Copper(II) complexes of inverted porphyrin and its methylated derivatives

The inverted porphyrins 2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin (CTPPH2) and its methylated derivatives 2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrin (2-NCH3CTPPH) and 2-aza-2-methvl-5,10,15,20-tetraphenyl-21-methyl-21-carbaporphyrin (2-NCH3-21-CH3CTPPH) stabilize the rare organocopper(II) complexes (CTPP)Cu-II (1), (2-NCH3CTPP)Cu-II (2), (CTPPH)(CuX)-X-II (3-X), (2-NCH3CTPPH)(CuX)-X-II (4-X) (X = Cl-, TFA), and (2-NCH3-21-CH3CTPP)(CuCl)-Cl-II (5), The EPR spectra recorded for 1, 2, 4, and 5 revealed typical features diagnostic of the copper(II) electronic structure. The superhyperfine coupling pattern indicates a presence of three nitrogen donors in the first coordination sphere. An addition of HX acid to 1 and 2 to yield the species 3-X and 4-X. The reaction mechanism includes protonation of the inner C(21) carbon accompanied by an axial coordination of anion, Methylation of (2-NCH3CTPP)Cu-II (2) with methyl iodide resulted in formation of (2-NCH3-21-CH3CTPP)(CuCl)-Cl-II (5) which implies an existence of a sigma -carbanion-copper(II) bond in 2. The H-2 NMR investigations carried out for the pyrrole deuterated derivatives (CTPP-d(7))Cu-II, (2-NCH3-21-CH3CTPP-d(7))Cu-II-Cl, and the methyl deuterated (2-NCH3-21-CD3CTPP)(CuCl)-Cl-II one confirmed independently the copper(II) electronic structure with the considerable d(x2-y2) metal orbital contribution to the SOMO. The redox properties of copper(II) inverted porphyrins were studied by the cyclic and differential pulse voltammetry. The halfwave potentials indicate a metal-centered oxidation of 1 (390 mV) and 2 (343 mV). The dimethylated homologue 5 reveals the reduction process at -224 mV attributed to the Cu-II/Cu-I transformation.