Palladium(II) triggered rearrangement of heptaphyrins to N confused porphyrins.
A recent surge in the chemistry of expanded porphyrins is largely due to their attractive optical, electrochemical, and coordination properties, which arise from their large p conjugated frameworks. The unique chemical reactivity of expanded porphyrins means that they often undergo metalation induced skeletal rearrangements, as metalation reactions require specific coordination structures and expanded porphyrins have flexible electronic systems that are reactive toward such structural distortions. 3] The first examples of expanded porphyrins were the octaphyrins(1.1.1.0.1.1.1.0) reported by Vogel et al. which were followed by our reports on 1) the splitting reaction of a bis(Cu octaphyrin) into two Cu porphyrins, 2) the boron(III) triggered splitting reaction of Cu heptaphyrins to Cu porphyrins and B subporphyrins, and 3) the boron(III) induced rearrangement of a hexaphyrin(1.1.1.1.1.1) to form a hexaphyrin(2.1.1.0.1.1) These skeletal rearrangements are intriguing in making "chemical connections" between important porphyrinoids such as octaphyrins, heptaphyrins, hexaphyrins, porphyrins, and subporphyrins. Despite these results, N confused porphyrins (NCPs) which have a key position in porphyrin chemistry, 5] have not been included in this approach to date. Herein, we report that an NCP type conjugated system is formed from [32]heptaphyrin(1.1.1.1.1.1.1) upon rearrangement triggered by metalation with Pd ions. meso Aryl substituted [32]heptaphyrins(1.1.1.1.1.1.1) are interesting macrocycles in terms of their flexible conformations, multiple N fusion reactions, facile formation of twisted M bius aromatic species upon protonation, formation of three coordinated Cu complexes, and oxidative ring opening to form conjugated helical molecules. We have previously reported that a M bius aromatic complex, 2, was formed in 88 yield from meso heptakis(2,6 dichlorophenyl) substituted [32]heptaphyrin 1 upon treatment with Pd(OAc)2 in CH2Cl2. [7c] Careful examination of this reaction led to an isolation of brown complex 3 as a side product in 9% yield. When the metalation reaction was carried out in acetone, the yield of 3 was improved to 22 at the expense of the yield of 2 (Scheme 1) High resolution electrospray ionization time of flight mass spectroscopy (HR ESI TOF MS) indicated the parent ion peak of 3 at m/z 1659.7423 (calcd for C77H34N7Cl14Pd [M H] 1659.7485) The structure of 3 was unambiguously determined by single crystal X ray
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