Porphyrins macrocycles

Other anionic nitrogen-containing ligands which have been examined in the search for new non-metallocene catalysts include macrocyclic porphyrins and tetraazaannulenes. However, activities with these catalysts are low. 

Planar (closed) macrocycles porphyrins, corrins and phthalocyanines 770... 

According to a recently proposed definition, expanded porphyrins possess more than 16 atoms in the inner or, more precisely, smallest circuit of the macrocycle (porphyrin 1 contains exactly 16 atoms in the smallest macrocyclic circuit) [11], In addition to porphyrinoid macrocycles traditionally recognized as expanded, i.e., possessing more than four cyclic subunits or more than four meso bridges, this new definition encompasses some other systems, such as p-benziporphyrin 150. Regardless of the exact definition, expanded porphyrins constitute an unusually rich and diverse family of structures, and have been the subject of several excellent reviews [2, 5, 11, 146], The relationship between aromaticity and tautomerism in... 

The fact that vanadyl tetraphenylporphine was less reactive is not inconsistent with this rationalization although in this instance all four methine carbons have phenyl substituents. It is likely that the formation of the mono-substituted carbonium ion would be inhibited because of steric interactions at the methine position involved. However, a more important consideration is that the benzene ring attached to the methine carbon is not coplanar with the macrocyclic porphyrin ring. The extent of deviation from planarity is enough that a positive charge generated on the methine carbon would receive no resonance stabilization but considerable inductive destabilization as a consequence of the unsaturated substituent. 

This section includes selected examples of electrochemistry of gold and silver complexes with other ligands and structural types that were not included in previous sections. We have also included a list of references divided into the following areas that can be consulted for additional information sulfur- and nitrogen-containing macrocycles , porphyrins " and clusters . 

Fig. 4 A dynamic combinatorial library of cyclic and linear arrays of mixed metallopoi-phyrins which, upon addition of a 4.4 -dipyridine guest, transforms quantitatively into a macrocyclic porphyrin tetramer. (Adapted from Ref. [1 1].) View this art in color at WWW. dekker. com.)...

Metal-mediated cross-coupling reactions involving mcw-haloporphyrins enable the fabrication of porphyrin arrays that exhibit exceptional electronic interactions between their constituent porphyrinic building blocks. Because mew-halopor-phyrins derive from direct halogenation of the porphyrinic aromatic macrocycle, porphyrins bearing unsubstituted meso positions are important synthetic precursors to these supramolecular, multichromophoric systems. 

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