Cyclohexane | EPFL Graph Search

Cyclohexane is a cycloalkane with the molecular formula . Cyclohexane is non-polar. Cyclohexane is a colourless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohexane is mainly used for the industrial production of adipic acid and caprolactam, which are precursors to nylon. Cyclohexyl () is the alkyl substituent of cyclohexane and is abbreviated Cy. Production Modern On an industrial scale, cyclohexane is produced by hydrogenation of benzene in the presence of a Raney nickel catalyst. Producers of cyclohexane account for approximately 11.4% of global demand for benzene. The reaction is highly exothermic, with ΔH(500 K) = -216.37 kJ/mol. Dehydrogenation commenced noticeably above 300 °C, reflecting the favorable entropy for dehydrogenation. : Early Unlike benzene, cyclohexane is not found in natural resources such as coal. For this reason, early invest

Chiral Cyclopentadienyls: Enabling Ligands for Asymmetric Rh(III)-Catalyzed C-H Functionalizations

Nicolai Cramer, Baihua Ye

Transition-metal catalyzed C-H functionalizations became a complementary and efficient bond-forming strategy over the past decade. In this respect, Cp*Rh(III) complexes have emerged as powerful catalysts for a broad spectrum of reactions giving access to synthetically versatile building blocks. Despite their high potential, the corresponding catalytic enantioselective transformations largely lag behind. The targeted transformations require all the remaining three coordination sites of the central rhodium atom of the catalyst. In consequence, the chiral information on a competent catalyst can only by stored in the cyclopentadienyl unit. The lack of suitable enabling chiral cyclopentadienyl (Cp-x) ligands is the key hurdle preventing the development of such asymmetric versions. In this respect, an efficient set of chiral Cp-x ligands useable with a broad variety of different transition-metals can unlock substantial application potential. This Account provides a description of our developments of two complementary classes of C-2-symmetric Cp-x derivatives. We have introduced a side- and back-wall concept to enforce chirality transfer onto the central metal atom. The first generation consists of a fused cyclohexane unit having pseudo axial methyl groups as chiral selectors and a rigidifying acetal moiety. The second ligand generation derives from an atrop-chiral biaryl-backbone and which possesses adjustable substituents at its 3,3'-positions. Both ligand families can be modulated in their respective steric bulk to adjust for the specific needs of the targeted application. The cyclopentadienes can be metalated under standard conditions. The corresponding chiral rhodium(I) ethylene complexes are relatively air and moisture and represent storable stable precatalysts for the targeted asymmetric Rh(III)-catalyzed C-H functionalizations. These complexes are then conveniently oxidized in situ by dibenzoyl peroxide to give the reactive (CpRh)-Rh-x(III)(OBz)(2) species. For instance, this catalyst is used for directed C-H activations of aryl hydroxamates and the subsequent enantioselective trapping with olefins, providing dihydroisoquinolones in very high enantioselectivities. In addition, we have established highly selective intramolecular trapping reactions with tethered higher substituted alkenes giving dihydrobenzofurans with quaternary stereogenic centers. Concerning intermolecular reactions, allene coupling partners allow for an enantioselective hydroarylation yielding substituted allylated compounds. A trapping process of the cyclometalated intermediate with diazo reactants enables the enantioselective construction of isoindolinones. Moreover, the catalysts can be used for the construction of atropchiral biaryl motives using a dehydrogenative Heck-type reaction. The development of flexibly adjustable chiral Cp-x ligands is described in this Account showcasing their applicability for a variety of Rh(III) catalyzed CH functionalization reactions. These Cp-x derivatives hold promise as powerful steering ligands for further transition-metals used in asymmetric catalysis.

American Chemical Society2015

An efficient Pt nanoparticle–ionic liquid system for the hydrodeoxygenation of bio-derived phenols under mild conditions

Lu Chen, Paul Joseph Dyson, Zhaofu Fei, Cornel Fink, Gabor Laurenczy

Platinum nanoparticles (NPs) were synthesized in situ in the ionic liquid (IL) [Emim]NTf2 (1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide) as well as in mixtures of [Emim]NTf2 with a second IL, Lewis acid or Brønsted acid, but in the absence of additional stabilizers. The resulting NP/IL systems catalyze the hydrodeoxygenation of a phenol under mild conditions (60 °C, 1.0 MPa H2), achieving full substrate conversion and a high deoxygenation rate (over 95%) to cyclohexane and cyclohexene. The combination of [Emim]NTf2 and [Bmim]PF6 results in the best catalytic performance. Also the transform- ation of other substituted phenols and dimers such as catechol, guaiacol and diphenyl ether was studied in the Pt NP/[Emim]NTf2–[Bmim]PF6 system and in most cases afforded cyclohexane in good yield.

Royal Society of Chemistry2017

Rhodium(I)-Catalyzed Enantioselective Activation of Cyclobutanols: Formation of Cyclohexane Derivatives with Quaternary Stereogenic Centers

Nicolai Cramer

The activation of carbon-carbon œÉ bonds is a complementary method to access uncommon and difficult-to-prep. organometallic species. Herein, we describe the activation of tert-cyclobutanols through an enantioselective insertion of a chiral rhodium(I) complex into the C-C œÉ bond of the cyclobutane, forming a quaternary stereogenic center and an alkyl-rhodium functionality that initiates ring-closure reactions. This technol. provides access to a variety of substituted cyclohexane derivs. with quaternary stereogenic centers. The formation of different product families can be controlled by the employed set of reaction conditions and additives. In general, high yields and excellent enantioselectivities of up to 99 % ee are obtained.

Wiley-VCH Verlag GmbH & Co. KGaA2010

Chiral Cyclopentadienyls: Enabling Ligands for Asymmetric Rh(III)-Catalyzed C-H Functionalizations

Nicolai Cramer, Baihua Ye

American Chemical Society2015