Modulation of metal species as control point for Ni-catalyzed stereodivergent semihydrogenation of alkynes with water

Abstract

A base-assisted metal species modulation mechanism enables Ni-catalyzed stereodivergent transfer semihydrogenation of alkynes with water, delivering both olefinic isomers smoothly using cheap and nontoxic catalysts and additives. Different from most precedents, in which E-alkenes derive from the isomerization of Z-alkene products, the isomers were formed in orthogonal catalytic pathways. Mechanistic studies suggest base as a key early element in modulation of the reaction pathways: by adding different bases, nickel species with disparate valence states could be accessed to initiate two catalytic cycles toward different stereoisomers. The practicability of the method is showcased with nearly 70 examples, including internal and terminal triple bonds, enynes and diynes, affording semi-hydrogenated products in high yields and selectivity.

Surmounting Alkoxide Trap Strategy: N-Heterocyclic Carbene Chromium(0)-Catalyzed C-Alkylation between Alcohols

“…Rational catalyst design is one of the most challenging tasks in Chemistry. Tuning the electronic structure and oxidation state of the metal center is extremely important in the rational design and development of nonprecious metal-based catalysts. − However, little attention has been paid to the fundamental d-wall issue in catalyst design for BH/HA reactions. The metal-alkoxide intermediate is crucial in BH/HA transformations when using alcohols as alkylating agents. − For high oxidation state transition metal centers, the d-p π interaction between half-filled or empty d orbitals and the oxygen lone pair stabilizes the metal-alkoxide intermediate in BH/HA transformations, causing an alkoxide trap .…”

Recent advances in the selective semi-hydrogenation of alkyne to (E)-olefins

“…Induction of CF 3 CO 2 Na induces a lower oxidation state of Ni, which leads to the formation of vinyl–Ni( i ) intermediate G and subsequently undergoes isomerization to form the thermodynamically more stable species H, allowing the desired alkene (Scheme 32). 43…”

Spin-Crossing in the (Z)-Selective Alkyne Semihydrogenation Mechanism Catalyzed by Mo3S4 Clusters: A Density Functional Theory Exploration

“…The stereoselective catalytic semihydrogenation of internal alkynes into ( E )- or ( Z )-alkene isomers is among the most relevant processes in synthetic organic chemistry . To date, a plethora of heterogeneous and homogeneous metal-based catalysts for internal alkyne semihydrogenation have been reported. − In spite of the many advances in the field, there are still some unsolved problems such as overreduction and isomerization. , For that reason, most of the current efforts are devoted to rendering selective catalysts working under mild conditions, with these ideally being also inexpensive, atom-economic, and environmentally benign. Thus, the interest to replace noble metals by nonprecious ones together with using hydrogen as reducing agent is notably increasing.…”