A Structural Diversity of Molecular Alkaline-Earth-Metal Polyphosphides: From Supramolecular Wheel to Zintl Ion.

A series of molecular group 2 polyphosphides has been synthesized by using air-stable [CpFe(η -P )] (Cp=C Me ) or white phosphorus as polyphosphorus precursors. Different types of group 2 reagents such as organo-magnesium, mono-valent magnesium, and molecular calcium hydride complexes have been investigated to activate these polyphosphorus sources. The organo-magnesium complex [( BDI-Mg(CH )) ] ( BDI={[2,6- Pr C H NCMe] CH} ) reacts with [CpFe(η -P )] to give an unprecedented Mg/Fe-supramolecular wheel. Kinetically controlled activation of [CpFe(η -P )] by different mono-valent magnesium complexes allowed the isolation of Mg-coordinated formally mono- and di-reduced products of [CpFe(η -P )]. To obtain the first examples of molecular calcium-polyphosphides, a molecular calcium hydride complex was used to reduce the aromatic cyclo-P ring of [CpFe(η -P )]. The Ca-Fe-polyphosphide is also characterized by quantum chemical calculations and compared with the corresponding Mg complex. Moreover, a calcium coordinated Zintl ion (P ) was obtained by molecular calcium hydride mediated P reduction.