Gemini-Porphyrazines: The synthesis and characterization of metal-capped cis- and trans-porphyrazine tetrathiolates

Article abstract of DOI:10.1021/ja961912x

Peripherally-functionalized porphyrazines of the form M[pz(A(n):B(4-n))] (inset 1), where A and B symbolize functional moieties (e.g., a-d in Table 1) fused directly to the β-positions of the pyrroles, have the potential to serve in a wide range of applications. Previously, we reported the synthesis of porphyrazine di- and octathiolate ligands, M[pz(b₃:c₁)] and M[pz(c₄)], respectively, where b is a fused benzo ring and c represents two thiolates fused at the β-pyrrole positions to form a dithiolene capable of the peripheral chelation of a metal ion. We describe here a general strategy that solves the more difficult problem of preparing and isolating the porphyrazinetetra- and hexathioethers and the porphyrazinetetra- and hexathiolates, with the focus being the trinuclear metal complexes of the trans- and cis-porphyrazinetetrathiolate isomers (trans- and cis-M[pz(b₂:d₂)]), denoted as gemini porphyrazines. Spectroscopic and electrochemical studies reveal that the physical properties of the cis- and trans-tetrathioether porphyrazines exhibit intriguing differences associated with their distinct molecular symmetries. These functionalized macrocycles have been used to prepare the trans- and cis-gemini porphyrazines 14 and 16, the two isomeric porphyrazinetetrathiolate macrocycles that are peripherally-metalated with two bis(triethylphosphine)platinum(II) moieties. The X-ray structure of the trans isomer, 14, is presented; it is the first structure of a porphyrazine or phthalocyanine having a trans-type substitution pattern.

Full text of DOI:10.1021/ja961912x

J. Am. Chem. Soc. 1996, 118, 10487-10493
10487
gemini-Porphyrazines: The Synthesis and Characterization of
Metal-Capped cis- and trans-Porphyrazine Tetrathiolates
John W. Sibert,†,§ Theodore F. Baumann,† David J. Williams,‡
Andrew J. P. White,‡ A. G. M. Barrett,*,‡ and Brian M. Hoffman*,†
Contribution from the Department of Chemistry, Northwestern UniVersity,
EVanston, Illinois 60208, and Department of Chemistry, Imperial College of Science,
Technology and Medicine, South Kensington, London SW7 2AY, U.K.
ReceiVed June 7, 1996X
Abstract: Peripherally-functionalized porphyrazines of the form M[pz(An:B4-n)] (inset 1), where A and B symbolize
functional moieties (e.g., a-d in Table 1) fused directly to the â-positions of the pyrroles, have the potential to serve
in a wide range of applications. Previously, we reported the synthesis of porphyrazinedi- and octathiolate ligands,
M[pz(b3:c1)] and M[pz(c4)], respectively, where b is a fused benzo ring and c represents two thiolates fused at the
â-pyrrole positions to form a dithiolene capable of the peripheral chelation of a metal ion. We describe here a
general strategy that solves the more difficult problem of preparing and isolating the porphyrazinetetra- and
hexathioethers and the porphyrazinetetra- and hexathiolates, with the focus being the trinuclear metal complexes of
the trans- and cis-porphyrazinetetrathiolate isomers (trans- and cis-M[pz(b2:d2)]), denoted as gemini porphyrazines.
Spectroscopic and electrochemical studies reveal that the physical properties of the cis- and trans-tetrathioether
porphyrazines exhibit intriguing differences associated with their distinct molecular symmetries. These functionalized
macrocycles have been used to prepare the trans- and cis-gemini porphyrazines 14 and 16, the two isomeric
porphyrazinetetrathiolate macrocycles that are peripherally-metalated with two bis(triethylphosphine)platinum(II)
moieties. The X-ray structure of the trans isomer, 14, is presented; it is the first structure of a porphyrazine or
phthalocyanine having a trans-type substitution pattern.
Introduction
porphyrazine periphery. We discuss here a strategy that solves
the far harder problem of synthesizing and isolating both the
cis and trans-M[pz(A2:B2)] macrocycles, and use this strategy
to prepare the first trinuclear metal complexes of the trans- and
cis-porphyrazine tetrathiolate isomers, the gemini-porphyrazines,
14 and 16 (inset 2).
Peripherally-functionalized porphyrazines of the form, M[pz-
(An:B4-n)] (inset 1) where A and B symbolize functional groups
(e.g., a-d in inset 1) fused directly to the â-positions of the
pyrroles have the potential to exhibit novel magnetic and
electronic properties and serve as building blocks in the
assembly of higher order, metal-linked, multiporphyrinic arrays.1
The preceding paper (J. Am. Chem. Soc. 1996, 118, 10479)
describes the synthesis of unsymmetrical M[pz(A1:B3)] macro-
cycles,2a including the solitaire-porphyrazines2 which have one
metal ion bound to a single dithiolato chelation site at the
This synthesis of heterofunctionalized porphyrazines begins
with the cocyclization of a pair of maleonitrile derivatives.
Normally, it would be prohibitively difficult to isolate and purify
each of the six possible porphyrazines produced in a cocycliza-
tion. The synthesis of the solitaire-porphyrazines described in
the previous paper employed a procedure that yielded only
M[pz(A1:B3)] and M[pz(B4)] and that used reactants chosen so
that only the former was soluble,2 but this approach is not
applicable to the preparation of the other mixed porphyrazines
(inset 1). Instead, we have used a strategy that involves dinitrile
pairs with groups A and B that have disparate polarities. As a
result, even though the cyclization procedure produces all
possible substituted porphyrazines as products, it is possible to
chromatographically separate porphyrazines with different n,
in particular the cis and trans n ) 2 isomers, in acceptable
yields. This permits the subsequent steps in the preparation of
gemini-porphyrazines to be performed with chemically and
isomerically pure reactants. As an illustration, we report the
synthesis of the n ) 2 and 3 porphyrazines, 8-10 (Table 1), as
well as the preparation of the trimetallic gemini-porphyrazines,
† Northwestern University.
‡ Imperial College of Science, Technology and Medicine.
§ Present address: Department of Chemistry, East Carolina University,
Greenville, NC 27858-4353.
X Abstract published in AdVance ACS Abstracts, October 1, 1996.
(1) For alternative designs of multi-porphyrinic arrays, see: (a) Hanan,
G. S.; Arana, C. R.; Lehn, J.-M.; Fenske, D. Angew Chem., Int. Ed. Engl.
1995, 34, 1122-1124. (b) Seth, J.; Palaniappan, V.; Johnson, T. E.;
Prathapan, S.; Lindsey, J. S.; Bocian, D. F. J. Am. Chem. Soc. 1994, 116,
10578-10592. (c) Anderson, H. L. Inorg. Chem. 1994, 33, 972-981. (d)
Lin, V. S.-Y.; Dimagno, S. G.; Therien, M. J. Science 1994, 264, 1105-
1111. (e) Crossley, M. J.; Burn, P. L. J. Chem. Soc., Chem. Commun.
1991, 1569-1571.
(2) (a) Baumann, T. F.; Nasir, M. S.; Sibert, J. W.; White, A. J. P.;
Olmstead, M. M.; Williams, D. J.; Barrett, A. G. M.; Hoffman, B. M. J.
Am. Chem. Soc. preceding paper (J. Am. Chem. Soc. 1996, 118, 10479).
(b) Baumann, T. F.; Sibert, J. W.; Olmstead, M. M.; Barrett, A. G. M.;
Hoffman, B. M. J. Am. Chem. Soc. 1994, 116, 2639-2640.
S0002-7863(96)01912-9 CCC: $12.00 © 1996 American Chemical Society

10488 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Table 1. Compounds Prepared in This Study
Sibert et al.
of Mg-porphyrazines by overnight treatment with trifluoroacetic acid
(30 mL) prior to separation of the individual porphyrazines. The
resulting blue solution was poured into ice water (300 mL) and stirred,
causing the immediate formation of a precipitate. Following neutraliza-
tion with concentrated NH4OH, the solid was collected by filtration
and washed thoroughly with water, MeOH, and a small amount of Et2O.
The crude product was dissolved in a minimum of CH2Cl2 and
chromatographed using the Chromatotron (1 or 2 mm plate; 0-0.5%
MeOH/CH2Cl2 as eluent). Each of the porphyrazine products was
collected in the order listed below.
2,3,7,8,12,13,17,18-Octakis[(4-butyloxycarbonylbenzyl)thio]por-
phyrazine, H2[pz(a4)], 3. This porphyrazine was collected as the first
purplish-blue band to elute. No attempt was made at determining a
yield for this compound: 1H NMR (CDCl3) δ (ppm) 7.70 (d, 16H, ar
(benzyl)), 7.34 (d, 16H, ar (benzyl)), 5.15 (s, 16H, ArCH2-), 4.21 (t,
16H, -CH2O), 1.67 (qn, 16H, -OCH2CH2-), 1.40 (sx, 16H, -CH2CH3),
0.90 (t, 24H, -CH2CH3), -3.10 (s, 2H, NH); UV-vis(CHCl3) λmax 354,
508, 648, 716 nm; FAB-MS 2113 (M + H+).
2,3,7,8,12,13-Hexakis[(4-butyloxycarbonylbenzyl)thio]-17,18-ben-
zoporphyrazine, H2[pz(a3:b)], 4. This blue porphyrazine was collected
as the second band to elute from the Chromatotron. Recrystallization
from CH2Cl2/MeOH yielded a microcrystalline product (160 mg;
7%): 1H NMR (CDCl3) δ (ppm) 8.76 (m, 2H, ar (fused benzo)), 8.05
(m, 2H, ar (fused benzo)), 7.80 (m, 12H, ar (benzyl)), 7.34 (m, 12H,
ar (benzyl)), 5.24 (s, 4H, ArCH2-), 5.13 (s, 4H, ArCH2-), 5.08 (s, 4H,
ArCH2-), 4.21 (t, 12H, -CH2O), 1.65 (qn, 12H, -OCH2CH2-), 1.39 (sx,
12H, -CH2CH3), 0.90 (t, 18H, -CH2CH3), -2.90 (s, 2H, NH); UV/vis-
(CHCl3) λmax 356, 500, 624, 680, 726 nm; FAB-MS 1698 (M + H+).
2,3,12,13-Tetrakis[(4-butyloxycarbonylbenzyl)thio]-7,8;17,18-
dibenzporphyrazine, H2[trans-pz(a2:b2)], 5. This purplish-pink por-
phyrazine was the third band to elute from the Chromatatron.
Recrystallization from CH2Cl2/MeOH yielded a microcrystalline product
(130 mg; 5%); 1H NMR (CDCl3) δ (ppm) 8.61 (m, 4H, ar (fused
benzo)), 7.89 (m, 4H, ar (fused benzo)), 7.80 (d, 8H, ar (benzyl)), 7.34
(d, 8H, ar (benzyl)), 5.28 (s, 8H, ArCH2-), 4.16 (t, 8H, -CH2O), 1.63
(qn, 8H, -OCH2CH2-), 1.38 (sx, 8H, -CH2CH3), 0.90 (t, 12H, -CH2CH3),
-3.36 (s, 2H, NH); UV/vis(CH2Cl2) λmax 350, 590, 708, 747 nm; FAB-
MS 1304 (M + H+).
2,3,7,8-Tetrakis[(4-butyloxycarbonylbenzyl)thio]-12,13;17,18-
dibenzporphyrazine, H2[cis-pz(a2:b2)], 6. This blue porphyrazine was
isolated as the fourth band to elute from the Chromatotron. Recrys-
tallization from CH2Cl2/MeOH yielded a microcrystalline product (285
mg; 11%): 1H NMR (CDCl3) δ (ppm) 8.55 (m, 4H, ar (fused benzo)),
7.91 (m, 4H, ar (fused benzo)), 7.79 (m, 8H, ar (benzyl)), 7.45 (d, 4H,
ar (benzyl)), 7.36 (d, 4H, ar (benzyl)), 5.11 (s, 4H, ArCH2-), 5.06 (s,
4H, ArCH2-), 4.18 (m, 8H, -CH2O), 1.62 (m, 8H, -OCH2CH2-), 1.37
(m, 8H, -CH2CH3), 0.89 (m, 12H, -CH2CH3), -2.40 (s, 2H, NH); UV/
vis(CH2Cl2) λmax 352, 628, 652, 692 nm; FAB-MS 1304 (M + H+).
2,3-Bis[(4-butyloxycarbonylbenzyl)thio]norphthalocyanine, H2-
[pz(a:b3)], 7. This blue porphyrazine was the fifth and final band
collected from the Chromatatron. Characterization of this compound
was as previously reported.4
compd
M
pz(An:B4-n)
3
4
5
6
7
2H
2H
2H
2H
2H
Ni
pz(a)4
pz(a3:b)
trans-pz(a2:b2)
cis-pz(a2:b2)
pz(a:b3)
8
pz(a3:b)
9
Ni
Ni
Mn
Mn
Ni
Ni
Ni
Ni
trans-pz(a2:b2)
cis-pz(a2:b2)
trans-pz(a2:b2)
cis-pz(a2:b2)
trans-pz(c2:b2)
trans-pz(d2:b2) (M ) Pt, L ) (PEt3)2)
cis-pz(c2:b2)
10
11
12
13
14
15
16
cis-pz(d2:b2) (M ) Pt, L ) (Pet3)2)
14 and 16 (inset 2). The characterization of these molecules
includes the X-ray structure determination of 14, the first one
of a porphyrazine or phthalocyanine having a trans-type
substitution pattern.3
Materials and Methods
THF was distilled from sodium benzophenone ketyl. All other
solvents were reagent grade and used as supplied. Anhydrous ammonia
(Linde Specialty Gases) was ultra-high-purity grade. 1,2-Dicyanoben-
zene, 1, was purchased from Aldrich and used as received. 2,3-Di-
[(4-butyloxycarbonylbenzyl)thio]-2Z-butenedinitrile ((BCB)2mnt), 2,
was prepared as reported.2a All other reagents were used as supplied
without further purification. Radial chromatography was performed
on a Chromatotron (Model 7924T), Harrison Research, Palo Alto, CA.
The chromatotron plates were coated with Merck silica gel (TLC grade
7749 with gypsum binder).
1H and 31P NMR spectra were obtained using a Gemini 300
spectrometer. The 31P NMR spectra were referenced using a 5% H3-
PO4 external reference. Electronic spectra were recorded using a
Hewlett-Packard HP8452A spectrophotometer. Cyclic voltammetry
experiments were performed at room temperature in freshly-distilled
methylene chloride with 0.1 M tetrabutylammonium hexafluorophos-
phate as the supporting electrolyte using a Cypress Systems 2000
electroanalytical system. A platinum working electrode and Ag/AgCl
reference electrode were used with ferrocene as an internal calibrant.
Fast-atom bombardment mass spectra (FAB-MS) were obtained by Dr.
Doris Hung using a VG-70-250E instrument. Elemental analyses were
performed by Searle Laboratories, Skokie, IL and Oneida Research
Services, Whitesboro, NY (supporting information, Table 1).
Synthesis of H2[pz(an:b4-n)]. Magnesium metal (0.064 g, 0.0027
mol) was added to butanol (16 mL), and the solution was heated to
reflux. A small chip of iodine was added to initiate the formation of
the magnesium butoxide suspension. After 16 h, 1,2-dicyanobenzene
(0.50 g, 0.004 mol) and (BCB)2mnt (2.04 g, 0.004 mol) were
simultaneously added to the solution. The reaction was heated at reflux
for 24 h under a N2 atmosphere. The butanol was removed under
vacuum, and the crude reaction mixture dissolved in CHCl3. The blue-
green mixture was filtered to remove the insoluble Mg(pc) formed as
a byproduct in the cyclization. After concentration on a rotary
evaporator, the filtrate was passed through a silica column (1-2%
MeOH/CHCl3 as eluent) which removed non-porphyrazine byproducts
and afforded all of the Mg-porphyrazines as a mixture. Isolation of
the Mg-porphyrazines was achieved by chromatography using the
Chromatotron (1 or 2 mm plate; 0.5-1% MeOH/CH2Cl2 as eluent).
This method, however, worked poorly due to the formation of broad
chromatographic bands and did not produce analytically pure products.
A better approach begins with the demetalation of the entire mixture
Synthesis of [2,3,7,8,12,13-Hexakis[(4-butyloxycarbonylbenzyl)-
thio]-17,18-benzporphyrazinato]nickel(II) Ni[pz(a3:b)], 8. Metal-
free 4 (0.200 g, 0.12 mmol), anhydrous Ni(OAc)2 (0.21 g, 1.2 mmol),
chlorobenzene (10 mL), and DMF (5 mL) were heated to 100 °C under
nitrogen for 5 h. Following removal of the solvent under vacuum, the
product was washed with 5% HCl in MeOH, pure MeOH, and then
Et2O. Recrystallization from CH2Cl2/MeOH yielded microcrystalline
product in near quantitative yield: 1H NMR (CDCl3) δ (ppm) 8.68
(m, 2H, ar (fused benzo)), 8.00 (m, 2H, ar (fused benzo)), 7.78 (m,
12H, ar (benzyl)), 7.32 (m, 12H, ar (benzyl)), 5.08 (s, 4H, ArCH2-),
5.06 (s, 4H, ArCH2-), 5.02 (s, 4H, ArCH2-), 4.21 (t, 12H, -CH2O),
1.66 (qn, 12H, -OCH2CH2-), 1.39 (sx, 12H, -CH2CH3), 0.92 (t, 18H,
-CH2CH3); UV/vis(CHCl3) λmax 326, 644, 682 nm; FAB-MS 1755 (M
+ H+).
Synthesis of [2,3,12,13-Tetrakis[(4-butyloxycarbonylbenzyl)thio]-
7,8;17,18-dibenzoporphyrazinato] nickel(II), Ni[trans-pz(a2:b2)], 9.
Porphyrazine 9 was prepared from 5 by an identical procedure to that
used in the preparation of 8. Recrystallization from CH2Cl2/MeOH
yielded microcrystalline product in near quantitative yield: 1H NMR
(3) For examples of unsymmetrical phthalocyanines having a trans-type
substitution pattern without crystal structures, see: (a) Kobayashi, N.;
Ashida, T.; Osa, T.; Konami, H. Inorg. Chem. 1994, 33, 1735-1740. (b)
Kobayashi, N.; Ashida, T.; Osa, T. Chem. Lett. 1992, 2031-2034. (c) Ikeda,
Y.; Konami, H.; Hatano, M.; Mochizuki, K. Chem. Lett. 1992, 763-766.
(4) (a) Schramm, C. S.; Hoffman, B. M. Inorg. Chem. 1980, 19, 383-
385. (b) Linstead, R. P.; Whalley, M. J. Chem. Soc. 1952, 4839-4846.

gemini-Porphyrazines
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10489
Table 2. Crystallographic Data for 14
(CDCl3) δ (ppm) 8.42 (m, 4H, ar (fused benzo)), 7.80 (m, 12H, ar
(fused benzo, benzyl)), 7.36 (d, 8H, ar (benzyl)), 5.04 (s, 8H, ArCH2-
), 4.22 (t, 8H, -CH2O), 1.67 (qn, 8H, -OCH2CH2-), 1.38 (sx, 8H, -CH2-
CH3), 0.92 (t, 12H, -CH2CH3). Uv/vis(CH2Cl2) λmax 354, 605, 722 nm;
FAB-MS 1360 (M + H+).
Synthesis of [2,3,7,8-Tetrakis[(4-butyloxycarbonylbenzyl)thio]-
12,13;17,18-dibenzporphyrazinato]nickel(II), Ni[cis-pz(a2:b2)], 10.
Porphyrazine 10 was prepared from 6 by an identical procedure to that
used in the preparation of 8. Recrystallization from CH2Cl2/MeOH
yielded microcrystalline product in near quantitative yield: 1H NMR
(CDCl3) δ (ppm) 8.21 (m, 4H, ar (fused benzo)), 7.81 (m, 8H, ar
(benzyl)), 7.69 (m, 4H, ar (fused benzo)), 7.40 (d, 4H, ar (benzyl)),
7.33 (d, 4H, ar (benzyl)), 5.00 (s, 4H, ArCH2-), 4.97 (s, 4H, ArCH2-),
4.20 (m, 8H, -CH2O), 1.64 (m, 8H, -OCH2CH2-), 1.38 (m, 8H, -CH2-
CH3), 0.90 (t, 12H, -CH2CH3). UV/vis(CH2Cl2) λmax 336, 602, 659
nm; FAB-MS 1360 (M + H+).
chem formula
fw
crystal system
space group
a, Å
C48H68N8NiP4Pt2S4‚2[C6H4Cl2]
1752.1
monoclinic
P21/c
13.006(4)
b, Å
c, Å
18.645(8)
14.469(6)
â, deg
105.86(3)
3375(2)
2
V, Å3
Za
T, K
λ(Cu KR), Å
293(2)
1.54178
1.72
117.8
F
calcd, g/cm3
µ, cm-1
GOFb on F2
1.039
final R indicesc [I > 2σ(I)]
R1 ) 0.0350, wR2 ) 0.0848
Synthesis of [2,3,12,13-Tetrakis[(4-butyloxycarbonylbenzyl)thio]-
7,8;17,18-dibenzporphyrazinato]-chloromanganese(III), MnCl-
[trans-pz(a2:b2)], 11. Metal-free 5 (0.200 g, 0.12 mmol), excess MnCl2,
chlorobenzene (10 mL), and DMF (5 mL) were heated to 100 °C under
nitrogen for 5 h. Following removal of the solvent under vacuum, the
product was washed with water MeOH and then ethyl ether. Purifica-
tion by silica gel chromatography (4% MeOH/CH2Cl2) produced 11
as a green solid in near quantitative yield: UV/vis(CH2Cl2) λmax 382,
654, 780 nm; FAB-MS 1356 (M - Cl-).
a The molecule has crystallographic Ci symmetry. b bGOF ) [∑[w(Fo2
- Fc2)2]/(M - N)]1/2 where M is the number of reflections and N is the
number of parameters refined. c R1 ) ∑||Fo - Fc||/∑|Fo|; wR2
)
2
2
[∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2
.
Scheme 1a
Synthesis of [2,3,7,8-Tetrakis[(4-butyloxycarbonylbenzyl)thio]-
12,13;17,18-dibenzoporphyrazinato]chloromanganese(III), MnCl-
[cis-pz(a2:b2)], 12. Porphyrazine 12 was prepared from 6 by an
identical procedure to that used in the preparation of 11. The product
was isolated by silica gel chromatography (4% MeOH/CH2Cl2) as a
brown oily solid in near quantitative yield: UV/vis(CH2Cl2) λmax 357,
473, 712 nm; FAB-MS 1356 (M - Cl-).
Synthesis of Sodium [7,8;17,18-dibenzporphyrazinato]nickel(II)-
2,3,12,13-tetrathiolate, Ni[trans-pz(c2:b2)], 13. Schlenk techniques
were used in this step. Compound 9 (0.100 g, 0.074 mmol) was
suspended in a solution of liquid NH3 (25 mL) at -78 °C. Socium
metal (0.027 g, 1.18 mmol) was freshly cut under hexanes and added
to the suspension. Once the sodium dissolved, THF (10 mL) was added
to solubilize the porphyrazine. The solution was allowed to reflux at
-33 °C for 30 min, whereupon the solution turned purple and then
green. Following the addition of ammonium chloride (0.031 g, 0.6
mmol), solvent was evaporated under a stream of argon, yielding a
fine blue powder containing sodium chloride and the sodium salt of
the tetrathiolate. Due to the air-sensitive nature of this solid, no attempt
was made to isolate the product.
Synthesis of Ni[trans-pz(b2:d2)] (M ) Pt,L ) (PEt3)2), 14. To
the deep blue solution of crude tetrathiolate 13 in deaerated MeOH
(30 mL) was added (Et3P)2PtCl2 (0.074 g, 0.148 mmol). After 30 min,
the blue precipitate that formed was collected by filtration under ambient
conditions. The product was dissolved in CH2Cl2 and chromatographed
on silica gel using 2% MeOH in CH2Cl2 as the eluent. The major
purple band was collected to yield product 14 (45 mg; 40% based on
9). X-ray diffraction quality, cube-shaped crystals were grown by slow
evaporation of a CH2Cl2 solution in the presence of 1,2-dichloroben-
zene: 1H NMR (CD2Cl2) δ (ppm) 9.39 (m, 4H, ar (fused benzo)), 8.22
(m, 4H, ar (fused benzo)), 2.40 (m, 24H, -CH2CH3), 1.36 (m, 36H,
-CH2CH3); 31P NMR (CD2Cl2, H3PO4 external reference) δ (ppm) 7.33
(JPt-P ) 2708 Hz); UV/vis(CH2Cl2) λmax 330, 568, 600, 676 nm; FAB-
MS 1457 (M + H+).
Synthesis of Sodium [12,13;17,18-dibenzporphyrazinato]nickel-
(II)-2,3,7,8-tetrathiolate, Ni[cis-pz(b2:c2)], 15. Complex 10 (0.100
g, 0.074 mmol) was deprotected by the method described above for
compound 13. Again, due to the air-sensitive nature of the tetrathiolate,
no attempt was made to isolate the product.
Synthesis of Ni[cis-pz(b2:d2)] (M ) Pt,L ) (PEt3)2), 16. To the
blue solution of crude tetrathiolate 15 in deaerated MeOH (30 mL)
was added (Et3P)2PtCl2 (0.074 g, 0.148 mmol). After 30 min, the blue-
green precipitate that formed was collected by filtration under ambient
conditions. The product was dissolved in CH2Cl2 and chromatographed
on silica gel using 2% MeOH in CH2Cl2 as the eluent. The major
aqua-blue band was collected to yield product 16 (45 mg; 40% based
on 10). Crystallization by slow diffusion of methanol into a CH2Cl2
solution produced 16 as blue needles: 1H NMR (CD2Cl2) δ (ppm) 9.36
a i. (a) Mg(OBu)2, BuOH, 120 °C (b) CF3COOH. ii. M(II)X2 (M
) Ni, Mn; X ) OAc, Cl) DMF, PhCl, 100 °C.
(m, 4H, ar (fused benzo)), 8.11 (m, 4H, ar (fused benzo)), 2.40 (m,
24H, -CH2CH3), 1.37 (m, 36H, -CH2CH3); 31P NMR (CD2Cl2, H3PO4
external reference) δ (ppm) 7.23, 6.82 (JPt-P ) 2704 Hz, JP-P ) 23
Hz); UV/vis(CH2Cl2) λmax 328, 604, 680 nm; FAB-MS 1457 (M +
H+).
Structure Determination for gemini-Porphyrazine 14. Single-
crystal X-ray diffraction data for 14 were collected using a Siemens
P4/RA diffractometer with Cu-KR radiation (graphite monochromator)
using ω-scans. A bronze irridescent rhombahedron of dimensions 0.11
× 0.07 × 0.07 mm was used. Crystallographic data and refinement
parameters are summarized in Table 2. The structure was solved by
direct methods, and all the non-hydrogen atoms of the complex were
refined anisotropically. The o-dichlorobenzene solvent was highly
disordered (three overlapping, partial occupancy orientations were
identified), and only the chlorine atoms of the two major occupancy
optimized molecules were refined anisotropically. Full-matrix least-
squares refinement based on F2 gave R1 ) 0.035, wR2 ) 0.085 for
4294 independent observed reflections [|Fo| > 4σ(|Fo|), 2θ2 120°] and
374 parameters.
Results and Discussion
Synthesis of the gemini-Porphyrazine Complexes. As
illustrated in Scheme 1, preparation of the n ) 2 and 3
peripherally-functionalized porphyrazines begins with the Mg-
(II) template cyclization4 of a pair of maleonitrile derivatives,
1 and 2 in this case, to yield a mixture of macrocycles. To
prepare peripherally metalated porphyrazines this is followed
by purification of the desired protected mixed porphyrazine,
thiolate deprotection, and peripheral chelation of a metal
complex. The cyclization step, unlike the equivalent one in
the synthesis of solitaire-porphyrazines,2 is nonspecific, produc-
ing all six possible porphyrazine products with n ) 0-4
dithioether moieties (inset 1) incorporated into the macrocycle,
including the cis and trans isomers of the n ) 2 porphyrazine.
The use of a pair of dinitriles that have different polarities,5
such as 1 and 2 not only permits separation of porphyrazines

10490 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Sibert et al.
with different n, but further allows for the separation of the cis
and trans geometries of the n ) 2 porphyrazine macrocycles.
The n ) 2 porphyrazines in the trans geometry have no net
dipole and quickly elute from silica gel. In the cis geometry
the dipole moments of the pyrroles of one type add vectorially,
the molecules are relatively polar and, thus, elute from silica
gel more slowly. In general, the greater the disparity (or
opposition) in polarity of the peripheral substituents on the
porphyrazine, the better the chromatographic separation of the
six porphyrazine products and, in particular, of the two n ) 2
isomers.
Commercially available phthalonitrile, 1, was a cheap and
convenient choice as the nonpolar dinitrile for development of
this strategy. The protected dithiomaleonitrile derivative, 2,
where R ) 4-butyloxycarbonylbenzyl (BCB) was chosen as the
polar protecting group because it is easily prepared,2a robust to
the cyclization conditions, readily subject to reductive cleavage,
and enhances the solubility of the porphyrazine products.
Template cyclization of equimolar quantities of 1 and 2 produces
all six porphyrazine products (Scheme 1). Of these, Mg(pc)
was trivially separated from the other five because it is relatively
insoluble in ordinary organic solvents. The remaining Mg-
[porphyrazines] were demetalated with trifluoroacetic acid to
remove the Mg(II) ion, a step that facilitates further separations.
The free-base macrocycles, 3-7, were isolated individually by
radial chromatography. The trans- and cis- protected porphyra-
zines, 5 and 6, were obtained in 5% and 11% yields, respec-
tively; the n ) 3 macrocycle, 4, was obtained in 8% yield.
Subsequently, 4-6 were each treated with Ni(OAc)2 and/or
MnCl2 producing the metalated BCB-protected porphyrazines,
8-12, in nearly quantitative yields.6
Figure 1. 31P NMR spectra of gemini-porphyrazines 14, a, and 16, b,
in CD2Cl2.
Table 3. 31P NMR Chemical Shifts and Coupling Constants for
gemini-Porphyrazines 14 and 16 and Related Complexesa
Reductive debenzylation of 9 and 10, carried out with sodium
metal in liquid ammonia/THF produced, respectively, the cis-
and trans-porphyrazine tetrathiolates, 13 and 15, as dark-blue
solutions in MeOH. The tetrathiolates were then treated
individually with (Et3P)2PtCl2 to yield the trinuclear metal
complexes 14 and 16.
compd
δ (ppm)
JPt-P (Hz)
JP-P (Hz)
14
7.33(s)
4.82(s)
7.32(d)
6.82(d)
19.04(d)
18.35(d)
2708
2749
2704
2704
1577
1500
Pt(PEt3)2(mnt)7a
16
23
23
22.1
22.1
Pt(PPh3)2(ecda)7b
1H NMR Studies of the Unsymmetrical Porphyrazines,
H2[pz(an:b4-n)], 3-7. Proton NMR spectroscopy played a key
role in distinguishing the unsymmetrically substituted porphyra-
zines, 3-7, with the clearest distinction observed in the region
δ ) 4.0-6.0 ppm. The resonances in this region are assigned
to the methylene protons of the BCB-protecting group (-CH2-
C6H4-CO2CH2-(CH2)2CH3) and clearly reveal the molecular
symmetry of a given porphyrazine. For example, the 1H NMR
spectrum of the D4h symmetric porphyrazine 3 (n ) 4) contains
one triplet (-CO2CH2-) and one singlet (S-CH2-C6H4-) at δ )
4.21 and 5.15 ppm, respectively, since all eight BCB moieties
are chemically equivalent. The spectrum of the C2V symmetric
n ) 3 porphyrazine 4 contains a broadened triplet (δ ) 4.21
ppm) and three distinct singlets (δ ) 5.08, 5.13, and 5.24 ppm)
corresponding to the three chemically inequivalent BCB-
protecting groups. The spectrum of the D2h symmetric trans
macrocycle 5 exhibits just one triplet (δ ) 4.16) and one singlet
(δ ) 5.28) because the four BCB groups are equivalent. This
pattern is doubled in the cis macrocycle 6 (C2V) whose spectrum
contains a multiplet (δ ) 4.18) and two distinct singlets (δ )
5.06 and 5.11). Finally, the C2V symmetry of porphyrazine 7
(n ) 1) leads to a spectrum with only one triplet and one
singlet.2a The aromatic region of the proton spectra for 3-7
contain signals from the protons of the para-substituted benzyl
a 31P NMR spectra were taken in dichloromethane-d. Chemical shifts
reported in ppm relative to 5% H3PO4-D2O.
groups and the fused benzo rings. Although these resonances
overlap such that analysis is more difficult, they, nonetheless,
show splitting patterns consistent with the various symmetries
of the macrocycles.
In addition, spectra of each of the free-base porphyrazines,
3-7, contain singlets between -2.0 and -3.5 ppm which are
assigned to the internal pyrrole protons.
31P NMR Studies of the Trimetallic cis- and trans-gemini-
Porphyrazines, 14 and 16. The molecular symmetries of the
cis- and trans-gemini-porphyrazines, 14 and 16, are clearly
manifest in their 31P NMR spectra (Figure 1); the 31P NMR
chemical shifts and coupling constants are listed in Table 3.
The four peripheral phosphine ligands of the D2h-symmetric
trans complex, 14, are all symmetry-equivalent, and, thus, the
31P NMR spectrum contains three peaks centered at 7.33 ppm.
The central line is from [Pt(PEt3)2]2+ moieties containing
isotopes of platinum with I ) 0 (67% abundance). The flanking
doublet results from [195Pt(PEt3)2]2+ 195Pt: I ) 1/2; 33%
(
abundance); the magnitude of the doublet splitting (JPt-P) is 2708
Hz. In contrast, for the C2V-symmetric cis complex 16 the
triethylphosphine ligands in [Pt(PEt3)2]2+ are symmetry-in-
equivalent. Thus, the 31P NMR spectrum of 16 contains
doublets at 6.82 and 7.23 ppm for the two types of phosphorus
atoms associated with the I ) 0 isotopes of platinum; the
magnitude of the coupling constant (JP-P) is 23 Hz. The non-
first-order spectrum arises from the similarity in magnitude of
(5) A similar strategy has been used to prepare an unsymmetrically
substituted phthalocyanine. Linâen, T. G.; Hanack, M. Chem. Ber. 1994,
127, 2051-2057.
(6) Velazquez, C. S.; Fox, G. A.; Broderick, W. E.; Andersen, K.;
Anderson, O. P.; Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc.
1992, 114, 7416-7424.

gemini-Porphyrazines
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10491
Figure 2. X-ray structure of 14 with hydrogen atoms omitted for clarity.
Table 4. Symmetry-Averaged Bond Distances and Bond Angles
for gemini-Porphyrazines 14 and Related Macrocycles
the coupling constant, JP-P, and the chemical shift difference
between the two types of P atoms. The splitting pattern is
repeated in the 195Pt satellites, where JPt-P ) 2704 Hz. The
two types of P atoms in principle should couple differently with
the 195Pt center, but this is not observed in the spectrum of 16.
Apparently, the two coupling constants (JPt-P) are too nearly
equal to be distinguishable. The 31P chemical shifts and
coupling constants are similar to those reported for analogous
square-planar Pt(II) complexes with cis-diphosphine ligands and
both symmetrical and unsymmetrical dithiolene ligands (Table
3).7
X-ray Crystal Structure of trans-gemini-Porphyrazine 14.
X-ray quality crystals of 14, the trans-gemini-porphyrazine that
contains a centrally-bound Ni(II) ion and two [Pt(PEt3)2]2+
moieties coordinated to the periphery in a trans geometry, were
grown from CH2Cl2/dichlorobenzene. The structure is shown
in Figure 2. Table 4 presents selected symmetry averaged bond
distances and bond angles for 14, M(pc),8 and Ni[pz(d)4]9 where
M ) Ni, L ) (1,1′-diphenylphosphino)ethane. All bond lengths
and angles within the two distinct types of pyrroles in 14 are
nearly equivalent with the exception of the CR-Npyrrole-CR bond
angles. The angles in pyrroles with the fused benzo rings
(106.8(5)°) are larger than those in the sulfur-appended pyrroles
(104.8(5)°). They are consistent with larger CR-Npyrrole-CR
bond angles reported for M(pc) rather than those in Ni[pz(d)4].
The porphyrazine core is planar to within 0.007 Å and contains
a centrally-bound Ni(II) ion and two bis(triethylphosphine)-
platinum moieties coordinated to the periphery in a trans
geometry. The nickel atom lies on a crystallographic center of
symmetry and the coordinated Ni-N bond lengths are 1.894-
(5) Å and 1.879(5) Å to N(1) and N(15), respectively. The
deviations from square-planar geometry are negligible; the
M(pc)a[Ni(dppe)]4[Ni(pzot)]b
Ni-Np
CR-Np
CR-Câ
Câ-Câ
CR-Nm
Câ-Cγ
Cγ-Cδ
Cδ-Cδ
Câ-S
1.87(3)
1.41(1)
1.46(3)
1.36(1)
1.34(3)
1.71(1)
3.25
S‚‚‚S
Bond Angles (deg)c
Câ-Câ-S
124.0(5)
129.2(5)
106.6(5)
105.8(5)
127.7(5)
120.3(5)
110.6(5)
121.7(6)
132.7(6)
120.9(6)
117.6(6)
121.5(7)
90.0(2)
123.5(5)
129.5(13)
107.0(8)
103.5(7)
126.3(12)
120.8(19)
110.0(14)
122.8(17)
CR-Câ-S
CR-Câ-Câ
CR-Np-CR
Nm-Ca-Np
CR-Nm-CR
Np-CR-Câ
Nm-CR-Câ
CR-Câ-Cγ
Câ-Câ-Cγ
Câ-Cγ-Cδ
Cγ-Cδ-Cδ
Np-Ni-Np
Np-Ni-Np′
106.7(3)
108.1(8)
127.7(1)
123.2(5)
109.3(4)
123.0(2)
132.2(2)
121.3(2)
117.3(2)
121.6(1)
90
90.0(17)
178.1(1)
180.0(1)
180
a Reference 8. b Reference 9. c Number in parentheses is the standard
deviation in the last one or two digits of the values used in the symmetry
average.
N-Ni-N angles are 89.6(2) and 90.04(2)°. The planarity of
the central core extends to include both thiolate sulfur atoms
and the platinum centers, the maximum deviation from planarity
being 0.08 Å for one of the sulfur atoms. As the structure is
centrosymmetric there is only one independent Pt(II) position.
The peripheral platinum(II) ions are coordinated by the P atoms
of the two triethylphosphines and two macrocyclic S atoms in
a roughly square-planar geometry. The P-Pt-P angle is
noticeably enlarged at 97.47(6)° as a consequence of the bulky
triethylphosphine substituents. The bite of the dithiolate moiety
appears to be optimal, the S-Pt-S angle being 89.86(6)°. The
Pt-P and Pt-S bond lengths (Pt-P(1) 2.286 (2); Pt-P(2) 2.293
(3); Pt-S(1) 2.333(3); Pt-S(2) 2.338(2) Å) are similar to those
reported for related Pt(II) complexes having trans phosphorus
and sulfur ligands.10
(7) (a) Fitzmaurice, J. C.; Slawin, A. M.; Williams, D. J.; Woollins, J.
D.; Lindsay, A. J. Polyhedron 1990, 9, 1561-1565. (b) Bevilacqua, J.
M.; Zuleta, J. A.; Eisenberg, R. Inorg. Chem. 1994, 33, 258-266.
(8) Schramm, C. J.; Scaringe, R. P.; Stojakovic, D. R.; Hoffman, B. M.;
Ibers, J. A.; Marks, T. J. J. Am. Chem. Soc. 1980, 102, 6702-6713.
(9) Velazquez, C. S.; Baumann, T. F.; Olmstead, M. M.; Hope, H.;
Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1993, 115, 9997-
10003.
(10) (a) Bevilacqua, J. M.; Eisenberg, R. Inorg. Chem. 1994, 33, 2913-
2923. (b) Chan, L. T.; Chen, H.-W.; Fackler, J. P.; Masters, A. F.; Pan,
W.-H. Inorg. Chem. 1982, 21, 4291-4295. (c) Weigand, W.; Bosl, G.;
Polborn, K. Chem. Ber. 1990, 123, 1339-1342. (d) Cavell, K. J.; Jin, H.;
Skelton, B. W.; White, A. W. J. Chem. Soc., Dalton Trans. 1992, 2923-
2930.

10492 J. Am. Chem. Soc., Vol. 118, No. 43, 1996
Sibert et al.
Figure 3. Packing diagram for complex 14.
The intramolecular Ni‚‚‚Pt and Pt‚‚‚Pt distances are 7.18 and
14.36 Å, respectively. The nearest intermolecular Ni‚‚‚Pt and
Pt‚‚‚Pt distances are shorter at 6.66 and 6.29 Å, respectively.
The macrocycles pack in a slipped stack, “herring-bone” fashion
(Figure 3), similar to that observed for Ni-phthalocyanine.11
Here, however, the distance between neighboring parallel-
aligned porphyrazines is much larger, the Ni‚‚‚Ni separation
being 13.01 Å (i.e., a lattice translation in the crystallographic
a direction). The interplanar separation is 3.33 Å, but there is
no π-π overlap. It must therefore be concluded that the bulky
triethylphosphine ligands disrupt potential intermolecular π-π
stacking forces.
Electronic Absorption Spectroscopy. Porphyrazines, like
phthalocyanines, typically show an intense B (Soret) band at λ
<400 nm and a Q band that has its principal absorption at λ >
600 nm, with additional vibronic structure to shorter wave-
length.12 As seen with unsymmetrically-substituted phthalo-
cyanines,5 peripheral functionalization of a porphyrazine can
significantly affect the electronic structure of the porphyrazine
π-system, with this being most clearly seen in perturbations of
the Q band. Gouterman’s highly simplified four-orbital model13
for porphyrinic macrocycles provides a qualitative description
of the optical spectra of the M[pz(An:B4-n)] compounds (Figure
4). In a D4h-symmetric macrocycle such as Ni(pc), the LUMO
is doubly degenerate (eg) and to a first approximation the Q
and B bands are associated with transitions from the two highest
occupied MOs (a1u, a2u) into the LUMO. This pattern is doubled
in the lowered symmetry (D4h to D2h) of H2(pc) with the splitting
into two “0-0” (Qx,Qy) bands by 710 cm-1 being particularly
clear.14 The reduction in symmetry of the macrocycle removes
the degeneracy of the eg LUMO and gives rise to a split Q band.
Likewise, visible spectra of the previously reported n ) 1
porphyrazine, Ni[pz(a:b3)], show a Q band with slightly split
profile, presumably due to the lowered symmetry of the
macrocyclic core from D4h to C2V.2 Similar effects are seen in
the optical spectra of the C2V-symmetric n ) 3 porphyrazine,
Figure 4. Qualitative orbital energy diagram for the Q and B (Soret)
bands of the Ni[pz(an:b4-n)] porphyrazines, n ) 0-4, showing the effect
that the symmetry of the conjugated porphyrazine core has on the
electronic structure of the macrocycle.
8, whose optical spectrum resembles that of the C2V-symmetric
n ) 1 porphyrazine, but with the transitions clearly broadened,
due probably to the presence of underlying n to π* transitions
from the lone pairs on the six peripheral sulfur atoms (Figure
5).
In the case of the n ) 2 porphyrazines, the spectra of the cis
and trans isomers are markedly different. Considering the D2h
symmetric trans-porphyrazines, splitting of the LUMOs (Figure
4) by the different substituents in the “x” and “y” directions of
the porphyrazine core leads to large splittings of the Q band in
the M[trans-pz(a2:b2)] porphyrazines, 5 (M ) 2H), 9 (M ) Ni),
and 11 (M ) Mn),15 with quite distinct Qx (605 nm for 9; 654
nm for 11) and Qy (722 nm for 9; 780 nm for 11) transitions,
Figure 5. The splittings of ∆E ) 2680 cm-1 for 9 and 2470
cm-1 for 11 are similar to that recently reported for a trans-
substituted porphyrazine3a and nearly four times larger than those
for H2 (pc) or for unsymmetrically-substituted phthalocyanines.3b,5
The reduction of symmetry is accentuated in the free-base trans-
macrocycle, 5, where the splitting of the Q band is 3560 cm-1
(transitions at 590 and 747 nm).
(11) Robertson, J. M.; Woodward, I. J. Chem. Soc. 1937, 219-230.
(12) Stillman, M. J.; Nyokong, T. In Phthalocyanines: Properties and
Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH: New York, 1989;
Chapter 3.
(13) (a) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. III, pp 1-165. (b) Mack, J.; Kirkby, S.;
Ough, E. A.; Stillman, M. J. Inorg. Chem. 1992, 31, 1717-1719. (c) Cory,
M. G.; Hirose, H.; Zerner, M. C. Inorg. Chem. 1995, 34, 2969-2979. (d)
Liang, X. L.; Flores, S.; Ellis, D. E.; Hoffman, B. M.; Musselman, R. L. J.
Chem. Phys. 1991, 95, 403-417.
(14) Lever, A. B. P. AdV. Inorg. Chem. Radiochem. 1965, 7, 27-114.
(15) We ignore the axial ligand to Mn(III) in discussing symmetry.

gemini-Porphyrazines
J. Am. Chem. Soc., Vol. 118, No. 43, 1996 10493
Table 5. Comparison of Half-Wave Potentialsa of the Ring
Reductions (RR) for the Porphyrazine Series. H2[pz(an:b4-n)]
macrocycle
E1/2 (RR1) (V)
E1/2 (RR2) (V)
H2(pc)b
7, n ) 1
-1.20
-1.2
-1.0
-0.8
-0.8
-0.8
-1.54
-1.6
-1.4
-1.2
-1.2
-1.2
6, n ) 2 cis
5, n ) 2 trans
4, n ) 3
3, n ) 4
a Half-wave potentials are reported versus (Fc+/Fc) couple. Elec-
trochemical experiments for 3-7 were performed in distilled CH2Cl2
with 0.1 M TBAPF6 as the electrolyte using a Pt working electrode
and a Ag/AgCl reference electrode. b Reference 17.
electronic structure of the porphyrazine, the electrochemistry
of the free-base macrocycles 3-7 was investigated. Phthalo-
cyanines typically show two reversible ring reductions but no
reversible oxidation processes. Each macrocycle in this series
also showed two reversible waves that can be attributed to ring-
centered reductions (Table 5). A comparison of the potentials
of H2(pc)17 with those of the thioether-appended porphyrazines
3-7 shows that both H2(pc) and H2[pz(a:b3)], 7, have a similar
pair of reduction potentials at ∼ -1.2 and ∼ -1.6 V versus
the Fc+/Fc couple, while the n ) 2 trans, n ) 3, and n ) 4
compounds (5, 4, and 3, respectively) all show a pair of
reductions at -0.8 and -1.2 V. Only the cis-macrocycle, 6,
has intermediate reduction potentials of -1.0 and -1.4 V.
Within the limit (+1.5 V) allowed by the solvent (CH2Cl2), no
oxidation processes associated with the ring were observed.
Finally, no obvious correlation between the reduction potentials
of the thioether-appended porphyrazines and their respective
electronic spectra was observed.
Figure 5. Electronic absorption spectra (in CH2Cl2) for the unsym-
metrical 2H-, 4-6, and Ni-porphyrazines, 8-10.
In contrast, the C2V-symmetric metalated n ) 2 cis-porphyra-
zine isomers, 10 and 12, show only a single Q band at 660
(Figure 5) and 712 nm, respectively, despite the fact that there
are no doubly-degenerate representations in C2V.16 This apparent
anomaly also can be explained within the four-orbital picture;
the substituents along the “x” and “y” directions are, in fact,
the same, so the LUMO remains accidentally degenerate (Figure
4), and there should be only a single Q band, as observed. Thus,
this latter case is intriguingly equivalent to that seen in D4h
symmetric macrocycles. Not surprisingly, the metal-free cis-
porphyrazine, 6, shows a split Q-band. The further lowering
of molecular symmetry of this macrocycle has removed the
accidental degeneracy of the LUMO by the same amount as
for H2 (pc), ∼700 cm-1 (peaks at 652 and 692 nm).
Conclusion
We have presented the synthesis and characterization of the
binuclear solitaire porphyrazines2 and of the trinuclear cis- and
trans-gemini-porphyrazines. The preparation of the gemini
compounds involves a general synthetic strategy that employs
relatively inexpensive or easily prepared starting materials. The
use of a dinitrile pair with disparate polarities allows for the
selective purification of each porphyrazine M[pz(an:b4-n)], n
) 0-4, including the cis and trans n ) 2 isomers. The gemini-
porphyrazine, 14, is the first structurally-characterized por-
phyrazine or phthalocyanine with a trans-type substitution
pattern. The different molecular symmetries of the n ) 1-4
protected precursors, 3-12, have a profound effect on the
electronic structure of each macrocycle. The approach described
here allows for the preparation of a wide number of novel
gemini-porphyrazines whose properties will be the subject of
future reports.
Interestingly, upon coordination of the peripheral metal ions,
both the cis- and trans-gemini-porphyrazines, 14 and 16, show
spectra similar to that of 6, with a single Q band and additional
vibronic features. The different molecular geometries of each
isomer are no longer observable in their optical spectra. It thus
appears that the peripheral metal-ion chelates interact with the
porphyrazine ring to an extent similar to that of a fused benzene
ring, and the LUMO remains accidentally degenerate, as it is
by symmetry in the D4h symmetric case. This same effect was
seen in the optical spectra of the solitaire porphyrazine
complexes.2
Acknowledgment. This work was supported by the National
Science Foundation (CHE-9408561) and the Wolfson Founda-
tion (U.K.) for equipment. J.W.S. thanks the National Institutes
of Health (GM14876) for their support.
Supporting Information Available: Tables of elemental
analyses, crystal data and structure refinement, atomic coordi-
nates and equivalent isotropic displacement parameters, bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates (8 pages). See any current masthead page
for ordering and Internet access instructions.
Electrochemistry of the H2[pz(an:b4-n)] Series. To further
probe the effect of ring substituents and their symmetry on the
(16) Cotton, F. A. Chemical Applications of Group Theory; J. Wiley &
Sons: New York, 1990; Appendix IIA.
(17) Bottomley, L. A.; Chiou, W. J. H. J. Electroanal. Chem. 1986, 198,
331-346.
JA961912X