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

Arthurs, Ross A., Horton, Peter N., Coles, Simon J. and Richards, Christopher J. (2018) 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. Chemistry - A European Journal, 24 (17), 4310-4319. (doi:10.1002/chem.201705113).

Abstract

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.

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Contributors

Author: Peter N. Horton

Author: Simon J. Coles

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