NMR

Article abstract of DOI:10.1021/ic990038g

The ¹H NMR spectra of iron(III) complexes of dimeric 5,5′-bis(10,15,20-triphenylporphyrin) [(TrPPH₂)₂], 5,5′-bis(10,15,20-tris(p-methoxyphenyl)porphyrin) [(Tr(p-MeOP)PH₂)₂], and hybrid (TrPPH₂)(Tr(p-MeOP)PH₂) and the respective monomeric 5,10,15-triphenylporphyrin (TrPPH₂) and 5,10,15-tris(p-methoxyphenyl)porphyrin [Tr(p-MeOP)PH₂] have been investigated in order to elucidate an impact of a direct meso-meso linkage on the electronic structure of corresponding high- and low-spin iron(III) porphyrins.

Full text of DOI:10.1021/ic990038g

3040
Inorg. Chem. 1999, 38, 3040-3050
1H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions
in Iron(III) Complexes of meso-meso-Linked 5,5′-Bis(10,15,20-triphenylporphyrin)
Jacek Wojaczyn´ski, Lechosław Latos-Graz3yn´ski,* Piotr J. Chmielewski,
Pamela Van Calcar, and Alan L. Balch
Department of Chemistry, University of Wrocław, 14 F. Joliot-Curie Street, Wrocław 50 383, Poland,
and Department of Chemistry, University of California, Davis, California 95616
ReceiVed January 6, 1999
1
The H NMR spectra of iron(III) complexes of dimeric 5,5′-bis(10,15,20-triphenylporphyrin) [(TrPPH2)2], 5,5′-
bis(10,15,20-tris(p-methoxyphenyl)porphyrin) [(Tr(p-MeOP)PH2)2], and hybrid (TrPPH2)(Tr(p-MeOP)PH2) and
the respective monomeric 5,10,15-triphenylporphyrin (TrPPH2) and 5,10,15-tris(p-methoxyphenyl)porphyrin [Tr(p-
MeOP)PH2] have been investigated in order to elucidate an impact of a direct meso-meso linkage on the electronic
structure of corresponding high- and low-spin iron(III) porphyrins. The following species, covering the representative
spin/oxidation states, have been investigated: (TrPP)2(FeIIICl)2 (high spin); [(TrPP)2(FeIII(CN)2)2]2- (low spin);
[(TrPP)2(FeIIICl)2]+ (high-spin iron(III), diporphyrin radical); [(TrPP•)2(FeIIICl)2]2+ (high-spin iron(III), diradical
of diporphyrin). The iron(III) diporphyrins (TrPP)2(FeIIICl)2, [(TrPP)2(FeIII(CN)2)2]2-, {[(TrPP)FeIII(CN)2][(Tr(p-
1
MeOP)P)FeIII(CN)2]}2-, and [(TrPP)2(FeIIICl)2]2+ revealed the H NMR features which have been typically
encountered in the spectra of the relevant monomeric complexes. Thus magnetic interactions between two subunits
via skeleton appear to be minor. The characteristic broadening and/or paramagnetic shifts of 3-H and 7-H resonances
were determined and are diagnostic features of the meso-meso linkage. One-electron, ligand-based oxidation of
(TrPP)2(FeIIICl)2 to produce [(TrPP)2(FeIIICl)2]+ was observed with the unpaired electron delocalized over both
macrocycles. The structure of (Tr(p-MeOP)P)ZnII‚0.4CH2Cl2, the fundamental building block in synthesis of
diporphyrins, was determined by X-ray crystallography. (Tr(p-MeOP)P)ZnII crystallizes in the monoclinic space
group C2/c with a ) 47.744(9) Å, b ) 9.090(2) Å, c ) 15.571(2) Å, â ) 93.770(13)°, and Z ) 8. The refinement
of 494 parameters and 4361 reflections yields R1 ) 0.0756, wR2 ) 0.2169. The (Tr(p-MeOP)P)ZnII presents
characteristic features of zinc(II) tetraphenylporphyrin. The molecular periphery of (Tr(p-MeOP)P)ZnII has a fully
exposed meso position and two partially exposed pyrrole rings.
Introduction
In general, distance, geometry, and orientation have been
recognized as important factors for control of the efficiency of
the energy and electron-transfer processes.1 Therefore, oligo-
meric porphyrins in which π-systems can directly interact have
particular interest. Crossley and co-workers described a synthetic
approach to molecular wires based on rigid π-conjugated
porphyrins that are bridged by a coplanar aromatic fragment.
Theoretical analysis of the conjugation pathway for oligopor-
phyrins connected by 1,4,5,8-tetrazaantracene moieties suggests
that the interaction between the porphyrins and the aromatic
bridge is weak contrary to the anticipated aromatic π-delocal-
ization.2,8 Recently a conjugated oligoporphyrin system based
on fused pyrrole blocks has been synthesized by Smith and co-
workers.9
Oligomeric porphyrins and metalloporphyrins of various
structures are under intensive investigation due to their relevance
to the mechanism of photosynthesis and their potential applica-
tion in the molecular electronics and as new photonic materials.1-3
For instance, the spectacular photonic molecular wires based
on side-by-side oligomerization of meso-functionalized por-
phyrins have been shown to absorb light at one end and then to
emit a different photon on the other end.4 Other studies of
oligomeric metalloporphyrins were directed toward generation
of artificial allosteric systems.5 Polymetalloporphyrins were
investigated as polyelectron redox molecular catalysts in the
four-electron reduction of dioxygen6 or in proton reduction.7
* To whom correspondence should be addressed
(1) (a) Wasielewski, R. Chem. ReV. 1992, 92, 435. (b) Gust, D.; Moore,
T. A. Topics in Current Chemistry; Springer-Verlag: Berlin, 1991;
Vol. 159, pp 103-156.
(6) (a) Ni, C.-L.; Abdalmuhdi, I.; Chang, C. K.; Anson. F. C. J. Phys.
Chem. 1987, 91, 1158. (b) Collman, J. P.; Hutchison, J. E.; Lopez,
M. A.; Tabard, A.; Guilard, R.; Seok, W. K.; Ibers, J. A.; L’Her, M.
J. Am. Chem. Soc. 1992, 114, 9689.
(7) Collman, J. P.; Ha, Y.; Wagenknecht, P. S.; Lopez, M.-A.; Guilard,
R. J. Am. Chem. Soc. 1993, 115, 9080.
(8) Crossley, M. J.; Burn, P. L.; Chew, S. S.; Cuttance, F. B.; Newsom,
I. A. J. Chem. Soc., Chem. Commun. 1991, 1564. (b) Crossley, M. J.;
Burn, P. L.; Langford, S. J.; Pyke, S. M.; Stark, A. G. J. Chem. Soc.,
Chem. Commun. 1991, 1567. (c) Lu¨, T. X.; Reimers, J. R.; Crossley,
M. J.; Hush, N. S. J. Phys. Chem. 1994, 98, 11878. (d) Crossley, M.
J.; Govenlock, L.; J.; Prashar, J. K. J. Chem. Soc., Chem. Commun.
1995, 2379.
(2) (a) Crossley, M. J.; Burn, P. L. J. Chem. Soc., Chem. Commun. 1987,
39. (b) Crossley, M. J.; Burn, P. L. J. Chem. Soc., Chem. Commun.
1991, 1569.
(3) (a) Cosmo, R.; Kautz, C.; Meerholz, K.; Heinze, J.; Mu¨llen, K. Angew.
Chem., Int. Ed. Engl. 1989, 28, 604. (b) Lamrabte, A.; Momenteau,
M.; Maillard, P.; Seta, P. J. Mol. Electron. 1990, 6, 145. (c) Ono, N.;
Tomita, H.; Maruyama, K. J. Chem. Soc., Perkin Trans. 1 1992, 2453.
(4) Wagner, R. W.; Lindsey, J. S. J. Am. Chem. Soc. 1994, 116, 9759.
(b) Anderson, H. L.; Martin, S. J.; Bradley, D. D. C. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 655.
(5) Tabushi, I. Pure Appl. Chem. 1988, 60, 581.
10.1021/ic990038g CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/29/1999

1H NMR Investigations of Triphenylporphyrin Metal Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3041
An alternative approach to construct the porphyrin array with
strongly interacting π-electron systems involves the formation
of direct links between meso-carbons without any spacer
element.10 Such molecules have been recently synthesized via
oxidative coupling of zinc porphyrins. Up to eight porphyrinic
moieties have been linked in this fashion to create linear arrays.
A stepwise process has been reported in which the bridging
meso-meso fragment was initially synthesized and subsequently
incorporated into the bis-macrocycle.10d
The extent of the coupling between porphyrin moieties within
oligomeric porphyrins, in which the π-electron systems are
expected to interact, remains a major concern. We have decided
to explore this issue for iron(III) complexes of 5,5′-linked
diporphyrins obtained from meso-triaryl-substituted porphyrins.
1H NMR spectroscopy has been shown to be uniquely
definitive method for detecting and characterizing iron por-
phyrins. The hyperfine shift patterns that have been recorded
for such paramagnetic complexes are sensitive to the iron
oxidation, spin and ligation state.11 Particularly pyrrole protons
Figure 1. A perspective view (with 50% probability ellipsoids) of
(Tr(p-MeOP)P)ZnII. The lower drawing emphasizes the planarity of
the macrocycle.
evidence of oligomerization.13-15 Specially, the paramagnetic
shift of the 3-H resonance of [(2-O-TPP)MIII]3 reflects simul-
taneous contributions to contact shifts derived from two
neighboring paramagnetic metal centers.14
1
This work is concerned with the H NMR characterization
of high- and low-spin iron(III) complexes of hexa-meso-phenyl-
substituted meso-meso-linked diporphyrins. We have found that
the 1H NMR spectroscopic properties of the dimeric complexes
resemble those of the isolated subunit, i.e., iron(III) 5,10,15-
triphenylporphyrin, in analogous spin/electronic states.
provided a direct probe of the spin density around the porphyrin
macrocycle. Previously we have investigated the specific mode
of the tetraphenylporphyrin modifications (â-substitution, a
selective symmetrical extension of a single pyrrole ring,
replacement of meso-aryls by meso-alkyl substituents).12 In
related spectroscopic investigations on trimeric or dimeric
paramagnetic [(2-O-TPP)FeIII]3, [(2-O-TPP)MnIII]3, [(2-O-TPP)-
Results and Discussion
Synthesis of Diporphyrins and Their Complexes. 5,10,15-
Triphenylporphyrin, (TrPPH2) and 5,10,15-tris(p-methoxy-
phenyl)porphyrin (Tr(p-MeOP)PH2) have been synthesized in
5-7% yield by the condensation of pyrrole, benzaldehyde (or
p-methoxybenzaldehyde), and paraformaldehyde. The procedure
followed the methodology typically used for synthesis via a
mixed aldehyde-pyrrole condensation.16 The (Tr(p-MeOP)P)-
ZnII complex has been characterized by X-ray crystallography
(Figure 1). As expected, the molecular periphery of (Tr(p-
MeOP)P)ZnII has a fully exposed meso position and two partially
exposed pyrrole rings. Thus the molecule periphery presents
blending of structural features which are typical for (TPP)ZnII
and (OEP)ZnII. The bond lengths and angles are within the limits
expected for zinc(II) porphyrins (Table 1).17 The porphyrin
macrocycle is practically flat. The zinc(II) ion is located in the
porphyrin plane.
FeIII]n[(2-O-TPP)MnIII]3-n, [(OEPO)FeIII]2, and [(OEPO)FeIII]2
+
complexes we have established the 1H NMR “fingerprint”
(9) Jaquinod, L.; Siri, O.; Khoury, R. G.; Smith, K. M. Chem. Commun.
1998, 1261.
(10) (a) Susumu, K.; Shimidzu, T.; Tanaka, K.; Segawa, H. Tetrahedron
Lett. 1996, 37, 8399. (b) Osuka, A.; Shmidzu, H. Angew. Chem., Int.
Ed. Engl. 1997, 36, 135. (c) Yoshida, N.; Shimidzu, H.; Osuka, A.
Chem. Lett. 1998, 55. (d) Khoury, R. G.; Jaquinoid, L.; Smith, K. M.
Chem. Commun. 1997, 1057. (e) Ogawa, T.; Nishimoto, Y.; Yoshida,
N.; Ono, N.; Osuka, A. Chem. Commun. 1998, 337. (f) Nakano, A.;
Osuka, A.; Yamazaki, I.; Yamazaki, T.; Nishimura, Y. Angew. Chem.,
Int. Ed. Engl. 1998, 37, 135.
(11) (a) La Mar, G. N.; Walker, F. A. in The Porphyrins, Dolphin, D.,
Ed.; Academic Press: New York, 1979; pp 61-312. (b) Bertini, I.,
Luchinat, C. NMR of Paramagnetic Molecules in Biological Systems;
The Benjamin/Cummings Publishing Co.: Reading, MA, 1986. (c)
Bertini, I.; Luchinat, C. Coord. Chem. ReV. 1996, 150, 131. (d) Walker
F. A., Simonis U. In Biological Magnetic Resonance, Volume 12:
NMR of Paramagnetic Molecules; Berliner L. J., Reuben J., Eds.;
Plenum Press: New York, 1993; p 133.
(12) (a) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Hrycyk, W.; Pacholska, E.;
Rachlewicz, K.; Szterenberg, L. Inorg. Chem. 1996, 35, 6861. (b)
Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Głowiak, T. Inorg. Chem. 1997,
36, 6299. (c) Wołowiec, S.;. Latos-Graz˘yn´ski, L.; Mazzanti, M.;
Marchon, J.-C. Inorg. Chem. 1997, 36, 5761. (d) Wołowiec, S.; Latos-
Graz˘yn´ski, L.; Toronto, D.; Marchon, J.-C. Inorg. Chem. 1998, 37,
724. (e) Mazzanti, M.; Marchon, J.-C.; Wojaczyn´ski, J.; Wołowiec,
S.; Latos-Graz˘yn´ski, L.; Shang, M.; Scheidt W. R. Inorg. Chem. 1998,
37, 2476.
The (TrPP)ZnII complex undergoes a regiospecific meso-
meso coupling mediated by a two-electron oxidizing reagent,
(13) (a) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1995, 34, 1044.
(b) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1995, 34, 1054.
(c) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1996, 35, 4812.
(d) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Olmstead, M. M.; Balch,
A. L. Inorg. Chem. 1997, 36, 4548.
(14) Balch, A. L.; Latos-Graz˘yn´ski, L.; Noll, B. C.; Olmstead, M. M.;
Zovinka, E. P. Inorg. Chem. 1992, 31, 2248.
(15) Balch, A. L.; Latos-Graz˘yn´ski, L.; St. Claire, T. Inorg. Chem. 1995,
34, 1395.
(16) Lindsey J. S. In Metallopophyrins Catalyzed Oxidations; Montanari,
F., Casella, L., Eds.; Kluwer Academic Publishers: Netherlands 1994;
p 49.

3042 Inorganic Chemistry, Vol. 38, No. 13, 1999
Wojaczyn´ski et al.
Scheme 1
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
(Tr(p-MeOP)P)ZnII‚0.4CH2Cl2
thallium(III) trifluoroacetate (TTFA), to produce zinc(II) 5,5′-
bis(10,15,20-triphenylporphyrin) [(TrPP)2ZnII ], described previ-
2
Zn-N(21)
Zn-N(22)
Zn-N(23)
Zn-N(24)
2.033(5)
2.019(6)
2.041(5)
2.027(5)
N(21)-Zn-N(23)
N(22)-Zn-N(24)
N(21)-Zn-N(22)
N(22)-Zn-N(23)
N(23)-Zn-N(24)
N(24)-Zn-N(21)
179.4(2)
180.0(2)
89.4(2)
90.5(2)
89.5(2)
90.7(2)
ously.10 The coupling procedure performed with a mixture of
(TrPP)ZnII and (Tr(p-MeOP)P)ZnII yields three diporphyrin
complexes: (TrPP)2ZnII , (Tr(p-MeOP)P)2ZnII , and [(TrPP)-
2
2
ZnII][(Tr(p-MeOP)P)ZnII]. The last species contains two distinct
subunits. Zinc(II) diporphyrins can be easily demetalated by
treatment with acid to produce the dimeric free bases (TrPPH2)2,
(Tr(p-MeOP)PH2)2, and (TrPPH2)(Tr(p-MeOP)PH2). Subse-
quently, diporphyrins can be readily metalated with gallium(III)
acetyloacetonate or indium(III) chloride to form (TrPP)2-
(GaIIICl)2 or (TrPP)2(InIIICl)2. The insertion of iron into TrPPH2,
Tr(p-MeOP)PH2, (TrPPH2)2, (Tr(p-MeOP)PH2)2, and (TrPPH2)-
(Tr(p-MeOP)PH2) resulted in formation of (TrPP)FeIIICl, (Tr(p-
MeOP)P)FeIIICl, (TrPP)2(FeIIICl)2, (Tr(p-MeOP)P)2(FeIIICl)2,
and [(TrPP)FeIIICl][(Tr(p-MeOP)P)FeIIICl], respectively.
For a dimeric porphyrin with simple planar coordination in
each macrocycle (i.e. for (TrPP)2ZnII ), the molecule possesses
2
at least the D2 symmetry. In the drawing of Scheme 1, this dimer
is shown with one subunit in the plane of the paper and the
other perpendicular to the page and indicated by a thick line.
In such a dimer again four distinct types of pyrrole protons
(labeled a-d) and two types of phenyl groups (labeled A and
B) are present. The analysis carried out for four-coordinate
(TrPP)2ZnII holds for the six-coordinate (TrPP)2(MIIIL2)2 as
1H NMR Studies of Diamagnetic Metallodiporphyrins. To
understand the spectral data, the structural characteristics of the
monomeric and dimeric porphyrins are systematized in Scheme
1. The monomeric triphenylporphyrin unit will have maximal
2
well.
For the dimeric porphyrin with five-coordinate metal centers
in each porphyrin, the structure is more complex. The results
of molecular mechanics calculations which have been used to
visualize the structure of the gallium(III) diporphyrin are shown
in Figure 2. The ionic radius and the charge of gallium(III) (and
of indium(III) and high-spin iron(III) as well) impose five-
coordinate square-pyramidal structures on each (TrPP)GaIIICl
subunit. Accordingly, these metal ions are displaced from the
porphyrin plane. In the minimization procedure we have used
the standard MM+ parametrization of the HyperChem program
with an exception for the metal ion coordination surroundings
where the constraints, reflecting the size of the gallium(III) ion,
have been imposed. The characteristic features of gallium(III)
tetraphenylporphyrins included a displacement of the ion from
the plane of four nitrogens by ca. 0.4 Å and relatively long
C2V symmetry when the porphyrin has identical ligation on both
sides of the porphyrin plane or Cs symmetry when the ligation
on either side is different. In both cases four distinct types of
pyrrole protons (labeled a-d) and two types of phenyl groups
(labeled A and B) are present.
(17) (a) Scheidt, W. R.; Mondal, J. U.; Eigenbrot, C. W.; Adler, A.;
Radonovich, L. J.; Hoard, J. L. Inorg. Chem. 1986, 25, 795. (b) Byrn,
M. P.; Curtis, C. J.; Khan, S. I.; Sawin, P. A.; Tsurumi, R.; Strouse,
C. E. J. Am. Chem. Soc. 1990, 112, 1865. (c) Byrn, M. P.; Curtis, C.
J.; Goldberg, I.; Hsiou, Y.; Khan, S. I.; Sawin, P. A.; Tendick, S. K.;
Strouse, C. E. J. Am. Chem. Soc. 1991, 113, 6549. (d) Byrn, M. P.;
Curtis, C. J.; Hsiou, Y.; Khan, S. I.; Sawin, P. A.; Tendick, S. K.;
Terzis, A. Strouse, C. E. J. Am. Chem. Soc. 1993, 115, 9480.

1H NMR Investigations of Triphenylporphyrin Metal Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3043
Figure 2. Drawing of (TrPP)2(GaIIICl)2 as obtained from the Hyper-
chem MM+ molecular mechanics calculations. The labels are related
1
to the H NMR spectra of (TrPP)2(GaIIICl)2 ((TrPP)2(MIIIX)2) in the
paper.
Ga-N bonds (2.05 Å). The structural parameters are in the range
found for a variety of gallium(III) porphyrins by X-ray crystal-
lography.18,19 The calculations indicate that two subunits of
(TrPP)2(GaIIICl)2 are not necessarily orthogonal. The dimeric
molecule has the C2 symmetry with the C2 axis perpendicular
to the C(5)-C(5′) bond, and the two (TrPP)GaIII subunits are
equivalent. However, as seen in Scheme 1, the pyrrolic positions
7-H(a) and 3-H(a′), 8-H(b), and 2-H(b′), as well as 12-H(c) and
18-H(c′), and 13-H(d) and 17-H(d′) are no longer equivalent as
1
Figure 3. The downfield region of H NMR spectra (300 MHz): A,
(TrPP)GaIIICl; B, (TrPP)2ZnII2; C, (TrPP)2(InIIICl)2; D, (TrPP)2(GaIII-
Cl)2. Their assignments correspond to those in Scheme 1 and Figure 2
(o, ortho proton resonances). Some resonances from an admixture of
(TPP)InIIICl (trace C) and (TPP)GaIIICl (traces A and D) marked with
asterisks.
resonance furthest upfield assigned to the a type pyrrole protons.
The upfield shifts result from the ring current effect of the
adjacent macrocycle, as noted earlier.10
they are in the monomeric TrPPH2 or in (TrPP)2ZnII . Addition-
2
ally, the symmetry lowering in these five-coordinate complexes
renders the three phenyl substituents on each porphyrin in-
equivalent. On each meso phenyl ring, the two ortho and two
meta protons are not equivalent because the porphyrin plane
bears different substituents on opposite sides and rotation about
the meso-carbon-phenyl bond is restricted. As an additional
complication, five-coordinate (TrPP)2(MIIICl)2 has an optical
asymmetry associated with direction of the axial orientation on
the metal(III) ions, as shown in the Scheme 1. The geometric
considerations described above for gallium(III) are also relevant
for other five-coordinate metals, indium(III), and high-spin
iron(III).
The geometric differences between the monomeric and
dimeric species are further exemplified by comparison of
(TrPP)GaIIICl and (TrPP)2(GaIIICl)2. Due to the lower symmetry
of the dimer, four different AB patterns are observed in the 1H
NMR spectra of (TrPP)2(GaIIICl)2 [and in (TrPP)2(InIIICl)2 as
well]. Thus in dimeric molecules the 7-H, 3-H, 8-H, and 2-H
(a, a′, b, b′) protons experience large upfield chemical shifts
due to their proximity to the π-system of the adjacent porphyrin.
These 1H NMR spectral characteristics are essential since the
zinc(II), gallium(III), and indium(III) complexes will be used
as the appropriate diamagnetic references for the paramagnetic
low-spin and high-spin iron(III) complexes of meso-meso-
linked diporphyrins, respectively. Chemical shift data of these
and other diamagnetic compounds are given in Table 2.
High-Spin Iron Porphyrinss1H NMR Studies. Representa-
1
Figure 3 shows the H NMR spectra of monomeric (TrPP)-
GaIIICl and dimeric (TrPP)2ZnII , (TrPP)2(GaIIICl)2, and (TrPP)2-
2
(InIIICl)2. For (TrPP)GaIIICl, the pyrrole protons produce two
AB patterns as expected for the effective Cs symmetry. The
mirror plane passes through the gallium(III) ion, the axial
chloride, and the unsubstituted meso-carbon. Note that in
monomeric (TrPP)GaIIICl the 3,7-H(a) protons have chemical
shifts that are downfield of the other pyrrole protons, because
they do not experience a ring current shift from an adjacent
meso-phenyl group. The unique meso proton resonance is
located at 10.41 ppm.
tive H NMR spectra of high-spin (TrPP)FeIIICl and (TrPP)-
1
FeIIII complexes are shown in Figure 4. Resonance assignments
which are given in Figure 4 and in Table 3 have been made on
the basis of relative intensities and line width analysis. Direct
comparisons to iron(III) tetraphenylporphyrin derivatives fa-
cilitated the assignment.11,20 The multiplicity of the respective
resonances is directly related to the symmetry of the molecule
as discussed in detail for the analogous (TrPP)GaIIICl. Thus,
the four unequivalent pyrrole positions produce the four
downfield shifted pyrrole resonances for well-resolved spectrum
of (TrPP)FeIIII.
The 1H NMR spectra of the diporphyrinic complexes reveals
the absence of a meso proton resonance and unusual chemical
shifts of the pyrrole resonances. For (TrPP)2ZnII , all of the
2
pyrrole resonances experience an upfield bias with the pyrrole
The line width of the pyrrole resonances is practically
identical for the four pyrrole lines in the spectrum of (TrPP)-
FeIIII. The line width increases, as expected, in the series (TrPP)-
FeIIII < (TrPP)FeIIIBr < (TrPP)FeIIICl.11,20 Two of the four
pyrrole lines overlap in the case of (TrPP)FeIIICl. These
downfield resonances are accompanied by an upfield meso
(18) (a) Coutsolelos, A.; Guilard, R.; Boukhris, A.; Lecomte, C. J. Chem.
Soc., Dalton Trans. 1986, 1779. (b) Boukhris, A.; Lecomte, A.;
Coutsolelos, A.; Guilard, R. J. Organomet. Chem. 1986, 303, 151.
(c) Coutsolelos, A.; Guilard, R.; Bayeul, D.; Lecomte, C. Polyhedron
1986, 5, 1157. (d) Serr, R., B.; Headford, C. E. L.; Anderson, O. P.;
Elliott, C. M.; Spartalian, K.; Fainzilberg, V. E.; Hatfield, W. E.; Rohrs,
B. R.; Eaton, S. S.; Eaton, G. R. Inorg. Chem. 1992, 31, 5450.
(19) Balch, A. L.; Hart, R. L.; Parkin, S. Inorg. Chim. Acta 1993, 205,
137.
(20) Behere, D. V.; Birdy, R.; Mitra, S. Inorg. Chem. 1982, 21, 386.

3044 Inorganic Chemistry, Vol. 38, No. 13, 1999
Wojaczyn´ski et al.
Table 2. 1H NMR Chemical Shifts (ppm) for Diamagnetic Systemsa
meso-phenyl
m-H
pyrrole
b
o-H
p-H
p-OCH3
compound
a
c, d
meso
A
B
A
B
A
B
A
B
NH
TrPPH2
9.32 8.99 8.84, 8.87 10.20
9.38 9.07 8.94, 8.97 10.24
9.51 9.22 9.10, 9.11 10.41
9.36 9.09 8.97, 8.98 10.21
8.15-8.25
8.15-8.25
8.0-8.4
7.7-7.8
7.7-7.8
7.65-7.9
7.23-7.29
7.7-7.8
7.7.-7.8
7.65-7.9
-
-
-
-
-3.03
-
(TrPP)ZnII
(TrPP)GaIIICl
(Tr(p-MeOP)P)ZnII
(TrPPH2)2
-
8.08-8.14
4.09 4.07
-
-2.25
-2.22
8.04 8.55 8.87, 8.89
8.03 8.56 8.88, 8.91
8.05 8.58 8.90, 8.94
8.03 8.57 8.89, 8.91
8.08 8.63 8.96, 8.99
8.07 8.62 8.96, 8.99
-
-
8.15-8.21 8.23-8.28 7.60-7.66 7.75-7.81 7.60-7.66 7.75-7.81
8.16-8.22 8.25-8.28 7.62-7.67 7.75-7.80 7.62-7.67 7.75-7.80
-
(TrPPH2)
(Tr(p-MeOP)PH2)
(Tr(p-MeOP)PH2)2
8.10
8.09
8.17
8.17
7.17
7.17
7.31
7.32
3.98 4.11 -2.25
3.97 4.11 -2.22
-
-
-
-
(TrPP)2ZnII
8.17-8.20 8.25-8.28 7.62-7.64 7.75-7.80 7.62-7.64 7.75-7.80
8.27-8.30 8.36-8.39 7.65-7.76 7.84-7.87 7.65-7.76 7.84-7.87
-
-
-
2
[(TrPP)ZnII]
[(Tr(p-MeOP)P)ZnII] 8.08 8.65 8.98, 9.02
8.16
8.10
8.24
8.18
7.16
7.16
7.30
7.30
3.97 4.10
3.97 4.11
-
(Tr(p-MeOP)P)2ZnII 8.07 8.65 8.98, 9.02
-
-
-
2
(TrPP)2(GaIIICl)2
(TrPP)2(InIIICl)2
8.14 8.75 9.10, 9.15
8.53 8.88 9.11, 9.16
8.19 8.78 9.09, 9.13
8.21 8.79 9.10, 9.12
7.95-8.15
7.5-7.9
7.5-7.9
7.5-7.9
-
-
8.2-8.4
8.0-8.2
8.3-8.5
-
7.5-7.9
-
a Resonances labeled as in Figures 2 and 3.
The 1H NMR spectra of (TrPP)2(FeIIIX)2 and (Tr(p-MeOP)P)2-
(FeIIIX)2 have been analyzed in the context of the appropriate
symmetry previously described for (TrPP)2(GaIIICl)2. Thus, the
eight unequivalent pyrrole positions should produce eight
downfield-shifted pyrrole resonances. In addition one can expect
six ortho, six meta, and three para or p-methoxyphenyl signals.
Additional differentiation of subunits in [(TrPP)FeIIIX][(Tr(p-
MeOP)P)FeIIIX] doubles the predicted number of resonances.
1
The representative H NMR spectra of high-spin complexes
[(TrPP)FeIIICl][(Tr(p-MeOP)P)FeIIICl] and [(TrPP)FeIIII][(Tr(p-
MeOP)P)FeIIII] are presented in Figure 5. Table 3 contains
further data for a wider range of complexes. In general, the
observed line width of (TrPP)2(FeIIIX)2 increases, as expected
for high-spin iron porphyrins, in the order I- < Br- < Cl-.11,20
Because of this trend, it has been expeditious to examine data
for the iodide complexes, since these have the narrowest, and
consequently the best resolved, resonances. In particular, two
broad pyrrole resonances located above 80 ppm are not readily
observed for chloride derivatives, and only one asymmetric
pyrrole signal is visible (Figure 5). The presence of two
paramagnetic centers produces marked variation of the pyrrole
line widths. The effect has been clearly demonstrated for iodide
derivatives. The (TrPP)2(FeIIII)2 spectrum reveals a multiplet
of six unequivalent pyrrole resonances centered at 80 ppm and
two well-separated although relatively broad resonances cor-
responding to a (88.7 ppm, ∆ν1/2 = 700 Hz) and a′ (83.9 ppm,
∆ν1/2 = 500 Hz) (Figure 6, trace A). The line widths of the
remaining six pyrrole resonances are markedly smaller (ca. 200
Hz). As expected, six well-resolved meta meso-phenyl reso-
nances of (TrPP)2(FeIIII)2 have been identified at the 12-16
ppm region (Table 3). Their number is doubled for [(TrPP)-
FeIIII][(Tr(p-MeOP)P)FeIIII] as shown in an expansion of this
region (Figure 5).
Figure 4. 300 MHz 1H NMR spectrum of (TrPP)FeIIICl (A) and
(TrPP)FeIIII (B) in chloroform-d solution at 293 K. Resonance assign-
ment: pyrrole-H, pyrrole proton resonances; ortho, meta, or para signals
of meso-phenyl protons; meso, meso-H peak; s, solvent.
signal (Table 3). The position of the meso resonances is
consistent with that found for (OEP)FeIIICl (δiso ) -55.6
ppm),11a although the effect is markedly larger. The multiplicity
and positions of the meso-phenyl resonances are consistent with
the structure of the complex. In the series Cl-, Br-, I- we have
observed a systematic downfield change of the resonance
positions related to the corresponding modification of the dipolar
effect.20
Treatment of (TrPP)FeIIIX with K2CO3 in water resulted in
formation of [(TrPP)FeIII]2O. A set of three pyrrole resonances
[13.2 (4H), 13.4 (4H), 13.6 ppm (8H)] reflects the symmetry
of the subunit. The spectral properties resemble those of (TPP)-
FeIIIO.22 The meso (20-H) resonance has been detected at δ )
6.3 ppm, which corresponds to 5.5 ppm (29 °C) determined for
[(OEP)FeIII]2O.21
The line widths have been used to correlate some of the
pyrrole resonances with the proton location in the dimeric
structure. The dipolar contribution to line width broadening is
presumed to be proportional to r-6, where r is the distance from
the paramagnetic center to the proton in question when ligand-
centered dipolar relaxation is insignificant.23,24 The contribution
(21) La Mar, G. N.; Eaton, G. R.; Holm, R. H.; Walker, F. A. J. Am. Chem.
Soc. 1973, 95, 63.
(22) La Mar, G. N.; Walker, F. A. J. Am. Chem. Soc. 1973, 95, 6950.
(23) Arasasingham, R. D.; Balch, A. L.; Cornman, C. R.; de Ropp, J. S.;
Eguchi, K.; La Mar, G. N. Inorg. Chem. 1990, 29, 1847.

1H NMR Investigations of Triphenylporphyrin Metal Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3045
meso-phenyl
Table 3. 1H NMR Chemical Shifts (ppm) for High-Spin Iron(III) Porphyrinsa
compound
(TrPP)FeIIICl
pyrrole
meso
o-H
m-H
p-H
p-OCH3
78.5 (2H), 81.1 (4H),
81.9 (2H)
-72.4 5.1 (3H), 8.2 (3H)
-72.3 5.6 (3H), 9.8 (3H)
-66.5 6.9 (3H), 12.7 (3H)
12.1, 12.3 (2H), 13.3,
13.5 (2H)
12.8, 13.0 (2H), 14.2,
14.5 (2H)
13.6, 13.9 (2H), 15.5,
15.8 (2H)
6.4 (2H), 6.5
-
(TrPP)FeIIIBr
(TrPP)FeIIII
79.4 (2H), 81.5 (2H),
81.9 (2H), 82.6 (2H)
79.7 (2H), 81.4 (2H),
82.1 (2H), 82.8 (2H)
13.2 (4H), 13.4 (4H),
13.6 (8H)
7.0 (2H), 7.1
7.7 (2H), 7.9
7-8
-
-
-
-
[(TrPP)FeIII]2O
(TrPP)2(FeIIICl)2
6.3 (2H)
7-8
7-8
∼80.8 (16H)b
-
-
-
-
-
-
∼5.5 (6H), ∼8.5 (6H) 11.9 (4H), 12.3 (2H),
13.1 (4H), 13.5 (2H)
∼5.1 (6H), ∼8.1 (6H) 11.5 (2H), 11.8 (3H), 12.2,
6.0 (2H), 6.2 (2H),
6.0 (2H)
5.9, 6.1, 6.7
[(TrPP)FeIIICl][(Tr(p-
∼80.5 (16H)b
4.7 (3H), 4.9 (3H),
5.3 (3H)
4.7 (3H), 4.8 (3H),
5.3 (3H)
MeOP)P)FeIIICl]
12.5 (2H), 13.0 (3H), 13.6
11.4 (4H), 11.8 (2H), 12.5
(4H), 13.0 (2H)
(Tr(p-MeOP)P)2(FeIIICl)2 ∼80.8 (16H)b
∼5 (6H), ∼8 (6H)
-
(TrPP)2(FeIIIBr)2
81.9 (14H), 84.9, 88.1
∼5.8 (6H), ∼10.3 (6H) 12.4, 12.6, 13.1, 13.8, 14.1, 6.2 (2H), 6.6 (2H),
14.7 (2H each) 7.2 (2H)
13.0, 13.3, 14.0, 14.8, 15.1, 6.9 (2H), 7.3 (2H),
16.0 (2H each) 8.3 (2H)
-
(TrPP)2(FeIIII)2
80.4, 80.9, 81.1 (12H);
83.2, 83.8, 88.7 (2H)
80.6, 81.6 (12H); 84.0
(2H), 89.2 (2H)
∼7 (6H), ∼13 (6H)
∼7 (6H), ∼13 (6H)
-
[(TrPP)FeIIII][(Tr(p-
MeOP)P)FeIIII]
12.6, 13.0, 13.3, 13.6, 14.0, 7.6, 7.7, 8.3
14.3, 14.6, 14.8, 15.2,
15.4, 16.0c
5.2 (3H), 5.6 (3H),
6.5 (3H)
a Chloroform-d, 293 K. b Asymmetric line composed from few components. c Intensities not determined, their sum equals 12H.
centered at 80 ppm which vary over a rather narrow range (ca.
200 Hz). The markedly larger line widths of a and a′ protons
can be split into two parts: the internal one, which is identical
as for other pyrrole positions, and the remaining external one.
The most likely the external contribution derives mainly from
the dominant dipolar contribution of the closely located external
iron(III) ion. Considering the relative position of the a and a′
protons relative to the external iron(III) (ra < ra′), the broadest
resonances could be unambiguously assigned. The downfield
shift of a and a′ resonances upon the dimer formation can be
tentatively explained by placement of these protons in the dipolar
shift deshielding zone produced by the neighboring iron(III)
porphyrin. With the iron(III) ion displaced from the porphyrin
plane, the effect is more pronounced for the a proton.
The collapse of the a, a′ doublet upon addition of I- in the
form of TBAI is illustrated in Figure 6. These changes are
accompanied by the parallel simplification of the other spectral
Figure 5. 1H NMR spectrum of [(TrPP)FeIIICl][(Tr(p-MeOP)P)FeIIICl]
in chloroform-d solution at 293 K (OMe, p-OCH3 resonances). Insets
regions. Consequently the three pyrrole resonances that are
present the pyrrole and meta-H regions of [(TrPP)FeIIII][(Tr(p-MeOP)-
discernible around 80 ppm are assigned to the collapsed pairs
P)FeIIII].
b and b′, c and c′, and d and d′, respectively. Accordingly the
multiplet of six m-phenyl resonances simplifies to two lines with
the 2:1 intensity ratio. As the result, the NMR spectrum of
(TrPP)2(FeIIII)2 presents the features expected for the higher
effective symmetry described already for (TrPP)2ZnII . To
2
account for the observed phenomenon, we suggest that the
associative mechanism described in Scheme 2 is operative. All
pairs do average since the activated [(TrPP)FeIIII2]- subunit has
the plane of symmetry through the porphyrin skeleton. The
analogous mechanism was presented previously for the (TPP)-
FeIIIX systems.25 This process also results in a mutual inter-
conversion of the iron(III) diporphyrin enantiomers.
The chromatography of (TrPP)2(FeIIIX)2 on a basic alumina
Figure 6. 1H NMR spectrum of (TrPP)2(FeIIII)2 (pyrrole region) in
chloroform-d, 293 K (A). Trace B presents H NMR spectrum from
1
the same solution after addition of the excess of TBAI. Labeling of
resonances is consistent with Scheme 2.
column or methathesis by stirring of its dichloromethane
(benzene) solution with an excess of sodium hydroxide results
in replacement of the halo ligands with hydroxy groups. The
1H NMR spectra indicate that the product contains both (TrPP)-
FeIII(OH) and -(TrPP)FeIIIOFeIII(TrPP)- moieties, although the
from the internal iron(III) ion via dipolar and scalar mechanisms
has been approximated by the line widths of pyrrole resonances
(24) Swift, J. In NMR of Paramagnetic Molecules; La Mar, G. N., Horrocks,
(25) (a) La Mar, G. N. J. Am. Chem. Soc. 1973, 95, 1662. (b) La Mar, G.
N.; Saterlee, J. D.; Snyder, J. J. Am. Chem. Soc. 1974, 96, 7137. (c)
Snyder, R. V.; La Mar, G. N. J. Am. Chem. Soc. 1977, 98, 4419.
W. D., Jr., Holm, R. H., Eds.; Academic Press: New York; 1973; p
53.

3046 Inorganic Chemistry, Vol. 38, No. 13, 1999
Wojaczyn´ski et al.
Scheme 2
Scheme 3
[(TrPP)FeIII(CN)2]- and [(TrPP)2(FeIII(CN)2)2]2-. Eight signals
in this spectral region are found for {[(TrPP)FeIII(CN)2][(Tr(p-
MeOP)P)FeIII(CN)2]}2-. These signals are accompanied by sets
of upfield shifted ortho and para meso-phenyl proton resonances
and downfield shifted meta signals. The meso-H peak has been
observed at δ ) -6.9 ppm (293 K) for [(TrPP)FeIII(CN)2]-.
The isotropic shift of the pyrrole resonances is consistent with
the (dxy)2(dxz,dyz)3 ground electronic state.11 The necessary
assignments required an application of two-dimensional NMR
techniques, 1H COSY and NOESY,12a and the results are shown
in Figure 7 and Table 4. The multiplicity of resonances is
consistent with the symmetry analysis presented previously. The
presence of two paramagnetic centers in [(TrPP)2(FeIII(CN)2)2]2-
and {[(TrPP)FeIII(CN)2][(Tr(p-MeOP)P)FeIII(CN)2]}2- is not
reflected in the essential changes of the isotropic shifts.
However, the analytically important broadening of resonances
has been evidently observed. Thus, the four pyrrole signals of
monomeric [(TrPP)FeIII(CN)2]- display the similar line widths.
In contrast, selective broadening of the a proton resonance of
[(TrPP)2(FeIII(CN)2)2]2- is observed (∆ν1/2 = 20 Hz, for three
others 12-14 Hz). Because of the proximity of the pyrrolic a
protons to the iron ion in the adjacent molecule, these protons
are strongly affected by dipolar relaxation from that paramag-
netic center. An analogous effect has been observed for
{[(TrPP)FeIII(CN)2][(Tr(p-MeOP)P)FeIII(CN)2]}2- (Figure 7)
where the a and a′ resonances are selectively broadened. This
spectrum consists of a superposition of the separate patterns of
two different subunits. The first set of [(TrPP)FeIII(CN)2]-
resonances shows chemical shifts in the range found for
[(TrPP)2(FeIII(CN)2)2]2-. The unambiguous assignment of a and
a′ resonances because of their broadening served as a convenient
starting point of the NOESY correlation, resulting in the full
assignment of the heterogeneous iron(III) diporphyrin.
relative amounts of two fragments vary. The (TrPP)FeIII(OH)
element has been identified by the very broad pyrrole resonance
at 81.3 ppm and m-phenyl signals at 12.3 and 13.5 ppm. In
particular, the pyrrole resonance is essentially broader than the
resonance of the precursor, (TrPP)2(FeIIICl)2, as expected for
the hydroxy coordination.26 The set of resonances at ca. 14 ppm
(293 K), which show anti-Curie behavior of the isotropic shift,
has been assigned to the µ-oxo bridged fragment -(TrPP)FeIII-
OFeIII(TrPP)-. These observations are consistent with the initial
formation of (TrPP)2(FeIII(OH))2, accompanied by eventual
generation of dimeric (oligomeric) species linked by the µ-oxo
bridge(s). The two terminal subunits remain five-coordinate with
the OH group in the axial position, as shown in the Scheme 3.
The steric constraints of the diporphyrin exclude the formation
of the cyclic (TrPP)2(FeIIIOFeIII)2(TrPP)2 complex with two
µ-oxo bridges linking subunits of two iron diporphyrins.
Low-Spin Iron PorphyrinssNMR Studies. Addition of an
excess of potassium cyanide to a solution of (TrPP)FeIIICl,
(TrPP)2(FeIIICl)2, or{[(TrPP)FeIIICl][(Tr(p-MeOP)P)FeIIICl]} in
methanol-d4 results in their conversion to six-coordinate low-
spin complexes: [(TrPP)FeIII(CN)2]-, [(TrPP)2(FeIII(CN)2)2]2-
,
and {[(TrPP)FeIII(CN)2][(Tr(p-MeOP)P)FeIII(CN)2]}2-. Repre-
Iron Porphyrin Cation RadicalssNMR Investigations.
1
sentative H NMR spectra are shown in Figure 7. Relevant
1
The oxidation of (TrPP)2(FeIIICl)2 has been monitored by H
chemical shift data are given in Table 4. The characteristic sets
of four upfield-shifted pyrrole resonances are observed for
NMR spectroscopy. The phenoxatiin cation radical in the form
of the hexachloroantimonium(V) salt (Phox•)(SbCl6) has been
used as the one-electron oxidant. This species is known to
oxidize iron(III) complexes, e.g. (TTP)FeIIICl, to iron(III)
(26) Cheng, R.-J.; Latos-Graz˘yn´ski, L.; Balch, A. L. Inorg. Chem. 1982,
21, 2412.

1H NMR Investigations of Triphenylporphyrin Metal Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3047
Figure 7. 1H NMR spectrum of {[(TrPP)FeIII(CN)2][(Tr(p-MeOP)P)FeIII(CN)2]}2- in methanol-d4 solution at 293 K (trace A). Resonances of
[(Tr(p-MeOP)P)FeIII(CN)2]- fragment labeled with ′. Insets present the upfield part of the spectra of [(TrPP)2(FeIII(CN)2)2]2- (B) and [(TrPP)FeIII(CN)2]-
(C).
Table 4. 1H NMR Chemical Shifts (ppm) for Low-Spin Iron(III) Porphyrinsa,b
meso-phenyl
pyrrole
o-H
m-H
p-H
p-OCH3
compound
a
b
c
d
meso
A
B
A
B
A
B
A
B
[(TrPP)FeIII(CN)2]-
(-9.5 and -12.3), (-9.7 and -10.5)
-6.9
-
-
6.1
5.8
5.8
5.7
5.1
5.3
5.3
5.1
7.8
8.0
8.0
7.7
7.3
7.8
7.8
7.4
6.7
6.6
6.8
6.4
6.4
6.4
-
-
[(TrPP)2(FeIII(CN)2)2]2-
{[(TrPP)FeIII(CN)2]
-9.4
-9.6
-8.7
-8.6
-9.0
-7.8
-8.0
-8.2
-7.3
-9.6
-9.9
-8.9
[(Tr(p-MeOP)P)FeIII(CN)2]}2-
3.9
3.7
a Methanol-d4, 293 K. b Labeling follows that in Figure 3.
complexes of porphyrin π-cation radicals, e.g. [(TTP•)FeIIICl]-
(SbCl6).27 Figure 8 shows the relevant spectra from the reaction
between (TrPP)2(FeIIICl)2 and a dichloromethane solution of
(Phox•)(SbCl6). Trace A shows the spectrum of (TrPP)2(FeIIICl)2
alone. Traces B and C present the spectrum after the additions
of successive aliquots of oxidant. The titration results in smooth
changes of the chemical shifts to achieve characteristic asymp-
totic values for each set of resonances, facilitating their
assignment. Thus, the pattern typical for iron(III) porphyrin
contains two five-coordinate [(TrPP•)FeIIICl]+ subunits. Thus,
as reflected by the multiplicity of resonances, the molecular
structure of [(TrPP•)2(FeIIICl)2]2+ retains the characteristic
geometry of the unoxidized precursor [(TrPP)2(FeIIICl)2] shown
in Scheme 2. For instance, the a and a′ protons, located in the
proximity of the bridging fragment, revealed the 20 ppm
chemical shift difference due to the five-coordinate geometry
of the iron(III). The correlation between the molecular geometry
of metallodiporphyrins and spectroscopic consequences has been
analyzed in the previous sections. In both cases, i.e., [(TrPP)2-
(FeIIICl)2](SbCl6) and [(TrPP‚)2(FeIIICl)2](SbCl6)2, the oxidation
can be reversed by treating the oxidized solution with zinc dust
to regenerate (TrPP)2(FeIIICl)2.
The spectroscopic data indicate that (TrPP)2(FeIIICl)2 can
undergo two reversible one-electron oxidations to form [(TrPP)2-
(FeIIICl)2]+ and [(TrPP‚)2(FeIIICl)2]2+. In solution, electron
exchange between (TrPP)2(FeIIICl)2 and [(TrPP)2(FeIIICl)2]+ is
sufficiently rapid to result in a single, population-averaged set
of 1H NMR resonances. In contrast, the rate of electron exchange
between [(TrPP)2(FeIIICl)2]+ and [(TrPP‚)2(FeIIICl)2]2+ is suf-
ficiently slow so that resonances from each component are
clearly resolved (as seen in Figure 8, trace D). The pattern of
resonances of [(TrPP)2(FeIIICl)2]+ is similar in several ways to
that of [(TPP•)FeIIICl]+.27 The observed features are consistent
with presence of a ligand-based a2u radical antiferromagnetically
coupled to the high-spin iron(III) center.27 Thus the initial one-
electron oxidation generates the product that contains two
iron(III) centers, one (TrPP)2- ligand and one oxidized (TrPP•)-.
The observation of one set of triphenylporphyrin resonances
instead of two separate sets (one corresponding to (TrPP)FeIIICl
and one to [(TrPP•)FeIIICl]+) may indicate that the two fragments
are equivalent. Consequently, the ligand-based unpaired electron
must be delocalized over both macrocycles. Alternatively, the
1
π-cation radical is observed which resembles the H NMR
spectrum of [(TPP•)FeIIICl](SbCl6). However, the paramagnetic
shift changes of meso phenyl resonances upon one-electron
oxidation to give [(TrPP)2(FeIIICl)2](SbCl6) are roughly one-
half that expected for a monomeric porphyrin: the ortho-H
signal is observed at 24 ppm, para-H at 19 ppm, and meta-H
at -2 ppm. Some differentiation of the pyrrole resonances has
been noted as well, although they remain centered around 80
ppm (Figure 8). Addition of further (Phox•)(SbCl6) does not
alter the spectrum assigned to [(TrPP)2(FeIIICl)2](SbCl6). How-
ever, a new set of resonances grows while the lines of [(TrPP)2-
(FeIIICl)2](SbCl6) gradually diminish in intensity. The new
multiplets assigned to the meso-phenyls appear in the regions
overlapping with those determined for [(TPP•)FeIIICl](SbCl6).
The pyrrole resonances are split to form a complex set located
at ca. 80 ppm and accompanied by two strongly shifted sets of
resonances at 95 and 115 ppm, assigned to a and a′ pyrrole
protons (trace D). The broader components can be attributed to
axial ligand replacement, although the identity of the ligands
could not be determined. On the basis of the similarity of
patterns of resonances we ascribe new features in the 1H NMR
spectrum to the formation of [(TrPP•)2(FeIIICl)2]2+, which
(27) Gans, P.; Buisson, G.; Due´e, E.; Marchon, J.-C.; Erler, B. S.; Scholz,
W. F.; Reed, C. A. J. Am. Chem. Soc. 1986, 108, 1223.

3048 Inorganic Chemistry, Vol. 38, No. 13, 1999
Wojaczyn´ski et al.
or the contribution of the Fe-O linkage was considered to be
quite significant in providing a conjugative path for delocal-
ization.15
Two-electron oxidation results in [(TrPP•)2(FeIIICl)2]2+, where
two iron(III) porphyrin π-cation radicals are located in close
proximity. Formally the system contains four centers of
magnetism, which opens a route to a rather complex pattern of
magnetic interactions. However, the mutual interaction between
subunits is rather small since the paramagnetic shifts resemble
those for monomeric [(TPP•)FeIIICl]+, but with the significant
exception of a and a′ resonances. Thus paramagnetic shifts of
a and a′ reflect simultaneously a contribution of all four magnetic
centers, namely, the iron(III) center, the cation radical localized
on the porphyrin, the iron(III) center of the adjacent porphyrin,
and the porphyrin cation radical of the adjacent porphyrin. The
contribution of the cation radical of one subunit to the
paramagnetic shift of the second one can be evaluated by
assuming the simple additivity of the contributions. Since the
formation of the cation radical has the rather minor influence
on the shift of the remaining pyrrolic protons, as expected for
the a2u ground electronic state, we have assumed that the
difference in the shifts seen for [(TrPP•)2(FeIIICl)2]2+ and
(TrPP)2(FeIIIX)2 results solely from the factor of interest (the
relevant lines of (TrPP)2(FeIIICl)2 were too broad to be observed,
so the corresponding values for (TrPP)2(FeIIIBr)2 have been
considered). Accordingly, the pertinent factors are equal to 26
and 11 ppm. At the present stage, the interpretation of these
changes is rather difficult, as they may reflect either the
additional contribution of the π-spin density and/or the modi-
fication of external contribution to the dipolar shifts.
Figure 8. 1H NMR spectra of (TrPP)2(FeIIICl)2 with (Phox•)(SbCl6)
in dichloromethane-d2 (295 K): trace A, (TrPP)2(FeIIICl)2; traces B,
C, after addition of succesive alliquots of (Phox•)(SbCl6) in dichloro-
methane-d2; trace D was obtained by overnight oxidation of [(TrPP)2-
(FeIIICl)2] with the slurry of (Phox•)(SbCl6). Signals of [(TrPP)2-
(FeIIICl)2]+ and [(TrPP•)2(FeIIICl)2]2+ labeled with 1 and 2, respectively.
Resonances of residual [(TPP•)FeIIICl]+ are identified by asterisks. The
0-10 ppm region of all spectra was omitted from the figure.
Conclusions
meso-meso-Linked diporphyrin presents the simplest ex-
ample of porphyrin arrays where the porphyrinic fragments are
linked via meso-meso positions without any spacer. In our
investigations we have focused on the hexaphenyl derivative
of the 5,5′-bisporphyrin. The ligand of interest can be formally
treated as the product of the replacement of one of the phenyls
of tetraphenylporphyrin with another type of aromatic substitu-
ent, i.e., the triphenylporphyrin moiety. To trace the extent of
communication between two closely linked porphyrinic frag-
ments, we have decided to explore the differences in the
paramagnetic shift pattern of those seen for iron(III) diporphyrins
(TrPP)2(FeIIICl)2 and the corresponding monomeric species
(TrPP)FeIIICl. As the mechanisms of the spin density distribution
are directly related to the spin/electronic state of the iron
internal exchange of the unpaired electron between two struc-
tural fragments of [(TrPP)2(FeIIICl)2]+ must be very fast (eq 1)
[(TrPP•)FeIIICl][(TrPP)FeIIICl]+ h
[(TrPP)FeIIICl][(TrPP•)FeIIICl]+ (1)
As the partial consequences of this delocalization, the
paramagnetic shifts for the meso-phenyl resonances of [(TrPP)2-
(FeIIICl)2]+ are smaller than those for [(TrPP•)2(FeIIICl)2]2+, in
which each macrocyle is oxidized by one electron. The extensive
delocalization of the positive hole that is seen for [(TrPP)2-
(FeIIICl)2]+ is of interest in the context of the electron/energy
transfer using the polyporphyrinic meso-meso-linked arrays.
We can conclude that the proximity of two π-electronic
systems of porphyrinic subunits linked by a meso-meso bridge
facilitates the delocalization of the radical π spin density over
two macrocyclic fragments. One has to keep in mind that the
two porphyrinic systems can accept several nonorthogonal
orientations of the porphyrin planes. Molecular motion about
the meso-meso link allows the direct overlap of π-orbitals.
Previously it was shown that direct meso-meso connectivity
resulted in the strong excitonic splitting in the Soret bands of
1
porphyrin, we have extended H NMR investigations on the
1
representative states of iron(III) diporphyrins. Therefore, H
NMR spectra of iron(III) diporphyrin linked by the direct meso-
meso bond have been investigated for the following spin/oxi-
dation states: (TrPP)2(FeIIICl)2 (high spin); [(TrPP)2(FeIII(CN)2)2]2-
(low spin); [(TrPP)2(FeIIICl)2]+ (high-spin iron(III), diporphyrin
radical); and [(TrPP•)2(FeIIICl)2]2+(high spin iron(III), diradical
of diporphyrin). Generally, 1H NMR investigation indicated that
the interactions between two subunits of the diporphyrins are
relatively small. As a matter of fact, the iron(III) diporphyrins
(TrPP)2(FeIIICl)2, [(TrPP)2(FeIII(CN)2)2]2-
,
and [(TrPP•)2-
(FeIIICl)2]2+ revealed the features which have been typically
encountered in the spectra of the relevant monomeric complexes
with one but very important exception. In the listed examples
we have established the 1H NMR “fingerprint” evidence of the
(TrPP)2ZnII .10
2
The extensive delocalization of the ligand hole was previously
observed for other dimeric iron(III) porphyrin complexes such
as {[(TPP)FeIII]2O}+ and {[(OEPO)FeIII]2}+, although their
delocalization pathways are fundamentally different.15,28,29 The
proximity of porphyrin planes situated one above the other and/
(28) Goff, H. M.; Philllippi, M. A. J. Am. Chem. Soc. 1982, 104, 6026.
(29) Arena, F.; Gans, P.; Marchon, J.-C. NouV. J. Chim. 1985, 9, 505.

1H NMR Investigations of Triphenylporphyrin Metal Complexes
Inorganic Chemistry, Vol. 38, No. 13, 1999 3049
Table 5. Crystal Data and Data Collection Parameters for
(Tr(p-MeOP))ZnII‚0.4CH2Cl2
presence of the meso-meso link. Because of the proximity of
the a and a′ protons to the iron(III) of the adjacent macrocycle,
these protons are most strongly affected from the second
paramagnetic center. Consequently, their signals are selectively
broadened and in the case of high-spin complexes ((TrPP)2-
(FeIIIBr)2 and (TrPP)2(FeIIII)2) and of diradical [(TrPP•)2-
(FeIIICl)2]2+ markedly downfield relocated from the position of
other pyrrole resonances.
formula
fw
color and habit
crystal system
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C41.40H30.80Cl0.80N4O3Zn
726.03
red hexagonal plate
monoclinic
C2/c
47.744(9)
9.090(2)
15.571(2)
90
93.770(13)
90
6743(2)
154(2)
1
Importantly, the H NMR spectrum of [(TrPP)2(FeIIICl)2]+
indicated that a one-electron, ligand-based oxidation of (TrPP)2-
(FeIIICl)2 has occurred but the unpaired electron is delocalized
over both meso-meso-linked macrocycles providing the crucial
example of the very efficient unpaired spin density or electron
transfer via the meso-meso bridge.
T, K
Z
d
8
calcd, g cm-3
1.430
radiation, Å
Cu KR (1.541 78 Å)
Experimental Section
µ, mm-1
1.973
range of transm factors
no. unique data
no. parameters refined
Ra
0.71-0.91
4361
494
0.076
0.253
Solvents and Reagents. All solvents were purified by standard
procedures. Chloroform-d (CDCl3, Cambridge Isotope Laboratories)
was dried before use by passing through activated basic alumina.
Methanol-d4 and dichloromethane-d2 (Cambridge Isotope Laboratories)
were used as received. Phenoxatiinylium hexachloroantimonate [(Phox•)-
(SbCl6)] was synthesized as previously described.27
wR2b
a R ) ∑||Fo| - |Fc||/∑|Fo| (observed data, I > 2σ(I) ) 3179). b wR2
) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2 (all data).
2
2
Preparation of Compounds. 5,10,15-Triphenylporphyrin
(TrPPH2) and 5,10,15-tris(p-methoxyphenyl)porphyrin (Tr(p-
MeOP)PH2) have been obtained using the modification of the Lindsey
method by methodology developed for mixed aldehyde-pyrrole
condensation. Pyrrole (2 mL, 29 mmol), benzaldehyde (2.2 mL, 21.8
mmol), and paraformaldehyde (220 mg, 7.4 mmol) were dissolved in
deoxygenated chloroform (600 mL). After addition of boron trifluoride
etherate (0.3 mL), the reaction mixture was stirred in the dark and the
solution was refluxed for 1 h. p-Chloranil (5.6 g) was added and the
solution was refluxed for an additional 1h. The solution was then taken
to dryness under reduced pressure by rotatory evaporation. The product
was dissolved in dichloromethane and chromatographed on a basic
alumina column to remove tarry products. Chromatography on activated
basic alumina was than carried out. Two fractions containing tetra-
phenylporphyrin and 5,10,15-triphenylporphyrin were gradually eluted
with benzene, evaporated to dryness, and recrystallized from n-octane/
dichloromethane (1:1 v/v) to produce TrPPH2 in yields of 5.5-7%.
The spectroscopic characteristics correspond to those determined by
Callot et al. for TrPPH2 synthesized by the different procedure.30
100)]. The demetalation with concentrated HCl of [(TrPP)ZnII][(Tr(p-
MeOP)P)ZnII] yielded (TrPPH2)(Tr(p-MeOP)PH2) (8 mg).
Metal Ion Insertions and Axial Ligand Methathesis. Insertion of
zinc(II), iron(III), gallium(III), and indium(III) followed known routes.13
Corresponding chloro, bromo, and iodo derivatives of iron(III) por-
phyrins (diporphyrins) were obtained by stirring the dichloromethane
(benzene) solution of appropriate iron(III) porphyrin with an excess of
sodium hydroxide to produce µ-oxo diiron complex or respective
hydroxo complexes. The required derivatives were prepared by stirring
the dichloromethane solution of the hydroxo (µ-oxo) species with 1 M
aqueous HX (X ) Cl, Br, I). The organic layer was separated, dried,
and evaporated to dryness, yielding corresponding iron(III) high-spin
complexes.
The dicyano-ligated complexes of the investigated iron(III) porphyrin
were prepared by dissolution of 2-3 mg of the respective high-spin
complex in 0.4 mL of methanol-d4 saturated with KCN.
Oxidation of (TrPP)2(FeIIICl)2. Titrations were performed by the
addition of aliquots of saturated solution of (Phox•)(SbCl6) in dichlo-
romethane-d2 by means of a microliter syringe to a solution of (TrPP)2-
(FeIIICl)2 in dichloromethane-d2. The oxidizing reagent has limited
solubility in dichloromethane-d2. The concentrated solution of
[(TrPP•)2(FeIIICl)2]2+ was obtained by overnight oxidation of [(TrPP)2-
(FeIIICl)2] with the slurry of (Phox•)(SbCl6).
(Tr(p-MeOP)PH2) was obtained analogously (p-anisoaldehyde
instead of benzaldehyde was used).
5,5′-Bis(10,15,20-triphenylporphyrin) [(TrPPH2)2] and 5,5′-bis-
(10,15,20-tris(p-metoxyphenylporphyrin) [(Tr(p-MeOP)PH2)2] have
been obtained by a regiospecific meso-meso coupling of the corre-
sponding monomeric zinc(II) complexes, (TrPP)ZnII or (Tr(p-MeOP)P)-
ZnII, followed by demetalation with HCl. The synthetic details are given
below for a hybrid diporphyrin.
Molecular Mechanics Calculation. Molecular mechanics calcula-
tions using the HyperChem software (Autodesk) were carried out and
displayed on a PC Pentium computer. The standard MM+ force field,
with the constraints set on the coordination bonds to achieve a
gallium(III) porphyrin geometry, have been used as described in the
text.
(TrPPH2)(Tr(p-MeOP)PH2). (TrPP)ZnII (46.2 mg, 0.077 mmol) and
(Tr(p-MeOP)P)ZnII (26.5 mg, 0.038 mmol) were dissolved in the
mixture of 20 mL of dichloromethane and 15 mL of tetrahydrofuran.
Thallium(III) trifluoroacetate (75 mg, 0.138 mmol, 1.2 equiv) in 5 mL
of THF was added to this solution. The color changed immediately
from pink to green-brown. The stirring was continued for 15 min. Silica
was added to the solution and the reaction mixture was filtered through
a bed of silica gel. Dichloromethane eluted a red fraction which was
evaporated to dryness on the rotatory evaporator. The benzene solution
of the solid residue was subjected to chromatography on a silca gel
column (0.040-0.063 mm, 230-400 mesh, Merck). Elution with
benzene gave subsequently three main fractions, (TrPP)2ZnII2, [(TrPP)-
ZnII][(Tr(p-MeOP)P)ZnII], and (Tr(p-MeOP)P)2ZnII2, that were recov-
ered as the solvent was removed under vacuum. The hybrid zinc
Instrumentation. 1H NMR spectra were recorded on a Bruker AMX
spectrometer operating in the quadrature mode at 300 MHz. A typical
spectrum was collected over a 45 000 Hz spectral window with 16K
data points with 500-5000 transients for the experiment and a 50 ms
relaxation delay. The free induction decay (FID) was apodized using
exponential multiplication depending on the natural line width. This
1
induced 5-50 Hz broadening. The residual H NMR resonances of
the deuterated solvents were used as secondary references. An inver-
sion-recovery sequence was used to suppress the diamagnetic signals
in the selected spectra. 2D COSY and NOESY experiments were carried
out as described previously.12 Mass spectra were recorded on a Finnigan
MAT TSQ 700 spectrometer using the ESI technique.
1
dipoprhyrin was identified by H NMR (details are given in Table 2)
and mass spectrometry [ESI: m/z ) 1292.5 (M+, 90), 645.4 (M2+
,
X-ray Structure Determination. Crystals of (Tr(p-MeOP)P)-
ZnII‚0.4CH2Cl2 were prepared by diffusion of n-octane into a dichloro-
methane solution of the complex in a thin tube. Suitable crystal was
(30) Callot, H.; Schaeffer, E. J. Chem. Res. (S) 1978, 51; J. Chem. Res.
(M) 1978, 0690.

3050 Inorganic Chemistry, Vol. 38, No. 13, 1999
Wojaczyn´ski et al.
molecules. The largest peak in the final difference map (1.520 e Å-3
coated with light hydrocarbon oil and directly mounted in the 130 K
dinitrogen stream of the low-temperature apparatus.
)
is 0.902 from Cl(1) and 1.059 from Cl(4). Attempts to model this peak
into the framework of the dichloromethane molecules were unsuccess-
ful. All non-hydrogen atoms, except the minor component of the
disordered methoxy group and Cl(2), were refined anisotropically. The
hydrogen atoms were refined as a riding molecule with fixed isotropic
thermal parameters. An empirical absorption correction, XABS2, was
applied.32
X-ray Data Collections. Data were collected at 130 K on a Siemens
P4 diffractometer that was equipped with a rotating anode source and
a Siemens LT-2 low-temperature apparatus. Two check reflections
showed random (less than 2%) variation during the data collection.
The data were corrected for Lorentz and polarization effects. The
radiation employed was Ni-filtered Cu KR from a Siemens rotating-
anode source operating at 15 kW. Crystal data are compiled in Table
5.
Solution and Structure Refinement. Calculations were performed
on a PC with programs of SHELXTL version 5. Scattering factors for
neutral atoms and corrections for anomalous dispersion were taken from
the standard source.31 The solutions were obtained by Patterson
methods. The methoxy group C(28) to C(34) and O(2) is disordered
over two sites. The major site was refined to 0.79 fractional occupancy.
The C-O bond lengths within this group were fixed at 1.4 Å. Two
sites, which overlapped in space, were occupied by dichloromethane
molecules, which were defined by four chlorine atom positions at 0.20
fractional occupancy. Carbon atoms were not found for these two
Acknowledgment. The financial support of the Polish State
Committee for Scientific Research KBN (Grant 3 T09A 155
15) and the U.S. National Institutes of Health (Grant GM 26226)
is kindly acknowledged.
Supporting Information Available: Crystal data, atom coordinates,
complete listings of bond lengths, anisotropic displacement coefficients
and calculated hydrogen parameters. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC990038G
(31) International Tables for X-ray Crystallography; D. Reidel Publishing
Co.: Boston, MA, 1991; Vol. C.
(32) Parkin, S.; Moezzi, B.; Hope, H. J. Appl. Crystallogr. 1995, 28, 53.