Trinuclear Heterobimetallic Complexes with Binucleating Dithioxamides: Stereoselective Synthesis and Solution Behavior Involving Pd -N Bond Rupture

Bischelate platinum(II) complexes of the type [Pt(H-R2-N2C2S2)2] (H-R2-N2C2S2- = dialkyl-dithioxamidate) are ditopic receptors which, after coordination of the first Pd( 3-allyl)+ moiety, induce the orientation of the second palladium-allyl fragment. Thus, a series of trimetallic complexes of formula bis-[((eta)^3-allyl)-palladium(II)]((mu)-bis-dialkyl-dithioxamidate-platinum(II) (kappa)-S,S-(kappa)-Sʹ,Sʹ-Pt(kappa)-N,N-Pd-(kappa)-Nʹ,Nʹ-Pdʹ) has been prepared in which the allyl fragments are oriented toward the same side of the molecular plane. We have also prepared the trimetallic complex using a dithioxamide obtained from the racemic phenylethylamine. Only two isomers were produced in equimolar ratio: the racemate that has four homochiral alkyl substituents and the mesoform containing the meso-dithioxamide that has homochiral substituents on the same side of molecular plane. Under the effect of the temperature, the trimetallic Pd-Pt-Pd complexes undergo rapid allyl isomerization; the mechanism of the isomerization, which is similar to that found by us in an analogue Pt-Pd bimetallic complex, is discussed. The crystal and molecular structure of bis-[((eta)^3-allyl)-palladium(II)]( -bis-{S}phenylethyl-dithioxamidate-platinum(II) (kappa)-S,S-(kappa)-Sʹ,Sʹ-Pt-(kappa)-N,N-Pd-(kappa)-Nʹ,Nʹ-Pdʹ) has been reported.