Lone pair porphyrin

Whereas in porphyrins, chlorins and bacteriochlorins the 1871-aromatic perimeter includes two nitrogens excluding their lone pairs, the.1871 perimeter of the isobacteriochlorin includes three nitrogens, one with its electron lone pair as part of the aromatic perimeter. The electron pair of the /J,/J -C —C double bond of ring D of isobacteriochlorin is not involved in the cyclic conjugation path. 

A review has appeared on the synthesis of enantiomerically enriched aziridines by the addition of nitrenes to alkenes and of carbenes to imines.45 A study of the metal-catalysed aziridination of imines by ethyl diazoacetate found that main group complexes, early and late transition metal complexes, and rare-earth metal complexes can catalyse the reaction.46 The proposed mechanism did not involve carbene intermediates, the role of the metal being as a Lewis acid to complex the imine lone pair. Ruthenium porphyrins were found to be efficient catalysts for the cyclopropana-tion of styrenes 47 High diastereoselectivities in favour of the /ifr-product were seen but the use of chiral porphyrins gave only low ees. 

Delocalization of the chromophore is as indicated in XVII. Porphyrins and porphinoids closely resemble the 18-membered 18 7t-electron [18]an-nulenes, avoiding energetically unfavorable conjugation via pyrrolic nitrogen lone pairs. If interactions of this type are necessary for structural reasons [as in... 

The hole in the middle of a porphyrin is just the right size to take a divalent transition metal in the first transition series, and zinc porphyrins, for example, are stable compounds. Once the metal is inside a porphyrin, it is very difficult to get out. Two of the nitrogen atoms form normal covalent bonces (the ones that were NH in the porphyrin) and the other two donate their lone pairs to make four ligands around the metal. The complexed zinc atom is square planar and still has two vacant sites—-above and below the (more or less) flat ring. These can be filled with water molecules, ammonia, or other ligands. 

In the synthetic iron porphyrin, O2 affinity mainly depends on the strengths of the <7-donation from the lone pair of O2 to the heme-iron dz orbital and 7r-back donation from the d/r orbital on the iron to the Jt orbital of 2. To evaluate the O2 affinity and/or O2 binding dynamics in myoglobin and hemoglobin, O2 - protein interaction is a further important factor. For example, the O2 dissociation rate constant for oxymyoglobin is relatively smaller than those of O2 complexes... 

The lone-pair electrons on the pyrrole nitrogen of the porphyrin ring are more accessible to chelation of metal ions in the ring-strained conformation and leads to metalation of mesoporphyrin IX. Antibody 7G12 catalyzes the incorportain of Zn +, Cn +, Co, and Mn into mesoporphyrin IX, whereas ferrochetalase uses Fe, ZrP , and Ni as substrates in... 

One final example of a miscellaneous expanded porphyrin is the 24-mem-bered tetraphosphole macrocycle 4.213 reported by Mathey and coworkers in 1995. It was synthesized in 60% yield from the Wittig-type reaction between the phenyl-substituted 5,5 -bis(formyl)-2,2 -biphosphole 4.211 and the o-xylylidene bis-ylid 4.212 (Scheme 4.6.7). A single crystal X-ray structural analysis carried out on 4.213 revealed an aW-trans orientation of the four phosphorus lone pairs, and a macrocyclic diameter of ca. 6 A (Figure 4.6.4). Because of the steric influence of the phenyl substituents, macrocycle 4.213 is decidedly non-planar. Nevertheless, this macrocycle is expected to exhibit a rich coordination chemistry, particularly towards soft, heavy transition elements. Unfortunately, no such putative metal complexes have as yet been described in the literature. 

The direct labelling of TOPO capped semiconductor CdSe or CdSe/ZnS QDs with tetra-pyridyl substituted porphyrin (Fig. 1). Here P is based on the coordination of the pyridyl N lone pair with Zn or Cd atoms on the surface of QD. 

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