A Soft Grip: Magnesium Complexes with a Phosphine‐Modified Phosphonium Diylidic Lewis Base

Abstract

AbstractSimple strategies to obtain magnesium complexes with the soft chelating diylidic ligand [Ph2PCHPPh2(fluorenylidene)]− (dppmflu−) were developed to evaluate the influence of the hard acid (cation) and soft base (anion) mismatch on the stability and reactivity of the formed derivatives. Deprotonation of the precursor Ph2PCH2PPh2(flu) (dppmfluH) by an alkylmagnesium derivative or magnesium amide provided access to [{Mg(dppmflu)(μ‐nBu)}2], [Mg(dppmflu){N(SiMe3)2}], and [{Mg(dppmflu)(μ‐Me)}2], which were used as starting materials for further investigations. The reaction of [{Mg(dppmflu)(μ‐nBu)}2] with PhSiH3 in the presence of THF allowed isolation of the magnesium hydride complex [{Mg(dppmflu)(μ‐H)(thf)}2] without a stabilizing nitrogen donor ligand. Prolonged heating enforced ligand redistribution and [{Mg(dppmflu)(μ‐H)(thf)}2] was converted to [Mg(dppmflu)2] and MgH2. The homoleptic derivative [Mg(dppmflu)2], in which the magnesium center is in a very soft ligand environment, can open a THF molecule by frustrated Lewis pair reactivity to give [{Mg(dppmflu)(μ‐OC4H8dppmflu)}2].