Coordinatively Labile 18‐Electron Arene Ruthenium Iminophosphonamide Complexes

The thermodynamics of chloride dissociation from the 18e arene ruthenium iminophosphonamides [(η 6 ‐arene)RuCl{(R′N) 2 PR 2 }] ( 1 a – d ) [previously known with arene=C 6 Me 6 , R=Ph, R′= p ‐Tol ( a ); R=Et, R′= p ‐Tol ( b ); R=Ph, R′=Me ( c ); and new with arene= p ‐cymene, R=Ph, R′= p ‐Tol ( d )] was assessed in both polar and apolar solvents by variable‐temperature UV/Vis, NMR, and 2D EXSY 1 H NMR methods, which highlighted the influence of the NPN ligand on the equilibrium parameters. The dissociation enthalpy Δ H d decreases with increasing electron‐donating ability of the N ‐ and P ‐substituents ( 1 a , 1 d > 1 b > 1 c ) and solvent polarity, and this results in exothermic spontaneous dissociation of 1 c in polar solvents. The coordination of neutral ligands (MeCN, pyridine, CO) to the corresponding 16e complexes [(η 6 ‐arene)Ru{(R′N) 2 PR 2 }] + PF 6 − ( 2 a – d ) is reversible; the stability of the 2⋅L adducts depends on the π‐accepting ability of L. Carbonylation of 2 a and 2 d resulted in rare examples of cationic arene ruthenium carbonyl complexes ( 3 a , 3 d ), while the monocarbonyl adduct derived from 2 c reacts further with a second equivalent of CO with conversion to carbonyl‐carbamoyl complex 3 c , in which one CO molecule is inserted into the Ru−N bond. The new complexes 1 d , 2 d , 3 a , 3 c , and 3 d were isolated and structurally characterized.