Aluminum porphyrins, reactivity

Although photochemically induced cleavage of Al—C bonds in the aluminum porphyrin complexes has been exploited in several applications, relatively little is known about the intimate mechanism of this process. Similar reactivity is observed for the organo-gallium and indium porphyrins, and for these elements... 

Aluminum-porphyrin complex lb with an alkoxide ligand also demonstrates the same reactivity as la in the presence of only 0.1 mol.% of 2a. The polymerization rate with lb/2a catalyst system is dependent on the concentration of 2a in the range from 0.025 to 2.5 mol.%, the increase of 2a results in more rapid polymerization. On the other hand, molecular weight and the number of polymer chains are independent of the molar ratio of 2a to... 

In order to enhance the reactivity of aluminum porphyrins (J ) especially towards C02 in the copolymerization with epoxide (Equation 4), the effect of addition of an amine or phosphine as a possible sixth ligand to the aluminum porphyrin was examined. The enhancement in reactivity by the addition of a tertiary amine such as N-methyl-imldazole was actually observed for the epoxlde-C02 reaction. The product, however, was a cyclic carbonate (JO), not a linear copolymer. On the other hand, J he addition of trlphenylphosphlne was very effective in the formation of an alternating copolymer from epoxide and... 

Inoue et al. have developed photochemical carboxylation of ketones by the virtue of photo-enhanced nucleophilic reactivities of aluminum porphyrin complexes. Treatment of [(TPP)AlNEt2l with aromatic ketones produces the corresponding porphinatoaluminum enolate products,... 

As already described, aluminum complexes of tetra-azaannulene (9) and phthalocyanine (10) have much lower reactivities than aluminum porphyrins for the polymerization of epoxides (11). However, in the presence of appropriate Lewis acids such as 44 or 45, the polymerizations with these initiators take place rapidly to give polyethers with fairly narrow MWD. ... 

The nature of the porphyrin ring may influence reactions which are photoactivated or sensitized by visible light. Although electron transfer from metalloporphyrins to other substrates has been widely studied, examples for activation of the ligand bound to the metal upon irradiation have been very limited. The reactivity of o-bonded aluminum and indium porphyrins towards carbon dioxide has been studied. 

Table 4. Selected H NMR Data for Reactive Ends of Living Polymers with Aluminum and Zinc Porphyrins in CDCI3 at Room Temperature...

The covalent nature of the aluminum-X bond suggests that polymerization occurs following a coordination process. This hypothesis is reinforced by the exclusive presence of regular head-to-tail enchainments ° and tactidty which is dependent on porphyrin stmcture. ° Indeed the substituents in ortho positions of peripheral phenyl groups affect the reactivity of the Al-X bond polar groups lead to a very high initiation activity, whereas nonpolar substituents result in an opposite effect. 

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