engleski

Design, Synthesis, and X-ray Structural Analyses of Diamantane Diammonium Salts: Guests for Cucurbit[n]uril (CB[n]) Hosts

New bisprimary and bisquaternary diamantane-1, 6- and -4, 9-diammonium/diaminium salts were synthesized, and characterized by NMR spectroscopy and X-ray crystallography. The impetus for these syntheses were previously reported X-ray crystallographic investigations of adamantane mono- and bisquaternary ammonium ions [3, 5-diMeAda-1-NH3 or Ada-1, 3-di(NMe3)] complexed with cucurbit[n]uril (n = 7, 8). The crystal structures were analyzed with the goal to ascertain possible structural hypotheses for high binding affinity guests bound within various diameter pumpkin-shaped hosts. While Diam-4, 9-di(NMe3I) 5 could be readily prepared from the bisprimary precursor, the corresponding Diam-1, 6-di(NMe3I) 14 could not be obtained even under strong reaction conditions. Stereochemical analysis of this situation suggests very severe steric non-bonding cis-1, 3-diaxial type H…H interactions between the 'axial'-type NMe3 group and neighboring 'axial' proton neighbors. These same interactions are found in Ada-2, 6-di(NMe3I) analogues, but they are alleviated in this smaller polycyclic skeleton via tilting the axial C(methylene)—NMe3 bond away from its axial neighbors. However, similar structural relief for Diam-1, 6-di(NMe3I) is not possible, since the C(methine)—NMe3 bond therein is ligated to the diamondoid's rigid skeleton.

diamantane diamines; cucurbit[n]uril; CB[n]/diamine complexes; stereochemistry; X-ray crystallography

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