Influence of Charge Order on the Ground States of TMTTF Molecular Salts

(TMTTF)2AsF6 and (TMTTF)2SbF6 are both known to undergo a charge ordering phase transition, though their ground states are different. The ground state of the first is Spin-Peierls, and the second is an antiferromagnet. We study the effect of pressure on the ground states and the charge-ordering using 13C NMR spectroscopy. The experiments demonstrate that the the CO and SP order parameters are repulsive, and consequently the AF state is stabilized when the CO order parameter is large, as it is for (TMTTF)2SbF6. An extension of the well-known temperature/pressure phase diagram is proposed.Comment: 5pages, 5 figures, Proceeding of ISCOM2003, to appear in Journal de Physique I

Electron-lattice coupling and the broken symmetries of the molecular salt (TMTTF)2_2SbF6_6

(TMTTF)$_2$SbF$_6$ is known to undergo a charge ordering (CO) phase transition at $T_{CO}\approx156K$ and another transition to an antiferromagnetic (AF) state at $T_N\approx 8K$. Applied pressure $P$ causes a decrease in both $T_{CO}$ and $T_N$. When $P>0.5 GPa$, the CO is largely supressed, and there is no remaining signature of AF order. Instead, the ground state is a singlet. In addition to establishing an expanded, general phase diagram for the physics of TMTTF salts, we establish the role of electron-lattice coupling in determining how the system evolves with pressure.Comment: 4 pages, 5 figure

Competition and coexistence of bond and charge orders in (TMTTF)2AsF6

(TMTTF)2AsF6 undergoes two phase transitions upon cooling from 300 K. At Tco=103 K a charge-ordering (CO) occurs, and at Tsp(B=9 T)=11 K the material undergoes a spin-Peierls (SP) transition. Within the intermediate, CO phase, the charge disproportionation ratio is found to be at least 3:1 from carbon-13 NMR 1/T1 measurements on spin-labeled samples. Above Tsp, up to about 3Tsp, 1/T1 is independent of temperature, indicative of low-dimensional magnetic correlations. With the application of about 0.15 GPa pressure, Tsp increases substantially, while Tco is rapidly suppressed, demonstrating that the two orders are competing. The experiments are compared to results obtained from calculations on the 1D extended Peierls-Hubbard model.Comment: 4 pages, 5 figure

Gold(I)-Catalyzed Cycloisomerizations and Alkoxycyclizations of ortho-(Alkynyl)styrenes

Indenes and related polycyclic structures have been efficiently synthesized by gold(I)-catalyzed cycloisomerizations of appropriate ortho-(alkynyl)styrenes. Disubstitution at the terminal position of the olefin was demonstrated to be essential to obtain products originating from a formal 5-endo-dig cyclization. Interestingly, a complete switch in the selectivity of the cyclization of o-(alkynyl)-α-methylstyrenes from 6-endo to 5-endo was observed by adding an alcohol to the reaction media. This allowed the synthesis of interesting indenes bearing an all-carbon quaternary center at C1. Moreover, dihydrobenzo[a]fluorenes can be obtained from substrates bearing a secondary alkyl group at the β-position of the styrene moiety by a tandem cycloisomerization/1,2-hydride migration process. In addition, diverse polycyclic compounds were obtained by an intramolecular gold-catalyzed alkoxycyclization of o-(alkynyl)styrenes bearing a nucleophile in their structure. Finally, the use of a chiral gold complex allowed access to elusive chiral 1H-indenes in good enantioselectivitiesMinisterio de Economia y Competitividad (MINECO) and FEDER (CTQ2010-15358 and CTQ2013-48937-C2-1-P) and Junta de Castilla y Leon (BU237U13) for financial support. A.M.S. thanks the Junta de Castilla y Leon (Consejeria de Educacion) and the Fondo Social Europeo for a PIRTU contract. M.A.R. and P.G.-G. thank MEC for a "Young Foreign Researchers" (SB2009-0186) contract and MINECO for "Juan de la Cierva" contract, respectivelyThis is the peer reviewed version of the following article: Sanjuán, A. M., Rashid, M. A., García-García, P., Martínez-Cuezva, A., Fernández-Rodríguez, M. A., Rodríguez, F. and Sanz, R. (2015), Gold(I)-Catalyzed Cycloisomerizations and Alkoxycyclizations of ortho-(Alkynyl)styrenes. Chem. Eur. J., 21: 3042–3052. doi: 10.1002/chem.201405789, which has been published in final form at 10.1002/chem.201405789. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archivin

Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates

NOTICE: This is the peer reviewed version of the following book chapter: Varela J. A., González-Rodríguez C., Saá C. (2014). Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates. In: Dixneuf P., Bruneau C. (eds) Ruthenium in Catalysis. Topics in Organometallic Chemistry, vol 48, pp. 237-287. Springer, Cham. [doi: 10.1007/3418_2014_81]. This article may be used for non-commercial purposes in accordance with Springer Verlag Terms and Conditions for self-archiving.Vinylidenes are high-energy tautomers of terminal alkynes and they can be stabilized by coordination with transition metals. The resulting metal-vinylidene species have interesting chemical properties that make their reactivity different to that of the free and metal π-coordinated alkynes: the carbon α to the metal is electrophilic whereas the β carbon is nucleophilic. Ruthenium is one of the most commonly used transition metals to stabilize vinylidenes and the resulting species can undergo a range of useful transformations. The most remarkable transformations are the regioselective anti-Markovnikov addition of different nucleophiles to catalytic ruthenium vinylidenes and the participation of the π system of catalytic ruthenium vinylidenes in pericyclic reactions. Ruthenium vinylidenes have also been employed as precatalysts in ring closing metathesis (RCM) or ring opening metathesis polymerization (ROMP). Allenylidenes could be considered as divalent radicals derived from allenes. In a similar way to vinylidenes, allenylidenes can be stabilized by coordination with transition metals and again ruthenium is one of the most widely used metals. Metalallenylidene complexes can be easily obtained from terminal propargylic alcohols by dehydration of the initially formed metal-hydroxyvinylidenes, in which the reactivity of these metal complexes is based on the electrophilic nature of Cα and Cγ, while Cβ is nucleophilic. Catalytic processes based on nucleophilic additions and pericyclic reactions involving the π system of ruthenium allenylidenes afford interesting new structures with high selectivity and atom economy

Reactions of (polypyrazolylborato)(benzonitrile)rutheniums with terminal alkynes: Reactivity changeover by triethylamine toward arylalkyne polymerization or formation of (arylmethyl)(carbonyl) complexes

Reactions of (κ 3-polypyrazolylborato)(benzonitrile) rutheniums [RuCl{B(4-Ypz) 4}(PhCN) 2] {4-Ypz; 4-bromo-1-pyrazolyl (Y = Br) and 1-pyrazolyl (Y = H) groups} with terminal alkynes were studied. For the reactions with arylalkynes HC≡C(aryl) in the presence of NEt 3, (arylmethyl)(carbonyl)rutheniums [Ru{CH 2(aryl)}{B(4-Ypz) 4}(CO)(PhCN)] were yielded, indicating alkyne C≡C bond cleavage, whereas in the absence of NEt 3, arylalkyne polymerization proceeded instead of the (arylmethyl)ruthenium formation. Reasonably attributed reaction mechanism shows significant role of the vinylidene intermediates "Ru=C=CH(aryl)"