Stereoselective [2+2] photocycloaddition in bispseudosandwich complexes of bis(18-crown-6) stilbene with alkanediammonium ions

Due to hydrogen bonding, bis(18-crown-6) stilbene forms 1 : 1, 1 : 2, and 2 : 2 complexes with H(3)N(+)(CH(2))(n)NH(3)(+)2ClO(4)(-) salts (n = 2-10, 12). The length of the polymethylene chain in the diammonium ions affects the phototransformation direction of stilbene and the composition of the products. In the 2 : 2 bispseudosandwich complexes with relatively short alkanediammonium ions (n = 2-4), the stereoselective reaction of [2+2] photocycloaddition proceeds to form mainly the rctt-isomer of the cyclobutane derivative. The structure of rctt-cyclobutane derivative as a complex with H(3)N(+)(CH(2))(4)NH(3)(+)2ClO(4)(-) was confirmed by X-ray diffraction analysis.