Reduction of tert-butylphosphaalkyne and trimethylsilylnitrile with magnesium(i) dimers

Abstract

We report on the reactivity of magnesium(I) dimers, [Mg(nacnac)]₂ (nacnac = HC[C(Me)N(2,6-ⁱPr₂C₆H₃)]₂ ([^DippLMg]₂) and HC[C(Me)N(2,4,6-Me₃C₆H₂)]₂ ([^MesLMg]₂)), towards the phosphaalkyne ^tBuCP. The steric profile of the magnesium(I) dimer results in selectivity for different products. The larger diisopropylphenyl derivative yields exclusively the monomeric dimagnesiated phosphaalkene [^DippLMg]PC(^tBu)([^DippLMg]) (1), while the mesityl derivative facilitates reductive coupling of two phosphaalkyne equivalents to give access to the 1,3-diphosphacyclobutadienediide [^MesLMg]₂[(^tBu)₂C₂P₂](2). The reactivity differs in coordinating solvents such as THF, which allowed for the observation of C–P coupled products. For sake of comparison, reactions of magnesium(I) compounds with Me₃SiCN were carried out. In contrast to the reactions involving ^tBuCP, these afforded 1,3-diazabutadienediyl complexes via reductive coupling and silyl migration processes.