Electrochemical synthesis and catalytic activity of organonickel sigma-complexes

A new industrially applicable method of organonickel sigma-complexes production is developed. The technique is based on the reaction of the oxidative addition of ortho-substituted aromatic bromides to electrochemically generated nickel(0)-2,2′-bipyridyl complexes. Electrolysis is performed in undivided electrolyser supplied with sacrificial nickel anode with a periodic or continuous electrolyte loading. The electrochemically obtained organonickel sigma-complexes of type [NiBr(Ar)(bpy)], where Ar is 2,4,6-trimethylphenyl, 2,4,6-triisopropylphenyl, 2,6-dimethylphenyl, are highly effective precatalysts for ethylene oligomerization process, leading to the formation of linear alpha-olefines of C4–C12 fractions     

Photocatalytic liquid-phase dehydrogenation of cyclohexanol with rhodium porphyrin complex

Photocatalytic dehydrogenation of cyclohexanol to yield cyclohexanone and dihydrogen proceeded with chloro(tetraphenylporphyrinato)rhodium (III) complex under the excitation conditions of either the B or Q band. First-order rate dependence on concentrations of the Q band-excited catalyst species suggests that the same bimolecular mechanism between the excited and ground-state species previously proposed for 2-propanol dehydrogenation is applicable to cyclohexanol as well.     

A facile one-step synthesis of polymer supported rhodium nanoparticles in organic medium and their catalytic performance in the dehydrogenation of ammonia-borane

A new type of supported rhodium nanoparticles were reproducibly prepared from N(2)H(4)BH(3) reduction of [Rh(μ-Cl)(1,5-cod)](2) without using any solid support and pre-treatment technique. Their characterization shows the formation of well dispersed rhodium(0) nanoparticles within the framework of a polyaminoborane based polymeric support. These new rhodium(0) nanoparticles were found to be the most active supported catalyst in the catalytic dehydrogenation of ammonia-borane in water at room temperature.     

Modification of catalytic properties of silica-supported rhodium

A sharp change in the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion has been found for catalysts prepared via interaction between Rh(CO)₂Cl₂ and silica modified by Sn, Pb, Mo and W ions.

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, Rh(CO)₂Cl₂ , Sn, Pb, Mo W, , , -.

     

One-pot synthesis of colloidally robust rhodium(0) nanoparticles and their catalytic activity in the dehydrogenation of ammonia-borane for chemical hydrogen storage

Rhodium(0) nanoparticles stabilized by tert-butylammonium octanoate were prepared reproducibly from the reduction of rhodium(II) octanoate with tert-butylamine-borane in toluene at room temperature and characterized by ICP-OES, TEM, HRTEM, STEM, EDX, XRD, XPS, FTIR, UV-vis, (11)B, (13)C and (1)H NMR spectroscopy and elemental analysis. These new rhodium(0) nanoparticles show unprecedented catalytic activity, lifetime and reusability as a heterogeneous catalyst in room temperature dehydrogenation of ammonia-borane, which is under significant investigation as a potential hydrogen storage material.     

Alkyne insertion into cyclometallated pyrazole and imine complexes of iridium, rhodium and ruthenium; relevance to catalytic formation of carbo- and heterocycles

The cyclometallated complexes [MCl(C^N)(ring)] (HC^N = 2-phenylpyrazole, M = Ir, Rh ring = Cp*; M = Ru, ring = p-cymene) readily undergo insertion reactions with RC≡CR (R = CO(2)Me, Ph) to give mono insertion products, the rhodium complex also reacts with PhC≡CH regiospecifically to give an analogous product. The products of the reactions of the cyclometallated imine complexes [MCl(C^N)Cp*] (HC^N = PhCH=NR, R = Ph, CH(2)CH(2)OMe, Me; M = Ir, Rh) with PhC≡CPh depend on the substituent R; when R = CH(2)CH(2)OMe a monoinsertion is observed, however for R = Me the initial insertion product is unstable, undergoing reductive elimination with loss of the organic fragment, and for R = Ph no metal-containing product is isolated. With PhC≡CH the cyclometallated imine complexes can give mono or di-insertion products. The implications for catalytic synthesis of carbo- and heterocycles by a tandem C-H activation, alkyne insertion mechanism are discussed.     

Principles of catalytic dehydrogenation of alkyl aromatic hydrocarbons

Russian Chemical Bulletin -     

Synthesis and the thermal and catalytic dehydrogenation reactions of amine-thioboranes

A series of trimethylamine-thioborane adducts, Me(3)N·BH(2)SR (R = tBu [2a], nBu [2b], iPr [2c], Ph [2d], C(6)F(5) [2e]) have been prepared and characterized. Attempts to access secondary and primary amine adducts of thioboranes via amine-exchange reactions involving these species proved unsuccessful, with the thiolate moiety shown to be vulnerable to displacement by free amine. However, treatment of the arylthioboranes, [BH(2)-SPh](3) (9) and C(6)F(5)SBH(2)·SMe(2) (10) with Me(2)NH and iPr(2)NH successfully yielded the adducts Me(2)NH·BH(2)SR (R = Ph [11a], C(6)F(5) [12a]) and iPr(2)NH·BH(2)SR (R = Ph [11b], C(6)F(5) [12b]) in high yield. These adducts were also shown to be accessible via thermally induced hydrothiolation of the aminoboranes Me(2)N═BH(2), derived from the cyclic dimer [Me(2)N-BH(2)](2) (13), and iPr(2)N═BH(2) (14), respectively. Attempts to prepare the aliphatic thiolate substituted adducts R(2)NH·BH(2)SR' (R = Me, iPr; R' = tBu, nBu, iPr) via this method, however, proved unsuccessful, with the temperatures required to facilitate hydrothiolation also inducing thermal dehydrogenation of the amine-thioborane products to form aminothioboranes, R(2)N═BH(SR'). Thermal and catalytic dehydrogenation of the targeted amine-thioboranes, 11a/11b and 12a/12b were also investigated. Adducts 11b and 12b were cleanly dehydrogenated to yield iPr(2)N═BH(SPh) (22) and iPr(2)N═BH(SC(6)F(5)) (23), respectively, at 100 °C (18 h, toluene), with dehydrogenation also possible at 20 °C (42 h, toluene) with a 2 mol % loading of [Rh(μ-Cl)cod](2) in the case of the former species. Similar studies with adduct 11a evidenced a competitive elimination of H(2) and HSPh upon thermolysis, and other complex reactivity under catalytic conditions, whereas the fluorinated analogue 12a was found to be resistant to dehydrogenation.     

Oxidative dehydrogenation of n-butane IV. Kinetic and catalytic activity of copper oxide

Copper oxide is moderately active and selective in the oxidative dehydrogenation of n-butane. Selectivity to C₄ olefin is almost constant in the range of 200–520°C. The apparent activation energy determined between 200 and 360°C was 18.8 kcal/mol, and 9.2 kcal/mol at higher temperatures.

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-. C₄ 200–520°C. 200–360°C 18,8 /, 9,2 /.

     

An oxidative route to α-trimethylsilyl ketones by means of rhodium catalyzed dehydrogenation of β-trimethylsilyl alcohols

The transfer hydrogenation of β-trimethylsilyl alcohols catalyzed by HRh(PPh₃)₄ has been successfully applied to the efficient synthesis of α-trimethylsilyl ketones.     

Synthesis of carbazole under conditions for the catalytic dehydrogenation of cyclohexylamine

The dehydrogenation of cyclohexylamine on platinum catalysts is investigated. In addition to aniline and diphenylamine, significant amounts of carbazole are formed. A possible mechanism for its formation is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 617–619, May 1988.     

Unravelling the role of boron dopant in borocarbonitirde catalytic dehydrogenation reaction

Borocarbonitride(BCN) materials are newly developed metal-free catalytic materials exhibiting high selectivity in oxidative dehydrogenation(ODH) of alkanes. However, the in-depth understandings on the role of boron(B) dopants and the intrinsic activities of –C=O and –B–OH still remain unknown.Herein, we report a series of BCN materials with regulable B content and surface oxygen functional groups via self-assembly and pyrolysis of guanine and boric acid. We found that the B/C ratio is the key pa...     

Intramolecular alkyl phosphine dehydrogenation in cationic rhodium complexes of tris(cyclopentylphosphine)

[Rh(nbd)(PCyp(3))(2)][BAr(F) (4)] (1) [nbd = norbornadiene, Ar(F) = C(6)H(3)(CF(3))(2), PCyp(3) = tris(cyclopentylphosphine)] spontaneously undergoes dehydrogenation of each PCyp(3) ligand in CH(2)Cl(2) solution to form an equilibrium mixture of cis-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(2)][BAr(F) (4)] (2 a) and trans-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(2)][BAr(F) (4)] (2 b), which have hybrid phosphine-alkene ligands. In this reaction nbd acts as a sequential acceptor of hydrogen to eventually give norbornane. Complex 2 b is distorted in the solid-state away from square planar. DFT calculations have been used to rationalise this distortion. Addition of H(2) to 2 a/b hydrogenates the phosphine-alkene ligand and forms the bisdihydrogen/dihydride complex [Rh(PCyp(3))(2)(H)(2)(eta(2)-H(2))(2)][BAr(F) (4)] (5) which has been identified spectroscopically. Addition of the hydrogen acceptor tert-butylethene (tbe) to 5 eventually regenerates 2 a/b, passing through an intermediate which has undergone dehydrogenation of only one PCyp(3) ligand, which can be trapped by addition of MeCN to form trans-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(PCyp(3))(NCMe)][BAr(F) (4)] (6). Dehydrogenation of a PCyp(3) ligand also occurs on addition of Na[BAr(F) (4)] to [RhCl(nbd)(PCyp(3))] in presence of arene (benzene, fluorobenzene) to give [Rh(eta(6)-C(6)H(5)X){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (7: X = F, 8: X = H). The related complex [Rh(nbd){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] 9 is also reported. Rapid ( approximately 5 minutes) acceptorless dehydrogenation occurs on treatment of [RhCl(dppe)(PCyp(3))] with Na[BAr(F) (4)] to give [Rh(dppe){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (10), which reacts with H(2) to afford the dihydride/dihydrogen complex [Rh(dppe)(PCyp(3))(H)(2)(eta(2)-H(2))][BAr(F) (4)] (11). Competition experiments using the new mixed alkyl phosphine ligand PCy(2)(Cyp) show that [RhCl(nbd){PCy(2)(Cyp)}] undergoes dehydrogenation exclusively at the cyclopentyl group to give [Rh(eta(6)-C(6)H(5)X){PCy(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (17: X = F, 18: X = H). The underlying reasons behind this preference have been probed using DFT calculations. All the complexes have been characterised by multinuclear NMR spectroscopy, and for 2 a/b, 4, 6, 7, 8, 9 and 17 also by single crystal X-ray diffraction.     

Molecular-level understanding of the catalytic cycle of dehydrogenation of ethylbenzene to styrene over iron oxide-based catalyst

Dehydrogenation of ethylbenzene (EB) to styrene over iron oxide-based catalyst is an important industrial catalytic process. A great deal of insight into this reaction has been accomplished by surface science studies of the model catalysts. However, molecular understanding still lacks in the removal of the resultant hydrogen from the oxide surface. Employing gas-phase atomic hydrogen, we successfully prepared hydroxyls on an alpha-Fe2O3(0001) film with biphase surface structure under ultrahigh-vacuum conditions. Upon heating, hydroxyls react to form hydrogen and water, the latter of which results in the partial reduction of Fe2O3. These results add important insight into the complete understanding of the catalytic cycle of dehydrogenation of ethylbenzene to styrene over iron oxide-based catalyst.