Cyclometalated Ruthenium Pincer Complexes as Catalysts for the α-Alkylation of Ketones with Alcohols

Article abstract of DOI:10.1002/chem.202000396

Ruthenium PNP pincer complexes bearing supplementary cyclometalated C,N-bound ligands have been prepared and fully characterized for the first time. By replacing CO and H^? as ancillary ligands in such complexes, additional electronic and steric modifications of this topical class of catalysts are possible. The advantages of the new catalysts are demonstrated in the general α-alkylation of ketones with alcohols following a hydrogen autotransfer protocol. Herein, various aliphatic and benzylic alcohols were applied as green alkylating agents for ketones bearing aromatic, heteroaromatic or aliphatic substituents as well as cyclic ones. Mechanistic investigations revealed that during catalysis, Ru carboxylate complexes are predominantly formed whereas neither the PNP nor the CN ligand are released from the catalyst in significant amounts.

Full text of DOI:10.1002/chem.202000396

A Journal of
Accepted Article
Title: Cyclometalated Ruthenium Pincer Complexes as Catalysts for
the α-Alkylation of Ketones with Alcohols
Authors: Patrick Piehl, Roberta Amuso, Elisabetta Alberico, Henrik
Junge, Bartolo Gabriele, Helfried Neumann, and Matthias
Beller
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To be cited as: Chem. Eur. J. 10.1002/chem.202000396
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10.1002/chem.202000396
Chemistry - A European Journal
RESEARCH ARTICLE
Cyclometalated Ruthenium Pincer Complexes as Catalysts for the
α-Alkylation of Ketones with Alcohols
Patrick Piehl,[a] Roberta Amuso,[a,b] Elisabetta Alberico,[a,c] Henrik Junge,[a] Bartolo Gabriele,[b] Helfried
Neumann,[a] and Matthias Beller*[a]
[a]
P. Piehl, R. Amuso, Dr. E. Alberico, Dr. H. Junge, Dr. H. Neumann, and Prof. Dr. M. Beller
Leibniz-Institut für Katalyse e.V.
Albert-Einstein-Straße 29a, 18059 Rostock (Germany)
E-Mail: Matthias.Beller@catalysis.de
[b]
[c]
R. Amuso, Prof. Dr. B. Gabriele
Laboratory of Industrial and Synthetic Organic Chemistry (LISOC), Department of Chemistry and Chemical Technologies, University of Calabria,
Via Pietro Bucci 12/C, 87036 Arcavacata di Rende (CS), Italy
Dr. E. Alberico
Istituto di Chimica Biomolecolare, CNR,
tr. La Crucca 3, 07100 Sassari, Italy
Supporting information for this article is given via a link at the end of the document.
Abstract: Ruthenium PNP pincer complexes bearing supplementary
cyclometalated C,N-bound ligands have been prepared and fully
characterized for the first time. By replacing CO and H- as ancillary
ligands in such complexes, additional electronic and steric
modifications of this actual class of catalysts are possible. The
advantages of the new catalysts are demonstrated in the general
reactions.[10] Based on that, manifold variations concerning the
nature of the pincer ligand have been performed and the so
obtained complexes have shown to be interesting catalysts as
well.[1]
Looking at the popular pincer complexes, it is evident that
most of them rely on a similar set of ligands. Typically, besides
the pincer unit, carbon monoxide and hydride ligands are
employed herein. While this arrangement is generally known to
be crucial for reactivity and stability,[2d] obviously it does not allow
for any further variations. Hence, we had the idea to introduce
alternative ligands mimicking the behavior of CO and H- ligands.
More specifically, cyclometalation of N-heterocycles should
provide an active metal center due to the strongly σ-donating
C-donor (H- analogue) and the π-back bonding interaction with
the heterocycle (CO analogue).
α-alkylation of ketones with alcohols following
a hydrogen
autotransfer protocol. Herein, various aliphatic and benzylic alcohols
were applied as green alkylating agents for ketones bearing aromatic,
heteroaromatic or aliphatic substituents as well as cyclic ones.
Mechanistic investigations revealed that during catalysis
Ru carboxylate complexes are predominantly formed while neither
the PNP nor the CN ligand are released from the catalyst in significant
amounts.
Although neglected for a long time, in the past years cyclo-
metalated ruthenium complexes became of interest as redox
catalysts.[11] For example, Ru half-sandwich complexes bearing
Introduction
In the past two decades, metal pincer complexes have proven
to be exceptionally powerful catalysts for hydrogenation and
dehydrogenation reactions.[1-2] Especially ruthenium complexes
such as Ru-MACHO ([Ru]-1 in Scheme 1) were introduced for the
catalytic hydrogenation of esters,[3] organic carbonates,[4]
nitriles,[5] and others as well as for dehydrogenation reactions of
compounds like methanol[6] or ethanol.[7] In addition to that,
specifically [Ru]-1 was applied in hydrogen autotransfer reactions
producing γ-butyrolactones[8] and chiral N-alkyl sulfinamides.[9]
Furthermore, pyridine-based Ru pincer complexes [Ru]-2 and -3
were developed by Milstein and co-workers and have been
applied as efficient catalysts for numerous (de)hydrogenation
Scheme 2. Preparation of ruthenium pincer complexes bearing C,N-bound
heterocycle ligands.
Scheme 1. Frequently used Ru PNP pincer complexes.[1]
1
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10.1002/chem.202000396
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RESEARCH ARTICLE
bidentate ligands with a C and a P,[12] N,[13] or NHC[14] donor were
used for the transfer hydrogenation of ketones. Additionally,
ruthenacycles have been applied in the direct hydrogenation of
olefins,[15] the dehydrogenation of alcohols,[16] and the α-alkylation
of amides by a hydrogen autotransfer protocol.[17] In addition to
that, complexes bearing a carbon donor as part of the pincer
ligand were applied as catalysts for transfer hydrogenations,[18]
direct hydrogenations,[19] and acceptorless dehydrogenations.[20]
In line with this, Baratta and co-workers established highly
efficient Ru CNN complexes for the transfer hydrogenation of
ketones[21] or aldehydes,[22] the direct hydrogenation of
ketones,[23] and the racemization or deuteration of alcohols.[24]
Table 1: Catalyst comparison and optimization for α-alkylation of
acetophenone with 2-methoxyethanol.
#
[Ru]
Base
Base
Solvent
T
Yield (%)
Loading
(°C)
1
2
[Ru]-1
[Ru]-5
[Ru]-6
[Ru]-7
[Ru]-8
[Ru]-9
[Ru]-10
[Ru]-11
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
[Ru]-7
-
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
KOtBu
NaOtBu
NaOH
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
20 mol%
30 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
10 mol%
t-amyl alc.
t-amyl alc.
130
130
130
130
130
130
130
130
140
150
150
150
150
150
150
150
150
150
150
150
150
150
150
150
150
150
150
150
150
16
42
44
48
32
22
38
43
58
65
44
45
38
36
-
3
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
heptane
4
5
Results and Discussion
6
7
Following our concept vide supra, we attempted the synthesis
of [Ru]-5 via cyclometalation of [Ru(p-cym)Cl2]2 with 2-phenyl-
pyridine.[25] Next, an array of other heterocycles was employed to
prepare the corresponding intermediates, which were reacted
with aliphatic pincer ligands in 2-butanol. The desired complexes
[Ru]-5-12 precipitated during this reaction, giving powdery solids
ranging from bright yellow to ruby red in color (see Scheme 2). All
of them were subsequently characterized by NMR, IR, and MS
analyses and for representative examples, X-ray structural
analyses were performed (see Figure 1 and SI).
Having these novel complexes in hand, we were interested to
apply them in hydrogen autotransfer – also called hydrogen
borrowing – reactions.[26] In these cascade reactions, first,
hydrogen gets abstracted from an unreactive substrate, mostly an
alcohol, generating a more reactive intermediate like an aldehyde.
By this activation step, a variety of transformations is now
accessible, for instance forming new C‒C or C‒N double bonds
under elimination of water. Finally, the newly formed double bond
gets hydrogenated using the hydrogen abstracted in the first step.
More specifically, the α-alkylation of ketones with alcohols was of
interest.[27]
8
9
10
11
12
13
14
15
16
17
18[a]
19[b]
20[c]
21[b]
22[b]
23[b]
24[b]
25[b]
26[b]
27
28
29
K2CO3
NEt3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
-
66
64
57
68
60
41
38
53
37
10
-
toluene
THF
10 mol% 1,4-dioxane
10 mol%
-
water
t-amyl alc.
t-amyl alc.
t-amyl alc.
t-amyl alc.
Cs2CO3
Cs2CO3
Cs2CO3
10 mol%
10 mol%
10 mol%
-
[Ru]-12
[Ru]-1
46
31
Unless otherwise specified, reactions were carried out with 1a (1.0 mmol), 2a
(1.2 mmol), the catalyst (0.02 mmol), and the base (0.1 mmol) in 1 ml of solvent
at the indicated temperature for 22 h; [a] catalyst loading: 0.5 mol%; [b] catalyst
loading: 1 mol%; [c] catalyst loading: 3 mol%; yields determined by GC using
n-hexadecane as internal standard.
To compare the reactivity of the novel catalysts with the parent
Ru-MACHO system, the reaction of acetophenone with
2-methoxyethanol was investigated in tert. amyl alcohol at 130 °C
in the presence of catalytic amounts of cesium carbonate as base.
Under these conditions, [Ru]-1 only yielded in 16% of the desired
product (see Table 1, entry 1). In contrast, when the newly
synthesized catalysts are applied under identical conditions
higher yields up to 48% were obtained (Table 1, entries 2-8). Thus,
having confirmed that the introduced phenyl heterocycle ligands
can be beneficial for catalysis, we started optimizing the reaction
conditions using [Ru]-7, which bears benzo[h]quinoline as
additional ligand. Proceeding with this catalyst, an optimal yield of
68% could be obtained (Table1, entry 19). Notably, performing
the reaction without any catalyst or without base yielded in no
product formation at all. Interestingly, the application of [Ru]-12,
in which the NH is replaced by a N-methyl group gave 46% of the
desired product. This comparably high yield suggests that the NH
proton, while being beneficial to the catalyst performance, is not
Figure 1. Crystal structure of [Ru]-7. Displacement ellipsoids correspond to
30% probability. Hydrogen atoms (except the N-bound) and co-crystallized
solvent are omitted for clarity.
2
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10.1002/chem.202000396
Chemistry - A European Journal
RESEARCH ARTICLE
essential. For the [Ru]-12, where an outer-sphere mechanism
cannot be put forward, it can be proposed that the strong trans
influence of the C-Ru bond very likely promotes labilization of the
Ru-Cl bond and its substitution by the alkoxide. Although further
mechanistic investigations would be required to confirm the
following hypothesis, subsequent β-hydride elimination could
generate a Ru-hydride complex with ensuing formation of the
aldehyde.
satisfying yields (58 and 85%, respectively). Pleasingly, when
benzyl alcohol 2f is applied, the yield rises to 90%. Similarly,
substituted benzyl alcohols were used to give alkylated ketones
3ag and 3ah in 97 and 88% yield, respectively, and moreover,
1-naphthyl methanol 2i was converted to give the desired product
3ai in excellent 96% yield. Finally, 2-thiophenemethanol 2j and
3-pyridylmethanol 2k were applied as representatives of
heterocycle-bearing alcohols. Here, the corresponding products
were obtained in 62% and 69% yield, respectively.
Next, differently substituted acetophenone derivatives were
alkylated. Here, reactions preceded smoothly affording 38 to 58%
of the corresponding products 3ba to 3da. In line with this,
2-acetonaphthone was converted into 3ea in 57% yield and
2-acetyl heterocycles 1f and 1g gave 65 and 11%, respectively.
Furthermore, using α-tetralone 1h or 1-indanone 1i, the desired
products can be obtained in good yields of 89 and 85%,
respectively. In line with this, when substituted tetralone-derivates
1j and 1k are employed, the corresponding products are
generated in 81% yield in both cases.
This new class of complexes is not merely limited to the
beforehand discussed reactions, but they are as well able to
dehydrogenate amines allowing for their application in alkylating
ketones. To demonstrate this, 2-methoxyethylamine 4 was used
instead of the alcohol 2a, giving 3aa. In addition to that, diols like
1,2-benzenedimethanol
5 undergo cyclization to give the
corresponding cyclic lactone 6 under C-O bond formation in a very
good yield of 90%.
After having established
a gratifying substrate scope,
investigations concerning the reaction mechanism were carried
out. First, we wanted to find out, if the applied complex is capable
of forming stable ruthenium hydride species. In principle, it would
be possible that these species spontaneously release the hydride
Scheme 3. Substrate scope of the Ru-catalyzed α-alkylation of ketones and
related reactions. Isolated yields; [a] yield determined by GC using hexadecane
as internal standard.
Ultimately, we performed the reaction with 1a (1.0 mmol), 2a
(1.2 mmol), [Ru]-7 (0.01 mmol), and Cs2CO3 (0.1 mmol) in 1 ml
of t-amyl alcohol at 150 °C and chose these optimal conditions for
testing different substrates.
Reaction of 4-methoxybutanol (2b) gave 68% of the desired
product 3ab and exchanging the ether group for a tertiary amine,
the corresponding product 3ac was obtained in 38% yield.
Additionally, starting from simple, aliphatic alcohols like 1-butanol
2d or cyclohexylmethanol 2e, acetophenone was alkylated in
Scheme 4. Experiments to investigate the catalyst species involved in the
reaction.
3
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10.1002/chem.202000396
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RESEARCH ARTICLE
and the aryl heterocycle ligand via reductive elimination. However, activated by base probably through deprotonation of the NH group
when [Ru]-7 is treated with KHBEt3, two hydridic species can be
obtained and detected by 1H NMR spectroscopy (compare
Scheme 4, rct. I and SI). In a follow up experiment, one of these
hydride complexes is able to promptly hydrogenate
benzylideneacetophenone which corresponds to the last step of
the alkylation of ketones with alcohols.
and formation of a further N-Ru bond with displacement of the
carboxylate group, the same way chloride is displaced from [Ru]-
7.
Finally, experiments were performed concerning the stability
of the phenyl heterocycle ligand during catalysis. For this, the
NMR reaction was carried out under use of [Ru]-10 as catalyst to
investigate species involving this ligand by 19F NMR. Here again,
a species fitting to the corresponding carboxylate complex and
the starting material were observed. Besides this, only small
traces of other fluorine-containing species were detected,
indicating that the applied cyclometalated ligands in fact remain
bound to the complex during catalysis.
Subsequently, we wanted to find out, which catalyst species
are actually present under reaction conditions. For this, the
reaction was carried out in a pressure resistant NMR tube
(reaction conditions were adjusted to this by using THF-d8 as
solvent, shortened reaction times and higher catalyst loadings).
Here, besides starting complex [Ru]-7, one major species was
detected in 31P NMR (rct. II). To verify the nature of this species,
the NMR scale reaction was carried out using benzyl alcohol
instead of 2-methoxyethanol (rct. III). This resulted in a slightly
shifted 31P NMR signal suggesting that a different complex is
formed herein, when a different alcohol is deployed. Additionally,
the experiment was repeated without addition of the ketone
(rct. IV). Here, a similar species was detected by 31P NMR, while
it was not observed in a comparison experiment without alcohol
or ketone (see SI). The species formed in this reaction was further
characterized by NMR spectroscopy as well as X-ray structural
analysis. By this, it was revealed that the complex predominantly
present during catalysis is ruthenium carboxylate complex
[Ru]-13 (see Figure 2). Under reaction conditions, this species is
probably generated by hydration of the in situ formed aldehyde
followed by catalytic dehydrogenation of the so-formed gem-
diol.[6c, 28] The required water for this likely stems from the aldol
condensation taking place during catalysis or from moisture
present in the alcohols as these have not been dried prior to use.
Attempts to synthesize [Ru]-13 independently in the best case
yielded in a mixture of 78% of it and the starting complex [Ru]-7
(see SI for details). However, when this mixture was applied in the
standard reaction, the product was obtained in similar 68%. Due
to this, [Ru]-13 likely depicts a catalyst reservoir and can be
Conclusion
Summing up, cyclometalated aryl heterocycles can be used
as a tunable mimic of carbonyl and hydride ligands in popular
ruthenium pincer complexes. Following this concept, a series of
novel potent catalysts for (de)hydrogenations have been obtained.
The general advantage of such catalysts compared to the parent
complex is demonstrated for the green α-alkylation of ketones
with alcohols. Plausible reaction intermediates were investigated
for this, all still involving the intact phenyl heterocycle and the
pincer ligand. We believe this catalyst design can be used as a
guideline for the creation of a variety of other pincer complexes,
too; thus, opening the door for more effective catalysis.
Acknowledgements
We thank the state of Mecklenburg-Vorpommern, the
Bundesministerium für Bildung und Forschung (BMBF), and the
European Research Council (ERC) for financial support. We also
thank Dr. Anke Spannenberg and the analytical department of
LIKAT for technical support.
Keywords: Ruthenium • Metallacycles • Pincer Complexes •
Hydrogen Autotransfer • C-C Bond Formation
[1]
[2]
S. Werkmeister, J. Neumann, K. Junge, M. Beller, Chem. - Eur. J. 2015,
21, 12226-12250.
a) E. Peris, R. H. Crabtree, Chem. Soc. Rev. 2018, 47, 1959-1968; b) M.
A. W. Lawrence, K.-A. Green, P. N. Nelson, S. C. Lorraine, Polyhedron
2018, 143, 11-27; c) H. Valdés, M. A. García‐Eleno, D. Canseco‐
Gonzalez, D. Morales‐Morales, ChemCatChem 2018, 10, 3136-3172;
d) H. A. Younus, W. Su, N. Ahmad, S. Chen, F. Verpoort, Adv. Synth.
Catal. 2015, 357, 283-330; e) C. Gunanathan, D. Milstein, Chem. Rev.
2014, 114, 12024-12087; f) D. Benito-Garagorri, E. Becker, J.
Wiedermann, W. Lackner, M. Pollak, K. Mereiter, J. Kisala, K. Kirchner,
Organometallics 2006, 25, 1900-1913; g) D. Benito-Garagorri, K.
Kirchner, Acc. Chem. Res. 2008, 41, 201-213.
[3]
[4]
[5]
[6]
W. Kuriyama, T. Matsumoto, Y. Ino, O. Ogata (Takasago International
Corporation), WO20110487227, 2011.
Z. Han, L. Rong, J. Wu, L. Zhang, Z. Wang, K. Ding, Angew. Chem. Int.
Ed. 2012, 51, 13041-13045.
J. Neumann, C. Bornschein, H. Jiao, K. Junge, M. Beller, Eur. J. Org.
Chem. 2015, 2015, 5944-5948.
a) M. Nielsen, E. Alberico, W. Baumann, H.-J. Drexler, H. Junge, S.
Gladiali, M. Beller, Nature 2013, 495, 85-89; b) A. Monney, E. Barsch, P.
Sponholz, H. Junge, R. Ludwig, M. Beller, Chem. Commun. 2014, 50,
707-709; c) E. Alberico, A. J. J. Lennox, L. K. Vogt, H. Jiao, W. Baumann,
Figure 2. Crystal structure of [Ru]-13. Displacement ellipsoids correspond to
30% probability. Only one molecule of the asymmetric unit is shown. Hydrogen
atoms (except the N-bound) and co-crystallized solvent are omitted for clarity.
4
This article is protected by copyright. All rights reserved.

10.1002/chem.202000396
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RESEARCH ARTICLE
H.-J. Drexler, M. Nielsen, A. Spannenberg, M. P. Checinski, H. Junge,
[26] a) M. H. S. A. Hamid, P. A. Slatford, J. M. J. Williams, Adv. Synth. Catal.
2007, 349, 1555-1575; b) G. Guillena, D. J. Ramón, M. Yus, Angew.
Chem. Int. Ed. 2007, 46, 2358-2364; c) T. D. Nixon, M. K. Whittlesey, J.
M. J. Williams, Dalton Trans. 2009, 753-762; d) K. Krüger, A. Tillack, M.
Beller, ChemSusChem 2009, 2, 715-717; e) A. J. A. Watson, J. M. J.
Williams, Science 2010, 329, 635-636; f) G. Guillena, D. J. Ramón, M.
Yus, Chem. Rev. 2010, 110, 1611-1641; g) G. E. Dobereiner, R. H.
Crabtree, Chem. Rev. 2010, 110, 681-703; h) S. Bähn, S. Imm, L.
Neubert, M. Zhang, H. Neumann, M. Beller, ChemCatChem 2011, 3,
1853-1864; i) C. Gunanathan, D. Milstein, Science 2013, 341, 1229712;
j) Y. Obora, ACS Catal. 2014, 4, 3972-3981; k) F. Huang, Z. Liu, Z. Yu,
Angew. Chem. Int. Ed. 2016, 55, 862-875; l) Q. Yang, Q. Wang, Z. Yu,
Chem. Soc. Rev. 2015, 44, 2305-2329; m) G. Chelucci, Coord. Chem.
Rev. 2017, 331, 1-36; n) A. Corma, J. Navas, M. J. Sabater, Chem. Rev.
2018, 118, 1410-1459; o) T. Irrgang, R. Kempe, Chem. Rev. 2019, 119,
2524-2549.
M. Beller, J. Am. Chem. Soc. 2016, 138, 14890-14904.
[7]
[8]
[9]
M. Nielsen, H. Junge, A. Kammer, M. Beller, Angew. Chem. Int. Ed. 2012,
51, 5711-5713.
M. Peña-López, H. Neumann, M. Beller, Chem. Commun. 2015, 51,
13082-13085.
N. J. Oldenhuis, V. M. Dong, Z. Guan, J. Am. Chem. Soc. 2014, 136,
12548-12551.
[10] a) J. Zhang, M. Gandelman, L. J. W. Shimon, H. Rozenberg, D. Milstein,
Organometallics 2004, 23, 4026-4033; b) J. Zhang, G. Leitus, Y. Ben-
David, D. Milstein, J. Am. Chem. Soc. 2005, 127, 10840-10841; c) H.
Zeng, Z. Guan, J. Am. Chem. Soc. 2011, 133, 1159-1161; d) P. Hu, Y.
Diskin-Posner, Y. Ben-David, D. Milstein, ACS Catal. 2014, 4, 2649-
2652; e) E. Khaskin, M. A. Iron, L. J. W. Shimon, J. Zhang, D. Milstein,
J. Am. Chem. Soc. 2010, 132, 8542-8543; f) E. Balaraman, C.
Gunanathan, J. Zhang, L. J. W. Shimon, D. Milstein, Nat. Chem. 2011,
3, 609; g) C. Gunanathan, M. Hölscher, W. Leitner, Eur. J. Inorg. Chem.
2011, 3381-3386; h) C. A. Huff, M. S. Sanford, ACS Catal. 2013, 3, 2412-
2416.
[27] a) R. Martínez, G. J. Brand, D. J. Ramón, M. Yus, Tetrahedron Lett. 2005,
46, 3683-3686; b) R. Martínez, D. J. Ramón, M. Yus, Tetrahedron 2006,
62, 8988-9001; c) C. Schlepphorst, B. Maji, F. Glorius, ACS Catal. 2016,
6, 4184-4188; d) C. Xu, X.-M. Dong, Z.-Q. Wang, X.-Q. Hao, Z. Li, L.-M.
Duan, B.-M. Ji, M.-P. Song, J. Organomet. Chem. 2012, 700, 214-218;
e) F. Li, J. Ma, N. Wang, J. Org. Chem. 2014, 79, 10447-10455; f) D.
Wang, K. Zhao, P. Ma, C. Xu, Y. Ding, Tetrahedron Lett. 2014, 55, 7233-
7235; g) S. Elangovan, J.-B. Sortais, M. Beller, C. Darcel, Angew. Chem.
Int. Ed. 2015, 54, 14483-14486; h) C. Seck, M. D. Mbaye, S. Coufourier,
A. Lator, J. F. Lohier, A. Poater, T. R. Ward, S. Gaillard, J. L. Renaud,
ChemCatChem 2017, 9, 4410-4416; i) L. Bettoni, C. Seck, M. D. Mbaye,
S. Gaillard, J.-L. Renaud, Org. Lett. 2019, 21, 3057-3061; j) M. Peña-
López, P. Piehl, S. Elangovan, H. Neumann, M. Beller, Angew. Chem.
Int. Ed. 2016, 55, 14967-14971; k) A. Bruneau-Voisine, L. Pallova, S.
Bastin, V. César, J.-B. Sortais, Chem. Commun. 2019, 55, 314-317; l) D.
Banerjee, L. M. Kabadwal, J. Das, Chem. Commun. 2018, 54, 14069-
14072; m) G. Zhang, J. Wu, H. Zeng, S. Zhang, Z. Yin, S. Zheng, Org.
Lett. 2017, 19, 1080-1083; n) P. Piehl, M. Pena-Lopez, A. Frey, H.
Neumann, M. Beller, Chem. Commun. 2017, 53, 3265-3268.
[11] a) M. Albrecht, Chem. Rev. 2010, 110, 576-623; b) J.-P. Djukic, J.-B.
Sortais, L. Barloy, M. Pfeffer, Eur. J. Inorg. Chem. 2009, 817-853; c) P.
B. Arockiam, C. Bruneau, P. H. Dixneuf, Chem. Rev. 2012, 112, 5879-
5918; d) M. Simonetti, D. M. Cannas, X. Just-Baringo, I. J. Vitorica-
Yrezabal, I. Larrosa, Nat. Chem. 2018, 10, 724-731; e) M. Simonetti, R.
Kuniyil, S. A. Macgregor, I. Larrosa, J. Am. Chem. Soc. 2018, 140,
11836-11847.
[12] R. Sun, X. Chu, S. Zhang, T. Li, Z. Wang, B. Zhu, Eur. J. Inorg. Chem.
2017, 3174-3183.
[13] a) N. U. Din Reshi, D. Senthurpandi, A. G. Samuelson, J. Organomet.
Chem. 2018, 866, 189-199; b) W.-G. Jia, T. Zhang, D. Xie, Q.-T. Xu, S.
Ling, Q. Zhang, Dalton Trans. 2016, 45, 14230-14237.
[14] a) S. Bauri, S. N. R. Donthireddy, P. M. Illam, A. Rit, Inorg. Chem. 2018,
57, 14582-14593; b) G. Balamurugan, R. Ramesh, J. G. Malecki,
ChemistrySelect 2017, 2, 10603-10608.
[15] a) L. N. Lewis, J. Am. Chem. Soc. 1986, 108, 743-749; b) S. M. Islam, C.
R. Saha, J. Mol. Catal. A: Chem. 2004, 212, 131-140; c) B. Bagh, A. M.
McKinty, A. J. Lough, D. W. Stephan, Dalton Trans. 2015, 44, 2712-2723.
[16] D. Gong, B. Hu, D. Chen, Dalton Trans. 2019, 48, 8826-8834.
[17] D. Gong, B. Hu, W. Yang, D. Chen, ChemCatChem 2019, 11, 4841-4847.
[18] a) P. Dani, T. Karlen, R. A. Gossage, S. Gladiali, G. van Koten, Angew.
Chem. Int. Ed. 2000, 39, 743-745; b) M. Gagliardo, P. A. Chase, S.
Brouwer, G. P. M. van Klink, G. van Koten, Organometallics 2007, 26,
2219-2227.
[28] a) J. Kothandaraman, M. Czaun, A. Goeppert, R. Haiges, J.-P. Jones, R.
B. May, G. K. S. Prakash, G. A. Olah, ChemSusChem 2015, 8, 1442-
1451; b) Y. Zhang, A. D. MacIntosh, J. L. Wong, E. A. Bielinski, P. G.
Williard, B. Q. Mercado, N. Hazari, W. H. Bernskoetter, Chem. Sci. 2015,
6, 4291-4299.
[19] E. Fogler, E. Balaraman, Y. Ben-David, G. Leitus, L. J. W. Shimon, D.
Milstein, Organometallics 2011, 30, 3826-3833.
[20] a) S. Tang, N. von Wolff, Y. Diskin-Posner, G. Leitus, Y. Ben-David, D.
Milstein, J. Am. Chem. Soc. 2019, 141, 7554-7561; b) Q. Wang, H. Chai,
Z. Yu, Organometallics 2018, 37, 584-591.
[21] a) W. Baratta, G. Chelucci, S. Gladiali, K. Siega, M. Toniutti, M. Zanette,
E. Zangrando, P. Rigo, Angew. Chem. Int. Ed. 2005, 44, 6214-6219; b)
W. Baratta, M. Bosco, G. Chelucci, A. Del Zotto, K. Siega, M. Toniutti, E.
Zangrando, P. Rigo, Organometallics 2006, 25, 4611-4620; c) W. Baratta,
M. Ballico, S. Baldino, G. Chelucci, E. Herdtweck, K. Siega, S. Magnolia,
P. Rigo, Chem. - Eur. J. 2008, 14, 9148-9160; d) W. Baratta, F. Benedetti,
A. Del Zotto, L. Fanfoni, F. Felluga, S. Magnolia, E. Putignano, P. Rigo,
Organometallics 2010, 29, 3563-3570.
[22] W. Baratta, K. Siega, P. Rigo, Adv. Synth. Catal. 2007, 349, 1633-1636.
[23] a) W. Baratta, S. Baldino, M. J. Calhorda, P. J. Costa, G. Esposito, E.
Herdtweck, S. Magnolia, C. Mealli, A. Messaoudi, S. A. Mason, L. F.
Veiros, Chem. - Eur. J. 2014, 20, 13603-13617; b) S. Facchetti, V. Jurcik,
S. Baldino, S. Giboulot, H. G. Nedden, A. Zanotti-Gerosa, A. Blackaby,
R. Bryan, A. Boogaard, D. B. McLaren, E. Moya, S. Reynolds, K. S.
Sandham, P. Martinuzzi, W. Baratta, Organometallics 2016, 35, 277-
287; c) S. Giboulot, S. Baldino, M. Ballico, R. Figliolia, A. Pöthig, S.
Zhang, D. Zuccaccia, W. Baratta, Organometallics 2019, 38, 1127-1142.
[24] G. Bossi, E. Putignano, P. Rigo, W. Baratta, Dalton Trans. 2011, 40,
8986-8995.
[25] B. Li, T. Roisnel, C. Darcel, P. H. Dixneuf, Dalton Trans. 2012, 41, 10934-
10937.
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10.1002/chem.202000396
Chemistry - A European Journal
RESEARCH ARTICLE
Entry for the Table of Contents
Eight novel Ru pincer complexes were prepared by introduction of C,N-bound phenyl heterocycle ligands. These complexes were
applied as catalysts in the α-alkylation of ketones with alcohols via hydrogen autotransfer. Here, superior yields in comparison to
Ru-MACHO were achieved and 21 different alkylated ketones were synthesized in up to 97% yield. Moreover, investigations
regarding the catalyst species present during the reaction were conducted.
6
This article is protected by copyright. All rights reserved.