A general strategy is reported for the facile preparation of diamino-derivatized PNP-crowns, giving access to a large range of new host molecules of different sizes, shapes, and topology. Reactions of the tetrachloro-PNP-crown precursor 1 with polymethylene-diamines 2a-h (n ) 2-6, 8, 10, 12) proceed rapidly and regioselectively via substitution reactions of Cl at the PNP-crown-forming P-atoms; the reaction is assisted by the macrocyclic 1,3-oxy(tetraethylenoxy) substituent at the N 3 P 3 ring which provides a site for the hydrogen-bond-driven assembly of reagents 1 and 2. The products belong to three different classes of polytopic receptors: lateral macrobicycles (ansa, 5ah), bola-amphiphilic tritopic bis-crowns (bino, 6a-h), and tetratopic cylindrical macrotricycles (bisbino, 8a-h). The structures of 5, 6, 8, and 10b were established by MS and 31 P NMR spectroscopy, and an X-ray crystal structure was obtained for the bis-bino 1,3-diaminopropane PNP-crown derivative 8b. Preliminary screening by a simple TLC test of the metal-cation complexing properties of the series of compounds 5, 6, and 8 revealed their capacity to bind both harder (alkali and alkaline earth) and softer (transition) metal cations, with significant affinity being displayed toward potassium and silver cations by many of the ligands studied.
31P NMR spectroscopy and added chiral shift reagent (CSR) or chiral solvating agent (CSA) have been used to show that unsymmetrically substituted singly bridged macrocyclic phosphazene compounds exist as 1:1 diastereoisomers of two racemic mixtures, in contrast to previous work (ref 2) on symmetrically substituted diastereoisomeric analogues, which exist as meso and racemic forms. The cis-ansa cyclotriphosphazatriene-macrocycle, 1, is meso and monosubstitution of the >P(O-macrocycle)Cl group with 2-naphthol gives a racemic product (7), in which the macrocyclic ring exists in a trans-ansa configuration. Reaction of 7 with the di-secondary amine, piperazine, gives an unsymmetrically disubstituted racemic compound (8) having a cis-ansa configuration of the macrocyclic ring. Reaction of 8 with a further quantity of 1 forms a singly bridged derivative (9) with the macrocyclic rings in cis-trans configurations, and further reaction of 9 with pyrrolidine gives compound 10 with the macrocyclic rings in cis-cis configurations. Both 9 and 10 have four stereogenic centers giving rise to diastereoisomeric compounds existing as mixtures of two racemates. The results are consistent with inversion of configuration at phosphorus at each step of the reaction of >P(OR)Cl groups with nucleophile Z (i.e., Z = naphthoxy, piperazino, pyrrolidino) to form >P(OR)Z derivatives.
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