Shortest Double-Walled Carbon Nanotubes Composed of Cycloparaphenylenes.

Invited for this month's cover is the group of Prof. Dr. Shigeru Yamago at the Kyoto University (Japan). The image shows the host-guest possibilities of cycloparaphenylenes (CPPs) of different sizes. Size selective interaction between [n]CPP and [n+5]CPP affords a host-guest complex, [n+5]CPP⊃[n]CPP, which is the shortest double-walled armchair carbon nanotube. The size-selective complex formation illustrates the importance of van der Waals interactions. A ternary complex, [15]CPP⊃[10]CPP⊃C60 , also forms from [15]CPP, [10]CPP, and C60 . Read the full text of the article at 10.1002/cplu.201700097.

Shortest Double-Walled Carbon Nanotubes Composed of Cycloparaphenylenes.

The host-guest chemistry of cycloparaphenylenes (CPPs) of different sizes is described. [n]CPPs (n=5, 6, 7, 8, and 10) selectively interact with [n+5]CPPs, forming complexes [n+5]CPP⊃[n]CPP, which are the shortest double-walled armchair carbon nanotubes. The size selectivity is dictated by the difference in diameters of the CPPs (that is, 0.34-0.35 nm), which maximizes attractive van der Waals interactions. Theoretical calculations suggest that the orbital energies of the CPPs become perturbed upon complex formation, and orbital mixing between the two CPPs is predicted for large CPP pairs. The association constants in 1,1,2,2-[D2 ]tetrachloroethane, estimated by 1 H NMR titration, are approximately 103  mol L-1 at 50 °C. Van't Hoff plot analysis reveals that complexation is driven mainly by entropy owing to desolvation of the CPPs. [13]CPP also forms a complex with [4]cyclo-2,7-pyrenylene ([4]CPY), which is a π-extended [8]CPP. Theoretical calculations suggest that the formation of [13]CPP⊃[4]CPY is more exothermic than that of [13]CPP⊃[8]CPP. A ternary complex, [15]CPP⊃[10]CPP⊃C60 , is also formed by mixing [15]CPP and [10]CPP⊃C60 .

Phosphinoselenothioic acids and their salts: synthesis, characterization, and reaction with electrophiles.

[reaction: see text] Phosphinoselenothioic acid ammonium salts were synthesized in good yields by reacting phosphinoselenothioic acid S-[2-(trimethylsilyl)ethyl] esters with ammonium fluorides. Phosphinoselenothioic acid alkali metal salts were obtained as 18-crown-6 ether complexes with high efficiency by treating the esters with alkali metal fluorides and 18-crown-6 ether. The salts were stable under air and soluble in water. The structures of the phosphinoselenothioic acid tetramethylammonium salt and P-methylseleno-P-methylthiophosphonium triflate were determined by X-ray molecular structure analyses. These salts exhibited monomeric structures, and the central phosphorus atoms adopted tetrahedral structures. Alkylation of the ammonium salts selectively gave phosphinoselenothioic acid Se-alkyl esters, whereas acylation of the salts preferentially gave S-acyl products. Protonation of the salts selectively gave the phosphinoselenothioic S-acid. The S-acid generated in situ was reacted with alpha,beta-unsaturated carbonyl compounds and cyclohexene oxide to give the adducts. Molecular orbital calculations were carried out for the model compound H2P(Se)S- to elucidate the electronic structure.