Herein, we demonstrate the application of adducts of various N‐heterocyclic carbenes (NHCs) with CO2 (i.e., NHC–CO2) as precatalysts in the ring‐opening homopolymerization of propylene oxide (PO) onto diethylene glycol as a chain starter to give well‐defined polyether diols. The influence of various NHCs on the structure of the polymers and the mechanism of this reaction were investigated both experimentally and through DFT calculations. With this methodology, copolymers of PO and the monomers ε‐caprolactone and (S,S)‐lactide are accessible.
Abstract:The reductive formation of substituted anilines from amines and three well-defined aryl-, and chlorobis(triphenylphosphine)phenylgold-A C H T U N G T R E N N U N G (III) chloride (4) was studied. The reaction is stoichiometric in gold and represents a key step of a potential gold-catalyzed intermolecular amination reaction of arenes. It proceeds smoothly with a broad range of N-nucleophiles in the presence of sodium acetate (NaOAc) and enables the selective formation of N-substituted anilines in good yields. A mechanistic pathway is proposed and discussed as well.
A new room-temperature chromium tricarbonyl-mediated cycloaromatization of enediynes is reported. The reaction occurs with both cyclic and acyclic enediynes in the presence of [Cr(CO)3(η6-naphthalene)] and both a coordinating solvent and a hydrogen atom source, providing chromium–arene complexes in reasonable yield and good diastereocontrol. The mechanism of the reaction has been probed through DFT computational and spectroscopic methods. These studies suggest that direct C1–C6 bond formation from an η6-enediyne complex is the lowest-energy path, forming a metal-bound p-benzyne biradical. NMR spectroscopy suggests that enediyne alkene coordination occurs in preference to alkyne coordination, forming a THF-stabilized olefin intermediate; subsequent alkyne coordination leads to cyclization. While biradical quenching occurs rapidly and primarily via the singlet biradical, the triplet state biradical is detectable by EPR spectroscopy, suggesting intersystem crossing to a triplet ground state
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