EPR and H-2 NMR studies on the oxidation of nickel(II) tetraphenylcarbaporphyrin to form novel organometallic nickel(III) complexes

One-electron oxidation of nickel(II) 5,10,15,20-tetraaryl-2-aza 21-carbaporphyrin ((CTPP)Ni-II)and nickel(II) 2-methyl-5,10,15,20-tetraaryl-2-aza-21-carbaporphyrin ((MeCTPP)Ni-II) resulted in formation of rare organonickel-(III) derivatives. The half-wave potential for the first oxidation of (CTPP)Ni-II and (MeCTPP)Ni-II equals 0.66 V and 0.72 V, respectively (vs SCE, CH2Cl2 solution, TBAP). The EPR spectral patterns of the one-electron-oxidized species have been determined at 293 and 77 K. In both temperatures the spectral parameters markedly depend on the axial ligand introduced by oxidants or in methathesis. In each case the spin-Hamiltonian parameters (g(av) > 2.1 (77 K) or g(iso) > 2.1 (293 K)) reveal a metal-centered oxidation rather than a cation radical formation (g(iso) approximate to 2.002). The localization of the one-electron oxidation on the nickel ion has been supported by the observation of Ni-61 hyperfine splitting. The H-2 NMR investigations, carried out for pyrrole deuterated derivatives: (CTPP-d(7))(NiBr)-Br-III, (CTPP-d(7))Ni-III(NO3), and (Me-d(3)-CTPP)(NiOH)-O-III, confirmed independently by the nickel(III) electronic structure.