2719-52-0Relevant academic research and scientific papers
Reductive activation and hydrofunctionalization of olefins by multiphoton tandem photoredox catalysis
Czyz, Milena L.,Taylor, Mitchell S.,Horngren, Tyra H.,Polyzos, Anastasios
, p. 5472 - 5480 (2021/06/01)
The conversion of olefin feedstocks to architecturally complex alkanes represents an important strategy in the expedient generation of valuable molecules for the chemical and life sciences. Synthetic approaches are reliant on the electrophilic activation of unactivated olefins, necessitating functionalization with nucleophiles. However, the reductive functionalization of unactivated and less activated olefins with electrophiles remains an ongoing challenge in synthetic chemistry. Here, we report the nucleophilic activation of inert styrenes through a photoinduced direct single electron reduction to the corresponding nucleophilic radical anion. Central to this approach is the multiphoton tandem photoredox cycle of the iridium photocatalyst [Ir(ppy)2(dtbbpy)] PF6, which triggers in situ formation of a high-energy photoreductant that selectively reduces styrene olefinic π bonds to radical anions without stoichiometric reductants or dissolving metals. This mild strategy enables the chemoselective reduction and hydrofunctionalization of styrenes to furnish valuable alkane and tertiary alcohol derivatives. Mechanistic studies support the formation of a styrene olefinic radical anion intermediate and a Birch-type reduction involving two sequential single electron transfers. Overall, this complementary mode of olefin activation achieves the hydrofunctionalization of less activated alkenes with electrophiles, adding value to abundant olefins as valuable building blocks in modern synthetic protocols.
Visible-Light-Enhanced Cobalt-Catalyzed Hydrogenation: Switchable Catalysis Enabled by Divergence between Thermal and Photochemical Pathways
Mendelsohn, Lauren N.,MacNeil, Connor S.,Tian, Lei,Park, Yoonsu,Scholes, Gregory D.,Chirik, Paul J.
, p. 1351 - 1360 (2021/02/01)
The catalytic hydrogenation activity of the readily prepared, coordinatively saturated cobalt(I) precatalyst, (R,R)-(iPrDuPhos)Co(CO)2H ((R,R)-iPrDuPhos = (+)-1,2-bis[(2R,5R)-2,5-diisopropylphospholano]benzene), is described. While efficient turnover was observed with a range of alkenes upon heating to 100 °C, the catalytic performance of the cobalt catalyst was markedly enhanced upon irradiation with blue light at 35 °C. This improved reactivity enabled hydrogenation of terminal, di-, and trisubstituted alkenes, alkynes, and carbonyl compounds. A combination of deuterium labeling studies, hydrogenation of alkenes containing radical clocks, and experiments probing relative rates supports a hydrogen atom transfer pathway under thermal conditions that is enabled by a relatively weak cobalt-hydrogen bond of 54 kcal/mol. In contrast, data for the photocatalytic reactions support light-induced dissociation of a carbonyl ligand followed by a coordination-insertion sequence where the product is released by combination of a cobalt alkyl intermediate with the starting hydride, (R,R)-(iPrDuPhos)Co(CO)2H. These results demonstrate the versatility of catalysis with Earth-abundant metals as pathways involving open-versus closed-shell intermediates can be switched by the energy source.
Visible light enables catalytic formation of weak chemical bonds with molecular hydrogen
Park, Yoonsu,Kim, Sangmin,Tian, Lei,Zhong, Hongyu,Scholes, Gregory D.,Chirik, Paul J.
, p. 969 - 976 (2021/07/25)
The synthesis of weak chemical bonds at or near thermodynamic potential is a fundamental challenge in chemistry, with applications ranging from catalysis to biology to energy science. Proton-coupled electron transfer using molecular hydrogen is an attractive strategy for synthesizing weak element–hydrogen bonds, but the intrinsic thermodynamics presents a challenge for reactivity. Here we describe the direct photocatalytic synthesis of extremely weak element–hydrogen bonds of metal amido and metal imido complexes, as well as organic compounds with bond dissociation free energies as low as 31 kcal mol?1. Key to this approach is the bifunctional behaviour of the chromophoric iridium hydride photocatalyst. Activation of molecular hydrogen occurs in the ground state and the resulting iridium hydride harvests visible light to enable spontaneous formation of weak chemical bonds near thermodynamic potential with no by-products. Photophysical and mechanistic studies corroborate radical-based reaction pathways and highlight the uniqueness of this photodriven approach in promoting new catalytic chemistry. [Figure not available: see fulltext.].
Hydrogenation of alkenes via cooperative hydrogen atom transfer
Kattamuri, Padmanabha V.,West, Julian G.
supporting information, p. 19316 - 19326 (2020/11/13)
Radical hydrogenation via hydrogen atom transfer (HAT) to alkenes is an increasingly important transformation for the formation of thermodynamic alkane isomers. Current single-catalyst methods require stoichiometric oxidant in addition to hydride (H-) source to function. Here we report a new approach to radical hydrogenation: cooperative hydrogen atom transfer (cHAT), where each hydrogen atom donated to the alkene arrives from a different catalyst. Further, these hydrogen atom (H?) equivalents are generated from complementary hydrogen atom precursors, with each alkane requiring one hydride (H-) and one proton (H+) equivalent and no added oxidants. Preliminary mechanistic study supports this reaction manifold and shows the intersection of metal-catalyzed HAT and thiol radical trapping HAT catalytic cycles to be essential for effective catalysis. Together, this unique catalyst system allows us to reduce a variety of unactivated alkene substrates to their respective alkanes in high yields and diastereoselectivities and introduces a new approach to radical hydrogenation.
Cobalt-Catalyzed Hydrogenations via Olefin Cobaltate and Hydride Intermediates
Sandl, Sebastian,Maier, Thomas M.,Van Leest, Nicolaas P.,Kr?ncke, Susanne,Chakraborty, Uttam,Demeshko, Serhiy,Koszinowski, Konrad,De Bruin, Bas,Meyer, Franc,Bodensteiner, Michael,Herrmann, Carmen,Wolf, Robert,Von Jacobi Wangelin, Axel
, p. 7596 - 7606 (2019/08/20)
Redox noninnocent ligands are a promising tool to moderate electron transfer processes within base-metal catalysts. This report introduces bis(imino)acenaphthene (BIAN) cobaltate complexes as hydrogenation catalysts. Sterically hindered trisubstituted alkenes, imines, and quinolines underwent clean hydrogenation under mild conditions (2-10 bar, 20-80 °C) by use of the stable catalyst precursor [(DippBIAN)CoBr2] and the cocatalyst LiEt3BH. Mechanistic studies support a homogeneous catalysis pathway involving alkene and hydrido cobaltates as active catalyst species. Furthermore, considerable reaction acceleration by alkali cations and Lewis acids was observed. The dinuclear hydridocobaltate anion with bridging hydride ligands was isolated and fully characterized.
Recyclable cobalt(0) nanoparticle catalysts for hydrogenations
Büschelberger, Philipp,Reyes-Rodriguez, Efrain,Sch?ttle, Christian,Treptow, Jens,Feldmann, Claus,Jacobi Von Wangelin, Axel,Wolf, Robert
, p. 2648 - 2653 (2018/05/30)
The search for new hydrogenation catalysts that replace noble metals is largely driven by sustainability concerns and the distinct mechanistic features of 3d transition metals. Several combinations of cobalt precursors and specific ligands in the presence of reductants or under high-thermal conditions were reported to provide active hydrogenation catalysts. This study reports a new method of preparation of small, monodisperse Co(0) nanoparticles (3-4 nm) from the reduction of commercial CoCl2 in the absence of ligands or surfactants. High catalytic activity was observed in hydrogenations of alkenes, alkynes, imines, and heteroarenes (2-20 bar H2). The magnetic properties enabled catalyst separation and multiple recyclings.
Catalytic Use of Low-Valent Cationic Gallium(I) Complexes as π-Acids
Li, Zhilong,Thiery, Guillaume,Lichtenthaler, Martin R.,Guillot, Régis,Krossing, Ingo,Gandon, Vincent,Bour, Christophe
supporting information, p. 544 - 549 (2017/11/27)
Transformations of alkene and alkyne substrates relevant to π-Lewis acid catalysis have been performed using low-valent Ga(I) species for the first time. [Ga(I)(PhF)2]+[Al(ORF)4]? and gallium dichloride (i. e. [Ga(I)]+[GaCl4]?) proved to be efficient catalysts for cycloisomerizations, Friedel-Crafts reactions, transfer hydrogenations, and reductive hydroarylations. Their activity is compared to more common Ga(III) complexes. This study shows that even the readily available and yet overlooked gallium dichloride salt can be a more active π-Lewis acid catalyst than gallium trichloride or other Ga(III) species. (Figure presented.).
A Manganese Nanosheet: New Cluster Topology and Catalysis
Chakraborty, Uttam,Reyes-Rodriguez, Efrain,Demeshko, Serhiy,Meyer, Franc,Jacobi von Wangelin, Axel
supporting information, p. 4970 - 4975 (2018/03/28)
While the coordination chemistry of monometallic complexes and the surface characteristics of larger metal particles are well understood, preparations of molecular metallic nanoclusters remain a great challenge. Discrete planar metal clusters constitute nanoscale snapshots of cluster growth but are especially rare owing to the strong preference for three-dimensional structures and rapid aggregation or decomposition. A simple ligand-exchange procedure has led to the formation of a novel heteroleptic Mn6 nanocluster that crystallized in an unprecedented flat-chair topology and exhibited unique magnetic and catalytic properties. Magnetic susceptibility studies documented strong electronic communication between the manganese ions. Reductive activation of the molecular Mn6 cluster enabled catalytic hydrogenations of alkenes, alkynes, and imines.
Synthesis and Catalysis of Redox-Active Bis(imino)acenaphthene (BIAN) Iron Complexes
Villa, Matteo,Miesel, Dominique,Hildebrandt, Alexander,Ragaini, Fabio,Schaarschmidt, Dieter,Jacobi von Wangelin, Axel
, p. 3203 - 3209 (2017/08/29)
Reactions of various substituted bis(imino)acenaphthenes (R-BIANs) with FeCl2(thf)1.5 afforded the tetrahedral complexes (R-BIAN)FeCl2 (2) from bulky α-diimines and the octahedral complexes [Fe(R-BIAN)3][FeCl4]2 (3) from less bulky ligands. The driving force for the formation of complexes 3 is the high ligand-field stabilization of the low-spin FeII center. The two sets of complexes exhibit distinct charge-transfer band intensities and redox activities. (R-BIAN)FeCl2 complexes showed reversible ligand-centered reductions at ?0.9 V (vs. FcH/FcH+; FcH: ferrocene); further reduction led to decomposition. Irreversible oxidations were observed at 0.2 and 0.4 V, associated with a reduction at ?0.4 V, as well as a ligand-centered redox event at 1.0 V. First applications of the Fe(BIAN) complexes to hydrogenations of alkenes indicated good catalytic activity under mild conditions.
Catalytic Synthesis of “Super” Linear Alkenyl Arenes Using an Easily Prepared Rh(I) Catalyst
Webster-Gardiner, Michael S.,Chen, Junqi,Vaughan, Benjamin A.,McKeown, Bradley A.,Schinski, William,Gunnoe, T. Brent
, p. 5474 - 5480 (2017/04/27)
Linear alkyl benzenes (LAB) are global chemicals that are produced by acid-catalyzed reactions that involve the formation of carbocationic intermediates. One outcome of the acid-based catalysis is that 1-phenylalkanes cannot be produced. Herein, it is reported that [Rh(μ-OAc)(η2-C2H4)2]2 catalyzes production of 1-phenyl substituted alkene products via oxidative arene vinylation. Since C C bonds can be used for many chemical transformations, the formation of unsaturated products provides a potential advantage over current processes that produce saturated alkyl arenes. Conditions that provide up to a 10:1 linear:branched ratio have been achieved, and catalytic turnovers >1470 have been demonstrated. In addition, electron-deficient and electron-rich substituted benzenes are successfully alkylated. The Rh catalysis provides ortho:meta:para selectivity that is opposite to traditional acid-based catalysis.
