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

Simple strategies to obtain magnesium complexes with the soft chelating diylidic ligand [Ph PCHPPh (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 Ph PCH PPh (flu) (dppmfluH) by an alkylmagnesium derivative or magnesium amide provided access to [{Mg(dppmflu)(μ-nBu)} ], [Mg(dppmflu){N(SiMe ) }], and [{Mg(dppmflu)(μ-Me)} ], which were used as starting materials for further investigations. The reaction of [{Mg(dppmflu)(μ-nBu)} ] with PhSiH in the presence of THF allowed isolation of the magnesium hydride complex [{Mg(dppmflu)(μ-H)(thf)} ] without a stabilizing nitrogen donor ligand. Prolonged heating enforced ligand redistribution and [{Mg(dppmflu)(μ-H)(thf)} ] was converted to [Mg(dppmflu) ] and MgH . The homoleptic derivative [Mg(dppmflu) ], 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-OC H dppmflu)} ].