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
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.