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.