Synthesis and structural characterisation of some novel lithium and sodium N,N′-di(para-tolyl)formamidinate complexes

Treatment of N,N′-di(para-tolyl)formamidine (p-tolylformH) (1) with LiBun in THF, DME or hexane/TMEDA leads to deprotonation of the amidine affording [Li2(p-tolylform)2(THF)3]·2THF (2), [Li(DME)3][Li2(p-tolylform)3] (3) and [{Li2(p-tolylform)2(TMEDA)}∞] (4) respectively. Similar treatment of 1 with NaH or [Na{N(SiMe3)2}] in THF or DME yields trinuclear [Na3(p-tolylform)3(THF)4] (5) and dinuclear [{Na(p-tolylform)(DME)}2] (6). All complexes were characterised by spectroscopy (NMR and IR) and X-ray crystallography. These show p-tolylform to be a versatile ligand for alkali metals, exhibiting a wide variety of binding modes, viz. μ-η1:η1 in 2 and 3 (i.e. bridging mode), μ-η2:η1 in 4 and 6 (i.e. bridging and chelating) and μ-η2:η2 (i.e. bridging and double chelating) and μ3-η2:η1:η1 (i.e. chelating and bridging between three metal centres) in 5.