Core-Modified Porphyrin Incorporating a Phenolate Donor. Characterization of Pd(II), Ni(II), Zn(II), Cd(II), and Fe(III) Complexes

Coordinating properties of acetoxybenziporphyrin, (TPBPOAc)H, have been investigated for a number of metal ions. Insertion of Ni, Pd, and Fe results in the cleavage of the acetoxy group leading to complexes (TPBPO)NiII, (TPBPO)PdII, and (TPBPO)FeIIIX containing a M-O bond. No cleavage is observed with Zn(II) and Cd(II), which form complexes (TPBPOAc)MIICl, where M = Zn, Cd. (TPBPO)NiII can also be obtained from the dication of hydroxybenziporphyrin, [(TPBPOH)H3]Cl2, which is prepared by acid hydrolysis of the acetoxy compound. The diamagnetic (TPBPO)NiII can be transformed into the paramagnetic (TPBPOAc)NiIICl in a reaction with acetyl chloride. X-ray structures have been determined for (TPBPO)PdII and (TPBPOAc)ZnIICl. In the palladium species, the phenolate moiety forms a strong bond to the Pd ion and an unusual interaction geometry is observed, enforced by the macrocyclic environment. Association of a TFA molecule to the phenolic oxygen does not cause significant structural changes in the (TPBPO)PdII molecule. In (TPBPOAc)ZnIICl, the metal ion weakly interacts with the phenolic fragment. The paramagnetic Fe(III) complexes, (TPBPO) FeIIIX, have been investigated with 1H NMR spectroscopy. The observed spectral patterns are consistent with the presence of a high-spin Fe(III) center and (pi) delocalization of spin density onto the phenoxide fragment. Each of the compounds (TPBPO)FeIIIX exists in solution as a mixture of two isomers, which for X = I are shown to remain in a temperature-dependent equilibrium. The observed isomerism results from two nonequivalent orientations of the axial halide with respect to the puckered macrocyclic ring.