Chiral ferrocenylthiazolidines, new ligands for palladium complexes

The reaction of ferrocene with methyl or ethyl esters of l-cysteine in the presence of paraformaldehyde is studied. This process yields the optically pure derivatives: methyl or ethyl (R)-3-(ferrocenylmethyl)thiazolidine-4-carboxylates (1a or 1b), together with the corresponding N,N-bisthiazolidine derivatives (2a or 2b). When the reaction was carried out using the ethyl ester of l-cysteine, small amounts (ca. 9%) of the 1,1’-disubstituted ferrocene derivative (3b) were also isolated. The reactivity of compounds 1 versus palladium(II) species is studied, and has allowed us to isolate and characterise: [Pd(η3-C3H5)Br(1a)] (4a) and [Pd(η3-C3H5)Br(1b)] (4b), in which the ferrocenyl ligand behaves as a monodentate S-donor group. Compounds 4 evolve in the presence of dimethylsulfoxide to produce: [Pd(η1-C3H5)Br(1)(dmso)] (5) in which the palladium(II) is bound to the terminal carbon of the C3H5 group. The reactivity of ligands 1 with Na2[PdCl4] is also reported and has allowed us to isolate the dinuclear compounds [Pd2Cl4(μ-1a)2] (6a) and [Pd2Cl4(μ-1b)2] (6b)] in which the thiazolidine behaves as a bridging (N,S) donor group.