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Multifunctional Behavior by a Bis-(phosphinimino)methanide Ligand:  η2- vs η3-coordination vs Bronsted Basicity

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posted on 2004-03-03, 00:00 authored by Christine Bibal, Maren Pink, Yegor D. Smurnyy, John Tomaszewski, Kenneth G. Caulton
The reaction of [(Cymene)RuCl2]2 with the chelate LiHC(PPh2NPh)2 occurs to remove both chloride ligands, to furnish a cationic Ru(II) complex with the monoanionic ligand bound η3, through two N and an sp3 carbon. This cation is also produced from the conjugate acid of the ligand H2C(PPh2NPh)2 because this molecule can serve as a Brønsted base, to deprotonate the acidic carbon of another molecule of H2C(PPh2NPh)2. DFT calculations show an energy surface where (Cymene)RuHC(PPh2NPh)2L is more stable with a Ru−CH(PPh2NPh)2 bond and with L = Cl- or MeCN not coordinated to Ru, than to an η2-HC(PPh2NPh)2 structure with coordinated L; this is tested experimentally. The greater tendency for this ligand to be coordinated η3 vs analogous diketiminates is discussed. The nucleophilicity of Cγ in structure 1, vs that of donors L = Cl- or MeCN, is evaluated to understand the preference of the bis(phosphinimino)methanide to be bidentate or tridentate.

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