J. Am. Chem. Soc., 127 (8), 2388 -2389, 2005. 10.1021/ja042930e S0002-7863(04)02930-0
Web Release Date: February 4, 2005

Copyright © 2005 American Chemical Society

Synthesis of Planar Chiral Phosphapalladacycles by Highly Enantioselective Transcyclopalladation

Francesc X. Roca, Majid Motevalli, and Christopher J. Richards*

Department of Chemistry, Queen Mary, University of London, Mile End Road, London, E1 4NS, U.K.

c.j.richards@qmul.ac.uk

Received November 23, 2004

Abstract:

The first highly enantioselective synthesis of planar chiral ferrocene phosphapalladacycles was performed by high-yielding asymmetric transcyclopalladation with cobalt oxazoline palladacycles (COP). Use of di--acetatobis[(5-(S)-(pR)-2-(2'-(4'-isopropyl)oxazolinyl)cyclopentadienyl-C1,N3')(4-tetraphenylcyclobutadiene)cobalt]dipalladium(II), followed by acetate/chloride ligand exchange, gave (pS)-di--chloro[2-(2-dicyclohexylphosphino)phenylferroene-C1,P)dipalladium(II) (95% ee). Similarly, diastereomeric di--acetatobis[(5-(S)-(pS)-2-(2'-(4'-tert-butyl)oxazolinyl)cyclopentadienyl-C1,N3')(4-tetraphenylcyclobutadiene)cobalt]dipalladium(II) led to the enantiomeric (pR)-phosphapalladacycle (95% ee), revealing the control of these reactions by the element of planar chirality in COP. The reactions were extended to the synthesis of (pS)- and (pR)-di--chloro[2-(2-diphenylphosphino)phenylferroene-C1,P)dipalladium(II) (78 and 92% ee, respectively). In all cases, the palladium-free precursors to COP were recovered for recycling.

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