Ligand-Controlled Cobalt-Catalyzed Transfer Hydrogenation of Alkynes: Stereodivergent Synthesis of Z- and E-Alkenes

Abstract

Herein, we report a novel cobalt-catalyzed stereodivergent transfer hydrogenation of alkynes to Z- and E-alkenes. Effective selectivity control is achieved based on a rational catalyst design. Moreover, this mild system allows for the transfer hydrogenation of alkynes bearing a wide range of functional groups in good yields using catalyst loadings as low as 0.2 mol %. The general applicability of this procedure is highlighted by the synthesis of more than 50 alkenes with good chemo- and stereoselectivity. A preliminary mechanistic study revealed that E-alkene product was generated via sequential alkyne hydrogenation to give Z-alkene intermediate, followed by a Z to E alkene isomerization process.

Stereoselective Transfer Semi‐Hydrogenation of Alkynes to E‐Olefins with N‐Heterocyclic Silylene–Manganese Catalysts

“…The outcome of the transfer semi‐hydrogenation of 1 a is also not affected from the presence of TEMPO (2,2,6,6‐tetramethyl‐l‐piperidinoxyl), which rules out a possible radical mechanism (Table , entry 14). We propose the formation of active Mn–H species akin to the previously proposed metal hydride active species in the catalytic cycle; this is supported by the characteristic Mn–H vibration mode around 1900 cm −1[24] in the IR spectrum of the reaction mixture of [L1]MnCl 2 and AB (Figure S6, Supporting Information).…”

“…Due to the high percentage of H content (19.5 wt %) as well as the nonflammable and stable nature, AB has a promising potential as a hydrogen storage material . In addition to hydrogen storage, AB was successfully employed for transfer hydrogenation of various unsaturated organic substrates . This includes transfer semi‐hydrogenations of alkynes with Ni, Co, Au, and Cu complexes as precatalysts; Mn complexes, however, have merely been employed as precatalysts for H 2 evolution from AB, but not yet in transfer hydrogenation.…”

Recent Advances in Hydrometallation of Alkenes and Alkynes via the First Row Transition Metal Catalysis

“…[265] Using rapid evaluation of libraries of chiral phosphine ligands with a set of simple cobalt precursors, Chirik et al performed hydrogenation of functionalized and unfunctionalized alkenes with high enantioselectivity. [268] This hydrogenation reaction was also facilitated to α-alkylstyrenes without any isomerization products. [268] This hydrogenation reaction was also facilitated to α-alkylstyrenes without any isomerization products.…”

Cobalt Pincer Complexes for Catalytic Reduction of Carboxylic Acid Esters

“…Cobalt compounds, and here especially cobalt pincer type complexes, have been developed for a number of catalytic transformations such as polymerization, bond‐forming reactions, hydrogenations, transfer hydrogenations, hydrosilylations/hydroborations or N 2 activation . Although cobalt‐based reductions of ketones,, aldehydes , nitriles, or alkenes,,, have been studied, until now, hydrogenation of carboxylic acid esters in the presence of this metal has been scarcely examined…”