Publications
Sulfur-Containing Alkenes - A New Class of Chelating Ligands: Synthesis, Coordination to Palladium, and Structure of the Resulting Complexes
Stable 1,2-disulfanylalkene palladium complexes [(RS-CH=CR′-SR)PdCl2] were synthesized in 85–94% yield by reaction of palladium(II) chloride with sulfur-containing ligands RS-CH=C(R′)-SR (analogs of dithiolate ligands). The structure of the complexes was studied by NMR spectroscopy and quantum-chemical methods. The binding energy in palladium complexes with bis(arylsulfanyl)- and bis(alkylsulfanyl)alkenes was estimated (DFT) at 50 and 56 kcal/mol, respectively. Variation of substituents on the sulfur atoms is a convenient tool for fine tuning of the ligand properties and controlling the strength of the complex. The bite angle of the ligands does not depend on the substituent nature and is 88–89°, which is typical of square-planar complexes. According to the bite angle, the examined ligands are analogs of well known bidentate phosphine ligands, but the former are more labile since the corresponding binding energy is lower by 36 kcal/mol.
General Procedure of Pd-Catalyzed Selective Hydrophosphorylation of Alkynes
A novel catalytic system has been developed to accomplish the hydrophosphorylation of terminal and internal alkynes with high isolated yields (up to 96%) and excellent regio- and stereoselectivity (>99:1). The key factor was to apply a low-ligated palladium/triphenylphosphane (1:2) catalytic system in the presence of a catalytic amount of trifluoroacetic acid. The catalytic system so developed has been applied successfully to permit the formation of diverse alkenylphosphonates utilizing a variety of available H-phosphonates and alkynes.
Catalyst Leaching - an Efficient Tool for Constructing New Catalytic Reactions. Application to the Synthesis of Cyclic Vinylsulfides and Vinylselenides
Catalyst leaching from Pd and Ni particles stabilized by organic sulfur and selenium ligands occurs in solution in the presence of phosphanes. This process has been monitored in real time by 1D and 2D NMR spectroscopy and the nature of the metal species established. This catalyst leaching is shown to be a powerful tool for generating new catalytic activity from species formed in situ where the parent bulk particles are inactive. The catalytic system developed has been successfully implemented in a novel synthetic procedure that provides new types of cyclic sulfur and selenium compounds in high yields through the reaction between alkynes and dichalcogenides.
