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

Treatment of fluorinated β-ketoiminate ligands MokeimH or AlkeimH with NaH in THF solution afforded the corresponding ketoiminatosodium complexes [Na(Mokeim)]₄ 1 and [Na(Alkeim)]₄ 2, MokeimH = (CF₃)C(=O)CH=C(CF₃)NH(CH₂CH₂OMe) and AlkeimH = (CF₃)C(=O)CH=C(CF₃)NH(CH₂CH=CH₂). 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.