Reactivity of Permethylated Magnesium Complexes toward β-Diimines

The peralkylated magnesium complex Mg(AlMe4)2 reacts with bis-N,N′-diimine PhCHNCH2CH2NCHPh to yield the compound [PhCH(Me)NCH2CH2NCHPh]Mg(AlMe4)(AlMe3), via an alkyl migration. Such a 1,2-addition of the Mg–CH3 moiety to the unsaturated NC imino group is also observed for [MgMe2], affording dimagnesium complex [{PhCH(Me)NCH2CH2NCHPh}Mg(Me)]2. In contrast, treatment of PhCHNCH2CH2NCHPh with AlMe3 gives the donor-adduct [PhCHNCH2CH2NCHPh][(AlMe3)2]. Based on these distinct reactivities a plausible reaction mechanism for the formation of [PhCH(Me)NCH2CH2NCHPh]Mg(AlMe4)(AlMe3) is proposed. Donor-adduct formation is also observed when the perethylated barium aluminate [Ba(AlEt4)2]n is reacted with a β-diimine, affording the complex [Ba(AlEt4)2(PhCNCH2CH2NCPh)]n. The scope of this reaction behavior was further investigated by reacting Mg(AlMe4)2, AlMe3, and [MgMe2] with β-diimines bearing substituted phenyl rings. Neither the ortho-methyl- nor the meta-tert-butyl-disubstituted proligands show any reaction with [MgMe2], while adducts [(C6H3Me2-2,6)CHNCH2CH2NCH(C6H3Me2-2,6)][(AlMe3)2] and [(C6H3tBu2-3,5)CHNCH2CH2NCH(C6H3tBu2-3,5)][(AlMe3)2] are the prevalent reaction products when Mg(AlMe4)2 and AlMe3 are employed.