Synthesis and characterization of two novel tetranuclear sodium ketoiminate complexes; structural evidence for formation of dative Na⋯F and Na–C (olefin) bonding interactions

Abstract

Treatment of fluorinated β-ketoiminate ligands MokeimH or AlkeimH with NaH in THF solution afforded the corresponding ketoiminatosodium complexes [Na(Mokeim)]₄1 and [Na(Alkeim)]₄2, MokeimH = (CF₃)C(O)CHC(CF₃)NH(CH₂CH₂OMe) and AlkeimH = (CF₃)C(O)CHC(CF₃)NH(CH₂CHCH₂). These new complexes were characterized by spectroscopic methods, elemental analyses and X-ray diffraction studies. Complex 1 consists of a tetrameric Na₄O₄ cubane core arrangement, of which each sodium atom is surrounded by a tridentate ketoiminato ligand, two oxygen atoms from nearby ketoiminato ligands, and one or two weak Na⋯F dative interactions. The core structure of 2 is similar, but with formation of the uncommon allyl to sodium π interaction. The stabilization of this Na–C (olefin) bonding interaction is as effective as the Na–O (ether) dative bonding in 1 because 2 shows comparable thermal stability and even an enhanced volatility during sublimation.