Organocobaloximes: Cobalt-carbon bond stability and synthesis

Selective visible-light photocatalysis of acetylene to ethylene using a cobalt molecular catalyst and water as a proton source

The production of polymers from ethylene requires the ethylene feed to be sufficiently purified of acetylene contaminant. Accomplishing this task by thermally hydrogenating acetylene requires a high temperature, an external feed of H₂ gas and noble-metal catalysts. It is not only expensive and energy-intensive, but also prone to overhydrogenating to ethane. Here we report a photocatalytic system that reduces acetylene to ethylene with ≥99% selectivity under both non-competitive (no ethylene co-feed) and competitive (ethylene co-feed) conditions, and near 100% conversion under the latter industrially relevant conditions. Our system uses a molecular catalyst based on earth-abundant cobalt operating under ambient conditions and sensitized by either [Ru(bpy)₃]²⁺ or an inexpensive organic semiconductor (metal-free mesoporous graphitic carbon nitride) under visible light. These features and the use of water as a proton source offer advantages over current hydrogenation technologies with respect to selectivity and sustainability.

Irradiation-Induced Cobaloxime-Catalyzed C-H Monofluoroalkylation of Styrenes at Room Temperature

A cobaloxime-catalyzed photochemical synthesis of allyl monofluorides from styrenes is described herein. This method is characterized by mild reaction conditions, low-cost catalyst, and broad substrate scope. Furthermore, this convenient method will provide a facile synthesis toward novel monofluoroalkylated natural product and pharmaceutical derivatives. Mechanistic investigations indicate that a monofluoroalkyl radical is involved in the catalytic cycle.

Stereoselective cobalt-catalyzed halofluoroalkylation of alkynes

Stereoselective additions of highly functionalized reagents to available unsaturated hydrocarbons are an attractive synthetic tool due to their high atom economy, modularity, and rapid generation of complexity. We report efficient cobalt-catalyzed (E)-halofluoroalkylations of alkynes/alkenes that enable the construction of densely functionalized, stereodefined fluorinated hydrocarbons. The mild conditions (2 mol% cat., 20 °C, acetone/water, 3 h) tolerate various functional groups, i.e. halides, alcohols, aldehydes, nitriles, esters, and heteroarenes. This reaction is the first example of a highly stereoselective cobalt-catalyzed halo-fluoroalkylation. Unlike related cobalt-catalyzed reductive couplings and Heck-type reactions, it operates via a radical chain mechanism involving terminal halogen atom transfer which obviates the need for a stoichiometric sacrificial reductant.

Visible light-induced transition metal-catalyzed transformations: beyond conventional photosensitizers

Employment of simple transition metal (TM = Co, Fe, Cu, Pd, Pt, Au)-based photocatalyst (PC) has led to the dramatic acceleration of known TM-catalyzed reactions, as well as to the discovery of unprecedented chemical transformations. Compared to the conventional cooperative/dual photocatalysis (type B), this new class of unconventional PCs operates via a single photoexcitation/catalytic cycle, where the TM complex plays a "double duty" role by harvesting light and catalyzing the chemical transformation. Also, these TM photocatalysts participate in the bond-forming/breaking event in the transformation via a substrate-TM interaction, an aspect that is uncommon for conventional photocatalysis (type A). This tutorial review highlights the recent advances in this emerging area.

Kinetics of the reduction of 4-amino and 4-cyanopyridinechlorocobaloximes by iron(II)

Cobaloximes such as trans[Co(dmgH) 2(Py-NH2)Cl] and trans- [Co(dmgH) 2(Py-CN)Cl], where, dmgH = dimethylglyoximato anion, Py-NH 2 = 4-aminopyiridne and Py-CN = 4-cyanopyridine, were prepared and characterized by elemental analysis, UV-VIS, IR and NMR spectroscopy. The kinetics of iron(II) reduction of the complexes were studied spectrophotometrically at 300 nm in 2% (v/v) DMSO-H2O medium at 27?0.1?C and I = 0.25 M (LiClO4) at various hydrogen ion concentrations in the range 2.5 x 10-4 to 5.0x10-2 M under pseudo-first-order conditions using an excess of the reductant. The inverse dependence of rate on [H+] suggests an equilibrium between the protonated and unportonated forms of the complexes, the protonated form reacting slower than the unprotonated form. Computation of the data enabled the evaluation of the rate constants for the protonated and unprotonated from of the complexes, leading to an evaluation of the protonation constant for the complexes. .