The thermodynamics of chloride dissociation from the 18e arene ruthenium iminophosphonamides [(η -arene)RuCl{(R'N) PR }] (1 a-d) [previously known with arene=C Me , 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 H NMR methods, which highlighted the influence of the NPN ligand on the equilibrium parameters. The dissociation enthalpy ΔH 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 -arene)Ru{(R'N) PR }] PF (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.

Novel half-sandwich 18ē and 16ē arene ruthenium iminophosphonamide complexes [(η-CMe)RuCl{(R'N)PR}] (3a-c) and [(η-CMe)Ru{(R'N)PR}](X) (4a-c) (a, R = Ph, R' = p-Tol; b, R = Et, R' = p-Tol; c, R = Ph, R' = Me. X = BF, PF or BAr) were synthesized. The elongated Ru-Cl bond in the 18ē complexes is shown to dissociate even in apolar solvents to form the corresponding 16ē cations, which can be readily isolated as salts with non-coordinating anions. The coordinatively unsaturated 16ē complexes are stable species due to efficient π-electron donation from the nitrogen atoms of the zwitterionic NPN-ligand. The ruthenium iminophosphonamides are moderately active in the ROMP polymerization of norbornene; the 16ē complexes 4a,b yield high molecular weight polymers (M∼ 300 × 10) with a narrow distribution M/M∼ 1.6, while the 18ē complexes 3a,b give polymers of lower molecular weight (M < 50 × 10) with a wider polydispersity index M/M∼ 2.5.