Ruthenium(II) complexes with chiral tetradentate P2N2 ligands catalyze the asymmetric epoxidation of olefins with H2O2

The five-coordinate complexes of the type [RuCl(PNNP)]PF6 (PNNP = tetradentate ligand with a P2N2 donor set) are prepared by chloride abstraction from [RuCl2(PNNP)I. A mixture of Delta-cis-beta- and n-cis-beta-[RuCl2(1a-(K)4P,N,N,P)I (2a; la = N,N'-bis[o-(diphenylphosphino)benzylidenel-2,2'-diimino- 1,1'-(S)-binaphthylene), prepared by reaction of la with [RuCl2-(PPh3)(3)], reacts with Tl[PF6], giving the five-coordinate [RuCl(1a-(K)4P,N,N,P)]PFs (3a). The related trans-[RuCl2( 1b-(K)4P,N,N, P] (2b; Ib = N,N'-bis[o-(diphenylphosphino)benzylidene ( 1S,2S)-diiminocyclohexane) reacts with Tl[PF6] to give [RuCl(1b-(K)4P,N,N,P)]PF6 (3b). With the amino ligand N,N'-bis[o-(diphenylphosphino)benzylidene (1c), the aqua complex [RuCl(OH2)(1c-P-4(K),N,N,P)]PF6 (5c) is obtained by reaction of Tl-[PF6] with [RuCl2(PPh3)(1c-P-3(K),N,N)] (4), which has been isolated and structurally characterized. The reactivity of the five-coordinate 2b with CO and oxygen donors such as water, Et2O, THF, and methanol is reported. Both 3 and 5 catalyze the asymmetric epoxidation of olefins with hydrogen peroxide as oxidant; Enantiomeric excesses up to 42% were obtained in the enantioselective epoxidation of styrene and of other unfunctionalized olefins. The reaction is highly stereospecific, as the epoxidation of (Z)-2-methylstyrene gives a cis:trans ratio of 99:1.