Reactivity of [Tism^PrⁱBenz]MgH and [Tism^PrⁱBenz]MgMe Towards Esters: Alkoxide Elimination and C–C Bond Formation

The reactivity of Mg–H and Mg–Me bonds of [TismPriBenz]MgH and [TismPriBenz]MgMe towards esters reveals additional pathways to those that have been observed for aldehydes and ketones, namely insertion and enolate formation. For example, [TismPriBenz]MgH and [TismPriBenz]MgMe react with the formate ester HCO2Me to afford the methoxy derivative, [TismPriBenz]MgOMe, via a process that is proposed to involve β-methoxide elimination from a [TismPriBenz]MgOCH(X)OMe intermediate (X = H, Me). Likewise, [TismPriBenz]MgH reacts with the acetate ester, MeCO2Et, to afford the ethoxide complex, [TismPriBenz]MgOEt. In contrast, while the methyl complex [TismPriBenz]MgMe likewise reacts with MeCO2Et to form [TismPriBenz]MgOEt, the β-keto ester enolate derivative, [TismPriBenz]Mg(κ2-etac) [κ2-etac = MeC(O)CHC(O)OEt], is also obtained via a reaction that involves the formation of a C–C bond. The latter compound is additionally obtained by the reaction of [TismPriBenz]MgMe with ethyl acetoacetate, MeC(O)CH2C(O)OEt, presumably via a reaction with the enol tautomer, MeC(OH)CHC(O)OEt. [TismPriBenz]MgOMe and [TismPriBenz]Mg(κ2-etac) have been structurally characterized by X-ray diffraction.