Proton-template synthesis, structure, and characterization of a Robson- type macrocycle with a totally π-conjugated system

Article abstract of DOI:10.1021/jo9809736

π-Conjugated (1-4) and partially reduced (5) macrocyclic Schiff bases have been obtained by proton-template condensation of 2,6-diformyl-4-R₁- phenol (R₁ = Me, t-Bu) with 1,2-diamino-4,5-R₂-benzene (R₂ = H, Me).

Full text of DOI:10.1021/jo9809736

1442
J . Org. Chem. 1999, 64, 1442-1446
P r oton -Tem p la te Syn th esis, Str u ctu r e, a n d Ch a r a cter iza tion of a
Robson -Typ e Ma cr ocycle w ith a Tota lly π-Con ju ga ted System
Yunqi Tian,*,† J ian Tong,† Gerlinde Frenzen,‡ and J in-Yu Sun†
Department of Chemistry, Liaoning University, 110036 Shenyang, P. R. China, and
Fachbereich Biologie und Chemie der Universitaet GesamthochschulesKassel,
Heinrich-Plett-Strasse 40, D-34132 Kassel, Germany
Received May 21, 1998
π-Conjugated (1-4) and partially reduced (5) macrocyclic Schiff bases have been obtained by proton-
template condensation of 2,6-diformyl-4-R1-phenol (R1 ) Me, t-Bu) with 1,2-diamino-4,5-R2-benzene
1
(R2 ) H, Me). The macrocyclic ligands have been characterized by elemental analysis, by IR, H
NMR, and 13C NMR spectroscopy, and by electron impact mass spectrometry. Also, the X-ray crystal
structures of 1 and 2 were solved. The crystals were all grown from formic acid. Crystal 1 is triclinic,
space group P-1 with a ) 867.1(5), b ) 916.3(4), and c ) 1087.2(3) pm and R ) 69.62(2), â )
87.57(3), and γ ) 63.72(4)° for Z ) 1. Crystal 2 is monoclinic, space group P21/n with a ) 632.0(1),
b ) 1661.5(3), and c ) 1658.0(3) and â ) 99.87(3)° for Z ) 2. Both of the molecules are planar with
centers of symmetry. They are protonated twice while being neutralized by two negatively charged
perchlorate ions.
In tr od u ction
restricted mainly to those metal ions that can be em-
ployed as the template reagents, although sometimes
such complexes can also be obtained by metal-metal
exchange.24
Binuclear macrocyclic complexes of the Robson type are
of interest as models of biomolecules. Since the1970s they
have been prepared and widely studied.1-23 Because of
the methodology of the template route, the complexes are
Recently we reported the proton-template synthesis of
a metal-free macrocyclic ligand 1 composed of a totally
π-conjugated system, and from this ligand the binuclear
Ni(II)- and Cu(II)-complexes were successfully pro-
duced.25 It was earlier shown by Brychcy et al. that only
the binuclear Cu(II)-complex of 2 can be synthesized by
the metal template route. When other metals are em-
ployed as the template ions, they lead only to the
mononuclear complexes and in some cases the partially
reduced metal-free macrocycle is produced.26-28 If rare
earth metals are employed as template ions, the mono-
nuclear sandwich-like complexes result.29 From the metal-
free ligands, some other binuclear complexes, for ex-
ample, the mixed valence Co(II)-Co(III)-complexes30 can
be obtained. Because of the π-conjugated system of these
ligands, their complexes have shown extraordinary be-
haviors comparable to those of other Robson-type mac-
rocycles. In this paper, we report a serial synthesis of
the π-conjugated macrocycles 1-4 as well as partially
reduced macrocycle 5, and their characterization by IR,
UV, and NMR spectroscopic and X-ray crystal structure
analysis.
* To whom correspondence should be addressed. email: ytian@
lnu.edu.cn.
† Liaoning University.
‡ Universitaet Gesamthochschule-Kassel.
(1) Pilkington, N. H.; Robson, R. Aust J . Chem. 1970, 23, 2225.
(2) Okawa, H.; Kida, S. Inorg. Nucl. Chem. Lett. 1971, 7, 751; Bull
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Chem. Soc. 1979, 101, 4571.
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(10) Gagne, R. R.; Henling, L. M.; Kistenmacher, T. J . Inorg. Chem.
1980, 19, 1226-1231.
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W. R.; Shiemke, A. K. J . Am. Chem. Soc. 1981, 103, 4073.
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R. R.; Hendrickson, D. N. Inorg. Chem. 1981, 20, 1229.
(13) Long, R. C.; Hindrickson, D. N. J . Am. Chem. Soc. 1983, 105,
1513.
(14) Mandal, S. K.; Nag, K. J . Chem. Soc., Dalton Trans. 1983, 2429.
(15) Mandal, S. K.; Nag, K. J . Chem. Soc., Dalton Trans. 1984, 2141.
(16) Mandal, S. K.; Adhikary, B.; Nag, K. J . Chem. Soc., Dalton
Trans. 1986, 1175.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of th e Ma cr o-
cycles. The preparation of 1 was first attempted by the
(17) Mandal, S. K.; Thompson, L. K.; Nag, K.; Charland, J .-P.; Gabe,
E. J . Inorg. Chem. 1987, 26, 1391-1395.
(18) Mandal, S. K.; Thompson, L. K.; Nag, K.; Charland, J .-P.; Gabe,
E. J . Can. J . Chem. 1987, 65, 2815-2823.
(24) Dutta, S. K.; Ensling, J .; Werner, R.; Floeke, U.; Haase, W.;
Guetlich, P.; Nag, K. Angew. Chem. 1997, 109(1/2), 107-109.
(25) Tian, Y.-Q.; Tong, J . Chin. Chem. Lett. 1997, 8(2), 107-110.
(26) Brychcy, K.; Draeger, K.; J ens, K.-J .; Tilset, M.; Behrens, U.
Chem. Ber. 1994, 127, 465-476.
(19) Lacroix, P.; Kahn, O.; Theobald, F.; Leory, J .; Wakselman, C.
Inorg. Chim. Acta 1988, 142, 129-134.
(20) Mandal, S. K.; Thompson, L. K.; Newlands, M. J .; Gabe, E. J .
Inorg. Chem. 1989, 28, 3707-3713.
(21) Mandal, S. K.; Thompson, L. K.; Newlands, M. J .; Biswas, A.
K.; Adhiksry, B.; Nag, K.; Gabe, E. J .; Lee, F. L. Can. J . Chem. 1989,
67, 662-670.
(27) Brychcy, K.; J ens, K.-J .; Tilset, M.; Behrens, U. Chem. Ber.
1994, 127, 991-995.
(28) Brychcy, K.; Draeger, K.; J ens, K.-J .; Tilset, M.; Behrens, U.
Chem. Ber. 1994, 127, 1817-1826.
(22) Mandal, S. K.; Thompson, L. K.; Newlands, M. J .; Gabe, E. J .;
Nag, K. Inorg. Chem. 1990, 29, 1324-1327.
(29) Suresh-Kumar, D.; Alexander, V.; et al. Inorg. Chim. Acta. 1995,
63, 238
(23) Tandon, S. S.; Thompson, L. K.; Bridson, J . N.; McKee, V.;
Downard, A. J . Inorg. Chem. 1992, 31, 4635-4642.
(30) Tian, Y.; et al., unpublished results.
10.1021/jo9809736 CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/05/1999

Robson-Type Macrocycle with a π-Conjugated System
J . Org. Chem., Vol. 64, No. 5, 1999 1443
Sch em e 1
Schiff base condensation of 2,6-diformylphenol and o-
phenylenediamine at room temperature, but this led to
an oligomer, the terminal groups of which were identified
from IR spectra (νC)O1680 cm-1 and νNH 3420 cm-1). If a
drop of concentrated hydrochloric acid was used as
catalyst, the macrocycle 5 was produced, which had been
prepared in another way by Vigato et al.30 When twice
the amount of o-phenylenediamine was employed, the
product was the same as before rather than the [1 +2]
product 6. It is clear that the phenylenediamine functions
not only as a component of 5 but also as the reducing
reagent. It seems that the driving force for the construc-
tion of the macrocycle lies in the formation of hydrogen
bonds. If a small number of protons are provided, the
macrocycle most likely to result is the partially reduced
product 2, which positions the amino H to form a
hydrogen bond with the phenolic oxygen. In the mean-
time, the phenylenediamine can act as a reducing reagent
for the imido groups of the macrocycle. However such
reductions to our knowledge have never been reported.
Only when an equivalent amount of protons is provided
and the mixed solvent of ethanol and methanol is
employed is the totally π-conjugated macrocycle 1 formed
as its dihydrochloride. In this case the phenylenediamine
does not serve a reducing function. In this way, the
macrocycles 2-4 were produced.
to use o-phenylenediamine dihydrochloride and keep the
reaction system isolated from air.
Another important aspect of this macrocycle prepara-
tion is that the reaction must be carried out at room
temperature or lower, since the thermodynamics of
higher temperature do not permit the formation of the
hydrogen bonds that drive the reactant molecules to
assemble into the macrocycle.
The electron impact (EI) mass spectra of the macro-
cycles show peaks resulting from both molecular ions and
fragmentation products consistent with the structures
proposed in Scheme 1. The strong IR absorptions of the
CdN groups appear at about 1620 cm-1, and absorptions
for CdO and NH are absent. Since we found no suitable
solvent for recrystallization, adequate microanalyses for
the products H2L‚2HCl were not obtainable. Suitable
microanalytical results were obtained for 1-3 as H2L‚
2HClO4, which recrystallize from warm formic acid
(99-100%).
In the UV/vis spectra of H2L‚2HClO4, absorption bands
appear at about 300, 380, and 530 nm, which are
assigned to π-π* transitions (Table 1). Because of the
four methyl groups on the macrocyclic ring of 3 and 4,
all of the absorption bands are red-shifted about 5-15
nm.
Of the products 1-3, which are suitable for combustion
analysis, only 2 was characterized by NMR spectroscopy,
as permitted by its reasonable solubility in DMSO. Due
to the symmetry of the macrocycle, 1H NMR spectroscopy
reveals three singlets corresponding to the 18 methyl
Our results show that the concentrated hydrochloric
acid is a suitable proton source that brings relatively few
molecules water into the reaction system and has no
oxidative function. Therefore it is alternatively feasible

1444 J . Org. Chem., Vol. 64, No. 5, 1999
Tian et al.
F igu r e 1. Crystal structure of the macrocyclic ligands.
Ta ble 1. IR a n d UV Ba n d s of th e Ma cr ocyclic
Com p ou n d s
Ta ble 2. Selected Bon d Len gth s [p m ] a n d An gles [d eg]
compound 1
compound 2
IR (cm-1
)
UV- vis (nm)
λmax (log)
N(2)-C(2)
128.2(4)
142.2(4)
128.1(4)
142.5(4)
142.6(5)
144.1(4)
139.5(4)
140.8(4)
140.1(5)
132.8(4)
128.0(3)
121.1(3)
125.8(3)
123.5(3)
117.8(3)
118.5(3)
122.3(3)
121.6(3)
120.8(3)
119.1(3)
N(1)-C(1)
128.7(3)
145.1(3)
129.3(3)
142.9(3)
140.7(3)
134.3(2)
142.2(3)
142.0(3)
140.3(3)
140.5(3)
122.79(19)
125.1(2)
119.07(19)
123.01(19)
121.75(19)
117.43(19)
126.48(19)
119.53(18)
121.75(19)
117.37(18)
νCdN
νphenyl
π f π*
N(2)-C(21)
N(1)-C(11)
1
2
3
4
1631
1635
1635
1635
1618, 1525
1616, 1537
1603, 1538
1605, 1516
285 (4.6)
290 (4.7)
305 (5.0)
305 (4.7)
370 (4.4), 530 (4.1)
375 (4.6), 530 (4.3)
390 (4.6), 535 (4.6)
390 (4.6), 540 (4.4)
N(1)-C(1)
N(2)-C(2)
N(1)-C(26)
C(2)-C(12)a
C(2)-C(12)
C(11)-C(12)a
O(1)-C(11)
C(1)-C(16)a
C(21)-C(26)
C(11)-C(12)
C(11)-C(16)
C(11)-O(1)
N(1)-C(21)
N(2)-C(26)
protons (δ 1.33) and signals for the four aromatic protons
of the 4-tert-butylphenol rings (δ 7.91) and for the four
protons of the imido groups (δ 9.19), respectively, as well
as a pair of four aromatic-proton multiplets (δ 7.40 and
7.79). However, the 13C NMR spectra display only 8
carbon signals for the 10 different carbons, which may
result from the relatively low concentration of the sample.
The two missing carbon signals belong to Cqu and to CH.
Str u ctu r e of th e Ma cr ocyclic Liga n d s. Of the
compounds 1-4, only the perchlorates of 1 and 2 can be
prepared as suitable single crystals for X-ray structural
analysis. They are obtained by recrystallization from
warm formic acid. Both crystallize in the centrosymmet-
ric space group with the center of symmetry in the
macrocycle. As indicated by the carbon-nitrogen bond
parameters of the two compounds (Table 2), the mol-
ecules are totally π-conjugated, in that all of the nitrogen
and carbon atoms (except those of the methyl and tert-
butyl groups) exhibit typical sp2 hybridization, and the
imido CdN bond lengths are also typical. Therefore both
of the molecules can be regarded as planar, although 2
shows a small deviation from the plane.
C(11)-C(16)
C(21)-C(26)
N(1)C(1)C(16)
N(2)C(2)C(12)a
O(1)C(11)C(12)
C(11)C(12)C(2)a
C(11)C(16)C(1)
C(21)C(26)N(2)
C(2)N(2)C(26)
C(1)N(1)C(21)
O(1)C(11)C(16)
C(26)C(21)N(1)
C(2)N(2)C(21)
C(1)N(1)C(26)
N(2)C(2)C(12)
N(1)C(1)(C16)a
N(2)C(21)C(26)
C(21)C(26)N(1)
C(11)C(12)C(2)
C(11)C(16)C(1)a
O(1)C(11)C(16)
O(1)C(11)C(12)
a
Symmetry transformations used to generate equivalent at-
oms: -X + 1, -Y, -Z.
C(21)-C(26) but forms a dihedral angle of 15.9° with the
phenyl ring C(11)-C(16) and the phenolic oxygen atoms
depart from the N4 plane about (41 pm. If half of the
diagonal length of the tetragon N2O2 is taken to be radius
of the binucleating cavity, the average value is 184 pm
for 1 and 196 pm for 2. Between the six donor atoms of
N4O2, the two phenolic hydrogens and two guest protons
act as template ions linking the coordinate atoms with
hydrogen bonds. Of these the bonds O_H---N and H_O---H
make the greatest contributions to the stabilization of
the macrocycles: they measure 186.3 and 196.7 pm for
1 and 190.3 and 201.9 pm for 2, respectively. This
Molecule 1 has a N4O2 plane which is coplanar with
the phenyl ring C(21)-C(26) but has a 2.97° dihedral
angle with the phenyl ring C(11)-C(16). The molecule 2
has a N4 plane that is coplanar with the phenyl ring

Robson-Type Macrocycle with a π-Conjugated System
J . Org. Chem., Vol. 64, No. 5, 1999 1445
Ta ble 3. Su m m a r y of Cr ysta l Da ta In ten sity Collection
a n d Str u ctu r e Refin em en t P a r a m eter s
with water and the product was isolated by steam distillation
(yield 6.5%).
Syn th esis of H2L‚2HCl. The o-phenylenediamine (2 mmol)
was dissolved in 4 mL of absolute methanol. To the solution
was added 0.2 mL of concentrated hydrochloric acid and under
stirring an ethanol solution (50 mL) of 2,6-diformyl-4-alkyl-
phenol (2 mmol) was slowly dropwise added. The reaction
mixture was then stirred at room temperature for 6 h. The
formed red microcrystals or powder products were filtrated,
washed with ethanol and ether, and dried in a vacuum (yield
ca. 70%). Mass, m/z (%): 1, 472 (82) [M+], 455 (19) [M+ - OH];
2, 556 (80) [M+], 541(30) [M+ - CH3]; 3, 612 (100) [M+], 597
(70) [M+ - CH3]; 4, 528 (100) [M+].
Syn th esis of 5. o-Phenylenediamine (2 mmol) was dissolved
in 30 mL of absolute ether. To the solution was added a drop
of concentrated hydrochloric acid, and then an ethanol solution
of 2,6-diformyl-4-methylphenol (2 mmol in 50 mL of absolute
ethanol) was slowly added. The formed product was separated
as orange microcrystals by filtration, washed with ether, and
dried in a vacuum (yield ca. 60%). Mass [m/z (%)]: 476 (50)
[M+], 459 (5) [M+ - OH]. Anal. Calcd for C30H28N4O2: C 75.61,
H 5.92, N 11.76. Found: C 75.00, H 6.19, N 11.47.
P r ep a r a tion of H2L‚2HClO4. H2L‚2HCl (1 mmol) was
dissolved in 120 mL of formic acid (99-100%), and to the
solution was added Mn(CIO4)2‚4H2O. After ca. 1 min of
stirring, the microcrystals of H2L‚2ClO4were precipited. The
mixture was heated in a water bath to a transparent solution
and then slowly cooled to room temperature. The formed red
crystals were collected by filtration and washed with ether,
yield (30-40%).
1
2
formula
Mr
T (K)
crystal system
space group
λ (pm)
a (pm)
b (pm)
c (pm)
C
30H26Cl2N4O10
C36H38Cl2N4O10
757.60
133(2)
monoclinic
P21/n
71.073
632.0(1)
1661.5(3)
1658.0(3)
90
673.45
193(2)
triclinic
P-1
71.073
867.1(5)
916.3(4)
1087.2(3)
69.62(2)
87.57(3)
63.72(4)
0.7196(6)
1
R (deg)
â (deg)
99.87(3)
90
1.7152(5)
2
γ (deg)
V (nm3)
Z
De (Mg/m3)
µ (Mo KR, mm-1
2θ (deg)
F(000)
1.554
0.295
1.467
0.256
)
4.04-43.98
4.90-55.18
348
2101
1756
0.0424
0.2145
792
25705
3967
0.053
measd refln
unique refln
a
final R1
wR2
b
0.1085
R1 ) ∑(Fo - Fc)/∑Fo. wR2 ) [∑w(Fo - Fc2)2/∑wFo
] .
a
b
2
4 1/2
Ta ble 4. Releva n t Hyd r ogen Bon d s P a r a m eter s [Bon d
(p p m ), An gle (d eg)]
compound 1
compound 2
1‚2HCIO4. Anal. Calcd for C30H26N4O10Cl2: C 53.50, H 3.86,
N 8.32. Found: C 53.29, H 4.11, N 8.58. 2‚2HClO4. Anal. Calcd
for C36H38N4O10Cl2: C 57.07, H 5.02, N 7.40. Found: C 57.25,
H 4.98, N 7.39. 1H NMR (400.04 MHz, DMSO-d6, 297 K) δ:
1.33 (s,18H), 7.40 (m,4H), 7.79 (m,4H), 7.91 (s,4H), 9.19 (s,-
4H). 13C NMR (100.50 MHz, DMSO-d, 298 K) δ: 30.8 (CH3),
33.7 (Cqu), 117.3 (CH), 119.2 (Cqu), 128.8 (CH), 135.3 (Cqu),
138.9 (Cqu), 160.0 (CH). 3‚2HCIO4. Anal. Calcd for C40H46N4O10-
Cl2: C 59.05, H 3.66, N 6.89. Found: C 59.26, H 3.54, N 6.90.
Cr ysta l Str u ctu r e An a lysis. The crystal data intensity
collection and structure refinement parameters are given in
Table 3 for compounds 1 and 2.
N(1)‚‚‚H(1)
186.3
84.0
88.0
196.7
233.9
148.42
132.91
N(1)‚‚‚H(1)
1.903
84.3
O(1)-H(1)
O(1)-H(1)
N(2)‚‚‚H(2)
O(1b)‚‚‚H(2)
N(1)‚‚‚H(2)
N(1)H(1)O(1)
N(2)H(2)O(1b)
N(2)‚‚‚H(2)
O(1a)‚‚‚H(2)
N(1)‚‚‚H(2)
N(1)H(1)O(1)
N(2)H(2)O(1a)
86.2
201.9
230.5
147.19
131.20
explains why 2 in a proton-accepting solvent is more
unstable than 1. The relevant hydrogen bond parameters
are shown in Table 4.
The data intensity collection for 1 was carried out on a four-
circle diffractometer (Enraf-Nonius CAD4) by using graphite-
monochromated Mo KR radiation at 80 °C, ω-scan mode. A
semiempirical absorption correction (ψ-scan) was carried out
leading to a transmission in the region of 0.99 and 0.94. The
structure was solved by direct methods31 and subjected to full
matrix least-squares refinement based on F2 values,32 with
anisotropic displacement factors for all heavier atoms (data/
parameter: 2/1). The hydrogen atoms were included at ideal-
ized positions with fixed temperature factors using a Riding
model.33 Final reliability factors: R1 ) 0.042 for 1388 reflec-
tions with I > 2σ(I), wR2 ) 0.125(w ) 1/[σ2(Fo)2 + (0.0738P)2
Con clu sion
The fully π-conjugated metal-free macrocycles derived
from o-phenylendiamine and 2,6-diformyl-4-alkylphenol
can be prepared by the proton template method. (i) If a
stoichiometric amount of protons is supplied, the desired
macrocycle is produced. (ii) If the protons are provided
in a trace amount as a catalyst, the product is obtained
in the partially reduced form. (iii) In generating the fully
π-conjugated macrocycles, the formation of hydrogen
bonds between the donor atoms plays an important role.
Therefore stabilization of the hydrogen bonds must be
considered in choosing feasible conditions. (iv) The fully
π-conjugated macrocyclic compounds are structurally
planar and centrosymmetric molecules with two nucleat-
ing cavities of ca. 1.90 pm radius.
2
+ 0.4487P], with P ) [Fo + 2Fc2]/3) for all data.
The intensities of the crystal for 2 were collected on a Stoe-
Siemens-Huber four-circle diffractometer with Siemens CCD
area detector by using æ-scans on a shock cooled crystal in an
oil drop.34 Data integration was performed with the program
SAINT. A semiempirical absorption correction was applied.
The structure was solved by direct methods (SHELXS-97).35
Refinement of F2 was accomplished by the least-squares
methods (SHELXL-97).36 All non-hydrogen atoms were refined
Exp er im en ta l Section
(31) Sheldrick, G. M. SHELXS-86, Program for Structure Solution,
University of Goettingen, 1990.
(32) Sheldrick, G. M. SHELXL-93, Program for Graphic Refinement
of Crystal Structure from Diffraction Data, University of Goettingen,
1993.
(33) ZORTEP, Program for Graphic Representation of Crystal
Structures Zsolnay, University of Heidelberg, 1993.
(34) Kottke, T.; Stalke, D. J . Appl. Crystallogr. 1993, 26, 615.
(35) Sheldrick, G. M. SHELXS-97, Progam for Structure Solution,
Acta Crystallography 1990, A46, 467.
(36) Sheldrick, G. M. SHELXL-97, Program for Structure Refine-
ment, University of Goettingen, 1997.
Ma ter ia ls. All reagents and solvents were purchased from
commercial sources and used without further purification
unless otherwise described.
2,6-Difor m yl-4-m eth ylp h en ol was prepared according to
literature procedures.2 For the preparation of 2,6-diformyl-4-
tert-butyl-phenol, the method was modified as follows: 4-tert-
Butylphenol (20 g) and hexamethylenetetraamine (40 g) were
mixed in a mortar. The pulverized mixture was added to
polyphosphoric acid (300 g) at 110 °C under vigorous stirring.
After 10 min reaction the mixture was cooled and hydrolyzed

1446 J . Org. Chem., Vol. 64, No. 5, 1999
Tian et al.
anisotropically. For the hydrogen atoms the Riding model was
used. The hydrogen atoms bonded to oxygen and nitrogen were
refined free.
Crystallographic data (excluding structure factors) for the
structures of 1 and 2 reported in this paper have been
deposited with the Cambridge Crystallographic Data Center.
Sa fety Note. Perchlorate salts of organic compounds are
potentially explosive. In our preparations, only very small
amounts of samples have been handled and our procedures
proved to be safe as described. Nevertheless, protective
measures must be used.
J O9809736