N,N′-Di(tolyl)formamidinate complexes of potassium: studies of ancillary donor imposed molecular and supramolecular structure

Treatment of N,N′-di(tolyl)formamidines ((Tol)NC(H)N(H)(Tol)) HFTolP (TolP = para-tolyl) and HFTolM (TolM = meta-tolyl) with potassium hydride affords the colourless crystalline formamidinate complexes [{K2(FTolP)2(THF)3}∞], 1, and [{(K2(FTolM)2(THF)3)·THF}∞], 2 when conducted in THF. An analogous HFTolP preparation in 1,2-dimethoxyethane yields the DME analogue of 1; [{K(FTolP)(DME)}∞], 3, whilst treatment of HFTolP with potassium hydride in toluene followed by stoichiometric addition of 18-crown-6 gives monomeric [K(FTolP)(18-crown-6)], 4. Compounds 1–4 have been characterised by spectroscopy (1H NMR, 13C NMR and FTIR) and single crystal XRD. In the solid-state 1–3 display one-dimensional polymeric structures that exhibit μ-η2:η2-coordinated formamidinates. These approach η3-diazaallyl contact by virtue of dinuclear bridging. Compound 4, the first example of a poly-ether crown adducted monomeric Group 1 amidinate, exhibits both inter- and intra-molecular C–H⋯O hydrogen bonding in the solid-state. Supramolecularly, this renders 4 a two-dimensional hydrogen-bonded polymer. Complexes 1–4 are discussed with respect to known potassium benzamidinate/guanidinate complexes and related amido-2-pyridyl ligand species.