Pyridine ligands porphyrins

Instead of adding 4-substituted pyridine ligands trans to the carbene ligand, the complexes Os(CHR XTTP) (R = SiMe3, C02Et) add these donors to the carbene carbon atom with formation of an ylide species. This reaction is not observed for Os(CR2XTTP) with R = Ph [313c]. Nevertheless, the diphenylcar-bene or trimethylsilylmethylene osmium porphyrins crystallize as Os(CRR )-(TTP)THF with a THF molecule in trans position. 

The solid-state structure of (12) reveals that it consists of a planar, rhomboidal molecule with N-Pd-N angle of 84° and a C-l-C comer angle of 99°. Bis-pyridine ligands can be varied in numerous ways to yield a variety of diverse stractures these include macrocycles containing bis-pyridine functionalized Ceo molecules (13) and the bis-pyridine incorporated porphyrin compound (14). ... 

As for N-heterocyclic type ligands, four species namely pyridine type ligands, imidazole type ligands, porphyrin type ligands, and phthalocyanine type ligands were involved. The synthesis and structure characteristics of this type of complexes will be detailed below ... 

The iron(III) octamethylcorrole 2.136 was later studied in terms of its reactivity towards axial ligands. In this work, Licoccia, et al. determined that, like the ligand-free cobalt(III) corroles, aggregation of the macrocycles occurs in the absence of ligating base. In the presence of pyridine, on the other hand, there is evidence to support the coordination of one axial pyridine ligand. In this instance, the sixth coordination site at iron may be occupied by water. With axially coordinated pyridine, magnetic moment measurements were consistent with the iron center being in a mixed-spin state (5 = 1/2, 5/2). This behavior is similar to that seen for synthetic 5-coordinate iron(III) porphyrins wherein the metal atom is often found to be in a mixed-spin state. ... 

A mixed organic-inorganic 3D porphyrin network was obtained by cocrystallization of palladium mc n-tetrapyridylporphyrinate and cadmium nitrate. All four pyridyl units are bound to octahedral cadmium centres which are each coordinated by two nitrate, water and pyridyl ligands (Figure 7.27). One half of the py-Cd-py connections is linear, the other half bent (103°), having two cis pyridine ligands. As is common in mc o-tetraarylporphyrins,... 

Aqueous sodium hypochlorite is another low-priced oxidant. Very efficient oxidative systems were developed which contain a meso-tetraarylporphyrinato-Mn(III) complex salt as the metal catalyst and a QX as the carrier of hypochlorite from the water phase to the organic environment. These reactions are of interest also as cytochrome P-450 models. Early experiments were concerned with epoxidations of alkenes, oxidations of benzyl alcohol and benzyl ether to benzaldehyde, and chlorination of cyclohexane at room temperature or 0°C. A certain difficulty arose from the fact that the porphyrins were not really stable under the reaction conditions. Several research groups published extensively on optimization, factors governing catalytic efficiency, and stability of the catalysts. Most importantly, axial ligands on the Mn porphyrin (e.g., substituted imidazoles, 4-substituted pyridines and their N-oxides), 2 increases rates and selectivities. This can be demonstrated most impressively with pyridine ligands directly tethered to the porphyrin [72]. Secondly, 2,4- and 2,4,6-trihalo- or 3,5-di-tert-butyl-substituted tetraarylporphyrins are more... 

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