Pd and Ni-Catalyzed Formation of Vinyl Chalcogenides

In the pioneering study of Ogawa, Sonoda et id., published in 1991, it was shown that Ph2S2 and At2Se2 in the Pd(PPh3)4 atalyzed conditions can be added to terminal alkynes (benzene, 80 °C) in good yields (54-98%) and with high selectivity towards 

Important mechanistic data were provided in the study of the carbonylative addition reaction, which has proven that alkyne insertion is both stereo- and regio-selective with the Pd atom attached to the P-position and substituent R in the a-position of the alkyne unit [105]. Carbonylation of this intermediate alkenyl complex of Pd led to the formation of a single product  

Introdudng halogen substituent into the o-position of the phenyl ring substantially facilitated the reaction due to coordination with the Pd atom in syw-fashion [106], which was also confirmed by the study of alkyne insertion into the Pt-S bond [107]  

Dinuclear complexes of trans- and cis-geometry (trans-complexes are more thermodynamically stable) have the ArZ-Pd-ZAr structural unit, which is needed to operate in the catalytic cycle. The observed rate constant of the addition reaction of PhsSes to alkyne was linearly dependent on the concentration of dinuclear complexes [Pd(SePh)4(PPh3)2] [108]. Theoretical study at the density functional theory level has shown that alkyne insertion in the dinuclear complex preferentially involves the terminal ZAr group rather than the bridging ZAr group coordinated in mode [112]. A deficiency of the phosphine ligand under catalytic conditions resulted in rapid 

By using microwave irradiation the reaction time was shortened to 10 min and the catalyst amount was decreased to 0.1 mol%of Pd [114]. Various simple species like Pd (PPh3)4, Pd(OAc)2, or PdCl2 may, in the presence of PPhs, be utilized as catalyst precursors. To study catalytic reactions in the molten-state systems a special NMR technique was developed [116]. Using this technique intermediate dinuclear Pd complexes with the same trans-/cis- isomers ratio were detected in solvent-free/melt systems after conventional and microwave heating [116]. 

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