Synthesis and characterisation of magnesium complexes containing sterically demanding N,N'-bis(aryl)amidinate ligands.

Condensation reactions of carboxylic acids and anilines in the presence of polyphosphoric acid trimethylsilyl ester (PPSE) afforded a range of sterically demanding N,N'-bis(aryl)amidines, RN{C(R')}N(H)R [R = Mes (Mes = 2,4,6-trimethylphenyl), R' = Cy (Cy = cyclohexyl) L¹H; R = Dipp (Dipp = 2,6-diisopropylphenyl), R' = Cy L²H; R = Mes, R' = Ph L³H; R = Dipp, R' = Ph L⁴H; R = Mes, R' = Dmp (Dmp = 3,5-dimethylphenyl) L⁵H; R = Dipp, R' = Dmp L⁶H; R = Dmp, R' = Cy L⁷H]. Amidines L¹H-L⁷H have been characterised spectroscopically, and for L⁵H and L⁶H, by X-ray crystallography. Treatment of the amidines with di-n-butylmagnesium in THF solution afforded the monomeric magnesium bis(amidinates) [Mg(L¹)2(THF)] 1, [Mg(L²)2] 2, [Mg(L³)2(THF)] 3, [Mg(L⁵)2(THF)] 5, [Mg(L⁶)2] 6, [Mg(L⁷)2] 7, and the magnesium mono(amidinate) complex [Mg(L⁴)((n)Bu)] 4.