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

Abstract

In this chapter, discussions are focused on two types of mechanisms of transition-metal-catalyzed hydrochalcogenation, Type I and Type II, which are classified by the initial behavior of precatalysts. In Type I mechanism, precatalyst M-X (M ¼ Pd, Ni, Zr, Ln, and An) first undergoes protonolysis with REH (E ¼ O, S, and Se) to generate active catalyst M-ER, which then undergoes insertion of alkyne into the M-ER bond (chalcogenometalation) to give 2-chalcogenovinyl complex, followed by protonolysis of M-C vinyl with REH to produce the product and to regenerate active catalyst M-ER. Type II mechanism starts from oxidative addition of REH (E ¼ S and Se) to

Transition-Metal-Catalyzed C–S, C–Se, and C–Te Bond Formations via Cross-Coupling and Atom-Economic Addition Reactions. Achievements and Challenges

“…Mechanisms of catalytic cross-coupling reactions (see refs in the Introduction) and addition reactions ,− were extensively reviewed earlier, and these discussions will not be repeated here. In the present section, we outline a basic mechanistic framework for understanding a general concept of the catalytic processes discussed in the sections below.…”

Expanding the Role of Dimeric Species: On-Cycle Involvement, Improved Stability, and Control of Stereo-Specificity. A Case Study of Atom-Economic Catalytic Hydrothiolation

“…As a model reaction, the addition of thiophenol to heptyne-1 ( 1 ) in the presence of various palladium-based catalysts was chosen. Metal-catalyzed atom-economic hydrothiolation is a valuable synthetic task focused on achieving selective transformations. ,− The addition of thiols to alkynes can yield either Markovnikov 3 - or anti-Markovnikov 4a -( E )/ 4b -( Z )-type products (Scheme ). Markovnikov-type products are particularly interesting because they are actively used in organic synthesis, − coordination chemistry, and polymer chemistry. − Anti-Markovnikov products are also formed in noncatalytic reactions, while a high yield of Markovnikov products requires an efficient catalyst …”

Catalytic Asymmetric Hydroalkoxylation of C–C Multiple Bonds

“… 7 Herein, we will consider two general mechanistic scenarios that govern hydroalkoxylations/acyloxylations of alkenes proceeding through nucleophilic activation ( Scheme 4 ). 34 Type I describes a redox neutral cycle initiated by protonolysis of a M–X bond to yield an alkoxy/acyloxy metal complex (M–OR, 1 ). Alkene coordination and subsequent 1,2-insertion into the M–OR bond results in the branched product following protonolysis.…”