Cyclopalladation of Schiff's bases in the ruthenocene series. The possibility of application of the asymmetric version of the reaction to metalloceneimines

Abstract

p-Tolyliminoalkylruthenocenes --Schiff's bases of the ruthenocene series --react with sodium tetrachloropalladate in the presence of carboxylate anion similarly to their ferrocenyl analogs to give cyclopalladation products. The optical rotation values of the products resulting from carbonylation of palladated ferrocene and ruthenocene aldimines, prepared under conditions of asymmetric catalysis, followed by liberation of the aldehyde group were used to determine the stereochemistry and enantiomeric purity of the cyclopalladation products.

Abnormal cyclopalladation of Schiff bases made of metallocenyl aldehydes and α-ferrocenylethylamine: Unexpected formation of the heteroannular 3-atomic bridge

“…Cyclopalladation was performed following the procedure [13] that afforded dimeric organopalladium products hardly soluble in organic solvents. If there is no regio-and diastereoselectivity, monomeric product should be a mixture of four diastereoisomers whereas for dimers the number of isomers will be more.…”

Cooperative Bimetallic Asymmetric Catalysis: Comparison of a Planar Chiral Ruthenocene Bis-Palladacycle to the Corresponding Ferrocene

“…Most of the few known methods provide racemic or achiral palladacycles. To our knowledge the attempts toward direct enantioselective or diastereoselective cyclopalladations of ruthenocenes providing planar chiral Pd­(II)-complexes always resulted in poor to moderate stereoselectivity thus far. Highly enantioenriched ruthenocene palladacycles have only very recently been reported by Kündig et al, who employed indenyl derived ruthenocene substrates already containing the element of planar chirality prior to the cyclopalladation step, thus elegantly avoiding a stereoselectivity issue upon the cyclometalation event …”

New principle for palladacycle resolution: diastereoselective monomer to dimer conversion

“…The third method based on the asymmetric activation of the C-H bond under control of an optically active base [34][35][36][37][38][39] or ligand in the palladation agent [40][41][42] is not so popular and used mainly for prochiral substrates. Except in a few cases, 41 the latter approach does not provide palladacycles in enantiomerically pure form and requires further minor enantiomer removal at the final stages.…”