A group of P-stereogenic monodentate phosphines S-PPhRR′ (R ) 1-naphthyl, 9-phenanthryl, or o-biphenylyl and R′ ) CH 3 -, i-C 3 H 8 -, and Ph 3 SiCH 2 -) have been prepared by succesive substitution reactions on the oxazaphospholidineborane obtained from (-)ephedrine and bis(N,N-diethylamino)phenylphosphine. The reaction with binuclear allyl compounds [Pd(µ-Cl)(allyl)] 2 gives neutral [PdCl(allyl)P*] complexes. When allyl ) 2-CH 3 -C 3 H 4 (5), two isomers appeared in solution due to the R-or S-geometry around the palladium atom. The discrimination effect of the phosphines is small and the maximum isomeric ratio is observed for PPh(o-Ph 2 )(CH 2 SiPh 3 ). The molecular structure determined by X-ray diffraction of two complexes with P* ) PPh(o-Ph 2 )(i-Pr) and PPh(o-Ph 2 )(OMe) showed a very similar nonsymmetric coordination of the allyl moiety according to the greater trans influence of the phosphorus atom. When allyl ) 1-C 6 H 5 -C 3 H 4 (6), the NMR spectroscopy showed up to four isomers due to the R-or S-geometry around palladium and the Z-or E-disposition of P* and the phenyl substituent of the allyl moiety. The E-isomers are the major species in solution, unique with PPh(o-Ph 2 )(CH 2 SiPh 3 ). The usual, well-defined dynamic exchanges by π-σ-π and pseudorotation of the allyl moiety have been observed. The codimerization reaction between styrene and ethylene has been tested using filtered CH 2 Cl 2 solutions of [PdCl(2-CH 3 -C 3 H 4 )P*] (5) complexes and AgBF 4 as catalytic precursors. Moderate activity (TOF < 225 h -1 at 25 °C) and good selectivities to 3-Ph-1-butene (∼90% at 80% conversion) are obtained. The ee is moderate (<40% ee) and different from the discrimination effects observed in the solutions of neutral complexes [PdCl(ally)P*]. The reaction carried out with deuterated styrene shows the clean C-H addition to the vinyl double bond of stryrene and confirms the irreversible nature of the insertion of styrene in the palladium hydride intermediate. The hydrovinylation reaction using substituted styrene with a potentially secondary coordination atom occurs only when the substitution is in the phenyl ring and without significant improvements of the ee.

The five-coordinate complexes of the type [RuCl(PNNP)]PF 6 (PNNP ) tetradentate ligand with a P 2 N 2 donor set) are prepared by chloride abstraction from [RuCl 2 (PNNP)]. A mixture of ∆-cis-β-and Λ-cis-β-[RuCl 2 (1a-κ 4 P,N,N,P)] (2a; 1a ) N, N′-bis[o-(diphenylphosphino)benzylidene]-2,2′-diimino-1,1′-(S)-binaphthylene), prepared by reaction of 1a with [RuCl 2 -(PPh 3 ) 3 ], reacts with Tl[PF 6 ], giving the five-coordinate [RuCl(1a-κ 4 P,N,N,P)]PF 6 (3a). The related trans-[RuCl 2 (1b-κ 4 P,N,N,P)] (2b; 1b ) N, N′-bis[o-(diphenylphosphino)benzylidene]-(1S,2S)-diiminocyclohexane) reacts with Tl[PF 6 ] to give [RuCl(1b-κ 4 P,N,N,P)]PF 6 (3b). With the amino ligand N, N′-bis[o-(diphenylphosphino)benzylidene]-(1S,2S)-diaminocyclohexane (1c), the aqua complex [RuCl(OH 2 )(1c-κ 4 P,N,N,P)]PF 6 (5c) is obtained by reaction of Tl-[PF 6 ] with [RuCl 2 (PPh 3 )(1c-κ 3 P,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, Et 2 O, 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.

The enantioselective formation of a quaternary stereogenic center coinciding with a hydroxylation process is a very rare reaction from a homogeneous catalysis point of view. Indeed, to our knowledge, no asymmetric transition-metal-catalyzed direct hydroxylation has been reported before. We describe here our initial study concerning the enantioselective ␣-hydroxylation of various ␤-ketoesters catalyzed by Lewis-acidic complexes. Specifically, it was found that the Ti complex [TiCl2((R,R)-1-Np-TADDOLato)(MeCN)2] affords the hydroxylated products in high yield and enantioselectivities up to 94% enantiomeric excess when using 2-(phenylsulphonyl)-3-(4-nitrophenyl)oxaziridine as the oxidizing agent. Chiral enantiopure compounds of the latter type have been used previously in stoichiometric asymmetric hydroxylation reactions. We also show that, in a complementary approach with H2O2 as the oxidant, the Ru(II) complex [RuCl(OE 2)((S,S)-PNNP)]PF6 catalyzes the same type of transformation in a case of substrates showing a very substantial extent of enolization under reaction conditions; being, however, unreactive toward only weakly enolized ␤-ketoesters.R eactions involving both the formation of new carbonheteroatom bonds and the concomitant generation of a new stereogenic center are prototypical transformations in asymmetric catalysis. Thus, for example, hydroboration, hydrosilylation, epoxidation, and aziridination of olefins, as well as allylic substitutions with heteroatom nucleophiles, have been extensively studied (1). However, catalytic halogenations, in particular fluorinations, and direct hydroxylations have received much less attention in the asymmetric catalysis community.Recently, we developed an enantioselective catalytic process in which ␤-ketoesters are fluorinated at the 2-position with an electrophilic fluorine donor such as Selectfluor [also called F-TEDA (TEDA, triethylenediamine), 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis{tetrafluoroborate}] in the presence of a Lewis-acidic chiral titanium catalyst (1, Scheme 1, Fig. 1 (2-5). Our work inspired further developments involving chiral Pd catalysts (6) and chiral phase transfer catalysts for the same type of fluorination (7).The ␣-hydroxycarbonyl functional unit is ubiquitous in natural products and bioactive compounds, such as, e.g., carbohydrates, antibiotics, and antitumor agents; therefore, it is also present in synthetic intermediates and in chiral auxiliaries in view of the stereodirecting ability of the hydroxy group (8). The ␣-functionalization of carbonyl compounds most often relies on the reaction of enolate anions, or enol derivatives with electrophiles. The direct activation of the enol form of keto derivatives has recently been introduced as a new synthetic methodology to achieve ␣-amination (9) or, as already mentioned, ␣-halogenation (2-5). So far, the only straightforward enantioselective ␣-hydroxylation is the reaction of enolate salts with enantiopure N-sulfonyloxaziridines, acting as electrophilic oxygen sources, as dev...