Dimensionality Expansion of a Butterfly Shaped Pd4 Framework: Constructing Edge-Sharing Pd6 Tetrahedra

The construction of well-defined transition-metal clusters has attracted substantial attention due to their unique chemical and/or physical properties. Metal clusters with 1D or 2D structures are now accessible by template-synthesis methods, in which multiple metal atoms are arranged with the aid of template molecules and their 1D or 2D structures. However, the rational synthesis of 3D clusters remains challenging, mostly due to a lack of appropriate template molecules. Herein, we report the rational synthesis of a 2D butterfly shaped Pd₄ framework ( 2 ) and 3D edge-sharing Pd₆ tetrahedra ( 5 ) by treatment of easily available organosilicon compounds with Pd(CNtBu)₂. The diphenylsilylene moiety thereby serves as the key component to generate the butterfly structure of the Pd₄ clusters in 2 . A dimensionality expansion, induced by two Cl atoms, of two butterfly shaped Pd₄ subunits supported by two diphenylsilylene moieties afforded the edge-sharing tetrahedral architecture of the Pd₆ cluster in 5 .     

Scrambling time from local perturbations of the eternal BTZ black hole

Journal of High Energy Physics - The Goldstone equivalence theorem allows one to relate scattering amplitudes of massive gauge fields to those of scalar fields in the limit of large scattering...     

α‐Propargyl amino acid‐derived optically active novel substituted polyacetylenes: Synthesis,secondary structures,and responsiveness to ions

Novel optically active substituted acetylenes HC? CCH₂CR¹(CO₂CH₃)NHR² [(S)‐/(R)‐ 1 : R¹ = H, R² = Boc, (S)‐ 2 : R¹ = CH₃, R² = Boc, (S)‐ 3 : R¹ = H, R² = Fmoc, (S)‐ 4 : R¹ = CH₃, R² = Fmoc (Boc = tert‐butoxycarbonyl, Fmoc = 9‐fluorenylmethoxycarbonyl)] were synthesized from α‐propargylglycine and α‐propargylalanine, and polymerized with a rhodium catalyst to provide the polymers with number‐average molecular weights of 2400–38,900 in good yields. Polarimetric, circular dichroism (CD), and UV–vis spectroscopic analyses indicated that poly[(S)‐ 1 ], poly[(R)‐ 1 ], and poly[(S)‐ 4 ] formed predominantly one‐handed helical structures both in polar and nonpolar solvents. Poly[(S)‐ 1a ] carrying unprotected carboxy groups was obtained by alkaline hydrolysis of poly[(S)‐ 1 ], and poly[(S)‐ 4b ] carrying unprotected amino groups was obtained by removal of Fmoc groups of poly[(S)‐ 4 ] using piperidine. Poly[(S)‐ 1a ] and poly[(S)‐ 4b ] also exhibited clear CD signals, which were different from those of the precursors, poly[(S)‐ 1 ] and poly[(S)‐ 4 ]. The solution‐state IR measurement revealed the presence of intramolecular hydrogen bonding between the carbamate groups of poly[(S)‐ 1 ] and poly[(S)‐ 1a ]. The plus CD signal of poly[(S)‐ 1a ] turned into minus one on addition of alkali hydroxides and tetrabutylammonium fluoride, accompanying the red‐shift of λ_max. The degree of λ_max shift became large as the size of cation of the additive. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Remarkable potassium selectivity of ion sensors based on supramolecular gel membranes made from low-molecular-weight gelators without any ionophore

Supramolecular gels formed by low-molecular-weight gelators bearing diamide groups were used as ion-sensing membranes for the first time. Even though no special ionophore was added to the membranes, excellent ion selectivities for K(+) over alkali metal ions were realized with the sensor systems.     

Enantiodivergent syntheses of (−)- and (+)-dysibetaine CPa and N-desmethyl analog

The first total syntheses of (−)-dysibetaine CPa and the antipode have been achieved using enantioselective solvolysis of meso-cyclic anhydride mediated by quinine derivative as an organocatalyst. The synthesis features a demonstration of an enantiodivergent organic synthesis of both enantiomers of dysibetaine CPa whereby the absolute configurations of natural product were elucidated as (3R,4R). Application of the present methodology to an enantiomerically pure novel GABA analog is also reported.     

Characterization of Highly Coordinated Allylgermanes: Pivotal Players for Enhanced Nucleophilicity and Stereoselectivity

Allylgermanes with a 4‐, 5‐, and 6‐coordinated germanium center were characterized by X‐ray crystallography. Cationic 6‐coordinated group 14 allylmetals, which were hitherto assumed to be a transition‐state structure of allylations, were successfully isolated. Forming high coordination states significantly enhanced the reactivity of the allylgermanes. In contrast to the 4‐coordinated allylgermanes with low reactivity, the highly coordinated species readily reacted with several aldehydes. Furthermore, the high coordination states exerted a significant effect on the E/Z selectivity of allylation depending on external additives. The coordination structure had a dramatic influence on the electronic and steric environments around the Ge center, enabling the geometrically controlled allylation of aldehydes.     

Macrocyclic Dinuclear Palladium Complex as a Novel Doubly Threaded [3]Rotaxane Scaffold and Its Application as a Rotaxane Cross-Linker

A dinuclear Pd^II complex possessing a cyclic ligand was developed as a novel doubly threaded [3]rotaxane scaffold and applied as a rotaxane cross-linker reagent. The dinuclear complex (PdMC)₂ was prepared by one-step macrocyclization followed by the double palladation reaction. ¹H NMR analysis and UV/Vis measurements revealed the formation of a doubly threaded pseudo[3]rotaxane by the complexation of (PdMC)₂ with 2 equivalents of 2,6-disubstituted pyridine 3 through double metal coordination. The treatment of (PdMC)₂ with 2 equivalents of 4-vinylpyridine (VP) afforded a doubly threaded [3]rotaxane cross-linker (PdMC-VP)₂ . Radical co-polymerization of VP and t-butylstyrene in the presence of (PdMC-VP)₂ afforded a stable rotaxane cross-linked polymer (RCP). An elastic RCP was also prepared by using n-butyl acrylate as a monomer. The obtained RCPs exhibited higher swelling ability and higher mechanical toughness compared with the corresponding covalent cross-linked polymers.     

Encapsulation with the Protrusion of Cruciform 9,10‐Bis(arylethynyl)anthracene Derivatives in a Self‐Assembled Boronic Ester Cavitand Capsule: Photochemical and Photophysical Properties

The self‐assembled boronic ester cavitand capsule 3 quantitatively and tightly encapsulates 2,6‐diacetoxy‐9,10‐bis(arylethynyl)anthracene derivatives 4 a – 4 c as highly fluorescent cruciform guests to form complexes 4 a @ 3 , 4 b @ 3 , and 4 c @( 3 )₂. The structural features of capsule 3 , which possesses two polar bowl‐shaped aromatic cavity ends and four large equatorial windows connected by dynamic boronic ester bonds, made it possible to encapsulate cruciform 4 with protection of the reactive anthracene core inside the capsule and with two protruding arylethynyl groups, the π‐conjugated arms of compound 4 , through two of the equatorial windows of the capsule. Thus, complexes 4 a @ 3 , 4 b @ 3 , and 4 c @( 3 )₂ show greater resistance to photochemical reactions in solution and fluorescence quenching in the powder state compared to free guests 4 . In addition to the improved photostability, restriction of the free rotation of the arylethynyl groups of guests 4 upon encapsulation results in sharpening of the UV/Vis absorption peaks with a red‐shift and a significant increase in some of the two‐photon‐absorption peaks of complexes 4 a @ 3 , 4 b @ 3 , and 4 c @( 3 )₂ compared with free guests 4 .