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Peptide stereocomplexes cross-link polymers into hydrogels with enhanced mechanical properties and proteolytic stability relative to the individual constituent peptide–polymer conjugates. 

Pyridine-alkoxide (pyalk) ligands that support transition metals have been studied for their use in electrocatalytic applications. Herein, we used the pyalk proligands diphenyl(pyridin-2-yl)methanol ([H]PhPyalk, L1), 1-(pyren-1-yl)-1-(pyridin-2-yl)ethan-1-ol ([H]PyrPyalk, L2), 1-(pyridine-2-yl)-1-(thiophen-2-yl)ethan-1-ol ([H]ThioPyalk, L3), and 1-(ferrocenyl)-1-(pyridin-2-yl)ethan-1-ol ([H]FePyalk, L4) to synthesize CuII complexes that vary in nuclearity and secondary coordination sphere. Also, the proligand 1-(ferrocenyl)-1-(5-methoxy-pyridin-2-yl)ethan-1-ol ([H]FeOMePyalk, L5) was synthesized with a methoxy substituted pyridine; however, the isolation of a CuII complex ligated by L5 was not possible. Under variable reaction conditions, the pyalk ligands reacted with CuII precursors and formed either mononuclear or dinuclear CuII complexes depending on the amount of ligand added. The resulting complexes were characterized by single crystal X-ray diffraction, elemental analysis, and cyclic voltammetry. 

For nearly a century, chemists have explored how transition-metal complexes can affect the physical and chemical properties of linear conjugated polyenes and heteropolyenes. While much has been written about higher hapticity complexes (η4–η6), less is known about the chemistry of their η2 analogues. Herein, we describe a general method for synthesizing 5,6-η2-(1-azatriene) tungsten complexes via a 6π-azaelectrocyclic dihydropyridine ring-opening that is promoted by the π-basic nature of {WTp(NO)(PMe3)}. This study includes detailed spectroscopic and crystallographic data for the η2-dihydropyridine and η2-1-azatriene complexes, both of which were prepared as single regio- and stereoisomers. 

Abstract Main‐group element‐mediated C−H activation remains experimentally challenging and the development of clear concepts and design principles has been limited by the increased reactivity of relevant complexes, especially for the heavier elements. Herein, we report that the stibenium ion [(^pyCDC)Sb][NTf₂]₃(1) (^pyCDC=bis‐pyridyl carbodicarbene; NTf₂=bis(trifluoromethanesulfonyl)imide) reacts with acetonitrile in the presence of the base 2,6‐di‐tert‐butylpyridine to enable C(sp³)−H bond breaking to generate the stiba‐methylene nitrile complex [(^pyCDC)Sb(CH₂CN)][NTf₂]₂(2). Kinetic analyses were performed to elucidate the rate dependence for all the substrates involved in the reaction. Computational studies suggest that C−H activation proceeds via a mechanism in which acetonitrile first coordinates to the Sb center through the nitrogen atom in a κ¹fashion, thereby weakening the C−H bond which can then be deprotonated by base in solution. Further, we show that1reacts with terminal alkynes in the presence of 2,6‐di‐tert‐butylpyridine to enable C(sp)−H bond breaking to form stiba‐alkynyl adducts of the type [(^pyCDC)Sb(CCR)][NTf₂]₂(3 a–f). Compound1shows excellent specificity for the activation of the terminal C(sp)−H bond even across alkynes with diverse functionality. The resulting stiba‐methylene nitrile and stiba‐alkynyl adducts react with elemental iodine (I₂) to produce iodoacetonitrile and iodoalkynes, while regenerating an Sb trication.