Luis A. Oro

Transition metal liquid crystals: Advanced materials within the reach of the coordination chemist

This review serve to open the field to many coordination chemistry who can use specific expertise of new transition metal liquid crystals. Bibliography

Ligand-controlled regioselectivity in the hydrothiolation of alkynes by rhodium N-heterocyclic carbene catalysts.

Rh-N-heterocyclic carbene compounds [Rh(μ-Cl)(IPr)(η(2)-olefin)](2) and RhCl(IPr)(py)(η(2)-olefin) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl(IPr)(py)(η(2)-olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electronic and steric effects exerted by IPr, pyridine, and hydride ligands accounts for the observed regioselectivity. Both IPr and pyridine ligands stabilize formation of square-pyramidal thiolate-hydride active species in which the encumbered and powerful electron-donor IPr ligand directs coordination of pyridine trans to it, consequently blocking access of the incoming alkyne in this position. Simultaneously, the higher trans director hydride ligand paves the way to a cis thiolate-alkyne disposition, favoring formation of 2,2-disubstituted metal-alkenyl species and subsequently the Markovnikov vinyl sulfides via alkenyl-hydride reductive elimination. DFT calculations support a plausible reaction pathway where migratory insertion of the alkyne into the rhodium-thiolate bond is the rate-determining step.

Indenyl complexes of ruthenium(II). Crystal structure of [Ru(CO)(PPh3)2(η5-C9H7)]ClO4·12CH2Cl2

Abstract The compound [RuCl(PPh3)2(η5-C9H7)] (I) has been made in high yield by reaction of [RuCl2(PPh3)3] with indene and potassium hydroxide in ethanol and its reactions have been examined. Complex I reacts with appropriate nucleophiles to give the complexes [RuX(PPh3)2(η5-C9H7)] (X = H, CH3, I, SnCl3, C2Ph) and [RuCl(dppe)(η5-C9H7)]. Heating of complex I with methanol in a sealed tube leads to the elimination of the indenyl group and decarbonylation of methanol. Cationic complexes of formulae [RuL(PPh3)2(η5-C9H7)]ClO4 (L = CH3CN, 2-ClC6H4CN, CH2CHCN, 1,2-(CN)2C6H4, C2H4(CN)2, N2H4, CNBut, CO, CCHPh, and C2H4) and [Ru(L-L)PPh3(η5-C9H7)]ClO4 (L-L = 2,5-norbornadiene (nbd), tetrafluorobenzobarrelene (tfb), ethylenediamine (en), propylenediamine (pn), biimidazole (Hbim), 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen)) are obtained by treatment of complex I with the appropriate ligand and sodium perchlorate in methanol. Reaction of the vinylideneruthenium complex [Ru(η1-CCHPh) (PPh3)2(η5-C9H7)]ClO4 with oxygen gives [Ru(CO)(PPh3)2(η5-C9H7)]ClO4. The structure of [Ru(CO)(PPh3)2(η5-C9H7)]ClO4· 1 2 CH2Cl2 has been determined by X-ray diffraction. The space group is P 1 with lattice constants a 18.5513(14), b 12.9165(5), and c 9.6898(5) A, and α 80.942(5), β 104.998(7) and γ 111.130(4)°. Final R and Rw factors are 0.039 and 0.043, respectively, for the 6836 observed data (3σ(I) criterion). The metal is bonded to an indenyl group through the five-membered ring, and hexacoordination of the ruthenium atom is completed by two triphenylphosphine ligands and a carbonyl group.

Effective Fixation of CO2 by Iridium-Catalyzed Hydrosilylation†

Financial support from MINECO/FEDER (CTQ2010-15221, CSD2009-00050 CONSOLIDER-INGENIO 2010, CTQ2011-27593, “Ramon y Cajal” (P.J.S.M.) and “Juan de la Cierva” (M.I.) programs), and DGA/FSE (group E7), is acknowledged.

Pyrazolate bridged dinuclear rhodium complexes. X-ray structure of [Rh(Pz)(CO)P(OPh)3]2

Abstract The synthesis and properties of complexes of general formulae [Rh(Pz)(CO)L] 2 (Pz = pyrazolate ion, L = phosphorus donor ligand), [Rh(Pz)(diolefin)] 2 and [Rh(Pz)(C 2 H 4 ) 2 ] 2 are reported. The crystal structure of the novel complex [Rh(Pz)(CO)P(OPh) 3 ] 2 has been determined by X-ray methods. The crystals are triclinic, space group P 1 , with Z = 2 in a unit cell of dimensions a 14.061(10), b 17.140(13), c 9.937(7) A, α 102.19(7), β 10.9.55(8), γ 75.14(8)°. The structure has been solved by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.058 for 2514 independent observed reflections. The structure consists of discrete dimeric complexes in which each rhodium is in nearly square-planar arrangement, being bonded to a carbon atom of a carbonyl group, to a phosphorus of a triphenylphosphite ligand and to two nitrogen atoms of pyrazolate ligands bridging the metal atoms. The dihedral angle between the two square planes of 86.2° gives a bent configuration to the molecule in which the carbonyls and the phosphite ligands are in a trans arrangement.

The emergence of transition-metal-mediated hydrothiolation of unsaturated carbon-carbon bonds: A mechanistic outlook

The hydrothiolation of unsaturated carbon-carbon bonds is a practical and atom-economical approach for the incorporation of sulfur into organic frameworks. In recent years, we have witnessed the development of a range of transition-metal-based catalytic systems for the control of the regio- and stereoselectivity. In this Minireview we highlight the mechanistic background behind this transformation so as to help the design of more specific and active organometallic hydrothiolation catalysts.

Homogeneous catalytic reduction of CO2 with hydrosilanes

Catalytic CO2 hydrosilylation is a thermodynamically favored chemical process that could be potentially applied to large-scale transformations of this greenhouse gas. During the last decade, there have been an increasing number of experimental studies regarding metal-catalyzed CO2 hydrosilylation processes. The first examples of catalytic systems used for CO2 hydrosilylation employed late transition metals such as ruthenium and iridium. Presently, there are several examples of other catalysts, including transition metal species acting alone or together with B(C6F5)3, as well as metal-free frustrated Lewis pairs (FLPs) and organocatalysts which are able to perform this reaction.

Recent advances in homogeneous enantioselective Diels–Alder reactions catalyzed by chiral transition-metal complexes

Abstract The homogeneous enantioselective Diels–Alder reactions catalyzed by chiral transition-metal complexes are reviewed. Special attention has been paid to the mechanistic aspects of the process in order to account for the stereochemical outcome of the reactions.

Trimerisation of the Cationic Fragments [(η‐ring)M(Aa)]+ ((η‐ring) M=(η5‐C5Me5)Rh, (η5‐C5Me5)Ir, (η6‐p‐MeC6H4iPr)Ru; Aa=α‐amino acidate) with Chiral Self‐Recognition: Synthesis, Characterisation, Solution Studies and Catalytic Reactions of the Trimers [{(η‐ring)M(Aa)}3](BF4)3

The formation of [{(η-ring)M(Aa)}3](BF4)3trimers [(η-ring)M=(η5-C5Me5)Rh, (η5-C5Me5)Ir, (η6-p-MeC6H4iPr)Ru; Aa = α-amino acidate, one cation shown schematically] takes place by chiral self-recognition, the RMRMRM or SMSMSM trimers are equally configurated at the metal centres and are the only diastereomers detected. The equilibrium constant for the diastereomerisation process between both isomers depends on the solvent, amino acidate, and metal. The trimers catalyse the reduction of unsaturated aldehydes to unsaturated alcohols and the reduction of acetophenone to 2-phenylethanol with up to 75 % ee.

Enantioselective hydride transfer hydrogenation of ketones catalyzed by [(η6-p-cymene)Ru(amino acidato)Cl] and [(η6-p-cymene)Ru(amino acidato)]3(BF4)3 complexes

The new complexes (RRuSC, SRuSC)-[(η6-pCym)Ru(l-Aze)Cl] (6a, b), (RRuSC, SRuSC)-[(η6-pCym)Ru(l-Pip)Cl] (7a, b), (RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(η6-pCym)Ru(l-Aze)}3](BF4)3 (8a, b) and (RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(η6-pCym)Ru(l-Pip)}3](BF4)3 (9a, b) (l-Aze=l-2-azetidinecarboxylate, l-Pip=l-2-piperidinecarboxylate) were prepared, characterized and used, together with the known [{(η6-pCym)Ru(l-Pro)}3](BF4)3, 5 and [{(η6-pCym)Ru(l-Ala)}3](BF4)3, 10 (l-Pro=l-prolinate, l-Ala=l-alaninate), in hydride transfer reduction of acetophenone, a series of substituted acetophenones and several other ketones with moderate to high conversions and enantioselectivities up to 86% e.e.