Nickel(II) complexes of 21-C-alkylated inverted porphyrins: Synthesis, protonation, and redox properties

Article abstract of DOI:10.1021/ic034096k

Reaction of the nickel(II) complex of an inverted porphyrin, (5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrinato)-nickel(II) (1), with haloalkanes in the presence of proton scavengers yields 21-C-alkylated complexes. The products are separated and characterized spectroscopically. Chirality of the formed substituted metalloporphyrins is discussed on the basis of the ¹H NMR spectra. Diastereomers are observed for the complexes containing chiral substituents. Protonation of the external nitrogen of the inverted pyrrole is combined with coordination of the apical ligand that leads to paramagnetic nickel(II) complexes. Very strong differentiation of the isotropic shift for diastereotopic methylene protons is observed in ¹H NMR spectra of the protonated paramagnetic species. For the systems containing benzyl, allyl, and ethoxymethyl substituents a mild dealkylation in solution of protonated complexes is observed in the presence of oxygen. Redox properties of the alkylated complexes are studied by means of cyclic voltammetry. Oxidation of the nickel center in 21-alkylated systems takes place at the potentials comparable to that of unsubstituted complex 1. Protonation introduces small changes to the potential of the Ni ^II/Ni^III redox couple, but it stabilizes nickel(I) species. Products of chemical oxidation and reduction of the alkylated complexes are detected by means of the EPR spectroscopy indicating in both cases metal-centered redox processes.

Full text of DOI:10.1021/ic034096k

Inorg. Chem. 2003, 42, 5579−5593
Nickel(II) Complexes of 21-C-Alkylated Inverted Porphyrins: Synthesis,
Protonation, and Redox Properties
Izabela Schmidt and Piotr J. Chmielewski*
Department of Chemistry, UniVersity of Wrocław, F. Joliot-Curie Street 14,
50 383 Wrocław, Poland
Received January 29, 2003
Reaction of the nickel(II) complex of an inverted porphyrin, (5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrinato)-
nickel(II) (1), with haloalkanes in the presence of proton scavengers yields 21-C-alkylated complexes. The products
are separated and characterized spectroscopically. Chirality of the formed substituted metalloporphyrins is discussed
on the basis of the 1H NMR spectra. Diastereomers are observed for the complexes containing chiral substituents.
Protonation of the external nitrogen of the inverted pyrrole is combined with coordination of the apical ligand that
leads to paramagnetic nickel(II) complexes. Very strong differentiation of the isotropic shift for diastereotopic methylene
protons is observed in 1H NMR spectra of the protonated paramagnetic species. For the systems containing benzyl,
allyl, and ethoxymethyl substituents a mild dealkylation in solution of protonated complexes is observed in the
presence of oxygen. Redox properties of the alkylated complexes are studied by means of cyclic voltammetry.
Oxidation of the nickel center in 21-alkylated systems takes place at the potentials comparable to that of unsubstituted
complex 1. Protonation introduces small changes to the potential of the NiII/NiIII redox couple, but it stabilizes
nickel(I) species. Products of chemical oxidation and reduction of the alkylated complexes are detected by means
of the EPR spectroscopy indicating in both cases metal-centered redox processes.
Introduction
A special set of aromatic, porphyrin-related compounds
is constituted by macrocycles identified by the presence of
a CH motif in the macrocyclic interior. Among them are
carbaporphyrins with one3 or two4 pyrrole rings replaced by
an all-carbon ring(s), so-called inverted or N-confused
porphyrins that are isomers of porphyrins,5 doubly N-
confused porphyrin,6 and isomers of oxa-, thia-, dithia-, and
selenaporphyrins.7
The group of porphyrin analogues consists of a variety of
aromatic macrocyclic compounds containing pyrrole sub-
units. Programmed synthesis of a particular macrocycle
allows profound alteration or fine-tuning of the optical, acid-
base, or coordinating properties with regard to its potential
usability in medicine, photochemistry, molecular electronics,
catalysis, etc.1 Among the analogues are the core-modified
porphyrins in which at least one of the nitrogen atoms is
substituted by another element. In this class there are mono-
and diheteroporphyrins2 containing oxygen, sulfur, selenium,
and tellurium atom(s) in the macrocyclic interior. Such a
substitution changes an overall charge of the macrocyclic
ligand and consequently alters properties of the metal
complexes since a heteroatom replaces the NH group of the
porphyrin.
The attractiveness of these macrocycles comes from their
potential ability to form carbon-metal bonds. Such orga-
nometallic coordination may be additionally stabilized by
(3) (a) Berlin, K.; Breitmaier, E. Angew. Chem., Int. Ed. Engl. 1994, 33,
1246. (b) Lash, T. D. Angew. Chem., Int. Ed. Engl. 1995, 34, 2533.
(c) Lash, T. D.; Chaney, S. T. Tetrahedron Lett. 1996, 37, 8825. (d)
Lash, T. D.; Chaney, S. T. Angew. Chem., Int. Ed. Engl. 1997, 36,
840. (e) Berlin, K. Angew. Chem., Int. Ed. Engl. 1996, 35, 1820. (f)
Hayes, M. J.; Lash, T. D. Chem.sEur. J. 1998, 4, 508. (g) Lash, T.
D.; Chaney, S. T. Chem.sEur. J. 1996, 2, 944. (h) Lash, T. D.; Hayes,
M. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 840. (i) Lash, T. D.
Chem. Commun. 1998, 1683. (j) Lash, T. D.; Chaney, S. T.; Richter,
D. T. J. Org. Chem. 1998, 63, 9076. (k) Hayes, M. J.; Spence, J. D.;
Lash, T. D. Chem. Commun. 1998, 2409. (l) Lash, T. D. Synlett 2000,
279. (m) Richter, D. T.; Lash, T. D. Tetrahedron 2001, 57, 3659. (n)
Lash, T. D.; Hayes, M. J.; Spence, J. D.; Muckey, M. A.; Ferrence,
G. M.; Szczepura, L. F. J. Org. Chem. 2002, 67, 4860. (o) Graham,
S. R.; Colby, D. A.; Lash, T. D. Angew. Chem., Int. Ed. 2002, 41,
1371. (p) Colby, D. A.; Lash, T. D. Chem.sEur. J. 2002, 8, 5397.
(q) Liu, D.; Lash, T. D. Chem. Commun. 2002, 2426.
* To whom correspondence should be addressed. E-mail: pjc@
wchuwr.chem.uni.wroc.pl.
(1) (a) Jasat, A.; Dolphin, D. Chem. ReV. 1997, 97, 2267. (b) Sessler, J.
L.; Gebauer, A.; Vogel, E. In The Porphyrin Handbook; Kadish, K.
M., Smith, K. M., Guilard, R., Eds.; Academic Press: New York,
2000; Vol. 2, Chapter 8.
(2) (a) Latos-Graz˘yn´ski, L. In The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 2000;
Vol. 2, p 361. (b) Pacholska, E.; Latos-Graz˘yn´ski, L.; Ciunik, Z.
Angew. Chem., Int. Ed. 2001, 40, 4466.
10.1021/ic034096k CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/05/2003
Inorganic Chemistry, Vol. 42, No. 18, 2003 5579

Schmidt and Chmielewski
Chart 1. Inverted Porphyrin and Its Derivatives
the macrocyclic effect as well as by aromatic system of the
porphyrinoid allowing observation of systems that are
otherwise unstable. The interest in coordination chemistry
of carbaporphyrinoids is growing rapidly. To date inverted
porphyrin5a,d,8 and doubly N-confused6,9 porphyrin as well
as benzi-,10 oxybenzi-,11 benzocarba-, and azuliporphyrin12
have been shown to form stable complexes with transition
metal ions. In the complexes of the inverted porphyrin the
N-confused pyrrole can play a different roles depending on
the metal ion, its oxidation state, or the method of the
complex synthesis.8 The external nitrogen can be free8c,d or
proton-bearing.5a,e,8a,b,e,f,h It can also be involved in coordina-
tion.8e,g,i,j The internal carbon can be bonded to a metal ion
in several different ways.5a,e,8b,f,h Depending on the number
of protons leaving the macrocycle upon coordination, the
ligand can act as a mono-, di-, or trianion which can
compensate for charge on the metal ion. Such a variety of
coordination modes makes the inverted porphyrin versatile
and unique.
Discovery of the meso-tetraaryl-substituted inverted por-
phyrins among the products of the Rothemund synthesis
mixture5a,b and subsequent optimization of the synthesis5e
with respect to the inverted porphyrin make this macrocycle
a readily obtainable and therefore attractive subject of studies
and modifications (Chart 1). The inverted pyrrole is par-
ticularly reactive having an exposed nitrogen atom that can
be protonated,5a methylated,13 or fused in the porphyrin
interior.14 The tautomeric form of the macrocycle containing
protonated external nitrogen15 is susceptible to reaction in
position 3, i.e., on the external carbon atom in the vicinity
of the outer nitrogen.16 A facile autoxidation of the ethyl
substituent attached to this position leads to 3-hydroxyethyl
and 3-acetyl derivatives of inverted porphyrin.17 Both proton-
bearing carbons of inverted pyrrole can be brominated,14 and
nitration of its internal carbon takes place under mild
conditions.18
A particularly promising and simple method of modifica-
tion of inverted porphyrins is related to the reactivity of the
inverted pyrrole in metal complexes where the coordinating
carbon is deprotonated. It has been shown that methylation
of the internal carbon is possible for nickel(II)19 and copper-
(II)8b complexes under mild conditions. Also, the dienophilic
activity of the inverted pyrrole in the nickel(II) complex of
inverted porphyrin has been reported recently.20
(4) Lash, T. D.; Romanic, J. L.; Hayes, M. J.; Spence, J. D. Chem.
Commun. 1999, 819.
(5) (a) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.; Glowiak,
T. Angew. Chem., Int. Ed. Engl. 1994, 33, 779. (b) Furuta, H.; Asano,
T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 767. (c) Liu, B. Y.;
Bru¨ckner, C.; Dolphin, D. Chem. Commun. 1996, 2141. (d) Lash, T.
D.; Richter, D. T.; Shiner, C. M. J. Org. Chem. 1999, 64, 7973. (e)
Geier, G. R., III; Haynes, D. M.; Lindsey, J. S. Org. Lett. 1999, 1,
1455.
(6) Furuta, H.; Maeda, H.; Osuka, A. J. Am. Chem. Soc. 2000, 122, 803.
(7) (a) Heo, P. Y.; Shin, K.; Lee, C.-H. Tetrahedron Lett. 1995, 37, 197.
(b) Lee, C.-H.; Kim, H.-J. Tetrahedron Lett. 1997, 38, 3935. (c) Lee,
C.-H.; H. J.; Yoon, D.-W. Bull. Korean Chem. Soc. 1999, 20, 276.
(d) Sprutta, N.; Latos-Graz˘yn´ski, L. Tetrahedron Lett. 1999, 40, 8457.
(e) Pacholska, E.; Latos-Graz˘yn´ski, L.; Szterenberg, L.; Ciunik, Z. J.
Org. Chem. 2000, 65, 8188. (f) Sprutta, N.; Latos-Graz˘yn´ski, L. Org.
Lett. 2001, 3, 1933.
(8) (a) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1997, 36,
840. (b) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Schmidt, I. Inorg.
Chem. 2000, 39, 5475. (c) Furuta, H.; Ogawa, T.; Uwatoko, Y.; Araki,
K. Inorg. Chem. 1999, 38, 2676. (d) Ogawa, T.; Furuta, H.; Takahashi,
M.; Morino, A.; Uno, H. J. Organomet. Chem. 2000, 661, 551. (e)
Furuta, H.; Kubo, N.; Maeda, H.; Ishizuka, T.; Osuka, A.; Nanami,
H.; Ogawa, T. Inorg. Chem. 2000, 39, 5424. (f) Chen, W.-C.; Hung,
C.-H. Inorg. Chem. 2001, 40, 5070. (g) Srinivasan, A.; Furuta, H.;
Osuka, A. Chem. Commun. 2001, 1666. (h) Bohle, D. S.; Chen W.
C.; Hung, C. H. Inorg. Chem. 2002, 41, 3334. (i) Harvey, J. D.; Ziegler,
C. J. Chem. Commun. 2002, 1942. (j) Hung, C.-H.; Chen, W.-C.; Lee,
G.-H.; Peng, S.-M. Chem. Commun. 2002, 1516.
Alkylated inverted porphyrins are isomeric with their
regular analogues. The N-alkylated porphyrins and their metal
complexes have long been known and studied in the context
of their significance in heme metabolism. Many different
synthetic approaches were applied to modify the porphyrinic
interior with various N-alkyl substituents.21
In this paper we report the results of our study on the
alkylation of the nickel(II) complex of inverted porphyrin
(14) Furuta, H.; Ishizuka, T.; Osuka, A.; Ogawa, T. J. Am. Chem. Soc.
2000, 122, 5748.
(9) (a) Furuta, H.; Maeda, H.; Osuka, A. Chem. Commun. 2000, 1143.
(b) Araki, K.; Winnischofer, H.; Toma, H. E.; Maeda, H.; Osuka, A.;
Furuta, H. Inorg, Chem. 2001, 40, 2020.
(10) Ste¸pien´, M.; Latos-Graz˘yn´ski, L. Chem.sEur. J. 2001, 7, 5113.
(11) Ste¸pien´, M.; Latos-Graz˘yn´ski, L.; Lash, T. D.; Szterenberg, L. Inorg.
Chem. 2001, 40, 6892.
(15) (a) Furuta, H.; Ishizuka, T.; Osuka, A.; Dejima, H.; Nakagawa, H.;
Ishikawa, Y. J. Am. Chem. Soc. 2001, 123, 6207.
(16) Schmidt, I.; Chmielewski, P. J. Tetrahedron Lett. 2001, 42, 1151.
(17) Schmidt, I.; Chmielewski, P. J. Tetrahedron Lett. 2001, 42, 6389.
(18) Ishikawa, Y.; Yoshida, I., Akaiwa, K.; Koguchi, E.; Sasaki, T.; Furuta,
H. Chem. Lett. 1997, 453.
(12) (a) Graham, S. R.; Ferrence, G. M.; Lash, T. D. Chem. Commun. 2002,
894. (b) Muckey, M. A.; Szczepura, L. F.; Ferrence, G. M.; Lash, T.
D. Inorg. Chem. 2002, 41, 4840.
(19) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Głowiak, T. J. Am. Chem.
Soc. 1996, 118, 5690.
(20) Xiao, Z.; Patrick, B. O.; Dolphin, D. Chem. Commun. 2002, 1816.
(21) Lavalee, D. K. The Chemistry and Biochemistry of N-Substituted
Porphyrins: VCH Publishers: Weinheim, Germany, 1987.
(13) Chmielewski, P.; Latos-Graz˘yn´ski, L. J. Chem. Soc., Perkin Trans. 2
1995, 503.
5580 Inorganic Chemistry, Vol. 42, No. 18, 2003

Ni(II) 21-C-Alkylated InWerted Porphyrins
Scheme 1. Alkylation of Nickel(II) Complex of Inverted Porphyrin with Monohaloalkanes
using a selection of alkylating agents. We concentrate here
on the selectivity of the reaction with respect to the
21-monoalkylated product, chirality of the alkylated com-
plexes, and ability of the nickel center to change its spin
and oxidation states.
phyrin with MeI.19,22 In both cases the reaction took about 2
weeks. On the other hand the full conversion of 1 into
paramagnetic 2,21-dimethyl derivative is completed after 7
h of reflux of the starting complex with 30-fold excess of
MeI in dichloromethane/ethanol solution with a potassium
carbonate suspension.
Results and Discussion
In some cases (e.g. for CH3Br/K2CO3/dibenzo[18]crown-
6 in CH2Cl2) a considerable amount (about 30% of alkylated
product) of 2-methyl-substituted complex12 9 is formed, the
product that has not been observed in the case of alkylation
of 1 with methyl iodide in the absence of a base.19 It seems
to be in line with predicted activation of the external nitrogen
toward alkylation by proton scavengers. Likely, the relative
reaction rates of the internal and external alkylation depend
on the halogen in RX and on the form of the basic catalyst.
As we have reported recently,23 reaction of 1 with
dihalomethanes yields nickel(II) complexes of bis(porphy-
rinoid) products 10 and 11 (Chart 2). However, in the
presence of primary alcohol, e.g. ethanol, monomeric 2- and
21-alkoxymethyl-substituted derivatives (12 and 13) are
formed instead of dimeric species.24
Reaction of 1 with 1,2-dibromoethane yields both dimeric
21,21′-ethylene-linked dimer 14 and 2-bromoethyl-substi-
tuted monomer 15, while alkylation with 1,3-dibromopropane
results solely in the formation of the 21-allyl-substituted
derivative 16.24
Characterization. The alkylated derivatives of 1 have
been characterized by optical spectra, mass spectrometry, and
1H and 13C NMR including 2D homo- and heteronuclear
correlation techniques.
Syntheses. The general procedure involves addition of an
excess of RX to the solution of 1 in dichloromethane,
chloroform, or THF (Scheme 1). The reaction progress was
monitored by UV-vis and H NMR spectroscopy, and the
products were separated chromatographically.
1
The internal carbon atom of the inverted pyrrole in the
initial nickel(II) complex of inverted porphyrin 1 has the
character of an sp2 carbanion coordinated to the metal cation.
It can be reversibly protonated,5d,8b,17 which is accompanied
by a change of its hybridization to sp3, and the Ni-C bond
is preserved. Although exposed, the external nitrogen should
not be a primary alkylation target since it bears proton that
is hard to substitute under neutral conditions. It seemed likely
that the selectivity for alkylation at the internal carbon would
be improved in the absence of a basic catalyst. Under such
the conditions, however, the reaction proceeds only for the
most reactive iodoalkanes. It takes several days to convert
about 50% of the starting complex into alkylated products.
Moreover, the selectivity is rather poor since there are
comparable amounts of mono- and dialkylated products in
the reaction mixture.19
Somewhat surprisingly, in all but one case, application of
a basic catalyst not only accelerates the reaction but also
promotes alkylation with bromo- and chloroalkanes giving
apparently better reaction selectivity with respect to the
internally monoalkylated products. The reaction should be
carried out under anaerobic conditions since 1 is subjected
to autoxidation under basic conditions.8a The required
reaction period varies depending on the haloalkane.
For iodoalkanes such as methyl or ethyl iodide in the
presence of a basic catalyst a significant acceleration of the
formation reaction of 2,21-dialkylated products can be
observed as well. The dimethylated nickel(II) complex 8 was
previously generated either by methylation of 1 using methyl
iodide at room temperature or by treating the nickel(II)
complex of the 2-methylated homologue of inverted por-
In all cases, the apparent molecular ions in the mass spectra
agree with the assumed elemental composition having the
appropriate m/z ratio as well as the correct isotope pattern.
The UV-vis spectra of monomeric nickel(II) complexes of
inverted porphyrin possessing an alkyl bound to the internal
carbon of the inverted pyrrole are all similar regardless of
the substituents at 21-C.19,24
The proton NMR spectra of the monomeric compounds
having an alkyl bound to the internal carbon display a typical
(22) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 2000, 39, 5639.
(23) Schmidt, I.; Chmielewski, P. J. Chem. Commun. 2002, 92.
(24) Schmidt, I.; Chmielewski, P. J.; Ciunik, Z. J. Org. Chem. 2002, 67,
8917.
Inorganic Chemistry, Vol. 42, No. 18, 2003 5581

Schmidt and Chmielewski
Chart 2. Monomeric and Dimeric Products of Reaction of 1 with
Dihaloalkanes23,24
Figure 1. 1H NMR spectra (500 MHz, CDCl3, 298 K) of 21-alkylated
nickel(II) complexes of an inverted porphyrin: A, 3; B, 4; C, 7.
Assignments: pyrr, â-pyrrole; 3, inverted pyrrole; o-, m-, p-Ph, ortho, meta,
para protons of meso-phenyls; o, m, p, ortho, meta, para protons of benzyl
substituent in 7; 1′, methylene group attached directly to 21-C.
pattern that includes a low-field signal for proton 3 (9.5-
9.7 ppm), a set of six pairwise spin-spin-coupled signals
of â-pyrrole protons (8.3-8.8 ppm), broad signals of ortho-
protons (7.9-8.3 ppm at 298 K), and overlapping multiplets
for the remaining meso-phenyl protons (7.5-7.8 ppm). These
features are similar for all these compounds. The most
diagnostic for each of these complexes is a high-field region
of the spectra (-5 to 1 ppm) where some signals of the alkyl
substituents can be found. Their upper-field positions are
related to the diatopic current of the carbaporphyrinoid and
unequivocally indicate the intraannular location of the
substituents (Figure 1). For the benzyl-substituted species
the substituent signals are spread over a broader region. The
shielding effect of the ring current affects not only methylene
but also phenyl protons, according to their distance from the
aromatic porphyrin ring. Thus, the ortho-protons resonate
further upfield (by ∼1.5 ppm) than meta and para protons.
The molecules are nonplanar which is indicated by the
differentiation of the signals for the ortho-protons of the
meso-phenyls that are broad at room temperature due to fast
rotation but sharpen at 213 K. The pyramidal hybridization
Figure 2. 1H-13C HMBC map of 7 (CDCl3, 223 K). The graph shows
assignments of the correlation signals.
of 21-C can be derived from 13C NMR spectra of 21-
alkylated nickel complexes of inverted porphyrin where its
signal appears in the region of 30-40 ppm that is typical of
sp3 carbons with no proximal heteroatom. It can be easily
identified in the 1H-13C HMBC map since it correlates with
proton 3 (Figure 2).
Protons of the methylene group directly attached to the
inner carbon of the inverted pyrrole are diastereotopic, which
reflects the asymmetry of 21-C and the chirality of the
molecule. The differentiation can be seen most clearly for
the benzyl substituent in 7 (Figure 1C) for which two sharp
doublets appear around -1.5 ppm with a coupling constant
2J ) 13.7 Hz. These protons are spin-spin coupled with
carbon nuclei of the phenyl ring of the substituent and those
of the inverted pyrrole. The coupling constants of 1′-H with
21-C, ipso, and ortho carbon nuclei seem to be similar for
both protons since equally strong correlation peaks with these
5582 Inorganic Chemistry, Vol. 42, No. 18, 2003

Ni(II) 21-C-Alkylated InWerted Porphyrins
Scheme 2. Protonation of External Nitrogen of Inverted Pyrrole
a pyridine-like character in 2-7, 10, 12, 14, and 16. Thus,
protonation of this site is facile. Since such a protonation
changes the overall charge of the complex, the presence of
a counteranion is required. The counteranion coordinates to
the nickel(II) ion changing the geometry of its coordination
sphere from square-planar to square-pyramidal (Scheme 2).
Consequently, the metal ground state is transferred from
singlet to triplet and the complexes become paramagnetic.19
Coordination of an apical anionic ligand is a consequence
of protonation; thus, the character of the five-coordinated
complexes is very labile. The ligand exchange as well as
deprotonation with restitution of the diamagnetic precursor
is facile. In fact, the latter process can be accomplished by
addition of water to the solution of the protonated species
in dichloromethane or by passing the solution down a silica
gel column.
1
Figure 3. Low- and high-field parts of the H NMR spectra (500 MHz,
CDCl3, 298 K) of 5 (A) and 6 (B) presenting the occurrence of
diastereomers. The graphs show assignments of substituent protons. Labels
“a” and “b” differentiate protons of various diastereomers; pyrr ) â-pyrrole.
1
carbons are observed in the HMBC map (Figure 2).
However, they differ considerably in the values of 3JHC with
1-C and 4-C. Hence, there is only one correlation instead of
two in the HMBC map for each of the latter nuclei with
methylene protons 1′. We observe such a behavior for all
the other complexes that have a methylene fragment attached
to the 21-C. This may indicate restricted rotation around the
1′-21 bond reflecting dependence of a vicinal H-C coupling
on the torsional angle.
The alkylation of 1 is nonstereospecific when carried out
under the conditions described above. For substituents that
contain their own centers of chirality (i.e. sec-butyl in 5 and
2-methylbutyl in 6) the 1:1 mixtures of diastereomers are
formed. Their 1H NMR spectra show separate sets of signals
for each of the diastereomers, particularly in the high-field
region (Figure 3). In the case of 5, which contains two
directly bound asymmetric carbons, there are 12 signals of
â-pyrrole protons. A differentiation of chemical shifts and
coupling constants between the chemically equivalent protons
of the methylene groups is particularly well noticeable for
both diastereomers a and b of 5 and 6. For compound 6 the
diastereomers have different configuration only on 21-C since
a pure enantiomer S of 2-methylbutyl iodide has been used
for its synthesis. Since no racemization is expected for the
substituent, any enantiomer excess in the alkylation reaction
The H NMR spectra of the protonated species can be
obtained in situ by addition of a solution of acid directly to
the NMR tube, which allows the control on concentration
of acid and observation of possible consecutive equilibria.
An alternative method of sample preparation is dissolution
of protonated sample. However, this method limits the
concentration of the apical ligand that can lead in some cases
to dynamic phenomena related to its coordination and
consequently to the broadening of spectral lines. In such cases
addition of an excess of anionic ligand in the form of a
tetraalkylammonium salt is necessary to saturate the equi-
librium. We do so in the case of variable-temperature
experiments to eliminate interference of chemical exchange.
The spectra of the 2-protonated-21-alkylated complexes
from 2-HCl to 7-HCl, 10-HCl, and 16-HCl are typical for
the paramagnetic pentacoordinated nickel(II) complexes of
porphyrin analogues.2a,19,22,25 The assignment of the signals
is based on selective deuteration in all pyrrole positions,
application of deuterated acids, and relative line intensities
and widths. The spectra consist of widespread, relatively
narrow (line half-width < 200 Hz) low-field shifted signals
of â-pyrrole protons (20-80 ppm), the high-field-shifted
signals of 3-H (-15 to 1 ppm) and 2-NH (-30 to -20 ppm),
and aryl proton peaks occurring in the crowded region -10
to 15 ppm (Figure 4, Table 1). These features that are
common for all paramagnetic complexes under study result
from the spin density delocalization on the macrocyclic
1
would appear in H NMR as a higher concentration of one
of diastereomers.
Previously, we observed the 1:1 mixture of diastereomers
(i.e. racemate and a meso-form) for “symmetric” dimer 14
containing two chiral carbon atoms linked by the ethylene
bridge.24
Protonation. Alkylation of 21-C enhances the nucleophi-
licity of 2-N since it changes its pyrrolic character in 1 into
(25) (a) Latos-Graz˘yn´ski, L. Inorg. Chem. 1985, 24, 1681. (b) Lisowski,
J.; Latos-Graz˘yn´ski, L.; Szterenberg, L. Inorg. Chem. 1992, 31, 933.
(c) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1992, 31,
5231. (d) Latos-Graz˘yn´ski, L.; Pacholska, E.; Chmielewski, P. J.;
Olmstead, M. M.; Balch, A. L. Inorg. Chem. 1996, 35, 566. (e)
Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Olmstead, M. M. Balch, A.
L. Chem.sEur. J. 1997, 3, 182.
Inorganic Chemistry, Vol. 42, No. 18, 2003 5583

Schmidt and Chmielewski
Table 1. 1H NMR Data for Paramagnetic Nickel(II) Complexes of 2-Protonated-21-Alkylated Inverted Porphyrin in CDCl3
complex
meso-phenyl and other
(temp, K)
â-pyrrole
3-H
2-NH
-22.7
R
paramagnetically shifted protons
4-HCl (298)
57.2, 56.6, 49.9, 46.4, 26.2, 24.8 -2.2
90.1, 50.9 (1′)
11.2, 10.5, 10.1, 10.0, 9.2, 9.0,
8.8, 8.6, 6.9, 6.7, 6.5, 5.1,
4.7, 3.0
4-HCl (213)
5-HCl (298)
78.5, 78.0, 68.1, 62.8, 35.5, 33.8 -6.3
-38.2
140.3, 60.4 (1′), -0.2, -2.1
13.2, 12.1, 11.6, 11.2, 10.1,
10.0, 9.4, 8.5, 6.3, 5.7, 3.5, 2.9
10.5, 10.0, 9.4, 9.0, 8.6, 8.3,
5.7, 4.2, 3.7
(58.8, 55.7, 48.3, 46.5),a (58.3,
56.2, 50.4, 45.0),b
-6.1
(-21.5)b (-22.2)a 124.4, 105.9 (2′), 15.7 (3′)
29.6, 29.4, 29.0, 28.9
(80.7, 76.2, 65.5, 63.2, 41.1,
39.5),a (80.0, 76.8, 69.1,
60.5, 40.2, 39.2)b
5-HCl (213)
-13.7
(-37.0)c
189.6, 128.4 (2′), 31.9 (3′),
-1.4, -2.7
16.7,12.9, 12.5, 11.9, 11.7,
11.5, 10.7, 10.0, 9.7, 9.5,
9.3, 9.0, 8.5, 8.2, 8.1, 6.7,
6.2, 6.0, 4.4, 4.2, 3.9, 3.2,
2.9, 2.3
11.2, 10.6, 10.5, 10.3, 9.3, 9.2,
9.0, 8.7, 7.9, 6.9, 6.8, 4.3,
4.1, 3.7, 0.9
13.2, 12.6, 12.2, 11.9, 11.8,
11.7, 11.0, 10.3, 10.0, 9.9,
9.6, 9.2, 8.5, 7.7,6.4, 5.5,
3.5, 2.0, 1.8, 0.5
6-HCl (298 K) 57.1, 56.9, 56.8, 56.7, 50.9,
50.5, 46.9, 46.6, 27.2,
-1.5, -1.8 (-22.6)c
-3.5, -4.4 (-38.1)c
120.0, 89.5, 64.0, 31.4 (1′),
0.4, -1.8 (CH3), -4.7 (CH2)
26.7, 25.6, 24.9
6-HCl (213)
78.0, 77.9, 77.8, 77.5, 69.6,
69.1 63.3, 62.8, 36.7,
36.1, 34.5, 33.7
191.2, 161.1, 57.1, 26.2 (1′),
-0.5, -2.8 (CH3), -7.2 (CH2)
7-HCl (298)
7-HCl (213)
56.9, 56.3, 50.6, 46.6, 26.0, 24.3
1.1
-24.2
-40.4
-23.0
94.5, 47.3 (1′)
11.3, 10.6, 10.4, 10.3, 10.0, 9.3,
8.8, 8.7, 6.9, 6.4, 5.5, 5.0, 4.7,
4.3, 4.1
13.4, 12.2, 11.8, 10.9, 10.1, 9.7,
9.2, 8.8, 6.2, 5.5, 4.5, 3.3, 2.5,
0.6
11.1, 10.4, 10.0, 9.2, 8.9, 8.7, 8.6,
6.9, 6.5, 6.1, 6.0, 5.3, 4.8, 4.3,
4.2, 3.8
78.9, 78.8, 69.7, 63.8, 35.6, 33.3 -0.9
150.3, 51.1 (1′)
16-HCl (298) 57.0, 56.5, 50.2, 46.6, 26.1, 24.6
0.9
87.6, 55.3 (1′) 16.9 (2′)
16-HCl (213) 78.2, 77.8, 68.5, 62.9, 35.3, 33.5 -1.2
2-HCl (293)d 58.1, 58.1, 52.4, 48.2, 26.5, 24.9
-38.2
-23.1
136.1, 69.1 (1′) 23.1 (2′), 14.7 (3′) 13.2, 12.1, 11.6, 10.0, 9.6, 7.8,
6.2, 5.6, 3.6, 2.8
2.0
109.7
11.3, 10.7, 10.5, 10.4, 9.3, 9.2,
8.7, 7.8, 6.9, 6.4, 5.1, 4.9, 4.1
a Signals of diastereomer a. b Signals of diastereomer b. c The same chemical shift for both diastereomers. d Data from ref 19.
tion of the π-type orbitals in the spin density transfer results
in differentiation of isotropic shift of these signals and
determines the upfield position of 3-H and 2-NH signals.
For the latter protons the overlap of π-symmetry orbitals of
metal and ligand is effective due to a tilt of the inverted
pyrrole out of plane of the macrocycle.19,22 The substituent
protons attached to the carbon that is directly bound to the
21-C (assigned 1′ but 2′ in the case of 5-HCl) give
considerably broader signals, which reflect their closeness
to the paramagnetic center. The protons of the methylene
groups are diastereotopic, and the difference in their chemical
shifts reaches several tens up to more than a hundred ppm.
Protons located on the carbons that are further from 21-C
(more than two bonds) give less paramagnetically shifted
signals. For 5-HCl the methylene group of the secondary
butyl substituent (3′) has a significant downfield shift. In
16-HCl proton 2′ of the allyl substituent resonates at 16.9
ppm (298 K, CDCl3). Similarly, in the case of paramagnetic
unsymmetrical dimer 10-HCl only one pyrrole proton of the
N-substituted fragment (most likely proton 3, which is the
closest to the methylene linker) shows a paramagnetic shift
comparable to those of â-pyrrole protons of C-substituted
subunits.23
Diastereomers are observed for the complexes 5-HCl and
6-HCl containing substituents with their own chiral centers.
The chemical shifts of pyrrole protons are particularly
differentiated for the diastereomers of 5-HCl having a
secondary butyl group attached to the internal carbon of the
Figure 4. 1H NMR (500 MHz, CDCl3) of 5-HCl (A, 233 K), 6-HCl (B,
213 K), and 16-HCl (C, 233 K). Assignments are as in Figures 1-3.
ligand in which σ-orbitals are predominantly involved
causing a low-field shift of â-pyrrole signals. Some contribu-
5584 Inorganic Chemistry, Vol. 42, No. 18, 2003

Ni(II) 21-C-Alkylated InWerted Porphyrins
Figure 5. Curie plots of 4-HCl (A), 5-HCl (B), 6-HCl (C), and 7-HCl (D) based on the data taken for CDCl3 solutions of respective systems. The assignments
“a” and “b” are introduced to distinguish the diastereomers but are not related to labeling of the diamagnetic precursors in Figure 3. The nonlinear dependencies
have been traced by means of a second-order polynomial fitting procedure but are drawn only to join the experimental points.
inverted pyrrole. Moreover, for this complex the signals of
isomers differ also in line widths and in the integral signal
intensities indicating about 20% excess of one of them in
the temperature range 273-233 K in CDCl3 (Figure 4A).
At 213 K concentrations of both diastereomers are equal.
Since the mixture of their diamagnetic precursors contained
exactly the same concentrations of both diastereomers (Figure
3), the observed diastereoselectivity reflects different sus-
ceptibility of nickel(II) to apical ligation of chloride upon
protonation of 2-N in the stereoisomers. It results from the
different steric factors in the proximity of coordination center
in the diastereomers since the electronic substituent effect
is the same in both complexes. There is also a significant
difference (about 45 ppm at 233 K) in chemical shifts of
the protons 2′, i.e., those attached to the secondary carbon
that is directly bound to the 21-C. It may reflect an influence
of the preferred orientation of alkyl group on the contribution
of π-spin density delocalization to the isotropic shift.26
Deviation from planarity causes a considerable spin density
transfer from the metal to the inverted pyrrole via a π-orbital
framework and, consequently, the more upfield paramagnetic
shift of protons 3 and 2-NH. However, protons of the alkyl
groups attached directly to the ring, onto which spin density
is delocalized predominantly by the π-mechanism, display
a low-field shift.26 Spin density transfer via a σ-orbital
(26) Walker, F. A.; Simonis, U. In Biological Magnetic Resonance, Vol.
12: NMR of Paramagnetic Molecules; Berliner, L. J., Reuben, J., Eds.;
Plenum Press: New York, 1993; p 133.
Inorganic Chemistry, Vol. 42, No. 18, 2003 5585

Schmidt and Chmielewski
framework always gives a positive contribution to the
isotropic shift (low-field shifting) that attenuates as the
number of bonds between the paramagnetic metal center and
the given nucleus increases.26 Hence, in the case of protons
bound to the carbon attached to 21-C both σ- and π-contri-
butions to the isotropic shift are positive. Since these protons
are the least distant from the metal ion (3 bonds), their signals
are expected to be the most downfield-shifted among all
protons in the molecule. Indeed, for the complexes where
no diastereotopic differentiation of protons is observed, such
as 2-HCl19 or 5-HCl the signals of methyl protons or 2′-H,
respectively, are very strongly paramagnetically shifted to
the low field (δ > 100 ppm). On the other hand, for the
complexes with diastereotopic methylene bound to 21-C (4-
HCl, 6-HCl, 7-HCl, 10-HCl,23 16-HCl), one of the CH2
protons is much less downfield shifted than the other and
even less shifted than signals of some of the more distant (4
bonds) â-pyrrole protons. For example, in the case of 7-HCl
the difference of chemical shifts between methylene protons
of the benzyl group reaches 100 ppm (213 K, CDCl3). This
observation can be accounted for by a contribution of the
dipolar mechanism to spin delocalization onto these parts
of the molecule that are closest to the paramagnetic center.25
The variable-temperature 1H NMR experiments support such
an interpretation. Dependencies of δ vs 1/T (Figure 5) for
pyrrole protons are linear with extrapolated intercepts in most
cases only moderately deviated (by 1-5 ppm) from the
values predicted on the basis of chemical shifts of diamag-
netic references (i.e. unprotonated diamagnetic complexes
for pyrrole and alkyl protons, monocation of inverted
porphyrin5a for 2-NH). On the other hand, for the alkyl
protons 1′ (2′ in the case of 5-HCl) these dependencies are
either nonlinear or have intercepts very strongly deviating
from those expected. In one case (6-HCl), reverse temper-
ature dependencies of chemical shift are observed for two
out of four methylene protons 1′ of the diastereomers. The
difference in paramagnetic shifts and in the temperature
dependencies between the protons belonging to the same
methylene group can arise from their different mean orienta-
tion with respect to the principal axes of the magnetic
susceptibility tensor. In other words, the geometric factor
that governs the sign and value of the dipolar component of
the isotropic shift is responsible for the differentiation of
chemical shift of these diastereotopic protons 1′.27
Figure 6. Low-field part of the selected 1H NMR spectra (500 MHz, CD2-
Cl2) taken in the course of titration of 10 with TFAD: A, 1 equiv of acid,
213 K; B, 2 equiv of acid, 213 K; C, 4 equiv of acid, 213 K; D, 4 equiv of
acid 173 K; E, as in D + 2 equiv of [BzEt3N]Cl.
defined by the N3C(R) chromophore and coordination of an
apical anionic ligand. If H+ is attached to the internal carbon,
the charge of the proton is delocalized onto the external
nitrogen.
Asymmetric dimer 10 contains both types of potential
protonation targets, i.e., external nitrogen and internal carbon.
Addition of either TFAH or HCl23 effectively converts the
complex into the paramagnetic species 10-HX due to
protonation of the external nitrogen of the 21′-substituted
fragment. In the case of HCl, the increase of its concentration
does not change the number of spectral lines or their positions
1
in the H NMR spectrum either at room temperature or at
213 K. It suggests that in the case of hydrochloric acid only
one protonation site is involved. On the other hand, the
spectrum depends on the acid concentration when TFAH is
used for titration of 10 at low temperatures. Addition of 1
equiv of acid at 213 K results in a spectrum consisting of
six downfield-shifted â-pyrrole peaks of C-substituted frag-
ment and one signal of pyrrole proton of N-substituted
subunit of the dimer (Figure 6A). Further increase of acid
concentration causes considerable broadening of the spectral
lines. At 173 K in CD2Cl2 the lines sharpen up and double
in number due to a slowing down of the chemical exchange
(Figure 6D). By exploitation of the kinetic isotope effect,
the chemical exchange can be more effectively slowed when
deuterated trifluoroacetic acid (TFAD) is applied. The
number of peaks does not change any more with increasing
concentration of acid (up to 10-fold excess). This behavior
can be accounted for by a protonation of 21-C in the
N-substituted fragment of the complex and formation of the
diprotonated species [(10-TFAH)H]TFA (Scheme 3). The
doubling of the number of pyrrole signals likely reflects
presence of diastereomers due to the occurrence of two
As we8b,17,24 and others5d reported recently, protonation of
the internal carbon of the inverted pyrrole in nickel(II)
complexes of 21-unsubstituted inverted porphyrins results
in a distribution of the additional positive charge within the
molecule different from that observed in the paramagnetic
species described above. Consequently, nickel(II) ion remains
four-coordinated and diamagnetic despite analogous changes
of charge that take place upon protonation. It can be
accounted for by the bulkiness of the substituent bound to
the internal carbon in 21-C-alkylated complexes that may
facilitate displacement of the metal ion from the plane
(27) Jesson, J. P. In NMR of Paramagnetic Molecules; La Mar, G. N.,
Horrocks, W. D., Holm, R. H., Eds.; Academic Press: New York,
1973; p 1.
5586 Inorganic Chemistry, Vol. 42, No. 18, 2003

Ni(II) 21-C-Alkylated InWerted Porphyrins
Scheme 3. Protonation and Demetalation of Asymmetric Dimer 10
different stereogenic centers: the one that has a permanent
character is combined with C-subsituted fragment while the
other is induced by protonation of 21-C of N-substituted
subunit of the dimer. Alternatively, formation of a tight ion
pair between the C-protonated fragment of the diprotonated
species and TFA- can be accounted for the presence of two
species at higher acid concentration. Addition of 2-fold
excess of benzyltriethylammonium chloride to the sample
solution apparently converts the diprotonated complex to
monoprotonated since there is only one set of pyrrole signals
observed in the 1H NMR spectrum (Figure 6E). Also
spectrophotometric titration of 10 with TFAH at room
temperature shows consecutive formation of two species
whose relative concentration depends on the amount of acid.
The first protonated species is formed at relatively low
concentration of TFAH, thus, it can be formulated as a
monoprotonated complex 10-TFAH, while the second form,
dominating at much higher acid concentrations (over 6
equiv), should be assigned to the diprotonated complex
(Figure 7). Further addition of acid leads to the protonation
of internal coordination core of the macrocycle that is
combined with demetalation.
shifted considerably upfield (almost 3 ppm) with respect to
its position in 7. This indicates a change in the π-electron
density delocalization path causing less effective deshielding
of the external part of the inverted pyrrole by the ring current
(Chart 3).
Similarly, in the case of the 2,21′-CH2-linked diporphyrin
18 (Scheme 3), despite the lack of an asymmetric carbon
atom, the methylene protons are still diastereotopic due to
Demetalation and Dealkylation. Free ligands of 21-
alkylated inverted porphyrins can be obtained by acidification
of their solution with concentrated acids and neutralization
Figure 7. Selected optical spectra (CH2Cl2, 295 K) taken in the course of
titration of 10 with TFAH: solid line, 0 equiv; dashed line, 1.5 equiv; dotted
line, 10 equiv; dash-dotted line, 150 equiv.
1
of the initially formed cations. The H NMR spectrum of
Chart 3. Delocalization Paths in 7 and 17
5,10,15,20-tetraphenyl-21-benzyl-2-aza-21-carbaporphyrin (17)
shows features indicating nonplanarity of the ligand, e.g.
differentiation of ortho protons of meso-phenyls and di-
astereotopic methylene protons of the 21-benzyl substituent
(-3.53, -3.59 ppm, 2J ) 16.5 Hz, 298 K, CDCl3). The 21-C
adopts an sp2 hybridization in the free ligand which can be
inferred from the position of its signal in the 13C NMR
spectrum (106.6 ppm). Significantly, the signal of 3-H is
Inorganic Chemistry, Vol. 42, No. 18, 2003 5587

Schmidt and Chmielewski
late transition elements of the second and third row.28
Detailed study on the dealkylation of N-alkylated regular
porphyrins has been performed by Lavalee and co-work-
ers.21,29 The nucleophilic displacement of N-substituent was
shown to be effective for various complexes of divalent
transition metals ions. Stabilization of intermediate carbo-
cation in the case of benzyl group evidently promoted
dealkylation which is in line with the SN1 character of that
process.29
Scheme 4. Demetalation and Dealkylation of 7
In the case of 7, dealkylation of the protonated species is
driven by oxidation. In fact, we observe characteristic signals
of benzaldehyde (10.01 ppm, CHO group; 7.87, 7.62, 7.52
ppm, ortho-, para-, and meta-protons, respectively) together
1
with signals of 1 in the H NMR spectrum of the solution
the nonplanar geometry of the whole molecule. In a 1H NMR
spectrum of this compound (CDCl3, 233 K) the linker protons
are represented by an AB system (-2.42, -2.75 ppm, 2J )
16.0 Hz) resonating at noticeably higher field than the bis-
(nickel(II)) complex 10 (0.11, -0.47 ppm, 2J ) 15.6 Hz).23
The dimeric and asymmetric character of 18 is reflected by
the number of distinct signals for the pyrrole protons. There
are 12 â-pyrrole proton signals that can be assigned in the
spectrum on the basis of a COSY experiment. Two singlets,
those of proton 3 (5.65 ppm) and 3′ (6.71 ppm), are also
shifted to the higher field with respect to those in 10 (6.71
and 9.35 ppm, respectively). Proton 3 is spin-spin coupled
with proton 21-CH, which gives a signal at 0.15 ppm. The
23-NH proton with a signal at 3.16 ppm correlates in the
COSY map with two pyrrole protons which give a complex
signal at 7.68 ppm. Two internal NH protons of the
C-substituted fragment of the dimer show a relatively broad
signal at -3.30 ppm. Thus, diporphyrin 18 possesses two
different potentially dianionic coordination centers. Ring
current effect of these two aromatic systems affects chemical
shifts of some protons. In particular, protons of one of the
meso-phenyl show high-field shifts (5.58-6.61 ppm) with
respect to their usual positions. Moreover, these five protons
give distinct signals regardless of the temperature (213-
323 K), which indicate that rotation of this phenyl ring is
strongly restricted by the vicinity of a bulk substituent
constituted by the other porphyrin subunit.
that initially contained 7-HCl. Significantly, there is no such
dealkylation observed for 7-HCl when its solution is prepared
and stored in strictly anaerobic conditions. Evidently, nickel-
(II) ion and acid contributions are both necessary to ac-
complish that oxidative dealkylation since free ligand 17 is
stable in acidic conditions in the presence of air and so is
the unprotonated complex 7. The C-C bond-breaking
process seems to be dependent on the character of the
substituent. It is promoted by allylic/benzylic functionality
or strong electron-donating alkoxy group.
Redox Properties. Due to the potentially trianionic
coordination core the unsubstituted inverted porphyrin is
expected to stabilize higher oxidation states of the transition
metals.8a-d Alkylation of either external nitrogen or internal
carbon of the inverted pyrrole reduce the accessible negative
charge that may be introduced by a macrocyclic ligand from
-3 to -2. In fact, oxidation of 1 takes place without
deprotonation of the external nitrogen and, thus, an additional
anionic ligand is required8a to neutralize the positive charge
since the macrocycle remains bis-anionic. In the case of
nickel(II) complexes of inverted porphyrin and its externally
methylated derivative the first oxidation is observed at
potentials below 800 mV suggesting that the metal ion rather
than the ligand is oxidized.8a-c As expected, strong bases
(e.g. potassium tert-butoxide) capable of removing the 2-NH
proton24 considerably change the oxidation potential of the
complex shifting about 400 mV to the less positive values
(Table 2, [1]-). On the other hand, addition of acids that
can protonate the complex on 21-C have little or no effect
on the potential of NiII/NiIII couple (Table 2, 1-TFAH).
Cyclic voltammograms for the 21-alkylated nickel(II)
complexes of inverted porphyrin were recorded in CH2Cl2
solution with 0.1 M tetrabutylammonium perchlorate (TBAP)
as a supporting electrolyte and Ag/AgCl reference electrode
at room temperature. When being scanned into the positive
potentials, a typical voltammogram (Figure 8A) consists of
an irreversible or quasi-reversible couple (1) in the range of
In most cases, if protonation take place only on the external
nitrogen, full recovery of the starting diamagnetic alkylated
complexes is possible even for the long stored solutions of
the protonated species. However, in the case of 7-HCl, 12-
HCl, and 16-HCl a competitive dealkylation process takes
place. About 80% of 7 is converted to complex 1 (Scheme
4) after 2 h in refluxing DMF with an admixture of a dry
gaseous HCl. After a few days, dealkylation of 7, 12, and
16 can be observed at room temperature in chloroform or
dichloromethane solutions in the presence of acid. During
the period of 5 days of standing on the benchtop in a CDCl3
solution more than 85% of 7-HCl loses its 21-C substituent
yielding 1. Such a conversion requires breaking a bond
between 21-C and 1-C′.
(28) For a comprehensive review of C-C bond activation by metal
complexes in solution, see: Milstein, D.; Rybtchinski, B. Angew.
Chem., Int. Ed. 1999, 38, 870.
(29) (a) Lavalee, D. K. Inorg. Chem. 1976, 15, 691. (b) Lavalee, D. K.
Inorg. Chem. 1977, 16, 955. (c) Kuila, D.; Lavalee, D. K. Inorg. Chem.
1983, 22, 1095. (d) Lavalee, D. K.; Kuila, D. Inorg. Chem. 1983, 22,
3987. (e) Doi, J. D.; Compito-Magliozzo, C.; Lavalee, D. K. Inorg.
Chem. 1984, 23, 79.
There are several reports concerning C-C bond activation
in solution of organometallic compounds mostly containing
5588 Inorganic Chemistry, Vol. 42, No. 18, 2003

Ni(II) 21-C-Alkylated InWerted Porphyrins
Table 2. Cyclovoltammetric Potentialsa of Nickel(II) Complexes of Inverted Porphyrins in Dichloromethane
complex
Ea(1)
742
750
344
738
780
646
712
760
820
770
782
756, 896
808, 898
820, 934
661
Ec(1)
670
674
256
588
682
488
592
522
660
527
656
684, 824
720
733, 856
511
Ea(2)
Ec(2)
Ea(3)
Ec(3)
-522
Ea(4)
-900
Ec(4)
1
1120
1120
932
-1088
1-TFAH
-442
[1]-
2
939
-968
-880
-940
-980
-980
-1026
-940
-968
-825
2-TFAH
4
4-TFAH
5
5-TFAH
7
7-TFAH
10
10-TFAH
11
12
12-TFAH
-378
-383
-368
-335
-442
-446
-452
-431
-292
1200
1330
1093
1120
-856
-806
-894
-836
1146
1074
1156
1279
1453
908
1069
1190
1135
-950
-950
-864
-878
733
646
-370
-448
a All potentials (in mV) vs Ag/AgCl.
Figure 8. Cyclic voltammograms of 4 (A) and 4-TFAH (B, 2 equiv of
TFAH) in CH2Cl2 solutions (supporting electrolyte, 0.1 M TBAP; working
electrode, glassy carbon disk; reference electrode, Ag/AgCl; auxiliary
electrode, platinum wire; scan rate, 50 mV s-1).
Figure 9. Cyclic voltammograms of 10 (A) and 11 (B) in CH2Cl2 solutions
(supporting electrolyte, 0.1 M TBAP; working electrode, glassy carbon disk;
reference electrode, Ag/AgCl; auxiliary electrode, platinum wire; scan rate,
50 mV s-1).
520-770 mV that can be assigned to the NiII/NiIII process
and irreversible anodic wave (2) at the potentials over 1000
mV combined with oxidation of the ligand. On the negative
side, a well-defined quasi-reversible wave (4) at about -900
mV is observed which can be linked with a reduction process
of the aromatic macrocycle. The data for the representative
examples are collected in Table 2. For the monomeric
complexes containing methyl, sec-butyl, or benzyl substit-
uents (2, 5, and 7 in Table 2), the first oxidation potentials
do not differ considerably from that of the starting complex
1. Significantly lower potentials (by about 100 mV) are
observed for the complexes with substituents containing
oxygen, i.e., 2′-hydroxyethyl (4) and ethoxymethyl (12), that
suggest some inductive effect of the heteroatom.
protonated species but do not seem to preclude oxidation of
the high-spin metal center. The values of these potentials
are close to that of complex 1 which can be oxidized
chemically by various oxidants to the nickel(III) species.8a
On the other hand protonation promotes the reduction of the
metal ion. A reversible couple (3) at about -400 mV, which
is observed after addition of acid for all monomeric
complexes under study, can be assigned to the NiII/NiI redox
process (Figure 8B).
For both dimeric complexes with methylene linker the
oxidation pattern is more complicated indicating an inter-
action between the redox centers (Figure 9). For 10 there
are two anodic waves in the range of 750-900 mV of two
consecutive oxidations of different parts of the asymmetrical
dimer.23 A similar pattern is observed for the symmetrical
2,2′-CH2-linked dimer 11. The stepwise oxidation of por-
phyrin subunits in 10 and 11 implies an interaction between
Protonation with TFAH shifts potentials of anodic waves
of the first oxidation to the higher values (by 10-70 mV).
The alteration of potentials of cathodic peaks for this redox
process is more pronounced (by 110-140 mV). Higher
potentials reflect lower stability of the nickel(III) ion in
Inorganic Chemistry, Vol. 42, No. 18, 2003 5589

Schmidt and Chmielewski
Table 3. EPR Data of 21-Alkylated Nickel(III) Complexes of Inverted
Porphyrins in Dichloromethane/Toluene Solutiona
b
a
b
complex
4-Cl
gx
gy
gz
Ax
Ay Az
giso
Aiso
2.407 2.173 2.048
c
c
25 2.207
c
7-I
7-Br
7-Cl
2.305 2.127 2.040 60
2.360 2.146 2.052 30
80 163 2.169 74
40 124 2.168 59
2.407 2.175 2.054
c
c
25 2.207
c
c
7-I(TFAH) 2.290 2.125 2.058 60
7-H(TFA)2 2.425 2.244 2.082
75 148 2.159
2.250
10-I
10-Cl
2.290 2.120 2.040 55
2.410 2.198 2.062
80 160 2.168 74
28 2.208
c
c
c
a Frozen solution spectra were taken at 77 K; isotropic spectra were
recorded at 298 K. b Tensor components (in gauss) of hyperfine coupling
with one 127I, 79,81Br, or 35,37Cl nucleus, respectively. c Not resolved.
them resulting in modification of redox properties of the
second center upon oxidation of the first subunit. Observation
of only one two-electron oxidation process is expected for
the system containing two identical and noninteracting
porphyrin centers.30
According to cyclovoltammetric data chemical oxidation
of the 21-alkylated nickel(II) complexes of inverted porphy-
rin should be as effective as oxidation of the starting complex
1.8a Indeed, addition of iodine to a dichloromethane/toluene
solution of one of the complexes resulted in observation of
an EPR spectrum which can be attributed to nickel(III)
species on the basis of the considerable anisotropy of the
Zeeman tensor (Table 3).31,32 Observation of hyperfine
coupling with one 127I nucleus (nuclear spin I ) 5/2) reveals
coordination of one iodide ligand to the d7 metal ion.
Moreover, relation of principal components of tensors g and
Figure 10. EPR spectra of oxidized complex 7 with various apical ligands
in toluene/dichloromethane solution (30/70 v/v): A, 7-I, 77 K; A′, 298 K;
B, 7-Br, 77 K; B′, 298 K; C, 7-Cl, 77 K. The resolved hyperfine splittings
due to 127I, 79,81Br, or 35,37Cl in anisotropic spectra are marked. Conditions:
microwave frequency, ν ) 9.573 GHz for anisotropic spectra and 9.782
GHz for isotropic spectra; microwave power, 12.5 mW; modulation
amplitude, 8 G; modulation frequency, 100 kHz.
place without ligand exchange. It seems that the considerable
steric constraints caused by alkylation of 21-C preclude axial
coordination of two ligands. Consequently, it may be
anticipated that protonation of the external nitrogen is
accompanied by introduction of an additional anion into the
second coordination sphere. Addition of 4 equiv of TFAH
to the solution of the iodine-oxidized complex changes the
EPR spectrum that no longer indicates the presence of an
iodide ligand (7-H(TFA)2, Table 3). The difference in
Zeeman tensor parameters and lack of hyperfine splitting
suggest in this case protonation of 2-N with concurrent
exchange of ligand coordinating to nickel(III) center. How-
ever, solely on the basis of the EPR spectra, we cannot make
a definitive conclusion concerning stoichiometry of the
oxidized species formed upon addition of acid.
The asymmetric dimer 10 upon addition of iodine gave
an EPR spectrum that is very similar to those obtained for
monomeric complexes (Table 3). It suggests that only one
out of two different nickel(II) centers is oxidized by means
of this oxidant.
An attempt on isolation of any of the oxidized species
failed likely due to facile reduction of the nickel ion8a and
some decomposition processes that are linked to the oxidation
of the ligand.34 It should be noted that to date the only stable
and structurally characterized organometallic nickel(III)
systems, i.e., arenium “pincer” complexes, have oxidation
potentials about 500 mV lower33b than those of nickel
complexes of inverted porphyrin derivatives.
A(127I) allows one to determine the dz orbital as the major
2
metal contribution to the single occupied molecular orbital.
In such a case the lowest g-value (gz) should be close to
that of free electron (2.0023) and the hyperfine splitting due
to an apical ligand Az should be the largest.
The anionic ligand can be exchanged by addition of an
appropriate tetraalkylammonium salt, e.g. bromide or chlo-
ride (Figure 10). The spectra closely resemble those obtained
by van Koten and co-workers for the nickel(III) complexes
of the “pincer” NCN′ ligand.33 In each case hyperfine
splitting indicates the presence of one anionic ligand in the
first coordination sphere of NiIII. Acidification of the solution
of 7-I with 1 equiv of TFAH resulted in small but noticeable
changes in spin-Hamiltonian parameters (7-I(TFAH), Table
3) preserving the general pattern of the spectrum, in
particular, showing coordination of one apical iodide ligand.
This alteration of parameters can be due to protonation of
the external nitrogen of the inverted pyrrole, which takes
(30) Becker, Y.; Dolphin, D.; Paine, J. B.; Wijesekera, T. J. Electroanal.
Chem. 1984, 164, 335.
(31) Busch, D. H. Acc. Chem. Res. 1978, 11, 392.
(32) (a) Margerum, D. W.; Anlinker, S. L. In The Bioinorganic Chemistry
of Nickel; Lancaster, J. R., Jr., Ed.; VCH Publishers Inc.: Weinheim,
Germany, 1988; p 29. (b) Salerno, J. C. In The Bioinorganic Chemistry
of Nickel; Lancaster, J. R., Jr., Ed.; VCH Publishers Inc.: Weinheim,
Germany, 1988; p 53. (c) Moura, J. G.; Teixeira, M.; Moura, I.; LeGall,
J. In The Bioinorganic Chemistry of Nickel; Lancaster, J. R., Jr., Ed.;
VCH Publishers Inc.: Weinheim, Germany, 1988; p 191.
(33) (a) Grove, M. D.; van Koten, G.; Zoet, R. J. Am. Chem. Soc. 1983,
105, 1379. (b) Grove, M. D.; van Koten, G.; Mul, P.; Zoet, R.; van
der Linden, J. G. M.; Legters, J.; Schmitz, J. E. J.; Murral, N. W.;
Welch, A. J. Inorg. Chem. 1988, 27, 2466.
(34) Furuta, H.; Maeda, H.; Osuka, A. Org. Lett. 2002, 4, 181.
5590 Inorganic Chemistry, Vol. 42, No. 18, 2003

Ni(II) 21-C-Alkylated InWerted Porphyrins
Scheme 5. Redox Properties of the Metal Center in Alkylated
Inverted Porphyrin Nickel Complexes
Figure 11. EPR spectrum (solid line) of a species obtained in the reaction
of toluene solution of 7 with aqueous hydrazine dihydrochloride. The
simulated spectrum (dashed line) was calculated with the spin-Hamiltonian
parameters marked. Conditions: microwave frequency, ν ) 9.5779 GHz;
microwave power, 50.2 mW; modulation amplitude, 10 G; modulation
frequency, 100 kHz; temperature, 77 K.
porphyrins, where internal alkylation leads to monoanionic
character of their coordination core, the alkylated inverted
porphyrins can act as a bis-anionic ligands. In the case of
nickel(II) complexes the unprotonated external nitrogen
shows strong nucleophilic character which makes it capable
for coordination of other metal ions. The flexibility of the
system is reflected by proton-assisted change of spin state
and accessibility of three different oxidation states of the
metal ion.
A particularly attractive feature of the 21-alkylated systems
is their chirality. The stereogenic center is localized within
the coordination core, in the proximity of the ligation site
of a potential substrate and the metal-localized redox center.
It suggests application of these systems in stereoselective
catalysis; however, further studies aimed on separation of
enantiomerically pure complexes are required.
The potential variety in terms of the 21-C substituents is
very large and allows for extremely facile design for specific
purposes. Unlike in the case of chiral N-alkylated corroles,
synthesis of which leads to a mixture of regioisomers (21-N
and 22-N),38,39 only one internally alkylated product is formed
for the inverted porphyrin.
The mild dealkylation of some nickel complexes deserves
particular attention, and the study proceeds to elucidate
factors determining the C-C bond activation in these
systems.
Facile chemical reduction of the 2-protonated-21-alky-
lated nickel(II) complexes such as 7-HCl can be anticipated
on the basis of the electrochemical data (Table 2). In fact,
shaking a deaerated toluene/ethanol (10:1 v/v) solution of 7
with aqueous hydrazine dihydrochloride results in acidifica-
tion of the complex causing appropriate changes of its optical
spectrum19 while appearance of an EPR signal indicates
partial reduction of 7-HCl (Figure 11). The metal-centered
reduction and thus formation of d9 nickel(I) ion can be
inferred on the basis of the values of the Zeeman tensor
components (g1 ) 2.281, g2 ) 2.220, g3 ) 2.188, toluene,
77 K) that differ considerably from those expected for a free
radical.25e,35,36 Similar result can be obtained upon reduction
of 4-HCl with N2H6Cl2 (g1 ) 2.294 g2 ) 2.220, g3 ) 2.181,
toluene, 77 K). In the case of a structurally related system,
nickel(II) complex of 2,21-dimethylated inverted porphyrin
8, reduction has been accomplished by a homolytic cleavage
of the nickel-carbon bond with an apical alkyl or aryl ligand
leading to a variety of EPR-active products.22 The change
in stability of the lower oxidation state in the case of 4-HCl
or 7-HCl is related to the monoanionic character of the ligand
upon protonation. Similar stabilization has been observed
for nickel complexes of the other monoanionic core-modified
porphyrins having oxygen, sulfur, or selenium replacing one
nitrogen atom in the macrocyclic crevice.25e,35-37
Experimental Section
Instrumentation. Absorption spectra were recorded on a diode-
array Hewlett-Packard 8453 spectrometer. Mass spectra were
recorded on an AD-604 spectrometer using the electrospray and
electron impact techniques.
Scheme 5 summarizes the redox behavior of the alkylated
complexes under neutral and acidic conditions.
NMR spectra were recorded on a Bruker Avance 500 spectrom-
eter. The 1D and 2D experiments (COSY, NOESY, HMQC, and
HMBC) for diamagnetic substances were performed by means of
standard experimental procedures of Burker library. For paramag-
netic complexes usually 1000-10 000 scans were accumulated over
a 10 kHz bandwidth with 32K data points and with a delay time of
100 ms. The signal-to-noise ratio was improved by apodization of
the free induction decay, which typically induced 15-Hz broadening.
The peaks were referenced against solvent resonances.
Conclusions
Modifications of the inverted porphyrin can be ac-
complished by introducing of various alkyl substituents on
the internal carbon of the inverted pyrrole by means of
readily available haloalkanes. Unlike in the case of regular
(35) Chmielewski, P.; Grzeszczuk, M.; Latos-Graz˘yn´ski, L.; Lisowski, J.
Inorg. Chem. 1989, 28, 3546.
(36) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Pacholska, E. Inorg. Chem.
1994, 33, 1992.
(38) Jackson, A. H. In The Porphyrins; Dolphin, D., Ed.; Academic Press:
New York, 1979; Vol. I, Chapter 8.
(39) Gross, Z.; Galili, N. Angew. Chem., Int. Ed. 1999, 38, 2366.
(37) Pacholska, E.; Chmielewski, P. J.; Latos-Graz˘yn´ski, L. Inorg. Chim.
Acta 1998, 273, 184.
Inorganic Chemistry, Vol. 42, No. 18, 2003 5591

Schmidt and Chmielewski
Cyclovoltammetric measurements were performed in dichlo-
romethane on a EA9C MTM apparatus with glassy carbon disk as
a working electrode, Ag/AgCl reference electrode, and platinum
wire as an auxiliary electrode. Tetrabutylammonium perchlorate
(0.1 M) was used as a supporting electrolyte.
EPR spectra were obtained with a Bruker ESP 300E spectrom-
eter. The magnetic field was calibrated with a proton magnetometer
and EPR standards. The EPR spectra were simulated by assuming
orthorhombic symmetry. The details of the EPR simulations have
been given elsewhere.35,36
Preparation of Precursors. 5,10,15,20-Tetraphenyl-2-aza-21-
carbaporphyrin and (5,10,15,20-tetraphenyl-2-aza-21-carbaporphy-
rinato)nickel(II) (1) were synthesized according to known pro-
cedures.5a,e
Synthesis and characterization of complexes 10-16 were
described previously.23,24
Synthesis of (5,10,15,20-Tetraphenyl-21-methyl-2-aza-21-car-
baporphyrinato)nickel(II) (2). A mixture of 1 (30 mg, 0.045
mmol) and methyl iodide (45 mg, 0.32 mmol) in dichloromethane/
ethanol solution (50 mL, 80/20, v/v) containing a suspension of
K2CO3 was refluxed for 3 h under a blanket of nitrogen. The solvent
was evaporated under reduced pressure. The solid was dissolved
in dichloromethane and chromatographed on a silica gel column.
The second brown-reddish band that contained 2 was eluted with
dichloromethane and crystallized from a CH2Cl2/hexane mixture.
Yield: 22 mg (71%). The mass spectroscopic, UV/vis, and NMR
results are identical with the literature data.19
(1H, m, 1′-CH2); -2.56 (1H, m, 1′-CH2). 13C NMR (125 MHz,
298 K, CDCl3, partial data; δ): 178.1 (1-C); 155.8 (3-C); 153.1
(4-C); 152.7 152.4; 140.1; 132.5; 133.5; 134.1; 132.2; 132.7; 128.0;
127.6; 126.6; 130.8; 61.7 (2′-C); 34.7 (21-C); 32.8 (1′-CH2). UV/
vis (CH2Cl2) [λmax, nm (log ꢀ)]: 354 (4.29); 432 (4.59); 462 (sh);
610 (sh), 751 (2.30). HRMS (EI): m/z ) 714.1907 (714.1924 for
C46H31N4ONi + H+).
Synthesis of (5,10,15,20-Tetraphenyl-21-(sec-butyl)-2-aza-21-
carbaporphyrinato)nickel(II) (5). This product was obtained in
a way similar to that for 2 using 100 mg of 2-iodobutane instead
of CH3I and carrying out the reaction for 12 h. Yield: 19 mg (60%).
1H NMR (500 MHz, 298 K, CDCl3; δ): 9.76 (2H, s, 3-H, common
signal for both diastereoisomers A + B); 8.64 (1H, d, JAB ) 5.1
Hz); 8.60 (1H, d, JAB ) 4.6 Hz); 8.58 (1H, d, JAB ) 4.6 Hz); 8.55
(1H, d, JAB ) 5.0 Hz); 8.48 (1H, d, JAB ) 5.0 Hz); 8.46 (1H, d,
JAB ) 5.0 Hz); 8.45 (1H, d, JAB ) 5.0 Hz); 8.44 (1H, d, JAB ) 5.0
Hz); 8.43 (1H, d, JAB ) 5.0 Hz); 8.43 (1H, d, JAB ) 5.0 Hz); 8.42
(1H, d, JAB ) 5.0 Hz); 8.39 (1H, d, JAB ) 5.0 Hz); 8.38 (1H, d,
JAB ) 5.0 Hz); 8.19 (8H, b); 8.03 (2H, d, J ) 6.5 Hz); 7.84-7.56
(24H, overlapping multiplets); -0.37 (3H, 4′-CH3 B); -0.41 (1H,
m, 3′-CH (B)); -0.63 (3H, t, J ) 7.3 Hz, 4′-CH3 (A)); -0.74 (1H,
m, 3′-CH (A)); -0.99 (1H, m 3′-CH (B)); -1.23 (3H, d, J ) 6.4
Hz, 1′-CH3 (A)); -1.62 (1H, m, 3′-CH (A)); -1.7 (3H, d, J ) 6.9
Hz, 1′-CH3 (B)); -3.55 (2H, m, 2′-CH, (A + B)) (assignments A
and B introduced to distinguish signals of diastereoisomers). 13C
NMR (125 MHz, 298 K, CDCl3, partial data; δ): 181.5 (1-C); 156.5
(3-C); 155.7(4-C); 152.4; 149.7; 148.5; 147.6; 146.6; 140.5;
135.7: 135.3; 134.5; 132.0; 133.6; 131.4; 128.1; 127.8; 127.2;
126.9; 44.7 (2′-C); 41.0 (21-C); 27.9 (3′-C (B)); 27.2 (3′-C (A));
16.1 (1′-C); 12.5 (4′-C). UV/vis (CH2Cl2) [λmax, nm (log ꢀ)]: 358
(4.30); 435 (4.56); 469 (sh); 606 (sh), 734 (2.40). HRMS (EI): m/z
) 727.2127 (727.2371 for C48H36N4Ni + H+).
Synthesis of (5,10,15,20-Tetraphenyl-21-ethyl-2-aza-21-car-
baporphyrinato)nickel(II) (3). A mixture of 1 (30 mg, 0.045
mmol) and ethyl iodide (45 mg, 0.29 mmol) in dichloromethane
solution (50 mL) containing 2 mg of dibenzo-[18]-crown-6 and a
suspension of K2CO3 (10 mg) was refluxed for 3 h under a blanket
of nitrogen. The solvent was evaporated under reduced pressure.
The solid was dissolved in dichloromethane and chromatographed
on a silica gel column. The second brown-reddish band that
contained 3 was eluted with dichloromethane and crystallized from
Synthesis of (5,10,15,20-Tetraphenyl-21-(S-2′-methylbutyl)-
2-aza-21-carbaporphyrinato)nickel(II) (6). This product was
obtained in way similar to that for 2 using 50 mg of S-(+)-2-
(methyliodo)butane instead of CH3I. Yield: 22 mg (66%). 1H NMR
(500 MHz, 298 K, CDCl3; δ): 9.51 (1H, s, 3-H); 9.50 (1H, s, 3-H);
8.61 (2H, d, JAB ) 4.8 Hz); 8.58 (2H, d, JAB ) 5.0 Hz), 8.45 (2H,
1
a CH2Cl2/hexane mixture. Yield: 18 mg (57%). H NMR (500
MHz, 298 K, CDCl3; δ): 9.83 (1H, s, 3-H); 8.64 (1H, d, JAB
)
d, JAB ) 5.2 Hz.); 8.44 (1H, d, JAB ) 5.0 Hz.); 8.43 (1H, d, JAB
)
4.9 Hz); 8.62 (1H, d, JAB ) 4.9 Hz); 8.47 (2H, d, JAB ) 4.9 Hz);
8.43 (1H, d, JAB ) 5.7 Hz); 8.39 (1H, d, JAB ) 5.7 Hz); 8.22 (2H,
b); 8.07 (2H, b); 8.02 (1H, b); 7.98 (1H, b) 7.8-7.6 (12H,
overlapping multiplets); -0.93 (3H, t, J ) 7.0 Hz, 2′-CH3); -2.23
(2H, m, 1′-CH2). 13C NMR (125 MHz, 298 K, CDCl3, partial data;
δ): 179.4 (1-C); 154.5 (4-C); 156.5; 155.9; 152.8; 152.2; 140.6;
136.3; 133.8; 133.2; 128.0; 127.5; 127.3; 132.4; 38.6 (21-C); 24.8
(1′-C); 13.2 (2′-C). UV/vis (CH2Cl2) [λmax, nm (log ꢀ)]: 361 (4.29);
431 (4.60); 459 (sh); 550 (sh), 610 (sh), 759 (2.81) nm. HRMS
(EI): m/z ) 699.2537 (699.2059 for C46H32N4Ni + H+).
Synthesis of (5,10,15,20-Tetraphenyl-21-(2′-hydroxyethyl)-2-
aza-21-carbaporphyrinato)nickel(II) (4). A mixture of 1 (30 mg,
0.045 mmol) and 2-iodoethanol (100 mg, 0.6 mmol) in dichlo-
romethane solution (30 mL) was allowed to stand in a darkness
for 40 days. After that period solvent was evaporated under reduced
pressure. The solid was dissolved in dichloromethane and chro-
matographed on a silica gel column. The second brown-reddish
band that contained 4 was eluted with dichloromethane and
crystallized from a CH2Cl2/hexane mixture. Yield: 13 mg (40%).
1H NMR (500 MHz, 298 K, CDCl3; δ): 9.73 (1H, s, 3-H); 8.63
(1H, d, JAB ) 5.0 Hz); 8.61 (1H, d, JAB ) 5.0 Hz,); 8.47 (2H,
overlapping doublets, J ) 5.0 Hz); 8.44(1H, d, JAB ) 5.0 Hz);
8.40 (1H, d, JAB ) 5.0 Hz); 8.22 (2H, b); 8.06 (2H, b); 8.02 (1H,
b); 7.97 (1H, b); 7.8-7.6 (12H, overlapping multiplets); 1.56 (2H,
m, J ) 6.0 Hz, 2′-CH2); -0,14 (1H, t, J ) 6.0 Hz, OH); -2.42
4.8 Hz.); 8.42 (2H, d, JAB ) 4.8 Hz.); 8.38 (2H, d, JAB ) 4.8 Hz.);
8.23 (4H, b); 8.10 (2H, b); 8.07 (2H, b); 8.01 (2H, b); 7.95 (2H,
b); 7.85-7.60 (26H, overlapping multiplets); 0.03 (3H, t, J ) 7.3
Hz, 4′-H (B)); -0.11 (1H, m, 3′ (B)); -0.12 (3H, t, J ) 7.3 Hz, 4′
(A)); -0.23 (H, d, J ) 6.7 Hz, 1′′ (A)); -0.29 (1H, m, 3′ (A));
-0.37 (3H, d; J ) 6.7 Hz, 1′′-H (B)); -0.74 (2H, m, 2′-CH (A +
3
2
B)); -1.81 (1H, dd, J ) 4.3 Hz, J ) 14.2 Hz, 1′ (A)); -2.26
3
2
2
(1H, dd, J ) 5.5 Hz, J ) 14.1 Hz 1′ (B)); -2.44 (1H, dd, J )
3
2
3
14.1 Hz, J ) 6.4 Hz, 1′ (B)); -2,9 (1H, dd, J ) 14.2, J ) 7.8
Hz, 1′ (A)) (assignments A and B introduced to distinguish signals
of diastereomers). 13C NMR (125 MHz, 298 K, CDCl3, partial data;
δ): 178.3 (1-C); 155.7 (3-C); 155.4; 154.4 (4-C); 152.7; 149.8;
147.7; 140.1; 139.7; 136.8; 135.9; 133.7; 133.3; 132.7 132.3; 132.0
127.8; 127.2; 40.9 (21-C); 35.5 (1′-C (A + B)); 36.5 (2′-C (A +
B)); 29.5 (3′-C (A)); 28.4 (3′-C (B)); 19.5 (1′′-C (B)); 18.8 (1′′-C
(A)); 10.8 (4′-C (A + B)). UV/vis (CH2Cl2) [λmax, nm (log ꢀ)]:
359 (4.30); 434 (4.58); 465 (sh); 608 (sh), 740 (2.30). HRMS
(ESI): m/z ) 741.2528 (741.2523 for C49H38N4Ni + H+).
Synthesis of (5,10,15,20-Tetraphenyl-21-benzyl-2-aza-21-car-
baporphyrinato)nickel(II) (7). This product was obtained in way
similar to that for 3 using 100 mg of benzyl chloride instead of
C2H5I and refluxing the reaction mixture for 12 h. Yield: 27 mg
(80%). 1H NMR (500 MHz, 298 K, CDCl3; δ): 9.56 (1H, s, 3-H);
8.72 (2H, d, JAB ) 4.9 Hz); 8.55 (1H, d, JAB ) 4.6 Hz); 8.54 (1H,
5592 Inorganic Chemistry, Vol. 42, No. 18, 2003

Ni(II) 21-C-Alkylated InWerted Porphyrins
2
d, JAB ) 4.9 Hz); 8.47 (1H, d, JAB ) 4.6); 8.43 (1H, d, JAB ) 4.9);
8.13 (3H, b); 8.04 (1H, b); 8.00 (2H, b); 7.8-7.6 (12H, overlapping
multiplets); 7.00 (1H, m, para (benzyl)); 6.92 (2H, m, meta
-2.79 (1H, b, NH); -2.88 (1H, b, NH); -3.63 (1H, d, J ) 16.5
Hz, 1′-H); -3.94 (1H, d, 2J ) 16.5 Hz, 1′-H). 13C NMR (125 MHz,
233 K, CDCl3; δ): 157.6; 156.8 (1-C); 150.7; 141.4; 141.3 (3-C);
140.2; 139.6; 139.4; 138.8; 137.9 (4-C); 137.1 (ipso (benzyl));
136.4; 136.3; 135.2; 135.1; 134.8; 134.7; 128.7; 128.5; 128.4; 127.9;
127.81; 127.79; 127.7; 127.63; 127.58; 127.4; 127.3; 127.0; 126.98;
126.9; 126.8; 126.3; 126.2 (meta (benzyl)); 125.65 (ortho (benzyl);
125.6; 124.5 (para (benzyl)); 118.3; 116.9; 106.6 (21-C); 27.9 (1′-
C). UV/vis (CH2Cl2) [λmax, nm (log ꢀ)]: 449 (4.93); 515 (3.92);
551 (4.01); 594 (4.00); 691 (sh); 743 (3.80). HRMS (ESI): m/z )
705.2996 (705.3013 for C51H37N4 + H+).
2
(benzyl)); 5.55 (2H, m, ortho (benzyl)); -1.28 (1H, d, J ) 13.8
Hz, 1′-H); -1.57 (1H, d, 2J ) 13.8 Hz, 1′-H). 13C NMR (125 MHz,
223 K, CDCl3; δ): 177.6 (1-C); 157.2 (3-C); 155.9; 153.1 (4-C);
152.6; 150.2; 149.5; 147.6; 146.8; 140.7; 140.5; 139.6 (ipso-benzyl);
139.4; 138.0; 137.5; 137.1; 135.6; 135.5; 134.7; 134.4; 134.3; 133.9;
133.7; 133.6; 133.0; 132.6; 132.5; 132.2; 131.8; 128.8; 128.1; 128.0;
127.8 (o-benzyl)); 127.6 (m-benzyl); 127.4 (p-benzyl); 126.9; 126.0;
125.1; 123.5; 38.4 (21-C); 35.4 (1′-C). UV/vis (CH2Cl2) [λmax, nm
(log ꢀ)]: 358 (4.40); 433 (4.60); 461 (sh); 605 (sh); 762 (2.63).
HRMS (ESI): m/z ) 761.2183 (761.2215 for C51H34N4Ni + H+).
Synthesis of 5,10,15,20-Tetraphenyl-21-benzyl-2-aza-21-car-
baporphyrin (17). A solution of 7 (10 mg, 0.013 mmol) in
dichloromethane (10 mL) was shaken for 3 min with 1 mL of
concentrated hydrochloric acid and then neutralized with saturated
aqueous potassium carbonate. The organic layer was separated,
dried with anhydrous potassium carbonate, and chromatographed
on the basic alumina column with dichloromethane as an eluent.
Crystallization from a benzene/hexane mixture gave 7 mg of 17
(yield 75%). 1H NMR (500 MHz, 298 K, CDCl3; δ): 8.76 (1H, d,
JAB ) 4.9 Hz); 8.68 (1H, d, JAB ) 4.9 Hz); 8.49 (3H, overlapping
doublets); 8.42 (1H, d, JAB ) 4.9 Hz); 8.28 (2H, m); 8.24 (1H, m);
8.18 (2H, b); 8.15 (3H, m); 8.10 (1H, m); 7.81 (2H, m); 7.77 (2H,
m); 7.73 (9H, overlapping multiplets); 7.14 (1H, s, 3-H); 6.42 (1H,
m, para (benzyl); 6.27 (2H, m, meta (benzyl)); 4.33 (2H, m, ortho
(benzyl)); -2.55 (2H, b, 22,24-NH), -3.53 (1H, d, 2J ) 16.5 Hz,
Synthesis of 2-(21′-(5′,10′,15′,20′-Tetraphenyl-2′-aza-21′-car-
baporphyrin)methyl)-5,10,15,20-tetraphenyl-2-aza-21-carba-
porphyrin (18). This ligand was obtained similarly as 17, but the
dichloromethane solution of starting complex 10 was stirred with
1
concentrated HCl for 2 h. Yield: 60%. H NMR (500 MHz, 233
K, CDCl3; δ): 8.70 (1H, d, JAB ) 4.9 Hz); 8.57 (1H, d, JAB ) 4.6
Hz); 8.54 (1H, d, JAB ) 4.1 Hz); 8.47 (1H, d, JAB ) 4.1 Hz); 8.44
(1H, d, JAB ) 4.1 Hz); 8.32 (1H, d, JAB ) 4.1 Hz); 8.29 (1H, m);
8.26 (1H, m); 8.13 (1H, d, JAB ) 4.1 Hz); 8.02 (2H, m); 7.93 (1H,
d, JAB ) 4.6 Hz); 7.91-7.70 (overlapping multiplets); 7.68 (2H,
two overlapping doublets scalar coupled with 23-NH); 7.56 (2H,
m); 7.50 (1H, m); 7.47 (1H, d, JAB ) 4.6 Hz); 7.41 (2H, b); 7.12
(1H, d, JAB ) 4.6 Hz); 6.93 (1H, d, JAB ) 4.1 Hz); 6.71 (1H, s,
3′); 6.31 (1H, m); 6.03 (1H, m); 5.96 (1H, m); 5.77 (1H, m); 5.65
(1H, s, 3); 5.58 (1H, m); 3.16 (1H, s, 2-NH); 0.15 (1H, s, 21-CH);
-2.42 (1H, d, JAB ) 16.0 Hz); -2.74 (1H, d, JAB ) 16.0 Hz);
-3.28 (2H, b, 22′,24′). UV/vis (CH2Cl2) [λmax, nm (log ꢀ)]: 439
(4.63); 467 (sh); 557 (3.40); 608 (3.70); 682 (sh); 737 (3.80). MS
(ESI): m/z ) 1241.3 (1241.5 for C89H60N8 + H+).
2
1
1′-H); -3.79 (1H, d, J ) 16.5 Hz, 1′-H). H NMR (500 MHz,
233 K, CDCl3; δ): 8.80 (1H, d, JAB ) 4.9 Hz); 8.72 (1H, d, JAB
)
4.3 Hz); 8.53 (3H, overlapping doublets); 8.48 (1H, d, JAB ) 4.3
Hz); 8.28 (1H, m); 8.19 (4H, overlapping multiplets); 8.13 (1H,
m); 7.91 (1H, b); 7.83 (1H, m); 7.81 (1H, m); 7.76 (11H,
overlapping multiplets); 7.12 (1H, s, 3-H); 6.40 (1H, m, para
(benzyl)); 6.25(2H, m, meta (benzyl)); 4.25(2H, m, ortho (benzyl));
Acknowledgment. This work was supported by the State
Committee for Scientific Research of Poland (Grant Nos. 7
T09A 120 20 and 4 T09A 147 22).
IC034096K
Inorganic Chemistry, Vol. 42, No. 18, 2003 5593