Insights into Cobalta(III/IV/II)‐Electrocatalysis: Oxidation‐Induced Reductive Elimination for Twofold C−H Activation

The merger of cobalt‐catalyzed C?H activation and electrosynthesis provides new avenues for resource‐economical molecular syntheses, unfortunately their reaction mechanisms remain poorly understood. Herein, we report the identification and full characterization of electrochemically generated high‐valent cobalt(III/IV) complexes as crucial intermediates in electrochemical cobalt‐catalyzed C?H oxygenations. Detailed mechanistic studies provided support for an oxidatively‐induced reductive elimination via highly‐reactive cobalt(IV) intermediates. These key insights set the stage for unprecedented cobaltaelectro two‐fold C?H/C?H activation.     

Cobalt‐Catalyzed Regio‐ and Stereoselective Hydroboration of Allenes

An efficient pincer‐ligand‐based cobalt‐complex‐catalyzed allene hydroboration affording Z‐allylic boronates is described. The reaction demonstrates an excellent regio‐ as well as Z‐stereoselectivity and a wide substrate scope that tolerates many functional groups. Based on solvent‐assisted electrospray ionization mass spectrometry (SAESI‐MS) studies, a rationale for the cobalt‐catalyzed hydroboration involving the highly selective insertion of an allene into the Co?H bond to form Z‐allylic cobalt intermediates is proposed.     

Overcoming the Limitations of C−H Activation with Strongly Coordinating N‐Heterocycles by Cobalt Catalysis

Strongly coordinating nitrogen heterocycles, including pyrimidines, oxazolines, pyrazoles, and pyridines, were fully tolerated in cobalt‐catalyzed C?H amidations by imidate assistance. Structurally complex quinazolines are thus accessible in a step‐economic manner. Our findings also establish the relative powers of directing groups in cobalt(III)‐catalyzed C?H functionalization for the first time.     

不同催化剂对热解法制备CNx纳米管的影响

CNx nanotubes was synthesized by thermal decomposition ethylenediamine catalyzed by pure iron, cobalt, nickel, and ferrocene. The effect of the catalyst on the CNx nanotubes’ morphology and yield was studied. The catalysis growth mechanism was also discussed. The CNx nanotubes with the “bamboo-like” structure and lower yield are produced when iron or ferrocene is used as the catalyst, whereas the curved CNx nanotubes with many pleats through the nanotube walls and higher yield are generated when cobalt is used. The CNx nanotubes catalyzed by nickel are only helix tubes with the diameter of about 500 nm. Raman spectroscopy studies show that the CNx nanotubes catalyzed by ferrocene have a worse crystallinity due to a higher nitrogen incorporation.     

The regiospecific cobalt carbonyl catalyzed synthesis of dienones and trienones by phase transfer catalysis

The phase transfer catalyzed, cobalt carbonyl catalyzed reaction of dienes, and a triene, with methyl iodide and carbon monoxide [r.t., 1 atm. P] is highly regiospecific, affording E-conjugated enones.     

Mild C−H/C−C Activation by Z‐Selective Cobalt Catalysis

Cationic cobalt complexes enable unprecedented cobalt‐catalyzed C?H/C?C functionalizations with unique selectivity features. The versatile cobalt catalyst proved broadly applicable, enabled efficient C?H/C?C cleavage at room temperature, and delivered Z‐alkenes with excellent diastereocontrol.     

Cobalt‐Catalyzed Enantioselective Hydroboration/Cyclization of 1,7‐Enynes: Asymmetric Synthesis of Chiral Quinolinones Containing Quaternary Stereogenic Centers

An asymmetric cobalt‐catalyzed hydroboration/cyclization of 1,7‐enynes to synthesize chiral six‐membered N‐heterocyclic compounds was developed. A variety of aniline‐tethered 1,7‐enynes react with pinacolborane to afford the corresponding chiral boryl‐functionalized quinoline derivatives in high yields with high enantioselectivity. This cobalt‐catalyzed asymmetric cyclization of 1,7‐enyens provides a general approach to access a series of chiral quinoline derivatives containing quaternary stereocenters.     

Cobalt carbonyl catalyzed sRN1 carbonylation of aryl and vinyl halides by phase transfer catalysis

The phase transfer catalyzed, cobalt carbonyi catalyzed carbonylation (1 atm. P.) of aryl and vinyi bromides under photostimulation (350 nm) affords the corresponding unsaturated acids in high yield.     

A convenient method for the preparation of aromatic ketones from acyl chlorides and arylzinc bromides using a cobalt catalysis

Aromatic ketones are synthesized efficiently via cobalt catalyzed cross-coupling reaction between arylzinc bromides and acid chlorides. Arylzinc bromides prepared chemically via a cobalt catalysis undergo coupling without additional catalyst unlike their electrochemical analogs.     

羟基钴催化氢甲酰化反应的理论研究

采用有效核势能近似(ECP)从头算方法,在HF/LANL2DZ水平下研究了羰基钴催化的氢甲酰化反应循环中的羰基插入、H2 氧化加成和脱氢还原系列基元反应步骤的反应机理.优化得到了反应基态势能面的中间体、过渡态和产物的几何构型.计算了反应活化位垒,并对各过渡态进行了振动分析以确认.理论计算结果表明,羰基插入、H2 氧化加成、脱氢还原的基元反应步骤的活化位垒分别为67.79、139.11和44.78kJ·mol-1.     

Regio‐ and Enantioselective Cobalt‐Catalyzed Sequential Hydrosilylation/Hydrogenation of Terminal Alkynes

A highly regio‐ and enantioselective cobalt‐catalyzed sequential hydrosilylation/hydrogenation of alkynes was developed to afford chiral silanes. This one‐pot method is operationally simple and atom economic. It makes use of relatively simple and readily available starting materials, namely alkynes, silanes, and hydrogen gas, to construct more valuable chiral silanes. Primary mechanistic studies demonstrated that highly regioselective hydrosilylation of alkynes with silanes occurred as a first step, and the subsequent cobalt‐catalyzed asymmetric hydrogenation of the resulting vinylsilanes showed good enantioselectivity.     

Electrocatalytic hydrogen evolution using triaryl corrole cobalt complex

Three cobalt triaryl corroles bearing an electron-withdrawing or electron-donating group at 10-meso-phenyl were synthesized and characterized. Two of them are new cobalt corroles prepared in this study. These cobalt corroles were characterized using high-resolution mass spectrometry, UV–Vis., nuclear magnetic resonance, X-ray photoelectron spectroscopy, and single-crystal X-ray structure determination. All synthesized cobalt corroles efficiently catalyzed the hydrogen evolution reaction (HER) in neutral aqueous media at an overpotential of 838 mV. The HER activity of these cobalt corroles significantly depended on the virtue of peripheral substituents.     

Colloid and nanosized catalysts in organic synthesis: IV. Reduction of nitroarenes with hydrazine hydrate catalyzed with metal nanoparticles

Reduction of a series of nitroarenes with hydrazine hydrate catalyzed with colloid iron, cobalt, nickel, and copper particles has been studied. High catalytic activity of nickel and iron nanoparticles has been demonstrated. Special features of nitrobenzene reduction in the presence of cobalt particles have been revealed.     

Routine catalytic determination of trace amounts of cobalt in small urine samples

The oxidation of catechol by hydrogen peroxide, catalyzed by cobalt(II), is a highly sensitive and selective reaction. It makes it possible to analyze a small sample of urine (5.0 ml) for cobalt without the need for isolation of the analyte from the matrix. The sample is dried and dry-ashed according to a temperature programme, and the residue is dissolved in hydrochloric acid. After filtration of the solution, acetate buffer and sodium citrate are added and cobalt is determined catalytically in an aliquot of the solution, by the standard-addition method.     

Cobalt‐Catalyzed CH Cyanation of Arenes and Heteroarenes

Carboxylate assistance proved to be the key for the success of efficient cobalt(III)‐catalyzed C? H cyanations. Thus, an in situ generated cationic cobalt complex was identified as a versatile catalyst for the site‐selective synthesis of various aromatic and heteroaromatic nitriles with ample substrate scope.     

Cobalt(III)‐Catalyzed Redox‐Neutral Synthesis of Unprotected Indoles Featuring an N−N Bond Cleavage

A redox‐neutral cobalt(III)‐catalyzed synthetic approach for the direct synthesis of unprotected indoles showcasing an N?N bond cleavage is reported. The herein newly introduced Boc‐protected hydrazines establish a beneficial addition to the limited portfolio of oxidizing directing groups for cobalt(III) catalysis. Moreover, the developed catalytic methodology tolerates a good variety of functional groups.     

Highly enantioselective borohydride reductions of 2-phenacylpyridine catalyzed by optically active β-ketoiminato cobalt(II) complexes

The highly enantioselective reduction of 2-phenacylpyridine catalyzed by optically active β-ketoiminato cobalt(II) complexes with pre-modified sodium borohydride was achieved affording in high enantiomeric excess 1-phenyl-2-(2-pyridyl)ethanol, a precursor of sedamine derivatives. The enantioselective sense in the present reduction is discussed and compared to the asymmetric reduction catalyzed by other complex catalysts.     

Cobalt‐Catalyzed C?H Cyanation of Arenes and Heteroarenes

Carboxylate assistance proved to be the key for the success of efficient cobalt(III)‐catalyzed C H cyanations. Thus, an in situ generated cationic cobalt complex was identified as a versatile catalyst for the site‐selective synthesis of various aromatic and heteroaromatic nitriles with ample substrate scope.     

Direct Synthesis of Pyrroles by Dehydrogenative Coupling of Diols and Amines Catalyzed by Cobalt Pincer Complexes

Herein, the first example of base‐metal‐catalyzed dehydrogenative coupling of diols and amines to selectively form functionalized 1,2,5‐substituted pyrroles liberating water and hydrogen gas as the sole by‐products is presented. The reaction is catalyzed by pincer complexes of earth‐abundant cobalt.     

Catalytic hydrodebromination of aryl bromides by cobalt tetra-butyl porphyrin complexes with EtOH

Hydrodebromination of aryl bromides catalyzed by electron rich and sterically unhindered cobalt 5,10,15,20-tetrabutylporphyrin was achieved at mild conditions in good yields employing EtOH as the hydrogen source. The catalytic efficiency was enhanced compared with previously reported by cobalt tetra-aryl porphyrin catalysts. A revised mechanism of single electron transfer was proposed.