Uranyl-containing macrocycles

A variety of substituted uranyl superphthalocyanine complexes, such as the more soluble methyl 161 and butyl 162 substituted systems [118, 17] can be obtained from the general condensation reaction (Scheme 22). However, when the condensation reaction was carried out using 1,2-dicyanobenKnes with electron withdrawing substituents, or those which impose a greater steric congestion, no five subunit-containing macrocyclic products could be detected. 

With the original reports of the successM synthe of the sapphyrins [26,66,152] and uranyl superphthalocyanine [112, 118, 119], interest in other expanded porphyrin systems, was kindled. The next logical step (after sapphyrin), in the expanding series of all-pyrrole systems, was the pentaphyrin macrocycle 231 which contains five pyrroles and five meso-like methine bridgra. In 1983 Gossauer et al. reported the synthesis of the first prototypical member 231 of this macrocyclic family [158, 182, 183, 185-187]. This first synthesis was achieved by a 2 + 3 MacDonald-type condensation between an oc-firee dipyrromethane 233 and a tripyrrane dialdehyde 236. More recently, the synthesis of pentaphyrin 231 has l n achieve by using a dipyrromethane 5,5 -dicarboxylic acid 235 in place of an a-firee dipyrromethane [21]. Here, as is the case in many of these kind of reactions [21,26,27,66,155], decarboxylation occurs under the reaction conditions to produce the corresponding a-free species 233 in situ. (Scheme 40) [21]. 

The known uranium-macrocycle complexes of metal-templated origin are listed in table 22 all contain the trans-dioxouraniumCVI) ion, (uranyl), as the metal... 

The synthesis of metallocycles that contain an immobilized uranyl cation follows the route depicted in Scheme 1 [ref 8 and 14]. The appropiate dialdehyde and diamine undeigo a Ba -templated macrocyclization in methanol. Upon reaction with uranyl acetate the barium salt is eliminated. The cavity thus created can be occupied by small neutral molecules, which can coordinate to the uranyl cation. The uranyl cation provides a fifth coordination site in the equatorial plane. This planar coordination environment offers the possibility to complex neutral molecules, instead of doing reactions at the activated or reduced transition metal cation. Usually, the complexes are obtained with a water molecule filling the cavity. By introducing ffnent guest molecules that can coordinate to the electrophilic center it is possible to replace the water. 

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