Non-planar porphyrins with mixed substituent pattern: bromination and formylation of ethyl-substituted tetraphenylporphyrins and tetraalkylporphyrins

A series of 5,10,15,20-tetraphenylporphyrins (TPPs) bearing different numbe rs and orientations of P-ethyl substituents have been used for studies on t he functionalization of non-planar porphyrins. Attempts to monofunctionaliz e the diethyl-TPP via monobromination failed and resulted in the isolation of two different regioisomers. All ethyl-TPPs were easily converted into th e perbrominated porphyrins bearing twelve peripheral substituents but with different numbers of beta-bromo and -ethyl groups. These porphyrins are int eresting precursors for further mixing of the substituent pattern and are n ovel push-pull porphyrins bearing electron donating and withdrawing groups in a defined pattern directly on the ring system. They have a similar degre e of overall conformational distortion, however each with considerably alte red electronic effects due to the different number of bromine atoms. In ord er to gain access to monofunctionalized derivatives, some of the ethyl-TPPs were converted into the monoformyl derivatives. In a similar manner, a num ber of 5,10,15,20-tetraalkylporphyrins were formylated, albeit in lower yie lds than the ethyl-TPPs. Several compounds were investigated in detail by s ingle crystal X-ray crystallography and allowed a comparison of the influen ce of different substituent patterns on the conformation. The structural an alyses include a comparison of different crystalline modifications for some compounds. Structural data for perbrominated ethyl-TPPs present the first examples of highly non-planar, dodecasubstituted porphyrins bearing two dif ferent types of beta-substituents.