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

A study of the reactivity of enantiopure ferrocenylimine (SC)-[FcCHdouble bond; length as m-dashN–CH(Me)(Ph)] {Fc = (η5-C5H5)Fe{(η5-C5H4)–} (1a) with palladium(II)–allyl complexes [Pd(η3-1R1,3R2-C3H3)(μ-Cl)]2 {R1 = H and R2 = H (2), Ph (3) or R1 = R2 = 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(η3-3R2-C3H4){FcCHdouble bond; length as m-dashN–CH(Me)(Ph)}Cl] {R2 = 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(η3-1,3-Ph2-C3H3){FcCHdouble bond; length as m-dashN–CH(Me)(Ph)}Cl] (7a) was found. Additional studies on the reactivity of (SC)-[FcCHdouble bond; length as m-dashN–CH(R3)(CH2OH)] {R3 = 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 acis-arrangement to the nitrogen and (c) the allyl group binds to the palladium(II) in a η3-fashion. Solution NMR studies of 5a and 6a and [Pd(η3-1,3-Ph2-C3H3){FcCHdouble bond; length as m-dashN–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–CHdouble bond; length as m-dashCH–CH2Nu (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.