Multifunctional Behavior by a Bis-(phosphinimino)methanide Ligand:  η<sup>2</sup>- vs η<sup>3</sup>-coordination vs Bronsted Basicity

The reaction of [(Cymene)RuCl<sub>2</sub>]<sub>2</sub> with the chelate LiHC(PPh<sub>2</sub>NPh)<sub>2</sub> occurs to remove <i>both</i> chloride ligands, to furnish a cationic Ru(II) complex with the monoanionic ligand bound η<sup>3</sup>, through two N and an sp<sup>3</sup> carbon. This cation is also produced from the conjugate acid of the ligand H<sub>2</sub>C(PPh<sub>2</sub>NPh)<sub>2</sub> because this molecule can serve as a Brønsted base, to deprotonate the acidic carbon of another molecule of H<sub>2</sub>C(PPh<sub>2</sub>NPh)<sub>2</sub>. DFT calculations show an energy surface where (Cymene)RuHC(PPh<sub>2</sub>NPh)<sub>2</sub>L is more stable with a Ru−CH(PPh<sub>2</sub>NPh)<sub>2</sub> bond and with L = Cl<sup>-</sup> or MeCN <i>not</i> coordinated to Ru, than to an η<sup>2</sup>-HC(PPh<sub>2</sub>NPh)<sub>2</sub> structure with coordinated L; this is tested experimentally. The greater tendency for this ligand to be coordinated η<sup>3</sup> vs analogous diketiminates is discussed. The nucleophilicity of C<sub>γ</sub> in structure <b>1</b>, vs that of donors L = Cl<sup>-</sup> or MeCN, is evaluated to understand the preference of the bis(phosphinimino)methanide to be bidentate or tridentate.