Intermolecular Hydroalkoxylation of Terminal Alkynes Catalyzed by a Dipyrrinato Rhodium(I) Complex with Unusual Selectivity

Article abstract of DOI:10.1021/acs.organomet.5b00561

An operationally simple and atom-economical method for the E-selective preparation of enol ethers is described. A novel dicarbonyl(5-phenyldipyrrinato)rhodium complex, 2, was prepared in four synthetic steps, characterized by X-ray crystallography and NMR

Full text of DOI:10.1021/acs.organomet.5b00561

Article
pubs.acs.org/Organometallics
Intermolecular Hydroalkoxylation of Terminal Alkynes Catalyzed by
a Dipyrrinato Rhodium(I) Complex with Unusual Selectivity
†
,‡
†,‡
†
†,‡
§
Raphael H. Lam, D. Barney Walker, Matthew H. Tucker, Mark R. D. Gatus, Mohan Bhadbhade,
,
†,‡
and Barbara A. Messerle*
†
School of Chemistry, The University of New South Wales, Sydney 2052, Australia
‡
Department of Chemistry and Biomolecular Sciences, Macquarie University, North Ryde, 2109, Australia
§Mark Wainwright Analytical Centre, The University of New South Wales, Sydney 2052, Australia
*
S Supporting Information
ABSTRACT: An operationally simple and atom-economical
method for the E-selective preparation of enol ethers is
described. A novel dicarbonyl(5-phenyldipyrrinato)rhodium
complex, 2, was prepared in four synthetic steps, characterized
by X-ray crystallography and NMR spectroscopy, and then
investigated as a catalyst for the intermolecular hydro-
alkoxylation of terminal alkynes. Solvent and substrate studies
were used to gain insight into the mechanism of the reaction.
Cyclic voltammetry was also used to investigate the electronic
properties of 2. The rhodium(I)-catalyzed intermolecular alkyne hydroalkoxylation reaction reported here mediates excellent
substrate transformation with a high degree of E/Z selectivity which is opposite to that reported previously using alternative
catalysts.
INTRODUCTION
rhodium complex (1) (Scheme 1a) to selectively form (Z)-
■
enol ethers with no observable quantity of the undesired
The development of atom-economical methods for the
intermolecular hydroalkoxylation of alkynes is important,
because the reactive enol ethers formed are versatile building
9
Markovnikov product formed.
While the application of dipyrrin-based molecules for the
1
10
blocks in organic synthesis. Enol ethers can be hydrolyzed to
assembly of fluorescent dyes is well established, the use of
2
yield aldehydes and ketones, employed as substrates for cross-
bidentate dipyrrinato (dpm) ligands as scaffolds for promoting
3
4
coupling and ring-closing metathesis reactions. Enol ethers
can also be utilized as building blocks in cycloaddition
Scheme 1. Hydroalkoxylation of Terminal Alkynes: (a) Z
Selective, Kakiuchi; (b) E Selective, This Work
5
transformations and have consequently proved to be useful
intermediates in the programmed synthesis of bioactive
6
7
molecules with medicinal applications.
The potential utility of transition-metal-catalyzed addition of
oxygen nucleophiles to triple bonds has driven the growth of
interest in the intermolecular hydroalkoxylation of alkynes, and
8
this area has been comprehensively reviewed. There are two
mechanisms that are broadly accepted for this reaction:
coordination of the transition metal to the triple bond, enabling
nucleophilic attack by the oxygen, or the formation of a
vinylidene intermediate. The latter is more commonly observed
for terminal alkynes, as the mechanism is thought to involve a
β-hydride elimination step following deprotonation of the
terminal alkyne. Irrespective of the mechanism, controlling the
regioselectivity of the products formed following intermolecular
hydroalkoxylation has persisted as a major challenge, and
general and reliable methods are still sought after. In 2011,
Kakiuchi and co-workers made significant progress toward
controlling the regioselectivity of the reaction by demonstrating
that the intermolecular hydroalkoxylation reaction could be
catalyzed under mild conditions using an 8-quinolinolato
Received: June 27, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00561
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
transition-metal-mediated catalysis have not been as extensively
investigated. The Betley research group have made several
significant advances in the area of C−H bond activation using
Single crystals of 2 suitable for X-ray analysis were grown by
slow cooling of a hot, saturated solution of the complex in
toluene (Figure 1). The X-ray crystal structure confirms the
anticipated square-planar geometry of the primary coordination
sphere of 2 (Figure 1). The conformation of the flat rhodacycle
in complex 2 is in contrast to the distorted-boat conformation
11,12
iron and cobalt dpm complexes as catalysts.
Several other
groups have utilized the dpm motif within larger polydentate
ligand architectures, forming complexes with Ge and Ti for
13
15a
polymerizing CO and epoxides. Considering the utility of
adopted by the rhodacycle of complex 3 (Scheme 2).
2
complexes of first-row transition metals with dipyrrinato ligands
for catalysis, there are remarkably few examples of rhodium
dpm complexes that have been used for catalysis. The catalytic
properties of rhodium dipyrrinato complexes have barely been
investigated, with only one example in the literature using
Rh(III) for catalyzing the transfer hydrogenation of tereph-
Complex 2 has a mirror plane through the atoms C9a−C5a−
i
Rh1. The Rh−N1a/N1a bond lengths of 2.065 Å in complex 2
are shorter than the Rh−N bond lengths in the analogous
complex 3 due to the anionic charge of the dpm ligand. The
i
Rh−C1/C1 bond lengths of 1.855 Å in complex 2 are also
slightly shorter than the analogous bonds in complex 3. The
1
4
i
thalaldehyde and no examples of catalysis using Rh(I).
We became interested in investigating Rh(I) dpm complexes
as catalysts due to their structural similarity as well as a relative
electronic difference in comparison to our previously reported
positively charged bis(pyrazol-1-yl)methane (bpm) Rh(I) and
Ir(I) complexes, which have proven to be effective catalysts for
N1a−Rh1−N1a bond angle of 87° implies only a slight
distortion from the ideal angle of 90°. Additionally, the six-
membered metallacycle of complex 2 is close to being planar,
with the largest torsion angle within the metallacycle which
consists of the atoms C5a−C4a−N1a−Rh1 being 3.04°.
15
hydroelementation reactions. We were also interested in the
potential of the planar geometry of Rh(I) dpm complexes in
16
forming the basis of efficient hybrid catalyst materials or
15e
effective new bimetallic catalysts,
since previous examples
containing the bpm ligand motif can adopt various, easily
interconvertible conformations that prevent the determination
17
of a well-defined intermetallic distance. Here we report
dicarbonyl(5-phenyldipyrrinato)rhodium ([Rh(CO) dpm], 2)
2
as a catalyst for the intermolecular hydroalkoxylation of alkynes
(
Figure 1b) and show that this complex can promote the
synthesis of enol ethers with stereoselectivity opposite to that
Figure 1. Molecular structure of complex 2. Hydrogen atoms have
observed in Kakiuchi’s study.
been omitted for clarity. Ellipsoids are at the 50% probability level.
i
Selected bond lengths (Å) and angles (deg): Rh−C1 1.855, Rh−C1
RESULTS AND DISCUSSION
i
i
■
1.855, Rh−N1a 2.065, Rh−N1a 2.065; C1 −Rh1−C1 86.69, C1−
i i i
The complex [Rh(CO) dpm] (2) was readily prepared in four
Rh1−N1a 92.38, N1a −Rh1−N1a 88.58, N1a−Rh1−C1 92.38.
2
18
synthetic steps with an overall yield of 15% (Scheme 2).
The electron structure of the primary coordination sphere of
complex 2 is likely to closely match that of the 8-quinolinolato
rhodium complex 1, and so we reasoned that the dipyrrinato
Rh(I) complex 2 would have potential as a hydroalkoxylation
catalyst. A test run of the 2-catalyzed hydroalkoxylation
reaction was carried out using phenylacetylene (4a) and
methanol as substrates. Pleasingly, phenylacetylene (4a) was
cleanly converted to (2-methoxyvinyl)benzene (5a) when
stirred in methanol/N,N-dimethylacetamide (DMA) at 70 °C
Scheme 2. Synthesis of [Rh(CO) dpm] (2) and Structure of
2
the Closely Related Analogue [Rh(CO) bpm][BArF] (3)
2
1
for 24 h in the presence 2 mol% of 2, as determined by H
NMR spectroscopy (Table 1, entry 1). The reaction showed no
Markovnikov addition product, and the E:Z product ratio was
6
:1. Interestingly, the product selectivity was opposite to that
9
reported by Kakiuchi. Reducing the catalyst loading to 1 mol
did not affect substrate conversion and actually moderately
%
improved the selectivity of the reaction to a 7:1 ratio of E:Z
isomers (Table 1 entry 2). After purification, the isolated yield
of combined E:Z products was 95%.
Benzaldehyde was condensed with excess pyrrole in the
presence of an InCl Lewis acid catalyst, followed by oxidation
To verify the effect of oxygen and water, which can lead to
deactivation/decomposition of organometallic catalysts or
compete with substrates to occupy binding sites, the catalyzed
hydroalkoxylation reaction was repeated in the presence of O2
(Table 1, entry 3) or water (Table 1, entry 4), respectively. The
intermolecular hydroalkoxylation reaction under investigation
was shown to be sensitive to oxygen (Table 1, entry 3) with a
reduction in conversion to 50% observed when the reaction was
undertaken in the presence of oxygen, accompanied by a slight
increase in selectivity for the E product (8:1). The reaction
3
of the newly formed 5-phenyldipyrromethane using p-chloranil
to furnish 6′ in 31% yield over the two steps. 6′ was
deprotonated at the N position of the pyrrole ring with
triethylamine in the presence of [Rh(μ-Cl)(COD)] following
2
1
8b
a method similar to that reported by Yadav.
The
intermediate complex [Rh(COD)dpm] (7) formed was
purified by column chromatography and then treated with
CO gas to give 2 as a dark orange solid in 51% yield over two
steps.
B
DOI: 10.1021/acs.organomet.5b00561
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 1. Hydroalkoxylation of Phenylacetylene under
Various Reaction Conditions
Table 2. Hydroalkoxylation of Selected Alkyne Substrates
Catalyst
loading
Conversion
a
E:Z
ratio of 5a
Entry
Cosolvent
Catalyst
(mol %)
of 4a (%)
1
2
DMA
2
2
2
2
3
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
>98
>98
50
6:1
DMA
7:1
b
3
DMA/O2
8:1
c
4
DMA/H O
57
2:1
2
d
5
6
7
8
9
DMA
N/A
N/A
5:1
DMF
>98
>98
43
DMSO
THF
5.4:1
N/A
N/A
N/A
N/A
MeCN
Acetone
33
1
1
0
1
24
-
34
a
1
Determined by H NMR spectroscopy. Conversion was determined
by comparing the ratio of the alkyne proton resonance (ca. 3 ppm)
1
and product alkene resonance (5−7 ppm) using H NMR spectros-
b
c
copy. Solvents were aerated prior to reaction. Solvents were wetted
d
with 10 drops of water. Unidentifiable decomposition products
observed.
resulted in 57% conversion in the presence of water with
significantly lower product selectivity and a trace amount of
aldehyde (Table 1, entry 4). Interestingly, the closely related
bis(pyrazol-1-yl)methane complex 3 is a poor catalyst for this
reaction, resulting only in substrate decomposition to
unidentifiable products under reaction conditions similar to
those used here for 2 (Table 1, entry 5).
The effect of the cosolvent on the product formation was
further investigated following these initial studies (Table 1).
The previously observed excellent substrate conversion was
retained in both DMF and DMSO (Table 1, entries 6 and 7),
but the selectivity of the reaction was less pronounced. Moving
to less polar cosolvents such as EtOAc, THF, and acetone
resulted in poor conversions, and using these cosolvents several
uncharacterized byproducts were formed during the reaction
(
Table 1, entries 8−10). Surprisingly, the reaction proceeds
very poorly in neat MeOH, suggesting that the cosolvent plays
an important role in the reaction (Table 1, entry 11).
With an effective protocol for the selective synthesis of (E)-
(
2-methoxyvinyl)benzene in hand, we commenced an inves-
tigation into substrate scope using readily available substrates
Table 2). Substituting the methanol with ethanol did not affect
(
the conversion, but product formation was significantly less
selective, dropping to a 3:1 E:Z ratio (Table 2, entry 2).
Introducing an electron-donating or -withdrawing group in the
para position of the aryl acetylene under investigation had no
effect on the efficacy of the reaction (Table 2, entries 3−5).
However, when both ortho and para positions were occupied
by methyl groups (Table 2, entry 6), the substrate conversion
decreased significantly, most likely due to steric hindrance. The
hydroalkoxylation of an alkyne substrate with no aryl
substituents, 1-octyne, with methanol resulted in poor
conversion (14%, Table 2, entry 7), with predominant
formation of the E isomer. Replacing the saturated alkyl
substituents with a cyclic alkene led to high levels of conversion
to 5h. Interestingly, substituting the phenyl ring with pyridine
a
b
1
Isolated yield in parentheses. E:Z ratio determined by H NMR
spectroscopy.
(Table 2, entry 9) subdues the reaction efficiency with inversed
product selectivity in comparison to entries 1−6. Using internal
aromatic and alkyl alkynes (Table 2, entries 11 and 12) did not
yield any hydroalkoxylation products.
The observation that complex 2 only promotes the
transformation of terminal alkynes suggests that complex 2
C
DOI: 10.1021/acs.organomet.5b00561
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
may also form a vinylidene complex as a reaction intermediate
on reaction with the terminal alkynes, as proposed by Kakiuchi
second oxidized species. In contrast, complex 3 (Figure 2, blue)
showed an irreversible anodic peak at +1.14 V and no
observable reduction peak or multiple oxidized products. The
current intensity of this peak is substantially lower than the
anodic peaks of complex 2, despite both Rh(I) complexes being
examined by CV at 1 mM concentration. The reduced curren−t
intensity of 3 may be due to the bulkiness of the BArF
counterion reducing the diffusion coefficient or possible partial
9
et al. and supported by the computer simulation by Wang et
19
al. Formation of such a complex involves migration of the
terminal proton via a 1,2-β-hydride transfer before attack by the
alcohol.
The mechanism of the intermolecular hydroalkoxylation of
terminal acetylenes using 2 would appear to be very different
from the mechanism of intramolecular hydroalkoxylation of
alkynes using the bpm-based complex 3 that we have
22
ion pairing in CH Cl .
2
2
From the voltammograms, complex 2 was shown to oxidize
at a potential less positive than that of complex 3 by 180 mV.
Should the intermolecular hydroalkoxylation reaction proceed
via the vinylidene formation mechanism, complex 2 could lead
to an intermediate more stable than that formed on using
complex 3, whereas the intramolecular catalyzed reactions may
proceed via a different mechanism involving a Rh(I) ion (such
as π coordination to the triple bond). The second oxidized
species observed in the voltammogram of complex 2 may also
in fact be the active species during catalysis.
20
intensively investigated in our laboratory. In the case of the
latter, we have clearly shown using low-temperature NMR
spectroscopy that intramolecular dihydroalkoxylation is readily
promoted and the reaction proceeds via π coordination of the
alkyne substrate to the metal center followed by the sequential
15a
addition of two hydroxyl groups. We have not unambigu-
ously determined the mechanism of the anti-Markovnikov
addition of methanol to terminal acetylenes using complex 2.
However, it is likely that product formation is directed via a
8c
vinylidene rhodium intermediate that precludes Markovnikov
addition as well as the reaction of internal alkynes that do not
have the requisite terminal alkynyl proton. The origin of the
observed E selectivity is the subject of current investigation in
our laboratory.
CONCLUSIONS
■
In summary, we have determined that the dipyrrinato
rhodium(I) complex 2 is an effective catalyst for the
intermolecular hydroalkoxylation of terminal alkynes. In this
case it is likely that the reaction occurs via a vinylidene
intermediate, as internal alkynes were shown to be unreactive
with methanol under the reaction conditions investigated. The
intermolecular hydroalkoxylation reaction catalyzed by complex
To gain further insight into the reaction mechanism, the
electrochemical properties of complex 2 and the structurally
similar complex 3 were investigated using cyclic voltammetry
(CV, Figure 2) under inert conditions. Measurements were
2
was shown to be robust and selective for a range of substrates,
with good to excellent yields and preferential formation of the E
product in most cases. Cyclic voltammetry reveals that the
potential at which the Rh(I) metal center of complex 2 is
oxidized is 180 mV lower than the bis-pyrazole Rh(I) complex
3
, suggesting that a more readily accessible Rh(III) center may
play an important role in the hydroalkoxylation reaction.
However, we cannot rule out the possibility that a second more
active species may be formed during the reaction, which may go
some way in explaining the sensitivity of the reaction to the
cosolvent. Overall, the surprising catalytic activity promoted by
a Rh(I) complex containing the well-known dipyrrinato ligand
suggests that interesting catalyst scaffolds could be assembled
using this readily accessed planar moiety.
Figure 2. Cyclic voltammograms of complex 2 (red) and complex 3
(
blue), both 1 mM in 0.1 M [Bu N][PF ]/CH Cl supporting
4 6 2 2
EXPERIMENTAL SECTION
■
electrolyte at 100 mV/s.
General Procedures. All manipulations of metal complexes and
air-sensitive reagents were carried out using standard Schlenk
techniques; catalysis experiments were carried out using a Radleys
Discovery Technologies GreenHouse Parallel Synthesizer and stand-
initiated at 0 V at a scan rate of +100 mV/s. Electrode
potentials reported herein are referenced to the ferrocene/
ferrocenium couple, and the voltammograms are plotted
without correction.
The cyclic voltammogram of complex 2 (Figure 2, red)
indicates an irreversible anodic peak at +0.96 V. A small
reduction peak was observed at −0.88 V. On comparison with
the cyclic voltammograms of other planar Rh(I) complexes
containing anionic ligands and CO coligands, the anodic peak
at +0.96 V was assigned to be the Rh(I)/Rh(III) oxidation
process, whereas the reduction peak at −0.88 V corresponds to
the reduction of a Rh(III) species. The different intensities in
the anodic and cathodic peaks in the cyclic voltammogram of
complex 2 suggested that the oxidized Rh(III) species may have
ard Schlenk techniques under an N (g) atmosphere. Unless otherwise
2
stated, chemicals were purchased from Alfa Aesar Inc. or Aldrich
Chemical Co. Inc. and used as received. Rhodium(III) chloride
hydrate was purchased from Precious Metals Online P/L and used
without further purification. Pyrrole was distilled before use. [Rh(μ-
2
3
18a
Cl)(COD)] , 5-phenyldipyrromethane (6), and 5-phenyldipyrrin
2
2
4
(6′) were synthesized according to reported procedures. Solvents for
21
catalysis were deoxygenated with N
.
2
For the purposes of air-sensitive manipulations and preparation of
metal complexes, solvents were dispensed from a PuraSolv solvent
purification system and stored under a nitrogen or argon atmosphere
in glass ampules fitted with J. Young Teflon valves. Nitrogen gas for
Schlenk line operation came from in-house liquid nitrogen boil-off.
Bulk compressed gases of nitrogen (>99.5%) and carbon monoxide
21
been decomposing or diffusing into the bulk solution. In
addition, a small shoulder at 1.14 V grew after multiple scans
(
>99.5%) were obtained from Air Liquide.
X-ray Crystallography. Suitable single crystals of 2 selected under
(see the Supporting Information), indicating the formation of a
the polarizing microscope (Leica M165Z) were picked up on a
D
DOI: 10.1021/acs.organomet.5b00561
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
MicroMount (MiTeGen, USA) consisting of a thin polymer tip with a
wicking aperture. The X-ray diffraction measurements were carried out
on a Bruker Kappa-II CCD diffractometer at 150 K by using graphite-
monochromated Mo Kα radiation (λ = 0.710723 Å). The single
crystal, mounted on the goniometer using cryo loops for intensity
measurements, was coated with paraffin oil and then quickly
transferred to the cold stream using an Oxford Cryo stream
attachment. Symmetry-related absorption corrections using the
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00561.
■
*
S
1
Additional experimental details, H NMR spectra, and
crystallographic data (PDF)
X-ray crystal structure information for 2 (CIF)
25
program SADABS were applied, and the data were corrected for
2
6
Lorentz and polarization effects using Bruker APEX2 software. All
structures were solved by direct methods, and full-matrix least-squares
AUTHOR INFORMATION
Corresponding Author
E-mail for B.A.M.: barbara.messerle@mq.edu.au.
27
■
*
refinements were carried out using SHELXL. The non-hydrogen
atoms were refined anistropically. Key crystallographic data and
refinement details are given in Table S1. in the Supporting
Information.
Notes
Synthesis of the Intermediate Complex [Rh(COD)dpm] (7).
The authors declare no competing financial interest.
Et N (0.96 mL, 6.89 mmol) was added to a solution of 6′ in DCM/
3
MeOH (194 mg, 0.88 mmol; 30 mL of DCM and 20 mL of MeOH)
ACKNOWLEDGMENTS
■
followed by [Rh(μ-Cl)(COD)] (216 mg, 0.88 mmol). The resultant
2
R.H.L. acknowledges a Macquarie University Research Training
Pathway Scholarship. Financial support from the UNSW and
Macquarie University is gratefully acknowledged. This research
was supported under the Australian Research Council’s
Discovery Projects funding scheme (DP110101611).
dark red solution was stirred for 1 h at room temperature. The solvent
was evaporated under reduced pressure. The residue was redissolved
in DCM and then passed through an alumina column (neutral or
basic; eluent hexane/DCM 2/1 v/v). The clear red fractions were
combined, and the solvent was evaporated to yield 7 as a dark red solid
1
(
274 mg, 0.636 mmol, 72%). H NMR (300.2 MHz, CD Cl ): δ 1.88−
2
2
REFERENCES
■
2
6
2
.16 (m, 4H, COD −CH −), 2.38−66 (m, 4H, COD −CH −), 4.50−
2
2
3
3
(1) Effenberger, F. Angew. Chem., Int. Ed. Engl. 1969, 8, 295−312.
(2) (a) Kosarych, Z.; Cohen, T. Tetrahedron Lett. 1980, 21, 3959−
962. (b) Jung, M. E.; Cordova, J.; Murakami, M. Org. Lett. 2009, 11,
882−3885. (c) Sidoryk, K.; Korda, A.; Rarova, L.; Oklest’kova, J.;
́ ́ ̌ ́
Strnad, M.; Cmoch, P.; Pakulski, Z.; Gwardiak, K.; Karczewski, R.;
0 (m, 4H, COD CH−), 6.27 (dd, J
= 4.3 Hz, J
= 1.6 Hz,
H−H
H−H
3
4
H, PyH), 6.35 (dd, J
= 4.3 Hz, J
= 1.2 Hz, 2H, PyH), 7.10
H−H
H−H
3
3
(
m, 2H, PyH), 7.28−53 (m, 5H, ArH). The complex was used for the
carbonylation step without full characterization.
Synthesis of the Complex [Rh(CO) dpm] (2). 7 (250 mg, 0.57
2
Luboradzki, R. Tetrahedron 2015, 71, 2004−2012.
mmol) was dissolved in a minimum amount of DCM and degassed
with three freeze−pump−thaw cycles. The dark red solution was
stirred under a CO(g) atmosphere for 2 h. The mixture produced a
dark brown precipitate in a yellow solution. The precipitate was
(3) (a) Hayashi, T.; Katsuro, Y.; Kumada, M. Tetrahedron Lett. 1980,
2
1, 3915−18. (b) Pedzisa, L.; Vaughn, I. W.; Pongdee, R. Tetrahedron
Lett. 2008, 49, 4142−4144.
(4) Donohoe, T. J.; Fishlock, L. P.; Lacy, A. R.; Procopiou, P. A. Org.
Lett. 2007, 9, 953−956.
filtered, washed with pentane (3 × 20 mL), and dried in vacuo to yield
1
2
as a dark orange solid (156 mg, 0.414 mmol, 72%). H NMR (300.2
(5) (a) de los Santos, J. M.; Ignacio, R.; Es Sbai, Z.; Aparicio, D.;
Palacios, F. J. Org. Chem. 2014, 79, 7607−7615. (b) Gao, S.; Chen, J.-
R.; Hu, X.-Q.; Cheng, H.-G.; Lu, L.-Q.; Xiao, W.-J. Adv. Synth. Catal.
2013, 355, 3539−3544. (c) Donohoe, T. J.; Fishlock, L. P.; Lacy, A.
R.; Procopiou, P. A. Org. Lett. 2007, 9, 953−956. (d) Roche, C.;
Delair, P.; Greene, A. E. Org. Lett. 2003, 5, 1741−1744. (e) Shirakawa,
S.; Lombardi, P. J.; Leighton, J. L. J. Am. Chem. Soc. 2005, 127, 9974−
3
3
MHz, CD Cl ): δ 6.43 (dd, J
= 4.4 Hz, J
= 1.6 Hz, 2H,
2
2
H−H
H−H
3
4
PyH4), 6.55 (dd, J
= 4.3 Hz, J
= 1.1 Hz, 2H, PyH3), 7.28−59
H−H
13
H−H
(
m, 5H, ArH), 7.78 (m, 2H, PyH5). C NMR (75 MHz, CD Cl ): δ
2 2
1
1
1
7
18.67 (PyC3), 127.67 (m-ArC), 129.08 (p-ArC), 130.79 (o-ArC),
32.44 (PyC4), 136.78 (PyC2), 138.15 (i-ArC), 155.30 (PyC5),
55.33 (methine C), 186.75 (CO). Anal. Found: C, 54.02; H, 2.96; N,
.38. Calcd for C H N O Rh: C, 53.99; H, 2.93; N, 7.41.
9
975. (f) Puglisi, A.; Lee, A.-L.; Schrock, R. R.; Hoveyda, A. H. Org.
Lett. 2006, 8, 1871−1874.
6) (a) Sultana, S.; Indukuri, K.; Deka, M. J.; Saikia, A. K. J. Org.
, G.;
17
11
2
2
General Procedure for Catalyzed Hydroalkoxylation. Sub-
(
strate and cosolvent screenings were carried out in a Radleys Discovery
Technologies Parallel Synthesizer. Alcohol (0.5 mL), cosolvent (0.5
mL), alkyne (0.455 mmol), and catalyst (1.9 mg, 5.0 μmol, 1.1 mol %)
were charged into test tubes with a magnetic stirrer bar and placed in
the Synthesizer. The reaction chamber was carefully evacuated and
refilled with nitrogen gas over five cycles and then heated to 70 °C
with stirring for 24 h. When they were cooled to room temperature,
Chem. 2013, 78, 12182−12188. (b) Tomas, L.; Boije af Gennas
̈
Hiebel, M. A.; Hampson, P.; Gueyrard, D.; Pelotier, B.; Yli-
Kauhaluoma, J.; Piva, O.; Lord, J. M.; Goekjian, P. G. Chem. - Eur. J.
2
012, 18, 7452−7466. (c) Jahangiri, G. K.; Reymond, J.-L. J. Am.
Chem. Soc. 1994, 116, 11264−74.
(7) Fujimura, O.; Fu, G. C.; Grubbs, R. H. J. Org. Chem. 1994, 59,
4029−4031.
the reaction mixtures were diluted to 1.5 mL with Et O and washed
with LiCl solution (0.1 M, 2 × 2 mL). The organic phase was dried
(8) (a) Goodwin, J. A.; Aponick, A. Chem. Commun. (Cambridge, U.
K.) 2015, 51, 8730−8741 and references therein. (b) Alonso, F.;
Beletskaya, I. P.; Yus, M. Chem. Rev. 2004, 104, 3079−159. (c) Evano,
G.; Gaumont, A.-C.; Alayrac, C.; Wrona, I. E.; Giguere, J. R.;
Delacroix, O.; Bayle, A.; Jouvin, K.; Theunissen, C.; Gatignol, J.;
Silvanus, A. C. Tetrahedron 2014, 70, 1529−1616.
2
with saturated brine solution (3 mL) and Na SO , and the solvent was
2
4
1
removed in vacuo. Products were analyzed using H NMR
spectroscopy.
Scaled-up reactions were carried out in Schlenk flasks under a N (g)
2
(
9) Kondo, M.; Kochi, T.; Kakiuchi, F. J. Am. Chem. Soc. 2011, 133,
2−34.
10) (a) Loudet, A.; Burgess, K. Chem. Rev. (Washington, DC, U. S.)
atmosphere. Reagents were charged into Schlenk flasks, stoppered, and
heated with stirring at 70 °C for 24 h. When the mixtures were cooled,
3
(
crude products were diluted with Et O (20 mL) and washed with LiCl
2
2007, 107, 4891−4932. (b) Ulrich, G.; Ziessel, R.; Harriman, A.
Angew. Chem., Int. Ed. 2008, 47, 1184−1201. (c) Boens, N.; Leen, V.;
Dehaen, W. Chem. Soc. Rev. 2012, 41, 1130−1172.
(11) Hennessy, E. T.; Betley, T. A. Science (Washington, DC, U. S.)
2013, 340, 591−595.
solution (0.1 M, 2 × 30 mL). The organic phase was dried with
saturated brine solution (30 mL) and Na SO , filtered, and then
2
4
concentrated in vacuo. Crude products were purified on silica gel
column pretreated with Et N.
3
E
DOI: 10.1021/acs.organomet.5b00561
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
1
(
1
(
4
(
12) King, E. R.; Sazama, G. T.; Betley, T. A. J. Am. Chem. Soc. 2012,
34, 17858−17861.
13) Nakano, K.; Kobayashi, K.; Nozaki, K. J. Am. Chem. Soc. 2011,
33, 10720−10723.
14) Yadav, M.; Singh, A. K.; Pandey, D. S. Organometallics 2009, 28,
713−4723.
15) (a) Ho, J. H. H.; Hodgson, R.; Wagler, J.; Messerle, B. A. Dalton
Trans. 2010, 39, 4062−4069. (b) Tregubov, A. A.; Vuong, K. Q.;
Luais, E.; Gooding, J. J.; Messerle, B. A. J. Am. Chem. Soc. 2013, 135,
1
6429−16437. (c) Choy, S. W. S.; Page, M. J.; Bhadbhade, M.;
Messerle, B. A. Organometallics 2013, 32, 4726−4729. (d) Man, B. Y.
W.; Bhadbhade, M.; Messerle, B. A. New J. Chem. 2011, 35, 1730−
1
739. (e) Ho, J. H. H.; Choy, S. W. S.; MacGregor, S. A.; Messerle, B.
A. Organometallics 2011, 30, 5978−5984. (f) Field, L. D.; Messerle, B.
A.; Rehr, M.; Soler, L. P.; Hambley, T. W. Organometallics 2003, 22,
2
(
387−2395.
16) Tregubov, A. A.; Walker, D. B.; Vuong, K. Q.; Gooding, J. J.;
Messerle, B. A. Dalton Transactions 2015, 44, 7917−7926.
17) Timerbulatova, M. G.; Gatus, M. R. D.; Vuong, K. Q.;
(
Bhadbhade, M.; Algarra, A. G.; MacGregor, S. A.; Messerle, B. A.
Organometallics 2013, 32, 5071−5081.
(
18) (a) Laha, J. K.; Dhanalekshmi, S.; Taniguchi, M.; Ambroise, A.;
Lindsey, J. S. Org. Process Res. Dev. 2003, 7, 799−812. (b) Yadav, M.;
Kumar, P.; Pandey, D. S. Polyhedron 2010, 29, 791−800.
(
19) Dang, Y.; Qu, S.; Wang, Z.-X.; Wang, X. Organometallics 2013,
3
2, 2804−2813.
20) Messerle, B. A.; Vuong, K. Q. Organometallics 2007, 26, 3031−
040.
21) Ferreira, H.; Conradie, M. M.; Conradie, J. Electrochim. Acta
013, 113, 519−526.
22) Kumar, P. G. A.; Pregosin, P. S.; Goicoechea, J. M.; Whittlesey,
M. K. Organometallics 2003, 22, 2956−2960.
23) Choudhury, J.; Podder, S.; Roy, S. J. Am. Chem. Soc. 2005, 127,
162−6163.
24) Yu, L.; Muthukumaran, K.; Sazanovich, I. V.; Kirmaier, C.;
(
3
(
2
(
(
6
(
Hindin, E.; Diers, J. R.; Boyle, P. D.; Bocian, D. F.; Holten, D.;
Lindsey, J. S. Inorg. Chem. 2003, 42, 6629−6647.
(
(
(
25) SADABS; Bruker AXS, Madison, WI, USA, 2001.
26) APEX2 and SAINT; Bruker AXS, Madison, WI, USA, 2001.
27) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2
008, 64, 112−122.
F
DOI: 10.1021/acs.organomet.5b00561
Organometallics XXXX, XXX, XXX−XXX