Reactions of [2,]cyclophanes (N = 2,. . .6) with solvated electrons in 1,2-dimethoxyethane at 193 K have been studied by ESR. and ENDOR. spectroscopy. All but the two most highly bridged cyclophanes ( N = 5 and 6) are reduced to paramagnetic species under these conditions. Whereas the radical anions of [2.2]paracyclophane and p3] (1,2,4)-and p4] (1,2,4,5)cyclophanes are sufficiently persistent to be characterized by their hyperfine data, those of the remaining five cyclophanes undergo a rapid cyclization to the radical anions of4,5,9,10-tetrahydropyrenes. These have been identified as the unsubstituted tetrahydropyrene (from [2.2]metacyclophane and [23] (1,2,3)cyclophane), the 2,7-dimethyl-derivative (from [2,] (1,3,5)-and p4] (1,2,3,5)cyclophanes) and the 1,8-dimethyl-derivative (from [24] (1,2,3,4)cyclophane). The persistence of the cyclophane radical anions seems to depend on the numbers, nmeta and npa,a, of the meta-and para-positions of the bridging ethano groups in the two benzene rings. The prerequisite for the radical anion to be persistent is nmeta 6 npara.
Introduction. -In the last few years, all multiply bridged [2N]cyclophanes have been prepared [ 11. Their formulae are given below, along with a short-hand notation N ( ,ul,...,uN), where N stands for the number of ethano bridges, and ,ul,...pN specify the bridged centres of the benzene rings [2]. [2.2]Meta-and paracyclophanes, 2 (1,3) and 2 (1,4), respectively, are included in the series, but 2 (1,2) is not, since this dibenzo-1,5-cyclooctadiene can hardly be considered as [2.2]orthocyclophane. For the two highest homologues with five and six ethano bridges, the notations 5 (1,3,5) and 6 (1,3,5, have been abbreviated to 5 and 6.
The present paper gives a comprehensive account of the primary and secondary radical anions which are obtained upon reaction of [2,]cyclophanes with solvated 49 0018-019X/82/5/1391-07$01.00/0 *) Whereas formation of a C,C-bond between the two benzene rings requires an elimination of two H-atoms, conversion of the two methylene groups into methyl substituents implies an acquisition of two such atoms.