Roman Dobrovetsky
University of Toronto
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Featured researches published by Roman Dobrovetsky.
Science | 2013
Christopher B. Caputo; Lindsay J. Hounjet; Roman Dobrovetsky; Douglas W. Stephan
The Pull of Phosphorus Lewis acidity is primarily associated with compounds like boranes that lack a full complement of electrons in their coordination sphere and therefore attract electron donors (Lewis bases) to fill the gap. Caputo et al. (p. 1374; see the Perspective by Gabbaï) now show that a class of 4-coordinate phosphonium salts can act as surprisingly potent Lewis acids, despite their electronic saturation. The phosphorus cations, bearing fluorine and fluorinated aromatic substituents, can sever an alkyl carbon-fluorine bond by pulling away its fluoride—a process rendered catalytic through the use of a silane acceptor. Certain four-coordinate phosphorus cations prove sufficiently Lewis acidic to sever carbon-fluorine bonds. [Also see Perspective by Gabbaï] Prototypical Lewis acids, such as boranes, derive their reactivity from electronic unsaturation. Here, we report the Lewis acidity and catalytic application of electronically saturated phosphorus-centered electrophilic acceptors. Organofluorophosphonium salts of the formula [(C6F5)3–xPhxPF][B(C6F5)4] (x = 0 or 1; Ph, phenyl) are shown to form adducts with neutral Lewis bases and to react rapidly with fluoroalkanes to produce difluorophosphoranes. In the presence of hydrosilane, the cation [(C6F5)3PF]+ is shown to catalyze the hydrodefluorination of fluoroalkanes, affording alkanes and fluorosilane. The mechanism demonstrates the impressive fluoride ion affinity of this highly electron-deficient phosphonium center.
Journal of the American Chemical Society | 2013
Manuel Pérez; Lindsay J. Hounjet; Christopher B. Caputo; Roman Dobrovetsky; Douglas W. Stephan
Organofluorophosphonium salts of the formula [(C6F5)(3-x)Ph(x)PF][B(C6F5)4] (x = 0, 1) exhibit Lewis acidity derived from a low-lying σ* orbital at P opposite F. This acidity is evidenced by the reactions of these salts with olefins, which catalyze the rapid isomerization of 1-hexene to 2-hexene, the cationic polymerization of isobutylene, and the Friedel-Crafts-type dimerization of 1,1-diphenylethylene. In the presence of hydrosilanes, olefins and alkynes undergo efficient hydrosilylation catalysis to the alkylsilanes. Experimental and computational considerations of the mechanism are consistent with the sequential activation and 1,2-addition of hydrosilane across the unsaturated C-C bonds.
Proceedings of the National Academy of Sciences of the United States of America | 2014
Manuel Pérez; Christopher B. Caputo; Roman Dobrovetsky; Douglas W. Stephan
Significance For more than a century, hydrogenation has been limited to the use of transition metal-based catalysts. With the emerging focus on the chemistry of earth-abundant elements, the 21st century has seen a renaissance in main-group chemistry. In this work, an electrophilic phosphonium cation is shown to act as main-group catalyst effecting the dehydrocoupling of silane and amines, phenols, thiols, and carboxylic acids with the concurrent release of H2. In addition, performing the reactions in the presence of olefins, dehydrocoupling occurs with simultaneous hydrogenation of the olefin. This chemistry provides an unprecedented avenue to metal-free transfer hydrogenation catalysis of olefins. A major advance in main-group chemistry in recent years has been the emergence of the reactivity of main-group species that mimics that of transition metal complexes. In this report, the Lewis acidic phosphonium salt [(C6F5)3PF][B(C6F5)4] 1 is shown to catalyze the dehydrocoupling of silanes with amines, thiols, phenols, and carboxylic acids to form the Si-E bond (E = N, S, O) with the liberation of H2 (21 examples). This catalysis, when performed in the presence of a series of olefins, yields the concurrent formation of the products of dehydrocoupling and transfer hydrogenation of the olefin (30 examples). This reactivity provides a strategy for metal-free catalysis of olefin hydrogenations. The mechanisms for both catalytic reactions are proposed and supported by experiment and density functional theory calculations.
Angewandte Chemie | 2015
Thorsten vom Stein; Manuel Pérez; Roman Dobrovetsky; Daniel Winkelhaus; Christopher B. Caputo; Douglas W. Stephan
The combination of phosphorus(V)-based Lewis acids with diaryl amines and diaryl silylamines promotes reversible activation of dihydrogen and can be further exploited in metal-free catalytic olefin hydrogenation. Combined experimental and density functional theory (DFT) studies suggest a frustrated Lewis pair type activation mechanism.
Chemistry: A European Journal | 2015
Manuel Pérez; Zheng-Wang Qu; Christopher B. Caputo; Vitali Podgorny; Lindsay J. Hounjet; Andreas Hansen; Roman Dobrovetsky; Stefan Grimme; Douglas W. Stephan
The electrophilic phosphonium salt, [(C6 F5 )3 PF][B(C6 F5 )4 ], catalyses the efficient hydrosilylation of ketones, imines and nitriles at room temperature. In the presence of this catalyst, adding one equivalent of hydrosilane to a nitrile yields a silylimine product, whereas adding a second equivalent produces the corresponding disilylamine. [(C6 F5 )3 PCl][B(C6 F5 )4 ] and [(C6 F5 )3 PBr][B(C6 F5 )4 ] are also synthesised and tested as catalysts. Competition experiments demonstrate that the reaction exhibits selectivity for the following functional groups in order of preference: ketone>nitrile>imine>olefin. Computational studies reveal the reaction mechanism to involve initial activation of the Si-H bond by its interaction with the phosphonium centre. The activated complex then acts cooperatively on the unsaturated substrate.
Organic Letters | 2018
Karina Chulsky; Roman Dobrovetsky
In contrast to the well-known reductive cleavage of the alkyl-O bond, the cleavage of the alkenyl-O bond is much more challenging especially using metal-free approaches. Unexpectedly, alkenyl-O bonds were reductively cleaved when enol ethers were reacted with Et3SiH and a catalytic amount of B(C6F5)3. Supposedly, this reaction is the result of a B(C6F5)3-catalyzed tandem hydrosilylation reaction and a silicon-assisted β-elimination. A mechanism for this cleavage reaction is proposed based on experiments and density functional theory (DFT) calculations.
Journal of Materials Chemistry | 2018
Ajay Kumar Chinnam; Natan Petrutik; Kangcai Wang; Avital Shlomovich; Olga Shamis; Daniel Shem Tov; Muhamed Sućeska; Qi-Long Yan; Roman Dobrovetsky; Michael Gozin
A number of energetic ionic liquids (EILs) have been reported as promising hydrazine-replacement fuels for hypergolic rocket propulsion. However, most of these EILs were ignited using corrosive and hazardous concentrated fuming nitric acid. Very significant efforts were recently made to utilize “rocket grade” highly concentrated H2O2 (>90%) as a “green” alternative to fuming nitric acid and N2O4 oxidizers. Although “rocket grade” H2O2 is more challenging to use and less safe for storage than commercially available H2O2 (70%), the latter is not considered as a viable oxidizer for hypergolic propulsion. In this work, we focused on the development of novel iodine-rich promoters, capable of initiating hypergolic ignition reactions between a typical EIL fuel – 3-ethyl-1-methyl-1H-imidazol-3-ium cyanotrihydroborate – and H2O2. Among the prepared and evaluated promoters, the top performing [FcCH2NEtMe2+]2[B12I122−] compound 5 showed ignition delay times of 45 ms in the reaction of the tested EIL with H2O2 (70%) and 17 ms with H2O2 (95%). We believe that these findings provide a platform for the development and utilization of commercially available H2O2 as a potential “green” oxidizer for rocket propulsion.
Angewandte Chemie | 2013
Roman Dobrovetsky; Douglas W. Stephan
Dalton Transactions | 2015
Christopher B. Caputo; Daniel Winkelhaus; Roman Dobrovetsky; Lindsay J. Hounjet; Douglas W. Stephan
Israel Journal of Chemistry | 2015
Roman Dobrovetsky; Douglas W. Stephan