Organic molecules with heavy main-group elements frequently form supramolecular links to electron-rich centres. One particular case of such interactions is halogen bonding. Most studies of this phenomenon have been concerned with either dimers or infinitely extended structures (polymers and lattices) but well-defined cyclic structures remain elusive. Here we present oligomeric aggregates of heterocycles that are linked by chalcogen-centered interactions and behave as genuine macrocyclic species. The molecules of 3-methyl-5-phenyl-1,2-tellurazole 2-oxide assemble a variety of supramolecular aggregates that includes cyclic tetramers and hexamers, as well as a helical polymer. In all these aggregates, the building blocks are connected by Te…O–N bridges. Nuclear magnetic resonance spectroscopic experiments demonstrate that the two types of annular aggregates are persistent in solution. These self-assembled structures form coordination complexes with transition-metal ions, act as fullerene receptors and host small molecules in a crystal.

meso-Tetraaryl-2,3-dihydroxychlorins (1) were converted in one step to the novel free base macrocycles meso-tetraaryl-2,3-dialkoxy-2a-oxa-2a-homoporphyrins (morpholinochlorins, 3). Their bathochromically shifted chlorin-type UV-vis spectra indicate the presence of a nonplanar chromophore. The structure of meso-tetratolyldiethoxymorpholinochlorin (3b), as determined by X-ray crystallography, was found to be largely planar, suggesting significant conformational flexibility of these macrocycles. Oxidation of diol 1 with MnO(4)(-) generates known porpholactone 4 in high yields. [reaction--see text]

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The new complex [PtMe2(BPMA)], 1, BPMA = bis(2-pyridylmethyl)amine, is shown to contain bidentate BPMA with one of the pyridyl groups not coordinated to platinum. Complex 1 reacts with HX (X = Cl, BF4) at room temperature to yield [PtHMe2(BPMA)][X], which may exist in two isomeric forms, each containing tridentate BPMA. The major initial product 2 has the hydride trans to a pyridyl group, but this equilibrates with isomer 3 in which the hydride is trans to an amine. The cationic methyl(hydrido)platinum(IV) complexes 2 and 3 are stable at room temperature for several hours, but undergo slow reductive elimination of CH4 to yield [PtMe(BPMA)][X], 4. Complex 1 reacts with DCl to give [PtDMe2(BPMA)][X], and deuterium incorporation at the methyl group trans to amine occurs slowly; the methane formed by subsequent reductive elimination is a mixture of CH4, CH3D, and CH2D2. Reaction of 1 with MeI initially yields a mixture of two compounds, [PtMe3(BPMA)][I], 5a, and a neutral compound, [PtIMe3(BPMA)], 6, but 6 isomerizes to 5 over a period of 2 h at room temperature. Reaction of 1 with CD3I gives [PtMe2(CD3)(BPMA)][I], 5a *, and [PtIMe2(CD3)(BPMA)], 6 *, with CD3 largely trans to pyridyl or iodide, respectively, but equilibration gives a mixture of 5a * and 5a **, in which CD3 is trans to amine. In contrast to the reaction with MeI, oxidative addition of CF3SO3Me to 1 gives only [PtMe3(BPMA)][CF3SO3], 5b. Reaction of 1 with allyl bromide yields a mixture of two products, [PtMe2(CH2CHCH2)(BPMA)][Br], 7, and [PtBrMe2(CH2CHCH2)(BPMA)], 8; complex 8 isomerizes rapidly to 7. Complexes 4 and 7 have been characterized by X-ray structure determinations and are shown to contain the BPMA ligands in fac and mer coordination modes.