Homogeneous cis-dihydroxylation and epoxidation of olefins with high H2O2 efficiency by mixed manganese/activated carbonyl catalyst system

Article abstract of DOI:10.1016/S0040-4039(02)00292-7

The use of [Mn₂O₃(tmtacn)₂](PF₆)₂ (tmtacn=1,4,7-trimethyl-1,4,7-triazacyclononane) in combination with glyoxylic acid methylester methyl hemiacetal (GMHA) results in a highly active and hydrogen peroxide efficient catalyst for the epoxidation of olefins as well as the first homogeneous catalytic cis-dihydroxylation system with H₂O₂ and with turnover numbers up to 420.

Full text of DOI:10.1016/S0040-4039(02)00292-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2619–2622
Homogeneous cis-dihydroxylation and epoxidation of olefins with
high H2O2 efficiency by mixed manganese/activated carbonyl
catalyst system
Jelle Brinksma,a Lizette Schmieder,b Gerbert van Vliet,b Rob Boaron,b Ronald Hage,c
Dirk E. De Vos,d Paul L. Alstersb,* and Ben L. Feringaa,*
aLaboratory of Organic Chemistry, Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen,
The Netherlands
bDSM Fine Chemicals, Advanced Synthesis and Catalysis, PO Box 18, 6160 MD Geleen, The Netherlands
cUnilever Research Laboratory Vlaardingen, PO Box 114, 3130 AC Vlaardingen, The Netherlands
dCentre for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium
Received 18 January 2002; accepted 8 February 2002
Abstract—The use of [Mn2O3(tmtacn)2](PF6)2 (tmtacn=1,4,7-trimethyl-1,4,7-triazacyclononane) in combination with glyoxylic
acid methylester methyl hemiacetal (GMHA) results in a highly active and hydrogen peroxide efficient catalyst for the epoxidation
of olefins as well as the first homogeneous catalytic cis-dihydroxylation system with H2O2 and with turnover numbers up to 420.
© 2002 Elsevier Science Ltd. All rights reserved.
For economic and environmental reasons catalytic
olefin oxidations based on O2 or H2O2 are preferred
over traditional stoichiometric oxidations, e.g. epoxida-
tion with peracids and cis-dihydroxylation with per-
manganate.1 Several methods are available for catalytic
epoxidation with aqueous H2O2 (notably Re-, W-, and
Mn-based catalysts),2 but high turnovers for cis-dihy-
droxylation are only achieved using Os.3 However, the
high cost and toxicity of Os hamper large scale applica-
tion and provide a strong incentive to develop benign
Fe- or Mn-based cis-dihydroxylation catalysts. Que et
al. recently reported the first cis-dihydroxylation with
catalysts are known to be particularly effective in
decomposition of H2O2.6 This can be suppressed by
working in acetone;7 however, this solvent is not
acceptable for large-scale applications because of the
risk of formation of explosive cyclic peroxides. H2O2
decomposition by Mn–tacn complexes can be sup-
pressed by addition of oxalate8a or ascorbic acid8b as
co-catalysts, or by anchoring the tacn ligand to a solid
support.9 Significant amounts of cis-diols besides epox-
ides are formed during alkene oxidation with this het-
erogenised Mn catalyst.
H2O2 catalysed by
a
non-heme iron complex.4
Herein, we report efficient alkene oxidations with H2O2
catalysed by Mn–tmtacn 110 in the presence of GMHA
2 (Fig. 1). Surprisingly, the latter not only strongly
suppresses H2O2 decomposition by the Mn catalyst, but
also imparts the first homogeneous catalytic cis-dihy-
droxylation activity to a Mn catalyst. Catalytic oxida-
tions were performed by adding aqueous, 50%
hydrogen peroxide (1.3 equiv. with respect to the sub-
Although this system shows good cis-diol selectivities,
turnover numbers (t.o.n.) are rather low (up until 22
t.o.n.).
Recently Mn complexes based on tmtacn were found to
be highly active in catalytic oxidation,5 but apart from
high turnover, it is essential to develop catalytic systems
that employ H2O2 very efficiently, as many Mn or Fe
Keywords: hydrogen peroxide; cis-diols; epoxides; manganese; oxida-
tion.
* Corresponding authors. Tel.: +31 50 363 4278; fax: +31 50 363
4296; e-mail: b.l.feringa@chem.rug.nl
Figure 1. L=1,4,7-trimethyl-1,4,7-triazacyclononane.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00292-7

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J. Brinksma et al. / Tetrahedron Letters 43 (2002) 2619–2622
strongly on the alkene structure. The highest amount of
cis-diol was found for cyclooctene (entry 3), which
afforded the cis-diol as the main product (42%, 420
t.o.n.) besides the epoxide (36%, 360 t.o.n.). Minor
amounts of 2-hydroxycyclooctanone were also found
due to overoxidation of the diol. The ring size of
cycloalkenes has a profound influence on the epoxide/
cis-diol ratio (entries 1–4). For these cyclic olefins,
almost no trans-diol could be detected (ratio cis-diol/
trans-diol >99.5/0.5). cis-Diol formation is also
observed for aliphatic acyclic alkenes. Yields of diol are
significantly lower for trans-2-hexene than from cis-2-
hexene, but the epoxide/cis-diol ratio was similar for
both substrates. The aryl-substituted alkenes (entries 7,
8) yield epoxide nearly exclusively under these condi-
tions. Limited cis/trans isomerisation is observed in the
epoxide formation of cis-2-hexene. The cis/trans iso-
merisation points to epoxidation via a Mn oxo spe-
cies, with formation of epoxides from C-centred radical
intermediates with a lifetime sufficient for some CꢀC
bond rotation prior to reaction to the epoxide.12 In line
with this mechanism, olefins that form a relatively
long-lived radical intermediate, such as cis-stilbene,
show substantial loss of configuration in epoxide. No
diols were formed on replacing the substrate by epox-
strate) in 6 h to a mixture of alkene, Mn–tmtacn
catalyst (0.1 mol%), and GMHA (25 mol%) in MeCN
at 0°C. Under these reaction conditions, the presence of
GMHA as the co-catalyst enables high conversions
with only a 30% excess of oxidant with respect to
substrate (Table 1) and the H2O2 efficiency is drastically
improved compared to previous Mn systems using
excess of H2O2.5 In most cases the conversions were
also significantly higher than those obtained with
oxalate as co-catalyst and 1.3 equiv. of H2O2 (for
similar experiments with a larger excess of H2O2, see
Ref. 8a).
In particular, styrene afforded a high yield of styrene
oxide in the presence of GMHA, whereas the use of
oxalate resulted in only modest conversion of styrene.
When a mixture of GMHA (25 mol%) and oxalate (0.3
mol%) was used as the co-catalyst system, the epoxide
yields even surpassed those obtained with the Mn/
GMHA catalytic system, and high epoxide yields at
complete conversion were obtained for the non-steri-
cally hindered alkenes (Table 1, entries 1–3, 6, 8).
Unexpectedly, substantial amounts of cis-diols were
formed besides epoxides when only GMHA was present
as the co-catalyst. The epoxide/cis-diol ratio depends
Table 1. Oxidation of selected olefins by H2O2 with catalyst 111
Entry
Substrate
Conversion (%)e
Productd
Turnover number (t.o.n.)e
Additive:
Additive:
Additive:
oxalatec
Additive:
Additive:
Additive:
GMHAa (2)
2+oxalateb
GMHAa (2)
2+oxalateb
oxalatec
1
2
3
Cyclopentene
Cyclohexene
Cyclooctene
Norbornylene
97
88
90
95
100
100
100
92
73
52
Epoxide
cis-Diol
Cyclopentenone
Epoxide
cis-Diol
2-Cyclohexenone
Epoxide
cis-Diol
2-HO-cyclooctanone
exo-Epoxide
exo-cis-Diol
trans-Epoxide
cis-Epoxide
RR/SS-Diol
RS/SR-Diol
cis-Epoxide
trans-Epoxide
SR/RS-Diol
RR/SS-Diol
cis-Epoxide
trans-Epoxide
meso-Hydrobenzoin
Hydrobenzoin
Epoxide
610
260
80
590
90
860
0
10
820
0
80
840
60
80
530
60
550
30
90
0
820
30
10
0
260
160
30
20
860
50
30
770
0
100
610
0
70
410
0
0
360
0
240
0
0
80
360
420
220
540
180
210
50
150
0
450
40
280
10
260
200
40
40
860
60
4
5
88
93
59
37
trans-2-Hexene 77
0
6
7
8
cis-2-Hexene
cis-Stilbene
Styrene
93
82
97
100
77
80f
32
44
640
20
10
0
110
150
10
10
380
0
100
Ph(CH)(OH)CH2OH
PhC(O)CH2OH
10
0
a Co-catalyst GMHA (25 mol%).
b Co-catalyst mixture of GMHA (25 mol%) and oxalate (0.3 mol%).
c Co-catalyst oxalate (0.3 mol%), for similar experiments with a larger excess of H2O2, see Ref. 8a.
d All products were identical to independent samples and identified by GC and 1H NMR.
e Determined by GC.
f 32 mmol scale

J. Brinksma et al. / Tetrahedron Letters 43 (2002) 2619–2622
2621
Figure 2. Time profile of the oxidation of cyclooctene by H2O2 with catalyst 1 and GMHA; ꢀ epoxide; ꢁ cis-diol.
ide, thus excluding epoxide hydrolysis.13 This conclu-
sion is further supported by the time course profile of
the 1/GMHA-catalysed oxidation of cyclooctene, which
shows that both epoxide and diol increase progressively
with time (Fig. 2).
Attempts to increase the cis-diol selectivity by addition
of acid or base resulted in a dramatic decrease of
conversion. Besides GMHA, a few other carbonyl com-
pounds were tested as co-catalyst (25 mol%) for the
oxidation of cyclooctene with H2O2 (1.3 equiv.). In the
presence of glyoxylic acid hydrate, the epoxide was
formed in 840 t.o.n. and cis-diol formation was almost
completely suppressed. Modest cis-diol yields (<250
t.o.n.) and predominant formation of the epoxide were
seen with diethyl ketomalonate or 2-ketoglutaric acid as
the co-catalysts. However, cis-diol formation (370
t.o.n.) predominated over epoxide (310 t.o.n.) forma-
tion in the presence of chloral hydrate. Thus, a variety
of carbonyl compounds with an adjacent electron with-
drawing group are able to reduce H2O2 decomposition
by 1 and to impose cis-dihydroxylation activity on
manganese catalyst 1, albeit with variable cis-diol/epox-
ide ratios.
Scheme 1. Proposed cis-dihydroxylation mechanism (L=
tmtacn, X=CO2Me, CCl3).
combination with Mn–tmtacn results in a highly active
(up to 860 t.o.n.) and H2O2 efficient epoxidation sys-
tem. Besides epoxidation this new catalytic system also
provides, to the best of our knowledge, the most active
Os-free homogeneous catalyst for cis-dihydroxylation
(up to 420 t.o.n.). Compared with the anchored Mn–
tacn catalyst,9 the present homogeneous 1/activated
carbonyl compound system is much more accessible,
since both 1 and many activated carbonyl compounds
have large scale applications. Efforts to enhance diol
selectivity and to elucidate the cis-dihydroxylation
mechanism are in progress.
Since cis-diol formation through Mn-catalysed epoxide
hydrolysis can be excluded (vide supra), we propose
that the cis-diol is formed by reaction of the alkene
with an Mn oxo-hydroxo species. As in the case of
oxalate, hydrated activated carbonyl compounds14
might break down the catalase active binuclear Mn
complex 115 into a mononuclear Mn species via com-
plexation to the Mn centre. cis-Diol formation from an
Mn oxo-hydroxo species with a coordinated hydrated
carbonyl ligand could be induced through a hydrogen
bonded six-membered ring transition state (concerted
pathway, Scheme 1). Reoxidation of the Mn centre
with H2O2, release of the diol from Mn, and hydration
of the carbonyl compound closes the catalytic cycle. In
conclusion, use of activated carbonyl compounds in
Acknowledgements
We thank Dr. D. Schipper (DSM Food Specialities) for
NMR experiments on the GMHA/50% aq. H2O2 sys-
tem and DSM Fine Chemicals Austria for supply of
GMHA.

2622
J. Brinksma et al. / Tetrahedron Letters 43 (2002) 2619–2622
epoxidation catalyst: White, M. C.; Doyle, A. G.; Jacob-
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