Manganese-catalysed transfer hydrogenation of esters

Article abstract of DOI:10.1039/d0cc02598d

Manganese catalysed ester reduction using ethanol as a hydrogen transfer agent in place of dihydrogen is reported. High yields can be achieved for a range of substrates using 1 mol% of a Mn(i) catalyst, with an alkoxide promoter. The catalyst is derived from a tridentate P,N,N ligand.

Full text of DOI:10.1039/d0cc02598d

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DOI: 10.1039/D0CC02598D
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Manganese-Catalysed Transfer Hydrogenation of Esters.
Conor L. Oates, Magnus B. Widegren and Matthew L. Clarke*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Manganese catalysed ester reduction using ethanol as hydrogen
transfer agent in place of dihydrogen is reported. High yields can
be achieved for a range of substrates using 1 mol% of a Mn(I)
catalyst, with an alkoxide promotor. The catalyst is derived from a
tridentate P,N,N ligand.
H
Cl
H
H
PiPr2
CO
N
N
SEt
Fe
H
Ru
Cl
Ru
MeCN
MeCN
PiPr3
P
S
PPh3
iPr2
Et
BH3
The hydrogenation of esters has changed from being a very
problematic aspirational transformation 15 years ago, to a
highly efficient example of homogeneous catalysis. There are
quite a few effective Ru-based catalysts,1a-d but also Mn and Fe
based systems that show promise.2a-h,3 The use of molecular
hydrogenation is frequently the cleanest and most economic
reductant, but there are a variety of scenarios where the use
of a liquid reductant may be desirable. The importance of
transfer hydrogenation, using an alcohol as hydrogen donor, to
catalytic reductions cannot be doubted; there are many useful
practical applications for asymmetric transfer hydrogenation
of ketones.4a-e
Surprisingly, given the level of interest in transfer
hydrogenation, relatively few papers have described transfer
hydrogenation of esters.5a-d Dubey and Khaskin reported the
use of just 1 mol% of a ruthenium catalyst, using ethanol as
reductant and an alkoxide co-catalyst.5b The discovery by de
Vries and co-workers of an effective base-free Fe borohydride
catalyst using ethanol as reductant, this time requiring 5 mol%
catalyst loading, is a significant milestone.5d Catalysts such as
this, which are derived from an indefinitely sustainable metal
source, and that permit higher catalyst impurities than the 5-
10 ppm generally required as a minimum for precious metal
based catalysts6 are highly desirable. This significance has
spurred a lot of recent research on Mn catalysed reductions.
Figure 1 Catalysts previously used for transfer hydrogenation
of esters5
We have recently reported the use of catalyst 1 (in racemic
form) in some synthetically useful ester hydrogenations using
hydrogen as reductant,3 and more recently rationally designed
second generation systems, 2 and 3 (in enantiomerically pure
form) for highly efficient enantioselective hydrogenation of a
broad range of ketones (0.01 to 0.1 mol% catalyst loadings).7
These are amongst the most active of all non-precious metal
catalysts for the hydrogenation of esters and ketones. That
being said, transfer hydrogenation of ketones using any of
these catalysts was a more mixed picture, with only a handful
of typical substrates giving good results.7 De Vries and co-
workers also found that a Mn/ PNP hydrogenation catalyst was
entirely ineffective for ester transfer hydrogenation.5d To our
surprise, given this background, we have now found that a
highly effective transfer hydrogenation of a range of esters is
possible using the Mn catalysts 1 or 2, and report this
discovery here.
Our objective was to enable a Mn-based catalyst to conduct
ester transfer hydrogenation at a catalyst loading below the 5
mol% level used by de Vries and co-workers.5d A selection of
our Mn catalysts were investigated using conditions relatively
similar to those used in reference 5b. We chose the reduction
of ethyl 4-fluorobenzoate in EtOH as a model substrate to
identify suitable conditions (summarised in Table 1). The
optimal conditions identified during this study are shown in
entry 1. We first identified the most suitable catalysts from
those we have recently developed.2d,3,7
a. School of Chemistry, University of St Andrews, EaStCHEM, St Andrews, Fife, UK.
E-mail: mc28@st-andrews.ac.uk; Fax: +(44) 1334 463808; Tel: +(44) 1334 463850
b. Electronic Supplementary Information (ESI) available: Full experimental
procedures, analytical data, NMR spectra. See DOI: 10.1039/x0xx00000x. The
research data underpinning this publication can be accessed
at https://doi.org/10.17630/0a645625-3a7a-47ed-9f6d-63ef3b998d79.
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Table 1 Optimisation of conditionsa
R
View Article Online
DOI: 10.1039/D0CC02598D
H
N
O
N
Ar2P
2 (1 mol%)
tBuOK (20 mol%)
EtOH (2M), 22 h,
100 oC, Dark
Fe
OEt
OH
N
N
H
CO
CO
Br
F
F
Mn
RCSP
P
Ar= 3,5-Me2-4-OMeC6H2: 4
Fe
Ar2
CO
6
7
RCSP
Br
N
OC
OC
Entry
Change from Optimal
Conditions
Conversion
7
Mn
of 6(%)c
(%)c
R= H, Ar=Ph: 1
R= H, Ar= 3,5-Me2,4-OMeC6H2: 2
R= NMe2, Ar= 3,5-Me2,4-OMeC6H2: 3
N
1
2
3
4
-
90
85
76
90
76 (74)
74
57
76 (73)
CO
H2
1 mol% 1
5
1 mol% 3
(1 mol% 4 +
[Mn(CO)5Br])b
1 mol% 5
Figure 2 Catalysts investigated in this work
5
6
15
13
81
91
46
66
84
84
93
19
2
Trace
67
The use of either 1 mol% catalyst 1 or 2 gave similarly good
yields. Use of catalyst 3 (entry 3) led to poorer conversions.
This latter catalyst is slightly more active in pressure-
hydrogenation of esters below around 70oC.7 The kinetic
studies described in ref 7 show the catalyst degrades during
the reaction above this temperature; the lower yield here is
likely due to its lower thermal stability. The optimal base
loading was found to be 20 mol% of KOtBu: lowering to 10
mol% (entry 7) led to decreased conversion of starting
material and raising to 30 mol% (entry 8) lead to lower product
formation. Pleasingly, changing to the weaker K2CO3 at 20
mol% (entry 12) still produced useful levels of product albeit
with lower yield. We found the optimal concentration (wrt.
ester substrate) to be 2M. Lower concentrations (entries 9/
10) resulted in lower conversions to (7). The alternative
primary alcohol hydrogen donors we have examined are less
effective than EtOH (entries 13 & 14). Using MeOH (2M)
resulted in mostly transesterification to the methyl ester and
No Catalyst
10 mol% KOtBu,
30 mol% KOtBu
0.25M
0.5M
1M
20 mol% K2CO3
MeOH as solvent
nBuOH as solvent
7
8
52
9
43
10
11
12
13
14
53
76
67
19
Trace
a Standard reaction conditions: 6 (0.5 mmol), 1-methylnapthalene
(0.15 mmol), base and Mn Cat. (0.005 mmol) in dry solvent under N2
atmosphere at 100 °C for 22h. b 4 (0.05 mmol) and Mn(CO)5Br (0.05
mmol) in dry EtOH at 100 °C for 2h, then 6 (0.5 mmol), 1-
methylnapthalene (0.15 mmol) and KOtBu (0.10 mmol) added and
stirred at 100 °C for 24 h; all under N2 atmosphere. c Determined by
1H NMR using 1-methylnapthalene as internal standard. Isolated
yields (after chromatographic purification) in brackets.
We were then interested to see if the conditions were
applicable to aliphatic ethyl esters; all the examples tested
could be reduced with good yields. Reduction of
unfunctionalised 8l, 8m, and 8n worked well. The reduction of
lauryl and oleyl esters is a process important to the fine
chemical industry with oleyl (9o) and lauryl alcohols (9p)
seeing wide industrial and commercial use.9 Satisfyingly, the
reduction of ethyl laurate (8o) and ethyl oleate (8p) produced
their respective alcohols in good yield. (S)-Naproxen (8q) could
also be used to produce Naproxol (9q) in very good yield but
with epimerisation of the chiral centre. The amino acid ester
tolerance of the conditions was investigated by reducing ethyl
N,N-dibenzylglycine (8r) generating N,N-dibenzylamino
ethanol (9r) in good yield.
Esters derived from alcohols other than ethanol were then
investigated. The halogenated methyl 4-chlorobenzoate (8s)
and methyl 4-bromobenzoate (8t) were both reduced in very
good yield (Table 2). Heterocyclic methyl nicotinate (8u) was
reduced too in excellent yield. The α-β-unsaturated ester
methyl cinnamate (8v) was totally reduced to the saturated
compound 3-phenylpropanol (9m) in good yield. Finally, the
methyl (8w) and isopropyl (8x) 2-methoxybenzoate esters
produced 2-methoxybenzyl alcohol (9f) in good yields when
submitted to the standard conditions. Transesterification was
proven to occur using substrate 8x and 8t (see Scheme 2 and
ESI). The transesterification with ethanol occurring under the
reaction conditions led us to consider a one-pot esterification-
n
only a small amount of product formation. Use of BuOH (2M)
lead to almost no product being formed. Therefore, optimal
conditions for the reduction of 6 were 1 mol% of 2 in EtOH
with a 2M concentration at 100 °C for 22 h.
While the use of well-defined pre-catalysts has many
advantages, sometimes it is preferable to generate a catalyst
in situ. Pre-stirring 1 mol% of both 4 and [Mn(CO)5Br] for 2h at
o
100 C in EtOH and then adding 6/ base before stirring for a
further 24 h at 100 oC (Entry 4, Table 1) produced a
comparable yield of (7) as when well-defined 2 was used in the
standard conditions (we note that the yield drops to 63% if
there is no pre-stirring period for complexation, not shown).
With optimal conditions in hand we began investigating the
reaction scope (with the results summarised in Table 2); at first
focussing on aromatic ethyl esters to eliminate
transesterification between solvent and substrate. Further
demonstration of halogen tolerance was shown when ethyl 4-
iodobenzoate (8a) was reduced in good yield, as were
unfunctionalised esters, (8b) (8c). Examples of both oxygen
and nitrogen containing heterocycles are tolerated by the
conditions- demonstrated by the reduction of ethyl 2-furoate
(8d) and ethyl isonicotinate (8e) in good yields. While ether
functionality, even in the ortho position to the ester is
unproblematic (8f, 8h), the presence of free amino, hydroxy
and nitrile function was problematic thus far.
2 | J. Name., 2012, 00, 1-3
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reduction of carboxylic acids. Carboxylic acids cannot be To prove the viability of this concept we have eVxiaewmAirnticeledOjnulinset
DOI: 10.1039/D0CC02598D
reduced by any of the base-activated Ru or Mn amino- two randomly selected substrates: the ethyl esters were
phosphine catalysts, and are very difficult to hydrogenate, generated by modified Steglich esterification conditions11
despite some notable contributions.10a-d
using
N,N’-Diisopropylcarbodiimide
(DIC)
and
Dimethylaminopyridine (DMAP) in EtOH. Adding catalyst 2 and
base and heating then allowed the transfer hydrogenation to
proceed with a fairly similar yield to using pure ethyl esters to
afford the alcohol (Scheme 1). Since both of these protocols
worked similarly to using ethyl esters, we would therefore
suggest the catalysts have tolerance to these esterification
conditions and esters should be able to be made in situ.
Table 2 Products obtained from Mn-catalysed reductions.
2 (1 mol%)
tBuOK (20 mol%)
O
R1
OR2
8a-x
R
OH
9a-u
EtOH, dark
22 h, 100 o
C
i. DIC (1.15 eq.),
DMAP (10 mol%)
Et Esters:
ii. 2 (1 mol%)
tBuOK (20 mol%)
EtOH
O
OH
OH
R
OH
R
OH
10a/b
I
OH
22 h, 0-100 o
C
R= (2-MeO-Ph) 9f (73%)
R= Cy 9l (74%)
9a (81%)
9b (69%)
OH
Scheme 1 One-pot esterification/ reduction of carboxylic
acids. For experimental procedure, see SI. Isolated yields
(after chromatographic purification) in brackets.
OH
OH
N
O
9c (87%)
9e (83%)
9d (82%)
When the reaction mixtures are analysed before the reaction
completion, the range of intermediates forming becomes
clear. Using isopropyl (8x) 2-methoxybenzoate ester, there is
rapid transesterification with ethanol (see ESI). The ester
formed from the product alcohol, 9t can also be detected in
the mixture, as can small amounts of the acetate of the
product (Scheme 2). Transfer hydrogenation is an equilibrium
process and the conditions used enable high conversion to the
desired primary alcohol (and useful amounts isolated in pure
form), but complete conversion to the product is not
observed, unlike the pressure hydrogenation using hydrogen
gas.7 The mechanism is consistent with that discussed in
previous papers5 where dehydrogenation of the ethanol
reductant, which is in excess occurs alongside ester reduction
with the hemi-acetals produced also being dehydrogenated
(EtCHOH(OR) and reduced respectively (Scheme 2). The
formation of a Mn-hydride from 1-3 using basic alcohol
solutions has resisted our attempts at isolation and even
detection: in contrast to similar complexes with Ru and Ir, free
ligand is detected if the catalysts are activated without any
substrate to reduce. However, based on precedents from a
plethora of examples using a variety of metals, this should
initiate the cycle.
OH
OMe
OH
OH
BnO
HO
9h (48%)c
9g (10%)b
9f (76%)
OH
OH
NC
R2N
R= H 9j (Trace)b
R= Me 9k (10%)b
9l (78%)
9i (Trace%)b
OH
OH
OH
9n (71%)d
OH
9m (82%)
9o (77%)d
OH
Bn2N
OH
9p (76%)d
MeO
9r (63%)
9q (82%)(rac.)
Me Esters:
OH
OH
OH
N
X
OMe
X= Cl 9s (79%)
X= Br 9t (79%)
9u (84%)
9f (82%)
In reference 5d, essentially no activity was described for a
Mn/P,N,P catalyst in ester transfer hydrogenation. We believe
catalysts 1-3 are significantly more active ester hydrogenation
catalysts than the catalyst used in ref. 5d; indeed other
researchers have compared P,N,N and P,N,P /Mn catalysts and
found the former more reactive.12 In addition it is possible that
the formation of H2 with a Mn/P,N,P catalyst13 could reduce
the lifetime of the Mn-hydride needed to reduce the ester and
hence the transfer hydrogenation efficiency. The presence of
more N-donors might facilitate dehydrogenation without
dihydrogen formation. One P-donor is still seemingly required
for the hydride to be reactive enough to reduce an ester, as
evidenced by the lack of reactivity of a catalyst derived from a
simple bidentate N,N ligand, 5 (Table 1, entry 5). This catalyst
iPr Ester:
O
OMe
OH
OH
OMe
8v
9m (74%)
9f (77%)
a Standard reaction conditions: ester substrate (0.5 mmol), tBuOK
(0.1 mmol) and 2 (0.005 mmol) in dry EtOH (0.25 mL) under N2
atmosphere at 100 °C for 22h. Isolated yields (after chromatographic
purification) in brackets. b Determined by 1H NMR using 1,4-
dimethoxybenzene as internal standard. c 0.01 mmol of 2 d 0.0075
mmol of 2.
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Angew. Chem. Int. Ed., 2013, 52, 2538–2542. (g) G. A.
gives high turnover numbers in ketone transfer
hydrogenation,8 but we are not aware of ester pressure
hydrogenations with any metal centre, using only pure N,N
ligands. In summary, we have developed the first example of a
manganese-catalysed reaction for the transfer hydrogenation
of esters. The methodology operates using only 1 mol% of a
sustainable metal catalyst to effect reduction.
Filonenko, M. J. B. Aguila, E. N. SchulpDeOn,I:R1.0.v1a0n39VPi/eDuw0tAtCertCinc0l,e2JO5.9nl8inDe
Wiecko, C. Müller, L. Lefort, E. J. M. Hensen and E. A. Pidko,
J. Am. Chem. Soc., 2015, 137, 7620–7623.
2
Fe- (a) S. Chakraborty, H. Dai, P. Bhattacharya, N. T.
Fairweather, M. S. Gibson, J. A. Krause and H. Guan, J. Am.
Chem. Soc., 2014, 136, 7869–7872. (b) T. Zell, Y. Ben-David
and D. Milstein, Angew. Chem. Int. Ed., 2014, 53, 4685–4689.
(c) S. Werkmeister, K. Junge, B. Wendt, E. Alberico, H. Jiao,
W. Baumann, H. Junge, F. Gallou and M. Beller, Angew.
Chem. Int. Ed., 2014, 53, 8722–8726. (d) S. Elangovan, B.
Wendt, C. Topf, S. Bachmann, M. Scalone, A. Spannenberg,
H. Jiao, W. Baumann, K. Junge and M. Beller, Adv. Synth.
Catal., 2016, 358, 820–825. Mn- (e) S. Elangovan, M. Garbe,
H. Jiao, A. Spannenberg, K. Junge and M. Beller, Angew.
Chem. Int. Ed., 2016, 55, 15364–15368. (f) M. B. Widegren,
G. J. Harkness, A. M. Z. Slawin, D. B. Cordes and M. L. Clarke,
Angew. Chem. Int. Ed., 2017, 56, 5825–5828. (g) R. vanꢀ
Putten, E. A. Uslamin, M. Garbe, C. Liu, A. Gonzalez-de-
Castro, M. Lutz, K. Junge, E. J. M. Hensen, M. Beller, L. Lefort
and E. A. Pidko, Angew. Chem. Int. Ed., 2017, 56, 7531–7534.
(h) N. A. Espinosa-Jalapa, A. Nerush, L. J. W. Shimon, G.
Leitus, L. Avram, Y. Ben-David and D. Milstein, Chem. Eur. J.,
2017, 23, 5934–5938. (reviews on Mn-catalysed reduction)
(i) F. Kallmeier and R. Kempe, Angew. Chem. Int. Ed., 2018,
57, 46–60. (j) B. Maji and M. K. Barman, Synthesis, 2017, 49,
3377-3393
O
2 (1 mol%)
tBuOK (20 mol%)
OH
OMe
EtOH, 22 h,
100 oC, Dark
Br
Br
8t
9t
O
O
OMe
OEt
OH
Br
Br
Br
8t (Trace)
8t' (7%)
9t (79%)
O
O
O
O
Br
Br
Br
9t'' (3%)
9t' (2%)
3
4
M. B. Widegren and M. L. Clarke, Org. Lett., 2018, 20, 2654–
2658.
OH
O
-OEt
(a) S. Gladiali and E. Alberico, Chem. Soc. Rev. 2006, 35, 226-
236. (b) C. Wang, X. Wu and J. Xiao, Chem. Asian J., 2008, 3,
1750–1770. (c) J. Ito and H. Nishiyama, Tet. Lett., 2014, 55,
3133–3146. (d) P.-G. Echeverria, T. Ayad, P. Phansavath and
V. Ratovelomanana-Vidal, Synthesis, 2016, 48, 2523–2539.
(e) D. Wang and D. Astruc, Chem. Rev., 2015, 115, 6621–
6686. (f) R. Noyori and S. Hashiguchi, Acc. Chem. Res. 1997,
30, 97-102
(a) S.-H. Lee and G. I. Nikonov, ChemCatChem, 2015, 7, 107–
113. (b) A. Dubey and E. Khaskin, ACS Catal., 2016, 6, 3998–
4002. (c) I. D. Alshakova, B. Gabidullin and G. I. Nikonov,
ChemCatChem, 2018, 10, 4860–4869. (d) R. A. Farrar-Tobar,
B. Wozniak, A. Savini, S. Hinze, S. Tin and J. G. deꢀVries,
Angew. Chem. Int. Ed., 2019, 58, 1129–1133.
EtOAc
EtOH
OEt
OEt
OEt
R
R
OEt
[Mn]
OEt
H
H
O
O
O
[Mn]
[Mn]
[Mn]
[Mn]
[Mn]
[Mn]
[Mn] refers
to Mn complex,
see ESI.
O
OH
O
OH
5
6
-OEt
R
OEt
R
OEt
R
R
Scheme 2 Top: Species found at end of Me ester reduction
determined by 1H NMR using 1,4-dimethoxybenzene as internal
standard- see ESI. Below: Mechanistic proposal for ester transfer
hydrogenation using 2 and EtOH.
D. R. Abernethy, A. J. DeStefano, T. L. Cecil, K. Zaidi, R. L.
Williams and USP Metal Impurities Advisory Panel, Pharm.
Res., 2010, 27, 750–755.
7
8
9
M. B. Widegren and M. L. Clarke, Catal. Sci. Technol., 2019, 9,
6047–6058.
A. Bruneau-Voisine, D. Wang, V. Dorcet, T. Roisnel, C. Darcel
and J.-B. Sortais, Org. Lett., 2017, 19, 3656–3659.
M. A. Sánchez, G. C. Torres, V. A. Mazzieri and C. L. Pieck, J.
Chem. Tech. & Biotech., 2017, 92, 27–42.
Notes and references
‡ We would like to thank the University of St Andrews, and the
EPSRC Centre for Doctoral Training in Critical Resource Catalysis
(CRITICAT) for financial support [Ph.D. studentship to CO; Grant
code: EP/L016419/1]. We thank Solvias for ongoing
collaboration and the gift of chemicals.
10 Ru- (a) T. vom Stein, M. Meuresch, D. Limper, M. Schmitz, M.
Hölscher, J. Coetzee, D. J. Cole-Hamilton, J. Klankermayer
and W. Leitner, J. Am. Chem. Soc., 2014, 136, 13217–13225.
(b) X. Cui, Y. Li, C. Topf, K. Junge and M. Beller, Angew. Chem.
Int. Ed., 2015, 54, 10596–10599. (c) M. Naruto and S. Saito,
Nature Commun., 2015, 6, 1–9. Co- (d) T. J. Korstanje, J. Ivar
van der Vlugt, C. J. Elsevier and B. de Bruin, Science, 2015,
350, 298–302.
11 B. Neises and W. Steglich, Angew. Chem. Int. Ed., 1978, 17,
522–524.
12 Y. Wang, L. Zhu, Z. Shao, G. Li, Y. Lan, and Q. Liu, J. Am.
Chem. Soc., 2019, 141, 17337-17349
§ Throughout this work, we have used single enantiomer
catalysts since we had large amounts of these available, but we
note ref. 7 shows, as one would expect, similar results using
either single enantiomer or racemic catalysts in pressure
hydrogenation.
1
(a)(Review): M. L. Clarke, Catal. Sci. Technol., 2012, 2, 2418–
2423. (b) (Review) S. Werkmeister, K. Junge and M. Beller,
Org. Process Res. Dev., 2014, 18, 289–302. (c) E. Fogler, E.
Balaraman, Y. Ben-David, G. Leitus, L. Shimon J. W. and D.
Milstein, Organometallics, 2011, 30, 3826–3833. (d) L. A.
Saudan, C. M. Saudan, C. Debieux and P. Wyss, Angew.
Chem. Int. Ed., 2007, 46, 7473–7476. (e) W. Kuriyama, T.
Matsumoto, O. Ogata, Y. Ino, K. Aoki, S. Tanaka, K. Ishida, T.
Kobayashi, N. Sayo and T. Saito, Org. Process Res. Dev., 2012,
16, 166–171. (f) D. Spasyuk, S. Smith and D. G. Gusev,
13 D.H. Nguyen, X. Trivelli, F. Capet, J-F. Paul, F. Dumeignil, and
R. M. Gauvin, ACS Catalysis, 2017, 7, 2022-2032.
4 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/D0CC02598D
Manganese-Catalysed Transfer Hydrogenation of Esters.
Conor L. Oates, Magnus B. Widegren and Matthew L. Clarke
A manganese complex of a tridentate P,N,N ligand can catalyse the reduction of esters using
ethanol as the reductant.
Mn Cat.
KOtBu
O
R2
R1
R1
O
OH
EtOH
>20 Examples
No high pressures of H2 or autoclave
Cheap solvent
Low Loading of sustainable metal catalyst