Preparation of chiral ruthenium(IV) complexes and applications in regio- and enantioselective allylation of phenols.

International audienceFacile preparations of chiral [Ru(Cp*)]- and [Ru(Cp')]-based allyl complexes featuring N,O chelate derived from (+)-nopinone are described. Single crystal X-ray structural analysis of one complex revealed the preferential configuration of the ruthenium centre and the orientation of the unsymmetrical allylic substituent. Applications of these complexes in catalysis for nucleophilic allylic substitution allowed regio- and enantioselective formation of branched allyl ethers from phenols

Synthesis and photophysical studies of a pyrenylindole and a phenalenoindole obtained from dehydroamino acid derivatives : application as fluorescent probes for biological systems

Two pyrenyl-dehydroamino acid derivatives were cyclized by a metal-assisted C–N intramolecular cyclization developed in our research group, to give a pyrenylindole and a phenalenoindole. The pyrenylindole was inserted into a peptide by solid-phase coupling, with use of a 2-chlorotrityl chloride resin and a Fmoc strategy. The photophysical properties of the pyrenylindole and phenalenoindole in several solvents were studied and showed that these compounds can be used as fluorescence probes. The results obtained with the peptide labelled with the pyrenylindole moiety show potential for use of this compound as a fluorescence label avoiding the aggregation propensity of pyrene compounds. Photophysical studies of the pyrenylindole and of the phenalenoindole in lipid membranes were also carried out. Steady-state fluorescence anisotropy measurements revealed that both compounds adopt locations inside the lipid bilayers and are able to report the transition between the gel and liquid-crystalline phases. The results point to potential use of these compounds as fluorescent probes for biological systems.Fundação para a Ciência e a Tecnologia (FCT) - (SFRH/BPD/24548/2005), (SFRH/BD/38766/2007)Fundo Europeu de Desenvolvimento Regional (FEDER) - Project PTDC/QUI/81238/200

Efficient Thiophene Synthesis Mediated by 1,3‐Bis(carboxymethyl)imidazolium Chloride: C‐C and C‐S Bond Formation

Thiophene derivatives have been prepared by means of a functionalized imidazolium salt [1,3‐bis(carboxymethyl)imidazolium chloride] acting as a catalyst. The heterogeneous catalyst has allowed to carry out the reactions with no solvent or inert atmosphere. Different aryl methyl ketones have reacted with elemental sulfur to selective produce 2,4‐substituted thiophenes. Furthermore, the reaction of sulfur with cyclic ketones has enabled the preparation of polycyclic compounds. This protocol is simple and effective for preparing thiophene derivatives, even in a preparative scale. The thiophene synthesis described presents remarkable sustainability with an E‐factor of 7.4, the solvent‐free conditions being crucial for this feature. The catalyst is straightforwardly prepared, and it is easily separated from the reaction mixture, making its reuse possible.This work was financially supported by the University of Alicante (VIGROB-173, VIGROB-285, VIGROB-316FI and UAUSTI19-21), the Spanish Ministerio de Economía y Competitividad (CTQ2015-66624-P, CTQ2017-88171-P), the Spanish Ministerio de Ciencia, Innovación y Universidades (PGC2018-096616-B-I00) and the Generalitat Valenciana (AICO/2017/007). P. G. thanks the ISO (University of Alicante) for a grant

The reductive activation of CO2 across a Ti═Ti double bond: synthetic, structural, and mechanistic studies

[Image: see text] The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti(2)Pn(†)(2) (1) (Pn(†) = 1,4-{Si(i)Pr(3)}(2)C(8)H(4)) with CO(2) is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO(2) reaction is performed at −78 °C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO(2) molecule bound symmetrically to the two Ti centers in a μ:η(2),η(2) binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO(2) is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3. In situ NMR studies indicated that this decomposition proceeds in a stepwise process via monooxo (5) and monocarbonyl (7) double-sandwich complexes, which have been independently synthesized and structurally characterized. 5 is thermally unstable with respect to a μ-O dimer in which the Ti–Ti bond has been cleaved and one pentalene ligand binds in an η(8) fashion to each of the formally Ti(III) centers. The molecular structure of 7 shows a “side-on” bound carbonyl ligand. Bonding of the double-sandwich species Ti(2)Pn(2) (Pn = C(8)H(6)) to other fragments has been investigated by density functional theory calculations and fragment analysis, providing insight into the CO(2) reaction pathway consistent with the experimentally observed intermediates. A key step in the proposed mechanism is disproportionation of a mono(oxo) di-Ti(III) species to yield di-Ti(II) and di-Ti(IV) products. 1 forms a structurally characterized, thermally stable CS(2) adduct 8 that shows symmetrical binding to the Ti(2) unit and supports the formulation of 4. The reaction of 1 with COS forms a thermally unstable complex 9 that undergoes scission to give mono(μ-S) mono(CO) species 10. Ph(3)PS is an effective sulfur transfer agent for 1, enabling the synthesis of mono(μ-S) complex 11 with a double-sandwich structure and bis(μ-S) dimer 12 in which the Ti–Ti bond has been cleaved