6 2
)
4
6
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3 2
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23]
direct methods (SIR 2008)
and expanded using Fourier techniques.
The non-hydrogen atoms were refined anisotropically by full-matrix
&
&
Chem. Asian J. 2013, 00, 0 – 0
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www.chemasianj.org
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Received: March 13, 2013
Published online: && &&, 0000
Chem. Asian J. 2013, 00, 0 – 0
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ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

FULL PAPER
Dihydroxylation
Hideki Sugimoto,* Kenji Ashikari,
Shinobu Itoh*
&&&& — &&&&
Osmium ACHTUNGTRENNUNG( III) and Osmium(V)
Complexes Bearing a Macrocyclic
Ligand: A Simple and Efficient Cata-
lytic System for cis-Dihydroxylation of
Alkenes with Hydrogen Peroxide
The wizard of Os: A simple protocol
converted into the corresponding vici-
nal diols in good to excellent yields.It
has been confirmed that the
III
that uses [Os (OH)
ACHTUNGTRENNUNG( H O) CAHTUNGTENRUNN(G L-N Me )]
2 4 2
AHCTUNGTRENNUNG
(PF ) (1) and H O for efficient cis-
6
2
2
2
V
1,2-dihydroxylation of alkenes is pre-
Os (O)(OH) species (2) is the active
sented. Unfunctionalized (or aliphatic)
alkenes and alkenes/styrenes contain-
ing electron-withdrawing groups were
oxidant, which is formed via the hydro-
peroxide adduct A.
&
&
Chem. Asian J. 2013, 00, 0 – 0
8
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!