The reduction of water has been achieved through a non-noble-metal-based homogeneous catalyst system that is formed in situ. Optimisation of the ligand quantities increased catalyst turnover numbers compared to preformed complexes. Mechanistic studies confirm a heteroleptic Cu complex as the active photosensitiser (PS) and an in situ formed Fe-phosphido dimer complex as the water reduction catalyst. The in situ method has been used to screen a range of ligands for the active PS, which has led to the identification a number of structural features important to longevity and performance.
Given the important role played by 2-hydroxybiaryls in organic, medicinal and materials chemistry, concise methods for the synthesis of this common motif are extremely valuable. In seeking to extend the synthetic chemists' lexicon in this regard, we have developed an expedient and general strategy for the ortho-arylation of phenols and naphthols using readily-available boronic acids. Our methodology relies on in situ generation of a uniquely reactive Bi(V) arylating agent from a benchstable Bi(III) precursor via telescoped B-to-Bi transmetallation and oxidation. By exploiting reactivity
Aryl isocyanates are introduced as comonomers for ring opening copolymerization (ROCOP) with epoxides. Informed by studies of reaction kinetics, we show that divergent sequence selectivity for AB-and ABB-type copolymers can be achieved with a single dimagnesium catalyst. The resulting materials respectively constitute a new class of polyurethane (PU) and a new class of material featuring an unprecedented backbone structure, the polyallophanate (PA). The successful use of isocyanate comonomers in this way marks a new direction for the field of ROCOP, while providing distinct opportunities for expansion of PU structural diversity. Specifically, the methodology reported herein delivers PUs featuring fully substituted (tertiary) carbamyl nitrogen atoms, a structural motif that is almost inaccessible via extant polymerization strategies. Thus, in one step from commercially available comonomers, our methodology expands the scope of ROCOP and gives access to diverse materials featuring both privileged (PU) and unexplored (PA) microstructures.Controlled ring opening copolymerization (ROCOP) involving epoxide comonomers represents a significant accomplishment in the fields of catalysis and materials chemistry. By overcoming the synthetic challenges associated with selective alternate copolymerization, readily-available comonomers such as carbon dioxide, 1-3 its sulfur-analogs 4-15 or cyclic anhydrides 16 can be converted directly to valuable, biodegradable plastics such as poly(thio)carbonates (Scheme 1A) and polyesters. 17 Perhaps most notably, ROCOP strategies offer atom-economic access to materials with properties that can be readily tuned by varying both comonomers. While this advantage is regularly exploited in epoxide/cyclic anhydride ROCOP, 18 the same cannot be said for epoxide/heteroallene ROCOP where the scope with respect to heteroallene comonomers has remained limited to carbon dichalcogenides (CO2, COS or CS2). All materials synthesized via epoxide/heteroallene copolymerization must therefore be based on the (thio)carbonate linkage. Methods employing isocyanates as the heteroallene component would overcome this limitation 19,20 and provide concise access to polyurethanes (PUs), an iconic class of material with a market value predicted to exceed $79bn in 2023. 21,22 Current routes to PUs -including industrially ubiquitous copolymerization of diisocyanates with polyols -give secondary (NH) carbamyl linkages (Scheme 1B). There exists no general method for the direct synthesis of PUs featuring tertiary carbamyl linkages. 17a-c,22-25 Challenging post-polymerization N-H functionalization is thus necessary if all vectors of the PU chain are to be exploited. Scheme 1. Context and Strategic Blueprint for Copolymerization of Epoxides and Heteroallenes ASSOCIATED CONTENT Supporting InformationAdditional discussion, experimental procedures, kinetic data and simulations, and characterization data (hydrolysis studies, NMR spectra, GPC traces and DSC traces). This material is available free of charge via the Internet at...
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