Structural and synthetic studies of magnesium and zinc tolylformamidinate complexes

Abstract

The reaction of MgBu₂ with 2.0 equivalents of di(p-tolyl)formamidine (HFTolP) affords the colourless crystalline bis(formamidinate) species [Mg(FTolP)₂(thf)₂] (1), [Mg(FTolP)₂(dme)]_DME (3) and [Mg(FTolP)₂(tmeda)] (4) in moderate to high yield when conducted in tetrahydrofuran, 1,2-dimethoxyethane and toluene–TMEDA, respectively. Compounds 1, 3, 4 and the di(o-tolyl)formamidinate (FTolO) complex; [Mg(FTolO)₂(thf)₂] (2), synthesised in a manner identical to that employed for the preparation of 1, have been characterised by spectroscopy (¹H NMR, ¹³C NMR, FTIR) and single crystal XRD. In the solid state, all four species display monomeric octahedral bis(ƞ2-formamidinate) metal centres that differ solely on the basis of the steric and structural requirements of both the coordinating solvent donor and the formamidinate. Attempts to prepare analogous zinc complexes via the treatment of anhydrous ZnCl₂ with 2.0 equivalents of the known complex [{Li(FTolP)(Et₂O)}₂], or treatment of HFTolP with 0.5 equivalents of ZnEt₂ primarily yielded the novel lithium zincate species [(μ₅-O)Li₂Zn₃{(p-tolyl)NC(H)N(O)(p-tolyl)} ₆] (5), which includes a trapped dilithium oxygen unit, and the precedented tetrazinc oxygen cluster [(μ₄-O)Zn₄(FTolP)₆] (6), respectively. The molecular structures of complexes 1–6 are discussed, as are alternative routes to species 6.