Norbomadiene isomerization, photo

This photo-isomerization reaction is referred to as a valence isomerization. It is a reaction in which electron reshuffling occurs and the nuclei move to make or break new n and ct bonds. A number of polymers were, therefore, prepared with the norbomandiene moieties either in the backbone or as pendant groups. Among them are polyesters that were synthesized with donor-acceptor norbornadiene residues in the main chain [184] by polyaddition of 5-(4-methoxyphenyl)-l,4,6,7,7-pentamethyl-2,5-norbomadiene-2,3-dicarboxylic acid or 5,6-bis(4-methoxyphenyl)-7,7- dimethyl-2,5-norbomadiene-2. 

Kawashima et al. [188] reported preparation of donor-acceptor type norbomadiene carboxylic acids compounds with carbamoyl groups, such as dipropylcarbamoyl, methylphenylcarbamoyl, propylcarbamoyl, and phenyl-carbamoyl. Benzyl esters were also prepared. Addition of these groups to polystyrenes formed polymers with pendant donor-acceptor type norbomadiene. Some were formed with 100% substitution. It was found that the polymers containing phenylcarbamoyl groups exhibit especially high photo-reactivity. In addition, the rate of the photochemical reaction in films of these norbomadiene polymers increases efficiently by an addition of 4,4 -bis(diethyl-amino)benzo-phenone photosensitizer. As a result, all the norbomadiene groups of the polymers isomerize to the... 

According to our definitions, the well studied valence isomerization of quadricyclane to norbomadiene in the presence of appropriate transition metal complexes is also regarded as a photoinduced catalytic reaction. This reaction was recently discussed by Kutal[35], [36] as photo-generated catalysis. The observed quantum yield exceeds unity (( )s = 1.6) because a chain reaction is involved. Photochemically formed [Ru(bpy)3] , e.g., initiates the chain reaction by oxidation of quadricyclane to the corresponding cation radical which acts as chain carrier. The quadricyclane cation radical undergoes an isomerization to the more stable norbomadiene cation radical. The oxidation of quadricyclane by the latter one leads to the formation of norbomadiene as the product upon regeneration of the chain carrier. 

Kamogawa, H., Goucho, S., and Nakahara, M., Synthesis and photo valence isomerization of polyamide bearing norbomadiene unit. Bull. Chem. Soc. Jpn., 65, 2306—2308, 1992. 

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