Chiral Ruthenium PNNP Complexes of Non-Enolized 1,3-Dicarbonyl Compounds: Acidity and Involvement in Asymmetric Michael Addition

The chiral complexes [Ru( 2 )(PNNP)] 2+ ( 4a ) and [Ru( 3 )(PNNP)] 2+ ( 4b ), containing the non-enolized 1,3-dicarbonyl compounds 2-(( tert -butoxy)carbonyl)cyclopentanone ( 2 ) or α-acetyl- N -benzyl-δ-valerolactam ( 3 ), were deprotonated to the enolato complexes 5a, b . Complex 4a has a pseudo-aqueous p K a value of 4.6 ± 0.5 (with p K a (Ph 3 PH + ) = 2.7 as reference) and catalyzes the 1,4-addition of 2 to methyl vinyl ketone with up to 79% ee.