Palladium(II) Acetate in Pyridine as an Effective Catalyst for Highly Regioselective Hydroselenation of Alkynes

Abstract

A highly regioselective hydroselenation of terminal alkynes with benzeneselenol can be achieved by the combination of palladium acetate and pyridine, providing the corresponding terminal alkenes, (i.e., 2-phenylseleno-1-alkenes) as a sole product. In this hydroselenation, pyridine may act as a suitable ligand for active palladium intermediates.

Unusual Influence of the Structures of Transition Metal Complexes on Catalytic C–S and C–Se Bond Formation Under Homogeneous and Heterogeneous Conditions

“…Scheme 12. Much better results in the synthesis of Markovnikov product were achieved by using Pd(OAc) 2 catalyst in pyridine to perform the hydroselenation reaction. [52] The reaction was carried out at high temperature (100°C) for 15 h and gave 53-99 % yields of 13. It is interesting to point out that in THF or benzene solutions the Pd-catalyzed reaction gave mixtures of 13, 4, 5, and 14, while in pyridine solution the by-products 4, 5, and 14 were not detected.…”

The Mechanism for Transition-Metal-Catalyzed Hydrochalcogenation of Unsaturated Organic Molecules

“…Therefore, pyridine is considered to inhibit the polymerization and protect the catalyst from the poisoning [23].…”

“…A mechanism shown in Scheme 6 was proposed [23], which involves (i) ligand exchange of the AcO group with the PhSe group to give Pd(SePh) 2 L n as an active catalyst and AcOH; (ii) coordination of alkyne to the selenolato Pd(II) species; (iii) insertion of alkyne into the Pd-Se bond (syn-selenopalladation) to form (Z)-(2-phenylseleno)vinyl Pd(II) intermediate 2; (iv) the protonolysis of the …”

“…On the other hand, the reaction of PtH(SeTrip)(dppe) (49) [dppe ¼ 1,2-bis(diphenylphosphino)ethane] with DMAD in benzene was sluggish at 60 C, and heating in refluxing benzene for 38 h was necessary for complete consumption of 49 to yield (E)-44 (11%), (Z)-44 (21%), 1H-2-benzoselenin 47 (3%), and (TripSe) 2 (31%) (23). These products are considered to be formed by the reaction of TripSeH, generated by reductive elimination of 49, with DMAD.…”

Nickel(II) Chloride‐Catalyzed Regioselective Hydrothiolation of Alkynes

“…This explanation has been proposed for the amine effect in palladium-catalyzed hydroselenation reactions. [18] At the moment it is difficult to say which of the mechanisms (or both) takes place in the studied catalytic system. This question will be addressed in our future studies.…”