609-02-9Relevant articles and documents
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.
Preparation of mono-substituted malonic acid half oxyesters (SMAHOs)
Condon, Sylvie,Le Gall, Erwan,Pichon, Christophe,Presset, Marc,Xavier, Tania
supporting information, p. 2085 - 2094 (2021/09/02)
The use of mono-substituted malonic acid half oxyesters (SMAHOs) has been hampered by the sporadic references describing their preparation. An evaluation of different approaches has been achieved, allowing to define the best strategies to introduce diversity on both the malonic position and the ester function. A classical alkylation step of a malonate by an alkyl halide followed by a monosaponification gave access to reagents bearing different substituents at the malonic position, including functionalized derivatives. On the other hand, the development of a monoesterification step of a substituted malonic acid derivative proved to be the best entry for diversity at the ester function, rather than the use of an intermediate Meldrum acid. Both these transformations are characterized by their simplicity and efficiency, allowing a straightforward access to SMAHOs from cheap starting materials.
“Backdoor Induction” of Chirality: Trans-1,2-cyclohexanediamine as Key Building Block for Asymmetric Hydrogenation Catalysts
Glasovac, Zoran,Kirin, Sre?ko I.,Kokan, Zoran,Opa?ak, Sa?a,Peri?, Berislav
supporting information, p. 2115 - 2128 (2019/01/04)
This paper describes the synthesis and characterization of 21 chiral monodentate ligands L, assembled of three building blocks utilizing amide bonds: a metal binding triphenylphosphine, a chiral cyclic diamine and an additional substituent for fine-tuning the steric and/or electronic properties. Cis square-planar metal complexes of RhI and PtII with ML2 stoichiometry have been prepared and characterized by spectroscopic methods (NMR, IR, UV-Vis, CD) and DFT calculations. A key feature of the metal complexes is a prochiral metal coordination sphere and “backdoor induction” of chirality from a distant chiral source via an outer-coordination sphere, well-defined by aromatic stacking and hydrogen-bonding. The rhodium complexes were used as catalysts in asymmetric hydrogenation of α,β-dehydroamino acids with excellent yield and selectivity (up to 97 % ee), strongly supporting the “backdoor induction” hypothesis.