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

Citation
Rm. Stoop et al., Ruthenium(II) complexes with chiral tetradentate P2N2 ligands catalyze theasymmetric epoxidation of olefins with H2O2, ORGANOMETAL, 19(20), 2000, pp. 4117-4126
Citations number
71
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANOMETALLICS
ISSN journal
02767333 → ACNP
Volume
19
Issue
20
Year of publication
2000
Pages
4117 - 4126
Database
ISI
SICI code
0276-7333(20001002)19:20<4117:RCWCTP>2.0.ZU;2-B
Abstract
The five-coordinate complexes of the type [RuCl(PNNP)]PF6 (PNNP = tetradent ate 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-(dip henylphosphino)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 wate r, Et2O, THF, and methanol is reported. Both 3 and 5 catalyze the asymmetri c epoxidation of olefins with hydrogen peroxide as oxidant; Enantiomeric ex cesses up to 42% were obtained in the enantioselective epoxidation of styre ne and of other unfunctionalized olefins. The reaction is highly stereospec ific, as the epoxidation of (Z)-2-methylstyrene gives a cis:trans ratio of 99:1.