Allylpalladium Dimers with Metals Connected by Binucleating Dithiooxamidates in Two Different Coordination Modes: Solution Behavior and Solid-State Structure

Abstract

A series of allylpalladium dimers having metals connected by binucleating dialkyldithiooxamidate [N(R)SC-CS(R)N](2-) [R = methyl, ethyl, isopropyl, benzyl, isoamyl, (S)-1-(1-phenyl)ethyl, meso-(1-phenyl)ethyl, and rac-(1-phenyl)ethyl] were prepared by reacting the monochelate [(η(3)-allyl)Pd(N(R)SC-CS(R)NH κ-S,S Pd)] with [(η(3)-allyl)PdCl](2) in chloroform. At low temperature (20 °C), the bimetallic complexes [(η(3)-allyl)Pd](2)(μ-dialkyldithiooxamidate κ-N,N' Pd, κ-S,S' Pd') (kinetic compounds) are formed in a short reaction time (10 min). At a higher temperature (50 °C) and a longer reaction time (24 h), the corresponding bimetallic isomers [(η(3)-allyl)Pd](2)(μ-dialkyldithiooxamidate κ-N,S Pd, κ-N',S' Pd') (thermodynamic compounds) are obtained. Both kinetic and thermodynamic compounds can exist as endo or exo isomers, depending on the reciprocal orientation of the allyl cuspids. Both endo and exo isomers are only detectable in solution when the alkyl substituents are chiral alkyl groups. Moreover, diffractometric modeling agrees with the presence of both isomers in the solid state even when the alkyl substituent is an achiral alkyl group. In a chloroform solution, endo and exo isomers undergo isomeric conversion owing to the apparent allyl rotation that follows the Pd-N bond rupture in the (η(3)-allyl)Pd(N^N) frame of kinetic compounds or in the (η(3)-allyl)Pd(N^S) frame of thermodynamic compounds. The dithiooxamidate [N(R)SC-CS(R)N](2-), when engaged in a κ-N,S Pd, κ-N',S' Pd' coordination mode, behaves as a hybrid hemilabile binucleating ligand. At room temperature and in a chloroform solution, the kinetic compounds rearrange into the thermodynamically more stable isomers in about 3 or 4 days. The higher stability of the thermodynamic species was evaluated by means of computational studies in accordance with the maximum hardness principle. Finally, the crystal structures of [(η(3)-allyl)Pd](2)(μ-diethyldithiooxamidate κ-N,S Pd, κ-N',S' Pd'), [(η(3)-allyl)Pd](2)(μ-meso-(1-phenyl)ethyldithiooxamidate κ-N,S Pd, κ-N',S' Pd'), and [(η(3)-allyl)Pd](2)(μ-rac-(1-phenyl)ethyldithiooxamidate κ-N,N' Pd, κ-S,S' Pd') are reported.

Synthesis, Characterization and Anticancer Studies of Rh(I), Rh(III), Pd(II) and Pt(II) Complexes Bearing A Dithiooxamide Ligand

“…H 2 ‐isopropyl 2 DTO is a bidentate sulfur ligand which, by reacting with chloro bridges, can cleave them and form mononuclear complexes . Structurally, this secondary dithiooxamide is a chelating binucleating ligand which can also form binuclear complexes depending on the stoichiometric ratios and the nature of the chlorido‐bridged dimers . Ion pair complexes IP1‐IP4 were prepared by the reaction of H 2 ‐isopropyl 2 DTO with half molar of the related chlorido‐bridged dimers.…”

Crystal structure of (μ-N,N′-dibenzyldithiooxamidato-κN,S:N′,S′)bis[(η3-crotyl)palladium(II)]

“…For background to structures similar to that of the title compound in which Pd II atoms are linked to allyl groups, see: Lanza et al (2003Lanza et al ( , 2011. For the stereochemical descriptor of a 3 -crotyl plane, see: Schlö gl (1967).…”

“…The compound might exist in different diastereomeric forms: one, represented here, is a mesoform having crotyl CH 3 cis to sulfur; the other is a racemate having crotyl CH 3 cis to sulfur and crotyl cusps oriented toward the same side of palladium molecular square planes. A more detailed description of the stereochemistry of the title compound has been done by us previously (Lanza et al, 2000;Lanza et al, 2011). Both the other mesoform and the racemate having the crotyl CH 3 cis to the nitrogen probably cannot be formed because of close contact between the crotyl CH 3 and the DTO benzyl substituents.…”