A new synthetic strategy to prepare throne and calix diastereoisomers of parallel tris-Tröger's bases

A Modular Strategy for Expanding Electron-Sink Capacity in Noncanonical Cluster Assemblies

A modular synthetic strategy is described whereby organometallic complexes exhibiting considerable electron-sink capacity may be assembled by using only a few simple molecular components. The Fe₂(PPh₂)₂(CO)₅ fragment was selected as a common electroactive component and was assembled around aromatic cores bearing one, two, or three isocyanide functional groups, with the resultant complexes possessing electron-sink capacities of two, four, and six electrons, respectively. The latter complex is noteworthy in that its electron-sink capacity was found to rival that of large multinuclear clusters (e.g., [Ni₃₂C₆(CO)₃₆]^6– and [Ni₃₈Pt₆(CO)₄₈]^6–), which are often considered as benchmarks of electron-sink behavior. Moreover, the modular assembly bearing three Fe₂(PPh₂)₂(CO)₅ fragments was observed to undergo reduction to a hexaanionic state over a potential window of about −1.4 to −2.1 V (vs Fc/Fc⁺), the relatively compressed range being attributed to potential inversions operative during the addition of the second, fourth, and sixth electrons. Such complexes may be designated noncanonical clusters because they exhibit redox properties similar to those of large multinuclear clusters yet lack the extensive network of metal–metal bonds and the condensed metallic cores that typify the latter.

By use of a modular synthetic strategy and relatively few molecular components, organometallic complexes exhibiting considerable electron-sink capacity have been characterized. Complexes bearing one, two, or three Fe₂(PPh₂)₂(CO)₅ fragments bound to aromatic isocyanide cores were found to possess electron-sink capacities of two, four, and six electrons, respectively, the latter rivaling the electron-sink capacity of large polynuclear cluster benchmarks.

Modular Construction of Porous Hydrogen-Bonded Molecular Materials from Melams

Ordered materials with predictable structures and properties can be made by a modular approach, using molecules designed to interact with neighbors and hold them in predetermined positions. Incorporating 4,6-diamino-1,3,5-triazin-2-yl (DAT) groups in modules is an effective way to direct assembly because each DAT group can form multiple N-H⋅⋅⋅N hydrogen bonds according to established patterns. We have found that modules with high densities of N(DAT)₂ groups can be made by base-induced double triazinylations of readily available amines. The resulting modules can form structures held together by remarkably large numbers of hydrogen bonds per molecule. Even simple modules with only 1-3 N(DAT)₂ groups and fewer than 70 non-hydrogen atoms can crystallize to form highly open networks in which each molecule engages in over 20 N-H⋅⋅⋅N hydrogen bonds, and more than 70 % of the volume is available for accommodating guests. In favorable cases, guests can be removed to create rigorously porous crystalline solids analogous to zeolites and metal-organic frameworks.

Bowl-shaped Tröger's bases and their recognition properties

The electron rich bowl-shaped tris-Tröger bases calix-1 and calix-2 display fluorescence quenching in presence of nitroaromatic analytes. Crystal structures show the formation of inclusion complexes.

Twisted baskets

A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)-1syn) or left ((M)-1syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)-1syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)-1syn is accomplished by its transesterification with (1R,2S,5R)-(-)-menthol in the presence of a Ti(IV) catalyst to give diastereomeric 8(P) and 8(M). It was found that dendritic-like cavitands 8(P) and 8(M), in CD2Cl2, undergo self-inclusion ((1)H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was ((1)H NMR spectroscopy) found to be greater in the case of 8(P) than 8(M). Accordingly, it is suggested that different folding characteristic of 8(P) and 8(M) ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8(P)/8(M), encompassing right- and left-handed "cups", was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8(P)/8(M).