Dehydrogenation of 1-Phenylethanol Catalyzed by Nickel(II)diphosphine Complexes

Catalytic efficacy of the nickel(II)-diphosphine systems in the dehydrogenation of 1-phenylethanol to acetophenone under acceptorless conditions was investigated. Steric and electronic factors of the phosphine ligands were found to play an important role in the catalysis, while the nature of the base used and the reaction conditions, viz. time, tempe rature, and stoichiometry, have also shown major influence. Based on the preliminary analysis, a homogeneous pathway, perhaps involving nickel hydride species, was proposed. Due to the gradual disintegration of the catalytic species, deterioration of catalytic activity was observed resulting into low to moderate conversions. Among the series of catalysts examined, the highest conversion of 52% was exhibited by the catalyst C4, dichloro(1,2-bis(diphenylphosphino)ethane) nickel(II) (5 mol%), when loaded with 50 mol% of sodium ethoxide in toluene at 120 °C.

Secondary Phosphine Oxide-Activated Nickel Catalysts for Site-Selective Alkene Isomerization and Remote Hydrophosphination

Catalytic systems that are readily modifiable to achieve olefin migration or remote functionalization are highly sought-after in chemical synthesis. Here, we show that the combination of a commercially available nickel(II) pre-catalyst and a secondary phosphine oxide ligand enables site- and stereoselective alkene transposition for up to nine double-bond migrations within terminal and internal olefins under mild reductive conditions. Substrates bearing diverse functionalities including Brønsted acidic and reducible carbonyl groups are tolerated. Mechanistic and spectroscopic studies revealed the in situ generation of a catalytically active nickel-hydride species triggered by oxidative addition of the phosphine oxide. The reaction is amenable to regioconvergent isomerization as well as β-selective remote hydrophosphination when stoichiometric secondary phosphine oxide/base were employed.

Nickel-Hydride Catalyzed Remote Hydroarylation of Olefins

Metal hydride-catalyzed remote hydrofunctionalization has attracted extensive attention in the past decade, as it provides a complementary approach for selective functionalization of remote C(sp3)–H bonds. Recently, a wide variety of olefinic remote hydrofunctionalizationation reactions have been realized through the synergistic combination of NiH-catalyzed chain-walking and Ni-catalyzed cross-coupling. In this personal account we discuss our recent achievement in the remote hydroarylation of olefins as well as our recent achievement in asymmetric hydroarylation.

Nickel-Catalyzed Benzylic Alkynylation: Migratory Hydroalkynylation and Enantioselective Hydroalkynylation of Olefins with Bromoalkynes

A nickel-hydride catalyzed reductive migratory hydroalkynylation of olefins with bromoalkynes that delivers the corresponding benzylic alkynylation products in high yield and with excellent regioselectivity has been developed. Catalytic enantioselective hydroalkynylation of styrenes has been realized using a simple chiral PyrOx ligand. The obtained enantioenriched benzylic alkynes are versatile synthetic intermediates and can be readily transformed into synthetically useful chiral synthons

Nickel-Catalyzed Benzylic Alkynylation: Migratory Hydroalkynylation and Enantioselective Hydroalkynylation of Olefins with Bromoalkynes

A nickel-hydride catalyzed reductive migratory hydroalkynylation of olefins with bromoalkynes that delivers the corresponding benzylic alkynylation products in high yield and with excellent regioselectivity has been developed. Catalytic enantioselective hydroalkynylation of styrenes has been realized using a simple chiral PyrOx ligand. The obtained enantioenriched benzylic alkynes are versatile synthetic intermediates and can be readily transformed into synthetically useful chiral synthons

Nickel Hydride Catalyzed Cleavage of Allyl Ethers Induced by Isomerization

This report discloses the deallylation of O- and N-allyl functional groups by using a combination of a Ni-H precatalyst and excess Brønsted acid. Key steps are the isomerization of the O- or N-allyl group through Ni-catalyzed double-bond migration followed by Brønsted acid induced O/N–C bond hydrolysis. A variety of functional groups are tolerated in this protocol, highlighting its synthetic value.