Stereoselective and Stereospecific Reactions of Cobalt Sandwich Complexes: Synthesis of a New Class of Single Enantiomer Bulky Planar Chiral P−N and P−P Ligands

Ross A. Arthurs, Peter N. Horton, Simon J. Coles, Christopher J. Richards (Lead Author)

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Abstract

Starting from (η5-acetylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt(I), highly enantioselective (99 % ee) (S)-CBS catalysed ketone reduction followed by stereospecific alcohol-azide exchange, azide reduction and dimethyllation gave (R)-(η5-α-N,N-dimethylaminoethylcyclopentadienyl)(η4-tetraphenylcyclobutadiene) cobalt(I) (Arthurs’ amine). This underwent highly diastereoselective cyclopalladation to give di-μ-acetate-bis-(R)-[(η5-(Sp)-2-(α-N,N-dimethylaminoethyl)cyclopentadienyl, 1-C, N)(η4-tetraphenylcyclobutadiene)cobalt(I)]dipalladium, and highly diastereoselective lithiation to give (R)-(η5-(Sp)-1-(α-N,N-dimethylaminoethyl)-2-(diphenylphosphino)cyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt(I) (PPCA) following the addition as electrophile of chlorodiphenylphosphine. This PN-ligand was converted into (R)-(η5-(Sp)-1-(α-dicyclohexylphosphinoethyl)-2-(diphenylphosphino)cyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt(I), a PP-ligand (Rossiphos), by stereospecific amine-phosphine exchange using HPCy2. These air-stable P−N and P−P complexes are the first examples of a new class of bulky planar chiral ligands for application in asymmetric catalysis.
Original languageEnglish
Pages (from-to)4310-4319
JournalChemistry - A European Journal
Volume24
Issue number17
Early online date1 Feb 2018
DOIs
Publication statusPublished - 20 Mar 2018

Keywords

  • cobalt
  • sandwich complexes
  • ligands
  • diastereoselectivity
  • enantioselectivity

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