Norbornadiene bimolecular reactions

The Ir(bpy)2(bpy-C3)2 + complex has been used to photosensitize the conversion of norbornadiene to quadricyclene in a bimolecular process [96,97], The limiting quantum yield of the photosensitized isomerization is 0.72 and the Stern-Volmer rate constant is 1.4 x 10"8 M 1s 1. The more likely mechanism for this reaction is thought to be partial electron transfer from the excited state of the complex to norbornadiene [97],... 

The rate and the yield of the reaction shown in equation (128) depend on the nature of R and of the alkene to which the S3 unit is to be transferred. If this norbornene is also substituted in the 2-position the yields differ greatly depending on the substituent phenyl results in high, methyl in low, and methoxycarbonyl in intermediate yields. When an unsymmetrically-substituted norbornadiene is used as acceptor molecule, the two double bonds react at the same rate to give equal amounts of the two trithiolanes. Most probably, the transfer reaction proceeds by a concerted bimolecular mechanism. 

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