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1. Robust, remeltable and remarkably simple to prepare biomass–sulfur composites

   https://doi.org/10.1039/d0ma00538j  

   Lauer, Moira K. ; Karunarathna, Menisha S. ; Tennyson, Andrew G. ; Smith, Rhett C. ( October 2020 , Materials Advances)

   null (Ed.)

   Lignocellulosic biomass holds a tremendous opportunity for transformation into carbon-negative materials, yet the expense of separating biomass into its cellulose and lignin components remains a primary economic barrier to biomass utilization. Herein is reported a simple procedure to convert several biomass-derived materials into robust, recyclable composites through their reaction with elemental sulfur by inverse vulcanization, a process in which olefins are crosslinked by sulfur chains. In an effort to understand the chemistry and the parameters leading to the strength of these composites, sulfur was reacted with four biomass-derivative comonomers: (1) unmodified peanut shell powder, (2) allyl peanut shells, (3) ‘mock’ allyl peanut shells (a mixture containing independently-prepared allyl cellulose and allyl lignin), or (4) peanut shells that have been defatted by extraction of peanut oil. The reactions of these materials with sulfur produce the biomass–sulfur composites PSx , APSx , mAPSx and dfPSx , respectively, where x = wt% sulfur in the monomer feed. The influence of biomass : sulfur ratio was assessed for PSx and APSx . Thermal/mechanical properties of composites were evaluated for comparison to commercial materials. Remarkably, unmodified peanut shell flour can simply be heated with elemental sulfur to produce composites having flexural/compressive strengths exceeding those of Portland cement, an effect traced to the presence of olefin-bearing peanut oil in the peanut shells. When allylated peanut shells are used in this process, a composite having twice the compressive strength of Portland cement is attained. 

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2. An η 3 ‐Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex

   https://doi.org/10.1002/anie.201916410  

   Koby, Ross F. ; Doerr, Alicia M. ; Rightmire, Nicholas R. ; Schley, Nathan D. ; Long, Brian K. ; Hanusa, Timothy P. ( June 2020 , Angewandte Chemie International Edition)

   Milling two equivalents of K[1,3‐(SiMe₃)₂C₃H₃] (=K[A′]) with MgX₂(X=Cl, Br) produces the allyl complex [K₂MgA′₄] (1). Crystals grown from toluene are of the solvated species [((η⁶‐tol)K)₂MgA′₄] ([1⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η¹) allyl ligands. When recrystallized from hexanes, the unsolvated1forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands. The C−C bond lengths differ by only 0.028 Å, indicating virtually complete electron delocalization. This is an unprecedented coordination mode for an allyl ligand bound to Mg. DFT calculations indicate that in isolation, an η³‐allyl configuration on Mg is energetically preferred over the η¹‐ (σ‐bonded) arrangement, but the Mg must be in a low coordination environment for it to be experimentally realized. Methyl methacrylate is effectively polymerized by1, with activities that are comparable to K[A′] and greater than the homometallic magnesium complex [{MgA′₂}₂].

    

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3. An η 3 ‐Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex

   https://doi.org/10.1002/ange.201916410  

   Koby, Ross F. ; Doerr, Alicia M. ; Rightmire, Nicholas R. ; Schley, Nathan D. ; Long, Brian K. ; Hanusa, Timothy P. ( June 2020 , Angewandte Chemie)

   Milling two equivalents of K[1,3‐(SiMe₃)₂C₃H₃] (=K[A′]) with MgX₂(X=Cl, Br) produces the allyl complex [K₂MgA′₄] (1). Crystals grown from toluene are of the solvated species [((η⁶‐tol)K)₂MgA′₄] ([1⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η¹) allyl ligands. When recrystallized from hexanes, the unsolvated1forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands. The C−C bond lengths differ by only 0.028 Å, indicating virtually complete electron delocalization. This is an unprecedented coordination mode for an allyl ligand bound to Mg. DFT calculations indicate that in isolation, an η³‐allyl configuration on Mg is energetically preferred over the η¹‐ (σ‐bonded) arrangement, but the Mg must be in a low coordination environment for it to be experimentally realized. Methyl methacrylate is effectively polymerized by1, with activities that are comparable to K[A′] and greater than the homometallic magnesium complex [{MgA′₂}₂].

    

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4. A Hydride Migration Mechanism for the Mo‐Catalyzed Z ‐2‐Selective Isomerization of Terminal Alkenes

   https://doi.org/10.1002/cctc.202301052  

   Jenny, Sarah_E ; Serviano, Juan_M ; Nova, Ainara ; Dobereiner, Graham_E ( November 2023 , ChemCatChem)

   The catalytic one‐bond isomerization (transposition) of 1‐alkenes is an emerging approach toZ‐2‐alkenes. Design of more selective catalysts would benefit from a mechanistic understanding of factors controllingZselectivity. We propose here a reaction pathway forcis‐Mo(CO)₄(PCy₃)(piperidine) (3), a precatalyst that shows highZselectivity for transposition of alpha olefins (e. g., 1‐octene to 2‐octene, 18 : 1Z : Eat 74 % conversion). Computational modeling of reaction pathways and isotopic labeling suggests the isomerization takes place via an allyl (1,3‐hydride shift) pathway, where oxidative addition offac‐(CO)₃Mo(PCy₃)(η²‐alkene) is followed by hydride migration from one position (cisto allyl C³carbon) to another (cisto allyl C¹carbon) via hydride/CO exchanges. Calculated barriers for the hydride migration pathway are lower than explored alternative mechanisms (e. g., change of allyl hapticity, allyl rotation). To our knowledge, this is the first study to propose such a hydride migration in alkene isomerization.

    

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5. Small Molecule Activation with Intramolecular “Inverse” Frustrated Lewis Pairs

   https://doi.org/10.1002/chem.202005143  

   Manankandayalage, Chamila ; Unruh, Daniel K. ; Krempner, Clemens ( March 2021 , Chemistry – A European Journal)

   The intramolecular “inverse” frustrated Lewis pairs (FLPs) of general formula 1‐BR₂‐2‐[(Me₂N)₂C=N]‐C₆H₄(3–6) [BR₂=BMes₂(3), BC₁₂H₈, (4), BBN (5), BBNO (6)] were synthesized and structurally characterized by multinuclear NMR spectroscopy and X‐ray analysis. These novel types of pre‐organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via anortho‐phenylene linker, are capable of activating H−H, C−H, N−H, O−H, Si−H, B−H and C=O bonds.4and5deprotonated terminal alkynes and acetylene to form the zwitterionic borates 1‐(RC≡C‐BR₂)‐2‐[(Me₂N)₂C=NH]‐C₆H₄(R=Ph, H) and reacted with ammonia, BnNH₂and pyrrolidine, to generate the FLP adducts 1‐(R₂HN→BR₂)‐2‐[(Me₂N)₂C=NH]‐C₆H₄, where the N‐H functionality is activated by intramolecular H‐bond interactions. In addition,5was found to rapidly add across the double bond of H₂CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise,5is capable of cleaving H₂, HBPin and PhSiH₃to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules.

    

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