Mono- and dizinc complexes of diporphyrins with flexible spacers of variable length

Article abstract of DOI:10.1016/j.poly.2003.09.021

The di- and mono-zinc(II) complexes of diporphyrins (D) were synthesized, in which two porphyrin halves were covalently linked through a variable length hydrocarbon spacer (-CH₂)_n-, where n=2-4, D2-D4, respectively) attached via the ortho oxygen atom of the meso-phenyl ring. Three p-tolyl substituents were attached to other meso positions of both porphyrins. The zinc(II) complexes were studied by 1-D and 2-D COSY and NOESY ¹H NMR spectroscopy. The stability constants of dizincdiporphyrins with azaaromatic ligands: pyridine (py), pyrazine (pyr), and 4,4′-bipyridyl (bipy) were determined by spectrophotometric titration. The discriminating factor for stability of dinuclear complexes with diazaaromatic ligands was the length of the diporphyrin spacer. The formation constant for ZnTTP with pyr and bipy were very close to that for py, whereas they were about 1.3 orders of magnitude larger for D2Zn₂-pyr, D3Zn₂-bipy, and D4Zn ₂-bipy complexes which was attributed to the formation of nitrogen base bridged species. The monozincdiporphyrin complexes were demonstrated to be a convenient starting material for synthesis of heterodimetallodiporphyrins. The Zn(II)/Cu(II)diporphyrin complex was synthesized and characterized by EPR spectroscopy.

Full text of DOI:10.1016/j.poly.2003.09.021

Polyhedron 23 (2004) 33–39
www.elsevier.com/locate/poly
Mono- and dizinc complexes of diporphyrins
with flexible spacers of variable length
*
Joanna Borowiec, Irena Trojnar, Stanisław Wołowiec
Faculty of Chemistry, Rzeszoꢀw University of Technology, 6 Powstanꢀcoꢀw Warszawy Ave., Rzeszoꢀw 35-959, Poland
Received 3 July 2003; accepted 1 September 2003
Abstract
The di- and mono-zinc(II) complexes of diporphyrins (D) were synthesized, in which two porphyrin halves were covalently linked
through a variable length hydrocarbon spacer (–CH2)n–, where n ¼ 2–4, D2–D4, respectively) attached via the ortho oxygen atom of
the meso-phenyl ring. Three p-tolyl substituents were attached to other meso positions of both porphyrins. The zinc(II) complexes
were studied by 1-D and 2-D COSY and NOESY 1H NMR spectroscopy. The stability constants of dizincdiporphyrins with
azaaromatic ligands: pyridine (py), pyrazine (pyr), and 4,40-bipyridyl (bipy) were determined by spectrophotometric titration. The
discriminating factor for stability of dinuclear complexes with diazaaromatic ligands was the length of the diporphyrin spacer. The
formation constant for ZnTTP with pyr and bipy were very close to that for py, whereas they were about 1.3 orders of magnitude
larger for D2Zn2-pyr, D3Zn2-bipy, and D4Zn2-bipy complexes which was attributed to the formation of nitrogen base bridged
species. The monozincdiporphyrin complexes were demonstrated to be a convenient starting material for synthesis of heterodi-
metallodiporphyrins. The Zn(II)/Cu(II)diporphyrin complex was synthesized and characterized by EPR spectroscopy.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Diporphyrins; Zinc(II) complexes; Nitrogen base ligation; Stability constants
1. Introduction
In this paper, we have described the synthetic route for
obtaining the di- and monozinc complexes of the di-
porphyrins with flexible spacers. Two porphyrin halves
are linked via meso positions at which phenyl substitu-
ents are connected by variable length hydrocarbons at-
tached to the ortho oxygen. The monozincdiporphyrins
are useful starting materials for synthesis of heterodi-
metallodiporphyrins, which was exemplified by the
mixed-metal Zn(II)/Cu(II)diporphyrin complex, charac-
terized by EPR spectroscopy.
Diporphyrins are suitable ligands that are able to
coordinate two metal ions. This feature renders them
good candidates for synthesis of dinuclear complexes,
which can be applied as bifunctional catalysts, especially
in the case when two different catalytic metal ions are
incorporated. The diporphyrins linked with rigid spacers
attached to meso positions were studied in detail [1–7].
The most explored were those with ortho-, meta- or para-
phenylene [1,2] and pillard diporphyrins, in which
biphenylene, anthracene, xanthene and 1,10-phenan-
throline were attached to meso positions of the porphyrin
subunits [3–7]. Some heterodimetallodiporphyrins con-
taining for example Mn(III)/Cu(II) and Al(III)/Co(II)
metal ion pairs were characterized structurally [3,7].
Synthesis of heterodimetallodiporphyrins requires the
insertion of the metal ion under stoichiometric control.
2. Experimental
2.1. Syntheses
2.1.1. General syntheses
The 5-(ortho-hydroxyphenyl)-10,15,20-tris(p-tolyl)-
porphyrin (H2TTP-o-OH) and diporphyrins with
variable-length hydrocarbon spacers S attached to the
peripheral oxygen of two porphyrin macrocycles:
* Corresponding author. Tel.: +17-865-1657; fax: +17-854-3655.
E-mail address: sw@prz.rzeszow.pl (S. Wołowiec).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.09.021

34
J. Borowiec et al. / Polyhedron 23 (2004) 33–39
(H2TTP-o-OCH2)2(CH2)n: D2H4 (n ¼ 0, S ¼ 2), D3H4
(n ¼ 1, S ¼ 3) and D4H4 (n ¼ 2, S ¼ 4) were synthesized
as described previously [8–12]. The 5,10,15,20-tetra(p-
tolyl)porphyrin (TTPH2) was obtained as a side-product
and its zinc(II) complex (TTPZn) was used for com-
parative purposes.
experiments. The numbering scheme of the ligands is
presented in Fig. 1.
2.1.3. Synthesis of D2ZnCu
To the solution of D2ZnH2 (35 mg, 2.4 ꢀ 10ꢁ2 mmol)
in chloroform (50 cm3) containing 1 g K2CO3 under
reflux, 1.8-fold molar excess of CuCl2 was added drop-
wise as a 0.058 M methanolic solution. The color of the
mixture changed from pink-purple to orange-red. The
products of reaction were separated chromatographi-
cally on silicagel. The first compound eluted with 35%
CH2Cl2/hexane (v/v) was D2Cu2 (15 mg, 1.0 ꢀ 10ꢁ2
mmol, 42%), identified by comparison with an authentic
sample of the complex obtained in a separate synthesis,
while D2ZnCu was eluted with CH2Cl2 (yield 18 mg,
1.2 ꢀ 10ꢁ2 mmol, 50%).
2.1.2. Mono- and bis-zinc(II)diporphyrin complexes
(DSH2Zn, DSZn2, S ¼ 2, 3 and 4)
The insertion of the zinc(II) ion into diporhyrins
DSH4 was performed on the 30–75 lmol scale (50–100
mg of diporphyrins were used) by stepwise addition of
ca. 0.1 M zinc(II) chloride in methanol into a refluxing
solution of DSH4 in chloroform containing potassium
carbonate (about 1 g). The progress of reaction was
monitored by TLC on silicagel using 65/35 v/v% di-
chloromethane/hexane eluent The chromatographic
mobility decreased in order: DSH4 > DSZnH2 > DSZn2
in every case. The insertion procedure was continued
until the near disappearance of starting DSH4 was
noticed. Separation of DSZnH2 and DSZn2 was
achieved by column chromatography on silicagel using
dichloromethane/hexane eluent; traces of DSH4 were
eluted with 30% CH2Cl2, while fractions eluted with
35% and 45% CH2Cl2 contained almost pure of
DSZnH2 and DSZn2, respectively. The second fractions
were re-chromatographed using the same conditions in
order to obtain high-purity DSZnH2. Total yields of the
products of insertion were close to 100% (45% and 50%
for DSZnH2 and DSZn2, respectively). The free ligands
DSH4 were recoverable by the demetallation proce-
dure based on the extraction of a chloroform solution
of DSZnH2 and/or DSZn2 with 2 M HCl 1:1 H2O:
CH3OH within 1 h with about 20% loss of diporhyrin,
which in those conditions gave starting o-HOTTPH2
and other products, which were easy to separate from
DSH4 due to their chromatographic immobility under
standard conditions. The complexes have been identi-
D2ZnCu was demetallated by stirring of a chloroform
solution (20 cm3) of the complex with 2 M HCl H2O/
CH3OH (20 cm3) for 2 h, followed by chromatographic
separation of D2H4, which was identified easily by its 1H
NMR spectrum.
2.2. Analytical data
2.2.1. D4H4
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
)2.85 (4H, s, NH), )0.23 (4H, t, CH2(2)), 2.56 (4H, t,
CH2(1)), 2.65 (12H, s, 2x(p-CH3(1))), 2.68 (6H, s, CH3
(p-CH3(2))), 6.02 (2H, d, m6-H, J(m6-p) ¼ 7.4 Hz), 6.84
(2H, ddd, p-H, J(p-m5) ¼ 8.0 Hz, J(p-o5) ¼ 1.9 Hz), 6.97
(2H, dd, m5-H, J(m5-o5) ¼ 7.5 Hz), 7.40–7.56 (12H, m,
m1-m4-H), 7.73 (2H, dd, o5-H), 7.92–8.11 (12H, m, o1-
o4-H), 8.40 and 8.65 (4H and 4H, d and d, 2(8)-H, 3(7)-
H, Jð2; 3Þ ¼ 4:7 Hz), 8.82 (8H, s, 12,13,17,18-H).
RF ¼ 0.60.
2.2.2. D4Zn2
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
1
fied on the basis of their H NMR spectra. Resonances
1
were assigned using standard H COSY and NOSEY
CH3
H3C
m
CH3
H3C
m
2
4
p
o
2
p
1
o
4
2
17
18
m
m
1
3
o
o1
3
N
H
N
(2)
H
(CH2)n
2
13
12
N
N
(1)
N
N
3
CH2
H
N
H
H2C
O
N
O
o
2
m
m
8
2
6
7
o
o1
p
1
5
p
m
CH3
5
m
1
H3C
Fig. 1. The numbering scheme in diporphyrin. The variable length spacers S ¼ 2 (n ¼ 0), S ¼ 3 (n ¼ 1) and S ¼ 4 (n ¼ 2).

J. Borowiec et al. / Polyhedron 23 (2004) 33–39
35
)0.29 (4H, t, CH2(2)), 2.59 (4H, t, CH2(1)), 2.65 (12H, s,
2x(p-CH3(1))), 2.69 (6H, s, p-CH3(2)), 6.00 (2H, d, m6-
H, J(m6-p) ¼ 7.5 Hz), 6.66 (2H, ddd, p-H, J(p-m5) ¼ 8.1
Hz, J(p-o5) ¼ 1.9 Hz), 6.77 (2H, dd, m5-H, J(m5-o5) ¼ 7.1
Hz), 7.37–7.57 (12H, m, m1-m4-H), 7.63 (2H, dd, o5-H),
7.88–8.12 (12H, m, o1-o4-H), 8.38 and 8.75 (4H and 4H,
d + d, 2(8)-H, 3(7)-H, Jð2; 3Þ ¼ 4:7 Hz), 8.91 (8H, AB
spectrum, dA ¼ 8:89, dB ¼ 8:91, 12(18)-H, 3(17)-H,
Jð12; 13Þ ¼ 4:7 Hz).
(12H, m, m1-m4-H), 7.73 (2H, d, o5-H), 8.03–8.16
(12H, m, o1-o4-H), 8.53 and 8.82 (4H + 4H, d and d,
2(8)-H, 3(7)-H, Jð2; 3Þ ¼ 4:4 Hz), 8.96 (8H, s,
12,13,17,18-H).
RF ¼ 0.63.
UV–Vis: 420 (4.2 ꢀ 105, Soret band), 520 (4.0 ꢀ 103),
561(2.3 ꢀ 104), 601(3.9 ꢀ 103).
2.2.6. D3ZnH2
RF ¼ 0.44.
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
)2.79 (2H, s, NH), 0.59 (2H, m, CH2(2)), 2.69 (2H, m,
CH2(1)), 2.71 (18H, s, 2x(p-CH3(1) + p-CH3(2))), 2.83
UV–Vis: 422 (4.6 ꢀ 105, Soret band), 510 (5.2 ꢀ 103),
550 (2.7 ꢀ 104), 592 (4.9 ꢀ 103).
2.2.3. D4ZnH2
(2H, t, CH2(10)), 5.59 + 5.95 (1H + 1H, d + d, m6-
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
)2.88 (2H, s, NH), )0.24 (4H, m, CH2(2,20)), 2.48 (4H,
m, CH2(1,10)), 2.65 (12H, s, 2x(p-CH3(1,10))), 2.68 and
2.69 (3H and 3H, s and s, p-CH3(2) and p-CH3(20)), 5.79
H + m6 -H, J(m6-p) ¼ 8.0 Hz, J(m6 -p ) ¼ 8.0 Hz),
0
0
0
6.30 + 6.65 (1H + 1H, dd + dd, p-H + p0-H, J(p-m5) ¼ 8.0
0
0
Hz, J(p -m5 ) ¼ 8.1 Hz), 6.75 + 6.98 (1H + 1H, dd + dd,
0
0
0
m5-H + m5 -H, J(m5-o5) ¼ 8.0 Hz, J(m5 -o5 ) ¼ 8.0 Hz),
0
0
7.49-7.59 (12H, m, m1-m4-H + m1 -m4 -H), 7.65 + 7.86
0
0
(2H, d, m6-H, J(m6-p) ¼ 8.1 Hz), 6.18 (2H, d, m6 -H,
(1H + 1H, d + d, o5-H + o5 -H), 8.02–8.16 (12H, m, o1-o4-
0
0
0
0
J(m6 -p ) ¼ 8.1 Hz), 6.44 (2H, ddd, p-H, J(p-m5) ¼ 8.1
H + o1 -o4 -H), 8.39, 8.71 (4H, d + d, AB spectrum, 2(8)-
H, 3(7)-H), 8.69, 8.86 (4H, d + d, AB spectrum, 20(80)-H,
30(70)-H), 8.85 and 8.98 (4H and 4H, s and s,
12,13,17,18-H and 120,130,170,180-H).
Hz, J(p-o5) ¼ 1.9 Hz), 6.64 (2H, dd, m5-H, J(m5-o5) ¼ 7.5
Hz), 6.96 (2H, ddd, p0-H, J(p-m5) ¼ 8.1 Hz, J(p0-
0
0
0
0
o5 ) ¼ 1.9 Hz), 7.02 (2H, dd, m5 -H, J(m5 -o5 ) ¼ 7.1 Hz),
0
0
7.48–7.57 (12H, m, m1-m4-H + m1 -m4 -H), 7.68 (2H, dd,
RF ¼ 0.68.
o5-H), 7.78 (2H, dd, o5 -H), 7.88.- 8.12 (12H, m, o1-o4-
UV–Vis: 421 (4.0 ꢀ 105, Soret band), 519 (4.0 ꢀ 103),
561 (2.0 ꢀ 104), 595 (3.7 ꢀ 103).
0
0
0
H + o1 -o4 -H), 8.17, 8.61 (2H + 2H, d + d, 2(8)-H, 3(7)-
H, Jð2; 3Þ ¼ 4:7 Hz), 8.55, 8.77 (2H + 2H, d + d, 20(80)-H,
30(70)-H, J(20,30) ¼ 4.7 Hz), 8.79 (4H, AB spectrum,
dA ¼ 8:78, dB ¼ 8:80, 12(18)-H, 3(17)-H, Jð12; 13Þ ¼ 4:7
Hz), 8.91 (4H, AB spectrum, dA ¼ 8:89, dB ¼ 8:93,
120(180)-H, 30(170)-H, J(120,130) ¼ 4.7 Hz).
2.2.7. D2H4
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
)2.73 (4H, s, NH), 2.68 (12H, s, 2x(p-CH3(1))), 2.71
(6H, s, CH3 (p-CH3(2))), 3.34 (4H, s, 2xCH2), 5.82 (2H,
dd, p-H, J(p-m5) ¼ 8.1 Hz, J(p-m6) ¼ 8.1 Hz), 5.88 (2H,
d, m6-H), 6.43 (2H, dd, m5-H, J(m5-o5) ¼ 8.0 Hz), 7.46–
7.59 (12H, m, m1-m4-H), 7.61 (2H, d, o5-H), 8.00–8.15
(12H, m, o1-o4-H), 8.50 and 8.73 (4H and 4H, d and d,
AB spectrum, 2(8)-H, 3(7)-H, Jð2; 3Þ ¼ 4:7 Hz), 8.86
(8H, s, 12,13,17,18-H).
RF ¼ 0.56.
UV–Vis: 421 (4.3 ꢀ 105, Soret band), 510 (4.3 ꢀ 103),
550 (2.5 ꢀ 104), 592 (4.3 ꢀ 103).
2.2.4. D3H4
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
)2.76 (4H, s, NH), 0.60 (2H, q, CH2(2)), 2.71 (12H, s,
2x(p-CH3(1))), 2.72 (6H, s, CH3 (p-CH3(2))), 2.77 (4H, t,
2xCH2(1)), 5.82 (2H, d, m6-H, J(m6-p) ¼ 8.0 Hz), 6.58
(2H, ddd, p-H, J(p-m5) ¼ 8.0 Hz, J(p-o5) ¼ 1.5 Hz), 6.96
(2H, dd, m5-H, J(m5-o5) ¼ 8.4 Hz), 7.51–7.57 (12H, m,
m1-m4-H), 7.77 (2H, dd, o5-H), 8.03–8.14 (12H, m, o1-
do4-H), 8.56 and 8.73 (4H + 4H, d and d, 2(8)-H, 3(7)-H,
Jð2; 3Þ ¼ 4:8 Hz), 8.86 (8H, s, 12,13,17,18-H).
RF ¼ 0.73.
RF ¼ 0.63.
2.2.8. D2Zn2
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
2.66 (6H, s, CH3 (p-CH3(2))), 3.34 (4H, s, 2xCH2), 2.69
(12H, s, 2x(p-CH3(1))), 5.91 (2H, dd, p-H, J(p-m5) ¼ 8.0
Hz, J(p-m6) ¼ 8.0 Hz), 5.93 (2H, d, m6-H), 6.43 (2H, dd,
m5-H, J(m5-o5) ¼ 8.0 Hz), 7.45 (2H, d, o5-H), 7.46-7.59
(12H, m, m1-m4-H), 7.98–8.14 (12H, m, o1-o4-H), 8.50
and 8.81 (4H and 4H, d and d, AB spectrum, 2(8)-H,
3(7)-H, Jð2; 3Þ ¼ 4:7 Hz), 8.93 (8H, AB spectrum,
dA ¼ 8:92, dB ¼ 8:94, 12(18), 13(17) – H, Jð12; 13Þ ¼ 4:7
Hz).
2.2.5. D3Zn2
1H NMR (CDCl3, 298 K); chemical shift (ppm)
(intensity, multiplicity, assignment, coupling constant):
0.61 (2H, q, CH2(2)), 2.71 (18H, s, 2x(p-CH3(1) + p-
CH3(2))), 2.76 (4H, t, 2xCH2(1)), 5.76 (2H, d, m6-H,
J(m6-p) ¼ 8.1 Hz), 6.41 (2H, dd, p-H, J(p-m5) ¼ 8.1
Hz), 6.82 (2H, dd, m5-H, J(m5-o5) ¼ 8.0 Hz), 7.50–7.58
RF ¼ 0.45.
UV–Vis: 420 (4.3 ꢀ 105, Soret band), 510 (3.6 ꢀ 103),
548 (2.5 ꢀ 104), 586 (6.3 ꢀ 103).

36
J. Borowiec et al. / Polyhedron 23 (2004) 33–39
2.2.9. D2ZnH2
tively, A is the value of absorbance at the monitoring
wavelength, and K is the formation constant. The
monitoring wavelength corresponding to Q-bands was
chosen for every case.
1H NMR (CDCl3, 298 K); chemical shift (ppm) (in-
tensity, multiplicity, assignment, coupling constant):
)2.76 (2H, s, NH), 2.66 (12H, s, 2x(p-CH3(1)) + 2x(p-
CH3(10))), 2.69 (6H, s, CH3 (p-CH3(2)) + CH3(p-
CH3(20))), 3.29 and 3.31 (2H and 2H,s and s,
CH2(1) + CH2(10)), 5.86–6.06 (4H, m, p-H + m6-H +
2.4. Methods and instruments
0
0
p -H + m6 -H, J(p-m5) ¼ 8.0 Hz, J(p-m6) ¼ 8.0 Hz, J(p -
1H NMR spectra were obtained with a Bruker
AMX300 spectrometer operating in the quadrature
mode at 300 MHz. The residual peaks of deuterated
0
0
0
m5) ¼ 8.0 Hz, J(p -m6 ) ¼ 8.0 Hz), 6.26–6.51 (4H, m, m5-
0
H + m5 -H), 7.40–7.60 (12H, m, m1-m4-H, o5-H, and
1
0
o5 -H), 7.98–8.13 (12H, m, o1- o4-H), 8.37 and 8.69 (2H
solvents were used as internal standards. H COSY and
and 2H, d and d, AB spectrum, 2(8)-H, 3(7)-H, Jð2; 3Þ ¼
4:7 Hz), 8.59 and 8.82 (2H and 2H, d and d, AB spec-
trum, 20(80)-H, 30(70)-H, J(20,30) ¼ 4.7 Hz), 8.83 (4H, s,
12,13,17,18-H), 8.92 (4H, s, 120,130,170,180-H).
RF ¼ 0.50.
NOESY spectra were obtained using standard pulse
sequences as described before [10]. UV–Vis spectra were
recorded on Beckman DU 640 instrument. EPR spectra
were obtained with a Bruker ESP300E at X band for
frozen solutions (77 K) in CH2Cl2/toluene 1/3 v/v. The
mass spectrum was obtained on a Finnigan MAT TSQ
700 spectrometer by the ESI method at 4.5 kV ioniza-
tion potential and 250 °C capillary temperature in
chloroform.
UV–Vis: 420 (3.6 ꢀ 105, Soret band), 516 (7.5 ꢀ 103),
549 (1.5 ꢀ 104), 589 (4.0 ꢀ 103), 646 (1.4 ꢀ 103).
2.2.10. D2ZnCu
MS (ESI): m=e: (1þ) 1496 (40%); (1-Zn + 3H) 1434
(100%).
3. Results and discussion
2.3. Spectrophotometric titration of DSZn2 with nitrogen
bases
1
3.1. H NMR studies of DSH4, DSZn2 and DSZnH2
It has been demonstrated previously that the ring
current effect imposed by a porphyrin macrocycle
caused an upfield shift of the adjacent second porphy-
rin in diporhyrins [10,12]. It is especially pronounced in
the case of a peripheral meso-phenyl substituent to
which the spacer is attached (Table 1). A simple com-
parison of the chemical shifts of m6-H, p-H, m5-H and
o5-H in the diporphyrins studied here with those for the
mono-porphyrin reference compound (Table 1) shows
that: (i) the upfield shift decreases in order m6 > p >
m5 > o5 for S ¼ 3 and 4, and p > m6 > m5 > o5 for
S ¼ 2, (ii) the upfield shift of m6-H decreases with in-
creasing spacer length, i.e., in order of S; 2 ffi 3 > 4, (iii)
the same relationship holds for DSZn2 complexes as
well as for DSZnH2 and (iv) introducing one zinc(II)
ion into the porphyrin subunit induces considerable
differentiation of the chemical shifts of the two por-
phyrin subunits, which can be exemplified by D (where
D is the chemical shift difference between the corre-
sponding resonances of linking 5-phenyl and pyrrole
b-H protons in PH2 and PZn porphyrin halves
Formation constants of PZnL (where P is the por-
phyrin subunit in DSZn2 or TTP, and L ¼ pyridine (py),
pyrazine (pyr) or 4,40-bipyridyl (bipy)) have been ob-
tained by spectrophotometric titration of DSZn2 (con-
centration 3.00 ꢀ 10ꢁ5 mol/dm3) with L (concentration
varied in the 3.00 ꢀ 10ꢁ5–0.1 mol/dm3 range) with the
assumption that no other species are present in the
equilibrium except those defined by reaction scheme
PZn þ L () PZnL
Stability constants were calculated from the general
formula
ðe1CZn ꢁ AÞðe1 ꢁ e2Þ
K ¼
;
ðA ꢁ e2CZnÞ½CL0 ðe1 ꢁ e2Þ ꢁ e1CZn ꢁ Aꢂ
derived from initial equations:
C1 þ C2 ¼ CZn;
CL0 ¼ CL þ C2;
(see Fig. 2)). In the case of D3ZnH2 and D4ZnH2
decreases in the order:
D
C2
C1CL
K ¼
;
D3ZnH2: m6ð0:36Þ > pð0:35Þ > m5 ¼ b2;3
ð0:23Þ > o5ð0:21Þ > b12;13ð0:18Þ.
A ¼ e1C1 þ e1C2;
D4ZnH2: pð0:52Þ > m6ð0:39Þ > m5ð0:28Þ > b2;3ð0:13Þo5
ð0:10Þ > b12;13ð0:09Þ.
where C1 and C2 are concentrations of PZn starting
complex and PZnL adduct, respectively, CL0 is total
concentration of L, CL is concentration of free L, e1 and
e1 are extinction coefficients of PZn and PZnL, respec-
The largest values of D for D4ZnH2 indicate that the
ring current effect is most pronounced in this case. On
the other hand the D values for D2ZnH2 are very small

J. Borowiec et al. / Polyhedron 23 (2004) 33–39
37
Table 1
Relevant 1H NMR data of DSH4, DSZnH2 and DSZn2
Chemical shift (ppm) (chemical shift difference related to referencea)
Entry
Compound
m6
p
m5
o5
1
2
3
4
5
6
TTP-o-PrBra
D2H4
D2Zn2
7.32
7.76
7.37
8.04
5.88 ()1.44)
5.93 ()1.39)
5.82 ()1.50)
5.76 ()1.56)
5.95 ()1.37)
5.59 ()1.73)
6.02 ()1.30)
6.00 ()1.32)
5.79 ()1.53)
6.18 ()1.14)
5.82 ()1.84)
5.91 ()1.85)
6.58 ()1.18)
6.41 ()1.35)
6.65 ()1.11)
6.30 ()1.46)
6.84 ()0.92)
6.66 ()1.10)
6.44 ()1.32)
6.96 ()0.80)
6.43 ()0.94)
6.43 ()0.94)
6.96 ()0.41)
6.82 ()0.55)
6.98 ()0.39)
6.75 ()0.62)
6.97 ()0.40)
6.77 ()0.60)
6.64 ()0.73)
7.02 ()0.35)
7.61 ()0.43)
7.45 ()0.59)
7.77 ()0.27)
7.73 ()0.31)
7.86 ()0.18)
7.65 ()0.39)
7.73 ()0.31)
7.63 ()0.41)
7.68 ()0.36)
7.78 ()0.26)
D3H4
D3Zn2
D3ZnH2
7
8
9
D4H4
D4Zn2
D4ZnH2
a The chemical shifts were related to reference compound of C2v effective symmetry; 5-(ortho-(3-bromopropoxy)phenyl)-10,15,20-tris(para-meth-
ylphenyl)porphyrin (entry 1, TTP-o-PrBr).
3.2. Coordination of nitrogen aromatic ligands into
dizincdiporphyrins
(a)
*
Coordination of pyridine-type bases into PZn causes
red shift of the Soret band and a 14 nm red shift of the
m6
m5
Q-band centered at about 550–560 nm. The titration of
PZn indicated well-resolved isosbestic points for all
o5
p
studied systems at the concentration of L up to 10ꢁ2
M
(Fig. 3). Above that concentration of L a further red
shift (1–2 nm) of the Q-band could be detected, typical
for formation of PML2 (P – porphyrin or phthalocya-
nine) [13] with a very small change of extinction at the
analytical wavelength. In order to avoid overlapping
equilibrium related to the formation of bis-ligand
PZnL2 complexes only the points for base concentration
below 10ꢁ3 M were used for the calculation of formation
constants. The values of e1 and e2 were taken from
(b)
*
*
o'
o5
m'6
m6
p
m5m'5
p'
5
(c)
0,6
0,5
0,4
0,3
0,2
0,1
0,0
o5
m5
m6
p
9,5
9,0
8,5
8,0
7,5
7,0
6,5
6,0
5,5
Fig. 2. Relevant fragments of the 1H NMR spectra of D3H4 (a);
D3ZnH2 (b) and D3Zn2 (c). The residual CHCl3 resonance is labelled
with an asterisk. The resonances labelled with 0 at trace B were ten-
tatively attributed to the PZn part of D3ZnH2.
500
550
600
650
and the corresponding resonances of 5-meso-phenyl
substituents almost overlap. These features suggest that
in all DSZnH2 the two porphyrin subunits are in face-
to-face conformation, however, in the case of S ¼ 2 the
average conformation is slightly different from those for
S ¼ 3 and 4.
Fig. 3. The Q-band regions of UV–Vis spectra of the solutions con-
taining D4Zn2 (c ¼ 2:2 ꢀ 10ꢁ5 mol dmꢁ3) and pyr in CH2Cl2. Vertical
arrows indicate absorbance changes upon addition of pyr, whose
concentrations are (from top to bottom at 550 nm): 0; 3.0 ꢀ 10ꢁ5
;
6.0 ꢀ 10ꢁ5; 2.5 ꢀ 10ꢁ4; 5.0 ꢀ 10ꢁ3 and 0.10 mol ꢀ dmꢁ3
.

38
J. Borowiec et al. / Polyhedron 23 (2004) 33–39
Table 2
Formation constants of PZnL complexes (where L ¼ py, pyr and bipy) determined by spectrophotometric titration of PZn in methylene dichloride at
298 K
log K (K – formation constant in mol/dm3) (EM (mol dmꢁ3))
Entry
Starting complex
py
pyr
bipy
1
2
3
4
5
TTPZn
D2Zn2
D3Zn2
D4Zn2
D4ZnH2
3.61 (3.68)a
3.35
3.63
3.90
3.20
3.22
4.61 (0.00065)
4.90 (0.0012)
3.83
4.63 (0.017)
5.19 (0.062)
3.12
3.65
3.03
3.10
a Determined in benzene solution [14].
experimental data at an analytical wavelength chosen at
the maximum of two Q-bands of PZnL. The calculated
data on K are collected in Table 2. The formation
constants of PZnL, where L ¼ py are in every case close
to that of TTPZnL. Pyrazine and bipyridyl form in some
cases considerably stronger complexes, which was at-
tributed to an entropic factor due to the bridging mode
of coordination of the ligands. Thus, the best fit between
size of heteroaromatic base and length of spacer was
obtained for bipy and D4Zn2, while for pyr the best fit
was in the case of D3Zn2 and D2Zn2. The complemen-
tarity between host (dizincdiporphyrin) and bidentate
ligand (here pyr or bipy) can be rationalized using the
concept of effective molarity [15] expressed as
D2ZnCu
D2Cu2
2600
2800
3000
3200
3400
3600
EM ¼ K=Ki2;
Fig. 4. EPR spectra of D2ZnCu and D2Cu2 in CH2Cl2/toluene glass in
77 K.
where Ki is the microscopic equilibrium constant for
binding of monodentate ligand into metal ion.
This approach was successfully applied for quantifi-
cation of oligopyridyl ligands to butadiyne-linked
porphyrin dimers, trimers and tetramers [16]. The best
host–guest complementarity was found in the case of a
relatively rigid cyclic diporphyrin with bipy, resulting in
EM as large as 76 mol dmꢁ3, while in the case of the
corresponding linear diporphyrin the EM was merely
spectra (Fig. 4). The D2Cu2 complex was obtained in an
independent synthesis by insertion of Cu(II) into D2H4.
The mixed-metal D2ZnCu was identified by MS mea-
surement. Moreover, the complexes were demetallated
1
and the identity of D2H4 was verified by its H NMR
spectrum. The EPR spectrum of D2Cu2 is composed of
broad lines, probably due to weak interaction between
the two copper(II) centers and does not show superhy-
perfine coupling with nitrogen donors [17]. The char-
acteristic feature of D2ZnCu is the presence of 18 lines
0.5 mol dmꢁ3
.
Here the EMs were calculated using experimental Ki
obtained as the formation constant for binding biden-
tate ligand into TTPZn (entry 1 in Table 2). The values
of EM are listed in Table 2. Obtained EM are much
lower in comparison with those found for well-fitted
host–guest pairs based on rigid cyclic oligoporphyrins
[16], which seems reasonable considering the flexibility
of the diporhyrins studied here. Nevertheless, the best
complementarity within the D4Zn2/bipy and D3Zn2/pyr
pairs is clearly seen.
of superhyperfine structure related to two distinct g ,
?
typical for monomeric copperporphyrins [17].
4. Conclusion
We have presented the successful method of syn-
thesis and separation of mono-zinc diporphyrin com-
plexes, which are useful starting materials for the
synthesis of heterodimetallodiporphyrins. Heteromet-
allodiporphyrins with flexible spacers of tunable length
and geometry may be used as catalysts in many reac-
tions, depending on the metal ions incorporated. The
most promising is the application of diiron(II)dipor-
phyrins in activation of dioxygen and oxygen atom
3.3. Synthetic route to heterodimetallodiporphyrin
D2ZnCu
The insertion of Cu(II) ion into D2ZnH2 was ac-
companied by partial replacement of Zn(II) with Cu(II)
resulting in the formation of two species: D2ZnCu and
D2Cu2. The complexes were identified by their EPR

J. Borowiec et al. / Polyhedron 23 (2004) 33–39
39
[6] C. Pascard, J. Guilhem, S. Chardon- Noblat, J.P. Sauvage, New J.
Chem. 17 (1993) 331.
transfer from diferryldiporphyrins into dienes. Espe-
cially interesting seems to study the influence of differ-
ent metal ions in Fe(II)/M(II)diporphyrin complexes on
the chemoselectivity of such catalytic reaction.
[7] R. Guillard, M.A. Lopez, A. Tabard, P. Richard, C. Lecomte, S.
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[9] R.G. Little, J. Heterocycl. Chem. 15 (1978) 203.
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