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1. Diverse bimetallic mechanisms emerging from transition metal Lewis acid/base pairs: development of co-catalysis with metal carbenes and metal carbonyl anions

   https://doi.org/10.1039/C7CC09675E  

   Mankad, Neal P. (January 2018, Chemical Communications)

   The rational development of catalytic reactions involving cooperative behavior between two catalytic reactive sites represents a frontier area of research from which novel reactivity and selectivity patterns emerge. Within this context, this Feature highlights the development of a cooperative system involving transition metal Lewis acid/base pairs. Bimetallic systems consisting of copper carbene Lewis acids and metal carbonyl anion Lewis bases, (NHC)Cu–[M CO ], are easily synthesized from readily available organometallic building blocks (NHC = N-heterocyclic carbene; [M CO ] − = metal carbonyl anion, e.g. [FeCp(CO) 2 ] − , [Mn(CO) 5 ] − , etc. ). Stoichiometric reactivity studies indicate that the dative Cu←M bonds in these systems are labile towards heterolysis under mild conditions, thus providing in situ access both to polar metal–metal bonds and to “frustrated” transition metal Lewis acid/base pairs as dictated by reaction conditions. Catalytic transformations ranging from C–C and C–B coupling reactions to hydrogenation and other reductions have been developed from both manifolds: bimetallic catalysis involving (a) binuclear intermediates engaging in cooperative bond activation and formation, and (b) orthogonal mononuclear intermediates that operate in either tandem or co-dependent manners. Preliminary indications point to the future emergence of novel reactivity and selectivity patterns as these new motifs undergo continued development, and additionally demonstrate that the relative matching of two reactive sites provides a method for controlling catalytic behavior. Collectively, these results highlight the fundamental importance of exploring unconventional catalytic paradigms. 

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2. Catalytic reduction of aryl trialkylammonium salts to aryl silanes and arenes

   https://doi.org/10.1039/c9sc01083a  

   Rand, Alexander W.; Montgomery, John (January 2019, Chemical Science)

   A new approach for the reduction of aryl ammonium salts to arenes or aryl silanes using nickel catalysis is reported. This method displays excellent ligand-controlled selectivity based on the N-heterocyclic carbene (NHC) ligand employed. Utilizing a large NHC in non-polar solvents generates aryl silanes, while small NHCs in polar solvents promote reduction to arenes. Several classes of aryl silanes can be accessed from simple aniline building blocks, including those useful for cross-couplings, oxidations, and halogenations. The reaction conditions are mild, functional group tolerant, and provide efficient access to a variety of benzene derivatives. 

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3. Frustrated self-assembly of non-Euclidean crystals of nanoparticles

   https://doi.org/10.1038/s41467-021-25139-9  

   Serafin, Francesco; Lu, Jun; Kotov, Nicholas; Sun, Kai; Mao, Xiaoming (August 2021, Nature Communications)

   Abstract Self-organized complex structures in nature, e.g., viral capsids, hierarchical biopolymers, and bacterial flagella, offer efficiency, adaptability, robustness, and multi-functionality. Can we program the self-assembly of three-dimensional (3D) complex structures using simple building blocks, and reach similar or higher level of sophistication in engineered materials? Here we present an analytic theory for the self-assembly of polyhedral nanoparticles (NPs) based on their crystal structures in non-Euclidean space. We show that the unavoidable geometrical frustration of these particle shapes, combined with competing attractive and repulsive interparticle interactions, lead to controllable self-assembly of structures of complex order. Applying this theory to tetrahedral NPs, we find high-yield and enantiopure self-assembly of helicoidal ribbons, exhibiting qualitative agreement with experimental observations. We expect that this theory will offer a general framework for the self-assembly of simple polyhedral building blocks into rich complex morphologies with new material capabilities such as tunable optical activity, essential for multiple emerging technologies. 

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4. Ruthenium(0)-sequential catalysis for the synthesis of sterically hindered amines by C–H arylation/hydrosilylation

   https://doi.org/10.1039/c9cc04072b  

   Zhao, Qun; Zhang, Jin; Szostak, Michal (July 2019, Chemical Communications)

   We report sequential ruthenium(0)-catalysis for the synthesis of sterically-hindered amines via direct C–H arylation of simple imines and imine hydrosilylation. The method involves direct C–H arylation under neutral conditions with organoboranes enabled by ruthenium(0) catalysis. The catalytic hydrosilylation was performed in a one-pot fashion using Et 3 SiH. The reaction is compatible with a broad range of electronically- and sterically-varied imines, enabling rapid production of valuable biaryl amines in good to excellent yields. The method constitutes a two-step, one-pot procedure to synthesize sterically-hindered amines from aldehydes. The utility of this atom-economic strategy is demonstrated in one-pot, three-component coupling, direct in situ aldehyde arylation and the use of transfer hydrogenation. 

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5. Non-Reciprocal Wave Transmission in a Bilinear Spring-Mass System

   https://doi.org/10.1115/1.4045501  

   Lu, Zhaocheng; Norris, Andrew N. (April 2020, Journal of Vibration and Acoustics)

   Abstract Significant amplitude-independent and passive non-reciprocal wave motion can be achieved in a one-dimensional (1D) discrete chain of masses and springs with bilinear elastic stiffness. Some fundamental asymmetric spatial modulations of the bilinear spring stiffness are first examined for their non-reciprocal properties. These are combined as building blocks into more complex configurations with the objective of maximizing non-reciprocal wave behavior. The non-reciprocal property is demonstrated by the significant difference between the transmitted pulse displacement amplitudes and energies for incidence from opposite directions. Extreme non-reciprocity is realized when almost-zero transmission is achieved for the propagation from one direction with a noticeable transmitted pulse for incidence from the other. These models provide the basis for a class of simple 1D non-reciprocal designs and can serve as the building blocks for more complex and higher dimensional non-reciprocal wave systems. 

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