Late First-Row Transition-Metal Complexes of Texaphyrin

Abstract

The preparation of first-row transition-metal complexes of texaphyrin, a porphyrin-like, monoanionic penta-aza macrocyclic ligand, is reported. Specifically, the synthesis of organic-soluble Mn(II) (1), Co(II) (2), Ni(II) (3), Zn(II) (4), and Fe(III) (5) texaphyrin derivatives and their water-soluble counterparts (6-10) from appropriate metal-free, nonaromatic macrocyclic precursors is described. It was found that metal cations of sufficient reduction potential could act to oxidize the nonaromatic macrocyclic precursor in the course of metal insertion. Complexes were characterized by X-ray diffraction analysis, electrochemistry, flash photolysis, and EPR spectroscopy. The structural and electronic properties of these "expanded porphyrin" complexes are compared with those of analogous porphyrins. Notably, the texaphyrin ligand is found to support the complexation of cations in a lower valence and a higher spin state than do porphyrins. Interactions between the coordinated cation and the ligand pi system appear to contribute to the overall bonding. Texaphyrin complexes of Mn(II), Co(II), and Fe(III) in particular may possess sufficient aqueous stability to permit their use in pharmaceutical applications.

Synthetic Expanded Porphyrin Chemistry

“…In all cases, however, the transition-metal complexes of texaphyrins proved much easier to reduce than analogous metalloporphyrins, the difference being more than 500 mV in most cases. [53] Such findings are consistent Figure 11. Front (top) and side (bottom) views of the solid-state structure of 34.…”

“…(For example, the E 1/2 value for the gadolinium(iii) complex was found to be relatively substituent independent and about À294 mV versus Ag/AgCl when recorded in DMSO in the presence of 0.1m tetrabutylammonium perchlorate. [53] ) Furthermore, and perhaps more importantly, it was found that, once generated, the one-electron-reduced form of texaphyrin, Gd-Tex + C, was capable of reacting with oxygen to form superoxide in a fast, but slightly unfavorable equilibrium process [Eq. (1)].…”

Spectroscopic and electrochemical characterization of solutions and films of a new redox couple: Co(II)/Co(III) N-confused porphyrin

“…The spectrum is typical of a high spin (S = 3/2) 3d 7 Co(II) ion, similar to that reported for Co(II) texaphyrin [22] and unlike other Co(II) porphyrins which generally exist as low spin (S = 1/2) complexes [23].…”

Schiff base oligopyrrolic macrocycles as ligands for lanthanides and actinides

“…To date, texaphyrin has proved to be an excellent ligand for a number of transition metal cations [12] and for those of the trivalent lanthanide series [13]. These complexes are potentially interesting as drugs.…”