Dual cobalt – copper light-driven catalytic reduction of aldehydes and aromatic ketones in aqueous media

We present an efficient, general, fast, and robust light-driven methodology based on earth-abundant elements to reduce aryl ketones, and both aryl and aliphatic aldehydes (up to 1400 TON). The catalytic system consists of a robust and well-defined aminopyridyl cobalt complex active for photocatalytic water reduction and the [Cu(bathocuproine)(Xantphos)](PF6) photoredox catalyst. The dual cobalt–copper system uses visible light as the driving-force and H2O and an electron donor (Et3N or iPr2EtN) as the hydride source. The catalytic system operates in aqueous mixtures (80–60% water) with high selectivity towards the reduction of organic substrates (>2000) vs. water reduction, and tolerates O2. High selectivity towards the hydrogenation of aryl ketones is observed in the presence of terminal olefins, aliphatic ketones, and alkynes. Remarkably, the catalytic system also shows unique selectivity for the reduction of acetophenone in the presence of aliphatic aldehydes. The catalytic system provides a simple and convenient method to obtain α,β-deuterated alcohols. Both the observed reactivity and the DFT modelling support a common cobalt hydride intermediate. The DFT modelled energy profile for the [Co–H] nucleophilic attack to acetophenone and water rationalises the competence of [CoII–H] to reduce acetophenone in the presence of water. Mechanistic studies suggest alternative mechanisms depending on the redox potential of the substrate. These results show the potential of the water reduction catalyst [Co(OTf)(Py2Tstacn)](OTf) (1), (Py2Tstacn = 1,4-di(picolyl)-7-(p-toluenesulfonyl)-1,4,7-triazacyclononane, OTf = trifluoromethanesulfonate anion) to develop light-driven selective organic transformations and fine solar chemicals

Improved Electro- and Photocatalytic Water Reduction by Confined Cobalt Catalysts in Streptavidin

Incorporation of biotinylated aminopyridine cobalt complexes derived from the triazacyclononane scaffold into the streptavidin protein leads to formation of artificial metalloenzymes for water reduction to hydrogen. The synthesized artificial metalloenzymes have lower overpotential (at the half-peak up to 100 mV) and higher photocatalytic hydrogen evolution activity (up to 14- and 10-fold increase in TOF and TON, respectively, at pH 12.5) than the free biotinylated cobalt complexes. 1H-NMR, EPR and XAS highlight the presence of the metal complexes upon supramolecular attachment to the streptavidin. pHdependent catalytic studies and molecular dynamics (MD) simulations suggest that the increase in the catalytic activity could be induced by the protein residues positioned close to the metal centers. These findings illustrate the ability of the biotin−streptavidin technology to produce artificial metalloproteins for photo- and electrocatalytic hydrogen evolution reaction

CCDC 1060000: Experimental Crystal Structure Determination

Related Article: Teresa Corona, Florian F. Pfaff, Ferran Acuña-Pares, Apparao Draksharapu, Christopher J. Whiteoak, Julio Lloret Fillol, Wesley R. Browne, Kallol Ray, Anna Company|2015|Chem.-Eur.J.|21|15029|doi:10.1002/chem.201501841,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Octahedral iron(IV)–tosylimido complexesexhibiting single electron-oxidation reactivity

International audienceHigh valent iron species are very reactive molecules involved in oxidation reactions of relevance to biology and chemical synthesis. Herein we describe iron(iv)-tosylimido complexes [Fe-IV(NTs)(MePy(2)tacn)](OTf)(2) (1((IV))& xe001;NTs) and [Fe-IV(NTs)(Me-2(CHPy2)tacn)](OTf)(2) (2((IV))& xe001;NTs), (MePy(2)tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane, and Me-2(CHPy2)tacn = 1-(di(2-pyridyl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane, Ts = Tosyl). 1((IV))& xe001;NTs and 2((IV))& xe001;NTs are rare examples of octahedral iron(iv)-imido complexes and are isoelectronic analogues of the recently described iron(iv)-oxo complexes [Fe-IV(O)(L)](2+) (L = MePy(2)tacn and Me-2(CHPy2)tacn, respectively). 1((IV))& xe001;NTs and 2((IV))& xe001;NTs are metastable and have been spectroscopically characterized by HR-MS, UV-vis, H-1-NMR, resonance Raman, Mossbauer, and X-ray absorption (XAS) spectroscopy as well as by DFT computational methods. Ferric complexes [Fe-III(HNTs)(L)](2+), 1((III))-NHTs (L = MePy(2)tacn) and 2((III))-NHTs (L = Me-2(CHPy2)tacn) have been isolated after the decay of 1((IV))& xe001;NTs and 2((IV))& xe001;NTs in solution, spectroscopically characterized, and the molecular structure of [Fe-III(HNTs)(MePy(2)tacn)](SbF6)(2) determined by single crystal X-ray diffraction. Reaction of 1((IV))& xe001;NTs and 2((IV))& xe001;NTs with different p-substituted thioanisoles results in the transfer of the tosylimido moiety to the sulphur atom producing sulfilimine products. In these reactions, 1((IV))& xe001;NTs and 2((IV))& xe001;NTs behave as single electron oxidants and Hammett analyses of reaction rates evidence that tosylimido transfer is more sensitive than oxo transfer to charge effects. In addition, reaction of 1((IV))& xe001;NTs and 2((IV))& xe001;NTs with hydrocarbons containing weak C-H bonds results in the formation of 1((III))-NHTs and 2((III))-NHTs respectively, along with the oxidized substrate. Kinetic analyses indicate that reactions proceed via a mechanistically unusual HAT reaction, where an association complex precedes hydrogen abstraction

Triggering the generation of an iron(IV)-oxo compound and its reactivity toward sulfides by Ru(II) photocatalysis.

International audienceThe preparation of [Fe(IV)(O)(MePy2tacn)](2+) (2, MePy2tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane) by reaction of [Fe(II)(MePy2tacn)(solvent)](2+) (1) and PhIO in CH3CN and its full characterization are described. This compound can also be prepared photochemically from its iron(II) precursor by irradiation at 447 nm in the presence of catalytic amounts of [Ru(II)(bpy)3](2+) as photosensitizer and a sacrificial electron acceptor (Na2S2O8). Remarkably, the rate of the reaction of the photochemically prepared compound 2 toward sulfides increases 150-fold under irradiation, and 2 is partially regenerated after the sulfide has been consumed; hence, the process can be repeated several times. The origin of this rate enhancement has been established by studying the reaction of chemically generated compound 2 with sulfides under different conditions, which demonstrated that both light and [Ru(II)(bpy)3](2+) are necessary for the observed increase in the reaction rate. A combination of nanosecond time-resolved absorption spectroscopy with laser pulse excitation and other mechanistic studies has led to the conclusion that an electron transfer mechanism is the most plausible explanation for the observed rate enhancement. According to this mechanism, the in-situ-generated [Ru(III)(bpy)3](3+) oxidizes the sulfide to form the corresponding radical cation, which is eventually oxidized by 2 to the corresponding sulfoxide

CCDC 1003098: Experimental Crystal Structure Determination

Related Article: Anna Company , Gerard Sabenya , María González-Béjar , Laura Gómez , Martin Clémancey , Geneviève Blondin , Andrew J. Jasniewski , Mayank Puri , Wesley R. Browne , Jean-Marc Latour , Lawrence Que Junior, Miquel Costas , Julia Pérez-Prieto, and Julio Lloret-Fillol|2014|J.Am.Chem.Soc.|136|4624|doi:10.1021/ja412059c,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Novel bis(1,3,2-diazaphospholidine) ligands for asymmetric catalysis

A family of modularly designed chiral bis(1,3,2-diazaphospholidines) with N-aryl substituents (NP-PN) is reported. These compounds have been prepared in two steps from readily available (R,R)-1,2-diaminocyclohexane and tetrachlorodiphosphines. Examples in the set differ in the backbone and the aryl substituents, aiming at their application in asymmetric catalysis. Thus, [Rh(NBD)(NP-PN)]BF4 complexes lead to active catalysts in the hydrogenation of methyl α-acetamidoacrylate, which provide enantioselectivities up to 96% ee. In addition, NP-PN ligands also generate active catalysts in the hydroformylation of vinyl acetate, leading to high regioselectivities (iso:n ratio higher than 99:1) and enantioselectivities up to 65% ee. © 2013 American Chemical Society.Peer Reviewe