pages The mechanism for alkyl group migration in palladium(II) benzocarbaporphyrins was investigated by synthesizing a 23-methylcarbaporphyrin and reacting it with palladium(II) acetate. It was found that palladium insertion led to methyl group migration to C21 and it is proposed that this occurs through an oxidative addition onto the palladium metal center, followed by a reductive elimination to transfer the methyl to the internal carbon. A similar rearrangement was observed when

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... porphyrin was reacted with [Rh(CO)2Cl]2 and this resulted in the formation of a rhodium(III) complex containing a three-membered rhodacycle. The syntheses of rhodium(I) and rhodium(III) derivatives of other carbaporphyrins, including 21-and 22-methylbenzocarbaporphyrins, were probed and four of these metalated complexes were characterized by X-ray crystallography. To further investigate the effect of internal substituents on porphyrinoid systems, a series of N-methylated porphyrinoids were synthesized using the versatile '3+1' variant of the MacDonald condensation. The spectroscopic data for the internally methylated derivatives were compared to their N-unsubstituted counterparts. It was found that internal alkylation greatly affects the chromophore of these systems, as is evident by bathochromic shifts and peak broadening in the UV-Vis spectra. However, the aromatic character of these systems is fully retained after the introduction of an internal substituent, and proton NMR spectroscopy shows the presence of large macrocyclic ring currents.