Magnesium and Titanium Complexes of Polyanionic Phosphazenate Ligands

Polyanionic phosphazenates constitute polydentate ligands that offer several chelating sites, facilitating the accommodation of multinuclear metal arrays. Here, we describe their coordination behavior in the presence of magnesium and titanium. Reaction of the hexaprotic cyclotriphosphazene (ⁱBuNH)₆P₃N₃ (1) with ⁿBu₂Mg in thf in 1:2 ratio yields the dinuclear magnesium complex [(thf)Mg(ⁱBuN)₂(ⁱBuNH)₄P₃N₃]₂ (2), while a 1:4 ratio gives the octanuclear complex [(thf)₃(ⁿBuMg)₂Mg₂(ⁱBuN)₆P₃N₃]₂ (3). Both magnesium complexes exist as dimers in the solid state. In addition to metal ligand interactions, dimer 2 is supported by four hydrogen bonds (N−H···N interactions). The reaction of (CyNH)₆P₃N₃ (4) with two equivalents of (Me₂N)₄Ti produces the dinuclear complex {(Me₂N)₂Ti}₂(CyN)₄(CyNH)₂P₃N₃ (5), in which the phosphazenate ligand accommodates the two titanium atoms in tridentate coordination sites. The metalation reactions were followed by ³¹P NMR. Metal complexes 2, 3, and 5 were characterized by X-ray structure analysis.