Cobalt‐Catalyzed Chemoselective Transfer Hydrogenation of C=C and C=O Bonds with Alkanols

Abstract

An environmentally benign protocol of chemoselective transfer hydrogenation of C=C and C=O bonds with alkanols under base‐free conditions is developed by this study, wherein the cobalt‐ bidentate phosphine catalyst precursor is commercially available and the active low‐valent Co species could be generated in‐situ. For the conjugation enones, the vinyl group is selectively reduced, whereas with nonconjugated alkenones, the selectivity is changed to the carbonyl group. Besides, ortho‐alkenyl‐benzaldehydes/imines are well tolerated, and the reduction solely occurs at the C=O/C=N site with this protocol.

Transfer Hydrogenation of Aldehydes and Ketones in Air with Methanol and Ethanol by an Air-Stable Ruthenium–Triazole Complex

“…Although Meerwein–Ponndorf–Verley reduction has been widely utilized in both academic and industrial processes, the major drawbacks of this protocol are the requirement of a large amount of aluminum alkoxide reagent, unwanted side reactions, and moisture sensitivity of aluminum alkoxides. Over the last few decades, transfer hydrogenation of multiple bonds between carbon and heteroatoms (such as oxygen and nitrogen in carbonyls and imines, respectively) is a very active field of research and a large variety of homogeneous transition metal catalysts based on iron, − ruthenium, − osmium, − cobalt, − rhodium, − iridium, − nickel, − palladium, − and gold , have been developed. However, most of the efficient transfer hydrogenation protocols utilized ruthenium-, rhodium-, or iridium-based catalysts.…”

Catalytic and mechanistic studies of a highly active and E-selective Co(ii) PNNH pincer catalyst system for transfer-semihydrogenation of internal alkynes

“…11 Transfer hydrogenation chemistry using Co systems is a viable alternative that avoids the use of high-pressure equipment, however, significant progress has only been reported recently. 12 Examples for the use of cobalt complexes for TSH of alkynes using H 3 B•NH 3 include Luo and Liu's Co PNP pincer dichloride system that allows for stereodivergent formation of E-or Z-alkenes depending on the applied pincer ligand (Fig. 1, I).…”

Cobalt-Catalyzed Chemoselective Transfer Hydrogenative Cyclization Cascade of Enone-Tethered Aldehydes

“…Our group was contemporaneously focusing on Co-catalyzed transfer hydrogenations. As a result, the Co­(I)/diphosphine-catalyzed chemoselective hydrogenation of CC and CO bonds with alkanols was developed …”

“…On the basis of our previous studies and the present results, this low-valent Co-catalyzed Michael–Aldol cycloreduction may proceed via the famous Meerwein–Ponndorf–Verley reduction route . To identify whether it follows a concerted or stepwise fashion, the poisoning studies using TEMPO as an inhibitor were performed (Table S3).…”

“…New perspectives could be obtained by this study to solve some prominent problems in the field of cobalt catalysis. For example, the challenging Co-catalyzed β–H elimination , and the impeded hydride transfer from Co­(III)–H species to carbonyl moieties ,, can be approached by launching a proper cobalt valence and chelate environment. Further studies toward the Co-catalyzed enone-trigged cascade reactions are currently under way.…”