New diorganolead(IV) sulfanylpropenoates: Synthesis, characterization and analysis of their evolution in DMSO solution

Abstract The diorganolead(IV) sulfanylpropenoates [R 2 Pb(X-pspa)] {R = Me, Ph; H 2 (X-pspa) = 3-(4-X-phenyl)-2-sulfanylpropenoic acids; X = F, Cl, Br, I, CH 3 O, CF 3 O, HO} and [HQ] 2 [Ph 2 Pb(X-pspa) 2 ] (X = F, CH 3 O, HO; Q = diisopropylamine) were prepared. The structures of H 2 (Br-pspa) and [HQ] 2 [Ph 2 Pb(CH 3 O-pspa) 2 ]⋅2H 2 O were fully characterized in the solid state using X-ray diffraction. All sulfanylpropenoates and free sulfanylpropenoic acids are fairly soluble in DMSO. The acids are in general oxidised to the corresponding disulfide by DMSO except H 2 (I-pspa), a selective calpain inhibitor, which evolves to form two decomposition products neither of which is probably the disulfide. From the [Ph 2 Pb(X-pspa)] solutions in DMSO, several compounds have been isolated and identified by X-ray diffraction. Those with [Ph 2 Pb(Cl-pspa)(DMSO)] and [Ph 2 Pb(X-pspa)(DMSO)]⋅DMSO (X = Br, CH 3 O, F 3 CO) stoichiometries consist of molecules loosely associated in dimers. However, in solid [Ph 2 Pb(HO-pspa)(DMSO)]⋅2DMSO, the [Ph 2 Pb(HO-pspa)(DMSO)] molecules are assembled in chains along the x axis. NMR and ESI-MS measurements in freshly prepared [Ph 2 Pb(X-pspa)] solutions are compatible with the presence of dimeric or polymeric species such as those isolated in the solid state. However, the NMR spectra of [Me 2 Pb(X-pspa)] revealed that these compounds decompose quickly in DMSO due to redistribution reactions suffered by the organometallic moiety and the concomitant partial decomposition of the sulfanylpropenoates.