Synthesis and characterisation of magnesium methyl complexes with monoanionic chelating nitrogen donor ligands and their reaction with dioxygen

Abstract

Treatment of the Grignard reagent MeMgCl with the lithiates Li[L–X] (Li[L–X] = lithium β-diketiminate [HC{C(Me)NAr′}₂Li] (Ar′ = 2,6-diisopropylphenyl) or lithium N,N′-diisopropylaminotroponiminate, Li[(ⁱPr₂)ATI]) in THF provided four-co-ordinate methylmagnesium complexes [Mg(η²-L–X)Me(THF)]. The β-diketiminate complex has been characterised by X-ray crystallography, however the aminotroponiminate complex is an oil. Both complexes readily react with oxygen to provide methoxide-bridged dimeric complexes [Mg(μ-OMe)(η²-L–X)]₂ and the complex [Mg(μ-OMe){η²-(ⁱPr₂)ATI}]₂ has structurally been characterised. The methyl-bridged dimeric complex [Mg(μ-Me){HC[C(Me)NAr′]}₂]₂ may be obtained by removal of THF from the adduct under vacuum at 150 °C or by treatment of the β-diketimine (L–XH) with dimethylmagnesium in toluene with elimination of methane, and has also been characterised crystallographically. In contrast to this, treatment of MgMe₂ with the aminotriponimine H[(ⁱPr₂)ATI] provides only the bis-chelate complex [Mg{(ⁱPr₂)ATI}₂] which has also been characterised structurally. However the methyl bridged dimer [Mg(μ-Me){η²-(ⁱPr₂)ATI}]₂ may be formed by removal of THF from [MgMe{η²-(ⁱPr₂)ATI}(THF)] at 110 °C under vacuum.