Solutions of C60, C60O, or C70 and metal complexes of octaethylporphyrin (OEPH2) yield crystals
that contain both the fullerene and the porphyrin. The structures of C60·2CoII(OEP)·CHCl3, C60·2ZnII(OEP)·CHCl3, and C60O·2CoII(OEP)·CHCl3 are isomorphous and contain an ordered C60 cage surrounded by two
MII(OEP) units. Although there is no covalent bond between the fullerene and porphyrin components, the
separation between these units is shorter than normal van der Waals contact. Crystals of C70·CoII(OEP)·C6H6·CHCl3, C70·NiII(OEP)·C6H6·CHCl3, and C70·CuII(OEP)·C6H6·CHCl3 are also isomorphous with an ordered
fullerene, but have only one porphyrin/fullerene contact. Crystalline C60·ClFeIII(OEP)·CHCl3 lacks the close
face-to-face porphyrin/porphyrin contact that is common to all of the other structures reported here but retains
the intimate contact between the porphyrin and the fullerene. In (C120O)·CoII(OEP)·0.6C6H6·0.4CHCl3 the
fullerene dimer is enclosed by two CoII(OEP) moieties. Unfortunately disorder in the fullerene portion obscures
details of the geometry of the bridging region between the fullerenes.
Formylbiliverdin and related chlorophyll-derived
molecules are possible products of heme catabolism
and other biologically important oxidative processes and are likely to
be initially formed as metal complexes.
To explore the properties of the formylbiliverdin moiety bound to
transition metal ions, complexes of
octaethylformylbiliverdin (H2OEFB) with Cu(II),
Ni(II), and Co(II) have been prepared, since attempts
to
prepare an iron complex have produced only an unstable material.
Transmetalation of MgII(OEFB), made
by
photooxidation of MgII(octaethyl-porphyrin), with a
metal(II) acetate yields the low-spin complexes:
CuII(OEFB), NiII(OEFB), and CoII(OEFB).
Single-crystal X-ray diffraction of CuII(OEFB)
reveals that it consists
of a four-coordinate copper(II) center which is bound to the four
nitrogen atoms in distorted planar coordination.
The tetrapyrrole ligand has a helical geometry. The structure
of the solid is complicated by the existence of
three molecules in the asymmetric unit and C−H···O hydrogen
bonding between pairs of these in the tab/slot
arrangement seen in complexes of octaethylbiliverdin. Both
CuII(OEFB) and CoII(OEFB) can be
converted
to the verdoheme analogues,
[CuII(OEOP)]+ and
[CoII(OEOP)]+, where OEOP is the anion
of octaethyl-5-oxaporphyrin, by the addition of hydrogen peroxide. Additionally,
[CuII(OEOP)]+ can be produced by
heating
a toluene solution CuII(OEFB) in the presence of
trifluoroacetic acid under dioxygen. Carbon monoxide
is
produced when CuII(OEFB) is converted to
[CuII(OEOP)]+ by either method.
[CuII(OEOP)](PF6) has
been
characterized by single-crystal X-ray diffraction which shows that the
cation has a planar, porphyrin-like
structure. The room-temperature EPR spectrum of this complex shows
that the copper is four-coordinate with
four nitrogen based ligands, but frozen solutions of
[CuII(OEOP)]+ show a triplet EPR
spectrum indicative of
a dimeric species much like that in the X-ray crystal structure.
The 1H NMR spectrum of diamagnetic
NiII(OEFB) has been shown to be consistent with the helical structure
through the use of lanthanide and chiral
lanthanide shift reagents. The EPR spectra of
CoII(OEFB) show that it forms a low-spin adduct with
pyridine
and that this adduct acts as a reversible dioxygen carrier. The
geometric and electronic structural properties
of these complexes of formylbiliverdin are compared to those of
analogous compounds of biliverdin and of
porphyrins.
Oxidation of ( ) (OEP is the dianion of octaethylporphyrin) with thallium(III) trifluoroacetate is shown to form the previously unknown cis-dioxooctaethylporphodimethene (CIS-H2OEPO2) as well as the known, isomeric f/ww-dioxooctaethylporphodimethene (í/vms-H2OEPO2). While these have not been separated, their nickel (II) complexes are readily separated by chromatography on silica gel. Electronic absorption and NMR spectra are reported for these diamagnetic planar complexes. Addition of pyridine to either Nifirazir-OEPOz) or Ni(cfr-OEPO2) yields six-coordinate, paramagnetic (5=1) adducts. Dark violet Níii(ci'j-0EP02), C36H42N4N1O2, crystallizes in the tetragonal space group /4i/e with a = 14.664(7) A and c = 14.163(7) A at 130 K with Z = 4.Refinement of 745 reflections and 102 parameters yields R = 0.039, /?" = 0.043. The nickel is four-coordinate (Ni-N distance is 1.912(3) A), and its coordination geometry is planar, while the macrocycle displays a saddleshaped distortion. The keto groups are disordered over the four meso positions. Crystallization of Nin(irans-OEPO2) from pyridine yields dark orange (py^Nifí/ww-OEPCh), CseHsoNeNiOa, which crystallizes in the triclinic space group Plwith a = 9.878(4) A, b = 10.212(4) A, c = 10.503(4) A, a = 80.08(3)°, ß = 89.28(3)°, and = 66.50(3)°a t 130 K with Z = 1. Refinement of 2149 reflections and 260 parameters yields R = 0.030, Rv 0.040. The structure consists of a six-coordinate nickel ion at the center of the nearly planar macrocycle with the oxygen atoms disordered unequally into two sites so that it is clear that the fra/w-dioxo unit is present.
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