Metalloporphyrins capped

Selected examples of rotaxanes bearing very bulky stoppers include a [2]rotaxane with fullerenes <2003AGE3158>, [2]-, [3]-, and [4]rotaxanes end-capped with dendritic moieties <1996JA12012>, as well as derivatives 142 <2000CC847>, 143 <2001NJC166>, and 144 <2003EJO3744>, which rely on axially coordinated metalloporphyrins as stoppers. 

Figure 14 Chemical structure of metalloporphyrin 37-39, and schematic representation of the end-capping of the polymer chain of 37 by 38.

The impetus for this study was threefold. First, we sought to place the Mn capped porphyrin within the general framework of metalloporphyrin electrochemistry as recently reviewed by Kadish . Second, we hoped to discover and exploit the unique reactivity of the Mn capped porphyrin afforded by the presence of the nondisplaceable steric blocking group on one side of the macrocycle. Third, we wished to explore the chemistry of high valent Mn capped porphyrin. 

Sterically unhindered nitrido Mn(V) porphyrins have been prepared by either the photochemical decomposition of the azido Mn(III) porphyrin or by treatment of either the hydroxo or acetato Mn(III) porphyrin with sodium hypochlorite and aqueous ammonia. We found that NMnC2Cap could be prepared quantitatively from (acetato)MnC2Cap by the latter route. Despite the rather basic conditions, the ester linkages holding the cap above the metalloporphyrin core were not cleaved. Presumably, this is because the reaction occurs at the interface between two immiscible phases (CH2CI2 and the aqueous ammonia/sodium hypochlorite phases). The extent of this reaction is easily monitored spectroscopically, as depicted in Figure 2. 

Redox Reactivity of Manganese "Capped Metalloporphyrins L.A. Bottomley, J.F. Luck, F.L. Neely and J.S. Quick... 

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