Biphenyl-Strapped Diphenylporphyrins: Synthesis and Spectroscopic Characterization of a Series of Porphyrins with Ether-Linked Straps. Preliminary CO Binding Properties of Their Iron(II) Derivatives

Article abstract of DOI:10.1021/ic970705a

The synthesis of a series of meso-5,15-diphenylporphyrins strapped by 2,2′-disubstituted biphenyl units (6H₂, 7H₂, 8H₂) is described. The biphenyl straps used are linked via their 3.3′-positions by CH₂O groups to orthopositions of the phenyl rings of the 5,15-diphenylporphyrins. The straps of these porphyrins have their 2.2′-positions occupied by H (6H₂), Me (7H₂), and OMe (8H₂). The electronic spectral properties of these strapped porphyrins are given, and their conformational properties, which have been studied by ¹H NMR spectroscopy. are described. The synthesis and spectroscopic characterization of several iron(II) and iront (III) derivatives of these poiphyrins with different axial bases are also presented. The X-ray structure of the chloroiron(III) derivative of the diphenylporphyrin dianion 6 has been determined. Violet crystals of composition 6-FeCl·CH₃OH·CH₂Cl₂ have been obtained by slow evaporation of CH₂Cl₂/MeOH solutions of 6 - FeCl. These crystals belong to the monoclinic system, space group P2₁/c, with a = 10.164(3) A?, b = 28.977(9) A?, c = 14.283(4) A?, β= 106.22(2)°, and Z = 4. The iron atom of 6 - FeCl is five-coordinate, high-spin. The axial chloride ligand lies opposite to the strap. The average Fe - N_p bond distance is 2.046(6) A?, and the Fe - Cl bond length equals 2.234(2) A?. The porphyrin is slightly domed and ruffled with the iron atom lying at 0.45(1) A? out of the 4N_P mean-plane and 0.49(1) A? out of the 24-atom core mean-plane of the porphyrin ring. Ferrous carbonyl adducts of these porphyrins have been obtained in various solvents in the presence or absence of nitrogenous bases. Their structures have been studied by ¹H NMR and IR spectroscopy. Two CO stretching vibrations differing by 20 cm^-1 occur in the IR spectra of 6 - Fe(CO)(B) (B = py, ImH, NMelin). The possible origin of these two v_CO bands is discussed.

Full text of DOI:10.1021/ic970705a

1142
Inorg. Chem. 1998, 37, 1142-1149
Ar ticles
Biphenyl-Strapped Diphenylporphyrins: Synthesis and Spectroscopic Characterization of a
Series of Porphyrins with Ether-Linked Straps. Preliminary CO Binding Properties of
Their Iron(II) Derivatives
Laurent Jaquinod,† Lionel Pre´vot, Jean Fischer, and Raymond Weiss*
Laboratoire de Cristallochimie et de Chimie Structurale (UMR 7513), Institut Le Bel,
Universite´ Louis Pasteur, 4 Rue B. Pascal, 67070 Strasbourg, France
ReceiVed June 6, 1997
The synthesis of a series of meso-5,15-diphenylporphyrins strapped by 2,2′-disubstituted biphenyl units (6H2,
7H2, 8H2) is described. The biphenyl straps used are linked via their 3,3′-positions by CH2O groups to ortho-
positions of the phenyl rings of the 5,15-diphenylporphyrins. The straps of these porphyrins have their 2,2′-
positions occupied by H (6H2), Me (7H2), and OMe (8H2). The electronic spectral properties of these strapped
1
porphyrins are given, and their conformational properties, which have been studied by H NMR spectroscopy,
are described. The synthesis and spectroscopic characterization of several iron(II) and iron(III) derivatives of
these porphyrins with different axial bases are also presented. The X-ray structure of the chloroiron(III) derivative
of the diphenylporphyrin dianion 6 has been determined. Violet crystals of composition 6-FeCl‚CH3OH‚CH2-
Cl2 have been obtained by slow evaporation of CH2Cl2/MeOH solutions of 6-FeCl. These crystals belong to the
monoclinic system, space group P21/c, with a ) 10.164(3) Å, b ) 28.977(9) Å, c ) 14.283(4) Å, â ) 106.22(2)°,
and Z ) 4. The iron atom of 6-FeCl is five-coordinate, high-spin. The axial chloride ligand lies opposite to the
strap. The average Fe-Np bond distance is 2.046(6) Å, and the Fe-Cl bond length equals 2.234(2) Å. The
porphyrin is slightly domed and ruffled with the iron atom lying at 0.45(1) Å out of the 4Np mean-plane and
0.49(1) Å out of the 24-atom core mean-plane of the porphyrin ring. Ferrous carbonyl adducts of these porphyrins
have been obtained in various solvents in the presence or absence of nitrogenous bases. Their structures have
been studied by 1H NMR and IR spectroscopy. Two CO stretching vibrations differing by 20 cm-1 occur in the
IR spectra of 6-Fe(CO)(B) (B ) py, ImH, NMeIm). The possible origin of these two νCO bands is discussed.
Introduction
mainly on distal steric constraints.5 As a result, most of the
model porphyrins which were synthesized had alkyl chains
containing bulky groups as straps with the aim of sterically
impeding linear upright binding of CO.6 More recently,
emphasis has shifted on the stabilization of O2 binding by distal
polar interactions and destabilization of CO binding by por-
phyrin buckling.7-10
The binding of small molecules to iron(II) porphyrins
modeling the active sites of oxygen-carrying hemeproteins has
aroused considerable interest during the last 20 years. Numerous
“capped” and “strapped” porphyrins have been synthesized in
an attempt to discriminate between CO and O2 binding.1-4 For
a long period, it was assumed that CO/O2 discrimination is based
(5) (a) Nagai, K.; Luisi, B.; Shih, D.; Miyasaki, G.; Poyart, C.; De Young,
A.; Kwiatowski, L.; Noble, R. W.; Lin, S.-H.; Yu, N.-T. Nature 1987,
329, 858. (b) Olson, J. S.; Mathews, A. J.; Rohlfs, R. J.; Springer, B.
A.; Egeberg, K. D.; Sligar, S. G.; Tame, J.; Renaud, J.-P.; Nagai, K.
Nature 1988, 336, 265.
(6) (a) Peng, S.; Ibers, J. A. J. Am. Chem. Soc. 1976, 98, 8032. (b)
Collman, J. P.; Brauman, J. I.; Halbert, T. R.; Suslick, K. S. Proc.
Natl. Acad. Sci. U.S.A. 1976, 73, 3333. (c) Collman, J. P.; Brauman,
J. I.; Collins, T. J.; Iverson, B.; Sessler, J. L. J. Am. Chem. Soc. 1981,
103, 2450. (d) Collman, J. P.; Brauman, J. I.; Collins, T. J.; Iverson,
B. L.; Lang, G.; Pettman, R. B.; Sessler, J. L.; Walters, M. A. J. Am.
Chem. Soc. 1983, 105, 3038. (e) Collman, J. P.; Brauman, J. I.; Iverson,
B. L.; Sessler, J. L.; Morris, R. M.; Gibson, Q. H. J. Am. Chem. Soc.
1983, 105, 3052
* Corresponding author: (Fax)
weiss@chimie.u-strasbg.fr.
+ 33 (0)3 88416353; (E-mail)
† Present address: Department of Chemistry, University of California,
Davis, CA 95616-5295.
(1) Baldwin, J. E.; Perlmutter, P. In Topics in Current Chemistry;
Springer-Verlag: Berlin, 1984; Vol. 121, p 181.
(2) Morgan, B.; Dolphin, D. In Structure and Bonding; Springer-Verlag:
Berlin, 1987; Vol. 64, p 115.
(3) (a) Almog, J.; Baldwin, J. E.; Crossley, M. J.; Debernardis, J. F.; Dyer,
R. L.; Huff, J. R.; Peters, M. K. Tetrahedron 1981, 37, 3589. (b)
Shimizu, M.; Basolo, F.; Valleyo, M. N.; Baldwin, J. E. Inorg. Chim.
Acta 1984, 91, 247 (c) Shimidzu, M.; Basolo, F.; Valleyo, M. N.;
Baldwin, J. E. Inorg. Chim. Acta 1984, 91, 251.
(7) (a) Phillips, S. E. V.; Schoenborn, B. P. Nature 1981, 292, 81. (b)
Shaanan, B. Nature 1982, 296, 683.
(4) (a) Garcia, B.; Lee, C. H.; Blasco, A.; Bruice, T. C. J. Am. Chem.
Soc. 1991, 113, 8118. (b) Tang, H.; Wijesekra, T. P.; Dolphin, D.
Can. J. Chem. 1992, 70, 1366. (c) Mishida, T.; Kyuhara, M.;
Nishiyama, M.; Fitzgerald, J. P.; Sayo, H. Chem. Pharm. Bull. 1992,
40, 3157.
(8) (a) Traylor, T. G.; Koga, N.; Dearduff, L. A. J. Am. Chem. Soc. 1985,
107, 6504. (b) Traylor, T. G.; Tsuchiya, S.; Campbell, D.; Mitchell,
M.; Stynes, D.; Koga, N. J. Am. Chem. Soc. 1985, 107, 604.
(9) (a) Li, X.; Spiro, T. G. J. Am. Chem. Soc. 1988, 110, 6024. (b) Baltzer,
L.; Landergreen, M. J. Am. Chem. Soc. 1990, 112, 2804.
S0020-1669(97)00705-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/05/1998

Biphenyl-Strapped Diphenylporphyrins
Inorganic Chemistry, Vol. 37, No. 6, 1998 1143
prepared as described by Manka et al. by condensation of benzaldehyde
with 2,2′-dipyrrylmethane.11,12
5,15-Bis(2-hydroxyphenyl)porphyrin (2H2). To a mixture of 500
mg of 5,15-bis(2-methoxyphenyl)porphyrin12 and 20 mL of dichlo-
romethane was added 6 mL of BBr3 (1 M in CH2Cl2) at -78 °C. The
mixture was allowed to warm at room temperature and stirred under
argon overnight. A solution of MeOH/H2O (1:1 v/v, 10 mL) was slowly
added to the green solution. The mixture was then extracted with 5%
ether/dichloromethane (200 mL), washed with aqueous saturated
NaHCO3 and water, and dried over MgSO4. The solvent was removed,
and the residue was recrystallized from a dichloromethane/hexane
mixture to yield 380 mg of the title compound (80%). 1H NMR
(CDCl3): δ -3.19 (s, 2H, NH), 5.04 (s, 2H, OH), 7.40 (m, 4H, Ar H),
7.77 (t, 2H, J ) 7.7, Ar H), 8.05 (d, 2H, J ) 7.7, Ar H), 9.1 (d, 4H,
J ) 4.6, â-H), 9.43 (d, 4H, J ) 4.6, â-H), 10.35 (s, 2H). Anal. Calcd
(found) for C34H22N4O2: C, 77.72 (75.6); H, 4.48 (4.4); N, 11.3 (11.1).
UV/vis (ꢀ, 10-4 L mol-1 cm-1) (CH2Cl2): 406 (29.6), 501 (1.95), 534
(0.82), 574 (0.86), 627 (0.48) nm.
3,3′-Bis(bromomethyl)biphenyl (3). This compound was prepared
by bromination with N-bromosuccinimide of commercial 3,3′-dimeth-
ylbiphenyl; it had a melting point of 112 °C (lit.13 mp 115-117 °C).
1H NMR (CDCl3): δ 4.56 (s, 4H, CH2Br), 7.47 (m, 6H), 7.61 (s, 2H).
2,2′-Dimethyl-3,3′-bis(bromomethyl)biphenyl (4). This compound
was obtained by a multistep synthesis via 2,2′-dimethyl-3,3′-diiodobi-
phenyl (4a), 2,2′-dimethyl-3,3′-diformylbiphenyl (4b), and 2,2′-di-
methyl-3,3′-bis(hydroxymethyl)biphenyl (4c).
Figure 1. Schematic representations of the 2,2′-disubstituted biphenyl
4a. To a suspension of 1.5 g (7.1 mmol) of 2,2′-dimethyl-3,3′-
diaminobiphenyl,14 in concentrated HCl (15 mL) and water (10 mL),
cooled to -5 °C, was added a solution of sodium nitrite (1.12 g, 2.2
equiv) in water (6 mL). The resulting solution was stirred for 30 min
at 0/5 °C. At this time a saturated aqueous solution of potassium iodide
(7.8 g, 47 mmol) was added and the mixture was stirred overnight at
50 °C. The solution was poured into dichloromethane. The resulting
organic phase was washed with water, saturated aqueous NaHCO3,
saturated aqueous NaHSO3, and water, and the solvent was removed
under vacuum. The residue was purified by chromatography on a SiO2
column, eluated with CH2Cl2 to give 1.0 g of 4a (33%). 1H NMR
(CDCl3): δ 2.16 (s, 6H, Me), 6.90 (t, 2H, J ) 7.7), 7.05 (d, 2H, J )
7.5), 7.85 (d, 2H, J ) 7.7).
4b. To a stirred solution of 4a (0.8 g, 1.8 mmol) in dry ether (25
mL) at -15 °C under argon was added n-butyllithium (2.2 equiv, 2.5
mL, 1.6 M in hexane). After 1 h, 1 mL of anhydrous DMF was added
and the solution allowed to warm to room temperature. After 3 h, 20
mL of aqueous hydrochloric acid (2 M) was added and the mixture
stirred for an additional 30 min. The organic layer was separated and
washed with saturated aqueous NaHCO3 and water, and the solvent
was removed under vacuum. The residue was purified by chromatog-
raphy on a SiO2 column, eluated with CH2Cl2. Yield: 250 mg, 57%.
Mp: 149 °C. 1H NMR (CDCl3): δ 2.35 (s, 6H, Me), 7.40 (m, 4H),
7.87 (dd, 2H, J ) 7.6), 10.37 (s, 2H, CHO).
4c. A solution containing 4b (250 mg, 1.11 mmol), NaBH4 (25
mg, 0.65 mmol), and 10 mL of absolute ethanol was stirred for 1 h at
40 °C. The mixture was combined with water (100 mL) and extracted
with ether (2 × 50 mL). The organic layer was washed with water
twice and removed under vacuum. The biphenyl 4c was recrystallized
from hexane (210 mg, 84%), mp 136-137 °C. 1H NMR (CDCl3): δ
2.03 (s, 6H, Me), 4.77 (d, 4H, J ) 5.1, CH2 OH), 7.07 (d, 2H, J )
7.7), 7.25 (t, 2H, J ) 7.5), 7.39 (d, 2H, J ) 7.5). Anal. Calcd (found)
for C16H1802, 0.5 H2O: C, 76.47 (76.6); H, 7.49 (7.5).
4. A solution containing 4c (200 mg, 0.83 mmol) and 10 mL of
33% HBr in AcOH was warmed at 50 °C for 12 h. After cooling,
water was added (100 mL) and the mixture was extracted with
dichloromethane (100 mL). The organic layer was washed with water,
saturated aqueous NaHCO3, and water and dried over MgSO4. The
straps (a) and of the biphenyl-strapped 5,15-diphenylporphyrins (b).
To study CO/O2 discrimination by iron(II) porphyrins, we
have synthesized several diphenylporphyrins strapped with
biphenyl units which carry H (6H2), CH3 (7H2), OCH3 (8H2)
groups at their 2,2′-positions and are covalently linked by two
CH2O groups to the ortho-positions of the porphyrin phenyl
groups (see Figure 1). The functions of the 2,2′-substituents
of the biphenyl strap were 2-fold: (i) introduction of different
polar groups into the distal porphyrin cavity; (ii) upholding, by
steric interactions with the porphyrin cores, of the straps in
central position over the metal center. The X-ray structure of
the chloroiron(III) complex of such a biphenyl-strapped por-
phyrin is also described. The synthesis, structures, and proper-
ties of ferrous carbonyl adducts of these porphyrins, obtained
in various solvents in the presence or absence of nitrogenous
bases, are presented and discussed.
Experimental Section
General Methods. Toluene, ether, and THF were distilled from
their purple sodium benzophenone ketyl solutions. Dichloromethane
was distilled from CaH2. Dry solvents used for iron(II) complexes
were subsequently degassed on a vacuum line using freeze-pump-
thaw cycles. Other chemicals were obtained from Aldrich or Lancaster
and used without further purification. Melting points are uncorrected
and were measured on a Bu¨chi SMP-20. UV-visible data were
obtained using a Cary 5E spectrometer. 1H NMR spectra were recorded
on a Brucker WP 200 SY (200 MHz), chemical shifts δ are expressed
in ppm relative to deuterated chloroform (7.26 ppm) or other NMR
solvents (THF-d8, acetone-d6), and the coupling constants J are given
in hertz. IR spectra were obtained on a Brucker ISF 25 instrument.
Elemental analyses were performed in the Laboratoire de Recherche
Applique´e et de Transfert de Technologie (IUT-Strasbourg sud).
Chromatography columns were run on Merck No. 7734 silica gel and
Merck No. 1097 alumina.
(11) (a) Chong, R.; Clezy, P. S.; Liepa, A. J.; Nichol A. W. Aust. J. Chem.
1969, 22, 229. (b) Clezy, P. S.; Smythe, G. A. Aust. J. Chem. 1969,
22, 239.
Synthesis. 5,15-Bis(phenyl)porphyrin (1H2). This compound was
(12) Manka, J. S.; Laurence, D. S. Tetrahedron Lett. 1989, 30, 6989.
(13) Vo¨gtle, F. Liebigs Ann. Chem. 1969, 728, 17.
(14) Dibazo, P.; Mouneyrac, M. F. Bull. Soc. Chim. Fr. 1968, 2958.
(10) (a) Ray, G. B.; Lee, X.-Y.; Ibers, J. A.; Sessler, J. L.; Spiro, T. G. J.
Am. Chem. Soc. 1994, 116, 162.

1144 Inorganic Chemistry, Vol. 37, No. 6, 1998
Jacquinod et al.
solvent was removed under vacuum to give a brown oil which was
purified by chromatography on a SiO2 column, eluated with a mixture
of CH2Cl2/hexane (2:1) to give 225 mg (74%) of pure 4, mp 122-123
°C. 1H NMR (CDCl3): δ 2.09 (s, 6H, Me), 4.59 (s, 4H, CH2Br), 7.08
(d, 2H, J ) 7.5), 7.21 (t, 2H, J ) 7.5), 7.34 (d, 2H, J ) 7.5). Anal.
Calcd (found) for C16H16Br2: C, 52.21 (52.1); H, 4.38 (4.3).
7.5, Hc), 7.33 (d, 2H, Ar H), 7.67 (t, 2H, Ar H), 7.82 (t, 2H, Ar H),
8.83 (d, 2H, Ar H), 8.94 (d, 2H, J ) 4.6, â-H), 9.0 (d, 2H, J ) 4.6,
â-H), 9.21 (d, 2H, J ) 4.6, â-H), 9.24 (d, 2H, J ) 4.6, â-H), 10.06 (s,
2H). UV/vis (CH2Cl2): 408, 502, 534, 576, 630 nm. Treatment of
the mother liquor with an excess of ZnCl2 in refluxing THF yielded
the zinc(II) complex, which was purified by chromatography on silica
gel to yield a second crop of porphyrin 7-Zn (50 mg, 13%). No
demetalation occurred after several days by dissolution of 7-Zn in pure
trifluoroacetic acid.
2,2′-Dimethoxy-3,3′-bis(chloromethyl)biphenyl (5). This deriva-
tive was synthesized via 2,2′-dimethoxy-3,3′-diformylbiphenyl (5a) and
2,2′-dimethoxy-3,3′-bis(hydroxymethyl)biphenyl (5b). 5a. 2,2′-
Dimethoxydilithiobiphenyl was prepared in refluxing ether under
Gillman’s conditions on 20 g (93 mmol) of 2,2′-dimethoxybiphenyl in
the presence of 2.2 equiv of n-butyllithium (130 mL, 1.6 M in hexane).15
After cooling of the mixture to 0 °C, 25 mL of anhydrous DMF was
slowly added. The mixture was allowed to warm to room temperature
while being stirred under argon overnight and then hydrolyzed with
400 mL of 2 M aqueous hydrochloric acid. Stirring was maintained
for 30 min. The organic layer was filtered, washed with saturated
aqueous NaHCO3 and water, and removed under vacuum to give a
brown oil, 5a, which was recrystallized twice from ethanol. Yield:
5.5 g, 25%. Mp: 145-146 °C. 1H NMR (CDCl3): δ 3.58 (s, 6H,
OMe), 7.33 (t, 2H, J ) 7.7), 7.64 (dd, 2H, J ) 7.5, J ) 1.8), 7.93 (dd,
2H, J ) 7.7, J ) 1.9), 10.47 (s, 2H, CHO). Anal. Calcd (found) for
C16H14O4: C, 71.10 (70.84); H, 5.22 (5.05).
5b. Following the same procedure described for 4c, the reaction of
5a (3.0 g, 11 mmol) with NaBH4 (250 mg, 6.6 mmol) afforded 2.9 g
(95%) of 5b, mp 91 °C. 1H NMR (CDCl3): δ 2.4 (m, 2H, OH), 3.43
(s, 6H, OMe), 4.78 (d, 4H, J ) 5.9, CH2 OH), 7.21 (t, 2H, J ) 7.5),
7.32 (dd, 2H, J ) 7.6, J ) 1.8), 7.39 (dd, 2H, J ) 7.5, J ) 1.5). 1H
NMR (CDCl3 + D2O): δ 4.77 (s, 4H, CH2 OH). Anal. Calcd (found)
for C16H18O4: C, 70.06 (69.85); H, 6.61 (6.47).
5. A solution containing 5b (2.0 g, 7.3 mmol), 5 mL of SOCl2, and
10 mL of anhydrous CH2Cl2 was stirred overnight at room temperature.
The solvents were removed under vacuum, and the crude product was
recrystallized from n-hexane (2.05 g, 90%), mp 142-143 °C. 1H NMR
(CDCl3): δ 3.47 (s, 6H, OMe), 4.74 (s, 4H, CH2Cl), 7.18 (t, 2H, J )
7.7), 7.37 (dd, 2H, J ) 7.6, J ) 1.8), 7.44 (dd, 2H, J ) 7.5, J ) 1.8).
Anal. Calcd (found) for C16H16Cl2O2: C, 61.75 (61.69); H 5.18 (5.13).
General Procedure Used for the Preparation of the Porphyrins
with Straps Attached via CH2O Linkages (6H2-8H2). A 200 mg
amount of porphyrin 2H2, 1.5 equiv of 3,3′-dihalogenomethylbiphenyl
(3-5) (0.61 mmol) and 3 equiv of anhydrous K2CO3 (220 mg) were
mixed. This powder was added in little portions over a 12-h period to
a solution of 100 mL of anhydrous acetone refluxing under inert
atmosphere. After completion of the addition, refluxing was maintained
for 12 h. The mixture was then poured in 200 mL of water and then
extracted twice with methylene chloride (2 × 100 mL). The organic
layers were washed with water and removed under vacuum. The
residue was purified by column chromatography (SiO2, CH2Cl2).
Compounds 6H2-8H2 were recrystallized from CH2Cl2/n-hexane.
5,15-[o,o′-((3,3′-Biphenyldilyldimethylene)dioxy)diphenylene]-
porphyrin (6H2). A 200 mg amount of biphenyl 3 was used for the
preparation of 6H2 (150 mg, 53%). 1H NMR (CDCl3): δ -3.96 (s,
2H, NH), 3.36 (s, 2H, 2,2′-H), 4.42 (s, 4H, OCH2), 4.77 (d, 2H, J )
7.6, Ha), 5.90 (t, 2H, J ) 7.6, Hb), 6.23 (d, 2H, J ) 7.5, Hc), 7.52 (d,
2H, J ) 7.9, Ar H), 7.62 (t, 2H, J ) 7.7, Ar H), 7.83 (t, 2H, J ) 7.7,
Ar H), 8.46 (d, 2H, J ) 7.7, Ar H), 8.98 (d, 4H, J ) 4.5, â-H), 9.22
(d, 4H, J ) 4.5, â-H), 10.01 (s, 2H). UV/vis (CH2Cl2): 411, 506,
538, 577, 632 nm. Anal. Calcd (found) for C46H32N4O2: C, 82.12
(81.6); H 4.79 (4.7); N, 8.33 (7.9).
7-Zn. 1H NMR (CDCl3 + 1 drop of THF-d4): δ -2.72 (s, 6H,
Me), 3.62 (d, 2H, J ) 9.9, OCH2), 3.80 (d, 2H, J ) 9.8, OCH2), 5.75
(d, 2H, J ) 7.5, Ha), 6.29 (t, 2H, J ) 7.5, Hb), 6.50 (d, 2H, J ) 7.5,
Hc), 7.22 (d, 2H, J ) 8.1, Ar H), 7.54 (t, 2H, J ) 7.4, Ar H), 7.68 (t,
2H, J ) 7.7, Ar H), 8.71 (d, 2H, J ) 7.9, Ar H), 8.81 (d, 2H, J ) 4.6,
â-H), 8.88 (d, 2H, J ) 4.6, â-H), 9.10 (d, 2H, J ) 4.6, â-H), 9.14 (d,
2H, J ) 4.6, â-H), 9.90 (s, 2H). UV/vis (10-4ꢀ, L mol-1 cm-1
)
(THF): 393 (sh), 414 (57.3), 545 (2.45), 580 (0.41) nm. Anal. Calcd
(found) for C48H34N4O2Zn: C, 75.24 (75.7); H, 4.74 (4.6); N, 7.31 (7.5).
5,15-[o,o′-(((2,2′-dimethoxy-3,3′-biphenyldiyl)dimethylene)dioxy)-
diphenylene]porphyrin (8H2). A 160 mg amount of biphenyl 5 were
used for the preparation of 8H2 (120 mg, 41%). 1H NMR (CDCl3): δ
-3.26 (s, 2H, NH), -2.09 (s, 6H, OMe), 4.34 (m, 4H, OCH2), 6.28
(m, 4H, Ha + Hb), 6.57 (d, 2H, Hc), 7.18 (d, 2H, Ar H), 7.59 (t, 2H, J
) 7.4, Ar H), 7.81 (t, 2H, J ) 7.6, Ar H), 8.83 (d, 2H, J ) 7.2, Ar H),
8.92 (m, 4H, â-H), 9.18 (m, 4H, â-H), 9.98 (s, 2H). FABMS (m/e):
calcd for C48H36N4O4, 732.84; found, 733.1 (100, M+). UV/vis (CH2-
Cl2): 408, 502, 532, 575, 628 nm.
Iron Insertion into Porphyrins 1H2 and 6H2-8H2. Iron insertion
was performed with an excess of anhydrous ferrous chloride in refluxing
THF in the presence of 2,6-dimethylpyridine under an argon atmo-
sphere. The disappearance of the metal-free porphyrin was monitored
by TLC (SiO2, 5:95 ether/CH2Cl2). When the metalation was ended,
methylene chloride was added to the reaction mixture which was then
poured into aqueous hydrochloric acid. After workup, the iron(III)
chloride complexes were purified by chromatography on an alumina
column (basic grade I). Elution with MeOH/CH2Cl2 (5:95 v/v) gave
the red (µ-oxo)iron(III) dimers which were recrystallized in CH2Cl2-
hexane and isolated in 70-80% yields. These (µ-oxo)iron(III) dimers
showed typical UV/vis spectral bands in THF (λmax ) 403, 565 nm).
Elemental analyses were performed on these µ-oxo dimers. Indeed,
the metalloporphyrins were not isolated as iron(III) chloride complexes
owing to the difficulties to resolubilize them in all usual organic
solvents, except DMSO. Nevertheless, these chloroiron(III) complexes
were easily generated on bubbling HCl vapors from an opened bottle
containing concentrated HCl into the µ-oxo-dimer solutions.
1-FeCl. 1H NMR (CDCl3): δ 77.3 (s, â-H), 80.1 (s, â-H). UV/vis
(10-4ꢀ L mol-1 cm-1) (CH2Cl2): 373 (5.8), 406 (8.6), 501 (1.4), 572
(0.43), 662 (0.41) nm. Anal. Calcd (found) for C64H40N8OFe2, 1.5
H20: C, 71.5 (71.4); H, 4.03 (4.1); N, 10.4 (10.3).
6-FeCl. 1H NMR (CDCl3): δ 75.9 (s, â-H), 83.4 (s, â-H). UV/vis
(10-4ꢀ L mol-1 cm-1) (THF): 371 (4.7), 408 (8.8), 499 (1.5), 571 (0.80),
636 (0.72) nm. Anal. Calcd (found) for C92H60N8O5Fe2‚4H2O: C,
71.7 (71.5); H, 4.45 (4.6); N, 7.27 (7.2).
7-FeCl. 1H NMR (CDCl3): δ 74.4 (d, â-H), 82.9 (d, â-H). UV/
vis (10-4ꢀ L mol-1 cm-1) (THF): 370 (6.1), 406 (8.2), 498 (1.6), 570
(0.69), 634 (0.60) nm. Anal. Calcd (found) for C96H68N8O5Fe2‚
5H2O: C, 71.4 (71.1); H, 4.87 (4.80); N, 6.84 (6.7).
8-FeCl. 1H NMR (CDCl3): δ 76.8 (d, â-H), 86.6 (d, â-H). UV/
vis (10-4ꢀ L mol-1 cm-1) (THF): 376 (5.7), 405 (8.3), 497 (1.5), 572
(0.7), 634 (0.66) nm. Anal. Calcd (found) for C96H68N8O9Fe2‚
2.5H2O: C, 70.55 (70.5); H, 4.50 (4.5); N, 6.86 (6.7).
Crystallographic Data Collection and Structure Determination.
Violet prismatic single crystals of composition 6-FeCl‚MeOH‚CH2Cl2
were obtained by slow evaporation of CH2Cl2/MeOH solutions of
6-FeCl. Crystal data were collected at -100 °C in the θ/2θ flying
step-scan mode with a crystal of 0.40 × 0.20 × 0.10 mm3 dimensions
on a Philips PW1100/16 diffractometer using graphite-monochromated
Cu KR radiation. X-ray experimental data are given in Table 1. The
unit cell parameters have been refined using 24 high-angle reflections.
A total of 4886 independent reflections were collected in the range 3
< θ < 52.5° (limit imposed by the cooling device, -10 e h e 10, 0
5,15-[o,o′-(((2,2′-dimethyl-3,3′-biphenyldiyl)dimethylene)dioxy)-
diphenylene]porphyrin (7H2). Following the general procedure, the
condensation of biphenyl precursor 4 (140 mg) with 2H2 afforded
compound 7H2, which contained after column chromatography bis-
(porphyrin) impurities. These impurities were removed by repeated
crystallizations in dichloromethane/hexane mixtures to give pure 7H2
(135 mg, 35%). 1H NMR (CDCl3): δ -3.03 (s, 2H, NH), -2.36 (s,
6H, Me), 3.89 (d, 2H, J ) 9.8, OCH2), 3.97 (d, 2H, J ) 9,8, OCH2),
5.92 (d, 2H, J ) 7.4, Ha), 6.45 (t, 2H, J ) 7.5, Hb), 6.64 (d, 2H, J )
(15) Gilman, H.; Swiss, J.; Cheney, L. C. J. Am. Chem. Soc. 1940, 62,
1963.

Biphenyl-Strapped Diphenylporphyrins
Inorganic Chemistry, Vol. 37, No. 6, 1998 1145
Table 1. Crystallographic Data for 6-FeCl‚CH3OH‚CH2Cl2
formula: C48H36N4O3Cl3Fe
a ) 10.164(3) Å
b ) 28.977(9) Å
c ) 14.283(4) Å
â ) 106.22(2)°
µ ) 5.261 mm-1
V ) 4039(3) Å3
Z ) 4
fw: 879.05
space group: P21/c (No. 14)
T ) -100 °C
λ ) 1.541 84 Å
F
calc ) 1.45 g cm-3
transm coeff ) 0.61-1.00
R(Fo) ) 0.056
Rw(Fo) ) 0.087
e k e 29, 0 e l e 14) from which 3161 had I > 3σ(I). These latter
reflections were used to determine the structure by direct methods and
to refine it. After isotropic refinements, a difference map showed
maximas close to the positions expected for hydrogen atoms. These
atoms, with the exception of the methanol protons, were included at
their idealized positions as fixed contributors in structure factor
calculations with a C-H ) 0.95 Å and isotropic temperature factors
such as B(H) ) 1.3Beqv(C) Å2. At this stage, absorption corrections,
using DIFABS, were applied (min/max transmission coefficients )
0.61-1.00). Anisotropic refinements of all non-hydrogen atoms, with
the exception of the methanol C and O atoms, on |F|, with weights
given by w ) 4Fo /(σ2(Fo) + 0.0064Fo ), converged to R(Fo) ) 0.056,
Rw(Fo) ) 0.087, and GOF ) 1.887. No extinction corrections were
applied. A nonresolved electron-density residue of 1.4 e/Å3 remains
near the methanol molecule, indicating some disorder in the region
around this solvent. All calculations were performed using the
OpenMoleN package on a DEC Alpha work station.19a Scattering
factors and anomalous dispersion coefficients were taken from Cromer
and Waber.19b
2
4
Figure 2. (a) 1H NMR spectra of metal-free base 7 in CDCl3 at room
temperature. (b) 7-Fe(CO)(py-d5) in THF-d8 at room temperature.
Results
1
1
1
Table 2. HNH and Hmethine Chemical Shifts (ppm) in the H NMR
Spectra (in CDCl3) of (Figure 1a) the Metal-Free Porphyrin 2H2 and
the CH2O-Linked Biphenyl-Strapped Metal-Free Porphyrins
6H2-8H2
Conformational Properties of the Biphenyl-Strapped Por-
phyrins in Solution. The electronic absorption spectra of these
metal-free strapped porphyrins 6H2-8H2 showed only minor
changes relative to that of the precursor porphyrin 2H2. The
Soret bands are slightly red-shifted from 1 to 5 nm, the largest
shift of this band (5 nm) being observed for porphyrin 6H2 in
which the 2,2′-positions of the biphenyl strap are not substituted.
The small shifts of the Soret bands indicate that, relative to the
precursor porphyrin 2H2, the rings of 6H2-8H2 are somewhat
more distorted and less planar.16 The slight supplementary
distortions of the porphyrin rings are, most probably, induced
by the covalently attached biphenyl straps. However, because
the Soret band is most shifted for 6H2, in which the 2,2′-
positions of the biphenyl strap are not substituted, the observed
band shifts of 1-5 nm cannot be directly related to steric
interactions of the 2,2′-substituents with the porphyrin rings.
The free-base porphyrins were also studied by 1H NMR
spectroscopy. Figure 2a displays the 1H NMR spectrum
(CDCl3) of the metal-free porphyrin 7H2. As illustrated by this
spectrum, the methine proton signals of these strapped porphy-
rins 6H2-8H2, which appear between 9.98 and 10.06 ppm
(Table 2), are weakly upfield shifted by 0.29-0.37 ppm relative
to these proton signals in the precursor porphyrin 2H2. These
a
a
HNH
Hmethine
∆
HNH
Hmethine
∆
2H2 -3.19
6H2 -3.96
10.35
10.01
7H2 -3.03
-0.34 8H2 -3.26
10.06
9.98
-0.29
-0.37
a ∆ ) differences in the Hmethine chemical shifts for 6H2-8H2 relative
to the shift in 2H2.
small shifts confirm that small distortions occur in 6H2-8H2,
relative to 2H2.17 However again, because one of the largest
shifts of the methine proton resonances is observed for 6H2,
these distortions cannot be directly related to steric interactions
excerted by the 2,2′-substituents on the porphyrin rings.
The large upfield shifts observed for the 2,2′-substituent
singlets indicate that these groups are facing the porphyrin
macrocycle. The methyl and methoxy group resonances of
porphyrins 7H2 and 8H2 are upfield shifted by 4.45 and 5.56
ppm relative to the biphenyl precursors 4 and 5, respectively.
These orientations of the methyl and methoxy 2,2′-substituents
have been confirmed by the X-ray structures of the metal-free
porphyrins 7H2 and 8H2.18
Specific assignments of the â-pyrrole resonances are some-
what ambiguous. For porphyrin 6H2, the â-pyrrole signals
appear as two doublets integrating as four protons. This
apparent C2V symmetry indicates that a dynamic exchange
process is occurring. Interconversion of the two chiral atropi-
somers of this strapped porphyrin must proceed via a coplanar
conformation of the 2,2′-unsubstituted biphenyl strap. On the
other hand, the four doublets lying between 8.81 and 9.18 ppm
in the spectra of porphyrins 7H2 (Figure 2a) and 8H2, which
have been assigned to the four different types of â-pyrrolic
protons, show an actual C2 symmetry. An increase in temper-
ature to 60 °C does not produce significant variations in the
spectrum of 8H2, confirming that the dynamic exchange process
(16) (a) Wijesekera, T. P.; Paine, J. B.; Dolphin, D.; Einstein, F. W. B.;
Jones, T. J. Am. Chem. Soc. 1983, 105, 6747. (b) Simonis, U.; Walker,
F. A.; Lee, P. L.; Hanquet, B. J.; Meyerhoff, D. J.; Scheidt, W. R. J.
Am. Chem. Soc. 1987, 109, 2659.
(17) (a) Osuka, A.; Kobayashi, F.; Mayurama, K. Bull. Chem. Soc. Jpn.
1991, 64, 1213. (b) David, S.; Dolphin, D.; James, B. R.; Paine, J. B.;
Wijesekera, T. P. Can. J. Chem. 1986, 64, 208.
(18) Jaquinod, L.; Kyritsakas, N.; Fischer, J.;. Weiss, R. New J. Chem.
1995, 19, 453.
(19) (a) Frenz, B. A. The Enraf-Nonius CAD4-SDP. In Computing in
Crystallography; Schenk H., Olthof-Hazekamp, R., Van Koningveld,
H., Bassi, G. C., Eds.; Delft University Press: Delft, The Netherlands,
1978; pp 64-71. (b) Cromer, D. T.; Waber, J. T. International Tables
for X-ray Crystallography; Vol. IV, The Kynoch Press: Birmingham,
U.K., 1874; Vol. IV, Tables 2.2b and 2.3.1.

1146 Inorganic Chemistry, Vol. 37, No. 6, 1998
Jacquinod et al.
Table 3. Selected Averaged Bond Distances and Bond Angles and
Out-of-Mean-Plane Displacements in 6-FeCl
Fe-N (Å) Fe-Cl (Å)
2.046(6) 2.234(2)
∆(Fe)/4Np (Å): 0.45(1)
N-Fe-N (deg)
N-Fe-Cl (deg)
87.2(2)
102.7(2)
∆(Fe)/24-core (Å): 0.49(1)
coordinate systems of the FeCl(Porph) type.20 The perpendicu-
lar displacements of the porphyrin-core atoms of 6-FeCl relative
to their mean-plane indicate that the macrocycle is slightly
domed and ruffled (Figure 4). The doming, which is character-
ized by a separation of 0.04(1) Å between the 4Np and
porphyrin-core mean-planes, moves the 4Np mean-plane in the
opposite direction relative to the strap and thus increases slightly
the space between the strap and the porphyrin core. It is related
to the pentacoordination and out-of-plane displacement of
0.45(1) Å of the iron center relative to the four pyrrole nitrogen
mean-plane. The ruffling is characterized by a mean displace-
ment of 0.32(1) Å above the porphyrin core mean-plane of the
C5 and C15 meso-carbons, which lie on the same side of the
porphyrin ring as the strap. It is connected to the presence of
a strap covalently linked to an ortho position of both phenyl
rings of the 5,15-diphenylporphyrin. The distortions of the
porphyrin ring in 6-FeCl are more severe than those occurring
in the sterically protected chloroiron(III) porphyrin derivatives,
[FeIIICl(C2-cap)] and [FeIIICl(C4-Cap)].20 The average dis-
placements of the porphyrin core atoms relative to their mean-
plane is 0.15(1) Å in 6-FeCl, the largest deviation being 0.35(1)
Å. In contrast, in the chloroiron(III) complexes of the capped
tetraphenylporphyrins H2(C2-Cap) and H2(C4-Cap), the average
deviations from the porphyrin mean-planes are only 0.08 and
0.04 Å, respectively. The dihedral angle between the two
phenyl rings forming the biphenyl strap is 133.7(2)°. Thus, this
angle is slightly larger than 120°, a value known to occur in
one of the thermodynamically stable conformations of the free
2,2′-disubstituted biphenyls.21 The dihedral angles between the
two phenyl rings forming the strap and the porphyrin-core mean-
plane are 32.4(2) (C32-C37) and 108.8(2)° (C38-C43). The
cavity height occurring in 6-FeCl defined as the distance
between the centroid of the strap and the porphyrin-core mean-
plane is 4.817(7) Å. The lateral shift of the strap determined
as the distance between the centroid of the strap and the normal
to the porphyrin-core mean-plane passing through the center
Ct of the porphyrin ring is 1.002(7) Å.
Figure 3. ORTEP plot of 6-FeCl. Ellipsoids are scaled to enclose 50%
of the electronic density. Hydrogen atoms are omitted.
Figure 4. Pluto plot of the porphyrin core of 6-FeCl. Numbers in
parentheses indicate the deviations in 0.01 Å relative to the mean plane
porphyrin ring.
Synthesis and Spectroscopic Characterization of Iron(II)
Biphenyl-Strapped Porphyrins and Their CO Adducts. The
reduction of the ferric into ferrous porphyrin derivatives was
achieved by zinc/Hg amalgam in dry degassed solvents (THF,
toluene, dichloromethane). Addition of deoxygenated nitrog-
enous aromatic bases (imidazoles, pyridine) yielded pure high-
spin, five-coordinate complexes, except for porphyrin 6H2,
which formed, under these conditions, a low-spin six-coordinate
iron(II) complex. The five-coordinate iron(II) complexes were
of the strap occurring in 6H2 is prevented in 8H2 and in 7H2 by
the bulkiness of the 2,2′-substituents. Furthermore, the meth-
ylene protons of the CH2O links, which are diastereotopic in
nature due to the chirality of these strapped porphyrins, give
two well-defined doublets in the case of porphyrin 7H2 (J )
9.8 Hz) (Figure 2a), an apparent quartet in case of porphyrin
8H2, but only a singlet integrating as four protons in the
spectrum of porphyrin 6H2. This again shows that the strap
interconversion occurring in 6H2 is blocked in 7H2 and 8H2.
1
characterized by UV/vis and H NMR spectroscopy. In THF,
these compounds exhibited typical UV/vis spectra with bands
lying between 359 and 363, 423 and 425 (Soret), and 526 and
549 nm. The characteristic band lying in the range 359-363
nm, indicating the presence of pentacoordinated, high-spin
derivatives, does not appear in the electronic spectrum of
6-Fe(II) by addition of an aromatic base and disappears in all
the derivatives upon addition of CO. In THF, the six-coordinate
FeII(CO)(nitrogenous base) derivatives of porphyrins 7H2 and
Crystal Structure of 6-FeCl‚CH3OH‚CH2Cl2. The molec-
ular structure of 6-FeCl is displayed in Figure 3 together with
a part of the labeling scheme used. Figure 4 shows the
perpendicular displacements (in 0.01 Å units) of the porphyrin-
core atoms and the FeCl unit relative to the porphyrin-core
mean-plane. Selected average bond distances and bond angles
occurring in 6-FeCl are assembled in Table 3.
The iron atom of 6-FeCl is five-coordinate, high-spin. The
axial chloride ligand lies opposite to the strap. The coordination
geometry of the iron center is similar to that in other five-
(20) Sabat, M.; Ibers, J. A. J. Am. Chem. Soc. 1982, 104, 3715.
(21) (a) Almenningen, A.; Hartman, O.; Seip, H. Acta Chem. Scand. 1968,
22, 1013. (b) Hofmann, H. J.; Birner, P. Z. Chem. 1975, 15, 23.

Biphenyl-Strapped Diphenylporphyrins
Inorganic Chemistry, Vol. 37, No. 6, 1998 1147
Table 4. Chemical Shifts (ppm) of the 2,2′-Biphenyl Substituent
Table 5. CO Stretching Vibrations (cm-1) in 1-, 6-, 7-, and
8-Fe(CO)(L) in THF and in the Presence of a Nitrogenous Base L
(L ) Pyridine (py), Imidazole (ImH), and N-Methylimidazole
(N-MeIm))
Group Resonances and the Biphenyl Proton and Porphyrin Methine
1
Proton Signals Observed in the H NMR Spectra of
1-Fe(CO)(py-d5) (in CDCl3) and for 6-, 7-, and 8-Fe(CO)(py-d5) (in
THF-d8)a
compd
L ) Py
1976
1993
1992
2006, 1986
L ) ImH
L ) N-MeIm
compd
H(substituents)
H(biphenyl)
H(methine)
1-Fe(CO)(L)
6-Fe(CO)(L)
7-Fe(CO)(L)
8-Fe(CO)(L)
1969
1985
1987
1987
2000, 1981
1-Fe(CO)(py-d5)
6-Fe(CO)(py-d5)
9.82 (s, -0.48)
9.26 (s, -0.75)
1999, 1981
7-Fe(CO)(py-d5) -0.07 (s, 2.29) 6.32 (d, +0.78) 9.45 (s, -0.61)
6.63 (t, -0.18)
Table 6. CO Stretching Vibrations (cm-1) in 1-, 6-, and
8-Fe(CO)(py) in CH2Cl2 and Toluene
6.84 (d, +0.20)
8-Fe(CO)(py-d5) 1.16 (s, +3.25) 6.40 (s, +0.12) 9.39 (s, -0.59)
6.78 (m, +0.15;
+0.44)
compd
CH2Cl2
1975
1983
toluene
1980
1994
1-Fe(CO)(py)
6-Fe(CO)(py)
8-Fe(CO)(py)
a The nature of the signal and the difference in chemical shift relative
to the metal-free porphyrin are indicated in parentheses.
1999, 1983
2006, 1988
8H2 show UV/vis bands ranging between 416 and 419 (Soret)
In noncoordinating solvents such as CH2Cl2 and in the
absence of any nitrogenous base, 1-Fe, 6-Fe, and 7-Fe form
two carbonyl adducts showing one νCO band at 2029 cm-1 and
the other ranging between 1966 (1-Fe), 1962 (6-Fe), and 1954
cm-1 (7-Fe). Since, the dicarbonyl adduct of iron(II) tetraphen-
ylporphyrin ([Fe(CO)2(TPP)]) is characterized by a νCO band
and 511 and 523 nm.
1
The H NMR spectra of the pentacoordinated, high-spin,
ferrous species were measured in THF-d8 or CDCl3 solutions
containing the iron(II) porphyrins (c ≈ 10 mM) and pyridine-
d5 (c ≈ 2.5 M). Their pyrrole resonances appear downfield
between 45 and 55 ppm and show C2 symmetry. The methine
proton signals lie upfield between -10 and -15 ppm. A signal
lying at 17.1 ppm in the spectrum of 7-FeII(py-d5) has been
attributed to the 2,2′-methyl substituents on the basis of its
integration. The 2,2′-methoxy group resonances appear at 15.6
ppm in the spectrum of 8-FeII(py-d5).
located at 2042 cm-1 22 the 2029 cm-1 band, most probably,
,
corresponds to the ferrous bis-CO complexes of the porphyrin
dianions 1, 6, and 7. The second band ranging between 1966
and 1954 cm-1 corresponds probably to the νCO band of the
monocarbonylated (CO)out regioisomer. Under similar condi-
tions 8-Fe yields only one CO adduct characterized by a νCO
band at 1956 cm-1, which corresponds to the (CO)out regio-
isomer.
Addition of CO to the FeII(py-d5) NMR samples of porphyrin
dianions 7 and 8 yielded the corresponding six-coordinate, low-
spin, carbonyl adducts. Figure 2b displays the 1H NMR
spectrum of 7-FeII(CO)(py-d5).
As shown in Table 4, the methine proton signals are slightly
upfield shifted in the 1H NMR spectra of 6-, 7-, and 8-Fe(CO)-
(py-d5) with respect to the methine proton signal of 1-Fe(CO)-
(py-d5). These upfield shifts are compatible with a slight
increase in distortion of the porphyrin cores upon CO binding.
However, since the largest shift occurs in the spectrum of
6-Fe(CO)(py-d5) in which the strap is not substituted, the
distortions of the porphyrin cores in 6-, 7-, and 8-Fe(CO)(py-
d5) relative to that present in 1-Fe(CO)(py-d5) are, again, not
directly related to the size of the 2,2′-substituents.
Table 5 gives the CO stretching vibrations observed for 1-,
6-, 7-, and 8-Fe(CO)(B) in THF and in the presence of an axial
nitrogenous base B (B ) pyridine, imidazole, N-methylimid-
azole). The νCO bands shift to smaller wavenumbers when the
axial ligand strength increases from pyridine to imidazole and
N-methylimidazole.23 Table 6 gives the CO stretching vibrations
observed for 1-, 6-, and 8-Fe(CO)(py) as a function of solvent.
The 2,2′-disubstituted straps do not shield completely the bound
CO from the solvent. Indeed, upshifts of the νCO bands are
observed between CH2Cl2 and the less polar toluene. The CO
stretching vibrations of the carbonyl adducts obtained with these
strapped porphyrins in the presence of a nitrogenous axial base
lie often between 1980 and 2000 cm-1 and, thus, are quite
Binding of CO within the cavity formed by the porphyrin
core and the strap (distal side) results in large downfield shifts
of the proton resonances of the 2,2′-substituents in the 1H NMR
spectra of the carbonyl adducts relative to the resonances of
these groups in the spectra of the corresponding metal-free
elevated. The elevated νCO values, lying close to 2000 cm-1
,
indicate a close interaction of the carbonyl oxygen with the
π-cloud of an aromatic ring as in [FeCO(1-MeIm)(C2-Cap)].25b
1
porphyrins (Table 4). For instance, in the H NMR spectrum
In non- or weakly coordinating solvents and in the presence
of a nitrogenous base, the carbonyl adduct of 8-Fe always
exhibits two νCO bands (Figure 5) which, by reaction with O2
disappear, simultaneously, while keeping an identical intensity
ratio.
of 7-Fe(CO)(py-d5) (Figure 2b), shifts ranging from 2.5 to 3.5
ppm are observed relative to the resonances of these substituents
in the metal-free base 7H2 (Figure 2a) or zinc(II) derivative 7-Zn
(see Experimental Section).
In THF, in the absence of any nitrogenous base, complex
7-Fe(THF) seems to yield the regioisomer 7-Fe(CO)in(THF) in
which CO lies within the cavity (distal side). The main UV/
vis spectral bands (THF) of this complex lie at 410 and 513
nm, and the CO stretching vibration lies at 1983 cm-1. In
contrast, 8-Fe seems to yield in THF the regioisomer in which
CO lies outside the cavity (proximal side). Indeed, the
downfield shift of the methoxy group resonances, relative to
the metal free base, is very small (0.14 ppm) precluding the
hypothesis of CO lying inside the cavity. Furthermore, the main
bands in the UV/vis spectrum (THF) appear at 398 and 502
nm and the CO stretching vibration lies at 1955 cm-1 in the IR
spectrum.
Table 7 compares the CO pressures needed for half-saturation
(22) Wayland, B. B.; Mehne, L. F.; Swartz, J. J. Am. Chem. Soc. 1978,
100, 2379.
(23) Alben, J. O.; Caughey, W. S. Biochemistry 1968, 7, 175.
(24) (a) Jones, R. D.; Budge, J. R.; Ellis, P. E., Jr.; Linard, J. E.;
Summerville, D. A.; Basolo, F. J. Organomet. Chem. 1979, 181, 151.
(b) Johnson, M. R.; Seok, W. K.; Ibers, J. A. J. Am. Chem. Soc. 1991,
113, 3998.
(25) (a) Kim, K.; Fettinger, J.; Sessler, J. L.; Hugdahl, J.; Collman, J. P.;
Ibers, J. A. J. Am. Chem. Soc. 1989, 111, 403. (b) Kim, K.; Ibers, J.
A. J. Am. Chem. Soc. 1991, 113, 6077. (c) Slebodnick, C.; Fettinger,
J. C.; Peterson, H. B.; Ibers, J. A. J. Am. Chem. Soc. 1996, 118, 3216.
(d) Slebodnick, C.; Ibers, J. A. JBIC 1997, 2, 521.

1148 Inorganic Chemistry, Vol. 37, No. 6, 1998
Jacquinod et al.
induces large lateral and vertical movements of the handle,
pocket, or cap. Both these effects lead to a considerable
expansion of the distal cavities allowing the accommodation
of a non- or weakly tilted and linear or quasi-linear Fe-C-O
unit (Fe-C-O angles larger than 172°). Similar linear or quasi-
linear Fe-C-O conformations are probably also present in the
iron(II)-CO adducts of the 2,2′-substituted biphenyl-strapped
1
porphyrins 7H2 and 8H2, although the H NMR data seem to
indicate that the distortions of the porphyrin cores present in
these CO adducts relative to those present in the metal-free
macrocycles are small.
One important conformational rearrangement resulting from
the distal binding of CO involves the opening of the dihedral
angle of the phenyl moieties forming the biphenyl strap in order
to minimize the peripheral interaction with the 2,2′-substituents.
These steric effects, which are not strongly affected by the
expansion and/or distortion of the porphyrinic cores, depend
on the intrinsic nature of the substituents. Thus, in THF, in
the absence of a nitrogenous base, 7-Fe(THF) yields only the
regioisomer 7-Fe(CO)in(THF)out, despite the low affinity of THF
as axial base;28 whereas, under identical conditions, 8-Fe(THF)
forms only the 8-Fe(CO)out regioisomer. The large difference
in affinity observed for CO in toluene between 7-Fe(py) and
8-Fe(py) (Table 7) also illustrates the effects of the 2,2′-
substituents on the binding properties of these porphyrins.
Despite that porphyrin 8H2 possesses a distal symmetrical cavity,
the FTIR spectra of 8-Fe(CO)(B) (B ) Py, ImH, 1-MeIm) show
two νCO bands ranging in THF respectively from 2006 to 1999
cm-1 and from 1986 to 1981 cm-1 with intensity ratios of ca.
2:1. An equilibrium of the type 8-Fe(CO)2 and 8-Fe(CO)(py)
seems excluded here, since 8-Fe(II) does not form a bis-CO
adduct, even in noncoordinating solvents and in absence of any
nitrogenous base. Thus, the two CO bands indicate that two
linear or quasi-linear Fe-C-O units having slightly different
orientations are present in these compounds. The shift of 20
cm-1 in THF between the two νCO bands is, most probably,
due to a change in polarity around one CO within the cavity of
porphyrin dianion 8.23 Furthermore, as seen before, elevated
νCO bands indicate a negative polar environment around
CO.10,25b,29 Since, one of the νCO bands of the CO adducts
8-Fe(CO)(B) (B ) Py, ImH, 1-MeIm) has always a very high
stretching frequency (2006-1999 cm-1), most probably, due
to steric crowding within the cavity, the Fe-C-O orientation
displaying the more elevated νCO band interacts more strongly
than the other with the π-cloud of a benzene ring belonging to
the biphenyl strap. Thus, the 20 cm-1 difference observed
between the two νCO stretching vibrations is probably mainly
due to a stronger interaction of one of the Fe-C-O orientations
with one of the benzene rings of the biphenyl strap. However,
despite the occurrence of two νCO bands in the infrared spectrum
of the carbonyl adduct 8-Fe(CO)(py-d5) (B ) py-d5) and only
Figure 5. Infrared spectrum of 8-Fe(CO)(NMeIm) in THF in the CO
band region.
Table 7. CO Pressures in Torr for Half-Saturation (P1/2) and
Stability Constants KBCO in Toluene for 7- and 8-Fe in the
Presence of N-MeIm (0.3 M) and Comparison with the
Half-Saturation CO Pressures and KBCO Values Known for
Sperm-Whale Mb (H2O, pH ) 7.0-7.5) and Several Model
Porphyrins
compd
7-Fe
8-Fe
P1/2
KBCO
ref
a
9 × 10-2
8.3 × 105
3.4 × 101
(1.2-2.8) × 10-2
1.5 × 10-3
1.1 × 10-2
1.2 × 101
102
3.0 × 103
a
Mb
30
6b
27
26
25b
Fe(PocPiv)
Fe(piv2-C8)
Fe-SP-13b
Fe(OC2O)
6.7 × 107
9.4 × 106
8.3 × 103
1.0 × 103
a This work. b Benzene, 0.2 M N-MeIm.
(P1/2
)
26 of 7- and 8-FeII(N-MeIm) in toluene with the P1/2 values
known for sperm-whale Mb and several model porphyrins. This
table shows that 8-Fe(N-MeIm) displays a reduced affinity in
comparison with 7-Fe(N-MeIm).
Discussion
The synthetic methods used to prepare these biphenyl-
strapped diphenylporphyrins 6H2-8H2 allow the modification
of the distal periphery of the porphyrins via a systematic
variation of the size, polarity, and degree of freedom of the 2,2′-
biphenyl substituents. The size of the substituents is an
important parameter: (i) It controls the access of the bases and
solvents to the distal cavity. (ii) It should limit the lateral
displacement of the straps from their central positions. As a
consequence, our 2,2′-substituted biphenyl-strapped porphyrins
yield, even in the presence of a large excess of aromatic
nitrogenous bases (larger than 2000 equiv), pure high-spin, five-
coordinate, iron(II) species.
Earlier studies have shown that in the metal-free porphyrins
7H2 and 8H2 the mean-value of the cavity heights, defined as
the distance between the centroid of the straps and the porphyrin
mean-planes, is 5.293(4) Å.18 Upright binding of CO seems
not probable in such a small cavity. However, recent structural
data obtained on several five-coordinate iron(II) derivatives and
six-coordinate iron(II)-CO adducts of mixed picket basket-
handle,27 pocket, and capped porphyrins25 have shown that CO
binding increases the ruffling of the porphyrin core or/and
1
one in that of 7-Fe(CO)(py-d5), the H NMR spectra of these
two complexes are very similar, even at low temperature (-70
°C). This is also consistent with the presence in 8-Fe(CO)(B)
(B ) py, ImH, NMeIm) of two linear or quasi-linear Fe-C-O
groups which are oriented slightly differently and which are
interconverting more rapidly than the NMR time scale. While
several νCO stretching vibrations ascribed to different Fe-C-O
orientations or conformers (substates) are commonly observed
in carbonyl adducts of hemeproteins,30 the observation of more
than one νCO band in the IR spectra of model porphyrin
(26) Ward, B.; Wang, C. B.; Chang, C. K. J. Am. Chem. Soc. 1981, 103,
5236.
(27) (a) Momenteau, M.; Look, B.; Te´treau, C.; Lavalette, D.; Croisy, A.;
Schaeffer, C.; Huelet, C.; Lhoste, J. M. J. Chem. Soc., Perkin Trans.
2 1987, 249. (b) Tetreau, C.; Lavalette, D.; Momenteau, M.; Fischer,
J.; Weiss, R. J. Am. Chem. Soc. 1994, 116, 11840.
(28) Scheidt, W. R.; Haller, K. J.; Fons, M.; Mashiko, T.; Reed, C. A.
Biochemistry 1981, 20, 3653.
(29) Spiro, T. G.; Kozlowski, P. M. JBIC 1997, 2, 516

Biphenyl-Strapped Diphenylporphyrins
Inorganic Chemistry, Vol. 37, No. 6, 1998 1149
complexes is less common. We have obtained, recently, several
carbonyl adducts of unsymmetrically 2,2′-substituted biphenyl-
strapped diphenylporphyrins exhibiting two νCO bands which
differ by more than 20 cm-1 in their IR spectra.31 Occurrenceof
two such bands indicates again that two Fe-C-O units adopting
two slightly different orientations are present in these com-
pounds. Moreover, like the CO adducts of several hemepro-
teins,32 the CO adducts of these biphenyl-strapped model
porphyrins enriched with 13CO display only one 13C NMR signal
indicating that the two Fe-C-O orientations giving rise to the
two νCO bands interconvert more rapidly than the NMR time
scale.31
Supporting Information Available: Tables S1-S6, listing X-ray
experimental data, atomic coordinates and equivalent thermal parameters
for all non-hydrogen atoms, atomic coordinates and thermal parameters
for hydrogen atoms, thermal parameters for anisotropic atoms, bond
lengths in Å, and bond angles in deg (14 pages). Ordering information
is given on any current masthead page.
(30) (a) McCoy, S.; Caughey, W. S. In Probes of Structure and Function
of Macromolecules and Membranes; Chance, B., Yonetani, T.,
Mildvan, A. S., Eds; Academic Press: New York, 1971; Vol. II, p
289. (b) Potter, W. T.; Hazzard, J. H.; Choc, M. G.; Caughey, W. S.
Biochemistry 1990, 29, 6283. (c) Ansari, A.; Berendzen, J.; Braunstein,
D.; Cowen, B. R.; Frauenfelder, H.; Hong, M. K.; Iben, I. E. T.; Jonson,
J. B.; Ormos, P.; Sauke, T. B.; Scholl, R.; Schulte, A.; Steinbach, P.
J.; Vittitov, J.; Young, R. D. Biophys. Chem. 1987, 26, 337.
(31) Pre´vot, L.; Jaquinod, L.; Fischer, J.; Weiss, R. Inorg. Chim. Acta, in
press.
IC970705A
(32) (a) Saterlee, J. D.; Teintze, M.; Richards, J. H. Biochemistry, 1978,
17, 1456. (b) Caughey, W. S.; Shimada, H.; Choc, M. C.; Tucker, M.
P. Proc. Natl. Acad. Sci. 1981, 78, 2903. (c) Behere, D. V.; Gonzalez-
Vergara, E.; Goff, H. M. BBRC 1985, 131, 607. (d) Deo Park, K.;
Guo, K.; Adebodun, F.; Chiu, M. L.; Sligar, S. G.; Oldfield, E.
Biochemistry 1991, 30, 2333.