New catalytic system for S-S and Se-Se bond addition to alkynes based on phosphite ligands

A new catalytic system for the Ar2E2 (E = S, Se) addition to terminal alkynes (HC=C-R) has been developed to synthesize bis-element-substituted alkenes Z-H(ArE)C=C(EAr)R with high stereoselectivity and yields. Utilizing phosphite ligand P(OiPr)(3) allowed solving two major problems of this catalytic reaction: (1) prevent catalyst polymerization and (2) simplify product purification procedures. Key intermediates-trans-[Pd(SPh)(2)(P(OiPr)(3))(2)] and trans-[Pd-2(SPh)(4)(P(OiPr)(3))(2)]-were synthesized by S-S oxidative addition reaction to Pd(0) and studied by X-ray analysis. The equilibrium between the mononuclear and dinuclear complexes in solution was established by P-31 NMR spectroscopy. In addition to the advantages in the synthetic procedure, the isolation of the stable palladium complexes with phosphite ligand made possible a detailed mechanistic study of the catalytic reaction.