The reaction of [CH 2 (PPh 2 dNSiMe 3 )(PPh 2 dE)] (E = S (1), NSiMe 3 (2)) with Mg(Bu n ) 2 in refluxing toluene afforded the magnesium bis(phosphoranyl)methanediide complexes [{(PPh 2 dNSiMe 3 )-(PPh 2 dE)}CMg] 2 (E = S (3), NSiMe 3 (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-C methanediide electrostatic bonding. Treatment of 4 with water in toluene gave 2 and the magnesium hydroxide complex [HC(PPh 2 dNSiMe 3 ) 2 Mg(μ-OH)] 2 (5), confirmed by X-ray crystallography. The reaction of 1 with AlMe 3 in refluxing toluene afforded the aluminum bis(phosphoranyl)methanediide complex [{(PPh 2 dNSiMe 3 )(PPh 2 dS)}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-C methanediide is highly polar with weak covalent bonding, consistent with the topological analysis of electron densities of 6.