Remarkable Ligand Effect in Ni‐ and Pd‐Catalyzed Bisthiolation and Bisselenation of Terminal Alkynes: Solving the Problem of Stereoselective Dialkyldichalcogenide Addition to the CC Bond

Abstract

We have developed two new catalytic systems based on Ni and Pd complexes to solve the challenging problem of dialkyldichalcogenide (Alk2E2; E=S, Se) addition to alkynes. A comparative study of two catalytic systems-Ni/PMe2Ph and Pd/PCy2Ph-has revealed that the Ni catalyst is superior with respect to high catalytic activity and more general scope relative to the Pd system. A novel synthetic methodology was developed for the preparation of (Z)-bis(alkylthio)alkenes and (Z)-bis(alkylseleno)alkenes from terminal alkynes with excellent stereoselectivity and high yields.

The Formation of Csp 2 S and Csp 2 Se Bonds by Substitution and Addition Reactions Catalyzed by Transition Metal Complexes

“…Ligand excess was required to maintain high activity of the catalyst (L/Ni ¼ 10/1). The same effect was also reported for the Ni-catalyzed reaction of acyclic analogs [122]. Without excess of ligand, the formation of insoluble metal species was observed, which were isolated and studied by scanning electron microscopy (SEM).…”

“…Ligand Yield, % respectively [122]. This could be one of the reasons why different ligands are required to furnish the oxidative addition step involving these dichalcogenides.…”

“…This could be one of the reasons why different ligands are required to furnish the oxidative addition step involving these dichalcogenides. Indeed, it was found that Pd catalyst with Cy 2 PhP ligand did catalyze stereoselective Alk 2 Z 2 addition to the triple bond of alkynes (Scheme 3.70) [122]. The reaction was carried out at 140 C for 12 h and gave high yields for Z ¼ S and good yields for Z ¼ Se.…”

“…The ligand played a dramatic role in these catalytic reactions. For both metals R 2 PhP were found to be the ligands of choice: R ¼ Cy for Pd and R ¼ Me for Ni [122]. In spite of several efforts only terminal alkynes were involved in the reaction, while internal alkynes remained inactive.…”

Transition-Metal-Catalyzed S–H and Se–H Bonds Addition to Unsaturated Molecules

“…Some related nickel-catalyzed selenation reactions of unsaturated compounds are reported [94,95]. Indium(I) iodide is found to promote the regio-and stereoselective hydrothiolation of propargyl alcohols with (PhSe) 2 (Markovnikov-type addition and anti-addition) [96].…”