NMR spectra of the porphyrins. Part 39. Paramagnetic shifts in cobalt(II) porphyrins

Abstract

A model of the paramagnetism in cobalt(I1) porphyrin complexes has been developed which successfully calculates paramagnetic shifts for protons not affected by the contact term. The model utilizes a single large dipole positioned on the cobalt(I1) atom, and calculates the pseudo-contact shift using the dipole approximation.With this model the angle of twist of the peripheral meso phenyl rings in tetraphenylporphyrin (TPP) derivatives was determined. In TPP and the meta-and para-substituted derivatives studied the phenyl rings are at ca. 65" to the porphyrin plane, whereas in the ortho-substituted derivatives the phenyl rings are essentially orthogonal. Similarly, the geometry for the /?-ethyl group of octaethylporphyrin and etioporphyrin I was found to be 50" out of the plane of the porphyrin inclined to the meso proton, and that of the comparable propionate group of coproporphyrin I to be 55". Finally, the novel compound meso-tetra@-phenoxyphenyl)porphyrin, an analogue of diphenyl ether, was prepared to determine the twist angles between the two phenyl rings. These were found to be 60" by correlating observed paramagnetic shifts with those calculated. This agrees well with MNDO studies, which gave a value of 59".

Concerning the Deactivation of Cobalt(III)‐Based Porphyrin and Salen Catalysts in Epoxide/CO2 Copolymerization

“…For a quantitative evaluation, this reduction reaction is further investigated by 1 H NMR spectroscopy, taking advantage of the readily identifiable signals of the paramagnetic TPPCo II (see the Supporting Information, Figure S3). The found marginal shift of these proton resonances, compared with the literature,8 is probably due to the presence of PO.…”

Synthesis and characterization of novel cobalt aluminum cofacial porphyrins. First crystal and molecular structure of a heterobimetallic biphenylene pillared cofacial diporphyrin

“…large paramagnetic chemical shifts for the protons on axial ligands bound to aluminum as well as those for pyrrolic NHs of the monocobalt DPA and DPB complexes (see previous paragraph) could be interpreted by a simple dipole interaction (A6 = m(1 -3 cos2 6) ft3, where A8 is the change in chemical shift of a nucleus, u is the paramagnetic moment, and (1-3 cos2 6)jrl is the corresponding geometric term) 77. …”

A case study using spectroscopy and computational modelling for Co speciation in a deep eutectic solvent

“…In general, a broadening and shift to high ppm values of all the peaks were observed, consistent with the presence of a paramagnetic complex in the two Co containing systems compared to the neat EG : ChCl (4.5 : 1). [69][70][71] All the chemical shift values of protons in the neat solvent system and the two Co containing systems are given in Table 1.…”