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

A study of the reactivity of enantiopure ferrocenylimine (Sc)-[FcCH=N-CH(Me)(Ph)] {Fc= (eta(5)-C5H5)Fe{(eta(5)-C5H4)-} (la) with palladium(II)-allyl complexes [Pd(eta(3)-1R(1),3R(2)-C3H3)(mu-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 CH2Cl2 at 298 K produced [Pd(eta(3)-3R(2)-C3H4) {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(eta(3)-1,3-Ph-2-C3H3){FcCH=N-CH(Me)(Ph)}Cl] (7a) was found. Additional studies on the reactivity of (S-C)-[FcCH=N-CH(R-3)(CH2OH)] {R-3 = Me (1b) or CHMe2 (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 eta(3)-fashion. Solution NMR studies of 5a and 6a and [Pd(eta(3)-1,3-Ph-2-C3H3){FcCH=N-CH(Me)(CH2OH)}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(2)Nu (8) was preferred over the branched derivative (9). A comparative study of the potential utility of ligand 1a, complex 5a and the amine (Sc)H2N-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. (c) 2007 Elsevier B.V. All rights reserved.