Cobalt

About: Cobalt is a research topic. Over the lifetime, 69899 publications have been published within this topic receiving 1242058 citations. The topic is also known as: Co & Element 27.

Cobalt-Catalyzed Trimethylsilylmethylmagnesium-Promoted Radical Alkenylation of Alkyl Halides: A Complement to the Heck Reaction

Abstract: A cobalt complex, [CoCl2(dpph)] (DPPH = [1,6-bis(diphenylphosphino)hexane]), catalyzes an intermolecular styrylation reaction of alkyl halides in the presence of Me3SiCH2MgCl in ether to yield β-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can participate in the styrylation. A radical mechanism is strongly suggested for the styrylation reaction. The sequential isomerization/styrylation reactions of cyclopropylmethyl bromide and 6-bromo-1-hexene provide evidence of the radical mechanism. Crystallographic and spectroscopic investigations on cobalt complexes reveal that the reaction would begin with single electron transfer from an electron-rich (diphosphine)bis(trimethylsilylmethyl)cobalt(II) complex followed by reductive elimination to yield 1,2-bis(trimethylsilyl)ethane and a (diphosphine)cobalt(I) complex. The combination of [CoCl2(dppb)] (DPPB = [1,4-bis(diphenylphosphino)butane]) catalyst and Me3SiCH2MgCl induces intramolecular Heck-type cyclization reactions of 6-halo-1-hexenes ...

Gate-Controlled Ionization and Screening of Cobalt Adatoms on a Graphene Surface

Abstract: By varying the voltage on an isolated gate electrode beneath a graphene sheet, the ionization state of cobalt atoms on its surface can be controlled. This enables the electronic structure of individual ionized atoms, and the resulting cloud of screening electrons that form around them, to be obtained with a scanning tunnelling microscope.

Cobalt-catalyzed asymmetric hydrogenation of enamides enabled by single-electron reduction

Abstract: Identifying catalyst activation modes that exploit one-electron chemistry and overcome associated deactivation pathways will be transformative for developing first-row transition metal catalysts with performance equal or, ideally, superior to precious metals. Here we describe a zinc-activation method compatible with high-throughput reaction discovery that identified scores of cobalt-phosphine combinations for the asymmetric hydrogenation of functionalized alkenes. An optimized catalyst prepared from ( R , R )-Ph-BPE {Ph-BPE, 1,2-bis[(2 R ,5 R )-2,5-diphenylphospholano]ethane} and cobalt chloride [CoCl 2 ·6H 2 O] exhibited high activity and enantioselectivity in protic media and enabled the asymmetric synthesis of the epilepsy medication levetiracetam at 200-gram scale with 0.08 mole % catalyst loading. Stoichiometric studies established that the cobalt (II) catalyst precursor ( R , R )-Ph-BPECoCl 2 underwent ligand displacement by methanol, and zinc promoted facile one-electron reduction to cobalt (I), which more stably bound the phosphine.

Co, Ru and K loadings effects on the activity and selectivity of carbon nanotubes supported cobalt catalyst in Fischer–Tropsch synthesis

Abstract: An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNTs) supported cobalt catalysts with different loadings of cobalt, ruthenium and potassium is reported Up to 30 wt% of Co, 1 wt% of Ru and 00066 wt% of K were added to the catalyst by co-impregnation method The physico-chemical properties, activity and selectivity of the catalysts were assessed For the 15 wt%Co/CNT catalyst, most of the metal particles were homogeneously distributed inside the tubes and the rest on the outer surface of the CNTs Increasing the Co loading to 30 wt% increased the amount of Co on the outer surface of the CNTs, increased the cobalt cluster sizes and decreased the reduction temperature and dispersion Increasing the Co loading from 15 to 30 wt% increased the CO conversion from 48 to 86% and the C5+ selectivity from 70 to 77% Ruthenium was found to enhance the reducibility of Co3O4 to CoO and that of CoO to Co0, increase the dispersion and decrease the average cobalt cluster size However, potassium was responsible in shifting the reduction temperatures to higher temperatures 05 wt%Ru increased the FTS rate of 15 wt%Co/CNT catalyst by a factor of 14 while addition of 00066 wt%K decreased the FTS rate by a factor of 75 Both promoters enhanced the selectivity of FTS towards the higher molecular weight hydrocarbons however; the effect of Ru is less pronounced Potassium increased the olefin to paraffin ratio from 073 to 35 and the C5+ selectivity from 70 to 87%