Molecular Architecture. 2.¹Synthesis and Metal Complexation of Heptacyclic Terpyridyl Molecular Clefts

Abstract

Methods are described for the synthesis of a series of functionalized derivatives of 9-butyl-1,2,3,4,5,6,7,8-octahydroacridine ( 9 ), a building block for several types of highly preorganized host compounds. A key intermediate is 5-benzylidene-9-butyl-2,3,5,6,7,8-hexahydroacridin-4(1 H )-one ( 23 ), which can also be used in the syntheses of torands and hydrogen-bonding hexagonal lattice receptors. A tridentate cleft ( 20 ), consisting of 2,2‘;6‘,2‘‘-terpyridine imbedded in a heptacyclic framework, and a corresponding pentadentate diketone ( 6 ) were synthesized from 9 in five and seven steps, respectively. The picrate extraction method was used to estimate the solution stabilities of alkali metal complexes of heptacyclic terpyridyls 6 and 20, which was also compared with a flexible terpyridyl ( 37 ). Alkali metal complexes of both heptacyclic terpyridyls showed relatively high K s values, but low size selectivity. Pentadentate host 6 binds Na + and K + more strongly than do most hexadentate crown ethers; flexible tridentate analogue 37 failed to extract alkali metal picrates into chloroform. The complexation abilities of 6 and 20 are attributed to enforced orientation of functional group dipoles toward the center of the molecular cleft. Sodium and potassium picrate complexes of pentadentate cleft 6 were synthesized (1:1 stoichiometry), and a 2:1 complex of calcium triflate ( 6 2 ·Ca(CF 3 SO 3 ) 2 ) was also prepared.