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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
Author(s) -
Arthurs Ross A.,
Horton Peter N.,
Coles Simon J.,
Richards Christopher J.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201705113
Subject(s) - stereospecificity , cobalt , chemistry , cyclopentadienyl complex , phosphine , medicinal chemistry , ligand (biochemistry) , azide , enantioselective synthesis , stereoselectivity , enantiomer , stereochemistry , ketone , amine gas treating , planar chirality , catalysis , organic chemistry , biochemistry , receptor
Starting from (η 5 ‐acetylcyclopentadienyl)(η 4 ‐tetraphenylcyclobutadiene)cobalt(I), highly enantioselective (99 % ee ) ( S )‐CBS catalysed ketone reduction followed by stereospecific alcohol‐azide exchange, azide reduction and dimethyllation gave ( R )‐(η 5 ‐α‐ N , N ‐dimethylaminoethylcyclopentadienyl)(η 4 ‐tetraphenylcyclobutadiene) cobalt(I) (Arthurs’ amine). This underwent highly diastereoselective cyclopalladation to give di‐μ‐acetate‐bis‐( R )‐[(η 5 ‐( S p )‐2‐(α‐ N , N ‐dimethylaminoethyl)cyclopentadienyl, 1‐ C , N )(η 4 ‐tetraphenylcyclobutadiene)cobalt(I)]dipalladium, and highly diastereoselective lithiation to give ( R )‐(η 5 ‐( S p )‐1‐(α‐ N , N ‐dimethylaminoethyl)‐2‐(diphenylphosphino)cyclopentadienyl)(η 4 ‐tetraphenylcyclobutadiene)cobalt(I) (PPCA) following the addition as electrophile of chlorodiphenylphosphine. This PN‐ligand was converted into ( R )‐(η 5 ‐( S p )‐1‐(α‐dicyclohexylphosphinoethyl)‐2‐(diphenylphosphino)cyclopentadienyl)(η 4 ‐tetraphenylcyclobutadiene)cobalt(I), a PP‐ligand (Rossiphos), by stereospecific amine‐phosphine exchange using HPCy 2 . 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.