Metalloporphyrins unusual

M = Os) has not been established. This is very remarkable because a variety of other d6 metalloporphyrin moieties show an unusual lability at their axial coordination sites (see Sect. 3). The stability of the species [Os(OEP)L2]n (n = 0 or 1) representing the osmochrome/osmichrome system has allowed a complete physical and chemical characterization of the compounds [29a-k] listed in Table 9 and their cationic derivatives [Os(OEP)L2]PF6 (78, 80). 

Photodyncimics of metalloporphyrins have been extensively investigated on account of its importance in the understanding of photosynthesis and other processes of biological importance ( ). Particular atten-sion has been paid to the reason why the excited metalloporphyrins possess unique characteristics from the viewpoint of redox (2-4), energy transfer ( ), and other photodynamical processes (6,7). In comparison with the considerable knowledge accumulated on the photochemical properties of the lowest excited states, little has been known on the S2 - Sq fluorescence and Si Sq internal conversion processes which can also be regarded as unusual characters of metalloporphyrins. 

Only a few compounds containing Ru, Os, Rh or Ir do not possess type C. Notable are the metalloporphyrin dimers with Ru = Ru (entry 3) or Rh-In bonds (entry 34), the alkyl or acyl rhodium(III) (entries 31, 36, 38), alkyl-iridium(III) (entry 39) or arylruthenium(III) compounds (entry 12). All these species contain pentacoordinate noble metal ions, Type B. A reason for this unusual behavior of the metal ions is seen in the strong trans effect of the axial ligand L in these systems which is a strong o-donor (metalloporphyrinyl, alkyl, aryl, acyl) which precludes further coordination in the trans position of L. The reluctance of RhMe(OEP) to accept an axial ligand is shown by its crystallization as a re-dimer from n-hexane in presence of the base 1-Meim. 

With almost all of the conceivable coordination chemistry of the expanded porphyrins still left to be explored, it cannot be over-stres that the potential for new chemistry is enormous. This is i rticularly true when account is made of the fact that the chemistry of the metalloporphyrins has played a dominant role in modern inorganic chemistry. What with the possibility to enhance the stability of imusual coordination geometries (and, perhaps oxidations states) and the ability to form stable coordination complexes with a variety of unusual cations including those of the lanthanide and actinide series, the potential for new inorganic and organometallic discoveries are almost unlimited. For instance, as with the porphyrins, one may envision linear arrays of stacked expanded porphyrin macrocycles which may have unique conducting properties and/or which could display beneficial super- or semiconducting capabilities. Here, of course, the ability to coordinate not only to cations but also to anions could prove to be of tremendous utility. 

Although such a large k value is rather unusual in electron-transfer reactions of metalloporphyrins [1], the electron transfer kinetics for generation of iron(IV) por-... 

The use of metalloporphyrins which show metal-metal interactions can be an effective strategy for the synthesis of metal chain complexes. Some of these complexes exhibit high or unusual electric conductivities . Although much synthetic work has been devoted to metalloporphyrin chemistry ", only a few examples of porphyrin compounds containing metal-metal interactions have been published. Apart from the conducting polymeric porphyrins described by Ibers and Hoffman , two classes of metal-metal... 

Cullen. D. Meyer, E., Jr. Srivastava. T.S. Tsutsui. M. Unusual metalloporphyrins—Structure of product from reaction of dodecacarbonylruthenium with meso-tetra-phenylporphine—Dicarbonyltetraphenylporphinatomthe-nium (TT). J. Chem. Soc., Chem. Commun. 1972. 584-585. 

Figure 89. Molecular packing diagram of Mn[T(3, 5 -DHP)P](THF)2 CI 2THF SC6H5CH3 showing two-dimensional sheets of porphyrin linked by unusual square-planar Cl anions hydrogen bonding to four metalloporphyrins. Spheres indicate bridging chloride ions. Solvate molecules and coordinated THF ligands omitted for clarity. ...

Mansuy and coworkers [32] reported the first isolated metalloporphyrin-carbene complex in 1977 and it was an iron porphyrin carbene complex. It was suggested by the authors that iron carbene complexes could be involved in the metabohsm of xenobiotics. Thus, the five-coordinated (TPP)Fe(CCl2) was prepared as a purple red solid by treatment of (TPP)FeCl with CCI4 in the presence of an excess of iron powder (90% yield) [32]. It must be emphasized that the possible formation of carbene complexes after the reduction of iron deuteroporphyrin in CCI4 was initially proposed by Brault and coworkers [79]. An original method of reduction by aqueous sodium dithionite solution was described but, under these conditions, it was not possible to isolate any complex although the reaction leads to a compound of unusually good stability towards air. 

Tatsumi K, Hoffmann R. Metalloporphyrins with unusual geometries. 1. Mono-, di-, triatom-bridged porphyrin dimers. / Am Chem Soc 1981 103 3328-41. 

A number of porphyrins with new and/or unusual macrocycles were synthesized in the 1980s and 1990s and the redox properties of these compounds were often compared to potentials for the oxidation or reduction of analogous compounds containing the same metal ion and the well-known TPP or OEP macrocycle. Examples include, but are not limited to, highly halogenated metallopor-phyrins [27-39], metalloporphyrins with highly distorted macrocycles [37, 40-45], and metalloporphyrins linked to one or more other porphyrins or to different redox active molecules [46]. 

C. J. Carrano and M. Tsutsui. Unusual metalloporphyrins Synthesis and properties of a dimetallic boron prophyrin complex. /. Coordination Chem., 1977, 7, 125. 

Kadish KM, Davis DG, Fuhrhop JH (1972) Unusual oxidation states of metalloporphyrins octaethylporphinatosilver(lll) perchlorate. Ang Chem IntEd 11 1014—1016... 

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