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The present study explains the different catalytic activities of platinum and palladium in Se−Se addition reactions with alkynes. Under the catalytic conditions cis-[Pt(SePh)2(PPh3)2] undergoes fast isomerization to the trans isomer, which does not react with alkynes. Palladium complexes maintain their catalytic activity, due to the formation of the dinuclear structure [Pd2(SePh)4(PPh3)2]. It was shown that the palladium intermediate involved in the catalytic cycle can be prepared directly in the reaction mixture starting from the simple [PdCl2(PPh3)2] precursor, thus allowing replacement for the traditional Pd(PPh3)4 catalyst. X-ray analysis shows that the products of Se−Se addition reactions with alkynes possess the necessary geometry parameters for coordination as bidentate ligands.

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Regioselective Markovnikov-type addition of PhSH to alkynes (HC C-R) has been performed using easily available nickel complexes. The non-catalytic side reaction leading to anti-Markovnikov products was suppressed by addition of g-terpinene to the catalytic system. The other side reaction leading to the bis(phenylthio)alkene was avoided by excluding phosphine and phosphite ligands from the catalytic system. It was found that catalytic amounts of Et 3 N significantly increased the yield and selectivity of the catalytic reaction. Under optimized conditions high product yields of 60 -85% were obtained for various alkynes [R ¼ n-C 5 H 11 , CH 2 NMe 2 , CH 2 OMe, CH 2 SPh, C 6 H 11 (OH), (CH 2 ) 3 CN]. The X-ray structure of one of the synthesized products is reported.

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