Effect of Porphyrin Ring Distortion on Redox Potentials of .beta.-Brominated-Pyrrole Iron(III) Tetraphenylporphyrins

Partially and fully β-brominated Mn-porphyrins in P450 biomimetic systems: Effects of the degree of bromination on electrochemical and catalytic properties

“…Within the Mn(III)(Br x TCMPP)Cl (x = 0, 6, or 8) series, a linear relationship between the Mn(III)/Mn(II) reduction potential and the number of bromine on the porphyrin macrocycle was observed, yielding a 0.05 V anodic shift per bromine added. Such a linear trend is well documented for Fe-and Co-porphyrin systems [12,32,37], and has just recently been shown to be extendable to halogenated Mn-porphyrin systems [21]. These observed anodic shifts following b-bromination can be ascribed to bulky and electron-withdrawing bromine substituents in the b-pyrrole positions of the porphyrin ring.…”

“…Synthetic manganese porphyrins are remarkably active mimics for cytochromes P450, ligninases, and superoxide dismutases (SOD) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Their catalytic efficiency in these biomimetic systems is usually related to the metal-centered reduction potential [1,3,8,[19][20][21], a property that may be conveniently tuned by the appropriate design of the porphyrin ligand.…”

“…b-Halogenated manganese porphyrins comprise the third generation of porphyrin-based catalysts and are among the most efficient catalytic systems [17]. Such efficiency is markedly dependent on both the type and the number of halogen substituents in the b-pyrrole positions of the macrocycle [8,[12][13][14][15][21][22][23]. The introduction of more than four halogens into these positions on the ring, for example, results in a pronounced decrease in the porphyrin basicity (associated with the electron-withdrawing effect of the b-halogens) and causes severe distortions on the macrocycle (steric effect) [1,[24][25][26][27][28][29][30].…”

Synthesis and characterization of eight new tetraphenylporphyrins bearing one or two ferrocenes on the β-pyrrole positions

“…It should be noted that a similar effect was obtained by the bromination or chlorination of the beta-positions of the macrocycle and attributed to the saddle-shaped conformations of the porphyrins caused by the steric repulsion between the halogens and the meso-phenyl groups. 18 The UV-visible data for all the compounds are presented in Table 1. The analysis of 1 H NMR spectra of the compounds shows that there is some influence of the porphyrin ring current on the position and shape of the ferrocene signals while the pyrrole signals are less influenced by the presence of the organometallic residue.…”

Bromination of porphyrins (Review)

“…of N-bromosuccinimide in anhydrous CCl 4 . Porphyrinates containing between one and eight substituents were obtained with the use of various methods described above [65,66].…”