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The mechanism of reversible-deactivationradical polymerization (RDRP) mediated by chloro-substituted amine–bis(phenolate)ironcomplexes was studied via a combination of Mössbauer, EPR,NMR, and online Vis/NIR spectroscopy. It was found that styrene polymerizationoperates via an atom-transfer radical polymerization (ATRP) mechanismwhen alkyl halide is present, whereas an interplay between ATRP andorganometallic-mediated radical polymerization (OMRP) equilibria occursduring MMA polymerization. The preparation of the amine–bis(phenolate)iron(II)complex, [O2NN′]FeII, allowed polymerizationsto be performed under an OMRP-only regime free of alkyl halide thatyields dispersities as low as 1.29 for MMA polymerization. [ABSTRACT FROM AUTHOR]

A libraryof pyridyl- and picolyl-substituted imidazolium saltshave been synthesized and coordinated to copper, via transmetalationfrom silver(I)–N-heterocyclic carbenes (NHCs), to prepare severalcopper(I)– and copper(II)–NHC complexes. The copper(I)–NHCsarecomplexes of the type Cu(NHC)Br, with the solid-state structures revealinga variety of coordination environments around the copper centers.The stability of the copper(II) complexes is particularly unusual,given the absence of a “hard” anionic tethering groupappended to the ligands. The stability has been attributed to thepyridyl substituent, with the complexes being extremely stable, whilethose with an appended anionic group tend to be more sensitive toair/moisture. The ligands and complexes have been examined in an Ullmann-typeetherification reaction and exhibit improved activity in comparisonto copper in the absence of a ligand or the common Cu(I)–NHCcomplexes Cu(IMes)Cl and [Cu(IMes)2]PF6, indicatingstabilization of higher oxidation state species by the ligands duringthe catalytic cycle. [ABSTRACT FROM AUTHOR]

The behavior of N-heterocyclic carbene (NHC) ligands in organometallic chemistry is hugely important for catalysis, due to the effect of these ligands on catalytic pathways and their involvement in catalyst decomposition. In this report, a combined experimental and computational study is presented, which provides mechanistic understanding of the unprecedented oxidative coupling of NHCs at Cu. The presence of Cu(I) -, Cu(II) -, and Cu(III) -NHC complexes during the process is postulated, with the unusual Ccarbene -Ccarbene oxidative coupling reaction occurring under extremely mild reaction conditions. This process may represent a novel pathway for the decomposition of Cu-NHC complexes., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The preparation of a series of imidazolium salts bearing N-allyl substituents, and a range of substituents on the second nitrogen atom that have varying electronic and steric properties, is reported. The ligands have been coordinated to a copper(I) centre and the resulting copper(I)-NHC (NHC=N-heterocyclic carbene) complexes have been thoroughly examined, both in solution and in the solid-state. The solid-state structures are highly diverse and exhibit a range of unusual geometries and cuprophilic interactions. The first structurally characterised copper(I)-NHC complex containing a copper(I)-alkene interaction is reported. An N-pyridyl substituent, which forms a dative bond with the copper(I) centre, stabilises an interaction between the metal centre and the allyl substituent of a neighbouring ligand, to form a 1D coordination polymer. The stabilisation is attributed to the pyridyl substituent increasing the electron density at the copper(I) centre, and thus enhancing the metal(d)-to-alkene(π*) back-bonding. In addition, components other than charge transfer appear to have a role in copper(I)-alkene stabilisation because further increases in the Lewis basicity of the ligand disfavours copper(I)-alkene binding., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)