Three-dimensional structures that undergo reversible shape changes in response to mild stimuli enable a wide range of smart devices, such as soft robots or implantable medical devices. Herein, a dual thiol-ene reaction scheme is used to synthesize a class of liquid crystal (LC) elastomers that can be 3D printed into complex shapes and subsequently undergo controlled shape change. Through controlling the phase transition temperature of polymerizable LC inks, morphing 3D structures with tunable actuation temperature (28 ± 2 to 105 ± 1 °C) are fabricated. Finally, multiple LC inks are 3D printed into single structures to allow for the production of untethered, thermo-responsive structures that sequentially and reversibly undergo multiple shape changes.

Nickel catalysts represent a low cost and environmentally friendly alternative to palladium-based catalytic systems for Suzuki–Miyaura cross-coupling (SMC) reactions. However, nickel catalysts have suffered from poor air, moisture, and thermal stabilities, especially at high catalyst loading, requiring controlled reaction conditions. In this report, we examine a family of mono- and dinuclear Ni(II) and Pd(II) complexes with a diverse and versatile α-diimine ligand environment for SMC reactions. To evaluate the ligand steric effects, including the bite angle in the reaction outcomes, the structural variation of the complexes was achieved by incorporating iminopyridine- and acenaphthene-based ligands. Moreover, the impact of substrate bulkiness was investigated by reacting various aryl bromides with phenylboronic acid, 2-naphthylboronic acid, and 9-phenanthracenylboronic acid. Yields were the best with the dinuclear complex, being nearly quantitative (93–99%), followed by the mononuclear complexes, giving yields of 78–98%. Consequently, α-diimine-based ligands have the potential to deliver Ni-based systems as sustainable catalysts in SMC.

This review discusses various neodymium catalysts for stereospecific polymerization of dienes, vinyl monomers, and ε-caprolactone.

The usefulness of transition metal catalytic systems in C–S cross-coupling reactions is significantly reduced by air and moisture sensitivity, as well as harsh reaction conditions. Herein, we report four highly air- and moisture-stable well-defined mononuclear and bridged dinuclear α-diimine Ni­(II) and Pd­(II) complexes for C–S cross-coupling. Various ligand frameworks, including acenaphthene- and iminopyridine-based ligands, were employed, and the resulting steric properties of the catalysts were evaluated and correlated with reaction outcomes. Under aerobic conditions and low temperatures, both Ni and Pd systems exhibited broader substrate scope and functional group tolerance than previously reported catalysts. Over 40 compounds were synthesized from thiols containing alkyl, benzyl, and heteroaryl groups. Also, pharmaceutically active heteroaryl moieties are incorporated from thiol and halide sources. Notably, the bridged dinuclear five-coordinate Ni complex has outperformed the remaining three mono four- or six-coordinate complexes by giving almost quantitative yields across a broad substrate scope.

Molecular switches offer wide applicability through conformational changes which can be triggered by external stimuli. Azobenzenes are excellent candidates to contribute toward a rational design of molecular switches because they exist as either cis or trans isomers as a result of the dynamic photoisomerization process. In this study, we leverage the azobenzene stimuli response by attaching it as a pendant group on polycarbodiimides synthesized using screw sense polymerization. The exposure of the polymer sample in solution to UV light induces the transformation of the azobenzene pendant groups to the cis isomer with re-emergence of the trans conformer under visible light or heat. Corroborating experimental and computational data reveal that these events induce spring-like expansion–contraction motions throughout the helical backbone. Our finding suggests the use of polycarbodiimide-derived photoswitches as dynamic materials in biological applications and materials science.