title: Synthesis, structure and molecular recognition of functionalised tetraoxacalix[2]arene[2]triazines.
abstract: Functionalised dialkoxy-substituted tetraoxacalix[2]arene[2]triazine macrocycles 6 have been readily synthesised by the fragment coupling approach using methyl 3,5-dihydroxy-4-alkoxybenzoates and cyanuric chloride as the starting materials under very mild conditions. AlCl(3)-mediated deallylation and debenzylation reactions afforded the lower-rim dihydroxy-substituted tetraoxacalix[2]arene[2]triazine derivatives 11 and 13 in good yields. Although dialkoxy-substituted tetraoxacalix[2]arene[2]triazine macrocycles are fluxional in solution on the NMR spectroscopy timescale, they adopt a symmetric or slightly distorted 1,3-alternate conformation with the bridging oxygen atoms conjugated with the triazine rings. The dihydroxylated tetraoxacalix[2]arene[2]triazine 13 b, which gives a mixture of monomer and dimer in solution according to a diffusion NMR spectroscopy study, adopts a 1,3-alternate conformation and forms a cyclic tetrameric assembly in the solid state due to the formation of intermolecular hydrogen-bonding networks. This dihydroxylated macrocyclic host molecule, a hydrogen-bond donor macrocycle with a V-shaped cleft, interacts with 2,2'-bipyridine, 4,4'-bipyridine and 1,10-phenanthroline guests. Although in solution they form the corresponding 1:1 complexes with binding constants ranging from 37.7 to 213 M(-1), 2:2 host-guest complexes were observed in the crystalline state. Hydrogen-bonding interactions, along with other non-covalent interactions, such as lone-pair-electron-pi and C-H...pi interactions, were found to be the driving force for the formation of host-guest complexes.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P.R. China.
authors.forename: Qi-Qiang
authors.initials: QQ
authors.lastname: Wang
authors.forename: De-Xian
authors.initials: DX
authors.lastname: Wang
authors.forename: Hai-Bo
authors.initials: HB
authors.lastname: Yang
authors.forename: Zhi-Tang
authors.initials: ZT
authors.lastname: Huang
authors.forename: Mei-Xiang
authors.initials: MX
authors.lastname: Wang
mesh_terms: D047250:Calixarenes / Q000138:chemical synthesis* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D047028:Macrocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D014227:Triazines / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: D047028:Macrocyclic Compounds; D014227:Triazines; C532848:tetraoxacalix(2)arene(2)triazine; D047250:Calixarenes