Synthesis characterization and kinetic studies of metal porphyrazines
Mtunzi, Fanyana Moses
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The symmetrical 2,3,7,8,12,13,17,18-octakis (propyl) porphyrazine magnesium, Mg-pz1, was prepared from maleonitrile via Linstead's template cyclization. The free base, Pz1 -base and centrally metallated new compounds, M-pz1 , M = Cu(II), Co(II) were prepared by first demetallating Mg-pz1 with glacial acetic acid and then copper(II) and cobalt(II) metalions in acetic acid were inserted respectively. The N,N,N'N-tetramethylamino porphyrazine magnesmm hybrid was prepared from 2,3-dipropylmaleonitrile and 4, 7-bis(isopropyloxy)-1 ,3- iminoisoindoline. Magnesium was removed with glacial acetic acid to produce N,N,N'N-tetramethylamino porphyrazine hybrid base which was centrally metallated to give the new compounds, Cu(II)-pz2 and Co(II)-pz2 respectively. The 2,3,9,10,16,17,23,24-octa-substituted pthalocyanine was prepared from 1,2-diisocyano-4-benzyl alcohol in 1-pentanol and diazabicyclo[5.4.0]undec-7-ene (DBU) for sixteen hours. The macrocycle was then metallated to give the new compounds, Cu(II)-pc and Co(II)-pc respectively. Pioneering kinetic studies of the insertion of the metal ions, copper(II) and cobalt(II) into the centre of the macrocycles, 2,3,7,8,12,13 ,17,18-octakis (propyl) porphyrazines base, N,N,N'N' -tetramethylamino porphyrazines hybrid base, and 2,3 ,9,10,16,17,23,24-octa-substituted phthalocyanine showed that the reactions followed second order kinetics. The mechanism of insertion involved a rapid loss of magnesium, followed by a slow insertion of the metal ion. Insertion into the phthalocyanine was faster. Further pioneering study of the redox mechanism of metal porphyrazines, showed that the reduction of the copper(II) at the centre of the macrocycle followed second order kinetics. An electron tunnelling outer sphere mechanism was proposed. Just as in the case of insertion, the reduction of the Cu(II)-pc was faster than in the porphyrazines.