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

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
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 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·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) Å, b =
28.977(9) Å, c = 14.283(4) Å, 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−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.