Pacman porphyrins

Rosenthal J, Luckett TD, Hodgkiss JM, Nocera DG. Photocatalytic oxidation of hydrocarbons by a bis-iron(III)-/i-oxo Pacman porphyrin using 02 and visible light J Am Chem Soc 2006 128 6546-6547. 

II. SYNTHESIS AND PHYSICAL PROPERTIES OF PACMAN PORPHYRIN COMPLEXES... 

Figure 2. Cofacial Pacman porphyrin complexes of interest.

Figure 16. Crystal structures of dicobalt(II) Pacman porphyrins exhibit large variabilities in metal-metal distances.

Electrochemistry and O2 Reducing Ability of Dicobalt(ll) Pacman Porphyrins... 

The overall mechanism in Fig. 19 is satisfying on several counts. First, as mentioned above, a proper stoichiometry of one proton and three electrons needed for 0—0 bond cleavage is satisfied. Second, it clearly identifies the importance of the superoxo as the resting state for catalysis, a fact long known for the O2 reduction chemistry of Pacman porphyrins (54). Finally, the mechanistic cycle... 

When earlier transition metals are used in the cofacial DPX and DPD porphyrin motifs, oxidation reactions are promoted by a metal 0x0 intermediate. As for reductive catalysis, the oxidative catalytic reactions of the Pacman porphyrins are derived from PCET. The catalase reaction (H2O2 disproportionation to give 0.5 O2 and H2O) is exemplary of this PCET reactivity as the reaction includes both 0 0 bond making and bond-breaking catalysis coupled to proton transport. 

The synthesis of diiron(lll) Pacman porphyrin constructs can be prepared in a manner similar to that shown in Schemes 2 and 3. Initial synthetic targets were centered on diiron(lll) hydroxide bisporphyrin Pacman systems for applications involving electrochemical or photochemical water oxidation via a scheme that is the reverse of those implicated for O2 reduction by dicobalt(II) bisporphyrin... 

In most cases, the nature of the spacer is the governing factor as far as optical properties are concerned. Pacman porphyrins, with rigid spacers such as anthracene and biphenylene, have received much attention due to the electro-catalytic properties of their cobalt complexes. Variations of both the dihedral angle and the distance between the porphyrm rings in these architectures have afforded examples of cofacial porphyrins linked by xanthene and dibenzofurane derivatives. Recent examples are detailed hereafter. 

Chang CJ, Loh Z, Shi C, Anson FC, Nocera DG (2004) Targeted proton delivery in the catalyzed reduction of oxygen to water by bimetallic pacman porphyrins. J Am Chem Soc 126(32) 10013-10020... 

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