The chiral dicationic complexes [Ru(4a)(PNNP)]2+ (2a) and [Ru(4h)(PNNP)]2+ (2h, PNNP is (1S,2S)-N,N′-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine), containing non-enolized 2-tert-butoxycarbonylcyclopentanone (4a) or α-acetyl-N-benzyl-δ-valerolactam (4h), were prepared from [RuCl2(PNNP)] (1) by double chloride abstraction with (Et3O)PF6, followed by reaction with the 1,3-dicarbonyl compound. The estimated aqueous pK
a values for 2a (3.3 ± 0.3) and 2h (4.7 ± 0.1) were determined by deprotonation with Ph2NH and pyridine, respectively. The corresponding monocationic enolato complexes 3a and 3h were isolated and structurally characterized. Complex 2a catalyzes the 1,4-addition of 4a to methyl vinyl ketone with up to 93% ee when a CH2Cl2/Et2O (1:1) solvent mixture is used. Oxygen-containing cosolvents enhance both the rate and enantioselectivity of the Michael addition with a number of substrates. This observation is discussed in the context of our previous observation that the combined addition of diethyl ether and of β-keto ester 4a favors and accelerates the deprotonation of 2a in dichloromethane.