Phenanthroline-appended porphyrazines: Synthesis and conversion into solitaire Ru(II) complexes

Article abstract of DOI:10.1016/S0020-1693(01)00325-5

Unsymmetrical porphyrazines (tetraazaporphyrins) bearing a single bidentate phenanthroline chelating group M[pz(t-butylphenyl)₆phen] have been prepared by the base-catalyzed cross condensation of 3,4-bis(4-tert-butylphenyl)pyrroline-2,5-diimine (in excess) with 6,7-dicyanodipyridoquinoxaline. Treatment of these centrally metalated (M = Mg, Zn) ligands with various Ru(II) salts has yielded several bimetallic complexes including the first coordinatively linked porphyrazine trimer. The optical properties of these complexes are shown to be a function of the additional ligands surrounding the asymmetric ruthenium center.

Full text of DOI:10.1016/S0020-1693(01)00325-5

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Inorganica Chimica Acta 317 (2001) 143–148
Phenanthroline-appended porphyrazines: synthesis and conversion
into solitaire Ru(II) complexes
Antonio Garrido Montalban a, Efstathia G. Sakellariou a, Eric Riguet a,
Quentin J. McCubbin a, Anthony G.M. Barrett a,*1, Brian M. Hoffman b,*2
a Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London SW 7 2AY, UK
b Department of Chemistry, Northwestern Uni6ersity, E6anston, IL 60208, USA
Received 6 October 2000; accepted 10 January 2001
Abstract
Unsymmetrical porphyrazines (tetraazaporphyrins) bearing a single bidentate phenanthroline chelating group M[pz(t-
butylphenyl)6phen] have been prepared by the base-catalyzed cross condensation of 3,4-bis(4-tert-butylphenyl)pyrroline-2,5-di-
imine (in excess) with 6,7-dicyanodipyridoquinoxaline. Treatment of these centrally metalated (M=Mg, Zn) ligands with various
Ru(II) salts has yielded several bimetallic complexes including the first coordinatively linked porphyrazine trimer. The optical
properties of these complexes are shown to be a function of the additional ligands surrounding the asymmetric ruthenium center.
© 2001 Elsevier Science B.V. All rights reserved.
Keywords: Porphyrinoid complexes; Phenanthroline complexes; Ruthenium complexes
pyrrole rings, can be synthesized with n=1 to 4.
Although the peripheral A moieties generally involve
heteroatoms (S, N, O) appended to the porphyrazine
ring and are designed in order to bind an exocyclic
metal ion, the B groups are intended to confer a desired
solubility. Unsymmetrical porphyrazines having a sin-
gle peripheral metal-chelation site form complexes that
are designated as solitaire-porphyrazines [6]. In such
systems the metal in the central macrocyclic cavity and
periphery can be chosen independently [7], thus giving
rise to physical properties not seen in the pz or metal
fragments alone [8]. Another way to assemble multi-
metallic arrays is to fuse an aromatic ligand onto the
porphyrazine fragment. The 1,10-phenanthroline nu-
cleus, a well-known metal-chelating agent, is ideally
suited for the incorporation into multichromophore
systems [9]. Herein we report the synthesis and optical
properties of porphyrazines in which a 1,10-phenan-
throline is fused directly onto the b-positions of the
macrocycle, thus extending the p conjugation beyond
the tetrapyrrolic structure. In addition, we demonstrate
that, besides the metal in the central macrocyclic cavity,
these novel ligands can coordinate a metal ion at the
peripheral phenanthroline unit, including the first te-
1. Introduction
Coordination compounds prepared from ligand sys-
tems containing photo- and/or redox-active units allow
the possibility of long distance delocalization of elec-
tron density and metal–metal interactions between
multiple metal centers [1]. One strategy for the design
of such architectures is based on porphyrinic macrocy-
cles, and, in most of the systems studied so far, the
porphyrins are covalently linked to external coordina-
tion sites without any extended p conjugation [2]. Our
efforts in this area utilize the tetraazaporphyrin (por-
phyrazine, pz) ligand as a structural motif for the rigid
organization of the metal centers, and we have devel-
oped a new family of tetraaza macrocycles that have
metal-binding sulfur [3], nitrogen [4], or oxygen atoms
[5] attached to the pz periphery.
Peripherally functionalized porphyrazines of the form
M[pz(An:B4−n)], in which A and B symbolize func-
tional groups fused directly to the b-positions of the
1 *Corresponding author. Tel.: +44-207-594 5766; fax: +44-207-
594 5805; e-mail: agmb@ic.ac.uk
2 *Corresponding author.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00325-5

144
A.G. Montalban et al. / Inorganica Chimica Acta 317 (2001) 143–148
tranuclear metal-linked porphyrazine trimer via mutual
chelation of a ruthenium(II) ion.
\350°C; Rf 0.17 (CHCl3:MeOH 9:1); IR (CH2Cl2)
1731, 1606, 1488, 1460, 1366, 1266, 984, 778 cm−1
;
UV–Vis (CH2Cl2) umax (log m) 381 (4.45), 487 (3.61),
1
649 (4.20), 682 (4.15) nm; H NMR (300 MHz, pyri-
2. Experimental
dine-d5) l 1.50 (s, 36H), 1.55 (s, 18H), 7.81 (d, J=
8.4 Hz, 4H), 7.84 (d, J=8.7 Hz, 4H), 7.98 (d,
J=8.4 Hz, 4H), 8.02 (dd, J=4.7 and 7.4 Hz, 2H), 8.75
(d, J=8.4 Hz, 4H), 8.82 (d, J=8.4 Hz, 4H), 8.93 (d,
J=8.7 Hz, 4H), 9.50 (m, 2H), 10.36 (d, J=7.4 Hz,
2.1. General procedures
All reactions were conducted in oven- or flame-dried
glassware. Solvents used for reactions were distilled
prior to use: DMF [predried over BaO, distilled from
alumina (activity I)]; butanol (from Mg); quinoline
(from Zn). 3,4-bis(4-tert-Butylphenyl)pyrroline-2,5-di-
imine (8) [10], 1,10-phenanthroline-5,6-dione (3) [12]
and cis-RuCl2(bipy*)2 (13) [15] were synthesized ac-
cording to published procedures. All other reagents
were used as commercially supplied. TLC was carried
out on E. Merck precoated silica gel 60 F254 plates,
which were visualized using UV radiation (254 nm).
Chromatography refers to flash chromatography on E.
Merck silica gel 60, 40–60 mm or deactivated neutral
aluminum oxide (5% H2O), ꢀ150 mm (eluants are
given in parentheses). Size exclusion chromatography
was performed on Bio-Beads SX3 or Sephadex LH20.
2H); MS (FAB) m/z 1334 [M+ ]; HRMS (FAB) calc.
’
for C88H86MgN12: [M+2H]+, 1334.6949; found: [M+
2H]+, 1334.7082. Anal. Found: C, 76.17; H, 6.42; N,
11.79. Calc. for C88H84MgN12·3H2O: C, 76.15; H, 6.53;
N, 12.11%.
2.4. Zn[pz(t-butylphenyl)6 phen] (6)
A mixture of dicnq 4 (0.14 g, 0.5 mmol), pyrroline 8
(0.54 g, 1.5 mmol), Zn(OAc)2 (0.27 g, 1.5 mmol) and
quinoline (5 ml) was heated rapidly to 170°C using a
heat gun under N2. At the appearance of an intense
green color (ꢀ5 min) the reaction mixture was allowed
to cool, diluted with CH2Cl2 (10 ml) and washed suc-
cessively with 1 M HCl (3×15 ml), aqueous NaHCO3
(3×15 ml) and H2O (3×15 ml). The organic layer was
dried (MgSO4), rotary evaporated and the residue chro-
matographed on silica (CHCl3; CHCl3:MeOH 9:1) to
give Zn–porphyrazine 6 (0.13 g, 19%) as a dark-green
solid: m.p. \350°C; Rf 0.34 (CHCl3:MeOH 9:1); IR
(CH2Cl2) 1733, 1657, 1391, 1365, 1266, 1104, 1012,
755 cm−1; UV–Vis (CH2Cl2) umax (log m) 379 (4.51),
488 (3.72), 652 (4.23), 665 (4.30) nm; 1H NMR
(270 MHz, pyridine-d5) l 1.51 (s, 36H), 1.56 (s, 18H),
7.82 (d, J=8.4 Hz, 4H), 7.84 (d, J=8.7 Hz, 4H), 7.97
(d, J=8.4 Hz, 4H), 8.04 (dd, J=4.1 and 8.2 Hz, 2H),
8.78 (d, J=8.4 Hz, 4H), 8.85 (d, J=8.4 Hz, 4H), 8.97
(d, J=8.7 Hz, 4H), 9.53 (dd, J=2.0 and 4.1 Hz, 2H),
10.36 (dd, J=2.0 and 8.2 Hz, 2H); MS (FAB) m/z
2.2. 6,7-Dicyanodipyridoquinoxaline (dicnq) (4)
1,10-Phenanthroline-5,6-dione (3) (5.0 g, 23.8 mmol),
diaminomaleonitrile (2) (2.57 g, 23.8 mmol), acetic acid
(five drops) and EtOH (300 ml) were heated to reflux
for 2 h. The mixture was allowed to cool and the
resultant precipitate filtered and washed with EtOH to
give dinitrile 4 (3.07 g, 46%) as orange–brown needles:
m.p. 335°C (EtOH); IR (Nujol) 2240, 1584, 1505, 1262,
1222, 1141, 1074 cm−1; H NMR (300 MHz, DMSO-
1
d6) l 8.05 (dd, J=4.4 and 8.2 Hz, 2H), 9.36 (dd,
J=1.7 and 4.4 Hz, 2H), 9.42 (dd, J=1.7 and 8.2 Hz,
2H); 13C NMR (75 MHz, DMSO-d6) l 115.3, 125.2,
125.8, 132.6, 134.3, 141.7, 143.9, 148.7, 154.8; MS (EI)
1375 [M+ ]; HRMS (FAB) calc. for C88H86N12Zn:
’
m/z 282 (M+·); HRMS (EI) calc. for C16H6N6: [M+ ],
[M+2H]+, 1374.6390; found: [M+2H]+, 1374.6316.
Anal. Found: C, 73.78; H, 5.94; N, 11.15. Calc. for
C88H84N12Zn·3H2O: C, 74.02; H, 6.36; N, 11.78%.
’
282.0654; found: [M+ ], 282.0634. Anal. Found: C,
’
67.83; H, 2.07; N, 29.58. Calc. for C16H6N6: C, 68.08;
H, 2.14; N, 29.77%.
2.5. [(Zn[pz(t-butylphenyl)6 phen])Ru(Cp)(PPh3)]Cl (11)
2.3. Mg[pz(t-butylphenyl)6 phen] (5)
RuCl(Cp)(PPh3)2 (9) (42 mg, 58 mmol) was added to
porphyrazine 6 (40 mg, 29 mmol) in DMF (4 ml) and
the mixture heated at 80°C for 1 h under N2. The
mixture was allowed to cool and rotary evaporated and
the dark-green residue was dissolved in CH2Cl2 (20 ml)
and filtered. Rotary evaporation and chromatography
on alumina (CHCl3:MeOH 9:1) followed by gel filtra-
tion (Sephadex, CHCl3) gave complex 11 (29 mg, 55%)
A mixture of butanol (30 ml), Mg (0.12 g, 5 mmol)
and I2 (one small crystal) was heated to reflux for 12 h
under N2. The suspension was cooled and dicnq 4
(0.28 g, 1.0 mmol) followed by pyrroline 8 (1.08 g,
3.0 mmol) were added and the mixture further heated at
reflux for 48 h. The deep-green suspension was allowed
to cool, filtered (Celite) and the solids washed with
CH2Cl2. Rotary evaporation and chromatography on
silica (CHCl3; CHCl3:MeOH 9:1) gave Mg–por-
phyrazine 5 (0.3 g, 23%) as a dark-green solid: m.p.
as
a dark-green solid: m.p. \350°C; Rf 0.15
(CHCl3:MeOH 9:1); IR (CH2Cl2) 1606, 1480, 1366,
1266, 1139, 1104, 983, 841 cm−1; UV–Vis (CH2Cl2)

A.G. Montalban et al. / Inorganica Chimica Acta 317 (2001) 143–148
145
umax (log m) 399 (4.66), 662 (4.77) nm; 1H NMR
(270 MHz, pyridine-d5) l 1.47 (s, 18H), 1.50 (s, 36H),
5.15 (s, 5H), 7.01–7.19 (m, 15H), 7.78 (d, J=8.5 Hz,
4H), 7.80 (d, J=8.3 Hz, 4H), 7.86 (d, J=8.3 Hz, 4H),
8.00 (m, 2H), 8.72 (d, J=8.5 Hz, 4H), 8.76 (d, J=
8.3 Hz, 4H), 8.90 (d, J=8.3 Hz, 4H), 10.00 (m, 2H),
10.10 (m, 2H); MS (FAB) m/z 1804 [M−Cl]+. Anal.
Found: C, 72.62; H, 5.73; N, 9.50. Calc. for
(d, J=8.2 Hz, 4H), 7.82 (d, J=8.2 Hz, 4H), 8.03 (dd,
J=5.7 and 8.2 Hz, 2H), 8.18 (d, J=5.9 Hz, 2H), 8.28
(d, J=6.2 Hz, 2H), 8.72 (d, J=8.2 Hz, 4H), 8.77 (d,
J=8.2 Hz, 4H), 8.84 (d, J=8.4 Hz, 4H), 9.73 (d, J=
5.7 Hz, 4H), 10.24 (d, J=8.2 Hz, 2H); MS (FAB) m/z
1972 [M−2Cl]+. HRMS (FT-ICR) calc. for
C124H132MgN16Ru: [M−2Cl]2+
[M−2Cl]2+, 985.4807.
,
985.4858; found:
C111H104ClN12PRuZn: C, 72.47; H, 5.70; N, 9.14%.
2.8. [(Zn[pz(t-butylphenyl)6 phen])Ru(bpy*)2]Cl2 (15)
2.6. [(Zn[pz(t-butylphenyl)6 phen])Ru(p-cymene)Cl]Cl
(12)
Treatment of porphyrazine 6 (40.0 mg, 29.0 mmol)
under the same reaction conditions as above gave
complex 15 (6.7 mg, 11%) as a dark-green solid: m.p.
\350°C; Rf 0.06 (CHCl3:MeOH 9:1); IR (CH2Cl2)
1739, 1612, 1481, 1368, 1264, 1245, 1138, 1105, 982,
842 cm−1; UV–Vis (CH2Cl2) umax (log m) 399 (4.77),
[RuCl(m2-Cl)(p-cymene)]2 (10) (22 mg, 36.3 mmol)
was added to porphyrazine 6 (25 mg, 18.1 mmol) in
DMF (4 ml), the mixture heated at 80°C for 5 h under
N2, cooled, rotary evaporated and the dark-green
residue taken up in CH2Cl2 (20 ml) and filtered. Ro-
tary evaporation and chromatography on alumina
(CHCl3:MeOH 9:1) followed by gel filtration (Sep-
hadex, CHCl3) gave complex 12 (3.4 mg, 11%) as a
1
460sh, 673 (4.88) nm; H NMR (270 MHz, CDCl3) l
1.31 (s, 18H), 1.37 (s, 18H), 1.42 (s, 18H), 1.50 (s,
36H), 7.37 (d, J=7.9 Hz, 2H), 7.45 (d, J=6.9 Hz,
2H), 7.77 (d, J=8.2 Hz, 4H), 7.79 (d, J=8.2 Hz, 4H),
7.81 (d, J=8.2 Hz, 4H), 8.03 (dd, J=5.4 and 8.1 Hz,
2H), 8.16 (d, J=5.4 Hz, 2H), 8.26 (d, J=5.7 Hz, 2H),
8.71 (d, J=8.2 Hz, 4H), 8.75 (d, J=8.2 Hz, 4H), 8.84
(d, J=8.2 Hz, 4H), 9.76 (br s, 4H), 10.25 (d, J=
8.1 Hz, 2H); MS (FAB) m/z 2013 [M−2Cl]+. HRMS
dark-green
solid:
m.p.
\350°C;
Rf
0.20
(CHCl3:MeOH 9:1); IR (CH2Cl2) 1731, 1606, 1489,
1366, 1264, 987, 779 cm−1; UV–Vis (CH2Cl2) umax
1
(log m) 390 (4.97), 668 (4.95) nm; H NMR (270 MHz,
pyridine-d5) l 1.06 (d, J=6.8 Hz, 6H), 1.45 (s, 18H),
1.50 (s, 36H), 2.36 (s, 3H), 2.85 (h, J=6.8 Hz, 1H),
6.32 (d, J=6.2 Hz, 2H), 6.54 (d, J=6.2 Hz, 2H), 7.77
(d, J=8.4 Hz, 4H), 7.80 (d, J=8.4 Hz, 4H), 7.85 (d,
J=8.4 Hz, 4H), 8.38 (dd, J=4.9 and 8.4 Hz, 2H),
8.72 (d, J=8.4 Hz, 4H), 8.76 (d, J=8.4 Hz, 4H), 8.87
(d, J=8.4 Hz, 4H), 10.30 (d, J=8.4 Hz, 2H), 10.35
(d, J=4.9 Hz, 2H); MS (FAB) m/z 1646 [M−Cl]+.
Anal. Found: C, 67.95; H, 6.12. Calc. for
C98H98Cl2N12RuZn·3H2O: C, 67.82; H, 6.12%.
(FT-ICR) calc. for C124H132N16RuZn: [M−2Cl]2+
1005.4578; found: [M−2Cl]2+, 1005.4533.
,
2.9. (Mg[pz(t-butylphenyl)6 phen])3RuCl2 (16)
RuCl3·H2O (4.0 mg, 19.2 mmol), LiCl (2.5 mg,
57.6 mmol) and EtOH (five drops) were added to a
solution of porphyrazine 5 (90.0 mg, 67.4 mmol) in
DMF (5 ml), and the mixture heated at reflux for 10 h
under N2. The solution was allowed to cool and the
dark-green precipitate that formed upon the addition
of H2O (13 ml) filtered and washed with H2O. Chro-
matography of the crude residue on alumina (CH2Cl2;
CHCl3:MeOH 9:1) followed by gel filtration (Bio-
Beads, CH2Cl2 then Sephadex, CHCl3) gave com-
pound 16 (80.0 mg, 56%) as a dark-green solid: m.p.
\350°C; Rf 0.40 (CHCl3:MeOH 5.7:1); IR (CH2Cl2)
2.7. [(Mg[pz(t-butylphenyl)6 phen])Ru(bpy*)2]Cl2 (14)
cis-RuCl2(bpy*)2
(13)
(41.0 mg,
58.0 mmol)
(bipy*=4,4%-di-tert-butyl-2,2%-bipyridine) was added to
porphyrazine 5 (40.0 mg, 29.9 mmol) in DMF (4 ml),
and the mixture heated at reflux for 4 h under N2. The
mixture was allowed to cool, rotary evaporated and
the dark-green residue was dissolved in CH2Cl2 (20 ml)
and filtered. Rotary evaporation and chromatography
on alumina (CH2Cl2; CHCl3:MeOH 9:1) followed by
gel filtration (Sephadex, CHCl3) gave complex 14
(19.2 mg, 31%) as a dark-green solid: m.p. \350°C;
Rf 0.23 (CHCl3:MeOH 5.7:1); IR (CH2Cl2) 1726, 1612,
1605, 1478, 1366, 1245, 1138, 1104, 986, 841 cm−1
;
UV–Vis (CH2Cl2) umax (log m) 385 (5.32), 459 (4.75),
673 (5.33) nm; 1H NMR (270 MHz, pyridine-d5) l
1.49 (s, 54H), 1.50 (s, 108H), 7.74–7.90 (m, 36H), 8.28
(m, 6H), 8.75 (t, J=7.9 Hz, 24H), 8.85 (d, J=7.7 Hz,
12H), 9.14 (d, J=4.0 Hz, 6H), 10.42 (d, J=8.2 Hz,
6H); HRMS (FT-ICR) calc. for C264H253Mg3N36Ru:
1480, 1368, 1264, 1245, 1137, 1105, 983, 842 cm−1
;
UV–Vis (CH2Cl2) umax (log m) 390 (4.88), 460sh, 672
1
(4.89) nm; H NMR (270 MHz, pyridine-d5) l 1.31 (s,
[M+H−2Cl]3+, 1366.9833; found: [M+H−2Cl]3+
,
18H), 1.37 (s, 18H), 1.43 (s, 18H), 1.50 (s, 18H), 1.51
(s, 18H), 7.38 (dd, J=1.5 and 6.2 Hz, 2H), 7.46 (dd,
J=1.5 and 5.9 Hz, 2H), 7.77 (d, J=8.4 Hz, 4H), 7.79
1367.0006. Anal. Found: C, 76.06; H, 6.24; N, 11.99.
Calc. for C264H252Cl2Mg3N36Ru: C, 75.97; H, 6.08; N,
12.08%.

146
A.G. Montalban et al. / Inorganica Chimica Acta 317 (2001) 143–148
3. Results and discussion
cially available diaminomaleonitrile 2 (Scheme 1). Al-
though dicnq failed (decomposition under the
4
reaction conditions) to undergo macrocyclization on its
own (presumably due to steric reasons), co-cyclization
with an excess of diimine 8, using magnesium butoxide
in refluxing butanol or zinc acetate in quinoline, gave
the unsymmetrical porphyrazines 5 and 6 respectively,
along with the octa(tert-butylphenyl) porphyrazine 7
(Scheme 1). Owing to the different polarities of por-
phyrazines 5 (23%) and 6 (19%) when compared with
byproduct 7, separation was easily achieved via chro-
matography. However, their proton NMR spectra in
CDCl3 displayed very broad signals. This broadening
could be overcome by recording the NMR spectra in
pyridine-d5. Both, 5 and 6, show six well-resolved dou-
blets in the aromatic region (attributable to the three
different t-butylphenyl groups) and three resonances
associated with the phenanthroline part of the por-
phyrazines. In addition, ligands 5 and 6 seem to retain
residual water (despite heating under vacuum), as indi-
cated from their elemental analyses and proton NMR
spectra, very likely directly coordinated to the central
metals and phenanthroline part of the macrocycles via
hydrogen bonding [13]. All other spectroscopic data
were fully consistent with the proposed structures.
3.1. Synthesis of phenanthroline-appended
porphyrazines
As we have already shown, unsymmetrical por-
phyrazines of the form M[pz(A:B3)] 1 (Chart 1) are best
obtained by using one of the two maleonitrile deriva-
tives in excess (B) [6].
Chart 1.
3,4-bis(4-tert-Butylphenyl)pyrroline-2,5-diimine
(8),
used previously as the B component and found to
enhance the solubility of the resulting porphyrazines
and complexes thereof [10], proved suitable for this
study (vide infra). The required 1,10-phenanthroline-
appended dinitrile 4 (dicnq=dicyanodipyridoquinoxa-
line) [11], was obtained via condensation of
1,10-phenanthroline-5,6-dione (3) [12] with commer-
3.2. Peripheral metalation
In order to probe the coordination properties of our
two novel ligands 5 and 6, we decided to synthesize
diamagnetic low spin [(t2g)6] Ru(II) complexes. Oligonu-
clear Ru(II) complexes of polypyridyl ligands are cur-
rently subject to much investigation because of their
rich electro- and photo-chemical properties, known to
play a crucial role in numerous biological processes
such as photosynthetic mimetics and DNA oxidative
cleavage [14]. Thus, a number of experiments showed
that peripheral metalation was best achieved with DMF
as the solvent. Treatment of porphyrazine 6, for exam-
ple, with commercially available RuCl(Cp)(PPh3)2 (9)
or [RuCl(m2-Cl)(p-cymene)]2 (10) in hot DMF gave the
stable 18-electron tetracoordinated d6 complexes 11 and
12 in 55% and 11% yields respectively (Scheme 2). Both
complexes 11 and 12 were freely soluble in chlorinated
solvents and easily separated from the reaction mixture
by chromatography on alumina and subsequent gel
filtration. Proton NMR spectra of solitaire porphyr-
azines 11 and 12 in pyridine-d5 clearly showed, in
addition to the characteristic signature of the macrocy-
cles (vide supra), the distinctive singlet (5.15) of the
h5-cyclopentadienyl (h5-Cp) and doublets (6.32 and
6.54) of the h6-coordinated p-cymene respectively. Un-
fortunately, all attempts to grow crystals suitable for an
X-ray crystallographic study were unsuccessful. How-
ever, elemental analysis and mass ion measurement of
complexes 11 and 12 are fully consistent with their
identity.
Scheme 1.
Scheme 2.

A.G. Montalban et al. / Inorganica Chimica Acta 317 (2001) 143–148
147
3.3. Optical properties
In accordance with other porphyrazinic macrocycles,
the UV–Vis spectra of both 5 and 6 are dominated by
intense absorptions in the Soret region at 381 and
379 nm respectively and split Q-bands having Qx and
Qy absorbances at 649 and 682 nm and 652 and
665 nm respectively. The splitting reflects the C26 sym-
metry and can be rationalized by Gouterman’s four
orbital model [17]. In addition, less intense peaks ap-
pear at 487 nm and 488 nm respectively. We tenta-
tively assigned these absorptions as the p–p*
transitions (K-band) of the dipyridoquinoxaline moi-
eties. In comparison with other systems containing the
dipyridoquinoxaline group [18] the transitions are red-
shifted, thus indicating a lowering in energy of the
LUMO due to increased conjugation. Although the
B-bands do not change shape significantly upon pe-
ripheral metalation, a narrowing (no splitting) of the
Q-band is observed. More diagnostic changes occur in
the K region and can be interpreted in terms of com-
petitive symmetry (Laporte) allowed (t2g“p*) metal-
to-ligand charge transfer (MLCT) processes. Studies
on bipyridine and phenanthroline complexes have
demonstrated that increasing the backbonding ability
of the ligands results in a shift of the MLCT transi-
tion to higher energy [19]. Thus, it is likely that in
compounds 11 and 12, containing the p-complexing
ligands Cp and p-cymene respectively, the MLCT
transition is shifted to higher energy and masked by
the broad B-band. In contrast, complexes 14 and 15
with bipyridyls (poorer p acceptor ligands) display a
shoulder at 460 nm that we tentatively assigned as the
MLCT transition. A similar electronic transition at
459 nm is observed for trimer 16. Representative UV–
Vis spectra are shown in Fig. 1.
Scheme 3.
Scheme 4.
Similarly, treatment of porphyrazines 5 and 6 with
cis-RuCl2(bipy*)2 (13) [15] (bipy*=4,4%-di-tert-butyl-
2,2%-bipyridine) in refluxing DMF gave, after purifica-
tion, the soluble (chlorinated solvents) octahedral com-
plexes 14 and 15 in 31% and 11% yields respectively
(Scheme 3). The proton NMR spectra (pyridine-d5) of
solitaire porphyrazines 14 and 15 were qualitatively
the same, displaying, in addition to the characteristic
porphyrazine signature (vide supra), up to five distinct
singlets for the t-butyl groups and two sets of two
well-resolved doublets associated with the bipyridyl
moieties in which the adjacent rings are non-equiva-
lent. In addition, high-resolution mass ion measure-
ments using Fourier transform ion-cyclotron resonance
techniques (FT-ICR) were again in full agreement with
the proposed structures. Both complexes 14 and 15
displayed doubly charge molecular fragments as the
4. Conclusions
most intense peaks corresponding to [M−2Cl]2+
.
We have synthesized novel p-extended porphyrazines
substituted at their periphery with a single bidentate
phenanthroline chelating group and demonstrated that
these new ligands will coordinate Ru(II). In continua-
tion of our efforts toward the assembly of multipor-
phyrazine arrays, we have linked three macrocycles
by the mutual chelation of a ruthenium ion, thus form-
ing the first tetranuclear homoleptic porphyrazine
trimer. In addition, the optical properties of these
complexes can be adjusted through the right choice
of ligands. In analogy with their polypyridyl counter-
parts, it is expected that these materials should have
very rich and diverse but more adjustable physico-
chemical properties. Such work will be reported in due
course.
Finally, treatment of porphyrazine 5 with RuCl3·
H2O and ethanol as the reductant in DMF at reflux
gave, after repeated chromatography and gel filtration,
the microanalytically pure trimer 16 in 56% yield
(Scheme 4). The proton NMR spectra (pyridine-d5) of
the soluble (e.g. CHCl3, CH2Cl2) homoleptic octahe-
dral complex 16 and the parent porphyrazine 5 are
qualitatively the same. However, all resonances are
shifted and comparable to the chemical shifts reported
for the protons in phenanthroline and those of the
analogous D3 symmetric Ru(II) complex ([Ru(phen)3]-
Cl2) [16]. Again, high-resolution mass ion measure-
ments (FT-ICR) were fully consistent with the identity
of the tetranuclear complex 16 ([M+H−2Cl]3+).

148
A.G. Montalban et al. / Inorganica Chimica Acta 317 (2001) 143–148
ences Research Council (including the FT-ICR Mass
Spectrometry Service at the University of Warwick),
and NATO for generous support of our studies.
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We thank Glaxo Wellcome Ltd for the generous
endowment (A.G.M.B.), the Wolfson Foundation for
establishing the Wolfson Centre for Organic Chemistry
in Medical Science at Imperial College, the National
Science Foundation, the Engineering and Physical Sci-