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Your search keyword '"Tok, Oleg L."' showing total 238 results
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238 results on '"Tok, Oleg L."'

1. Intramolecular Pericyclic Re‐hydroboration via Six‐Membered Transition State: Synthesis of Fused Borolo[3,2‐b]siloles.

Author

Tok, Oleg L., Bavol, Dmytro, and Bould, Jonathan

Subjects
*NUCLEAR magnetic resonance spectroscopy, *HYDROBORATION, *SILOLES, *HEATING, *BORON
Abstract

We experimentally demonstrate a new type of the intramolecular reaction between non‐activated alkyne units and the dialkylboryl group (9‐BBN), which was previously only hypothesized and studied on a calculational level. The reaction described here can formally be classified as a 1,2‐hydroboration reaction, but, in contrast to the classical mechanism via a cyclic four‐membered transition state, the reaction proceeds by a pericyclic mechanism involving a six‐membered transition state. In practice, the reaction allows the synthesis of a new class of the borolenes fused with silole or dihydrosilole units. Thus, the heating (125 °C) of 2,3‐dihydrosiloles or 2,3‐dihydrosilolo[2,3‐b]silole bearing 9‐BBN and propargyl or dimethylpropargyl groups in positions 4 and 5, respectively, affords, in high to moderate yields, di‐ and tricyclic compounds containing a borolo[3,2‐b]silole unit. In all cases, the reactions are accompanied by an unprecedented dehydroboration of the 9‐BBN fragment, leading, in the final products, to a cyclooct‐4‐enyl group on the boron atom. The effects of the substituents on the rate and the selectivity of the reaction are discussed. The structures of all the new compounds have been determined from HRMS together with multinuclear 1D and 2D NMR spectroscopy, the results of which are in excellent agreement with DFT calculated chemical shifts. [ABSTRACT FROM AUTHOR]

Published
2024
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3. Experimental and Computational 77Se NMR Spectroscopic Study on Selenaborane Cluster Compounds

Author

Bould, Jonathan, Londesborough, Michael G. S., and Tok, Oleg L.

Abstract

Calculated and measured 77Se nuclear magnetic resonance (NMR) chemical shift data on a diverse collection of 13 selenaborane cluster compounds, containing a total of 19 selenium centers, reveals a correlation between chemical shifts and the intracluster coordination of selenium atoms within their borane frameworks. A plot of the measured against calculated 77Se NMR chemical shifts shows an approximately linear relationship that can serve as a predictive tool in assessing the chemical shift range in which a selenium vertex from a particular compound might be expected to be found, thereby reducing expensive experimental time. Furthermore, the relative chemical shifts between selenium vertices in clusters containing more than one selenium atom are consistent across the range, thus allowing the assignment of the selenium resonances with a high degree of confidence even in relatively low-level density functional theory calculations. A new macropolyhedral 20-vertex selenaborane Se2B18H20(A) is also reported.

Published
2024
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6. Stable exo-nido-metallacarboranes (M=[Os.sup.IV]) that incorporate meta-carborane-based dicarbollide ligands

Author

Balagurova, Elena V., Cheredilin, Dmitir N., Kolomnikova, Galina D., Tok, Oleg L., Dolgushin, Fedor M., Yanovsky, Alexander I., and Chizhevsky, Igor T.

Subjects
Carbon compounds -- Structure, Carbon compounds -- Chemical properties, X-rays -- Diffraction, X-rays -- Usage, Chemistry
Abstract

The synthesis of a short series of three stable 16-electron exo-nido-osmacarborane complexes is described. The dianionic [[nido-7-R-7, 9-[C.sub.2][B.sub.9][H.sub.10].sup.2-] cage ligand is bound to the Os(IV) containing moiety via the bidentate {B...H}...Os bonding interaction in each of these three complexes.

Published
2007

10. Synthesis and dynamic properties of cycloheptatrienyl(dipropyl)borane. Equilibrium with 7 --dipropylborylnorcaradiene

Author

Gridnev, Ilya D., Tok, Oleg L., Gridneva, Natalya A., Bubnov, Yuri N., and Schreiner, Peter R.

Subjects
Electron donor-acceptor complexes -- Research, Borane -- Research, Nuclear magnetic resonance spectroscopy -- Usage, Molecular orbitals -- Research, Cyclic compounds -- Research, Chemistry
Abstract

The synthesis and dynamic properties of cycloheptatrienyl(dipropyl)borane was determined through the exchange reaction of trimethyl(cycloheltatrienyl)tin and dipropylchloroborane and nuclear magnetic resonance spectroscopy. Ab initio calculations demonstrate that the donor-acceptor interaction between the Walsh orbital of the cyclopropane and the boron 2p AO is effective in the exo-norcaradiene form. Results also suggest that the boron 2p AO is necessary for the stabilization of the norcaradiene form.

Published
1998

12. First agostic closo-metallacarboranes with η 3-cyclooctenyl type ligand: synthesis and structural characterization of closo-3-[η 3-( endo-1,5-dimethylcycloocten-1-yl)]-1,2-μ-(1′,2′-xylylene)-3,1,2-IrC 2B 9H 9 and its isomerization to closo-3-[η 3-( exo-1-methylene-5-methylcyclooctene-1-yl)]-1,2-μ-[η 2-(1′,2′-xylylene)]-3,1,2-IrC 2B 9H 9

Author

Safronov, Alexander V, Zinevich, Tatiana V, Dolgushin, Fedor M, Vorontsov, Evgenii V, Tok, Oleg L, and Chizhevsky, Igor T

Published
2003
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16. Two isomeric phosphacarboranes 2,1- and 6,1-PCB (sub)8 H (sub)9, the first representatives of the 10-vertex closo phosphacarborane series

Author

Holub, Josef, Bakardjiev, Mario, Stibr, Bohumil, Hnyk, Drahomir, Tok, Oleg L., and Wrackmeyer, Bernd

Subjects
Chemistry, Inorganic -- Research, Phosphorus -- Physiological aspects, Hydrogen -- Physiological aspects, Carbon -- Physiological aspects, Isomerization -- Physiological aspects, Chemistry
Abstract

Research has been conducted on the phosphacarborane species. The isomerization cluster expansion and substitution reactions of these species have been investigated and the details are discussed.

Published
2002

31. Methyl camouflage in the ten-vertex closo-dicarbaborane(10) series. Isolation of closo-1,6-R2C2B8Me8 (R = H and Me) and their monosubstituted analogues.

Author

Bakardjiev, Mario, Tok, Oleg L., Růžička, Aleš, Růžičková, Zdeňka, Holub, Josef, Hnyk, Drahomír, Špalt, Zbyněk, Fanfrlík, Jindřich, and Štíbr, Bohumil

Subjects
*BORANE derivatives, *CARBORANES, *METHYLATION kinetics, *ALUMINUM chloride, *ALKYL group, *SUBSTITUTION reactions
Abstract

Reported are procedures leading to the first types of methyl camouflaged dicarbadecaboranes with fewer than eleven vertices. The compounds contain the closo-1,6-C2B8 scaffolding inside the egg-shaped hepta – decamethyl sheath, which imparts unusually high air and solvolytic stability to all of these compounds. [ABSTRACT FROM AUTHOR]

Published
2018
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33. 'Electronic lock' in chromiumtricarbonyl complex of cycloheptatrienyltin

Author

Gridnev, Ilya D. and Tok, Oleg L.

Subjects
Molecular dynamics -- Research, Organometallic compounds -- Structure, Organometallic compounds -- Chemical properties, Carbonyl compounds -- Structure, Carbonyl compounds -- Chemical properties, Chemistry
Abstract

The chromiumtricarbonyl group acts as a selective 'electronic lock' upon coordination to cycloheptatrienyltin. It is shown that organometallic derivatives of cycloheptatriene exhibit various types of intramolecular dynamics.

Published
2003

36. Synthesis of closo-1,2-H2C2B8Me8and 1,2-H2C2B8Me7X (X = I and OTf) Dicarbaboranes and Their Rearrangement Reactions

Author

Bakardjiev, Mario, Růžička, Aleš, Růžičková, Zdeňka, Tok, Oleg L., Holub, Josef, Hnyk, Drahomír, Fanfrlík, Jindřich, and Štíbr, Bohumil

Abstract

Methyl-camouflaged dicarbaboranes closo-1,2- and 1,10-H2C2B8Me8have been prepared in high yields either from nido-5,6-H2C2B8H10or closo-1,2-H2C2B8H8via electrophilic methylation reactions and cluster-rearrangement methods. Prepared were also monosubstituted derivatives of general formulation closo-H2C2B8Me7–X (X = I or OTf). The permethylated compounds exhibit extreme air stability in comparison to unprotected counterparts as a consequence of rigid, egg-shaped hydrocarbon structures incorporating inner C2B8carborane scaffolding. The structures of all compounds isolated were confirmed unambiguously by multinuclear (11B, 1H, 13C, and 19F) NMR measurements, supported by X-ray diffraction analyses and geometry optimization methods on several compounds.

Published
2019
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