Alkylidene porphyrins

Diazoalkanes are u.seful is precursors to ruthenium and osmium alkylidene porphyrin complexes, and have also been investigated in iron porphyrin chemistry. In an attempt to prepare iron porphyrin carbene complexes containing an oxygen atom on the /(-carbon atom of the carbene, the reaction of the diazoketone PhC(0)C(Ni)CH3 with Fe(TpCIPP) was undertaken. A low spin, diamagnetic carbene complex formulated as Fe(TpCIPP)(=C(CH3)C(0)Ph) was identified by U V-visible and fI NMR spectroscopy and elemental analysis. Addition of CF3CO2H to this rapidly produced the protonated N-alkyl porphyrin, and Bit oxidation in the presence of sodium dithionitc gave the iron(II) N-alkyl porphyrin, both reactions evidence for Fe-to-N migration processes. ... 

We have chosen to divide the porphyrinoids into two famihes the peripherally functionalized porphyrinoids (e.g., N-confiised porphyrins, jr-extended porphyrins, oligo-porphyrins) and the coie-fimctionalized (nonplanar) por-phyrinoids (e.g., porphyrinogens, alkylidene porphyrins, oxoporphyrinogens, and some oligopyrroles). The former contains mostly molecnles that have complex elaboration at their periphery, which leads to special snpramolecular properties. Core-snbstituted porphyrinoids inclnde N-snbstituted oxoporphyrinogens and even some metalloporphyrins and porphyrin dications. 

Porphyrin rings are formed in nature by a process that is remarkably similar to that shown above. Though the sequence contains some rather unusual features, the coupling process also involves nucleophilic attack on to an alkylidene pyrrolium cation. This may be generated from the precursor porphobilinogen by elimination of ammonia. 

An interesting C-metalation of a coordinated pyrrol ligand in a rhenium complex has been described [19a]. Methylated aromatic hydrocarbons have been activated by (ZrCU) [19b], A novel mode of electrophilic activation of an aliphatic C-H bond, assisted by porphyrin complexes ofZr(IV) and achieved by the use of hydrides of lithium, sodium or potassium, has been reported [19c]. It has been shown that the ligands 2,3,5,6-tetraphenylphenoxide and 3,5-dimethyl-2,6-diphenylphenoxide undergo intramolecular activation by tantalum alkylidene groups at rates 20 and 100 times slower than that of the simple 2,6-diphenylphenoxide ligand [19d]. 

The regioselective, Jt-extended pyrrole-fused porphyrinoids 13 have been prepared via the 1,3-dipolar cycloaddition ofmeso-alkylidene(benzi)-porphyrins (14CC9277) repeated cycloadditions, followed by oxidation-reduction of these pentaporphyrins gave Jt-extended porphyrin analogs. 

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