Metalloporphyrins, polymer-bound

In this chapter, the specific and reversible bindings of small molecules with metal complexes in macromolecules are described using the examples of silver-polymer complexes and metalloporphyrins coordinatively bound in macromolecules. Next, their structures are characterized, followed by potential applications such as gas-separation membranes and gas-carrying materials. 

Applications of esr spectroscopy for monitoring the degree of functionalization of a polymer are limited, primarily because esr-active groups are mostly used as probes rather than as reactive functionalities. Electron spin resonance spectroscopy has, however, been used to estimate the proximity of titanium groups in a titanocene polymer (Grubbs, et al., 1973 Bonds et al., 1975). It has also been used to demonstrate the presence of copper prophyrins in polymer-bound metalloporphyrins (Rollmann, 1975). 

Tetra(4-pyridyl) porphyrin (TPyP) metalloligands also were explored as potential MOF constituents. It is of more than passing interest that TPyPs are often capable of self-association via bonding of the pyridyl nitrogens to the coordina-tively unsaturated central metal of another porphyrin molecule. Several research groups have made an active study of such stmctures (111-117). However, because these coordination polymers tend to be formed from a single molecular component, rather than having the metalloporphyrin bound to a secondary metal center or SBU, they will be omitted from further discussion here. 

The use of a synthetic model system has provided valuable mechanistic insights into the molecular catalytic mechanism of P-450. Groves et al. [34]. were the first to report cytochrome P-450-type activity in a model system comprising iron meso-tetraphenylporphyrin chloride [(TPP)FeCl] and iodosylbenzene (PhIO) as an oxidant which can oxidize the Fe porphyrin directly to [(TPP)Fe =0] + in a shunt pathway. Thus, (TPP)FeCl and other metalloporphyrins can catalyze the monooxygenation of a variety of substrates by PhIO [35-40], hypochlorite salts [41, 42], p-cyano-A, A -dimethylanihne A -oxide [43-46], percarboxylic acids [47-50] and hydroperoxides [51, 52]. Catalytic activity was, however, rapidly reduced because of the destruction of the metalloporphyrin during the catalytic cycle [34-52]. When (TPP)FeCl was immobilized on the surface of silica or silica-alumina, catalytic reactivity and catalytic lifetime both increased significantly [53]. There have been several reports of supported catalysts based on such metalloporphyrins adsorbed or covalently bound to polymers [54-56]. Catalyst lifetime was also significantly improved by use of iron porphyrins such as mew-tetramesitylporphyrin chloride [(TMP)FeCl] and iron mcA o-tetrakis(2,3,4,5,6-pentafluorophenyl)por-phyrin chloride [(TPFPP)FeCl], which resist oxidative destruction, because of steric and electronic effects and thereby act as efficient catalysts of P-450 type reactions [57-65]. 

The metalloporphyrin-bound oxygen is photodissociated under flash irradiation [Eq. (8)], and the rapid oxygen-binding reaction can be analyzed. Photodissection and recombination of the bound oxygen from and to the cobalt-porphyrin in the solid polymer membrane was observed by improving pulse and laser flash spectroscopic techniques [2,29]. 

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