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Dicopper Alkyl Complexes: Synthesis, Structure, and Unexpected Persistence

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posted on 2018-08-08, 18:48 authored by Micah S. Ziegler, Nicole A. Torquato, Daniel S. Levine, Amélie Nicolay, Hasan Celik, T. Don Tilley
Cationic μ-alkyl dicopper complexes [Cu2(μ-η11-R)­DPFN]­NTf2 (R = CH3, CH2CH3, CH2C­(CH3)3; DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine NTf2 = N­(SO2CF3)2) were synthesized by treatment of the acetonitrile-bridged dicopper complex [Cu2(μ-η11-NCCH3)­DPFN]­(NTf2)2 with LiR or MgR2. Structural characterization by X-ray crystallography and NMR spectroscopy revealed that the alkyl ligands symmetrically bridge the two copper centers, and the complexes persist in room-temperature solution. Notably, the μ-methyl complex showed less than 20% decomposition after 34 days in room-temperature THF solution. Treatment of the μ-methyl complex with acids allows installation of a range of monoanionic bridging ligands. However, surprisingly insertion into the dicopper–carbon bond was not observed upon addition of a variety of reagents, suggesting that these complexes exhibit a fundamentally new reactivity profile for alkylcopper species. Electrochemical characterization revealed oxidation–reduction events that evidence putative mixed-valence dicopper alkyl complexes. Computational studies suggest that the dicopper–carbon bonds are highly covalent, possibly explaining their remarkable stability.

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