Solid-Liquid Phase Transfer Catalysis Without Solvent: Further Improvement in SNAr Reactions

Solid-liquid PTC without added solvent efficiently promotes SNAr reactions of a variety of anionic nucleophiles generated in situ. This methodology is applied with success to some examples concerning non-activated aromatic systems. TDA-1 is the most effective catalyst.     

SYNTHESIS OF TWO STABLE DIPHOSPHENES WITH A NEW STABILIZING SUBSTITUENT

Abstract

Two new diphosphenes 7 and 10 have been synthesized by action of DBU on trichlorogermylphosphines 4 and 8; this route involves the intermediate formation of chlorophosphines 5 and 9. Diphosphenes 7 and 10 are stabilized by the 2,6-bis(trifuoromethyl)phenyl group which presents both steric and electronic effects and is used for the first time in phosphorus chemistry.     

Copper-Photocatalyzed Borylation of Organic Halides under Batch and Continuous-Flow Conditions

The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (Cu^I/Cu^I*/Cu⁰) was suggested.     

Renewable Feedstocks: The Problem of Catalyst Deactivation and its Mitigation

Much research has been carried out in the last decade to convert bio‐based feedstock into fuels and chemicals. Most of the research focuses on developing active and selective catalysts, with much less attention devoted to their long‐term stability. This Review considers the main challenges in long‐term catalyst stability, discusses some fundamentals, and presents options for their mitigation. Three main challenges are discussed: catalyst fouling, catalyst poisoning, and catalyst destruction. Fouling is generally related to the deposition of insoluble components present in the feed or formed by degradation of the feed or intermediates. Poisoning is related to the deposition of electropositive contaminants (e.g. alkali and alkaline earth metals) on acid sites or of electronegative contaminants (e.g. N and S) at hydrogenation sites. Catalyst destruction results from the thermodynamic instability of most oxidic supports, solid acids/bases, and hydrogenation functions under hydrothermal conditions.     

Highly efficient metal‐free organic catalysts to design new Environmentally‐friendly starch‐based blends

A one‐step process is reported to directly synthesize blends of poly(trimethylene carbonate) (PTMC) with a modified granular starch. Trimethylene Carbonate (TMC) ring‐opening polymerization is performed in the presence of native starch particles in bulk conditions at 150 °C and the efficiency of metal‐free organic catalysts (TBD and phosphazene superbases P1‐t‐Oct, P2‐t‐bu, and P4‐t‐bu) are investigated to replace the organo‐metallic stannous octanoate initiator. TMC monomer is successively converted into PTMC and the robustness of organic catalysts is highlighted with significant activities at very low concentrations (<100 ppm), where stannous octanoate is inefficient. Reactivity of starch toward TMC ROP is deeply investigated by NMR techniques and a starch‐graft‐PTMC is indirectly evidenced. Starch substitution degree reaches 0.9% indicating that PTMC grafting only occurs at the surface of swollen granular starch. PTMC graft length from the starch surface remained low in the range 2–12 and model ROP reactions highlight the role of TMC hydrolysis on PTMC graft length. Despite low PTMC grafts, a fine dispersion of intact starch particles into the PTMC matrix is evidenced. Consequently, metal‐free organic catalysts at low concentrations are promising candidates for synthesizing blends of PTMC with high loadings of surface‐modified starch (32% by weight) in 2 min within a one‐step process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 493–503     

Biobased vinyl levulinate as styrene replacement for unsaturated polyester resins

Vinyl levulinate (VL) is used as a biobased reactive diluent in styrene (St)‐free unsaturated polyester resins (UPR). The reactivity ratios for the radical copolymerization of VL with diethyl fumarate (DEF) are determined by the Jaacks method (r_VL = 0.01 and r_DEF = 0.81 at 60 °C in DMSO‐d₆). The properties of UPRs having a stoichiometric ratio between unsaturated groups from the UPR and either St or VL are compared. Defect‐free, slightly yellow, transparent, and rigid thermosets are obtained after a mild curing cycle. Due to unfavorable reactivity ratios about 5.5 wt % of unpolymerized VL remains inside the network and acts as plasticizer. Consequently, compared with St‐based ones, VL‐based UPRs exhibit lower α relaxation (T_α = 180 and 100 °C, respectively), lower elastic moduli at the rubbery plateau (G′ = 10⁸ and 10⁷ Pa) and lower mechanical properties as measured by three points bending tests. Strain at break (ε_f = 1.8 ± 0.2%) and Charpy impact strength (～2.7 ± 0.3 kJ m^?2) are comparable independently of the RD chemical nature. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3356–3364     

Relaxation Dynamics and Magnetic Anisotropy in a Low‐Symmetry DyIII Complex

The magnetic behaviour of a Dy(LH)₃ complex (LH^? is the anion of 2‐hydroxy‐N′‐[(E)‐(2‐hydroxy‐3‐methoxyphenyl)methylidene]benzhydrazide) was analysed in depth from both theoretical and experimental points of view. Cantilever torque magnetometry indicated that the complex has Ising‐type anisotropy, and provided two possible directions for the easy axis of anisotropy due to the presence of two magnetically non‐equivalent molecules in the crystal. Ab initio calculations confirmed the strong Ising‐type anisotropy and disentangled the two possible orientations. The computed results obtained by using ab initio calculations were then used to rationalise the composite dynamic behaviour observed for both pure Dy^III phase and Y^III diluted phase, which showed two different relaxation channels in zero and non‐zero static magnetic fields. In particular, we showed that the relaxation behaviour at the higher temperature range can be correctly reproduced by using a master matrix approach, which suggests that Orbach relaxation is occurring through a second excited doublet.