Diastereoisomeric cationic pi-allylpalladium-(P,C)-MAP and MOP complexes and their relationship to stereochemical memory effects in allylic alkylation

GC Lloyd-Jones*, SC Stephen, M Murray, CP Butts, S Vyskocil, P Kocovsky

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The axially chiral ligands 2-(diphenylphosphanyl)-2'-methoxy-1,1'-binaphthalene (MOP; 6) and 2'-dimethylamino-2-(diphenylphosphanyl)-1,1'-binaphthalene (MAP; 7) coordinate to a cationic allylpalladium fragment in an unusual bidentate (P,C)-mode through the triarylphosphane and ipso-carbon atom (C1'). The readily prepared MAP and MOP complexes [Pd{(P,C)-(L)}(eta (3)-allyl)][OTf] (9 (L = 7) and 10 (L = 6)) have been characterised in solution (NMR), in which two diastereoisomeric rotamers are observed. The stereochemical identity of the rotamers is established by one- and two-dimensional NMR spectroscopy experiments. In both the solid state and in solution, the allyl unit is shown to coordinate in a slightly distorted eta (3)-mode that results in a more alkene-like character at the allyl terminus trans to phosphane ligand, The opposite allyl terminus, which is trans to the ipso-carbon atom (C1'), is more strongly bound and the dominant allyl stereodynamic process involves C-C bond rotation in an eta (1)-allyl intermediate bound through this carbon. Palladium complexes of MAP and MOP are very efficient catalysts for allylic alkylation of racemic cyclopentenyl pivalate with [NaCH(CO2Me)(2)] in THF. Isotopic desymmetrisation revealed that the reaction occurs with powerful stereochemical memory effects and consequently with low global ee values. The memory effect is suggested to arise through selective generation of diastereoisomeric [Pd{(P,C)-L}(eta (3)-cyclopentenyl)](+) ions (L = MAP or MOP) and subsequent capture by nucleophile before ion-pair collapse or equilibration occurs.

Original languageEnglish
Pages (from-to)4348-4357
Number of pages10
JournalChemistry - A European Journal
Volume6
Issue number23
Publication statusPublished - 1 Dec 2000

Keywords

  • isotopic labeling
  • memory effects
  • P,C coordination
  • palladium
  • pi-allyl complexes
  • PALLADIUM-MOP
  • ASYMMETRIC HYDROSILYLATION
  • OXIDATIVE ADDITION
  • KINETIC RESOLUTION
  • 2-AMINO-2'-DIPHENYLPHOSPHINO-1,1'-BINAPHTHYL MAP
  • (PI-ALLYL)PALLADIUM COMPLEXES
  • HOMOGENEOUS CATALYSIS
  • PD-COMPLEXES
  • SUBSTITUTION
  • LIGANDS

Cite this