Allylpalladium Complexes with P-Stereogenic Monodentate Phosphines. Application in the Asymmetric Hydrovinylation of Styrene

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• 作者：Arnald Grabulosa ; Guillermo Muller ; Juan I. Ordinas ; Antonio Mezzetti ; Miguel Á ; ngel Maestro ; Merc&egrave ; Font-Bardia ; and Xavier Solans
• 刊名：Organometallics
• 出版年：2005
• 出版时间：October 10, 2005
• 年：2005
• 卷：24
• 期：21
• 页码：4961 - 4973
• 全文大小：326K
• 年卷期：v.24,no.21(October 10, 2005)
• ISSN：1520-6041

文摘

A group of P-stereogenic monodentate phosphines S-PPhRR' (R = 1-naphthyl, 9-phenanthryl, or o-biphenylyl and R' = CH₃-, i-C₃H₈-, and Ph₃SiCH₂-) have been prepared bysuccesive substitution reactions on the oxazaphospholidineborane obtained from (-)-ephedrine and bis(N,N-diethylamino)phenylphosphine. The reaction with binuclear allylcompounds [Pd(-Cl)(allyl)]₂ gives neutral [PdCl(allyl)P*] complexes. When allyl = 2-CH₃-C₃H₄ (5), two isomers appeared in solution due to the R- or S-geometry around the palladiumatom. The discrimination effect of the phosphines is small and the maximum isomeric ratiois observed for PPh(o-Ph₂)(CH₂SiPh₃). The molecular structure determined by X-raydiffraction of two complexes with P* = PPh(o-Ph₂)(i-Pr) and PPh(o-Ph₂)(OMe) showed a verysimilar nonsymmetric coordination of the allyl moiety according to the greater trans influenceof the phosphorus atom. When allyl = 1-C₆H₅-C₃H₄ (6), the NMR spectroscopy showed up tofour isomers due to the R- or S-geometry around palladium and the Z- or E-disposition ofP* and the phenyl substituent of the allyl moiety. The E-isomers are the major species insolution, unique with PPh(o-Ph₂)(CH₂SiPh₃). The usual, well-defined dynamic exchangesby -- and pseudorotation of the allyl moiety have been observed. The codimerizationreaction between styrene and ethylene has been tested using filtered CH₂Cl₂ solutions of[PdCl(2-CH₃-C₃H₄)P*] (5) complexes and AgBF₄ 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 effectsobserved in the solutions of neutral complexes [PdCl(ally)P*]. The reaction carried out withdeuterated styrene shows the clean C-H addition to the vinyl double bond of stryrene andconfirms the irreversible nature of the insertion of styrene in the palladium hydrideintermediate. The hydrovinylation reaction using substituted styrene with a potentiallysecondary coordination atom occurs only when the substitution is in the phenyl ring andwithout significant improvements of the ee.