Steric Modulation of the Porphycene System by Alkyl Substituents: 9,10,19,20‐Tetraalkylporphycenes

Porphycene ( 2 ), a planar structural isomer of porphyrin ( 1 ) recognized and synthesized only recently, exhibits short N … N distances allowing exceptionally strong N‐H … N hydrogen bonds to be formed. Although the N 4 ‐coordination hole of 2 is smaller than that of 1 , the new tetrapyrrolic macrocycle is capable of complexation with a broad spectrum of metal ions to give the respective metalloporphycenes. In accord with model considerations, both N‐H … N hydrogen bonding and complexation of 2 may be modulated by peripheral alkyl groups through changes in the geometry of the porphycene skeleton arising from non‐bonded repulsions between the substituents. In this publication are delineated some of the consequences of structural variation of 2 by introduction of alkyl groups at the 9,10,19,20‐positions.