Synthesis and Characterization of Magnesium and Aluminum Bis(phosphoranyl)methanediide Complexes

The reaction of [CH2(PPh2NSiMe3)(PPh2E)] (E = S (1), NSiMe3 (2)) with Mg(Bun)2 in refluxing toluene afforded the magnesium bis(phosphoranyl)methanediide complexes [{(PPh2NSiMe3)(PPh2E)}CMg]2 (E = S (3), NSiMe3 (4)), respectively. The X-ray structures and DFT calculations of 3 and 4 show that they are bimetallic methanediide complexes of magnesium containing a strong Mg−Cmethanediide electrostatic bonding. Treatment of 4 with water in toluene gave 2 and the magnesium hydroxide complex [HC(PPh2NSiMe3)2Mg(μ−OH)]2 (5), confirmed by X-ray crystallography. The reaction of 1 with AlMe3 in refluxing toluene afforded the aluminum bis(phosphoranyl)methanediide complex [{(PPh2NSiMe3)(PPh2S)}CAlMe]2 (6). The X-ray structure of 6 shows that a methanediide carbon is bonded to one aluminum atom. DFT calculations of 6 demonstrate that Al−Cmethanediide is highly polar with weak covalent bonding, consistent with the topological analysis of electron densities of 6.