Platinum(IV) tetraphenylporphyrin dibromide complexes: synthesis, characterization, and electrochemistry

Platinum(IV) porphyrins of the type [Pt-IV(p-X)(4)TPP]Br-2 where (p-X)(4)TPP is a para-substituted tetraphenylporphyrin have been synthesized by direct oxidation of their Pt(II) precursors with Br-2. Both the Pt(II) and Pt(IV) complexes have been characterized by visible and H-1 NMR spectroscopy and their electrochemical properties. In both the oxidation and reduction processes, a substituent effect is evident, and the reduction of Pt-IV-->Pt-II is identified. The oxidation and reduction potentials of the [ Pt-IV(p-X)(4)TPP] Br-2 complexes are compared to those of the [Pt-II(p-X)(4)TPP] precursors and [Pt-IV(p-X)(4)TPP]Cl-2 analogs. Addition of I-2 or I- to Pt(II) porphyrins does not result in oxidative-addition to form Pt(IV) porphyrins. Instead, the addition of I- to [Pt-IV(p-X)(4)TPP]Br-2 results in the reduction of the platinum to form the corresponding [Pt-II(p-X)(4)TPP)]. (C) 2000 Elsevier Science Ltd All rights reserved.