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Liquid assisted ball milling of [NHC]HBr (NHC = N-heterocyclic carbene) salts with copper(I) chloride, and a range of alkali metal complexes was shown to efficiently produce (NHC)CuX (NHC = normal or RE-NHC, X = halide, alkoxide, amide, alkyl, aryl; RE-NHC = ring-expanded NHC). [ABSTRACT FROM AUTHOR]

Herein we report the synthesis, isolation and polymerisation activity of two new zinc compounds based on a 2,6-diisopropylphenyl (Dipp) β-diiminate (NacNac) ligand framework with zinc also ligated by an amidate (2-pyridonate or 6-methyl-2-pyridonate) unit. The compounds crystallised as either monomeric (6-Me-2-pyridonate derivative) or dimeric (2-pyridonate) species, although both were found to be monomeric in solution via1H DOSY NMR spectroscopy, which was supported by DFT calculations. These observations suggest that both complexes initiate ring-opening polymerisation (ROP) through a single-site monometallic mechanism. High molecular weight poly ε-caprolactone (PCL) was achieved via exogenous initiator-free ROP conditions with both catalysts. An increase in the 2-pyridonate initiator steric bulk (6-Me- vs. 6-H-) resulted in an improved catalytic activity, facilitating complete monomer conversion within 1 h at 60 °C. Pyridonate end-groups were observed by MALDI-ToF mass spectrometry, contrasting with previous observations for DippNacNac-Zn acetate complexes (where no acetate end groups are observed), instead this more closely resembles the reactivity of DippNacNac-Zn alkoxide complexes in ROP (where RO end groups are observed). Additional major signals in the MALDI-ToF spectra were consistent with cyclic PCL species, which are attributed to back-biting ring-closing termination steps occuring in a process facilitated by the pyridonate unit being an effective leaving group. To the best of our knowledge, these complexes represent the first examples of pyridonate, and indeed amidate, initated ROP. [ABSTRACT FROM AUTHOR]

σ‐Bond metathesis reactions between [(6‐Dipp)CuOtBu] (6‐Dipp=:C({Dipp}NCH2)2CH2, Dipp=2,6‐iPr2−C6H3) and three diboranes gave access to three new copper(I) boryl complexes [(6‐Dipp)CuBcat], [(6‐Dipp)CuBneop], and [(6‐Dipp)CuBhex] (cat=1,2‐O2C6H4; neop=(OCH2)2C(CH3)2; hex=OC(CH3)HCH2C(CH3)2O). Whilst [(6‐Dipp)CuBcat] and [(6‐Dipp)CuBneop] formed rapidly in toluene, access to [(6‐Dipp)CuBhex] required heating to 60 °C for days. The complexes were characterised by single‐crystal X‐ray crystallography which showed in all three cases that the systems were monomers and distorted‐linear at the copper atom. The stability of [(6‐Dipp)CuBneop] was found to be comparable to that of [(IPr*)Cu‐Bneop] (IPr*=1,3‐bis(2,6‐(diphenylmethyl)‐4‐methylphenyl)imidazol‐2‐ylidene); it persisted in solution for days with no sign of decomposition. [(6‐Dipp)CuBhex] is a rare crystallographically characterised example of a complex containing a boryl anion supported by the hexylene glycolato ligand. [ABSTRACT FROM AUTHOR]

Boron, boryl anion, carbene ligands, copper, ring-expanded N-heterocyclic carbene Front Cover: Ring-Expanded N-Heterocyclic Copper(I) Boryl Complexes: The Structures of [(6-Dipp)CuBcat], [(6-Dipp)CuBneop], and [(6-Dipp)CuBhex] (Eur. J. Inorg. Keywords: boron; boryl anion; carbene ligands; copper; ring-expanded N-heterocyclic carbene EN boron boryl anion carbene ligands copper ring-expanded N-heterocyclic carbene 1 1 1 05/04/23 20230502 NES 230502 B The Front Cover b shows a photograph taken by Dr. Mary F. Mahon on a visit to the subantarctic. [Extracted from the article]