One- and two-electron oxidative pathways leading to cyclopropane-containing oxidized porphyrinogens and C-C-coupled porphyrinogens from alkali cation- and transition metal-meso-octaethylporphyrinogen complexes

Article abstract of DOI:10.1021/ja982178f

This report deals with the different transition metal- and alkali cation-assisted oxidation pathways of the meso-octaethylporphyrinogen tetraanion [Et₈N₄]^4-. The two-electron oxidation of [Et₈N₄Mn{Na(thf)₂}₂], 4, with Cp₂FeBPh₄ led to the corresponding monocyclopropane derivative [Et₈N₄(Δ)Mn], 6, [Δ ≡ cyclopropane], while the one-electron oxidation with CuCl₂ or O₂ led to the Mn(III)-porphyrinogen [Et₈N₄Mn][Li(thf)₄], 5, which can be further oxidized by an excess of CuCl₂ to [Et₈N₄(Δ)₂Mn-Cl]⁺[Cu ₉Cl₁₁]_0.5, 7. The formation of 7 does not follow the expected sequence Mn(II) → Mn(III) → Mn(II)-monocyclopropane → Mn(II)-biscyclopropane-porphyrinogen. In the case of iron(II)-porphyrinogen, [Et₈N₄Fe{Li(thf)₂}₂], 9, the oxidation led in a preliminary stage to the iron(III) derivative [Et₈N₄Fe][Li(thf)₄], 10, then to the metalated form of the biscyclopropane-porphyrinogen [Et₈N₄(Δ)₂Fe-Cl]{μ-Cu ₄Cl₅}], 11. The supposed stabilization of the biscyclopropane by the copper(I) cluster was ruled out by carrying the oxidation of [Cy₄N₄Fe{Li(thf)₂}₂], 11, to [Cy₄N₄(Δ)₂Fe-Cl][Cu₂Cl ₄], 14. The stepwise oxidation of [Et₈N₄M(thf)₄] [M = Li, 1; M = Na, 2] with Cp₂-FeBPh₄ led to [Et₈N₄(Δ)Li₂thf₂], 15, [Et₈N₄(Δ)Li]BPh₄, 16, and [Et₈N₄(Δ)Na]BPh₄, 17. The reaction of 1 with 16 leading to 15 showed how the C-C moiety in cyclopropane can be engaged in an intermolecular electron transfer. The reaction of 17 with 18-crown-6 allowed the release of biscyclopropane-porphyrinogen [Et₈N₄(Δ₂)]. Particularly interesting is the thermal rearrangement of 15 to 19 occurring via intra- and intermolecular electron transfers with the transposition of the C-C bond of the cyclopropane to a C-C bridge across the β position of two adjacent pyrroles. In the case of metals, such as Ni(II), which do not undergo oxidation state changes, the primary oxidation product of a metalla-meso-octaalkylporphyrinogen is the monocyclopropane derivative, which reacting with the starting material masks an overall one-electron oxidation. In fact, the reaction of [Et₈N₄Ni{Li(thf)₂}₂], 20, with 2 equiv of Cp₂FeBPh₄ led to the expected [Et₈N₄(Δ)Ni], 21, while the reaction of 20 with 1 equiv of Cp₂FeBPh₄ led to the dimer [(β-β)(Et₈N₄)₂Ni₂], 22, which forms equally well from the reaction of 20 and 21. Complex 22 is a quite unique metallaporphyrinogen dimer, where the two monomeric units are joined via a C-C bond in the β position of a pyrrole. Such a reaction shows that the methodology can accede to oligomeric forms of metallaporphyrinogens.

Full text of DOI:10.1021/ja982178f

J. Am. Chem. Soc. 1999, 121, 1695-1706
1695
One- and Two-Electron Oxidative Pathways Leading to
Cyclopropane-Containing Oxidized Porphyrinogens and
C-C-Coupled Porphyrinogens from Alkali Cation- and Transition
Metal-meso-Octaethylporphyrinogen Complexes
Raffaella Crescenzi,† Euro Solari,† Carlo Floriani,*,† Angiola Chiesi-Villa,‡ and
Corrado Rizzoli‡
Contribution from the Institut de Chimie Mine´rale et Analytique, BCH, UniVersite´ de Lausanne,
CH-1015 Lausanne, Switzerland, and Dipartimento di Chimica, UniVersita` di Parma,
I-43100 Parma, Italy
ReceiVed June 22, 1998
Abstract: This report deals with the different transition metal- and alkali cation-assisted oxidation pathways
of the meso-octaethylporphyrinogen tetraanion [Et8N4]4-. The two-electron oxidation of [Et8N4Mn{Na(thf)2}2],
4, with Cp2FeBPh4 led to the corresponding monocyclopropane derivative [Et8N4(∆)Mn], 6, [∆ ≡ cyclopropane],
while the one-electron oxidation with CuCl2 or O2 led to the Mn(III)-porphyrinogen [Et8N4Mn][Li(thf)4], 5,
which can be further oxidized by an excess of CuCl2 to [Et8N4(∆)2Mn-Cl]+[Cu9Cl11]0.5, 7. The formation of
7 does not follow the expected sequence Mn(II) f Mn(III) f Mn(II)-monocyclopropane f Mn(II)-
biscyclopropane-porphyrinogen. In the case of iron(II)-porphyrinogen, [Et8N4Fe{Li(thf)2}2], 9, the oxidation
led in a preliminary stage to the iron(III) derivative [Et8N4Fe][Li(thf)4], 10, then to the metalated form of the
biscyclopropane-porphyrinogen [Et8N4(∆)2Fe-Cl]{µ-Cu4Cl5}], 11. The supposed stabilization of the biscy-
clopropane by the copper(I) cluster was ruled out by carrying the oxidation of [Cy4N4Fe{Li(thf)2}2], 11, to
[Cy4N4(∆)2Fe-Cl][Cu2Cl4], 14. The stepwise oxidation of [Et8N4M(thf)4] [M ) Li, 1; M ) Na, 2] with Cp2-
FeBPh4 led to [Et8N4(∆)Li2thf2], 15, [Et8N4(∆)Li]BPh4, 16, and [Et8N4(∆)Na]BPh4, 17. The reaction of 1
with 16 leading to 15 showed how the C-C moiety in cyclopropane can be engaged in an intermolecular
electron transfer. The reaction of 17 with 18-crown-6 allowed the release of biscyclopropane-porphyrinogen
[Et8N4(∆2)]. Particularly interesting is the thermal rearrangement of 15 to 19 occurring via intra- and
intermolecular electron transfers with the transposition of the C-C bond of the cyclopropane to a C-C bridge
across the â position of two adjacent pyrroles. In the case of metals, such as Ni(II), which do not undergo
oxidation state changes, the primary oxidation product of a metalla-meso-octaalkylporphyrinogen is the
monocyclopropane derivative, which reacting with the starting material masks an overall one-electron oxidation.
In fact, the reaction of [Et8N4Ni{Li(thf)2}2], 20, with 2 equiv of Cp2FeBPh4 led to the expected [Et8N4(∆)Ni],
21, while the reaction of 20 with 1 equiv of Cp2FeBPh4 led to the dimer [(â-â)(Et8N4)2Ni2], 22, which forms
equally well from the reaction of 20 and 21. Complex 22 is a quite unique metallaporphyrinogen dimer, where
the two monomeric units are joined via a C-C bond in the â position of a pyrrole. Such a reaction shows that
the methodology can accede to oligomeric forms of metallaporphyrinogens.
Introduction
Chart 1
A porphyrin skeleton forms from a six-electron oxidation of
porphyrinogen, as exemplified in Chart 1, with the loss of six
hydrogen atoms.1 However, the high tendency of the meso-
tetrahydrotetraalkylporphyrinogen to autoxidize to porphyrin
prevented inspection of such a fundamental reaction and trapping
of other oxidized forms of porphyrinogen which can have
relevant mechanistic and synthetic properties. To this purpose,
we approached the problem by studying the various aspects of
the oxidation of a stable porphyrinogen, namely, the meso-
octaalkylporphyrinogen in its tetraanionic form, when bonded
to a transition metal that can assist the process.2,3
rinogen-metal complexes led to two- and four-electron oxida-
tion (see B and C in Chart 2) with the introduction of one, then
two cyclopropane units, hereinafter abbreviated as ∆ ≡ cyclo-
(2) (a) De Angelis, S.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C. J. Am. Chem. Soc. 1994, 116, 5691. (b) De Angelis, S.; Solari, E.;
Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1994, 116,
5702. (c) Jubb, J.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem.
Soc. 1992, 114, 6571.
In the absence of any hydrogen in the meso positions and
within the N4 core the oxidation of the meso-octaalkylporphy-
* To whom correspondence should be addressed.
† Universite´ de Lausanne.
‡ Universita` di Parma.
(1) (a) The Porphyrins; Dolphin, D., Ed.; Academic Press: New York,
1978; Vols. 1-7. (b) Smith, K. M. Porphyrins and Metalloporphyrins;
Elsevier: Amsterdam, 1975.
(3) (a) Floriani, C. Chem. Commun. 1996, 1257. (b) Floriani, C. In
Transition Metals in Supramolecular Chemistry; Fabbrizzi, L., Poggi, A.,
Eds.; Kluwer: Dordrecht, The Netherlands, 1994; Vol. 448, p 191.
10.1021/ja982178f CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/09/1999

1696 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Crescenzi et al.
Elmer FT 1600 spectrophotometer. NMR spectra were recorded on a
200-AC Bruker instrument. Magnetic susceptibility measurements were
collected in the temperature range 80-300 K on a MPMS5 SQUID
susceptometer (Quantum Design Inc.) operating at a magnetic field
strength of 3 kOe. Corrections were applied for diamagnetism calculated
from Pascal constants. The synthesis of 16 and 206 was carried out as
reported, while a procedure modified from that reported was employed
for 9,2b 10,2b 11,2b and 12.7
Chart 2
Synthesis of 2. Degassed naphthalene (10.36 g, 80 mmol) and then
sodium (3.68 g, 160 mmol) were added to a yellow solution of
[Et8N4H4]8 (21.64 g, 40 mmol) in THF (250 mL), resulting in a green
solution, which was stirred at room temperature until the sodium had
completely dissolved. THF was evaporated under reduced pressure and
the resulting white solid collected with n-hexane (300 mL), filtered,
and dried (25 g, 81%). Anal. Calcd for C44H64N4Na4O2: C, 68.37; H,
propane, within the porphyrinogen skeleton.2,3 The monocy-
clopropane forms with a variety of transition metals, Ni, Cu,
Co, using p-benzoquinone as the oxidizing agent,2a while the
biscyclopropane form occurs only in the case of Co and Fe,
when CuCl2 is employed.2b In some cases, the use of high
oxidation state metals induces the intramolecular or intermo-
lecular formation of cyclopropane units. In the present paper
we report the pathway leading to the Mn- and Fe-porphy-
rinogen complexes containing cyclopropane units. Cp2FeBPh4
enabled us to establish the oxidative pathway leading to the
transition metal-free monocyclopropane, then to the biscyclo-
propane-porphyrinogen (C), which becomes available now by
means of a quite convenient, large-scale, synthetic process.
Another remarkable aspect covered by this paper is the
intramolecular and intermolecular electron transfer occurring
from the cleavage of the C-C bond of the cyclopropane
functionality and formation of a C-C bond across the two â
instead of R positions of two adjacent pyrroles. The electron
transfer in cyclopropane-containing porphyrinogen is very often
accompanied by the cleavage and formation of C-C bonds.2,4
When such an event occurs intermolecularly, the one-electron
oxidation of the porphyrinogen is achieved with the consequent
oxidative coupling of two metallaporphyrinogens. This observa-
tion established the synthetic methodology for the oligomer-
ization and polymerization of the metallaporphyrinogen moiety.
The synergetic metal-to-ligand interaction in the porphyrino-
gen derivative containing a cyclopropane moiety allowed a quite
novel strategy for masking unusually high oxidation states for
metals; thus the metal in complexes D can either behave as
metal(II) or metal(IV)3a depending on the reaction pathway in
which it is engaged (Chart 3). The relevance of the reversible
1
8.35; N, 7.25. Found: C, 68.55; H, 8.53; N, 7.03. H NMR (C5D5N,
200 MHz, 298 K, ppm): δ 6.42 (s, 8H, C4H2N); 3.67 (m, 8H, THF);
2.32 (m, 16H, CH2); 1.65 (m, 8H, THF); 0.99 (m, 24H, CH3).
Synthesis of 3. [MnCl2(thf)1.5] (1.56 g, 6.7 mmol) was added to a
colorless solution of 1 (5.8 g; 6.8 mmol) in benzene (250 mL), resulting
in a milky suspension, which was reacted for 48 h at room temperature,
then filtered to remove LiCl. The solvent was evaporated to dryness
under reduced pressure and the pale pink solid collected with n-hexane
(200 mL), filtered, and dried (4.2 g, 63%). Anal. Calcd for C52H80Li2-
MnN4O4: C, 69.87; H, 9.19; N, 6.27. Found: C, 69.47; H, 8.88; N,
6.34. IR (Nujol, νmax/cm-1): 3089 (s), 1260 (s), 1047 (m), 890 (m),
830 (s), 750 (m). µeff ) 5.91 µB at 293 K.
Synthesis of 4. [MnCl2(thf)1.5] (2.94 g; 12.6 mmol) was added to a
yellow solution of 2 (9.8 g; 12.7 mmol) in THF (250 mL), resulting in
a suspension, which was stirred for 24 h at room temperature. The
suspension slowly turned orange, while a thin white solid (NaCl)
formed, which was removed by filtration. The solution was taken to
dryness and the pink-white solid collected with n-hexane (150 mL),
filtered, and dried (6.91 g, 67%). Anal. Calcd for C52H80MnN4Na2O4:
C, 67.44; H, 8.71; N, 6.05. Found: C, 67.42; H, 8.77; N, 6.26. IR
(Nujol, νmax/cm-1): 3069 (s), 1319 (s), 1288 (w), 1233 (w), 1045 (s),
967 (m), 883 (m), 844 (m), 746 (m). µeff ) 6.19 µB a 293 K.
Synthesis of 5. [MnCl2(thf)1.5] (3.5 g, 15.0 mmol) was added to a
solution of 1 (13.19 g, 15.5 mmol) in toluene (250 mL), resulting in a
milky suspension, which was reacted for 24 h at room temperature.
Then [CuCl2(thf)0.5] (2.55 g, 15 mmol) was added, immediately giving
a red suspension, which was stirred for 1 day. The solvent was
evaporated at reduced pressure, and the red-brown solid was suspended
in benzene (250 mL) and refluxed for 24 h. After the removal of salts
by filtration, the red solution was taken to dryness and the resulting
solid dissolved in THF (100 mL), treated with n-hexane (200 mL),
filtered, and dried (8.41 g, 61%). Anal. Calcd for C52H80LiMnN4O4:
C, 70.41; H, 9.09; N, 6.32. Found: C, 70.45; H, 9.15; N, 6.30. IR
(Nujol, νmax/cm-1): 3088 (s), 1318 (m), 1246 (s), 1151 (s), 1076 (s),
1040 (s), 885 (s), 747 (s). µeff ) 5.00 µB at 293 K.
Chart 3
Synthesis of 6. Degassed Cp2FeBPh4 (5.15 g, 10.0 mmol) was added
to a THF (200 mL) solution of 4 (4.72 g, 5.1 mmol), cooled to -40
°C, obtaining a red solution, which was allowed to react for 24 h at
room temperature. The color slowly turned purple-red. The solvent was
evaporated to dryness under reduced pressure and the resulting solid
extracted with Et2O (100 mL). The product obtained after evaporation
of the mother liquor was treated with pentane (50 mL), filtered, and
dried (1.7 g, 56%). Anal. Calcd for C44H64MnN4O2: C, 71.81; H, 8.77;
N, 7.61. Found: C, 71.52; H, 8.51; N, 7.59. IR (Nujol, νmax/cm-1):
3088 (s), 1568 (s), 1236 (s), 1105 (s), 1072 (s), 1044 (s), 1002 (s), 816
(s), 746 (s). µeff ) 5.67 µB at 293 K.
formation and cleavage of the C-C bond in porphyrinogens is
not at all limited to such molecular skeletons. We should
mention in this context that a few chemical systems function
as “molecular batteries”, storing and releasing electrons via the
formation and cleavage of C-C bonds.5
Experimental Section
Synthesis of 7. [CuCl2(thf)0.5] (1.8 g, 10.6 mmol) was added to a
red solution of 5 (2.2. g; 2.5 mmol) in THF (70 mL). The color faded,
while an orange-yellow microcrystalline solid formed. The suspension
was stirred for 24 h at room temperature, then the volume was reduced
General Procedure. All reactions were carried out under an
atmosphere of purified nitrogen. Solvents were dried and distilled before
use by standard methods. Infrared spectra were recorded with a Perkin-
(4) Piarulli, U.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J.
Am. Chem. Soc. 1996, 118, 3634.
(5) Gallo, E.; Solari, E.; Re, N.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C. J. Am. Chem. Soc. 1997, 119, 5144. Solari, E.; Maltese, C.; Franceschi,
F.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Chem. Soc., Dalton Trans.
1997, 2903. De Angelis, S.; Solari, E.; Gallo, E.; Floriani, C.; Chiesi-Villa,
A.; Rizzoli, C. Inorg. Chem. 1996, 35, 5995.
(6) Jubb, J.; Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg.
Chem. 1992, 31, 1306.
(7) Brown, W. H.; Hutchinson, B. J.; MacKinnon, M. H. Can. J. Chem.
1971, 49, 4017.
(8) Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem.
Soc. 1993, 115, 3595, and references therein.

Cyclopropane-Containing Oxidized Porphyrinogens
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1697
Scheme 1
Scheme 2
the solid was collected with toluene (250 mL), and the undissolved
salts were filtered off. The red solution was concentrated to ∼50 mL
and the microcrystalline orange solid filtered and dried (2.7 g, 47%).
Anal. Calcd for C36H48Cl6Cu4FeN4‚(C7H8)1.5, C46.5H60Cl6Cu4FeN4: C,
46.61; H, 5.04; N, 4.68. Found: C, 46.18; H, 4.82; N, 4.28. IR (Nujol,
to ∼50 mL, and the resulting solid was filtered and dried (1.7 g, 61%).
Anal. Calcd for C72H96Cl13Cu9Mn2N8: C, 39.02; H, 4.37; N, 5.06.
Found: C, 39.41; H, 4.81; N, 4.45. IR (Nujol, νmax/cm-1): 3055 (s),
1562 (m), 1538 (m), 1046 (s), 961 (s), 814 (s). µeff ) 5.95 µB at 293
K.
Synthesis of 8. A solution of 2,2′-bipyridyl (1.5 g, 10 mmol) in
THF (80 mL) was reacted with 7 (0.9 g, 0.4 mmol) and the mixture
stirred at room temperature for 2 h. A pale green solid formed, which
was filtered off from a red solution, dried (0.70 g), and analyzed to be
[(CuCl2)(2,2′-bipyridyl)]. Anal. Calcd for C10H8Cl2CuN2: C, 41.33; H,
2.77; N, 9.64. Found: C, 42.02; H, 2.97; N, 9.35. From the red solution,
after addition of Et2O (70 mL), a red crystalline solid precipitated (0.50
g), which was analyzed by X-ray characterization as [Et8N4MnIII]-[Cu-
(2,2′bipy)2]+. IR (Nujol νmax/cm-1): 3058 (m), 1595 (s), 1570 (w), 1318
(s), 1240 (s), 1151 (s), 1077 (s), 1027 (w), 972 (w), 924 (w), 882 (w),
858 (w), 807 (w), 755 (s), 734 (w), 718 (w).
Synthesis of 9. [FeCl2(thf)1.5] (1.29 g, 5.5 mmol) was added very
slowly in a drybox to a solution of 1 (4.9 g; 5.7 mmol) in THF (250
mL), resulting in a pale yellow solution, which reacted for 5 h at room
temperature. The solution was taken to dryness and the solid collected
with Et2O (250 mL) and extracted with the mother liquor. After reducing
the volume of the ether, the product was filtered and dried (3.1 g, 61%).
Anal. Calcd for C52H80FeLi2N4O4: C, 69.79; H, 9.00; N, 6.26. Found:
C, 69.51; H, 8.73; N, 5.91.
ν
max/cm-1): 3062 (s), 1536 (m), 1558 (m), 1316 (m), 1059 (m), 1008
(m), 963 (s), 917 (m), 722 (m).
Synthesis of 12. Pyrrole (17.0 g; 250.0 mmol) was added dropwise
to a solution of cyclohexanone (24.8 g; 250 mmol) in ethanol (300
mL) cooled to -40 °C and methanesulfonic acid (3 mL), resulting in
an amber solution, which was refluxed for 2 h. A white microcrystalline
product formed, which was filtered, washed with ethanol, and dried.
To remove the excess ethanol, the solid was suspended in Et2O and
stirred overnight, filtered, and dried. Mp > 200 °C. Anal. Calcd for
C40H52N4: C, 81.59; H, 8.90; N, 9.51. Found: C, 81.88; H, 8.72; N,
9.41. 1H NMR (CDCl3, 200 MHz, 298 K, ppm): δ 7.08 (bs, 4H, NH);
5.92 (s, 4H, C4H2N); 5.90 (s, 4H, C4H2N); 1.96-1.89 (m, 16H, C6H10);
1.54 (m, 24H, C6H10).
Synthesis of 13. LiBun (100 mL, 1.6 M in n-hexane, 160 mmol)
was added dropwise to a THF (200 mL) suspension of 12 (23.60 g,
40.0 mmol), resulting in a milky suspension, which was refluxed for 2
h, until the release of gas stopped. The solvent was evaporated to
dryness at reduced pressure and the white solid collected with n-hexane
(120 mL), filtered, and dried (30.7 g, 85%). Anal. Calcd for C56H80-
Li4N4O4: C, 74.65; H, 8.95; N, 6.22. Found: C, 74.55; H, 8.35; N,
6.15. 1H NMR (C6D6, 200 MHz, 298 K, ppm): δ 6.40 (s, 8H, C4H2N);
Scheme 3
Synthesis of 10. [FeCl2(thf)1.5] (13.0 g, 55.4 mmol) was added to a
solution of 1 (23.61 g; 27.7 mmol) in THF (500 mL), resulting in a
dark red solution that reacted for 24 h at room temperature. The solution
was taken to dryness and the dark red solid extracted with Et2O (250
mL) to remove LiCl. After reducing the volume of the ether, the product
was filtered and dried (23.34 g, 95%). Anal. Calcd for C52H80-
FeLiN4O4: C, 70.33; H, 9.31; N, 6.31. Found: C, 70.21; H, 9.44; N,
6.19. IR (Nujol, νmax/cm-1): 3088 (s), 1317 (s), 1283 (m), 1235 (s),
1150 (s), 1072 (s) 1039 (s), 883 (m), 774 (s).
Synthesis of 11. FeCl2(thf)1.5 (1.15 g, 4.91 mmol) was added in a
drybox to a colorless solution of 1 (4.61 g, 5.4 mmol) in THF (300
mL), resulting in a yellow solution, which was reacted for 24 h at room
temperature. CuCl2(thf)0.5 (3.6 g, 21.7 mmol) was then added, obtaining
a red solution, which was reacted for 24 h. The solvent was removed,

1698 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Crescenzi et al.
3.27 (m, 16H, THF); 2.71-1.98 (m, 24H, C6H10); 1.72-1.36 (m, 16H,
C6H10), 1.26 (m, 16H, THF).
Scheme 4
Synthesis of 14. FeCl2‚thf1.5 (1.74 g, 7.4 mmol) was added to a milky
suspension of 13 (3.33 g, 3.7 mmol) in THF (250 mL). A red solution
was obtained, where a red microcrystalline solid formed rapidly. The
mixture was stirred at room temperature for 12 h, then CuCl2‚thf0.5
(3.25 g, 19.23 mmol) was added, which caused the slow formation of
a thin yellow solid. The suspension was reacted for 24 h, then filtered,
and the insoluble product was dried (1.5 g, 43%). Crystals suitable for
X-ray analysis were grown in CH3CN. Anal. Calcd for C40H48Cl3-
CuFeN4: C, 59.27; H, 5.97; N, 6.91. Found: C, 58.97; H, 6.13; N,
7.02. IR (Nujol, νmax/cm-1): 3080 (s), 1561 (w), 1550 (w), 1528 (w),
1400 (s), 1277 (m) 1211 (w), 1188 (w), 1127 (w), 1061 (m), 1055 (s),
900 (m) 800 (s), 783 (s), 711 (s), 689 (m).
Synthesis of 15, Method A. Degassed Cp2FeBPh4 (6.94 g, 13.7
mmol) was added to a solution of 1 (5.85 g, 6.86 mmol) in THF (150
mL) cooled to -40 °C. The solution suddenly turned red, was allowed
to reach room temperature, and left to react for 20 h. The solvent was
removed at reduced pressure, the solid was collected with benzene (120
mL) and stirred for about 2 h, and then the remaining undissolved solid
was filtered off. The solution was concentrated to ∼30 mL, then pentane
(∼50 mL) was added, and the solid, which formed, was filtered and
dried (2.9 g, 60%). Crystals suitable for X-ray analysis4 were obtained,
recrystallizing the product in THF/heptane. Anal. Calcd for C44H64-
Li2N4O2: C, 76.05; H, 9.28; N, 8.06. Found: C, 75.83; H, 9.03; N,
8.10. 1H NMR (C6D6, 200 MHz, 298 K, ppm): δ 6.87 (m, 2H, C4H2N);
6.49 (m, 6H, C4H2N); 3.25 (m, 8H, THF); 2.53 (m, 4H, CH2); 2.12
(m, 4H, CH2); 1.86 (m, 6H, CH2); 1.61 (m, 2H, CH2); 1.39 (m, 4H,
CH3); 1.34 (m, 8H, THF); 1.29-0.90 (m, 16H, CH3); 0.62 (m, 4H,
CH3).
Synthesis of 15, Method B. Complex 1 (0.73 g, 0.86 mmol) was
added to a yellow solution of 16 (0.82 g, 0.86 mmol) in THF (70 mL),
resulting in a red solution, which was reacted for 12 h. The solvent
was removed at reduced pressure, then the residual solid was dissolved
in Et2O (100 mL), and the undissolved salts were filtered off. The
solvent was evaporated to dryness and the solid collected with n-hexane
(80 mL), filtered, and dried (93%). The product was proven by 1H
NMR to be 15.
the white solid filtered and dried (2.2 g, 76%). Crystals suitable for
X-ray analysis were obtained by slow extraction with Et2O. Anal. Calcd
for C64H76BN4NaO: C, 80.82; H, 8.05; N, 5.89. Found: C, 81.11; H,
8.27; N, 5.78. IR (Nujol, νmax/cm-1): 3055 (s), 1938 (w), 1877 (w),
1816 (w), 1567 (s), 1266 (m), 1137 (m), 1032 (m), 958 (w), 837 (w),
1
807 (m), 771 (s), 730 (s), 612 (s). H NMR (CD2Cl2, 200 MHz, 298
K, ppm): δ 7.36 (d, J ) 4.9 Hz, 4H, C4H2N); 7.33 (m, 8H, BPh4);
7.02 (t, J ) 7.0 Hz, 8H, BPh4); 6.89 (t, J ) 7.0 Hz, 4H, BPh4); 6.54
(d, J ) 4.9 Hz, 4H, C4H2N); 3.41 (m, 4H, THF); 2.40 (m, 8H, CH2);
2.15 (m, 8H, CH2); 2.01 (m, 4H, THF); 0.96 (m, 12H, CH3); 0.85 (m,
12H, CH3).
Synthesis of 16, Method A. Degassed Cp2FeBPh4 (5.22 g, 10.32
mmol) was added to a colorless solution of 1 (2.2 g, 2.58 mmol) in
THF (120 mL) cooled to -40 °C, resulting in a red solution, which
was reacted for 24 h. The solvent was evaporated under reduced
pressure, and the impurities were removed by extraction in n-hexane.
The beige solid was treated with dioxane (200 mL) and stirred for ∼2
h, then some undissolved LiBPh4 was filtered off. The solution was
taken to dryness, then the product was collected with n-hexane (80
mL), filtered, and dried (1.4 g, 63%). Crystals suitable for X-ray
analysis4 were obtained by recrystallizing the product in THF/hexane.
Anal. Calcd for C64H76BLiN4O: C, 82.21; H, 8.19; N, 5.99. Found:
C, 82.48; H, 8.17; N, 6.00. 1H NMR (CDCl3, 200 MHz, 298 K, ppm):
δ 7.50 (m, 8H, BPh4); 7.30 (d, J ) 4.9 Hz, 4H, C4H2N); 7.10 (t, J )
6.8 Hz, 8H, BPh4); 6.94 (t, J ) 6.8 Hz, 4H, BPh4); 6.55 (d, J ) 4.9
Hz, 4H, C4H2N); 3.76 (m, 4H, THF); 2.42 (q, J ) 7.3 Hz, 4H, CH2);
2.34 (q, J ) 7.3 Hz, 4H, CH2); 2.15 (q, J ) 7.3 Hz, 4H, CH2); 1.99 (q,
J ) 7.3 Hz, 4H, CH2); 1.97 (m, 4H, THF); 1.10 (t, J ) 6.8 Hz, 6H,
CH3); 0.93 (t, J ) 6.8 Hz, 6H, CH3); 0.82 (m, 12H, CH3).
Synthesis of 18. 18-Crown-6 (0.36 g, 1.35 mmol) was added to an
amber suspension of 17 (1.19 g, 1.35 mmol) in benzene (120 mL).
The mixture became brighter, while a microcrystalline white solid
formed. The mixture was stirred for 12 h, the solid was filtered off,
and the solvent was removed at reduced pressure. The residue was
collected with n-hexane (80 mL), filtered, and dried. Anal. Calcd for
C36H48N4: C, 80.55; H, 9.01; N, 10.44. Found: C, 80.65; H, 9.55; N,
10.67. H NMR (CDCl3, 200 MHz, 298 K, ppm): δ 7.54 (d, J ) 4.9
Hz, 4H, C4H2N); 6.77 (d, J ) 4.9 Hz, 4H, C4H2N); 2.50-2.30 (m, 8H,
CH2); 2.19-1.94 (m, 8H, CH2); 0.85 (m, 24H, CH3).
1
Synthesis of 19, Method A. Degassed Cp2FeBPh4 (5.19 g, 10.3
mmol) was added to a colorless solution of 1 (4.38 g, 5.1 mmol) in
THF (120 mL) cooled to -40 °C, resulting in a red solution, which
was reacted overnight. The solvent was removed at reduced pressure,
and the solid was collected with n-hexane (80 mL), then extracted with
fresh n-hexane (120 mL). The mother liquor was concentrated to ∼50
mL, and the red-violet solid was filtered and dried (2.1 g, 59%). Crystals
suitable for X-ray analysis were obtained by recrystallizing the product
in n-hexane. Anal. Calcd for C44H63Li3N4O2: C, 75.41; H, 9.06; N,
Synthesis of 16, Method B. Degassed Cp2FeBPh4 (2.1 g, 4.2 mmol)
was added to a red solution of 15 (1.5 g, 2.1 mmol) in THF (100 mL)
cooled to -40 °C, resulting in a yellow-red solution, which was reacted
for 12 h at room temperature. The solvent was removed at reduced
pressure, then the residue solid was suspended in dioxane (100 mL)
and stirred for 2 h, and the undissolved LiBPh4 was filtered off. The
solvent was evaporated to dryness and the solid collected with n-hexane
(110 mL), filtered, and dried (1.18 g, 60%). The product was proven
1
8.00. Found: C, 75.55; H, 9.11; N, 8.15. H NMR (C6D6, 200 MHz,
298 K, ppm): δ 6.42 (d, J ) 2.4 Hz, 1H, C4H2N); 6.34 (m, 2H, C4H2N);
6.26 (d, J ) 2.4 Hz, 1H, C4H2N); 6.19 (d, J ) 2.4 Hz, 1H, C4H2N);
6.09 (d, J ) 2.4 Hz, 1H, C4H2N); 4.64 (d, J ) 2.4 Hz, 1H, C4H2N);
3.44 (m, 8H, THF); 2.49-2.18 (m, 7H, CH2); 2.01-1.72 (m, 8H, CH2);
1.52-1.46 (m, 1H, CH2); 1.26-1.16 (m, 14H, CH3 + THF); 1.02-
0.90 (m, 15H, CH3); 0.65 (t, J ) 7.3 Hz, 3H, CH3).
1
by H NMR to be 16.
Synthesis of 17. Degassed Cp2FeBPh4 (5.12 g, 10.0 mmol) was
added to a yellow solution of 2 (2.14 g, 2.5 mmol) in THF (125 mL)
cooled to -40 °C, resulting in a red solution, which was reacted for
24 h at room temperature. The solvent was removed at reduced pressure,
and the solid collected with Et2O (50 mL) and then extracted with fresh
Et2O (120 mL). The mother liquor was concentrated to ∼50 mL and
Synthesis of 19, Method B. An orange solution of 15 (1.0 g, 1.44
mmol) in benzene (50 mL) was heated at 80 °C. After 3 h, a sample
of the bulk of the reaction analyzed via 1H NMR showed the formation
of 19, [Et8N4H4], and 18, with some amount of 15 remaining. After 8
h, 15 disappeared and the three products 19, 18, and [Et8N4H4] formed
in the ratio 4:1:1. Prolonged heating gave rise to the decomposition of

Cyclopropane-Containing Oxidized Porphyrinogens
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1699
Scheme 5
Scheme 6
0.85 (s br, 48H, CH3). The different solvation degrees have been found
depending on the drying time in vacuo. The preliminary X-ray analysis
showed two THF molecules per lithium, as displayed in Scheme 6,
while the microanalysis was carried out on a sample dried for a very
long time. The samples used for NMR have different solvation degrees
because their preparation was carried out in vacuo. In this specific case,
we report the sample with three THF molecules.
Synthesis of 22 from 20 and 21, Method B. Solid 20 (0.62 g, 1
mmol) and 21 (0.93 g, 1 mmol) were mixed, then THF (70 mL) was
added to obtain a red solution, which was reacted for 12 h. The solvent
was evaporated and the yellow solid collected with n-hexane (50 mL),
1
filtered, and dried. The H NMR spectrum showed it to be 22.
X-ray Crystallography for Complexes 5, 7, 11, 14, and 19.
Suitable crystals were mounted in glass capillaries and sealed under
nitrogen. The reduced cells were obtained with the use of TRACER.9
Crystal data and details associated with data collection are given in
Tables 1 and S1. Data for 5, 7, 11, and 14 were collected on a single-
crystal diffractometer (Siemens AED for 5 and Rigaku AFC6S for 7,
11, 14) at 295 K for 5 and 7 and at 133 K for 11 and 14. For intensities
and background individual reflection profiles were analyzed.10 The
structure amplitudes were obtained after the usual Lorentz and
polarization corrections,11 and the absolute scale was established by
the Wilson method.12 Data for complex 19 were collected at 133 K on
a Stoe IPDS area detector. A total of 200 images from æ ) 0° to æ )
180° were recorded, each one exposed for 240.8 s. The diffraction data
were indexed and processed using the STOE program package. No
absorption correction was deemed necessary.
The crystal quality for all complexes was tested by ω scans showing
that crystal absorption effects could not be neglected for 7, 11, and 14.
For these complexes data were then corrected for absorption using a
semiempirical method.13 The function minimized during the least-
squares refinement was ∑w(∆F2)2. Anomalous scattering corrections
were included in all structure factor calculations.14b Scattering factors
for neutral atoms were taken from ref 14a for nonhydrogen atoms and
from ref 15 for H. Structure solutions were based on the observed
reflections [I > 2σ(I)]. The refinements were carried out using the
unique total reflections having I > 0.
18 and formation of undetectable products, while the thermally stable
19 and [Et8N4H4] were still present.
Synthesis of 21. Degassed Cp2FeBPh4 (2.61 g, 5.17 mmol) was
added to a yellow solution of 20 (2.32 g, 2.58 mmol) in THF (100
mL) cooled to -40 °C, resulting in a dark red solution, which was
stirred for 12 h. The solution was then evaporated to dryness and the
product extracted with n-pentane (120 mL) to remove insoluble impuri-
ties. The residue was dissolved in benzene (80 mL), then dioxane (40
mL) was added to completely precipitate LiBPh4. Salts were filtered
off and the red solution evaporated to dryness. The solid was collected
with n-pentane (80 mL), filtered, and dried (1.00 g; 65%). Anal. Calcd
for C36H48N4Ni: C, 72.61; H, 8.12; N, 9.41. Found: C, 72.47; H, 7.85;
N, 9.31. IR (Nujol, νmax/cm-1): 3086 (s); 1585 (s); 1300 (s); 1280 (s);
1077 (s); 1022 (s); 807 (s); 735 (s). 1H NMR (C6D6, 200 MHz, 298 K,
ppm): δ 6.68 (d, J ) 4.9 Hz, 2H, C4H2N); 6.54 (d, J ) 2.9 Hz, 2H,
C4H2N); 6.33 (d, J ) 2.9 Hz, 2H, C4H2N); 6.13 (d, J ) 4.9 Hz, 2H,
C4H2N); 3.57 (q, J ) 7.3 Hz, 2H, CH2); 2.85 (q, J ) 7.3 Hz, 2H, CH2);
2.56 (q, J ) 7.3 Hz, 2H, CH2); 2.29 (m, 2H, CH2); 1.84 (q, J ) 7.3 Hz,
4H, CH2); 1.62 (m, 2H, CH2); 1.42 (t, J ) 6.8 Hz, 6H, CH3); 1.27 (m,
2H, CH2); 1.02 (t, J ) 7.3 Hz, 6H, CH3); 0.86 (t, 3H, J ) 6.8 Hz, 3H,
CH3); 0.70 (t, J ) 7.3 Hz, 6H, CH3); 0.46 (t, J ) 6.8 Hz, 3H, CH3).
Synthesis of 22, Method A. Degassed Cp2FeBPh4 (1.8 g, 3.5 mmol)
was added to a THF solution of 20 (3.2 g, 3.5 mmol) cooled to -40
°C, resulting in a dark solution, which was reacted at room temperature
for 24 h. The solvent was evaporated, and the yellow solid was treated
with benzene (110 mL), stirred for 2 h, and then filtered to remove the
undissolved salts. The solvent was evaporated under reduced pressure
and the solid collected with n-hexane (80 mL), filtered, and dried (1.8
g; 75%). Anal. Calcd for C80H112Li2N8Ni2O2: C, 71.22; H, 8.37; N,
The structures of 5, 7, 14, and 19 were solved by the heavy-atom
method starting from a three-dimensional Patterson map. The structure
(9) Lawton, S. L.; Jacobson, R. A. TRACER (a cell reduction program);
Ames Laboratory, Iowa State University of Science and Technology: Ames,
IA, 1965.
(10) Lehmann, M.S.; Larsen, F. K. Acta Crystallogr., Sect. A: Cryst.
Phys., Diffr., Theor. Gen. Crystallogr. 1974, A30, 580-584.
(11) Data reduction was carried out on a Quansan personal computer
equipped with an INTEL Pentium processor and on an ENCORE 91
computer.
(12) Wilson, A. J. C. Nature 1942, 150, 151.
(13) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1968, A24, 351.
(14) (a) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV, p 99. (b) Ibid., p 149.
(15) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys.
1965, 42, 3175.
1
8.31. Found: C, 71.28; H, 8.40; N, 8.56. H NMR (C6D6, 200 MHz,
298 K, ppm): δ 6.20 (s br, 8H, C4H2N); 5.89 (s br, 8H, C4H2N); 4.68
(s br, 2H, CH2); 3.76 (s br, 2H, CH2); 2.95 (m, 8H, THF); 2.78 (m,
8H, THF); 2.44-1.61 (s br, 20H, CH2); 1.23 (m, 8H, THF); 1.53-

1700 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Crescenzi et al.
Table 1. Experimental Data for the X-ray Diffraction Studies on Crystalline Complexes 5, 7, 11, 14, and 19
5
7
11
14
19
formula
a, Å
b, Å
C36H48MnN4‚C16H32LiO4 C72H96Cl13Cu9Mn2N8 C36H48Cl6Cu4FeN4 3C4H8O‚0.5C2H3N C40H48ClFeN4‚0.5Cu2Cl4 C44H63Li3N4O2
16.181(2)
12.066(1)
15.839(3)
11.248(3)
97.20(2)
92.72(1)
87.75(1)
2129.1(7)
1
14.988(5)
15.614(7)
12.027(4)
108.44(3)
100.32(3)
85.78(3)
2627(2)
2
12.571(3)
15.259(5)
10.667(4)
105.49(2)
96.67(2)
81.00(2)
1941.6(11)
2
16.692(3)
12.704(3)
20.709(4)
90
111.79(3)
90
16.181(2)
39.222(3)
90
90
90
10 269(2)
8
c, Å
R, deg
â, deg
γ, deg
V, Å3
4048.6(17)
4
Z
formula weight
space group
T, °C
887.1
I41/acd (no. 142)
22
0.710 69
1.148
2.89
2216.3
P1h (no. 2)
22
0.710 69
1.729
29.38
0.568-1.000
0.062
1275.9
831.1
700.8
P1h (no. 2)
P1h (no. 2)
P21/c (no. 14)
-140
0.710 69
1.150
0.64
0.955-1.000
0.055
-140
-140
λ, Å
0.710 69
1.613
0.710 69
1.422
F
calc, g cm-3
µ, cm-1
22.20
0.874-1.000
0.050
11.65
0.782-1.000
0.059
transmission coeff 0.952-1.000
Ra
0.027
0.041
wR2b
0.188
0.156
0.169
0.139
2 2
a R ) ∑|∆F|/∑|Fo| calculated on the unique observed data [I > 2σ(I)]. b wR2 ) [∑w|∆F2|2/∑w|Fo | ]1/2 calculated on the unique data having I
> 0.
of 11 was solved using SHELX-86.16 Refinements were done by full-
matrix least-squares first isotropically, then anisotropically for all the
non-H atoms, except for disordered atoms. All hydrogen atoms (except
for those associated with the disordered molecules, which were ignored)
were located from difference Fourier maps and introduced in the
subsequent refinements as fixed atom contributions with isotropic U’s
fixed at 0.15 for 5, 0.10 for 7, 0.08 for 11, and 0.05 Å2 for 14 and 19.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Complexes 5 and 7
5
Mn(1)-N(1)
Mn(1)-N(2)
C(1)-C(2)
C(6)-C(7)
1.914(4)
1.957(3)
1.370(6)
1.339(5)
2
In the last stage of refinement the weighting scheme w ) 1/[σ2(Fo ) +
7
(aP)2] (with P ) (Fo2 + 2Fc2)/3 and a ) 0.0108, 0.1020, 0.0980, 0.1109,
and 0.0696 for 5, 7, 11, 14, and 19, respectively) was applied. The
final difference maps for 5, 7, 11, and 19 showed no unusual feature,
with no significant peak above the general background. In complex 14
the final difference map showed a residual peak of 3.16 e Å-3 in the
near proximity of Cu(1) along the Cu(1)-Cl(3) bond.
Mn(1)-Cl(1)
Mn(1)-N(1)
Mn(1)-N(2)
Mn(1)-N(3)
Mn(1)-N(4)
Cu(1)-C(2)
Cu(1)-C(3)
Cu(2)-C(7)
Cu(2)-C(8)
Cu(4)-Cu(5)
Cu(4)-Cl(4)
N(1)-C(1)
2.321(3)
2.214(8)
2.239(7)
2.214(7)
2.222(7)
2.116(9)
2.120(9)
2.158(9)
2.119(10)
3.005(2)
2.377(4)
1.298(12)
1.450(12)
1.427(12)
1.299(11)
1.305(12)
1.439(11)
N(4)-C(16)
1.436(12)
1.299(12)
1.544(12)
1.577(12)
1.543(12)
1.543(14)
1.587(12)
1.514(14)
59.3(6)
61.4(6)
59.3(6)
57.8(6)
62.5(6)
N(4)-C(19)
C(4)-C(5)
C(4)-C(6)
C(5)-C(6)
C(14)-C(15)
C(14)-C(16)
Refinement of complex 7 was carried out straightforwardly. In
complex 5 the C(44) carbon atom of the independent THF molecule
was found to be statistically distributed over two positions, called A
and B, isotropically refined with site occupation factors of 0.65 and
0.35, respectively. In complex 11 the O(3), C(49)-C(52) THF solvent
molecule of crystallization was affected by disorder, which was solved
by splitting the atoms over two positions, called A and B, isotropically
refined with a site occupation factor of 0.7 and 0.3, respectively. During
the refinement the C-O and C-C distances of the disordered THF
molecule were constrained to be 1.48(1) and 1.54(1) Å, respectively.
In complex 14 the acetonitrile solvent molecule of crystallization was
found to be disordered over two positions about an inversion center.
The N(5), C(41), and C(42) atoms were therefore isotropically refined
with site occupation factors of 0.5. In complex 19 the rather high
thermal parameters reached by the C(3) and C(7) carbon atoms of
adjacent pyrrole indicated the presence of disorder, which was solved
by splitting the atoms over two positions, called A and B, isotropically
refined with site occupation factors of 0.5.
C(15)-C(16)
C(5)-C(4)-C(6)
C(4)-C(5)-C(6)
C(4)-C(6)-C(5)
C(15)-C(14)-C(16)
C(14)-C(15)-C(16)
C(14)-C(16)-C(15)
N(1)-C(4)
N(2)-C(6)
59.6(6)
N(2)-C(9)
N(3)-C(11)
N(3)-C(14)
its activity in high oxidation states,20 we examined the synthesis
and the oxidation behavior of Mn-porphyrinogen. The synthesis
of 3 and 4 (see Scheme 1) has been performed from the
corresponding lithium and sodium derivatives, 18,21 and 2,
respectively. The synthesis and characterization of 2 are reported
here, while the synthesis and use of 1 are well-defined. The
use of 2 displays particular advantages over 1 for the synthesis
of transition metal-porphyrinogen complexes, because of the
much lower solubility of NaX vs LiX salts in the polar solvents
used during the synthesis and for the quite different binding
ability of Li+ vs Na+ toward the pyrrolyl anions.4,8,21,22
Therefore, under appropriate conditions we can synthesize either
dimetallic [M-Li] or alkali-free transition metal porphyrinogen
complexes. Under the experimental conditions used, both 3 and
All calculations were performed using SHELX7617 for the early
stages of solution and SHELXL9318 for refinements. Final atomic
coordinates are listed in Tables S2-S6 for non-H atoms and in Tables
S7-S11 for hydrogens. Thermal parameters are given in Tables S12-
S16, bond distances and angles in Tables S17-S21.19
Results and Discussion
(A) Oxidation Pathway of Manganese-Porphyrinogen.
Due to the relevant role of manganese in redox chemistry and
(16) Sheldrick, G. M. SHELXL86. Program for the solution of crystal
structures; University of Go¨ttingen, Germany, 1986.
(17) Sheldrick, G. M. SHELX76. Program for Crystal Structure Deter-
mination; University of Cambridge, Cambridge, England, 1976.
(18) Sheldrick, G. M. SHELXL93. Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1993.
(19) See paragraph at the end regarding Supporting Information.
(20) (a) Photosynthesis; Briggs, W. R., Ed.; ARL: New York, 1989.
(b) The Photosynthetic Reaction Center, Vol. I and II; Deisenhofer, J.,
Norris, J. R., Eds.; Academic: New York, 1993. (c) Manganese Redox
Enzymes; Pecoraro, V. L., Ed.; VCH: New York, 1992. (d) Wieghardt, K.
Angew. Chem., Int. Ed. Engl. 1989, 28, 1153.
(21) De Angelis, S.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C. J. Chem. Soc., Dalton Trans. 1994, 2467.

Cyclopropane-Containing Oxidized Porphyrinogens
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1701
Table 3. Comparison of Relevant Structural Parameters within the Metal-Porphyrinogen Units for Complexes 5, 7, 11, 14, and 19
5
7
11
14
19
-0.005(2)
0.005(2)
-0.007(2)
0.007(2)
distance of atoms from the N4 core, Å
N(1)
N(2)
N(3)
N(4)
Ma
0.000(-)
0.000(-)
0.006(8)
-0.004(7)
0.006(8)
-0.004(7)
0.948(2)
0.795(2)
0.816(2)
1.016(2)
1.088(2)
133.9(3)
133.7(2)
127.6(3)
125.5(2)
119.8(4)
112.9(4)
113.7(4)
111.7(4)
0.001(7)
-0.001(7)
0.001(7)
-0.001(7)
0.815(3)
0.998(2)
1.036(3)
1.002(3)
1.052(2)
130.5(2)
130.0(2)
130.1(2)
129.2(2)
122.3(3)
107.6(3)
106.3(3)
122.2(3)
0.004(3)
-0.004(3)
0.004(3)
-0.004(3)
0.869(1)
0.994(1)
1.025(1)
0.931(1)
1.035(1)
129.4(1)
128.8(1)
130.9(1)
128.5(1)
117.1(2)
109.6(2)
110.1(2)
119.3(2)
0.000(-)
0.000(-)
0.000(-)
0.844(4)
distance of M from A,b Å
distance of M from B,b Å
distance of M from C,b Å
2.629(5) [2.555(5)]c
2.644(5) [2.703(5)]
0.465(4)
distance of M from D,b Å
dihedral angles between the N4 core
and the A, B, C, D rings, deg
0.463(4)
(A)
(B)
(C)
(D)
152.6(1)
151.3(1)
97.6(1) [101.4(1)]
100.7(1) [97.4(1)]
123.1(1)
124.4(1)
dihedral angle between AB, deg
dihedral angle between AD, deg
dihedral angle between BC, deg
dihedral angle between CD, deg
141.1(1)
141.1(1)
141.1(1)
141.1(1)
92.7(1) [93.2(1)]
114.6(1) [116.4(1)]
117.3(1) [115.3(1)]
170.3(1)
a M should be read Mn(1) in 5 and 7; Fe(1) in 11 and 14; Li(1) in 19. b A, B, C, and D define the pyrrole rings containing the N(1), N(2), N(3),
and N(4) nitrogen atoms, respectively. In 5 N(3) and N(4) should be read N(1)′ and N(2)′, respectively (′ ) -0.25+y, 0.25+x, 0.25-z). c Values
in brackets refer to the A and B pyrrole rings containing C(3)B and C(7)B, respectively.
4 have a dimetallic structure sketched according to the structure
reported for other alkali-transition metal complexes, where the
alkali cation is η5-bonded to the peripheral pyrrolyl anions.6,8,21,22
Both 3 and 4 are very sensitive to air or any other oxidizing
agent. The oxidation over a short period of time with molecular
oxygen converted 3 to the Mn(III) derivative 5. Longer exposure
to oxygen led to the absorption of up to four moles of O2 per
manganese and did not allow any characterizable compound to
be isolated. Unlike in the case of Co-, Ni-, or Cu-
porphyrinogen complexes,2a oxidation with p-benzoquinone did
not lead to the expected two-electron-oxidized monocyclopro-
pane derivative. The synthesis of 6 was achieved by the use of
2 equiv of Cp2FeBPh4 as the oxidizing agent of 4. The nature
of the oxidizing agent along with that of the alkali cation can
have a significant influence on the nature of the oxidized
product. The same reaction carried out with the lithium
derivative 3 seems to proceed differently, but certainly did not
lead to 6. The reaction of 3 with a controlled amount of CuCl2
led primarily to the Mn(III) derivative, 5, followed by the
oxidation to the biscyclopropane form, 7. Although an excess
of CuCl2 should be used, the formation of 7 from 5 requires
formally 3 equiv of oxidizing agent, since the forth one is
provided by Mn(III) being reduced to Mn(II). The excess of
CuCl2 takes care of the Cl- not engaged in the reaction, with
the formation of counteranions different from [Cu9Cl11]2-. The
amount of the latter one forming from “CuCl” determines the
maximum yield of 7. The formation of 7 probably occurs with
some amount of other complexes containing the same cation,
but different counteranions. The use of an appropriate amount
of CuCl2 did not allow us to intercept the intermediate
monocyclopropane form 6, which has been obtained as reported
above. On the other hand any attempt to oxidize 6 to 7 using
CuCl2 failed. The structure assignment of complexes 3-7, which
have the expected analytical, spectroscopic, and magnetic data,
has been done according to the analogous Co(II), Ni(II), and
Cu(II) derivatives for 3, 4, and 6, while 5 and 7 have been
examined with an X-ray analysis.
Table 4. Structural Parameters Related to the Formation of the
Cyclopropane Unit in Complexes 7, 11, and 14
7
11
14
C(1)‚‚‚C(19) (Å)
C(4)‚‚‚C(6) (Å)
C(9)‚‚‚C(11) (Å)
C(14)‚‚‚C(16) (Å)
2.453(13)
1.577(13)
2.464(13)
1.588(12)
2.379(12)
1.621(10)
2.408(12)
1.638(10)
2.446(6)
1.591(6)
2.442(6)
1.587(7)
C(4)-C(5)-C(6) (deg)
C(9)-C(10)-C(11) (deg)
C(14)-C(15)-C(16) (deg)
C(1) -C(20)-C(19) (deg)
61.4(6)
108.1(8)
62.5(6)
107.3(8)
63.8(6)
103.7(6)
66.3(5)
101.7(6)
62.7(3)
106.4(3)
62.2(3)
106.5(3)
Figure 1. SCHAKAL view of the anion in complex 5. Prime, double
prime, and star denote a transformation of -0.25+y, 0.25+x, 0.25-z;
-x, 0.5-y, z; and 0.25-y, 0.25-x, 0.25-z, respectively.
conformational parameters are quoted. The structural parameters
concerning the geometry of the atoms related to the formation
of cyclopropane are listed in Table 4; the pyrrole rings
containing N1, N2, N3, and N4 are labeled A, B, C, and D,
respectively.
The structure of 5 is shown in Figure 1 and consists of discrete
[Et8N4MnIII]- anions and [Li(thf)4]+ cations. The complex
possesses a crystallographically imposed symmetry, manganese
lying at the intersection of three 2-fold axes, one of them
perpendicular to the N4 core, and the others running through
the Mn-N bonds. The conformation of the complex is close to
that observed in [Et8N4CuIII]-[Li(thf)4]+2a and in the isostructural
Selected bond distances and angles for complexes 5 and 7
are presented in Table 2. In Table 3 the most relevant
(22) De Angelis, S.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C. Angew. Chem., Int. Ed. Engl. 1995, 34, 1092. Jacoby, D.; Isoz, S.;
Floriani, C.; Schenk, K.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1995,
14, 4816. Jacoby, D.; Isoz, S.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J.
Am. Chem. Soc. 1995, 117, 2793. Solari, G.; Solari, E.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. Organometallics 1997, 16, 508.

1702 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Crescenzi et al.
Figure 2. SCHAKAL view of the cation in complex 7.
[Et8N4CoIII]-[Li(thf)4]+.23 The N4 core is planar, with Mn lying
in the N4 plane from symmetry requirements. The manganese
atom lies in the plane of the pyrrole rings. The Mn-N bond
distances [mean value 1.936(10) Å] are significantly shorter than
those quoted in the literature for five- or six-coordinate Mn-
(III)-porphyrinato species, e.g., 1.998(4)-2.016(4) Å in [Mn-
(TPP)(CN)],24 2.000(4)-2.022(4) Å in [Mn(TPP)(Cl)(Py)],25
while they are in good agreement with those found in the square
planar [Mn(II)(pc)] [1.933(5) Å],26 where the shortest contact
in the axial direction (3.169 Å) involves a nitrogen atom of an
adjacent molecule. Bond distances within the pyrrole rings are
consistent, with a remarkable double bond localization on C1-
C2 [1.370(6) Å] and C6-C7 [1.339(5) Å] (Table 2). The
nitrogen atoms do not show any pyramidality. The axial
coordination sites around the metal are filled by the meso-
methylene groups. The two pairs of carbon C21, C21′ and C21′′,
C21* cap the MnN4 plane on both sides, their C‚‚‚C separation
being 4.638(13) Å. Four hydrogens, one from each of the
aforementioned carbons, provide a flattened tetrahedral cage
around the metal (Mn‚‚‚H61 ) 2.80 Å).
The structure of 7 is shown in Figures 2-4 and consists of
[Et8N4(∆)2MnCl]+ cations, [Cu8Cl9]- anionic aggregates, and
[CuCl2]- anions in the molar ratio 2:1:1. Figure 2 shows a
SCHAKAL top view of the cation. Two centrosymmetric cations
are linked in dimers by a [Cu8Cl9]- anion through η2-interactions
involving the Cu1 and Cu2 coppers and the C2-C3 and C7-
C8 pyrrole double bonds (Figure 3). The resulting aggregates
are held together in infinite chains parallel to the [001] axis by
the bridging centrosymmetric [CuCl2]- anions. A stereoscopic
view of a chain is given in Figure 4. The introduction of
cyclopropane units into the porphyrinogen skeleton occurs with
the significant structure changes highlighted by a comparison
of the structural parameters of 5 and 7 (Table 3). In particular
the following has been observed: (i) a remarkable lengthening
of the Mn-N bond distances (Table 2); (ii) a strong deviation
of the metal from the planar N4 core (Table 3); (iii) remarkably
larger displacements of the metal from the pyrrole rings; (iv) a
greater bending of the pyrrole rings around the N4 core. As can
be seen from the data quoted in Table 3, the out-of-plane
distance of the metal center from the A and B rings (i.e., those
Figure 3. SCHAKAL view of the dimer in complex 7. A prime denotes
a transformation of -x, -y, -z.
Figure 4. SCHAKAL view of the chain along the [001] axis in
complex 7.
involved in η2-interaction with the [Cu8Cl9]- anions) is remark-
ably shorter than for the C and D rings. A small but significant
asymmetry is also observed in the bending of pyrrole rings
around the N4 core. Despite these differences, which could be
ascribed to the asymmetry of the interactions involving the
Cu8Cl9- anion, the complex shows a cone section conformation
(like a calix[4]arene) similar to that present in complex 11 and
reported for [Et8N4(∆2)FeCl]2+[FeCl4]2-2b and for [{Et8N4(∆2)-
CoCl}‚‚‚{Cu4Cl5}]2- 2b
. This conformation seems to be mainly
determined by the presence of the two cyclopropane units. On
moving from complex 5 to complex 7, the N4 core undergoes
a significant deformation from a square of 2.737(4) Å on one
edge to a larger rectangle of 2.732(11) × 2.949(11) Å (mean
value) in dimension, indicating that the M out-of-plane displace-
ment could not be attributed to a change in size of the N4 core
but mainly to the presence of chlorine in the fifth coordination
site. The direction of the Mn-Cl bond is perpendicular to the
N4 plane, the dihedral angle it forms with the normal to that
plane being 1.9(2)°. The configurations at the asymmetric C4,
C6, C14, and C16 carbon atoms are S, R, S, R, respectively.
Since the space group is centrosymmetric, the enantiomeric
diastereoisomer is also present in the structure. The variety of
the CuI coordination modes should be taken into account to
explain the chaining of the molecules. The Cu1 and Cu2 copper
atoms show a tetrahedral coordination (wherein the η2-bonded
carbon atoms are considered to occupy one coordination site),
while a trigonal coordination is observed for Cu4. The Cu3 and
(23) Floriani, C.; et al. Unpublished results.
(24) Scheidt, W. R.; Lee, Y. J. Luangdibok, W.; Haller, K. J.; Anzai,
K.; Hatano, K. Inorg. Chem. 1983, 22, 1616.
(25) Kirner, J. F.; Scheidt, W. R. Inorg. Chem. 1975, 14, 2081.
(26) Figgis, B. N.; Mason, R.; Williams, G. A. Acta Crystallogr. 1980,
B36, 2963.

Cyclopropane-Containing Oxidized Porphyrinogens
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1703
Cu5 atoms show a diagonal coordination. The four copper atoms
in the crystallographically independent [Cu4Cl5]- fragment de-
fine an irregular trapezoid whose mean plane (maximum dis-
placement 0.477(2) Å for Cu4) is bent to form a dihedral angle
of 38.5(2)° with the N4 core (Figure 3). As a consequence of
the distortion from planarity of the copper atoms (observed in
the Fe and Co derivatives), Cl6 is capping only three copper
atoms (instead of four) and it is removed from the cavity of the
porphyrinogen, the Mn‚‚‚Cl6 distance being 3.878(4) Å vs
3.154(2) Å in complex 11, and 3.097(3) Å in [{Et8N4(∆)2Co}
‚‚‚{Cu4Cl5}]. No interaction shorter than 3.48 Å is observed
between Cl6 and the carbon atoms. Cl5 lies on a center of
symmetry bridging adjacent Cu4Cl4 aggregates [Cu1-Cl5 )
2.325(3) Å, Cu1-Cl5-Cu1′, 180°] from symmetry requirements
giving rise to the dimer. The Cl2, Cl3, and Cl4 chlorines bridge
adjacent Cu atoms of the Cu4 fragment. The centrosymmetric
-
CuCl2 anion (Cu5, Cl7) acts as a bridge between adjacent
Cu8Cl9 anions, linking the molecules in chains [Cu5-Cl7,
2.127(4); Cl7-Cu4, 2.331(4) Å].
Figure 5. SCHAKAL view of complex 11.
Table 5. Selected Bond Distances (Å) for Complex 11
-
With the aim to set free the Mn-biscyclopropane form, we
tried to remove the Cu(I) cluster from complex 7. While carbon
monoxide and phosphines do not show any reactivity, 2,2′-
dipyridyl reacted with it. The reaction led first to the decom-
plexation of the Cu(I) cluster, followed, however, by the
reoxidation of Cu(I) to Cu(II) with concomitant reduction of
the cyclopropane units and the formation of the Mn(III)-
porphyrinogen 8. Complex 8 has been characterized by an X-ray
analysis, which does not show any real difference with the anion
present in complex 5.23
Fe(1)-Cl(1)
Fe(1)-N(1)
Fe(1)-N(2)
Fe(1)-N(3)
Fe(1)-N(4)
Cu(1)-C(2)
Cu(1)-C(3)
Cu(2)-C(7)
Cu(2)-C(8)
Cu(3)-C(12)
Cu(3)-C(13)
Cu(4)-C(17)
Cu(4)-C(18)
N(1)-C(1)
2.271(2)
2.162(6)
2.183(7)
2.161(6)
2.173(7)
2.134(7)
2.143(8)
2.112(8)
2.108(8)
2.101(8)
2.108(8)
2.113(9)
2.112(7)
1.292(10)
1.448(11)
N(2)-C(6)
N(2)-C(9)
N(3)-C(11)
N(3)-C(14)
N(4)-C(16)
N(4)-C(19)
C(4)-C(5)
1.445(10)
1.307(8)
1.320(8)
1.447(12)
1.425(10)
1.319(9)
1.536(14)
1.621(10)
1.530(12)
1.495(10)
1.469(10)
1.508(11)
1.638(10)
1.487(10)
C(4)-C(6)
C(5)-C(6)
C(6)-C(7)
C(13)-C(14)
C(14)-C(15)
C(14)-C(16)
C(15)-C(16)
(B) Oxidation Pathway of Iron-Porphyrinogen. The
present report gives an exhaustive account of the oxidation of
iron, which closely parallels the behavior of Mn and shows
significant differences compared with Co, Ni, and Cu. The
oxidation pathway of the iron(II)-porphyrinogen complex 9 is
shown in Scheme 2. The synthesis of 9 must be carried out
with a strictly controlled 1 equiv of [FeCl2‚thf1.5] since an excess
of it leads to the oxidation of 9 to 10, by a mechanism that is
not clear. We suggest, in fact, the unlikely formation of iron(I)
reduced species. The synthesis of 10 can be performed reacting
1 with 2 equiv of FeCl2‚thf1.5 in a single step. The oxidation of
10 with CuCl2 led to the fully oxidized form of porphyrinogen
in complex 11, containing two cyclopropane units within the
porphyrinogen skeleton.23 The explanation of the intriguing
stoichiometry is quite similar to that discussed in detail in the
case of Mn (see above). The oxidized form of porphyrinogen
complexed to the [Cu4Cl5]- cluster is shown in the picture of
11. When the oxidation by CuCl2 was carried out on 10 prepared
in situ, the formation of the copper-free biscyclopropane
derivative [Et8N4(∆)2FeCl]2+[FeCl4]2- occurred instead.2b The
oxidation performed in the presence of the reduced form of
FeCl2 has as a major consequence the formation of the copper
cluster-free iron-biscyclopropane-porphyrinogen with iron in
the oxidation state III rather than II, as it is in complex 11. In
all the oxidations, including those where Cp2FeBPh4 was used,
we were unable to trap the supposed intermediate monocyclo-
propane derivative. We should comment that, contrary to what
was observed for cobalt, in the case of manganese and iron the
monocyclopropane is not necessarily the precursor to the
biscyclopropane form. The structure assignment for complex
10 is essentially based on the correct analytical and spectroscopic
results and on the close relationship with those of the structurally
characterized complexes 5 and [(Et8N4Fe){Li(MeCN)4}].27
N(1)-C(4)
The structure of complex 11 is shown in Figure 5, and
selected bond distances and angles are listed in Table 5. It
consists of discrete [Et8N4(∆)2FeCl]+ cations, Cu4Cl5- anions,
and THF molecules as crystallization solvent in the molar ratio
of 1:1:3. Each copper(I) is η2-bonded to the terminal double
bonds of the pyrrole rings. The resulting geometry of the
molecule shows a cavity having a cone section conformation
with two double bonds localized within each pyrrole ring.
Complex 11 is isostructural with the corresponding cobalt(III)
derivative.2b The Cu4Cl5- anion has the framework previously
observed with the planar Cu4 core symmetrically interacting with
the four pyrrole rings. The Fe-Cl bond distance (Table 5) is
slightly yet significantly longer than that found in [Et8N4(∆)2-
FeCl]2+[FeCl4]2-, while the Fe-N bond distances are in a very
good agreement with those found in the same complex. The
direction of the Fe-Cl bond is perpendicular to the N4 plane,
the dihedral angle it forms with the normal to that plane being
0.8(2)°.
The most relevant conformational parameters are compared
in Table 3 with those of complex 7, indicating no remarkable
differences between them. In these two compounds a strong
displacement of the metal atom from the N4 core is observed
along with a strong deformation of the bond angles around the
metal, the N-Fe-N angles in the five-membered chelating rings
being narrower than those in the six-membered chelation rings.
The configurations of the C4, C6, C14, and C16 asymmetric
carbon atoms are the same as those observed for complex 7.
The geometry of complex 11 is very similar to that of the
[Et8N4(∆)2FeCl]2+ cation in [Et8N4(∆)2FeCl]2+[FeCl4]2-,2b which
rules out that the cone section conformation of the pyrrole rings
could be determined by the copper(I)-η2-pyrrole interaction.
(27) Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Chem. Soc.,
Chem. Commun. 1991, 220.

1704 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Crescenzi et al.
that found in the copper-free cation [Et8N4(∆)2FeCl]2+. The
configurations of the C(4), C(6), C(14), and C(16) asymmetric
carbon atoms are S, R, S, R, respectively. Since the space group
is centrosymmetric, the enantiomeric diastereoisomer is also
present in the structure.28
(C) Oxidation Pathway of Alkali-Porphyrinogen: The
Synthesis of the Metal-Free Biscyclopropane-Porphyrino-
gens. The results outlined in the previous sections have
emphasized the role of transition metal ions in driving the
oxidation of the porphyrinogen skeleton to the mono- and
biscyclopropane derivatives. The alternative route to use transi-
tion metal-free porphyrinogen would perhaps solve the problem
of having the biscyclopropane-porphyrinogen available for
further complexation with any kind of transition metal. In this
perspective, we decided to look to the oxidation of 1 and 2
(see Scheme 4). They undergo a quite clean two-electron
oxidation by Cp2FeBPh4 to the previously reported monocy-
clopropane derivative 15,2c,4 although the present synthesis is
much easier and more convenient. Compound 15 undergoes a
further oxidation to 16 by two more equivalents of [Cp2FeBPh4].
The best synthetic access, however, to the biscyclopropane form
is the oxidation of 1 and 2 with 4 equiv of Cp2FeBPh4, leading
to 16 and 17, the former one having previously been structurally
characterized.4 The previous synthetic procedure, however, was
too complex to become synthetically useful. We should also
admit that between the two alkali derivatives, 17 is by far the
more accessible by a very simple experimental procedure (see
Experimental Section). The sodium cation can be removed from
17 using 18-crown-6, thus obtaining the metal-free biscyclo-
propane-porphyrinogen, 18. Although the reaction is feasible,
it produces a rather low yield of the desired product. This is
mainly due to some instability of the metal-free form of the
biscyclopropane-porphyrinogen 18, although we did not in-
vestigate so far its possible rearrangement pathway. It should
be emphasized that 15 can be synthesized from equimolar
amounts of 1 and 16 (see Experimental Section). This is a quite
remarkable reaction, showing how the cyclopropane units can
be engaged in intermolecular electron transfers.2,5 Very likely,
this process is assisted by the lithium cation, which can bridge
different porphyrinogen units, taking advantage of its coordina-
tion mode to the pyrrolyl anion.5,6,22 Such a redox behavior
would be a key point for understanding the thermal rearrange-
ment of 15. When 15 was heated to 80 °C in n-hexane, it
rearranges to a mixture of 19, 18, and Et4N4H4 in a ratio of
4:1:1, as we monitored via NMR spectroscopy. The proposed
rearrangement mechanism is depicted in Scheme 5, where the
porphyrinogens are drawn as anionic forms rather than associ-
ated to lithium cations. Such a rearrangement would follow two
pathways, a and b. The disproportionation of the monocyclo-
propane form 15 into the biscyclopropane 18 and 1 occurs
according to pathway a. Complex 19 is derived (pathway b)
from the conversion of a cyclopropane into a cyclopentane unit
across two pyrrolyl anion units. The latter forms from the
transposition of a C-C bond between the R-carbon of two
adjacent pyrroles into a C-C bond between two â-carbons via
the rearrangement of two R-radicals derived from the C-C bond
cleavage in the cyclopropane unit (see A in Scheme 5), into
â-radicals (see B in Scheme 5), which then couple leading to
C. This process is followed by the monodeprotonation of C
(Scheme 5) by the porphyrinogen tetraanion, 1, derived from
the disproportionation reaction (pathway a). Knowledge of the
redox and the acid-base chemistry of porphyrinogen will enable
one to manage the C-C bond formation. The 15 f 19
Figure 6. SCHAKAL view of the cation in complex 14.
Table 6. Selected Bond Distances (Å) for Complex 14
Fe(1)-Cl(1)
Fe(1)-N(1)
Fe(1)-N(2)
Fe(1)-N(3)
Fe(1)-N(4)
N(1)-C(1)
N(1)-C(4)
N(2)-C(6)
N(2)-C(9)
N(3)-C(11)
2.249(1)
2.171(4)
2.183(4)
2.154(3)
2.187(4)
1.302(6)
1.443(5)
1.422(6)
1.311(5)
1.313(5)
N(3)-C(14)
N(4)-C(16)
N(4)-C(19)
C(4)-C(5)
1.425(5)
1.427(5)
1.297(6)
1.525(6)
1.591(6)
1.531(5)
1.541(5)
1.587(7)
1.532(7)
C(4)-C(6)
C(5)-C(6)
C(14)-C(15)
C(14)-C(16)
C(15)-C(16)
The only significant difference concerns the Câ-Câ distances
within the pyrrole rings, averaging 1.377(7) Å in complex 11
and 1.335(10) Å in the [Et8N4(∆)2FeCl]2+ cation. This small
yet significant lengthening could be related to the interactions
involving Cu4Cl5-, in agreement with the trend of the bond
distances observed in complex 7. The structural features of the
-
Cu4Cl5 anion are very similar to those found in the cobalt
derivative.2b
The formation of the copper(I) cluster can be avoided, as
mentioned earlier, carrying out the oxidation with CuCl2 with
the iron(III) porphyrinogen prepared in situ.2b This synthetic
aspect has been confirmed in the oxidation of the meso-
octacyclohexylporphyrinogen-iron. The synthetic sequence is
shown in Scheme 3. The biscyclopropane form 14 has been
isolated free of any copper(I) clusters, while the counteranion
is in the present case [Cu2Cl4]2- rather than [FeCl4]2- 2b
The
cyclohexyl substituent in the meso-carbon does not affect the
cyclopropane unit formation.
.
The structure of 14 is shown in Figure 6. It consists of discrete
[(C6H10)4N4(∆)2FeCl]2+ cations, [Cu2Cl4]2- anions, and aceto-
nitrile solvent molecules of crystallization in the molar ratio of
1:0.5:0.5. The [Cu2Cl4]2- anion possesses a crystallographically
imposed Ci symmetry. The presence of four cyclohexyl groups
instead of eight ethyl groups at the meso-carbon atoms does
not affect the overall geometry of the cation, which as a result
is very similar to that observed in complexes 7 and 11 (Table
6). The N4 core is planar within experimental error, the metal
protruding by 0.869(1) Å toward the chlorine atom. The Fe-
Cl vector is perpendicular to the N4 core, the dihedral angle it
forms with the normal to the plane being 0.3(1)°. The Fe-Cl-
(1) bond distance [2.249(1) Å] as well as the Fe-N bond
distances [mean value 2.171(8) Å] are in good agreement with
those observed in 11. The bonding sequence shown in Scheme
3 is supported by the structural data (see Table 6). In particular,
the Câ-Câ average distance [1.337(7) Å] is in agreement with
(28) Structural information on the counteranion [Cu2Cl4]2- is available
as Supporting Information.

Cyclopropane-Containing Oxidized Porphyrinogens
J. Am. Chem. Soc., Vol. 121, No. 8, 1999 1705
Table 7. Selected Bond Distances (Å) for Complex 19a
Li(1)-N(3)
Li(1)-N(4)
Li(1)-C(1)
Li(1)-C(2)
Li(1)-C(3)B
Li(1)-C(7)A
Li(1)-C(8)
Li(1)-C(9)
Li(2)-N(2)
Li(2)-N(3)
Li(2)-Cp(C)
Li(3)-O(2)
Li(3)-N(1)
Li(3)-N(4)
Li(3)-Cp(D)
1.958(5)
1.954(5)
2.712(5)
2.771(5)
2.713(6)
2.804(7)
2.861(6)
2.786(6)
2.099(4)
2.332(4)
2.077(4)
1.946(5)
2.079(4)
2.296(5)
2.092(4)
N(1)-C(1)
N(1)-C(4)
N(2)-C(6)
N(2)-C(9)
N(3)-C(11)
N(3)-C(14)
N(4)-C(16)
N(4)-C(19)
C(3)A-C(7)A
C(3)B-C(7)B
C(4)-C(5)
1.412(2)
1.329(4)
1.334(3)
1.417(3)
1.376(3)
1.383(3)
1.376(3)
1.379(3)
1.531(8)
1.534(8)
1.521(3)
1.533(4)
1.442(5)
1.521(6)
C(5)-C(6)
C(6)-C(7)A
C(6)-C(7)B
a Cp(C) and Cp(D) refer to the centroids of the C and D pyrrole
rings, respectively.
Figure 7. SCHAKAL view of complex 19. Disorder affecting the C(3)
and C(7) carbon atoms has been omitted for clarity.
[O(1) and O(2) for Li(2) and Li(3), respectively] and η5-bonding
one pyrrole ring, as indicated by values of the Li-N and Li-C
bond distances quoted in Table 7. The trend of bond distances
and angles within the C and D pyrrole rings is consistent with
a partial double bond localization on the CR-Câ [mean value
1.389(2) Å] bonds and with the single bond character of the
Câ-Câ bonds [mean value 1.415(2) Å]. The configurations of
the C(3)A and C(7)B asymmetric carbon atoms are R and S,
respectively. Since the space group is centrosymmetric, the
enantiomeric diastereoisomer is also present in the structure.
(D) One- vs Two-Electron Oxidation Pathway: Intra- and
Intermolecular C-C Bond Formation. The results so far
reported, related to the oxidation of metal-meso-octaalkylpor-
phyrinogen complexes, showed that the formation of mono- and
biscyclopropane derivatives are overall two- and four-electron
oxidation processes.2-4 When the appropriate transition metal
ions are used, namely, Cu and Co, it is possible to single out
the two monoelectronic steps leading to the formation of a
cyclopropane moiety.2a The first one occurs with the oxidation
of the metal(II) to metal(III), while in the second step the
formation of the cyclopropane reduces the metal back to metal-
(II).2a Our concern was the one-electron oxidation of a porphy-
rinogen complex containing a metal such as Ni(II), which does
not usually undergo a change of oxidation state. This was
attempted in the past using p-benzoquinone, CuCl2, or other
oxidants but did not lead to successful results. The use of Cp2-
FeBPh4, however, enabled us to identify the monoelectronic
oxidation of Ni(II)-meso-octaethylporphyrinogen, 20 (see
Scheme 6). The overall reaction is an oxidative dimerization
of 20 occurring via the C-C bond formation between the pyrrole
â-carbons of two different units, thus ending up with 22. The
proposed structure of 22 is supported by analytical and
spectroscopic data, including an X-ray analysis, which is not
reported due to the rather low quality, but which undoubtedly
shows the proposed atom connectivity. When the oxidation of
20 was carried out with 2 equiv of Cp2FeBPh4, the expected
monocyclopropane derivative 212a formed in a good yield.
Complex 22 should not be considered, however, an intermediate
to 21, which does not form from 22, reacted with two more
equivalents of Cp2FeBPh4. The results mentioned here and in
the previous section suggest a plausible mechanism leading
either to the intramolecular or intermolecular C-C bond
formation. We should admit that the primary monoelectronic
oxidation product should be the R-radical, as expected from the
reactivity of the pyrrole,29 followed by a rather fast oxidation
transformation cannot be reversed upon acidification with PyHCl
1
of 19. The H NMR spectrum of 19 is quite diagnostic of its
structure (see Experimental Section) and shows fast proton
exchange between the two equivalent â-protons. A crystal-
lographic account of the structure of 19 is reported here.
In the crystal structure both the molecules corresponding to
the loss of the hydrogen atom at the C(3) or C(7) carbon atoms
are present in the same ratio, resulting in the C(3) and C(7)
atoms being distributed over two positions (hereafter referred
as A and B) with site occupation factors of 0.5. The perspective
view of complex 19 given in Figure 7 coincides with the C(3)
[sp3] and C(7) [sp2] atoms occupying their A positions. The C-C
bond formation between â-carbon atoms gives rise to an
unprecedented conformation of the porphyrinogen macrocycle,
where the C and D pyrrole rings are nearly parallel [dihedral
angle 9.7(1)°] while the A and B rings are strongly tilted upward
to be nearly perpendicular [dihedral angle 92.7(1)° and 93.2-
(1)° for the pyrrole rings containing the C(3) and C(7) carbon
atoms in the A and B positions, respectively]. In comparison
with the previous complexes, the conformation of the macro-
cycle also differs remarkably in the orientation of the A and B
pyrrole rings with respect to the N4 core [dihedral angles N4∧A,
97.6(1)°; N4∧B,100.7(1)°] and in the out-of-plane distance of
the central metal cation [Li(1)] from these rings (Table 3).
Despite this conformation, the N4 core maintains its planarity,
the Li(1) cation being displaced by 0.844(4) Å (Table 3). The
lithium cations exhibit different coordination modes to the
trianionic ligand. The Li(1) cation is σ-coordinated to the N(3)
and N(4) nitrogen atoms and η-coordinated to the A and B
pyrrole rings, the entity of the interaction depending on the
presence of the C(3) and C(7) carbon atoms in the A or B
position. When the A position is considered, the cation could
be described as η2-coordinated to the A pyrrole ring [Li(1)-
C(1), 2.712(5) Å; Li(1)-C(2), 2.771(5) Å; the distances
involving the N(1), C(3)A, C(4) atoms are longer than 2.90 Å]
and η3-coordinated to the B pyrrole ring [Li(1)-C(7)A, 2.804-
(7) Å; Li(1)-C(8), 2.861(6) Å; Li(1)-C(9), 2.786(6) Å; the
distances involving the N(2) and C(6) atoms are longer than
2.96 Å]. The opposite situation is observed with the C(3) and
C(7) carbons in the B position, so a η3-coordination of Li(1) to
the A pyrrole ring [Li(1)-C(1) and Li(1)-C(2) as before; Li-
(1)-C(3)B, 2.713(6) Å] and a η2-coordination to the B pyrrole
ring [Li(1)-C(8) and Li(1)-C(9) as before] could be proposed.
The Li(2) and Li(3) cations achieve a trigonal coordination by
σ-bonding one nitrogen atom [N(2) and N(1) for Li(2) and Li-
(3), respectively] and one oxygen atom from a THF molecule
(29) Gilchrist, T. L. Heterocyclic Chemistry, 2nd ed.; Longman: Essex,
U.K., 1992. Eicher, T.; Hauptmann, S. The Chemistry of Heterocycles;
Thieme: Stuttgart, Germany, 1995.

1706 J. Am. Chem. Soc., Vol. 121, No. 8, 1999
Crescenzi et al.
to the monocyclopropane derivative 21. Therefore, the formation
of 22 would not occur via the rearrangement of the R- to the
â-radical at the pyrrole ring. The former one would be
intercepted by the oxidant before rearranging to the â, which
would couple to 22. In addition, the high yield of 21 from the
oxidation of 20 with 2 equiv of Cp2FeBPh4 rules out two, intra-
and intermolecular, parallel pathways. The answer to the
question how complex 22 originates comes from its formation
from a reaction carried out mixing an equimolar amount of 20
and 21 in THF at room temperature. This reaction is particularly
relevant for a number of reasons. First, it shows the ease of
intermolecular electron transfer processes that we believe to be
assisted by alkali cations, mainly lithium ions, which are able
to bridge porphyrinogens in a different oxidation state, via rather
strong ion-pyrrole interactions.5,8,21,22 Therefore, the formation
of the two-electron-oxidized form of the porphyrinogen contain-
ing a cyclopropane seems to precede any other oxidized forms.
The reaction between 20 and 21 should produce the R-radicals
[D] (see Scheme 6), which rearrange to the â-radicals [E], which
ends coupling to form 22. The coupling reaction followed by
the hydrogen shift to the C-C adjacent positions is quite general
in the acid-base chemistry of porphyrinogen. In the preceding
section we found that the thermally induced rearrangement of
15 to 19 requires the C-C bond cleavage of the cyclopropane
in 15, rearrangement of R- to â-radicals (see Scheme 5), which
couple intramolecularly producing 19. The reactions in Scheme
6 show an important synthetic consequence of the one-electron
oxidation of the porphyrinogen tetraanion, namely, the oxidative
coupling leading to C-C bond linked dimers. The results
reported in this section and in the preceding one serve to clarify
the role of the transition metal and the oxidizing agent in driving
the oxidation of the porphyrinogen tetraanion. The choice of
the metal-oxidizing agent couple is particularly crucial. p-
Benzoquinone and CuCl2 cannot be employed in the case of
the lithium derivative. Under the conditions of using the same
innocent oxidant, i.e. Cp2FeBPh4, mono- and biscyclopropane
form regardless of the presence of a transition metal or an alkali
cation. In the latter case, we were, however, unable to detect
compounds derived from an overall one-electron oxidation
process. In the case of transition metals we have to distinguish
between metals that usually do not change oxidation state in
the coordination environment determined by the porphyrinogen
skeleton, i.e., Ni(II), and those that have different easily
accessible oxidation states. In the latter case, the stepwise
formation of cyclopropane is assisted by the one-electron redox
chemistry at the metal, and we do not really achieve nor see
the overall one-electron oxidation of the porphyrinogen ligand.
In the case of nickel, the overall one-electron oxidation, through
the mechanism outlined above, leads to the oxidative C-C
coupling between two metallaporphyrinogen moieties. This is
a quite important pathway, which, coupled with the deproto-
nation reaction,30 will allow the formation of dimeric, oligo-
meric, and polymeric metallaporphyrinogen complexes.
Precedents in intermolecular oxidative coupling between two
macrocycles such as tmtaa [tmtaa ) dibenzotetramethyltetraaza-
[14]annulene] are known, although the dimerization always
occurs via the meso-carbons.31 Analogous coupling through
meso-carbons was proposed earlier for the dimerization of
metallaporphyrin π-cation radicals.32 The dimerization via a
direct link between pyrrole is characteristic of fully meso-
alkylated forms, as in the case of meso-octaalkylporphyrinogens.
Conclusions
The oxidations carried out on metalla-meso-octaalkylporphy-
rinogens follow different pathways as a function of the metal
and the metal-oxidant couples. The use of Cp2FeBPh4 allowed
the oxidation to be carried out on both transition metal and
alkali-metal derivatives and to distinguish between one- and two-
electron processes. Regardless of the metal and the porphy-
rinogen/oxidant ratio, all of the reactions ended in intra- or
intermolecular C-C bond formation. The precursor for the
different pathways is the cyclopropane functionality, which can,
eventually, rearrange. Such rearrangements require intermo-
lecular electron transfers between metallaporphyrinogen units
which are assisted by alkali cations. The consequence of such
rearrangements are (i) intramolecular C-C bonds different from
cyclopropane and (ii) the formation of C-C-bonded metal-
laporphyrinogen dimers. The latter result opens the methodology
for the synthesis of dimeric, oligomeric, and, maybe, polymeric
forms of porphyrinogen. Studying the oxidation of Mn(II)-
Fe(II)-porphyrinogen, we succeeded in isolating Fe(II)-,
Fe(III)-, and Mn(II)-biscyclopropane-porphyrinogen com-
plexes. The oxidation of alkali cation porphyrinogen complexes
was found to be the best synthetic access to biscyclopropane-
porphyrinogens available for the complexation of any metal and,
for the first time, to the metal-free biscyclopropane-porphy-
rinogens. We should emphasize the potential of the reversible
bond formation and cleavage within the porphyrinogen skeleton,
which functions as a sort of molecular battery for storing and
releasing electrons.
Acknowledgment. We thank the “Fonds National Suisse de
la Recherche Scientifique” (Bern, Switzerland, Grant No. 20-
53336.98) and Ciba Specialty Chemicals (Basel, Switzerland)
for financial support.
Supporting Information Available: ORTEP drawings,
tables giving crystal data and details of the structure determi-
nation, bond lengths, bond angles, anisotropic thermal param-
eters, and hydrogen atom locations for 5, 7, 11, 14, and 19.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JA982178F
(31) (a) Mountford, P. Chem. Soc. ReV. 1998, 27, 105. (b) Dabrowiak,
J. C.; Fisher, D. P.; McElroy, F. C.; Macero, D. J. Inorg. Chem. 1979, 18,
2304, and references therein. (c) Bailey, C. L.; Bereman, R. D.; Rillema,
D. P. Inorg. Chem. 1986, 25, 3149, and references therein.
(32) Balch, A. L.; Noll, B. C.; Reid, S. M.; Zovinka, E. P. J. Am. Chem.
Soc. 1993, 115, 2531.
(30) Bonomo, L.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J.
Am. Chem. Soc. 1998, 120, 12972.