Co-ordination chemistry of 3S-aminopyrrolidine and 3S-(methylamino)pyrrolidine: crystallisation of the two diastereomers of dichloro[3S-(R,S-methylamino)pyrrolidine]palladium(II)

Abstract

Complexes of divalent Cu, Ni, Pd and Pt with 3S-aminopyrrolidine (S-ap) have been prepared and characterised by a combination of NMR, CD, electronic, IR and microanalytical techniques. The chosen chirality of the stereogenic carbon (S) forces the secondary nitrogen to adopt the R stereochemistry on co-ordination with the conformation of the 5-membered chelate being λ. The planar [M(S-ap)2]2+ complexes exist as a mixture of cis and trans isomers in the solid state and in solution. The trans arrangement is forced upon co-ordination of an axial donor (X = halide, thiocyanate or nitrite) in the five-co-ordinate ions [Cu(S-ap)2X]+. Methylation of the primary amine of S-ap generates another secondary nitrogen centre in the new ligand 3S-(methylamino)pyrrolidine, S-meap. This exocyclic nitrogen is not restricted to a single configuration on co-ordination. The complexes [M(S-meap)Cl2], where M = Pd or Pt, have been prepared and characterised. Both diastereoisomers (R- and S-NMe) of [Pd(S-meap)Cl2] crystallise from aqueous solution as distinct crystal forms which can be separated by mechanical means. The structure of the NMe(R) isomer has been determined by X-ray crystallography.