Cyclic Ether Induced Asymmetric Cyclopalladation: Synthesis and Structural Characterization of Enantiopure Bis(μ-acetato)-Bridged Dimers of Planar Chiral Cyclopalladated Ferrocenylimines and Their Derivatives
journal contributionposted on 12.08.1999, 00:00 by Gang Zhao, Qing-Chuan Yang, Thomas C. W. Mak
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Enantiopure bis(μ-acetato)-bridged planar chiral cyclopalladated products (R = H, Me) have been obtained by asymmetric cyclopalladation of the corresponding chiral ferrocenylimines with palladium(II) acetate and sodium acetate in methanol at room temperature with a high level of diastereoselectivity (product ratio syn-(+)-(Rp,R,R,Rp):syn-(−)-(Sp,R,R,Sp) ≈ syn-(−)-(Sp,S,S,Sp):syn-(+)-(Rp,S,S,Rp) ≈ 9:1). One or both acetato groups can be readily substituted by other anionic ligands to yield novel mixed-bridge or bis(μ-anion)-bridged planar chiral dimers of ferrocene derivatives. The first cis-type syn-(Rp,Sp) cyclopalladated dimer of ferrocenylimine has been obtained. The diphenylacetylene insertion reaction of a variety of anion-bridged planar chiral dimeric cyclopalladated derivatives of ferrocene has also been investigated. The absolute configurations of bis(μ-acetato)-, bis(μ-halogeno)-, (μ-1κS:2κN)-(μ-1κN:2κS)-thiocyanato-, and (μ-1κO:2κN)-(μ-1κN:2κO)-nitrito-bridged planar chiral dimers and bis(diphenylacetylene) insertion products have been elucidated by single-crystal X-ray analysis.