The study of π-π interaction in layered [3.3]orthocyclophanes. Charge- transfer complexes of [3.3]orthocyclophanes with tetracyanoethylene

Dibenzo[3.3]orthocyclophanes ([3.3]OCPs) with a bicyclo[4.4.1]undecane substructure form charge-transfer (C-T) complexes with tetracyanoethylene (TCNE). 3,4: 8,9-Dibenzobicyclo[4.4.1]undecane (9) and its 11-methylene derivative 8 are flexible molecules and take a chair-boat conformation. Complexes 8- and 9-TCNE exhibit the absorption maximum at ca. 420 nm, which coincides with the value for the TCNE complex of o-xylene. On the other hand, acetal 5, methylcarbinol 6, and dimethylmethylene derivative 7 are rigid, layered [3.31]OCPs with stacked benzene rings. Compounds 5, 6, and 7 form a 1: 1 complex with TCNE in solution. The absorption maxima of the complexes at ca. 500 nm suggest an enhanced C-T complexation due to a π-π through-space interaction in 5, 6, and 7. A 2: 1 complex of rigid [3.3]OCP 7 with TCNE crystallized from dichloromethane; while OCP 8 gave a red crystalline 2: 3 complex with TCNE. X-ray crystallographic analyses of these two complexes is given.