The half-sandwich 18- and 16-electron arene ruthenium iminophosphonamide complexes†
Abstract
Novel half-sandwich 18ē and 16ē arene ruthenium iminophosphonamide complexes [(η6-C6Me6)RuCl{(R′N)2PR2}] (3a–c) and [(η6-C6Me6)Ru{(R′N)2PR2}]+(X−) (4a–c) (a, R = Ph, R′ = p-Tol; b, R = Et, R′ = p-Tol; c, R = Ph, R′ = Me. X = BF4, PF6 or BArF4) 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 (Mn ∼ 300 × 103) with a narrow distribution Mw/Mn ∼ 1.6, while the 18ē complexes 3a,b give polymers of lower molecular weight (Mn < 50 × 103) with a wider polydispersity index Mw/Mn ∼ 2.5.