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

Treatment of the Grignard reagent MeMgCl with the lithiates Li[L-X] (Li[L-X]=lithium beta-diketiminate [HC{C(Me)=NAr'}(2)Li] (Ar'=2,6-diisopropylphenyl) or lithium N,N'-diisopropylaminotroponiminate, Li[(Pr-i(2))ATI]) in THF provided four-co-ordinate methylmagnesium complexes [Mg(eta(2)-L-X)Me(THF)]. The beta-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(mu-OMe)(eta(2)-L-X)](2) and the complex [Mg(mu-OMe){eta(2)-(Pr-i(2))ATI}](2) has structurally been characterised. The methyl-bridged dimeric complex [Mg(mu-Me){HC[C(Me)NAr']}(2)](2) may be obtained by removal of THF from the adduct under vacuum at 150 degrees C or by treatment of the beta-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[(Pr-i(2))ATI] provides only the bis-chelate complex [Mg{(Pr-i(2))ATI}(2)] which has also been characterised structurally. However the methyl bridged dimer [Mg(mu-Me){eta(2)-(Pr-i(2))ATI}](2) may be formed by removal of THF from [MgMe{eta(2)-(Pr-i(2))ATI}(THF)] at 110 degrees C under vacuum.