Core-modified porphyrin incorporating a phenolate donor. Characterization of Pd(II), Ni(II), Zn(II), Cd(II), and Fe(III) complexes

Article abstract of DOI:10.1021/ic0345121

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)Ni^II, (TPBPO)Pd^II, and (TPBPO)Fe^IIIX containing a M-O bond. No cleavage is observed with Zn(II) and Cd(II), which form complexes (TPBPOAc)M^IICl, where M = Zn, Cd. (TPBPO)Ni^II can also be obtained from the dication of hydroxybenziporphyrin, [(TPBPOH)H ₃]Cl₂, which is prepared by acid hydrolysis of the acetoxy compound. The diamagnetic (TPBPO)Ni^II can be transformed into the paramagnetic (TPBPOAc)Ni^IICl in a reaction with acetyl chloride. X-ray structures have been determined for (TPBPO)Pd^II and (TPBPOAc)Zn^IICl. 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)Pd^II molecule. In (TPBPOAc)Zn^IICl, the metal ion weakly interacts with the phenolic fragment. The paramagnetic Fe(III) complexes, (TPBPO)Fe^IIIX, have been investigated with ¹H NMR spectroscopy. The observed spectral patterns are consistent with the presence of a high-spin Fe(III) center and π delocalization of spin density onto the phenoxide fragment. Each of the compounds (TPBPO)Fe^IIIX 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.