Anion recognition by silanetriol in acetonitrile.

The anion recognition ability of 2,4,6-triisopropylphenylsilanetriol 5 has been evaluated by 1H NMR titrations in MeCN-d3. The anion recognition ability of silanetriol 5 was greater than those of the structurally related silanediols and silanemono-ol, although less effective than those of 1,3-disiloxane-1,3-diol and 1,3-disiloxane-1,1,3,3-tetraol. From the comparison of the association constants and DFT calculations, all three silanol groups of 5 cooperatively hydrogen bonded to anionic species. The catalytic ability of silanetriol 5 for the addition of indole to ß-nitrostyrene in CH2Cl2 has also been evaluated. Silanetriol 5 acts as a more effective organocatalyst than the corresponding silanediol in this reaction.

Correction: A facile and high-yield formation of dipyrrin-boronic acid dyads and triads: a light-harvesting system in the visible region based on the efficient energy transfer.

Correction for 'A facile and high-yield formation of dipyrrin-boronic acid dyads and triads: a light-harvesting system in the visible region based on the efficient energy transfer' by Masaki Yamamura et al., Org. Biomol. Chem., 2015, 13, 2574-2581.

A Hierarchical Self-Assembly System Built Up from Preorganized Tripodal Helical Metal Complexes.

The hierarchical organization strategy has realized elaborate supramolecular structures that are difficult to achieve by a one-pot thermodynamically driven self-assembly. Self-assembly via Schiff base formation of the preorganized tripodal helical unit 2(2+), which is composed of the tris(bipyridyl) ligand 1 and octahedral metal ion (Ru(II) and Fe(II)), lead to two supramolecular structures, i.e., a macrobicyclic dimer and an interlocked helicate. Notably, the interlocked helicate had a unique motif with an elongated shape (∼ 58 Å) and linearly aligned metal centers with homochiral configurations (all-Δ or all-Λ), which shows potential for allosteric regulation based on the long-range transmittance of the structural information.

Regioselective and Stereospecific Dehydrogenative Annulation Utilizing Silylium Ion-Activated Alkenes.

Treatment of dialkylbenzylsilanes (1) with trityl tetrakis(pentafluorophenyl)borate (TPFPB) afforded the corresponding silylium ions in equilibrium with their intra- or intermolecular π-complexes, which underwent dehydrogenative annulation with various alkenes to form 1,2,3,4-tetrahydro-2-silanaphthalenes (4) in up to 82% isolated yield. Sterically bulkier substituents on the silicon atom tended to increase the yield of cyclic products 4. The annulation products retained the stereochemistry in cases of the reactions using internal alkenes. The use of diisopropyl(1-naphthyl)silane (2) instead of 1 also resulted in annulation to obtain the 2,3-dihydro-1-sila-1H-phenalene derivatives 6. Electrophilic aromatic substitution at the 8-position was predominant, despite the two potentially reactive positions on the naphthyl group. The steric hindrance of the naphthyl group prevented addition of the cis-alkene to the silylium ion, which would considerably decrease yields of the desired products from 2 compared to those from 1.

A facile and high-yield formation of dipyrrin-boronic acid dyads and triads: a light-harvesting system in the visible region based on the efficient energy transfer.

Artificial light-harvesting systems, Ar,O-BODIPY dyads and triads conjugated with a light harvester, were synthesized in high yield by the reaction of an N2O2-type dipyrrin with boronic acids. Dyad 2 having a pyrene unit underwent quantitative Förster resonance energy transfer (FRET) from the antenna unit, pyrene, to the fluorophore unit, Ar,O-BODIPY. Triads 3·5 and 4·5 were quantitatively prepared by mixing pyridine-appended compounds 3 and 4 with saloph·Zn complex 5, respectively. Triad 4·5 underwent efficient FRET from the saloph·Zn complex unit to the fluorophore unit at the rate of 2.0 × 10(11) s(-1). Interestingly, the fluorescence quenching process in the excited state of the triad 3·5 took place following the energy transfer event. Thus, appropriate positioning of the energy donor and acceptor is necessary to construct a highly efficient FRET system.

Phosphorus-containing chiral molecule for fullerene recognition based on concave/convex interaction.

A C3-symmetric chiral concave molecule having a phosphorus atom at the center was synthesized, and its enantiomers were resolved. The chiral concave shape and absolute structure of the concave molecules were revealed by X-ray analysis. The concave molecule exhibited intense chiroptical properties with a large anisotropy, which was derived from molecular orbitals delocalized to the side chains. In the co-crystal with pristine C60, four of the enantiopure concave molecules perfectly wrapped the surface of C60. MALDI-TOF mass, NMR, and circular dichromism spectra also supported the concave/convex interaction between the concave molecule and fullerene. These results suggest that the phosphorus-containing molecule with a concave shape plays an important role as a chiral host molecule for C60.

Coordination-driven macrocyclization for locking of photo- and thermal cis→trans isomerization of azobenzene.

Both trans and cis isomers of azobenzene-linked bis-terpyridine ligand L1 were incorporated in rigid macrocycles linked by Fe(II) (tpy)2 (tpy: terpyridine) units. The complex of the longer trans-L1 is dinuclear [(trans-L1)2 ⋅Fe(II) 2 ], whereas the complex of the shorter cis-L1 is mononuclear [cis-L1⋅Fe(II) ]. The complex cis-L1⋅Fe(II) was not only thermally stable but also photochemically inactive. These results indicate a perfectly locked state of cis-azobenzene. The stable macrocyclic structure of cis-L1⋅Fe(II) causes locking of the isomerization. To the best of our knowledge, this is first example of dual locking of photo- and thermal isomerization of cis-azobenzene.

Red/near-infrared luminescence tuning of group-14 element complexes of dipyrrins based on a central atom.

A dipyrrin complex has been one of the most utilized fluorescent dyes, and a variety of dipyrrin complexes show intriguing functions based on the various coordination structures of the central element. We now report the synthesis, structure, and photophysical properties of germanium and stannane complexes of the N2O2-type tetradentate dipyrrin, L·Ge and L·Sn, which are heavier analogues of the previously reported dipyrrin silicon complex, L·Si. The central group-14 atoms of the monomeric complexes have geometries close to trigonal bipyramidal (TBP), in which the contribution of the square-pyramidal (SP) character becomes higher as the central atom is heavier. Interestingly, L·Sn formed a dimeric structure in the crystal. All complexes L·Si, L·Ge, and L·Sn showed a fluorescence in the red/NIR region. Fluorescence quantum yields of L·Ge and L·Sn are higher than that of L·Si. These results indicated that the central atom on the dipyrrin complexes contributes not only to the geometry difference but also to tuning the fluorescence properties.

Structural interconversion and regulation of optical properties of stable hypercoordinate dipyrrin-silicon complexes.

Novel pentacoordinate dipyrrin-silicon complexes showed efficient red or near-IR fluorescence, and the structural interconversion between silanol and siloxane derivatives resulted in significant changes in the optical properties.

Nuclearity control of a trisaloph zinc cluster complex dependent on minute structural differences in the bridging anions.

The Zn(6) cluster complex 2 of the trisaloph ligand was synthesized using EtCO(2)(-) anions as bridging ligands. Complex 2 has a dimeric structure in the crystalline state, while two monomeric isomers were in equilibrium in solution. The anion-exchange reaction successfully resulted in nuclearity control from Zn(7) to Zn(6).

Synthesis of a chiral metallo-capsule composed of concave molecules and chirogenesis upon fullerene binding.

An enantiopure molecular capsule was synthesized quantitatively using complexation of four phosphangulenes as concave molecules with four Zn2+ ions and applied to fullerene binding and chirogenesis. The capsule encapsulated selectively fullerene and its derivatives based on the size of cavity. The fullerene C60 incorporated in the capsule exhibited induced-CD signals at the transitions of C60.

Crucial role of N...Si interactions in the solid-state coloration of disilylazobenzenes.

2,2'-Bis(fluorodiphenylsilyl)azobenzenes bearing two methyl and butyl groups at the 4- and 4'-positions were synthesized, and their X-ray crystallographic analyses revealed that they have tetracoordinated and pentacoordinated silicon atoms, respectively. Although the two compounds showed almost the same spectra in solution, the reflectance spectra of the solid revealed that the pentacoordinated state had a weaker absorbance in the long-wavelength region compared with that of the tetracoordinated state, which is ascribed to the shift of the n-pi* transition. This difference in the absorptions due to the n-pi* transition drastically affects the color of the azobenzenes: the color of the pentacoordinated state becomes apparently paler than that of the tetracoordinated state.

Correction: Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties.

Correction for 'Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties' by Makoto Saikawa et al., Chem. Commun., 2016, 52, 10727-10730.

Activation of invariant natural killer T cells stimulated with microbial α-mannosyl glycolipids.

Some synthetic and bacterial glycolipids presented by CD1d specifically activate invariant NKT (iNKT) cells bearing an invariant Vα14-Jα18 (mouse) or Vα24-Jα18 (human) TCR. The antigenic glycolipids identified to date consist of two hydrophobic chains and an α-glycoside in which the 2'-OH group is in the cis orientation toward the anomeric group, namely, either an α-galactoside or an α-glucoside. Several microbial α-mannosyl glycolipids, in which the 2'-OH group is in the trans orientation, were herein examined to establish whether they have potential to activate iNKT cells. We found that α-mannnosyl1-3 (6'-O-acyl α-mannosyl)-1-1 monoacylglycerol and cholesteryl 6'-O-acyl α-mannoside, found in Saccharopolyspora and Candida albicans, respectively, induced the activation of iNKT cells, dependent on CD1d. In contrast, α-mannosyldiacylglycerol found in Streptococcus suis or α-mannosylceramide demonstrated markedly less antigenicity for iNKT cells. The potentially antigenic α-mannosyl glycolipids contributed to the protection of mice against infection with S. pneumoniae in which iNKT cells have previously been found to participate. Furthermore, these glycolipids induced the production of proinflammatory cytokines by macrophages, thereby suggesting their recognition by specific pattern recognition receptors (PRRs). Collectively, these results suggest that these microbial α-mannosyl glycolipids are capable of being recognized by both the invariant TCR and PRRs and inducing immune responses.

An efficient synthetic method for organometallic radicals: structures and properties of gold(i)-(nitronyl nitroxide)-2-ide complexes.

One-pot synthesis of (nitronyl nitroxide)-gold(i)-phosphine (NN-Au-P) complexes has been developed using chloro(tetrahydrothiophene)gold(i), phosphine ligands, nitronyl nitroxide radicals, and sodium hydroxide. The NN-Au-P complexes can be easily handled because they were quite stable under aerated conditions in both solution and crystalline states. They showed weak absorption bands with vibrational structures in the 450-650 nm region. The oxidation potentials assigned to the NN moieties of NN-Au-P complexes with aromatic phosphines were observed around -0.1 V vs. Fc/Fc+ (-0.11 V for NN-Au-1, -0.08 V for NN-Au-2, -0.13 V for NN-Au-5, and -0.07 V for NN-Au-6), somewhat lower than that of NN-Au-P complexes with aliphatic phosphines (-0.25 V for NN-Au-3 and -0.17 V for NN-Au-4).

Synthesis of Phosphorus-Centered and Chalcogen-Bridged Concave Molecules: Modulation of Bowl Geometries and Packing Structures by Changing Bridging Atoms.

A series of phosphorus-centered concave molecules having oxygen and sulfur as bridging atoms, C3v-symmetric P4 and Cs-symmetric P2 and P3, were newly synthesized. The packing diagrams of the concave molecules P1-P4 are dependent on the bridging atoms, columnar structures for P1 and P4, and zigzag structures for P2 and P3. The bowl depth becomes shallower in the order of P1, P2, P3, and P4 as the number of bridging sulfur atoms increases.

Synthesis and Chiroptical Properties of a Ring-Fused BODIPY with a Skewed Chiral π Skeleton.

A twisted chiral boron-dipyrrin complex (BODIPY) was synthesized by oxidative annulation of the biphenyl units at the ß positions. The chiral BODIPY has two asymmetric carbons in the large planar skeleton, which were generated upon the ring-fused reaction. Its π-elongated and twisted structure resulted in the Cotton effect in the red region (λmax = 614 nm, Δε = 60 M(-1)·cm(-1)) as well as the strong fluorescence (ΦF = 0.73) and circularly polarized luminescence (CPL).

Chiroptical switching caused by crystalline/liquid crystalline phase transition of a chiral bowl-shaped molecule.

The liquid crystal of a chiral bowl-shaped molecule having a central-phosphorus atom and long alkyl chains was developed. The DSC and XRD analyses suggested the formation of columnar liquid crystals of both the enantiopure and racemic compounds. The condensed phase of the enantiopure compound in a thin film exhibited a significant signal in CD spectra, which was switched by a reversible phase transition between the crystalline and liquid crystalline states.

Synthesis of a new family of ionophores based on aluminum-dipyrrin complexes (ALDIPYs) and their strong recognition of alkaline earth ions.

Mononuclear and dinuclear aluminum-dipyrrin complexes (ALDIPYs) were synthesized as a new family of ionophores. They exhibited colorimetric and fluorometric responses to alkaline earth ions in an aqueous mixed solvent. The strong recognition was achieved via multipoint interactions with the oxygen atoms appropriately incorporated into the ligand framework.

Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties.

A macrocyclic bisBODIPY (bis(boron-dipyrromethene)) complex [1B2] with a figure-of-eight helicity was synthesized and successfully resolved. [1B2] was proven to be one of the most efficient red-emitting CPL (circularly polarized luminescence) fluorophores reported to date (λ = 663 nm, |glum| = 9 × 10(-3), ΦF = 0.58).