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Kinetic Studies Of The Reduction Of Platinum (Iv) Porphyrins By Amines

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Description: A series of platinum (II) and platinum (IV) porphyrins have been prepared and characterized. Addition of amines (such as piperidine) reduces the Pt(IV) porphyrins to the Pt(II) oxidation state. The kinetics of these reductions have been studied. The reaction was found to be overall second order, first order in both porphyrin and piperidine, in the initial stages, but then the kinetics became complex. The initial rate constant for Pt(IV)TPPCl(,2) was 6.73 ((+OR-) .46) x 10('-4) M('-1) sec('-1), while that for Pt(IV)OEPCl(,2) was 2.33 ((+OR-) .10) x 10('-4) M('-1) sec('-1). The free energies of activation were 21 kcal/mole, with an entropy of activation of - 30 cal/mole K. The product of the piperidine oxidation was identified as pyridine. A unique six-electron oxidation was identified as pyridine. A unique six-electron oxidation has been postulated. The intermediates tetrahydropyridine and dihydropyridine are believed to be responsible for the complex kinetic behavior observed. The proposed mechanism involves formation of a weak piperidine porphyrin ring complex followed by a direct outer-sphere two-electron transfer. Tertiary amines such as quinuclidine are also effective reductants, although the rates are much slower. The first published syntheses for AuTPPCl and AuTPPBr are also reported.
Language: English
Format: Degree Work