Acid-functionalized dissymmetric salen ligands and their manganese(III) complexes

Article abstract of DOI:10.1016/j.tetlet.2007.01.023

Acid-functionalized symmetric and dissymmetric salen-type ligands were synthesized via a novel self-protection step in a quantitative yield. This synthetic method allows one to quickly prepare salen-based dissymmetric chiral compounds with tailorable coor

Full text of DOI:10.1016/j.tetlet.2007.01.023

Tetrahedron Letters 48 (2007) 2591–2595
Acid-functionalized dissymmetric salen ligands
I
and their manganese(III) complexes
ꢀ
ꢀ
*
You-Moon Jeon, Jungseok Heo and Chad A. Mirkin
Department of Chemistry and the International Institute for Nanotechnology, Northwestern University,
145 Sheridan Road, Evanston, IL 60208-3113, USA
2
Received 13 November 2006; revised 18 December 2006; accepted 3 January 2007
Available online 7 January 2007
Abstract—Acid-functionalized symmetric and dissymmetric salen-type ligands were synthesized via a novel self-protection step in a
quantitative yield. This synthetic method allows one to quickly prepare salen-based dissymmetric chiral compounds with tailorable
coordinating properties. Therefore, this approach provides a blueprint for synthesizing and evaluating a new class of acid-function-
alized salen ligands that can be used as chiral building blocks for a wide range of catalysts and coordination polymers with chemi-
cally tailorable properties.
ꢀ
2007 Elsevier Ltd. All rights reserved.
Salen ligands are important components of many types
of catalysts, metal–organic-frameworks (MOFs), and
greater structural variation in the resulting catalysts
and infinite coordination polymers, allow for the sys-
tematic optimization of both the steric and electronic
properties of the ligand, and create better ways of con-
trolling polymerization in the context of the infinite
coordination polymer structures (different functionality
allows one to use different metals in the polymerization
process). Indeed, it has been reported that metal com-
plexes derived from unsymmetrical salen ligands some-
times exhibit better enantioselectivities when compared
1
–6
coordination polymers.
MOFs, in particular, have
been the focus of many recent studies due to their encap-
sulating properties and potential applications in magne-
tism, catalysis, sensing, mixture separations, molecular
electronics, and small molecule transport.7–10 MOFs
have been made from a combination of many types of
metal ions and polyfunctional ligands, and the salen
ligand has been the focus of several researchers in this
field because of its utility in catalysis. In this regard, pyr-
idine functionalized salens have been the building block
of choice, primarily because of the ease in which one can
1
1,12
with their symmetric counterparts.
Herein we report
the first general synthetic approach for the preparation
of acid-functionalized symmetric and dissymmetric salen
ligands via self-protected intermediates. Note that this
method does not need deliberate and time consuming
protection or deprotection steps for the synthesis of
the dissymmetric salen ligands as do previous stepwise
4
prepare such ligands.
Acid-functionalized salens are also outstanding targets
as building blocks for MOF structures because of the
wealth of inorganic coordination chemistry that takes
advantage of the carboxylate moiety. However, at pres-
ent, there are no methods for preparing such ligands. In
this regard, both symmetrically and dissymmetrically
functionalized ligands are desirable. The desymmetriza-
tion of the salen core would create the possibility for a
1
3,14
approaches.
These ligands can be easily metalated
with Mn(III) in the salen core to form precursors that
have the appropriate peripheral functionality for metal
coordination driven polymerization (not studied in this
manuscript).
Our strategy takes advantage of the condensation of
(
1R,2R)-(ꢀ)-1,2-diaminocyclohexane 1 with acid-func-
Keywords: Dissymmetric; Salen; Catalyst; Self-protection; Coordina-
tion; Metal–organic-framework; MOF.
q
CAM acknowledges the NSF and ARO for the support of this work.
tionalized salicylaldehyde 2A–C to form the self-pro-
tected zwitterionic intermediates 3A–C (Scheme 1).
1
5
*
Corresponding author. Tel.: +1 847 467 7302; fax: +1 847 467
123; e-mail: chadnano@northwestern.edu
Compounds 3A–C precipitate during the reaction,
allowing one to easily isolate these intermediates in near
quantitative yields. The precipitates were collected by
5
ꢀ
These authors contributed equally to this work.
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.01.023

2592
Y.-M. Jeon et al. / Tetrahedron Letters 48 (2007) 2591–2595
Scheme 1. Synthesis of self-protected zwitterionic intermediates.
Table 1. Zwitterionic intermediates and their spectroscopic and analytical characterization data
Ligand precursor
Intermediate (Yield)
Analytical data
1
H NMR (CD
3
OD/K
.40 (s, 9H, –C(CH
CH–), 2.88 (m, 1H, –CH–), 7.48 (s, 1H, Ar–H), 7.51 (s, 1H,
2
CO
3
): d 1.15–1.33 (br m, 4H, –CH
2
–),
1
–
3
)
3
), 1.46–1.88 (br m, 4H, –CH
2
–), 2.66 (m, 1H,
Ar–H), 7.54 (d, 2H, Ar–H), 7.88 (d, 2H, Ar–H), 8.55 (s, 1H,
+
–
CH@N–). MS (ESI, m/z): M = 394.05 (Calcd for C24
30 2 3
H N O =
3
94.23). Elemental Anal. Calcd for C24 CH OH: C, 71.68;
H
30
N
2
O
3
3
H, 7.86; N, 6.82. Found: C, 71.31; H, 7.60; N, 6.87
1
3 2 3 2
H NMR (CD OD/K CO ): d 1.18–1.41 (br m, 8H, –CH –), 2.99
(
m, 2H, –CH–), 6.78 (d, 1H, Ar–H), 7.96 (d, 1H, Ar–H), 8.47
+
(
s, 1H, Ar–H), 9.02 (s, 1H, –CH@N–). MS (ESI, m/z): (M+H)
=
2
63.45 (Calcd for C14
for C14 Æ1/3H
2.89; H, 6.74; N, 10.14
H
19
N
2
O
3
= 263.14). Elemental Anal. Calcd
H
18
N
2
O
3
2
O: C, 62.67; H, 7.01; N, 10.44. Found: C,
6
1
6 2
H NMR (DMSO-d ): d 1.30–1.73 (br m, 8H, –CH –), 2.93
(
(
m, 1H, –CH–), 3.06 (m, 1H, –CH–), 7.27 (s, 1H, Ar–H), 7.31
d, 1H, Ar–H), 7.36 (s, 1H, Ar–H), 8.55 (s, 1H, –CH@N–).
+
MS (ESI, m/z): (M+H) = 263.71 (Calcd for C14
H
19
N
2
O
3
=
2
18 2 3
63.14). Elemental Anal. Calcd for C14H N O : C, 64.10; H,
6
.92; N, 10.68. Found: C, 63.89; H, 6.66; N, 10.49
filtration and washed with hot methanol (ꢁ50 ꢁC),
for X-ray analysis were taken directly from the precipi-
tate. The solid-state structure is consistent with the
which in all cases gave analytically pure compounds
1
6
(
Table 1).
proposed solution structure (Fig. 1a). As shown in
Figure 1b, compound 3C is zwitterionic and one hydro-
gen atom of the amine moiety exhibits a Hꢂ ꢂ ꢂO distance
The formation of the self-protected zwitterionic inter-
mediate 3C was confirmed by a single crystal X-ray
diffraction study (Fig. 1). Single crystals of 3C suitable
˚
(1.96 A) consistent with a strong hydrogen bonding
with the carboxylate ion of an adjacent molecule
˚
(
Nꢂ ꢂ ꢂO = 2.74 A). This results in the formation of a
loosely coordinated one-dimensional helical polymer.
The other two hydrogen atoms on the amine also exhibit
Hꢂ ꢂ ꢂO distances that are consistent with hydrogen
˚
bonds with two water molecules (Nꢂ ꢂ ꢂO = 2.78 A)
avg
included in the crystal (not shown).
The desired symmetric or dissymmetric salen-type
ligand 4A–E can be obtained by reacting one of the
mono-substituted zwitterionic intermediate 3A–C with
an equivalent of a second salicylaldehyde 2A–E in
1
7
refluxing pyridine, respectively (Scheme 2). After a
few min, the turbid reaction mixture became a clear yel-
low solution. Note that pyridine in this reaction is used
both as a solvent and as a base. In all cases, the analyt-
ically pure product 4A–E was isolated in a near quanti-
tative yield by a simple evaporation of the solvent after
the reaction (Table 2). The acid-functionalized symmet-
Figure 1. X-ray crystal structure of 3C with thermal ellipsoids shown
at 70% probability (two water molecules have been omitted for clarity):
(a) asymmetric unit and (b) hydrogen-bonding scheme.

Y.-M. Jeon et al. / Tetrahedron Letters 48 (2007) 2591–2595
2593
2 2
Scheme 2. Reagents and conditions: (a) pyridine, reflux; (b) Mn(OAc) Æ4H O, pyridine or EtOH, reflux; LiCl, air, reflux.
Table 2. Acid-functionalized salen ligands and their precursors
Intermediate
Aldehyde
Product
Yield (%)
3A
94
3B
99
3
3
3
C
D
E
99
91
96

2594
Y.-M. Jeon et al. / Tetrahedron Letters 48 (2007) 2591–2595
rical salen ligand 4A can be synthesized alternatively by
the reaction of (1R,2R)-(ꢀ)-1,2-diaminocyclohexane 1
with 2 equiv of 4-(3-hydroformyl-4-hydroxy-5-t-butyl-
phenyl)benzoic acid 2A in refluxing pyridine. Finally,
the resulting salen-type ligands 4A–E with acid func-
tional groups can be metalated easily with Mn(OAc)2/
LiCl in air to form complexes 5A–E using a literature
which 3481 were unique (Rint = 0.1131). Refinement
proceeded to wR = 0.1227 (all data), R = 0.0561 and
GOF = 0.808 [I > 2r(I)]. Maximum residual electron
density was 0.234 e A . Crystallographic data (excluding
structure factors) for the structure in this paper have been
deposited with the Cambridge Crystallographic Data
Centre as the supplementary publication number CCDC-
2
1
˚
ꢀ3
6
23453. Copy of the data can be obtained, free of charge,
procedure analogous to those used to synthesize (R,R)-
on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [fax: +44(0)-1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk.
0
(
ꢀ)-1,2-cyclohexanediamine-N,N -bis(3-tert-butyl-5-(4-
III
4,18
pyridyl)salicylidene)Mn Cl (Scheme 2).
1
7. A slurry of 3A (0.31 g, 0.79 mmol) and 5-(4-pyridyl)sali-
cylaldehyde 2E (0.20 g, 0.79 mmol) in pyridine (20 mL)
was heated to reflux for 1 h, which gave a clear yellow
solution. The solvent was removed under reduced pressure
and the resulting solid was sonicated with ether (10 mL).
The solvent was evaporated and dried under vacuum to
give an analytically pure yellow solid 4E (0.48 g, 96%).
This work demonstrates that one can synthesize acid-
functionalized symmetric and dissymmetric salen-type
ligands via a novel self-protection step in a quantitative
yield. This synthetic method allows one to quickly pre-
pare salen-based dissymmetric chiral compounds with
tailorable coordinating properties. Therefore, this
approach provides a blueprint for synthesizing and eval-
uating a new class of acid-functionalized salen ligands
that can be used as chiral building blocks for a wide
range of MOFs with potentially tailorable asymmetric
catalytic activity.
Analytical data for compounds 4A–E are as follows:
1
6
Compound 4A: H NMR (DMSO-d ): d 1.34 (s, 9H,
–C(CH ) ), 1.42–1.99 (br m, 4H, –CH –), 3.46 (br s, 1H,
3
3
2
–CH–), 7.48 (s, 1H, Ar–H), 7.51 (s, 1H, Ar–H), 7.60 (d,
2H, Ar–H), 7.93 (d, 2H, Ar–H), 8.57 (s, 1H, –CH@N–),
1
2.89 (br s, 1H, –CO
2
H), 14.41 (br s, 1H, –OH). HRMS
+
(
EI, m/z) M = 673.3341 (Calcd for C H N O =
4
2
46
2
6
6
7
74.3356). Elemental Anal. Calcd for C42
H
46
N
2
O
6
: C,
4.75; H, 6.87; N, 4.15. Found: C, 74.39; H, 6.81; N, 4.15.
1
References and notes
5
Compound 4B: H NMR (pyridine-d ): d 1.55 (d, 9H,
–
C(CH ) ), 1.38–1.95 (br m, 8H, –CH –), 3.41 (br m, 2H,
3 3 2
1
. Larrow, J. R.; Jacobsen, E. N. Top. Organomet. Chem.
004, 6, 123–152.
–CH–), 7.11 (d, 1H, Ar–H), 7.54 (m, 3H, Ar–H), 7.69 (m,
1H, Ar–H), 8.30 (m, 1H, Ar–H), 8.40 (dd, 1H, Ar–H), 8.59
(s, 1H, –CH@N–), 8.60 (s, 1H, –CH@N–), 8.79 (d, 1H,
2
2
. Jacobsen, E. N. Acc. Chem. Res. 2000, 33, 421–431.
. Yoon, T. P.; Jacobsen, E. N. Science 2003, 299, 1691–
3
Ar–H), 8.82 (d, 1H, Ar–H), 14.40 (br s, 1H, –CO H),
2
1
693.
14.79 (s, 1H, –OH), 14.82 (s, 1H, –OH). MS (ESI, m/z):
ꢀ
4
. Cho, S. H.; Ma, B. Q.; Nguyen, S. T.; Hupp, J. T.;
Albrecht-Schmitt, T. E. Chem. Commun. 2006, 2563–2565.
. Gianneschi, N. C.; Bertin, P. A.; Nguyen, S. T.; Mirkin, C.
A.; Zakharov, L. N.; Rheingold, A. L. J. Am. Chem. Soc.
[MꢀH] = 498.64 (Calcd for C30
H
32
N
Æ1/4H
3
O
4
= 498.24). Ele-
O: C, 71.48; H,
mental Anal. Calcd for C30
H
33
N
O
3
4
2
5
6.70; N, 8.34. Found: C, 71.42; H, 6.54; N, 8.78.
1
Compound 4C: H NMR (pyridine-d
5
): d 1.57 (s, 9H,
2003, 125, 10508–10509.
–C(CH ), 1.37–1.88 (br m, 8H, –CH –), 3.40 (br m, 2H,
3
)
3
2
6
7
8
9
. Gianneschi, N. C.; Cho, S. H.; Nguyen, S. T.; Mirkin, C.
A. Angew. Chem., Int. Ed. 2004, 43, 5503–5507.
. Bradshaw, D.; Claridge, J. B.; Cussen, E. J.; Prior, T. J.;
Rosseinsky, M. J. Acc. Chem. Res. 2005, 38, 273–282.
. Rowsell, J. L. C.; Yaghi, O. M. Microporous Mesoporous
Mater. 2004, 73, 3–14.
–CH–), 7.41 (d, 1H, Ar–H), 7.52 (dd, 2H, Ar–H), 7.59 (d,
1H, Ar–H), 7.71 (d, 1H, Ar–H), 7.86 (d, 1H, Ar–H), 8,11
(s, 1H, Ar–H), 8.55 (s, 1H, –CH@N–), 8.59 (s, 1H,
–CH@N–), 8.78 (dd, 2H, Ar–H), 13.79 (br s, 1H, –CO
2
H),
ꢀ
14.80 (br s, 1H, –OH). MS (ESI, m/z): [MꢀH] = 498.41
(Calcd for C30
for C30
H
32
N
Æ1/4H
3
O
4
= 498.24). Elemental Anal. Calcd
. Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.;
Eddaoudi, M.; Kim, J. Nature 2003, 423, 705–714.
H
33
N
3
O
4
2
O: C, 71.48; H, 6.70; N, 8.34.
1
Found: C, 71.45; H, 6.67; N, 8.41. Compound 4D:
NMR (DMSO-d ): d 1.33 (s, 18H, –C(CH
(br m, 8H, –CH –), 3.42 (br s, 2H, –CH–), 7.36-8.04 (m,
10H, Ar–H), 8.54 (br m, 2H, –CH@N–, 2H, Ar–H), 12.99
(br s, 2H, –CO H), 14.36 (br s, 2H, –OH). HRMS (EI,
H
1
0. Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y.
J.; Kim, K. Nature 2000, 404, 982–986.
1. Kim, G. J.; Shin, J. H. Catal. Lett. 1999, 63, 83–90.
2. Renehan, M. F.; Schanz, H. J.; McGarrigle, E. M.;
Dalton, C. T.; Daly, A. M.; Gilheany, D. G. J. Mol. Catal.
A: Chem. 2005, 231, 205–220.
6
) ), 1.67–1.95
3 3
2
1
1
2
+
m/z): M = 673.3356 (Calcd for C42
H
46
N
2
O
6
= 674.3356).
Elemental Anal. Calcd for C42
H
46
N
2
O
6
: C, 74.75; H, 6.87;
1
1
1
3. Campbell, E. J.; Nguyen, S. T. Tetrahedron Lett. 2001, 42,
N, 4.15. Found: C, 74.37; H, 6.81; N, 4.56. Compound 4E:
1
1221–1225.
H NMR (DMSO-d
1.94 (br m, 8H, –CH
(br m, 8H, Ar–H), 7.94 (br d, 2H, Ar–H), 8.51 (br m, 2H,
–CH@N–, 2H, Ar–H), 12.95 (br s, 1H, –CO H), 14.38 (br
s, 1H, –OH), 14.51 (br s, 1H, –OH). HRMS (EI, m/z):
): d 1.32 (s, 18H, –C(CH
6
) ), 1.66–
3 3
4. Holbach, M.; Zheng, X. L.; Burd, C.; Jones, C. W.; Weck,
2
–), 3.35 (br m, 2H, –CH–), 7.48–7.60
M. J. Org. Chem. 2006, 71, 2903–2906.
5. A mixture of (1R,2R)-(ꢀ)-1,2-diaminocyclohexane
1
2
(
0.16 g, 1.37 mmol) and 4-(3-hydroformyl-4-hydroxy-5-t-
+
butylphenyl)benzoic acid 2A (0.40 g, 1.34 mmol) in meth-
anol (50 mL) was heated to reflux for 1 h. The resulting
precipitate was filtered and washed with hot methanol
M = 631.3414 (Calcd for C40
H
N
45
N
3
O
4
= 631.3410). Ele-
mental Anal. Calcd for C40
H
45
3
O
4
Æ1/2H O: C, 74.97; H,
2
7.24; N, 6.56. Found: C, 74.82; H, 7.00; N, 6.516.
18. The free base ligand 4E (0.20 g, 0.31 mmol) and
Mn(OAc) Æ4H O (0.086 g, 0.35 mmol) were combined
with absolute EtOH (50 mL) and heated to reflux for 2 h
under N atmosphere. LiCl (0.041 g, 0.97 mmol) was then
(
ꢁ50 ꢁC, 3 · 10 mL) and dried under vacuum to give a
pale yellow solid 3A (0.51 g, 95%).
2
2
1
22 2 5
6. Selected X-ray crystallographic data of 3C: C14H N O ,
˚
monoclinic,
space
group
C2,
a = 21.208(5) A,
2
˚
˚
b = 5.9408(13) A, c = 12.526(3) A, b = 105.933(4)ꢁ, V =
added and the resulting solution was refluxed for an
additional hour in air before being cooled to room
temperature. The solvent was removed under reduced
˚
3
1
517.5(6) A , Z = 4.
A colorless plate type crystal
was used to measure 6922 reflections at T = 153 K, of

Y.-M. Jeon et al. / Tetrahedron Letters 48 (2007) 2591–2595
2595
ꢀ
1
pressure, after which the precipitate was sonicated with
water (20 mL). Product 5E was isolated by filtration and
dried under vacuum (0.21 g, 93%). Analytical data for
compounds 5A–E are as follows: Compound 5A: IR (KBr
(KBr pellet, cm ): 573 (w), 635 (w), 820 (w), 1272 (m),
1315 (w), 1344 (m), 1386 (s), 1423 (w), 1436 (w), 1553 (s),
+
1596 (vs), 2944 (w). MS (ESI, m/z): [MꢀCl] = 552.83
3 4
(Calcd for C30H31MnN O = 552.52). Elemental Anal.
ꢀ1
pellet, cm ): 575 (w), 757 (w), 780 (w), 1174 (w), 1255 (m),
3 4
Calcd for C30H31MnN O Cl: C, 65.21; H, 5.66; N, 7.61.
1
2
C
C
313 (m), 1342 (m), 1384 (m), 1537 (m), 1603 (s), 1693 (w),
Found: C, 65.53; H, 5.88; N, 7.72. Compound 5D: IR
(KBr pellet, cm ): 576 (w), 637 (w), 771 (w), 1269 (m),
+
ꢀ1
951 (w). MS (ESI, m/z): [MꢀCl] = 727.99 (Calcd for
42
42
H
44MnN
2
O
6
= 727.26). Elemental Anal. Calcd for
1341 (m), 1310 (m), 1341 (m), 1390 (m), 1538 (m), 1611 (s),
ꢀ
H44ClMnN
2
O
6
: C, 66.10; H, 5.81; N, 3.67. Found: C,
1700 (w), 2949 (w). MS (ESI, m/z): [MꢀClꢀH] = 726.07
6
6.41; H, 5.92; N, 3.77. Compound 5B: IR (KBr pellet,
(Calcd for C H MnN O = 726.25). Elemental Anal.
4
2
43
2
6
ꢀ1
cm ): 573 (w), 637 (w), 656 (w), 818(w), 1175 (w), 1274
Calcd for C42
Found: C, 66.45; H, 6.08; N, 3.66. Compound 5E: MS
(ESI, m/z) = 719.37 (Calcd for C40 43ClMnN = 719.23).
Elemental Anal. Calcd for C H ClMnN O ÆH O:
2 6
H44ClMnN O : C, 66.10: H, 5.81: N, 3.67.
(
(
s), 1308 (s), 1343 (m), 1382 (m), 1437 (w), 1553 (m), 1598
vs), 1944 (w). MS (ESI, m/z): [MꢀCl] = 552.76 (Calcd
+
H
3 4
O
for C H MnN O = 552.52). Elemental Anal. Calcd for
30
31
3
4
40 43
3
4
2
C
30
H31ClMnN
3
O
4
ClÆ1/4H
2
O: C, 61.28; H, 5.31; N, 7.15.
C, 65.08; H, 6.14; N, 5.69. Found: C, 65.26; H, 6.50; N,
Found: C, 60.85; H, 5.31; N, 7.04. Compound 5C: IR
5.73.