Multi-layer 3D chirality: new synthesis,AIE and computational studies

New synthesis of multi-layer 3 D chiral molecules has been developed under novel conditions to give better outcomes. The aggregation-induced emission(AIE), UV irradiation/excitation, charge transfer(CT) and local excited(LE) ππ* transitions have been investigated on a representative individual enantiomer of pseudo C_2 asymmetry which was made possibly by differentiating moieties on phosphorous on N-phosphonyl ring of chiral sandwich framework. Meanwhile, a new tandem C–N/C–C coupling reaction was unexpectedly rendered providing a novel access to special benzo[a]carbazoles.     

BIAN‐Fe(η6‐C6H6): Synthesis,characterization, and l‐lactide polymerization

The α‐diimine‐ligated Fe‐complex, BIAN‐Fe(C₆H₆) , was synthesized and evaluated for the polymerization of l ‐lactide. Characterization of BIAN‐Fe(C₆H₆) reveals that it is redox non‐innocent and suggests that it is an Fe(I) species bearing a radical‐anionic ligand. We will demonstrate that BIAN‐Fe(C₆H₆) is active for the ring‐opening polymerization of l ‐lactide, and that polymer is produced with, or without, the use of an added external initiator. Interestingly, very high molecular weight polymers are produced in the absence of external initiator whereas polymer molecular weights that agree with theoretical calculations are produced in the presence of external initiator. To the best of our knowledge, BIAN‐Fe(C₆H₆) is the first Fe‐based α‐diimine catalyst reported to be active for the polymerization of l ‐lactide. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2824–2830     

An efficient synthesis of 4-substituted coumarin derivatives via a palladium-catalyzed Suzuki cross-coupling reaction

An efficient Pd-catalyzed Suzuki cross-coupling reaction of sterically crowded 4-chlorocoumarin derivatives with air- and moisture-stable potassium organotrifluoroborates is developed. This methodology has been used to generate a series of novel alkyl, aryl, and vinyl substituted coumarin derivatives in good to excellent yields. The twisted conformation of the vinyl groups in the X-ray crystal structures of (2-oxo-4-vinyl-2H-chromen-3-yl)methyl acetate (2) and (2-oxo-4-vinyl-2H-chromen-3-yl)methyl 2,2,2-trichloroacetimidate (3), along with the atropisomerism of 3-(hydroxymethyl)-4-(2-methoxyphenyl)-2H-chromen-2-one (1d), are evidence of the steric crowding in these adducts.     

Mechanochemical Rhodium(III)‐ and Gold(I)‐Catalyzed C−H Bond Alkynylations of Indoles under Solventless Conditions in Mixer Mills

Mechanochemical activations in Rh^III‐ and Au^I‐catalyzed C?H alkynylations lead selectively to C₂‐ and C₃‐alkynylated indoles. The processes show excellent functional group tolerance, do not require additional heating and proceed under solventless conditions. Compared to solvent‐based standard protocols, the reaction times are shorter and the catalyst quantities lower resulting in high product yields under ambient atmosphere in mixer mills.     

Colossal Anisotropic Thermal Expansion in a Diazo-Functionalized Compound with Switchable Solid-State Behavior

Achieving substantial anisotropic thermal expansion (TE) in solid-state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material exhibits distinct and switchable TE behaviors within different temperature regions. At high temperature, two-dimensional, area zero TE and colossal, positive linear TE (α=211 MK⁻¹) are attained due to dynamic motion, while at low temperature, moderate positive TE occurs in all directions. Investigation of the solid-state motion showed the change in enthalpy and entropy are quite different in the two temperature regions and solid-state NMR experiments support motion in the solid. Cycling experiments demonstrate that the solid-state motions and TE behaviors are completely reversible. These results reveal strategies for designing significant anisotropic and switchable behaviors in solid-state materials.     

Tyrosyl rotamer interconversion rates and the fluorescence decays of N-acetyltyrosinamide and short tyrosyl peptides

It has long been recognized that the fluorescence lifetimes of amino acid residues such as tyrosine and tryptophan depend on the rotameric configuration of the aromatic side chain, but estimates of the rate of interchange of rotameric states have varied widely. We report measurements of the rotameric populations and interchange rates for tyrosine in N-acetyltyrosinamide (NATyrA), the tripeptide Tyr-Gly-Gly (YGG), and the pentapeptide Leu-enkephalin (YGGFL). The fluorescence lifetimes were analyzed to determine the rotameric interchange rates in the context of a model incorporating exchange among three rotameric states. Maximum entropy method analysis verified the presence of three fluorescence decay components for YGGFL and two for YGG and NATyrA. Rotameric exchange between the gauche(-) and trans states occurred on the nanosecond time scale, whereas exchange with the gauche(+) state occurred on a longer time scale. Good agreement was obtained with rotameric populations and exchange rates from molecular dynamics simulations. Quenching by iodide was used to vary the intrinsic fluorescence lifetimes, providing additional constraints on the determined interchange rates. The temperature dependence was measured to determine barriers to exchange of the two most populated rotamers of 3, 5, and 7 kcal/mol for NATyrA, YGG, and YGGFL, respectively.     

Inelastic neutron and low-frequency Raman scattering in a niobium-phosphate glass for Raman gain applications

We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (“boson peak”). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers.     

Methyl methylphenylphosphinate,MePh(MeO)PO complexes of the first row transition metals

Summary Methyl methylphenylphosphinate (L) complexes with 3d metal perchlorates were synthesized by interaction of L and metal salt solutions in triethyl orthoformate (61 molar ratio) and characterized by means of spectral, magnetic and conductance studies. In most cases (Mⁿ⁺ = Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ or Zn²⁺), complexes involving 41 L: metal ratios, similar to those obtained with bulky triorganophosphine oxides and neutral phosphonate or phosphate esters, were formed. These complexes contain exclusively terminal L groups and were characterized as monomeric of the types [CrL₄(OClO₃)₂](ClO₄), [ML₄(OH₂)](ClO₄)₂ (M = Mn or Ni), [ML₄(OClO₃)](ClO₄) (M = Co or Zn) and [CuL₄](ClO₄)₂. In contrast, Fe²⁺ and Fe³⁺ perchlorates formed, rather unexpectedly, complexes involving 21 L: Fe ratios. These compounds appear to be binuclear and of the type [(O₃ClO)(H₂O)₂LFeL₂FeL(OH₂)₂(OClO₃)](ClO₄)_n (n=2 for Fe²⁺; n=4 for Fe³⁺), containing both terminal and bridging coordinated L ligands. The bridging L groups in the iron complexes seem to be exclusively coordinated through the P=O oxygen, which acts as a bridging group between two adjacent Fe²⁺ or Fe³⁺ions, rather than functioning as bidentate bridging O,O-ligands, with both the P=O and methoxy oxygens involved in coordination. Spectral evidence suggests that L is a weaker ligand than triorganophosphine oxides and a stronger ligand than neutral phosphonate and phosphate esters, as anticipated.