Palladium(II)–allyl complexes containing chiral N-donor ferrocenyl ligands

Abstract

A study of the reactivity of enantiopure ferrocenylimine ( S C )-[FcCH N–CH(Me)(Ph)] {Fc = (η 5-C 5H 5)Fe{(η 5-C 5H 4)–} ( 1a) with palladium(II)–allyl complexes [Pd(η 3-1R 1,3R 2-C 3H 3)(μ-Cl)] 2 {R 1 = H and R 2 = H ( 2), Ph ( 3) or R 1 = R 2 = Ph ( 4)} is reported. Treatment of 1a with 2 or 3 {in a molar ratio Pd(II): 1a = 1} in CH 2Cl 2 at 298 K produced [Pd(η 3-3R 2-C 3H 4){FcCH N–CH(Me)(Ph)}Cl] {R 2 = H ( 5a) or Ph ( 6a)}. When the reaction was carried out under identical experimental conditions using complex 4 as starting material no evidence for the formation of [Pd(η 3-1,3-Ph 2-C 3H 3){FcCH N–CH(Me)(Ph)}Cl] ( 7a) was found. Additional studies on the reactivity of ( S C )-[FcCH N–CH(R 3)(CH 2OH)] {R 3 = Me ( 1b) or CHMe 2 ( 1c)} with complex 4 showed the importance of the bulk of the substituents on the palladium(II) allyl–complex ( 2– 4) or on the ferrocenylimines ( 1) in this type of reaction. The crystal structure of 5a showed that: (a) the ferrocenylimine adopts an anti-( E) conformation and behaves as an N-donor ligand, (b) the chloride is in a cis-arrangement to the nitrogen and (c) the allyl group binds to the palladium(II) in a η 3-fashion. Solution NMR studies of 5a and 6a and [Pd(η 3-1,3-Ph 2-C 3H 3){FcCH N–CH(Me)(CH 2OH)}Cl] ( 7b) revealed the coexistence of several isomers in solution. The stoichiometric reaction between 6a and sodium diethyl 2-methylmalonate reveals that the formation of the achiral linear trans-( E) isomer of Ph–CH CH–CH 2Nu ( 8) was preferred over the branched derivative ( 9). A comparative study of the potential utility of ligand 1a, complex 5a and the amine ( S C )-H 2N–CH(Me)(Ph) ( 11) as catalysts in the allylic alkylation of ( E)-3-phenyl-2-propenyl ( cinnamyl) acetate with the nucleophile diethyl 2-methylmalonate (Nu −) is reported.