A Simple Nickel Catalyst Enabling anE‐Selective Alkyne Semihydrogenation

Abstract

Stereoselective alkyne semihydrogenations are attractive approaches to alkenes, which are key building blocks for synthesis. With regards to the most atom‐economic reducing agent dihydrogen (H2), only few catalysts for the challenging E‐selective alkyne semihydrogenation have been disclosed, each with a unique substrate scope profile. Here, we show that a commercially available nickel catalyst facilitates the E‐selective alkyne semihydrogenation of a wide variety of substituted internal alkynes. This results in a simple and broadly applicable overall protocol to stereoselectively access E‐alkenes employing H2, which could serve as a general method for synthesis.

Electrochemical Proton Reduction over Nickel Foam for Z‐Stereoselective Semihydrogenation/deuteration of Functionalized Alkynes

“…Raney nickel is a common example of a highly active base‐metal catalyst for reduction reactions; however, its pyrophoric nature is a significant limitation. [16] Other nickel complexes or nanoparticles have been reported to be good reduction catalysts, sometimes needing high hydrogen pressure and high temperature,[ 17 , 18 , 19 , 20 , 21 ] or an excess of the reductants, such as NaBH 4 or formic acid. [ 22 , 23 , 24 , 25 , 26 ] Hydrogen obtained from fossil resources can also be replaced by hydrogen produced electrochemically from water.…”

Ruthenium‐Catalyzed E‐Selective Partial Hydrogenation of Alkynes under Transfer‐Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source

“…Traditionally, E ‐alkenes obtain from the Birch reduction using dissolved metals which precludes the use of base‐labile and sensitive substrates [41–45] . To date, there is a handful of widely applicable direct procedures for the selective reduction of alkynes to E ‐alkenes by means of catalytic semi‐ (transfer)hydrogenation [30,46–49] . Scheme 1a shows some of the successful E ‐selective alkene synthesis procedures using H 2 gas as the hydrogenation source [39–40,50–53] .…”

“…[17] Reduction of alkynes selectively to Zalkenes can be carried out using the well-known Lindlar catalyst, [18] and even base metal catalysts. [19][20] Various transition metal catalysts [5,10,13,15,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] have been developed so far which in combination with different transfer hydrogenation sources [21][22][23][24][25][26][27][28][29][30][31] or dihydrogen gas [32][33][34][35] can be used for the stereoselective semi-hydrogenation (reduction) of alkynes to olefins. In this regard, selective formation of E-alkenes is more challenging and less well-studied.…”

“…[41][42][43][44][45] To date, there is a handful of widely applicable direct procedures for the selective reduction of alkynes to E-alkenes by means of catalytic semi-(transfer)hydrogenation. [30,[46][47][48][49] Scheme 1a shows some of the successful E-selective alkene synthesis procedures using H 2 gas as the hydrogenation source. [39][40][50][51][52][53] Application of H 2 gas in these examples, however, requires a more expensive setup and increases the safety issues.…”

Bench‐Stable Dinuclear Mn(I) Catalysts in E‐Selective Alkyne Semihydrogenation: A Mechanistic Investigation**

“…Significant work remains to uncover the nature of Mncatalyzed hydrogenation reaction mechanisms, and dinuclear catalysts have not been explored in detail. Furthermore, the importance of E-SASH to prepare biologically active compounds [16][17][18][19] using first row metals [20][21][22][23][24][25][26] holds promise for an applications-based outcome as a longer-term goal in sustainable metal catalysis. [27] As shown by us previously, bench-stable complexes such as 1 can be prepared in a single step from commercially available starting materials, namely HPR 2 and Mn 2 (CO) 10 (Scheme 1 and TOC graphic).…”