An effective cis-β-octahedral Mn(iii) SALPN catalyst for the Mukaiyama-Isayama hydration of α,β-unsaturated esters

Article abstract of DOI:10.1039/c9cc03921j

Two cis-β-Mn^IIISALPN catalysts were synthesised and tested in the Mukaiyama-Isayama hydration of α,β-unsaturated esters. The Mn^IIIEtOSALPN(acac) complex 7 is the most active and catalyses hydration with little or no detectable undesired alkene reduction. This catalyst is superior for alkene hydration compared to the originally reported Mn(dpm)₃ catalyst.

Full text of DOI:10.1039/c9cc03921j

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: M. A. Rizzacasa, P.
S. Donnelly, A. J. North, N. C. Radjah, M. Ricca, A. M. Robertson and J. White, Chem. Commun., 2019,
DOI: 10.1039/C9CC03921J.
This is an Accepted Manuscript, which has been through the
Volume 52 Number
1 4 January 2016 Pages 1–216
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Accepted Manuscripts are published online shortly after
Chemical Communications
www.rsc.org/chemcomm
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
first methanofullerene derivatives of Sc N@D5h-C80
=
3
rsc.li/chemcomm

Please do not adjust margins
Page 1 of 4
ChemComm
View Article Online
DOI: 10.1039/C9CC03921J
Chemical Communications
COMMUNICATION
An Effective cis--Octahedral Mn(III) SALPN Catalyst for the
Mukaiyama-Isayama Hydration of -Unsaturated Esters†§
Paul S. Donnellya,*, Andrea North,a Natalia Caren Radjah,a Michael Ricca,a Angus Robertson,a
Jonathan M. White,a Mark A. Rizzacasa.a,*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Two cis--Mn(III)SALPN catalysts were synthesised and tested in In the absence of oxygen, reduction by hydrogen atom transfer
the Mukaiyama-Isayama hydration of -unsaturated esters. The (HAT)7 and protonation occurs to give saturated esters 4. On
Mn(III)EtOSALPN(acac) complex 7 is the most active and catalyses several occasions, we have observed that treatment of
hydration with little or no detectable undesired alkene reduction. unsaturated esters (1) with catalyst 2 and PhSiH3 in the
This catalyst is superior for alkene hydration compared to the presence of O2 gas gave the desired hydration product but also
originally reported Mn(dpm)3 catalyst.
significant amounts of unwanted material arising from
reduction through hydrogen atom transfer. We therefore
elected to examine an alternative Mn(III) coordination complex
that would favor hydration over reduction.
Magnus noted that Jacobsen’s catalyst (a trans-Mn(salen)X2
complex) did not catalyse the Mukaiyama-Isayama hydration
and this also failed in our hands.4,8 We reasoned that
coordination geometry about the metal ion in the catalyst
allowing for conformational flexibility was key and elected to
investigate cis--octahedral Mn(III) complexes which features
an ethoxySALPN Schiff base ligand,9 prepared by the
The hydration of polar alkenes using a CoII catalyst, PhSiH3 and
dioxygen was reported by Isayama and Mukaiyama in 1989.1
Further developments included the regioselective direct and
predominantly -hydration of -unsaturated esters (1)
catalyzed by MnII(dpm)2 in the presence of PhSiH3 and dioxygen
in iPrOH to afford -hydroxy esters (3) after reductive workup
(Scheme 1).2 Some 10 years later, this Mn catalysed hydration
was reinvestigated by Magnus and co-workers3,4 and the active
catalyst was revealed by analysis by X-ray crystallography to be
octahedral complex MnIII(dpm)3 (2)5 and suggested this was the
catalyst and not MnII(dpm)2 as reported as MnII complexes
typically oxidise rapidly to MnIII in air.6
condensation
of
1,3-diaminopropane
with
3-
ethoxysalicylaldehyde (5) (Scheme 2). The use of a -diketone
bidentate co-ligand promotes the formation of cis- MnIII
complexes. The Schiff base derived from commercially available
aldehyde 5 was used to improve solubility of the complex in i-
PrOH which is the solvent of choice for this alkene hydration.
Scheme 1: Mukaiyama Hydration of -unsaturated esters
Scheme 2: Synthesis of cis--SALPN catalysts 6 and 7
Reaction of the Schiff base with Mn(III) complex 2 or MnIII(acac)3
in methanol afforded the complexes MnIIISALPN(dpm) 6 and
MnIIISALPN(acac) 7 respectively in good yields. Each of these
recrystallized from CH2Cl2 to provide crystals that were suitable
for analysis by X-ray crystallography.10 The X-ray structures for
aSchool of Chemistry, The Bio21 Molecular Science and Biotechnology Institute,
The University of Melbourne, Parkville, Australia 3010.
† Electronic Supplementary Information (ESI) available: Experimental details and
NMR spectra. See DOI: 10.1039/x0xx00000x
§In memory of Professor Teruaki Mukaiyama
This journal is © The Royal Society of Chemistry 2019
Chem. Commun., 2019, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 4
COMMUNICATION
Org. Biomol. Chem.
6 and 7 (Figure 1) confirm that the Mn(III) complexes possess particularly evident in 7 along the N1-Mn-O5 axis (Mn-N1 =
View Article Online
DOI: 10.1039/C9CC03921J
the cis- coordination geometry.
2.1846(13), Mn-O5 = 2.1725(12)).
We next tested each of the complexes in a Mukaiyama- Isayama
hydration reaction of a selection of -unsaturated esters
(Scheme 3 and Table 1). Each reaction was also conducted using
the standard Mn(dpm)3 catalyst for comparison. All the
reactions were carried out in i-PrOH solvent with PhSiH3 was
used as the hydride source in all cases. Other co-solvents such
as CH2Cl2 and the application of the more reactive silane
PhSi(Oi-Pr)H2 as reported by Shenvi12 offered no significant
improvement to the yields or reaction times. We also found that
adding P(EtO)3 in order to reduce any peroxides as described in
the original procedure2,3 was not required (suggesting
hydroperoxides are not formed in significant amounts) and only
complicated purification. It appears that the use of excess silane
may also serve to reduce the small amounts of hydroperoxide
formed. In addition, the use of t-BuOOH as an additive13 was not
necessary as the O2 can effectively oxidise the any Mn(II).
Scheme 3: General hydration reaction
Hydration
Product
Yields
Cat. 2
Yields
Cat. 7
Entry
Substrate
[O] 38% [O] 70%
[R] 53% [R] 0%
[O] 44% [O] 67%
1
2
[R] 21%
[R] 0%
[O] 51%
[R] 30%
[O] 70%
[R] 0%
3
4
Figure 1: ORTEP representations (40% probability, H atoms
omitted) of X-ray crystal structures for Mn(III) complexes 6 and
[O] 44% [O] 61%
7. Selected bond lengths: 6 [O1–Mn1.8685(91),
N2–Mn
1:3  1:30 
1.990(102), O3–Mn 1.999(120), O5–Mn 2.038(130), N1–Mn
2.0769(125) O6–Mn 2.1081(118)]; 7 [N1–Mn 2.1836(13), N1–
Mn 2.1836(13), N2–Mn 2.0083(14), O1–Mn 1.9155(10) O3–Mn
1.8710(11), O5–Mn 2.1725(12), O6–Mn 2.0171(11)]
[R] 0%
[R] 0%
[O] 0%
[R] 0%
[O] 20%
[R] 0%
5
6
7
The solid-state structures of 6 and 7 differed considerably in the
conformation of the SALPN ligand. The distance between
aromatic phenolic carbon atoms (C1 and C13, Figure 1) of both
rings is almost 1 Å longer in the complex 6 possibly due to the
ethoxy substituent on one aromatic ring interacting with the t-
Bu group of the dpm ligand which forces the rings further apart.
The six-membered chelate ring involving the 3-carbon bridge,
two nitrogen atoms and the Mn atom adopts a twist boat-like
(skew) conformation in 6 whilst this ring is chair-like in complex
7. In both structures the MnIII is in distorted octahedral
environment. The Mn-N and Mn-O bond distances are similar
to those found in the X-ray structure of [Mn(SALPN)acac].11
Both complexes exhibit Jahn-Teller distortions that would be
expected for high spin d4 MnIII.11 A tetragonal distortion is
[O] 6%
[O] 72%
[R] 6%
[R] 80%
[O] 17% [O] 68%
[R] 71% [R] 6%
[O] 69% [O] 32%
3.7:1  1:2.6 
8
[R] 0%
[R] 0%
Table 1: [O]=yield of hydration product; [R]=yield of reduction
product. All reactions carried out under an O2 balloon with using
20 mol% catalyst, (Except entries 5 and 7, 10 mol% catalyst), rt,
16h.
2 | Chem. Commun., 2019, 00, 1-3
This journal is © The Royal Society of Chemistry 2019
Please do not adjust margins

Page 3 of 4
ChemComm
Please do not adjust margins
Journal Name
COMMUNICATION
The MnIII(SALPN)(dpm) complex 6 catalysed the hydration of The ionic mechanism shown is modified from thatVpierwoAprtoicsleeOdnlbinye
-unsaturated esters but the rate was extremely slow with Magnus.3 Conjugate reduction of the -unsaturated ester
DOI: 10.1039/C9CC03921J
most reactions failing to go to completion after several days. affords the Mn enolate A which is then oxidised with O2 to the
Pleasingly, the MnIII(SALPN)(acac) complex 7 was more active, peroxide B or manganeseperoxyenolate C. Alternatively, a -
catalysing the hydrations in 16 h in most cases with no oxo dimer type complex could be involved as we17 and others11
detectable reduction (HAT). For simple benzyl esters (entries 1- have observed the formation of Mn(IV) -oxo complexes from
3), the complex 7 was superior to dmp complex 2 in all cases cis--Mn(III) complexes. Oxidation of the enolate then gives the
affording good yields of the -hydration products and no -hydroxyester. In the case of our catalyst 7, little
reduction whilst original catalyst 2 gave considerable amounts hydroperoxide appears to form which suggests there is a
of reduction products.
preference for O-O cleavage rather than O-Mn in this step.3 In
Cinammate ester (entry 4) gave mostly the -hydration product, addition, the SAPLN ligand could shield the enolate from
again with catalyst 7 giving the best yields and high -selectivity. protonation retarding formation of the reduction by-product.
This result reinforces the suggestion that a radical process is
occurring as opposed to the ionic mechanism suggested by
Magnus.3 A stark result was obtained for the -
unsaturated substrate (entry 5) which afforded the -hydration
product in 20% using catalyst 7 but gave only decomposition
with the original catalyst 2. The alternative synthesis of this
hydration product involves multiple steps with comparable
overall yields.14 -Unsaturated lactones were also effectively
hydrated with catalyst 7 (entries 6 and 7) providing far superior
results to those for catalyst 2. Some stereoselectivity was
observed in the case of the 5-membered lactone (entry 6) and
a small amount of reduction was seen with catalyst 7 for for the
6-membered lactone (entry 7). The -hydroxylactone (entry 6)
can also be synthesised by oxidation of the enolate derived from
the corresponding saturated lactone however, this involves the
use of the toxic oxidant MoOPH.15 The final entry 8 involving a
cyclohexylidene substrate is the only example where the yields
using the original catalysts are superior to SALPN catalyst 7.
Interestingly, with both catalysts 2 and 7, reduction was not
observed but -selectivity was higher for catalyst 7.
Mukaiyama first suggested that the mechanism of this
hydration involves a radical intermediate2 whilst Magnus
proposed an ionic mechanism.3 More recently, Carreira has
shown that hydroazidation and hydrohydrazinations of
Scheme 4: Proposed hydration reaction mechanisms
essentially non-polar olefins catalysed by Mn and Co complexes
In conclusion, we have developed a useful catalyst for the
probably proceed via a free radical or metal-radical pairs as
Mukaiyama hydration of -unsaturated esters. The catalyst 7
can be easily synthesised from commercial starting materials in
supported by radical clock experiments.13 In addition, Nojima
has suggested that Co(III)-catalyzed triethylsilylperoxidation of
a one pot operation. Investigations into further applications of
alkenes using Et3SiH as the hydride source proceeds via Co(III)-
catalyst 7 and related complexes are underway.
alkyl or alkylperoxo complex.16 Our results suggest that a radical
intermediate could be involved as some products (entries 4 and
8) appear to be the result of a more stable radical intermediate
whilst the other regioisomers might result from ionic type
mechanism and two speculative rationales are shown in
Scheme 4.
Conflicts of interest
There are no conflicts to declare.
Treatment of the catalysts 7 with PhSiH3 gives the metal hydride
I which can then add to the polar alkene for form regioisomers
II and III. Loss of Mn(II) follows and either a benzylic or tertiary
free radical V (R2 = Ph or R2 = R3 = alkyl) or -radical IV (R2 = H;
R3 = alkyl) is formed and then captured by O2 to give the
peroxides formation of metal-peroxy complexes followed
reduction provides the hydroxyesters. The steric bulk of the
SALPN ligand combined with the conformational flexibility
allows for a more stable metal-peroxy intermediate complex
without rapid reduction by HAT to the reduced by-product.
Notes and references
1.
2.
S. Isayama; T. Mukaiyama Chem. Lett. 1989, 18, 1071.
S. Inoki; K. Kato; S. Isayama; T. Mukaiyama Chem. Lett.
1990, 19, 1869.
3.
4.
P. Magnus; A. Payne; M. Waring; D. Scott; V. Lynch
Tetrahedron Lett. 2000, 41, 9725.
P. Magnus; M. J. Waring; D. A. Scott Tetrahedron Lett.
2000, 41, 9731.
This journal is © The Royal Society of Chemistry 2019
Chem. Commun., 2019, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 4
COMMUNICATION
Org. Biomol. Chem.
5.
G. S. Hammond; D. C. Nonhebel; C.-H. S. Wu Inorg. Chem.
1963, 2, 73.
View Article Online
DOI: 10.1039/C9CC03921J
6.
7.
W. C. Fernelius; B. E. Bryant Inorg. Synth. 1957, 5, 105.
S. W. M. Crossley; C. Obradors; R. M. Martinez; R. A.
Shenvi Chem. Rev. 2016, 116, 8912.
8.
For application of the Co varient of Jaconsen’s catalyst in
H-atom transfer see: S. W. M. Crossley; F. Barabé; R. A.
Shenvi J. Am. Chem. Soc. 2014, 136, 16788.
M. Maiti; D. Sadhukhan; S. Thakurta; S. Sen; E. Zangrando;
R. J. Butcher; R. C. Deka; S. Mitra Eur. J. Inorg. Chem.
2012, 2013, 527.
9.
10.
Crystallographic data. For 6: M = 634.65, triclinic, a =
10.2610(16), b = 10.8556(15), c = 14.6929(15), a =
81.588(10)° b = 85.042(10)° g = 85.486(12)° U = 1609.3(4)
Å3, T = 130.0 K, space group P-1, Z = 2, (Mo-K) =0.460
mm−1, 7657 reflections measured, 7657 unique (refined
as a two-component twin). The final wR was 0.0757, CCDC
deposit code 1908184. For 7: M = 607.39, triclinic, a =
7.9107(4), b = 11.7226(7), c = 15.1375(7) a = 85.161(10)° b
= 87.054(4)° g = 87.105(4)°, U = 1395.40(13) Å3, T = 130.0
K, space group P-1, Z = 2, (Mo-K) =0.708 mm−1, 19556
reflections measured, 12720 unique, (R = 0.0360). The
final wR was 0.0522, CCDC deposit code 1908183., In
E. J. Larson; V. L. Pecoraro J. Am. Chem. Soc. 1991, 113,
3810.
C. Obradors; R. M. Martinez; R. A. Shenvi J. Am. Chem.
Soc. 2016, 138, 4962.
J. Waser; B. Gaspar; H. Nambu; E. M. Carreira J. Am.
Chem. Soc. 2006, 128, 11693.
G.-Q. Tian; J. Yang; K. Rosa-Perez Org. Lett. 2010, 12,
5072.
11.
12.
13.
14.
15.
16.
W. Li; J. Gan; D. Ma Angew. Chem. Int. Ed. 2009, 48, 8891.
T. Tokuyasu; S. Kunikawa; A. Masuyama; M. Nojima Org.
Lett. 2002, 4, 3595.
17.
D. Loits; S. Bräse; A. J. North; J. M. White; P. S. Donnelly;
M. A. Rizzacasa Eur. J. Inorg. Chem. 2016, 3541.
4 | Chem. Commun., 2019, 00, 1-3
This journal is © The Royal Society of Chemistry 2019
Please do not adjust margins