G. I. Nikishin

Abstract: The dimerization of 1-alkynes catalyzed by RhCl(PMe 3 ) 3 yields conjugated enynes I and II (I/II = 1.4–2.4), with a selectivity of 95–98%. The data indicate that the reaction proceeds by alkyne insertion into the metal-hydride bond of the intermediate (alkynyl)(hydride)Rh III complexes VII, VIII to give the (alkynyl)(vinyl)Rh III species cis - (IX) and cis - (X) which were isolated. The thermal decomposition of IX and X in solution gives the enynes I and II correspondingly.

Abstract: The kinetics and mechanism of intramolecular hydroacylation catalyzed by complexes Co2(μ-N2)(PPh3)6 (III) and (PPh3)2Co(dppe) (IV) (dppe-1,2-bis(di-phenylphosphino)ethane) were studied. The active monomeric 17-electron intermediate, (Ph3P)2Co(CH2CHCH2CH2CHO) (Vb) was isolated in the cyclisation of 4-pentenal (I), catalyzed by complex III. Crystals of Vb are stable in an inert atmosphere at room temperature for a month. A well defined EPR spectrum of Vb in toluene glass at 77 K was obtained. According to the IR spectrum of complex Vb aldehyde I is bonded to the metal as a bidentate π,π-ligand. The ligand exchange reaction was found to proceed readily between Vb and dppe to form free I (85%) and Co(dppe)2. The complex Vb is the first example of a cobalt(0) complex with a coordinated aidehyde group. The analogous intermediate, (dppe)Co(CH2CHCH2-CH2CHO) (Va) was identified by EPR in solution during the 4-pentenal cyclization, catalyzed by complex IV. For the 4-pentenal hydroacylation reaction, catalyzed by complex Vb, zero and first order kinetic laws were found for the aldehyde I and the catalyst concentrations respectively in accordance with the equation: W0 = k[Vb], k = (8.5 ± 0.5) × 10−4 s−1 at 70°C. It is suggested that the reaction mechanism involves oxidative addition of coordinated I to cobalt(0) within the complex Vb to give an acyl hydride intermediate (rate-determining step). The subsequent rearrangement of the acyl hydride complex to the acylalkylcobalt derivative, followed by a reductive elimination reaction yields the ketone II and the parent cobalt(0) complex. Unlike well-known catalytic processes, in which diamagnetic CoI and CoIII species are key intermediates, the catalytic cycle of the intramolecular hydroacylation reaction seems to involve only mononuclear paramagnetic Co0 and CoII species. Chelation of the cobalt atom by an unsaturated aldehyde was found to be an important requirement for this reaction to occur.

Abstract: Data on methods of electrochemical synthesis of cyclopropanes are summarized and described systematically. Direct electrochemical methods to afford cyclopropanes in both cathodic and anodic processes are considered. Among indirect electrochemical methods such as the processes employing electrogenerated bases and also those involving electrogenerated metal complexes, attention is focused on the most promising methods for the synthesis of functionally substituted cyclopropanes, namely, the electrocatalytic cascade and multicomponent transformations of CH acids and also the joint electrolysis of CH acids and activated alkenes or carbonyl compounds in the presence of alkali metal halides as mediators. The bibliography includes 62 references.

Abstract: Aliphatic and alicyclic gem-bis-hydroperoxides and their derivatives, bis(1-hydroperoxycycloalkyl) and bis(1-hydroperoxyalkyl) peroxides, dispiro- and tetraalkyl-1,2,4,5-tetroxanes were synthesized by the reaction of aliphatic and alicyclic acetals and enol ethers with H2O2 in the presence of BF3 in anhydrous Et2O.

Abstract: The reaction of primary alcohols with formalin or paraformaldehyde initiated by t-butyl peroxide in a glass apparatus under atmospheric pressure leads to the formation of alkane-1,2-diols.

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Abstract: Catalytic C–H activation has emerged as a powerful tool for sustainable syntheses. In the recent years, notable success was achieved with the development of cobalt-catalyzed C–H functionalizations with either in situ generated or single-component cobalt-complexes under mild reaction conditions. Herein, recent progress in the field of organometallic cobalt-catalyzed C–H activation is reviewed until November 2015.

Abstract: Several researchers conducted studies to demonstrate metal catalyzed alkene and alkyne hydrocylation. A team of researchers developed a method for the synthesis of cyclooctenones using the intramolecular hydrogenation. Eight-membered ring formation was achieved by the incorporation of a cyclopropane ring in the substrate to demonstrate metal catalyzed alkene and alkyne hydrocylation. The key step of the method involved the fragmentation and isomerization of rhodacycle 25 into ring-expanded rhodacycle 26. The researchers investigated the reactions of the two isomers of a deuterium-labeled substrate to explore the mechanism in operation. Another team of researchers prepared a series of medium-ring sulfur heterocycles using intramolecular hydroacylation to demonstrate the investigations.