Synthesis and catalytic properties of p-acylthio(phenylacetylene)n substituted chiral manganese salen complexes

Article abstract of DOI:10.1039/b104103g

The syntheses of three new salen ligands that are tethered to a p-acylthio(phenylacetylene)_n linker are described. The two key steps in the syntheses are coupling of the p-acylthio(phenylacetylene)_n linker (n = 0-2) with a 5-iodosali

Full text of DOI:10.1039/b104103g

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Synthesis and catalytic properties of p-acylthio(phenylacetylene)n
substituted chiral manganese salen complexes
Morten Nielsen and Kurt V. Gothelf*
1
Center for Metal-Catalysed Reactions, Department of Chemistry, Aarhus University,
DK-8000 Aarhus C, Denmark
Received (in Cambridge, UK) 4th May 2001, Accepted 13th August 2001
First published as an Advance Article on the web 13th September 2001
The syntheses of three new salen ligands that are tethered to a p-acylthio(phenylacetylene)n linker are described.
The two key steps in the syntheses are coupling of the p-acylthio(phenylacetylene)n linker (n = 0–2) with a
5-iodosalicylaldehyde and the subsequent condensation of the aldehyde moiety of the formed adducts with
the monoimine of (S,S)-1,2-diphenylethylenediamine to give the salen ligands. In the catalytic asymmetric
epoxidation reactions of (Z)-2-methylstyrene, performed using the Mn–salen complexes of these new ligands,
high diastereoselectivities of up to 20 : 1 and enantioselectivities of up to 89% ee are obtained. The results are
compared with the analogous reaction using Jacobsen’s asymmetric epoxidation catalyst and the results are very
similar. The synthesised ligands are promising candidates for the immobilisation of chiral Mn–salen complexes
on gold electrodes and surfaces.
Introduction
Results and discussion
The immobilisation of organic molecules on a conducting
surface allows the study of direct electron-transfer between the
immobilised molecule and the surface. Self-assembled mono-
layers (SAMs) of thiols on gold surfaces1 have often been the
preferred model for such studies,2 due to their ease of prepar-
ation and the relatively large potential window within which
such electrodes can operate.3 These systems have been applied
to the development of electronic bio- and chemosensors4 and in
molecular electronics.5 Jagessar and Tour have used oligo-
(phenylacetylene)s as conducting ‘organic wires’ between the
gold surface and a redox-active center.6 In a series of papers,
Lindsey et al. have recently described the synthesis of phenyl-
acetylene linked porphyrin molecules.7
Synthesis of the ligands
Our strategy for the synthesis of the desired ligands has been
first to connect the acetylthio(phenylacetylene)n moiety of 1
(n = 1, 2) with one of the salicylaldehyde groups of the desired
salen moiety using a Sonogashira coupling.11 The salicylalde-
hyde 2a, was iodinated with ICl in acetic acid to give the 3-tert-
butyl-5-iodosalicylaldehyde 3 in 93% yield (Scheme 1).12
The bromination of 2a was also performed,13 but the resulting
5-bromosalicylaldehyde could not be used for the following
The target of the work described in this paper is to develop
new ligands for asymmetric redox-catalysts that can be
immobilised on an electrode via a conducting wire. This enables
the direct monitoring of the redox processes at the catalyst
center and the possible development of new electrocatalysts. We
present here the syntheses and testing of catalytic properties of
three new chiral manganese–salen complexes8 1 that are substi-
tuted with a conducting organic wire consisting of (phenyl-
acetylene)n (n = 0, 1, 2) units. These new manganese complexes
are functionalised with a terminally protected sulfur moiety,
which allows immobilisation of the catalyst on gold electrodes
that can be applied for studies of catalytic and electrocatalytic
epoxidation reactions.8–10
Scheme 1
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J. Chem. Soc., Perkin Trans. 1, 2001, 2440–2444
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b104103g

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coupling reaction. The TMS protected acetylthio(phenylacetyl-
ene)n linkers 4a, b were synthesised according to the procedures
described by Tour14 and by Sita,15 respectively, and the free
terminal acetylenes 5a, b were obtained in high yields by
deprotection with TBAF.14 The coupling reaction between the
linkers 5a, b with iodosalicylaldehyde 3 was performed to give
the adducts 6a and 6b, respectively. The catalysts for this
reaction were (Ph3P)2PdCl2 (7 mol%) and CuI (7 mol%) with
triethylamine as the solvent. The products were obtained in
83% yield for 6a and 55% yield for 6b. When carried out in
Hünig’s base–THF, the reactions proceeded with slightly lower
yields.
and 8b in the presence of the free amine 7. Thus, it was observed
for these condensations that, upon prolonged reaction times,
the only imine product formed was the C2-symmetric salen
ligand 9. However, when the non-symmetric imines 8a, b were
isolated after shorter reaction times, they were stable.
The third ligand in this series, 8c, was prepared with the
sulfur handle directly attached to the salen moiety (Scheme 3).
The right-hand side of the desired ligands in 1a, b was
prepared by condensation of enantiopure (1S,2S)-1,2-
diphenylethylenediamine and 3,5-di-tert-butylsalicylaldehyde
2b (Scheme 2). The best result, in which 7 was isolated in 78%
Scheme 3
The coupling between 3-tert-butyl-5-iodosalicylaldehyde 3 and
Cu() thiobenzoate 10 was performed in HMPA to produce the
benzoylthio-substituted salicylaldehyde 11 in 31% yield.16,17 The
subsequent condensation reaction with the monoimine 7, per-
formed as described for the analogous reaction of 6a, b, gave
the non-symmetric salen ligand 8c in 49% yield.
With the three new ligands 8a–c in hand, the next step was to
insert the manganese metal core in the ligands. This was per-
formed by dissolving the ligands in a solution of Mn(OAc)2ؒ
H2O in methanol with stirring for 30 min under air at 50 ЊC
(Scheme 4).18 Under these conditions Mn() is oxidised to
Scheme 2
yield, was obtained when the reaction was performed in CH2Cl2
in the presence of molecular sieves (MS, 3 Å). If MgSO4 was
used as the drying agent or if MeOH was used as the solvent,
the yield decreased due to an increased tendency to form the
symmetric salen ligand 9 instead of the desired monoimine 7.
The syntheses of the ligands 8a and 8b were completed by con-
densation of 7 with 6a and 6b, respectively, using MS (3 Å) in
CH2Cl2 as described for the synthesis of 7. The two new salen
ligands 8a and 8b were obtained in 27 and 56% yield, respect-
ively. The reason for the relatively low yields obtained in these
reactions is that a substantial amount of the symmetric ligand
9 was formed. This by-product was probably formed by a
favoured disproportionation of the non-symmetric amines 8a
Scheme 4
Mn(). Subsequent exchange of the acetate ligand with chlor-
ide using NaCl, yielded the Mn–salen complexes 1a–c.
J. Chem. Soc., Perkin Trans. 1, 2001, 2440–2444
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Table 1 Comparison of the selectivities obtained in the asymmetric
epoxidation of (Z)-2-methylstyrene in the presence of 5 mol% of the
known Mn–salen complexes 12a, b with the new catalysts 1a–ca
In summary, we have synthesised three new sulfur functional-
ised (phenylacetylene)n–Mn–salen complexes 1a–c and we have
shown that the selectivities obtained in the catalytic asymmetric
epoxidation reaction are very similar to the values obtained
using two well-known Mn–salen catalysts. The ligands 8a–c
are promising candidates for the immobilisation of chiral
Mn–salen complexes on gold electrodes and surfaces. The lig-
ands can also be applied for the immobilisation of other metal–
salen complexes on gold for the study of their redox chemistry
and for the possible development of asymmetric electro-
catalysts.
Entry
Catalyst
cis : transb
Ee(cis)b (%)
Ee(trans)b (%)
1
2
3
4
5
12a
12b
1a
14 : 1
89
59
26
27
14
26
20 : 1 (15 : 1)c
20 : 1
88 (88)c
89
1b
15 : 1
18 : 1
81
86
1c
a 0 ЊC, 2.5 h, NMO (5 eq.), MCPBA (2 eq.), quenched by addition of
1 M NaOH. Conversions of >90% were observed for all entries.
b Determined by chiral GC-MS with an Astec B-DM column.
c Selectivities obtained by Jacobsen and co-workers in a similar
reaction.8c
Experimental
General methods
Dichloromethane and triethylamine were dried using standard
methods. Pd(PPh3)2Cl2, 3-tert-butylsalicylaldehyde and (1S,
2S)-diphenylethylenediamine were purchased from Aldrich,
3,5-di-tert-butylsalicylaldehyde was received from Lancaster
and (Z)-2-methylstyrene was purchased from ICN Bio-
medicals. Copper() thiobenzoate 10,16 4-(acetylthio)phenyl-
acetylene 5a14 and 1-(4-{2-[4-(acetylthio)phenyl]ethynyl}-
phenyl)-2-trimethylsilylacetylene 4b15 were prepared according
to literature procedures. Enantiomeric excesses of the products
were determined by chiral GC-MS using an Astec B-DM
column. High resolution mass spectral analyses were performed
with a Micromass LC-TOF instrument.
Catalytic properties
The catalytic properties of the three new phenylacetylene
tethered catalysts 1a–c were tested and compared with the Mn–
salen epoxidation catalyst 12a and the commercially available
Jacobsen catalyst 12b (Scheme 5). The test reaction of choice
3-tert-Butyl-5-iodosalicylaldehyde (3)12
3-tert-Butylsalicylaldehyde 2a (1.63 g, 9.92 mmol) was dis-
solved in glacial acetic acid (10 mL) in a 100 ml round-
bottomed flask equipped with a reflux condenser. Iodine mono-
chloride (2.26 g, 13.9 mmol), dissolved in glacial acetic acid
(15 mL), was added dropwise to the solution and the reaction
mixture was refluxed for 4 h. The mixture was cooled to rt,
stirred overnight and then poured into water (100 mL). The
crude reaction mixture was extracted with CH2Cl2 (3 × 25 mL),
the organic layers were washed with sodium thiosulfate, dried
over MgSO4 and the solvent was evaporated in vacuo. The
residue was purified by flash chromatography (silica gel, 5%
Et2O in pentane) to yield the product 3 (2.85 g, 9.22 mmol,
93%) as a pale yellow solid after evaporation of the solvent;
mp 43–44 ЊC; δH(400 MHz; CDCl3; Me4Si) 1.40 (s, 9 H),
7.69 (d, J 2.0 Hz, 1 H), 7.72 (d, J 2.0 Hz, 1 H), 9.80 (s,
1 H), 11.74 (s, 1 H); δC(100 MHz; CDCl3; Me4Si) 29.2, 35.3,
122.7, 140.2, 141.6, 142.8, 161.1, 164.2, 196.2; m/z (GC-MS)
304 (Mϩ).
Scheme 5
was the epoxidation of (Z)-2-methylstyrene with MCPBA as
the oxygen source and N-methylmorpholine N-oxide (NMO) as
the co-oxidant. The reaction time was 2.5 h at 0 ЊC and the
epoxidation reactions proceeded to give the epoxide with >90%
conversion.
The results of these epoxidation reactions are collected in
Table 1. For the two Mn–salen catalysts 12a and 12b the cis-
epoxide was obtained in 89 and 88% ee, respectively (entries 1,
2). These results are very similar to those obtained by Jacobsen
and co-workers, when using 2–4 mol% of catalyst 12b at 0 ЊC.8c
The new Mn–salen catalysts 1a–c induce diastereo- and enantio-
selectivities that are comparable to the known C2-symmetric
catalysts (Table 1, entries 3–5). The comparison between 1a–c
and 12a is especially interesting because these ligands have
the same diphenyl backbone in contrast to 12b, which has
a cyclohexane backbone. The highest diastereo- and enantio-
selectivities of the three new catalysts were obtained for 1a,
which induces 89% ee of the cis-epoxide, which is similar to the
result obtained when using the C2-symmetric catalysts (entries
1, 2). When applying catalyst 1b with two phenylacetylene units
the enantioselectivity decreases to 81% ee (entry 4). The catalyst
ligand with the sulfur handle connected directly onto the salen
core 1c induced 86% ee for the cis-epoxide (entry 5). For all the
catalysts 1a–c comparable cis-selectivities of 15 : 1 to 20 : 1 are
obtained, which is also similar to the results obtained when
using 12a, b. The selectivities obtained in the enantioselective
epoxidation reaction of (Z)-2-methylstyrene using the three
new Mn–salen complexes 1a–c are thus similar, or slightly
lower, than the selectivities obtained with the well-known
catalysts 12a, b.
4-{2-[4-(Acetylthio)phenyl]ethynyl}phenylacetylene (5b)
The silyl protected bis(phenylacetylene) derivative 4b (0.80 g,
2.3 mmol) was dissolved in dry THF (10 mL) in a flame dried
Schlenk flask. The solution was cooled to 0 ЊC followed by
the dropwise addition of a prepared solution of tert-butyl-
ammonium fluoride (11.5 mL, 1.0 M solution in THF, 11.5
mmol), acetic acid (0.69 mL, 10.0 mmol) and acetic anhydride
(1.02 g, 10.0 mmol). The solution was stirred at 0 ЊC for
1 h, followed by stirring at rt for 1 h. The reaction mixture
was poured into water (50 mL) and extracted with CH2Cl2
(3 × 20 mL). The combined organic layers were washed with
brine, dried over MgSO4 and the solvent was evaporated
in vacuo. The residue was purified by flash chromatography
(silica gel, 10% Et2O in pentane) to yield the product 5b
(586 mg, 2.1 mmol, 92%) as a yellow oil after evaporation of the
solvent; δH(400 MHz; CDCl3; Me4Si) 2.44 (s, 3 H), 3.18 (s, 1 H),
7.40 (d, J 8.2 Hz, 2 H), 7.48 (s, 4 H), 7.55 (d, J 8.2 Hz, 2 H);
δC(100 MHz; CDCl3; Me4Si) 30.6, 79.3, 83.4, 90.7, 90.8, 122.4,
123.6, 124.4, 128.6, 121.8, 132.3, 132.4, 134.5, 193.7; HRMS
(ES) calc. for C18H12OS 276.0609; found 276.0612.
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J. Chem. Soc., Perkin Trans. 1, 2001, 2440–2444

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5-{2-[4-(Acetylthio)phenyl]ethynyl}-3-tert-butylsalicylaldehyde
(6a)
CH2Cl2 (dry, 5 mL) were added and the mixture was stirred for
5 h under an argon atmosphere. The solids were filtered off and
the volume of solvent was decreased to 0.5 mL by evaporation
in vacuo. The residue was purified by flash chromatography (sil-
ica gel, 40% CH2Cl2 in pentane) to give 8a (48 mg, 0.063 mmol,
27%) as a yellow solid after evaporation of the solvent; mp 114–
A mixture of (PPh3)2PdCl2 (35 mg, 0.050 mmol) and CuI
(9.5 mg, 0.050 mmol) was stirred for 1 h under vacuum in a
flame dried Schlenk flask. 4-(Acetylthio)phenylacetylene 5a
(115 mg, 0.65 mmol), iodosalicylaldehyde 3 (200 mg, 0.65
mmol) and triethylamine (dry, 5 mL) were added and the mix-
ture was stirred overnight at 70 ЊC under an argon atmosphere.
The solvent was evaporated in vacuo and the residue was puri-
fied by flash chromatography (silica gel, 18% Et2O in pentane)
to yield 6a (180 mg, 0.53 mmol, 83%) as a pale yellow solid after
evaporation of the solvent; mp 96–97 ЊC; δH(400 MHz; CDCl3;
Me4Si) 1.43 (s, 6 H), 1.51 (s, 3 H), 2.43 (s, 3 H), 7.39 (d, J 8.6 Hz,
2 H), 7.54 (d, J 8.6 Hz, 2 H), 7.61 (d, J 2.0 Hz, 1 H), 7.66 (d,
J 8.6 Hz, 1 H), 9.87 (s, 1 H), 11.93 (s, 1 H); δC(100 MHz; CDCl3;
Me4Si) 29.3, 30.6, 35.2, 87.8, 90.3, 114.2, 120.7, 124.6, 128.2,
132.3, 134.5, 135.5, 137.3, 139.2, 161.7, 193.8, 196.9; HRMS
(ES) calc. for C21H20O3S 352.1133; found 352.1138.
116 ЊC; νmax (KBr)/cmϪ1 3448 (OH), 2959 (CH), 2346 (C᎐C),
᎐
᎐
1702 (CO), 1627 (C᎐N), 1441, 1273; δ (400 MHz; CDCl ;
᎐
H
3
Me4Si) 1.15 (s, 9 H), 1.35 (s, 9 H), 1.37 (s, 9 H), 2.35 (s, 3 H),
4.63 (d, J 8.2 Hz, 1 H), 4.67 (d, J 8.2 Hz, 1 H), 7.11–7.19
(m, 12 H), 7.26 (d, J 2.3 Hz, 1 H), 7.30 (d, J 8.2 Hz, 2 H), 7.33
(d, J 2.0 Hz, 1 H), 7.43 (d, J 8.2 Hz, 2 H), 8.24 (s, 1 H), 8.25
(s, 1 H), 13.45 (s, 2 H); δC(100 MHz; CDCl3; Me4Si) 29.4, 29.6,
30.5, 31.6, 34.3, 35.1, 35.3, 80.2, 80.3, 86.9, 91.6, 112.3, 117.9,
118.7, 125.2, 126.4, 127.7, 127.8, 127.9, 128.2, 128.2, 128.6,
128.6, 128.7, 132.2, 133.2, 133.9, 134.4, 136.7, 138.0, 139.4,
139.7, 140.4, 158.1, 161.2, 166.5, 167.7, 193.9; HRMS (ES) calc.
for C50H54N2O3S 762.3855; found 762.3901.
(1S,2S)-N-{5-[2-(4-{2-[4-(Acetylthio)phenyl]ethynyl}phenyl)-
ethynyl]-3-tert-butylsalicylidene}-NЈ-(3,5-di-tert-butylsalicyl-
idene)-1,2-diphenylethylenediamine (8b)
5-[2-(4-{2-[4-(Acetylthio)phenyl]ethynyl}phenyl)ethynyl]-3-tert-
butylsalicylaldehyde (6b)
A mixture of (PPh3)2PdCl2 (53 mg, 0.060 mmol) and CuI
(12 mg, 0.060 mmol) was stirred for 1 h under vacuum in a
flame dried Schlenk flask. Compound 5b (205 mg, 0.74 mmol),
iodosalicylaldehyde 3 (280 mg, 0.91 mmol) and dry triethyl-
amine (6 mL) were added and the mixture was stirred overnight
at 55 ЊC under an argon atmosphere. The reaction mixture was
poured into water and extracted with CH2Cl2 (4 × 20 mL). The
combined organic layers were washed with brine, dried over
MgSO4 and the solvent was evaporated in vacuo. The residue
was purified by flash chromatography (silica gel, 20% Et2O in
pentane) to yield the product 6b (186 mg, 0.41 mmol, 55%) as a
yellow wax after evaporation of the solvent; δH(400 MHz;
CDCl3; Me4Si) 1.44 (s, 9 H), 2.44 (s, 3 H), 7.41 (d, J 8.2 Hz,
2 H), 7.51 (s, 4 H), 7.56 (d, J 8.2 Hz, 2 H), 7.63 (d, J 2.0 Hz,
1 H), 7.67 (d, J 2.0 Hz, 1 H), 9.88 (s, 1 H), 11.95 (s, 1 H);
δC(100 MHz; CDCl3; Me4Si) 29.3, 30.6, 35.2, 88.3, 90.6, 90.7,
90.9, 114.3, 120.7, 122.9, 123.5, 124.5, 128.5, 131.7, 131.9,
132.4, 134.5, 135.4, 137.3, 139.2, 161.6, 193.7, 196.9; HRMS
(ES) calc. for C29H24O3S 452.1446; found 452.1440.
A Schlenk flask containing MS (3 Å, 1.5 g) and a magnetic
stirrer bar was dried with a flame under vacuum. Salicylalde-
hyde 6b (48 mg, 0.106 mmol), amine 7 (60 mg, 0.14 mmol) and
CDCl3 (5 mL) were added and the mixture was stirred over-
night under an argon atmosphere. Then MgSO4 (50 mg) was
added and the suspension was stirred for another 24 h. The
solids were filtered off and the volume of solvent was decreased
to 0.5 mL by evaporation in vacuo. The residue was purified by
flash chromatography (silica gel, 10% Et2O in pentane) to give
8b (51 mg, 0.063 mmol, 56%) as a yellow solid after evaporation
of the solvent; mp 118–120 ЊC; νmax (KBr)/cmϪ1 3442 (OH),
᎐
2956 (CH), 2350 (C᎐C), 1710 (CO), 1625 (C᎐N), 1441, 1384;
᎐
᎐
δH(400 MHz; CDCl3; Me4Si) 1.15 (s, 9 H), 1.35 (s, 9 H), 1.38 (s,
9 H), 2.37 (s, 3 H), 4.64 (d, J 8.2 Hz, 1 H), 4.67 (d, J 8.2 Hz,
1 H), 6.87 (d, J 2.3 Hz, 1 H), 7.09–7.19 (m, 11 H), 7.26 (d, J 2.3
Hz, 1 H), 7.32–7.50 (m, 9 H), 8.26 (s, 1 H), 8.27 (s, 1 H), 13.48
(s, 2 H); δC(100 MHz; CDCl3; Me4Si) 29.3, 29.4, 29.6, 30.6, 31.6,
34.4, 35.2, 80.2, 80.3, 88.3, 90.7, 90.9, 91.1, 112.4, 117.9, 118.7,
124.1, 124.8, 125.5, 126.4, 127.8, 128.2, 128.2, 128.6, 128.7,
128.7, 130.2, 131.5, 131.5, 131.8, 132.3, 132.4, 133.1, 133.8,
134.5, 136.7, 138.0, 139.4, 139.7, 140.4, 143.6, 166.5, 167.7,
193.7. HRMS (ES) calc. for C58H58N2O3S 862.4168; found
862.4190.
(1S,2S)-N-(3,5-Di-tert-butylsalicylidene)-1,2-diphenylethylene-
diamine (7)
A Schlenk flask containing MS (3 Å, 1.5 g) and a magnetic
stirring bar was dried with a flame under vacuum. 3,5-Di-tert-
butylsalicylaldehyde 2b (157 mg, 0.67 mmol), (1S,2S)-1,2-
diphenylethylenediamine (144 mg, 0.68 mmol) and CH2Cl2
(dry, 5 mL) were added and the mixture was stirred for 3 h at rt
under an argon atmosphere. The solids were filtered off and the
volume of solvent was decreased to 0.5 mL by evaporation in
vacuo. The residue was purified by flash chromatography (silica
gel, 30% EtOAc in pentane) and, after evaporation of the
solvent, 7 (226 mg, 0.53 mmol, 78%) was obtained as a yellow
foam containing some minor impurities, arising from dis-
proportionation of the product. Due to the lability of 7, it was
used directly in the next step without further purification;
δH(400 MHz; CDCl3, Me4Si) 1.29 (s, 9 H), 1.48 (s, 9 H), 1.62 (s,
2 H), 4.31 (d, J 7.8 Hz, 1 H), 4.42 (d, J 7.8 Hz, 1 H), 7.08 (d, J
2.3 Hz, 1 H), 7.12–7.21 (m, 10 H), 7.40 (d, J 2.7 Hz, 1 H), 8.46
(s, 1 H), 13.59 (s, 1 H); HRMS (ES) calc. for C29H36N2O
428.2828; found 428.2826.
5-Benzoylthio-3-tert-butylsalicylaldehyde (11)
The copper thiobenzoate 10 (1.75 g, 8.7 mmol) was added to a
solution of iodoaldehyde 3 (1.00 g, 3.2 mmol) in HMPA (20
mL) in a flame dried Schlenk flask under an argon atmosphere.
The mixture was stirred at 110 ЊC for 3 h and then poured into
water (100 mL). The crude reaction mixture was extracted with
diethyl ether (3 × 50 mL). The combined organic phases were
washed with brine and water, dried over MgSO4 and concen-
trated in vacuo. The residue was purified by flash chromato-
graphy (silica gel, 10% Et2O in pentane) to yield the product 11
(312 mg 0.99 mmol, 31%) as a thick brown oil after evaporation
of the solvent; δH(400 MHz; CDCl3; Me4Si) 1.37 (s, 9 H), 7.43
(t, J 7.6 Hz, 2 H), 7.50 (s, 1 H), 7.51 (s, 1 H), 7.55 (t, J 6.8 Hz,
1 H), 7.95 (d, J 7.8 Hz, 2 H), 9.81 (s, 1 H), 11.92 (s, 1 H). δC(100
MHz; CDCl3; Me4Si) 29.6, 35.3, 117.1, 121.5, 127.7, 128.4,
129.1, 134.1, 136.5, 139.3, 140.1, 140.9, 162.5, 196.9; HRMS
(ES) calc. for C18H18O3S 314.0977; found 314.0972.
(1S,2S)-N-(5-{2-[4-(Acetylthio)phenyl]ethynyl}-3-tert-butyl-
salicylidene)-NЈ-(3,5-di-tert-butylsalicylidene)-1,2-diphenyl-
ethylenediamine (8a)
(1S,2S)-N-(5-Benzoylthio-3-tert-butylsalicylidene)-NЈ-(3,5-di-
tert-butylsalicylidene)-1,2-diphenylethylenediamine (8c)
A Schlenk flask containing MS (3 Å, 1.5 g) and a magnetic
stirrer bar was dried with a flame under vacuum. Salicylalde-
hyde 6a (78 mg, 0.23 mmol), amine 7 (100 mg, 0.23 mmol) and
A Schlenk flask containing MS (3 Å, 1.5 g) and a magnetic
stirrer bar was dried with a flame under vacuum. Salicylalde-
J. Chem. Soc., Perkin Trans. 1, 2001, 2440–2444
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hyde 11 (53 mg, 0.17 mmol), amine 7 (72 mg, 0.17 mmol) and
CDCl3 (dry, 5 mL) were added and the mixture was stirred
overnight at room temperature under an atmosphere of argon.
The solids were filtered off and the volume of solvent was
reduced to 0.5 mL by evaporation in vacuo. The residue was
purified by flash chromatography (silica gel, 40% CH2Cl2 in
pentane) to yield 8c (60 mg 0.083 mmol, 49%) as a yellow foam
after evaporation of the solvent; νmax (KBr)/cmϪ1 3448 (OH),
Acknowledgements
The authors are indebted to The Danish Technical Research
Council and The Danish National Research Foundation for
financial support.
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2958 (CH), 2870, 1671 (CO), 1624 (C᎐N), 1435, 1204; δ (400
᎐
H
MHz; CDCl3; Me4Si) 1.24 (s, 9 H), 1.43 (s, 18 H), 4.74 (d, J 8.0
Hz, 1 H), 4.77 (d, J 8.0 Hz, 1 H), 6.98 (d, J 2.3 Hz, 1 H), 7.15–
7.26 (m, 11 H), 7.33 (dd, J 6.2 Hz, J 2.0 Hz, 2 H), 7.46 (t, J 7.4
Hz, 2 H), 7.59 (t, J 7.4 Hz, 1 H), 7.99 (d, J 8.2 Hz, 2 H), 8.34
(s, 1 H), 8.38 (s, 1 H), 13.52 (s, 2 H); δC(100 MHz; CDCl3;
Me4Si) 29.4, 29.6, 31.6, 32.0, 34.3, 35.2, 79.9, 80.2, 114.9, 118.0,
119.6, 126.5, 127.6, 127.6, 127.8, 127.9, 128.2, 128.2, 128.6,
128.6, 128.9, 133.8, 136.6, 136.7, 136.9, 137.2, 139.0, 139.5,
139.8, 140.3, 158.2, 162.0, 166.4, 167.6, 191.3; HRMS (ES) calc.
for C47H52N2O3S 724.3699; found 724.3696.
5 C. Joachim, J. K. Gimzewski and A. Aviram, Nature, 2000, 408, 541;
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General procedure for metal insertion
6 R. C. Jagessar and J. M. Tour, Org. Lett., 2000, 2, 111.
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To a solution of the salen ligand (8a, b or c) (0.005 mmol) in
methanol (7 mL) was added manganese() acetate tetrahydrate
(2.5 mg, 0.010 mmol) and the solution was stirred for 30 min
at 50 ЊC. Brine (0.5 mL) was added and the mixture was stirred
for another 30 min at 50 ЊC. The solvent was evaporated
in vacuo and the residue was dissolved in CH2Cl2 and washed
with brine and H2O. The organic phase was dried over Na2SO4
and evaporated in vacuo to give a quantitative yield of the
catalysts 1a–c as brownish solids. The catalysts were applied in
the epoxidation reaction without further purification.
8 (a) E. N. Jacobsen, W. Zhang, A. R. Muci, J. R. Ecker and L. Deng,
J. Am. Chem. Soc., 1991, 113, 7063; (b) J. F. Larrow, E. N. Jacobsen,
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Epoxidation reaction
9 T. Katzuki, Coord. Chem. Rev., 1995, 140, 189.
To a solution of the salen–MnCl catalyst 1a–c (0.005 mmol),
NMO (58.5 mg, 0.50 mmol) and (Z)-2-methylstyrene (11.8 mg,
0.10 mmol) in dry CH2Cl2 (5 mL) was added MCPBA (58 mg,
57–86% w/w, 0.20 mmol) in three portions at 0 ЊC. The solution
was stirred for 2.5 h at 0 ЊC under an atmosphere of argon. The
reaction was quenched by addition of 0.5 mL 1 M NaOH. The
organic phase was separated and washed with brine and H2O,
dried over MgSO4 and the solvent evaporated in vacuo. The
enantiomeric excess and diastereomeric ratio were determined
by chiral GC-MS using an Astec B-DM column. A 1 mM solu-
tion was injected and an initial column temperature of 70 ЊC
was maintained for 5 minutes after which time it was increased
at a rate of 5 ЊC minϪ1 for 15 min. The retention times were tR
(cis-epoxide) = 11.8 min (major) and 12.5 min (minor) and tR
(trans-epoxide) = 11.3 min and 11.4 min.
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2444
J. Chem. Soc., Perkin Trans. 1, 2001, 2440–2444