Osmium-catalyzed oxidation of primary alcohols with molecular oxygen

Article abstract of DOI:10.1021/om200684m

OsHCl(CO)(PⁱPr₃)₂ (1) reacts with O ₂ to afford the dioxygen derivative OsHCl(CO)(η²- O₂)(PⁱPr₃)₂ (2), which under atmospheric pressure of oxygen promotes the oxidation of 4-methoxybenzyl alcohol, benzyl alcohol, and 4-chlorobenzyl alcohol to the corresponding aldehydes. Under the same conditions, 1-hexanol and 1-octanol give hexyl hexanoate and octyl octanoate, respectively. On the other hand, cinnamyl alcohol undergoes disproportionation to 3-phenylpropanol and cinnamaldehyde.

Full text of DOI:10.1021/om200684m

Article
pubs.acs.org/Organometallics
Osmium-Catalyzed Oxidation of Primary Alcohols with
Molecular Oxygen
,†
‡
‡
†
́
Miguel A. Esteruelas,* Tania Garcıa-Obregon, Juana Herrero, and Montserrat Olivan
́
́
†
́
́
́
Departamento de Quımica Inorgan
́
ica-Instituto de Sıntesis Quımica y Catal
́
isis Homogen
́
ea (ISQCH), Universidad de
Zaragoza-CSIC, 50009 Zaragoza, Spain
‡
́
́
́
́
Departamento de Ingenierıa Quımica y Quımica Inorganica, Universidad de Cantabria, 39005 Santander, Spain
S
* Supporting Information
ABSTRACT: OsHCl(CO)(PiPr3)2 (1) reacts with O2 to afford the
dioxygen derivative OsHCl(CO)(η 2-O2)(PiPr3)2 (2), which under
atmospheric pressure of oxygen promotes the oxidation of 4-metho-
xybenzyl alcohol, benzyl alcohol, and 4-chlorobenzyl alcohol to the
corresponding aldehydes. Under the same conditions, 1-hexanol and
1-octanol give hexyl hexanoate and octyl octanoate, respectively. On
the other hand, cinnamyl alcohol undergoes disproportionation to
3-phenylpropanol and cinnamaldehyde.
INTRODUCTION
■
Oxidations of alcohols have been traditionally performed with
stoichiometric amounts of inorganic oxidants. They are
relatively expensive and generate copious amounts of waste.1
Consistently, there is an increasing demand to use molecular
oxygen as an oxidant, since it is available and inexpensive and
such oxidations are high-atom-economical methodologies.2
However, oxidation of primary alcohols to aldehydes or esters
remain a challenging procedure, even in the presence of
transition-metal catalysts.3 Although the reduction of metal−
oxo compounds by the alcohols can directly occur,4 the
resultant reduced metallic species is hardly reoxidized by
molecular oxygen.
absorption to 862 cm−1 in the IR. The position of the dioxygen
ligand trans to the hydride (δ −2.40, JH−P = 30.0 Hz), a very
good σ-donor, is probably responsible for this strong Os(η 2-O2)
binding.Treatment of benzene-d6 solutions of 2 with 3 equiv of
benzyl alcohol at 80 °C, for 35 min under an argon atmosphere,
regenerates 1 and yields 2 mol of benzaldehyde and water,
according to eq 2.
The activation of molecular oxygen promoted by osmium
complexes has been demonstrated.5 Despite this fact, the
catalytic oxidation of primary alcohols that employ osmium
systems is scarce.6 The five-coordinate complex OsHCl(CO)-
7
(PiPr3)2 (1) has proved to be an active catalyst for the
reduction of organic substrates,8 the addition of silanes to
alkynes,9 the dimerization of the latter to butatrienes,10 and the
ring-opening metathesis polymerization (ROMP) and tandem
ROMP-hydrogenation of norbornene and 2,5-norbornadiene.11
Now we show that this complex catalyzes the oxidations of
benzylic alcohols to benzaldehydes and aliphatic alcohols to
esters and the disproportionation of cinnamyl alcohol.
Equations 1 and 2 form a catalytic cycle for the oxidation of
benzyl alcohol to benzaldehyde using molecular oxygen as an
oxidant. Because the coordination of the oxygen molecule to
the osmium atom of 1 is much faster than the reaction of 2
with the alcohol, the latter should be the rate-determining step
of the catalysis. In agreement with this, at 120 °C, the toluene
solutions of 1 catalyze the oxidation of 4-methoxybenzyl
alcohol, benzyl alcohol, and 4-chlorobenzyl alcohol to the
corresponding aldehydes under atmospheric pressure of oxygen
RESULTS AND DISCUSSION
■
1. Benzyl Alcohols. Complex 1 coordinates molecular
oxygen in air or under an oxygen atmosphere to afford the
12
η2-O2 complex OsHCl(CO)(η2-O2)(PiPr3)2 (2), according
to eq 1. The dioxygen ligand is strongly bound to the osmium
atom. This fact is reflected not only by the stability of 2 under
vacuum but also by the lowering of the O−O stretching
Received: July 26, 2011
Published: November 10, 2011
© 2011 American Chemical Society
6402
dx.doi.org/10.1021/om200684m|Organometallics 2011, 30, 6402−6407

Organometallics
Article
31P
1H
(eq 3). The substituent at the phenyl group of the alcohol has
a marked influence on the reaction. The electron-releasing
OsHCl(CO)(η2-O2)(PCy3)2 (3: δ 13; δ −2.65, JH−P
=
30.4 Hz) exchange phosphine oxide to afford the mixed
compound OsHCl(CO)(η2-O2)(PiPr3)(PCy3) (4: δP Pr 23;
i
3
1
δPCy 14, JP−P = 94 Hz; δ H −2.57, JH−P = JH−P′ = 30.1 Hz). The
3
phosphine oxidation should generate the 16-valence-electron
oxo derivative A, which should be responsible for the alcohol
oxidation: i.e., the formation of the phosphine oxide promotes
the activation of 2 for the oxidation of the first 1 mol of alcohol
(black pathway in Scheme 1). The coordination of this 1 mol of
alcohol to the unsaturated center of A should give B. The
subsequent hydrogen migration from the coordinated alcohol
to the oxo group could afford the unsaturated 16-valence-
electron intermediate C. Then, the coordinated alkoxide ligand
should undergo a β-hydrogen elimination reaction to yield D,
containing a coordinated aldehyde molecule. The release of the
aldehyde and the subsequent reductive elimination of water
from the metal center of the resulting species E should lead
to F. This reduced metallic species should be reoxidized by the
phosphine oxide to regenerate A, which should oxidize the
second 1 mol of alcohol (red pathway in Scheme 1). The
coordination of the phosphine, resulting from the reduction of
the phosphine oxide, to F should afford 1 and to begin the
process again. In support of the connection between
intermediates A and F and complexes 1 and 2, we have
observed that, at 120 °C under an argon atmosphere, the
addition of 2.0 equiv of PCy3 to the toluene-d8 solutions of the
dioxygen complex 2 leads after 70 min to an equimolecular
methoxy group facilitates the oxidation. However, the electron-
withdrawing chlorine slows the process. In the presence of 1
mol % of metal complex, 4-methoxybenzaldehyde is obtained
in quantitative yield after 20 h, whereas benzaldehyde and
4-chlorobenzaldehyde are formed in 95% and 74% yields,
respectively, after 48 h. As expected from the water formation,
activated molecular sieves facilitates the oxidation. For instance,
in the presence of 250 mg of this material, benzaldehyde is
formed in 74% yield after 18 h, while only 62% of aldehyde is
obtained in its absence.
1
A careful examination of the 31P{1H} and H NMR spectra
of the reaction shown in eq 2 reveals the transitory formation of
OPiPr3 (δ 59) as well as two monohydride intermediates
31P
1
(δ H −18.1, JH−P = 23 and −18.8 Hz, JH−P = 22 Hz), containing
only one phosphine ligand attached to the osmium atom, during
the oxidation. This suggests that the phosphine oxide plays the
main role during the catalysis and that the process occurs via
monophosphine intermediates. The contribution of these
species to the formation of the aldehydes can be rationalized
according to the mechanistic proposal shown in Scheme 1.
Each oxygen atom of the oxygen molecule oxidizes 1 mol of
an alcohol. Thus, since complex 1 is recovered at the end of the
oxidation process (eq 2), the phosphine oxide should play two
different roles, one for each oxygen atom, involving phosphine
oxidation (black cycle) and oxide reduction (red cycle).
The dioxygen complex 2, formed according to eq 1, is an
18-valence-electron species. Its coordinatively saturated char-
acter prevents the access of the alcohols to the metal center
and therefore the catalysis. Its activation should occur by
means of the release of OPiPr3. In agreement with this, we
have observed that, in toluene-d8, 2 and its PCy3 counterpart
i
31
mixture of OP Pr3 and OPCy3 (δ P 50), a 1:1:2 mixture of
1, OsHCl(CO)(PCy3)2 (5), and the mixed compound
OsHCl(CO)(PiPr3)(PCy3) (6: δP Pr 43; δPCy 37, JP−P = 254
i
3
3
Hz; δ −32.7, JH−P = JH−P′ = 23 Hz), PiPr3, and PCy3. The
1H
formation of OPiPr3 again supports the dissociation of
phosphine oxide from 2 to afford A, which reacts with PCy3 to
give OPCy3 and F. The coordination of PCy3 to the latter
affords 6. The presence of OPCy3 in the reaction mixture is
consistent with the coordination of PCy3 to A and the
subsequent release of OPCy3. The formation of 5 can be
rationalized as the result of the coordination of PCy3 to a PCy3
counterpart of F, which is generated by coordination of PCy3
Scheme 1
6403
dx.doi.org/10.1021/om200684m|Organometallics 2011, 30, 6402−6407

Organometallics
Article
to A, and subsequent release of OPiPr3. The presence of the
phosphines in the mixture is consistent with the formation of A,
or its PCy3 counterpart, by reaction of F, or its PCy3
counterpart, with phosphine oxide. Certainly, these processes
can occur under catalytic conditions. Thus, under an oxygen
atmosphere, in the presence of 8 equiv of benzyl alcohol, the
1H and 31P{1H} NMR spectra resulting from the addition of
2.0 equiv of PCy3 to a toluene-d8 solution of 2 shows after
30 min at 120 °C the formation of 2.7 equiv of benzaldehyde,
an equimolecular mixture of phosphine oxides, and a 1:1:2
mixture of 2, 3, and 4.
The influence of the substituent of the phenyl group of the
benzylic alcohols on the catalysis can be rationalized in terms of
the β-elimination steps, the transformation from intermediates
C into intermediates D. The electron-donating p-methoxy
group makes the C−H bonds of the CH2 group electron-rich,
so that a β-hydrogen can be easily eliminated and it thus
becomes easier to form the aldehyde. On the other hand, the
electron-withdrawing p-chlorine makes the C−H bonds of the
CH2 group electron deficient and therefore the β-hydrogen
elimination to afford the corresponding aldehyde is more
difficult. A similar effect of the substituent has been observed
by Lei and co-workers for the palladium-catalyzed aerobic
oxidative esterification of benzylic alcohols.13 The accumulation
of phosphine oxide during the catalysis indicates that the rate of
the oxidation is determined by the rate of a step of the black
cycle between the oxidation of the phosphine and the reduction
of the oxide. The marked influence of the substituent of the
phenyl group of the alcohol suggests that β-elimination is
precisely the rate-determining step of the aldehyde formation.
2. Aliphatic Alcohols. 1-Hexanol and 1-octanol, in
contrast to the benzylic alcohols, undergo oxidative dimeriza-
tion to afford esters (eq 4). In the presence of 1 mol % of
β-hydrogen elimination in the COH group. The ester could be
also generated from G by means of reductive coupling between
the acyl and alcoholate ligands. A similar reductive elimination
has been previously proposed for osmium-promoted Tishchen-
ko reactions.18
The OC−H bonds of aldehydes are about 23 kcal mol−1
weaker than the C−H bonds of a phenyl group. In spite of this,
in contrast to the case for aliphatic aldehydes, benzaldehydes
show a high tendency to undergo ortho metalation,19 in
particular with some osmium systems.17,20 The coordination of
the formyl oxygen atom to the metal center appears to direct
the activation toward the ortho C−H bond of the phenyl
group.21 The low trend of aromatic aldehydes to undergo
OC−H bond activation could explain why this type of aldehyde
does not give rise to the corresponding esters.
3. Cinnamyl Alcohol. The characteristic chemical reac-
tions of an organic compound are determined by a specific
moiety within the molecule, the functional group. Transition-
metal elements have the remarkable ability to enhance the
reactivity of some parts of the organic molecules and to inhibit
the reactions of others. A crucial consequence of this ability is
the dramatic increase of the influence of the substituents. The
behavior of the alcohols previously mentioned and cinnamyl
alcohol is a nice example of this. In contrast to the case for
benzylic and aliphatic alcohols, under the same conditions,
cinnamyl alcohol undergoes disproportionation to 3-phenyl-
propanol and cinnamaldehyde (eq 5). After 24 h, 80% of the
starting alcohol has been transformed into the products. About
3% of 3-phenylpropanal is also formed as a consequence of the
oxidation of 3-phenylpropanol.
The disproportionation reaction can be rationalized as an
intermolecular hydrogen transfer process, where the hydrogen
donor is a molecule of cinnamyl alcohol and the hydrogen
acceptor is the carbon−carbon double bond of another
molecule of cinnamyl alcohol. The role of the molecular oxygen
appears to be the activation of the metal center by means of the
creation of a coordination vacancy in the catalyst precursor
complex 2, as a result of the oxidation of one of the phosphine
ligands. In agreement with this, similar results were obtained by
using 1 under oxygen or 2 under argon as a source of the
catalytic species.
The unsaturated species A (Schemes 1 and 2) could catalyze
the disproportionation through an inner-sphere transfer hydro-
genation mechanism22 (Scheme 3) involving (i) the coordina-
tion of the CC double bond of the alcohol to the unsaturated
osmium center of A, (ii) the insertion of the coordinated CC
double bond into the Os−H bond, (iii) the protonation of
the resulting alkyl intermediate with another alcohol molecule
to liberate the saturated alcohol, and (iv) the β-hydrogen
elimination of the resulting alkoxide to regenerate A and afford
the unsaturated aldehyde.
complex 1, under atmospheric pressure of oxygen in toluene at
120 °C, 1-hexanol is transformed into hexyl hexanoate in
almost quantitative yield after 45 h. Under the same conditions
1-octanol forms octyl octanoate in 72% yield after 46 h. The
oxidative esterification of primary alcohols, which proceeds
under mild conditions with molecular oxygen as oxidant, is of
great interest. These reactions are promoted by several
transition-metal complexes.13,14 However, to the best of our
knowledge, no osmium-catalyzed reactions are known.
The formation of the esters can be rationalized according to
Scheme 2. Once the aldehyde has been formed according to the
black cycle, its oxidative addition to intermediate C of the red
cycle should afford the hydride−acyl species G. The oxidative
addition of the OC−H bond should be facilitated by the
slowness of the β-hydrogen elimination process in the
alcoholate group, the rate-determining step of the aldehyde
formation. Intermediate G could undergo tautomerization to
the hydroxycarbene H, by a 1,3-hydrogen shift from the metal
center to the oxygen atom.15 The hydride−acyl/hydroxycar-
bene tautomerization has been studied in a few cases.16 An alkyl
substituent at the C(sp2) atom appears to stabilize the hydro-
xycarbene form.17 The migration of the alcoholate group from
the metal center of H to the carbene carbon atom should afford
the hemiacetal I, which could lead to E releasing the ester by
CONCLUSION
■
In conclusion, the five-coordinate complex OsHCl(CO)-
(PiPr3)2 catalyzes the oxidation of alcohols with molecular
oxygen. The products of the catalysis depend upon the nature
of the substrates. Benzylic alcohols afford the corresponding
aldehydes, whereas aliphatic alcohols form esters through a
6404
dx.doi.org/10.1021/om200684m|Organometallics 2011, 30, 6402−6407

Organometallics
Article
Scheme 2
(5)25 were prepared by published procedures. The analysis of the
products of the reactions was carried out on a Hewlett-Packard 6890
series gas chromatograph with a flame ionization detector, using a
100% cross-linked methyl silicone gum column (30 m × 0.25 mm,
with 0.25 μm film thickness) and p-xylene as the internal standard.
The oven conditions used are as follows: 40 °C (hold 6 min) to
280 °C at 25 °C/min (hold 4 min). The reaction products were
identified by comparison of their retention times with those observed
for pure samples. GC-MS experiments were run on an Agilent 5973
mass selective detector interfaced to an Agilent 6890 series gas
chromatograph system. Samples were injected into a 30 m × 0.032
mm × 0.25 μm HP-5MS 5% diphenyl−95% dimethyl polysiloxane
column. The GC oven temperature was programmed as follows: 40 °C
for 6 min to 280 °C at 25 °C/min (hold 4 min). The carrier gas
tandem process23 involving the oxidation of an alcohol
molecule to aldehyde and the coupling of the latter with
another alcohol molecule. In contrast to both of those types of
alcohols, cinnamyl alcohol undergoes disproportionation to
3-phenylpropanol and cinnamaldehyde.
EXPERIMENTAL SECTION
■
1. General Information. All manipulations were carried out using
standard Schlenk techniques. Solvents were dried by known
procedures and distilled under argon prior to use. Benzyl alcohol,
4-methoxybenzyl alcohol, and 1-octanol were dried by known
procedures and distilled prior to use. 4-Chlorobenzyl alcohol,
1-hexanol, and cinnamyl alcohol were used without further
purification. OsHCl(CO)(PiPr3)2 (1),24 OsHCl(CO)(η2-O2)(PiPr3)2
(2),12 OsHCl(CO)(η2-O2)(PCy3)2 (3),25 and OsHCl(CO)(PCy3)2
1
was helium at a flow of 1.9 mL/min. H and 31P{1H} NMR spectra
were recorded either on a Bruker AV300 or on a Bruker AXR 300
instrument. Chemical shifts are referenced to residual solvent peaks
(1H) or external H3PO4 (31P).
2. Reaction of OsHCl(CO)(η2-O2)(PiPr3)2 with Benzyl Alco-
hol. Benzyl alcohol (8.7 μL, 0.08 mmol) was added to an NMR tube
containing a solution of OsHCl(CO)(η 2-O2)(PiPr3)2 (17 mg, 0.028
mmol) in benzene-d6 (0.4 mL). The resulting mixture was heated at
Scheme 3
1
80 °C for 35 min. H and 31P{1H} NMR spectra were recorded after
this time. The 1H NMR spectrum shows the formation of benzaldehyde
(δ 9.65, CHO), water (very broad at about 3 ppm), and
OsHCl(CO)(PiPr3)2 (δ −31.6 ppm, OsH). In addition, the high-field
region of the 1H NMR spectrum shows two doublets of small intensity
at −18.1 (JH−P = 23 Hz) and −18.8 (JH−P = 22 Hz), corresponding to
uncharacterized monophosphine osmium derivatives. The 31P{1H}
NMR spectrum shows peaks assigned to OsHCl(CO)(PiPr3)2 (δ 47)
and OPiPr3 (δ 59), along with other signals of very low intensity.
3. Reaction of OsHCl(CO)(η2-O2)(PiPr3)2 with OsHCl(CO)(η2-
O2)(PCy3)2: Formation of OsHCl(CO)(η2-O2)(PiPr3)(PCy3) (4). A
solution of OsHCl(CO)(η2-O2)(PiPr3)2 (5 mg, 0.008 mmol) and
OsHCl(CO)(η 2-O2)(PCy3)2 (7 mg, 0.008 mmol) in toluene-d8
(0.5 mL) under an argon atmosphere was periodically checked by
1H and 31P{1H} NMR spectroscopy, showing the formation of the
mixed phosphine compound OsHCl(CO)(η 2-O2)(PiPr3)(PCy3) (4).
1H NMR (300 MHz, toluene-d8, hydride region): δ −2.57 (vt, JH−P
=
JH−P′ = 30.1, 1H, Os-H). 31P{1H} NMR (121.4 MHz, toluene-d8):
δ(PiPr3) 23; δ(PCy3) 14; JP−P = 94 Hz.
6405
dx.doi.org/10.1021/om200684m|Organometallics 2011, 30, 6402−6407

Organometallics
Article
4. Reaction of OsHCl(CO)(η2-O2)(PiPr3)2 with 2.0 equiv of
PCy3. PCy3 (17.9 mg, 0.064 mmol) was added to an NMR tube
containing a solution of OsHCl(CO)(η 2-O2)(PiPr3)2 (19.4 mg, 0.032
mmol) in toluene-d8 (0.4 mL) under an argon atmosphere. The
Social Fund is acknowledged. We thank Carmen Vicario for
technical assistance.
1
resulting mixture was heated at 120 °C for 70 min. 31P{1H} and H
REFERENCES
■
NMR spectra were recorded after this time. The 31P{1H} NMR
spectrum shows peaks assigned to OPiPr3 (δ 59) and OPCy3 (δ
50) in a 1:1 ratio, OsHCl(CO)(PiPr3)2 (δ 47), OsHCl(CO)(PCy3)2
(δ 37), and the mixed compound OsHCl(CO)(PiPr3)(PCy3) (6)
(δ(PiPr3) 43; δ(PCy3) 37; JP−P = 254) in a 1:1:2 ratio, PiPr3 (δ 19),
and PCy3 (δ 9). The 1H NMR spectrum shows the resonances
corresponding to the aforementioned species. In particular, we note a
virtual triplet at −32.7 ppm with JP−H coupling constants of 23 Hz,
assigned to 6.
(1) Wilkinson, S. G. In Comprehensive Organic Chemistry; Barton, D.,
Ollis, W. D., Eds.; Pergamon Press: Oxford, U.K., 1979; Vol. 1, p 644.
(2) (a) Schultz, M. J.; Sigman, M. S. Tetrahedron 2006, 62, 8227.
(b) Sigman, M. S.; Jensen, D. R. Acc. Chem. Res. 2006, 39, 221.
(c) Piera, J.; Backvall, J.-E. Angew. Chem., Int. Ed. 2008, 47, 3506.
̈
(d) Gligorich, K. M.; Sigman, M. S. Chem. Commun. 2009, 3854.
(e) Suzuki, T. Chem. Rev. 2011, 111, 1825.
(3) (a) ten Brink, G.-J.; Arends, I. W. C. E.; Sheldon, R. A. Science
2000, 287, 1636. (b) Enache, D. I.; Edwards, J. K.; Landon, P.;
Solsona-Espriu, B.; Carley, A. F.; Herzing, A. A.; Watanabe, M.; Kiely,
C. J.; Knight, D. W.; Hutchings, G. J. Science 2006, 311, 362. (c) Jiang,
B.; Feng, Y.; Ison, E. A. J. Am. Chem. Soc. 2008, 130, 14462.
(d) Gunanathan, C.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc.
2009, 131, 3146.
5. Reaction of OsHCl(CO)(η2-O2)(PiPr3)2 with 2.0 equiv of
PCy3 in the Presence of 8.0 equiv of PhCH2OH under an
Oxygen Atmosphere. PCy3 (9.8 mg, 0.035 mmol) was added to
an NMR tube containing a solution of OsHCl(CO)(η 2-O2)(PiPr3)2
(10.6 mg, 0.017 mmol) and benzyl alcohol (14.4 μL, 0.127 mmol) in
toluene-d8 (0.4 mL). The argon atmosphere was replaced by an
oxygen atmosphere. The resulting solution was heated to 120 °C for
(4) (a) Green, G.; Griffith, W. P.; Hollinshead, D. M.; Ley, S. V.;
1
30 min. 31P{1H} and H NMR spectra were recorded after this time.
Schroder, M. J. Chem. Soc., Perkin Trans. 1 1984, 681. (b) Hornstein,
̈
The 1H NMR spectrum shows the formation of 2.7 equiv of
benzaldehyde (δ 9.65, CHO) and water (very broad at about 3 ppm)
as well as resonances due to 2−4, OPiPr3, and OPCy3. The
31P{1H} NMR spectrum shows signals characteristic of 2−4, OPiPr3,
B. J.; Dattelbaum, D. M.; Schoonover, J. R.; Meyer, T. J. Inorg. Chem.
2007, 46, 8139. (c) Wang, Q.; Sheng, X.; Horner, J. H.; Newcomb, M.
J. Am. Chem. Soc. 2009, 131, 10629.
(5) (a) Bourgault, M.; Castillo, A.; Esteruelas, M. A.; Onate, E.; Ruiz,
̃
N. Organometallics 1997, 16, 636. (b) Esteruelas, M. A.; Modrego, F.
and OPCy3.
J.; Onate, E.; Royo, E. J. Am. Chem. Soc. 2003, 125, 13344.
̃
6. Catalytic Oxidations: General Procedure. The oxidation
reactions were carried out in a two-necked flask fitted with a condenser
and containing a magnetic stirring bar under 1 atm of O2 (N45
Alphagaz). The second neck was capped with a Suba-Seal to allow
samples to be removed by syringe without opening the system. The
reaction conditions were as follows: a 0.024 mmol portion of catalyst
was dissolved in 1 mL of a toluene solution containing 2.42 mmol
of the corresponding alcohol and 200 μL of p-xylene. The flask was
then immersed in a bath at 120 °C, and the solution was magnetically
stirred. The reactions were periodically checked by GC and GC-MS.
7. Catalytic Oxidations in the Presence of Molecular Sieves.
Molecular sieves 4 Å (250 mg) were placed in the flask. A 0.024 mmol
portion of catalyst was dissolved in 1 mL of a toluene solution
containing 2.42 mmol of the corresponding alcohol and 200 μL of
p-xylene. The flask was then immersed in a bath at 120 °C, and the
solution was magnetically stirred. The reactions were periodically
checked by GC and GC-MS.
(6) (a) Coleman, K. S.; Coppe, M.; Thomas, C.; Osborn, J. A.
Tetrahedron Lett. 1999, 40, 3723. (b) Dobler, C.; Mehltretter, G. M.;
̈
Sundermeier, U.; Eckert, M.; Militzer, H.-C.; Beller, M. Tetrahedron
Lett. 2001, 42, 8447.
(7) Esteruelas, M. A.; Oro, L. A. Adv. Organomet. Chem. 2001, 47, 1.
(8) (a) Esteruelas, M. A.; Sola, E.; Oro, L. A.; Werner, H.; Meyer, U.
J. Mol. Catal. 1988, 45, 1. (b) Esteruelas, M. A.; Sola, E.; Oro, L. A.;
Werner, H.; Meyer, U. J. Mol. Catal. 1989, 53, 43. (c) Andriollo, A.;
́
Esteruelas, M. A.; Meyer, U.; Oro, L. A.; Sanchez-Delgado, R. A.; Sola,
E.; Valero, C.; Werner, H. J. Am. Chem. Soc. 1989, 111, 7431.
(d) Esteruelas, M. A.; Valero, C.; Oro, L. A.; Meyer, U.; Werner, H.
Inorg. Chem. 1991, 30, 1159. (e) Esteruelas, M. A.; Oro, L. A.; Valero,
́
C. Organometallics 1992, 11, 3362. (f) Sanchez-Delgado, R. A.;
Rosales, M.; Esteruelas, M. A.; Oro, L. A. J. Mol. Catal. A: Chem. 1995,
96, 231.
(9) Esteruelas, M. A.; Oro, L. A.; Valero, C. Organometallics 1991, 10,
8. Disproportionation of Cinnamyl Alcohol Catalyzed by
Complex 2. Complex 2 (14.6 mg, 0.024 mmol) was dissolved in
1 mL of a toluene solution containing 2.42 mmol of cinnamyl alcohol
(308 μL, 2.4 mmol) and 200 μL of p-xylene. The flask was then
immersed in a bath at 120 °C, and the solution was magnetically stirred.
The reaction was periodically checked by GC and GC-MS. After 24 h
the chromatograms showed that 78% of the starting cinnamyl alcohol
had been converted into cinnamaldehyde and 2-phenylpropanol (ratio
1:1), along with a small amount of 3-phenylpropanal.
462.
(10) Esteruelas, M. A.; Herrero, J.; Lop
Organometallics 2001, 20, 3202.
(11) (a) Cobo, N.; Esteruelas, M. A.; Gonzal
Lopez, A. M.; Lucio, P.; Olivan, M. J. Catal. 2004, 223, 319.
(b) Esteruelas, M. A.; Gonzalez, F.; Herrero, J.; Lucio, P.; Olivan, M.;
Ruiz-Labrador, B. Polym. Bull. 2007, 58, 923.
́ ́
ez, A. M.; Olivan, M.
́
ez, F.; Herrero, J.;
́
́
́
́
(12) Esteruelas, M. A.; Sola, E.; Oro, L. A.; Meyer, U.; Werner, H.
Angew. Chem., Int. Ed. Engl. 1988, 27, 1563.
(13) Liu, C.; Wang, J.; Meng, L.; Deng, Y.; Li, Y.; Lei, A. Angew.
Chem., Int. Ed. 2011, 50, 5144.
ASSOCIATED CONTENT
* Supporting Information
Text giving experimental details. This material is available free
of charge via the Internet at http://pubs.acs.org.
■
(14) (a) Suzuki, T.; Morita, K.; Matsuo, Y.; Hiroi, K. Tetrahedron
Lett. 2003, 44, 2003. (b) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein,
D. J. Am. Chem. Soc. 2005, 127, 10840. (c) Izumi, A.; Obora, Y.;
Sakaguchi, S.; Ishii, Y. Tetrahedron Lett. 2006, 47, 9199. (d) Arita, S.;
Koike, T.; Kayaki, Y.; Ikariya, T. Chem. Asian J. 2008, 3, 1479.
(e) Bertoli, M.; Choualeb, A.; Lough, A. J.; Moore, B.; Spasyuk, D.;
Gusev, D. G. Organometallics 2011, 30, 3479. (f) Musa, S.;
Shaposhnikov, I.; Cohen, S.; Gelman, D. Angew. Chem., Int. Ed.
2011, 50, 3533. (g) Gowrisankar, S.; Neumann, H.; Beller, M. Angew.
Chem., Int. Ed. 2011, 50, 5139.
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: maester@unizar.es.
■
ACKNOWLEDGMENTS
Financial support from the MICINN of Spain (Projects
CTQ2008-00810 and Consolider Ingenio 2010 CSD2007-
00006), the Departamento de Ciencia, Tecnologıa y Uni-
versidad del Gobierno de Arago
■
(15) Kunz, D. Angew. Chem., Int. Ed. 2007, 46, 3405.
(16) Casey, C. P.; Czerwinski, C. J.; Fusie, K. A.; Hayashi, R. K.
J. Am. Chem. Soc. 1997, 119, 3971.
́
(17) Esteruelas, M. A.; Hernan
Rubio, L. Organometallics 2008, 27, 799.
́ ́
dez, Y. A.; López, A. M.; Olivan, M.;
́
6406
dx.doi.org/10.1021/om200684m|Organometallics 2011, 30, 6402−6407

Organometallics
Article
(18) Barrio, P.; Esteruelas, M. A.; Onate, E. Organometallics 2004, 23,
̃
1340.
(19) (a) Robinson, N. P.; Main, L.; Nicholson, B. K. J. Organomet.
Chem. 1988, 349, 209. (b) Cambie, R. C.; Metzler, M. R.; Rutledge, P.
S.; Woodgate, P. D. J. Organomet. Chem. 1990, 398, C22. (c) Kakiuchi,
F.; Sato, T.; Igi, K.; Chatani, N.; Murai, S. Chem. Lett. 2001, 386.
(20) Eguillor, B.; Esteruelas, M. A.; Olivan
Organometallics 2004, 23, 6015.
́
, M.; Onate, E.
̃
(21) Matsubara, T.; Koga, N.; Musaev, D. G.; Morokuma, K.
Organometallics 2000, 19, 2318.
(22) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev.
2004, 248, 2201.
(23) Wasilke, J.-C.; Obrey, S. J.; Baker, R. T.; Bazan, G. C. Chem. Rev.
2005, 105, 1001.
(24) Esteruelas, M. A.; Werner, H. J. Organomet. Chem. 1986, 303,
221.
(25) Parent, J. S.; McManus, N. T.; Rempel, G. L.; Power, W. P.;
Marder, T. B. J. Mol. Catal. A: Chem. 1998, 135, 285.
6407
dx.doi.org/10.1021/om200684m|Organometallics 2011, 30, 6402−6407