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(1H)-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.The discovery of alkali metal complexation by crown ethers 2 foreshadowed development of several other host families, 3 including podands, cryptands, 4 lariat ethers, 5 spherands, 6 cryptahemispherands, 6c and torands. 7 The examples shown in Figure 1 illustrate the general trend toward ion encapsulation and ligand rigidity for cryptands, spherands and cryptaspherands, compared with crown ethers. These structural modifications generally produce higher selectivity and stronger binding of alkali metals

Selective synthesis of U-shaped terpyridines. Versatile ligands for the preparation of platinum complexes

“…A very similar mechanism has been discussed by Bell et al, who have applied this method successfully to the synthesis of heptacyclic terpyridyl clefts. 15 Both studies let us conclude, that the large excess of ammonia present in the reaction mixture strongly favours the formation of 9 which in consequence leads to the S-shaped terpyridine 3.…”

“…Fused polypyridine compounds also constitute an effective route to preorganised clefts and cavities for the complexation of metals 14- 16 and organic guests. 17, 18 Previously, several toroidal macrocycles having potentially useful metal binding properties 15 have been synthesized. 19 Lippard's findings that (2,2Ј:6Ј,2Љ-terpyridine)-platinum() complexes bind to double-stranded DNA by intercalation have led to new approaches in cancer therapy.…”

Synthesis of Novel Functionalized Bi- and Oligopyridines

“…Upon condensation by an aldol-type mechanism, 26 was formed. An alternative mechanism via an α,β-amino enone was discussed by Bell [19] for a similar condensation reaction. The structure of 26 was elucidated by 1 H and 13 C NMR spectroscopy and mass spectrometry.…”

“…Heptacyclic terpyridyl hosts such as 22 exhibit potent complexation abilities [19] which can be attributed to enforced orientation of relatively large ligand functional group dipoles towards the center of the molecular cleft. Reduction of 22 and subsequent introduction of two oxo groups at the α-positions with help of known procedures [38] should afford a compound that is an important precursor for the preparation of dodecahydrohexaazakekulene.…”

“…The simplicity of our method makes it an alternative to known synthetic routes. [19] The reaction of 24 with 1 was also accomplished, to afford 25. All pyridine nuclei in hexacyclic 25 were synthesized in a similar fashion.…”