Coordinatively Unsaturated [RhCp*Rf2] (Cp* = C5Me5; Rf = C6F3Cl2-3,5), General Precursor to Cp*-Diaryl and Cp*-Halo-Aryl RhIII Complexes. Observing and Testing the Effect of Cp* as Electronic Buffer

Producción CientíficaThe pentacoordinated [RhCp*Rf2] (Rf = C6F3Cl2-3,5) and the octahedral (μ-Cl)2[RhCp*Rf]2, obtained by stoichiometric rearrangement with (μ-Cl)2[RhCp*Cl]2, are general precursors of [RhCp*RfXL] (X = Rf, Cl; L = ligand) complexes, which were studied by NMR (L dissociation and fluxional processes) and X-ray diffraction (structural effects affecting the Rh–Cp* distances) techniques. The Rh–Cp*centroid distances decrease markedly for identical L in the order [RhCp*Rf2L] > [RhCp*RfClL] > [RhCp*Cl2L] and are further influenced regularly within each family by the trans influence of L (longer distances for higher trans influence of L). The structural effects observed reveal a remarkable capability of Cp* to act as an electron-density buffer, which attenuates the Rh electron density variations induced by the substituents in front of Cp* by releasing toward Rh or polarizing toward Cp*, on demand, the electron density of the Rh–Cp* bonds. This buffer effect explains the easy L dissociation from [RhCp*Rf2L] and the accessibility to formally 16e pentacoordinated [RhCp*Rf2].2019-09-092019-09-09Ministerio de Economía, Industria y Competitividad (Projects CTQ2016-80913-P, CTQ2014-52796-P, and CTQ2017-89217-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA051P17

The stille reaction, 38 years later

Producción CientíficaThe first now named Stille reaction was published 38 years ago, and the last comprehensive revision of this catalysis was in 2004. Since then the knowledge of the different steps of the three possible (and sometimes competing) reaction pathways (cyclic, open, and ionic) has been almost completed by synergistic experimental and theoretical studies: the Stille reaction is perhaps the best characterized catalytic process if we consider the number of intermediates that have been detected. This review concentrates on the mechanistic new knowledge, and on important aspects as the revolution with the use of bulky phosphines, the bimetallic alternative of the Stille reaction, the enantioselectivity in Stille and palladium free Stille processes, the meaning of copper effect, or the possible approaches to make Stille coupling a greener process.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. GR 169 and VA256U13)Ministerio de Economía, Industria y Competitividad (CTQ2013-48406-P

Some Singular Features of Gold Catalysis: Protection of AuI Catalysts by Substoichiometric Agents, and Associated Phenomena

Producción CientíficaThis study deals with two striking phenomena: the complete protection against decomposition of hypothetically monocoordinated AuI intermediates [AuL]Y (L = strongly coordinating ligand; Y– = poorly coordinating anion) by addition of small substoichiometric amounts (5 mol% relative to Au) of not strongly coordinating ligands (e.g. AsPh3), and the fact that, in contrast, strongly coordinating ligands cannot provide this substoichiometric protection. The two phenomena are explained considering that: i) the existence of real monocoordinated [AuL]Y is negligible in condensed phases, and the kinetically efficient existing species are dicoordinated [AuL(W)]Y (W = any very weekly coordinating ligand existing in solution, including OH2, the solvent, or the Y– anion); and ii) these [AuL(W)]Y intermediates give rise to decomposition by a disproportionation mechanism, via polynuclear intermediates formed by associative oligomerization with release of some W ligands. It is also shown that very small concentrations of [AuL(W)]Y are still catalytically efficient, and can be stabilized by overstoichiometric adventitious water, so that full decomposition of the catalyst is hardly reached although eventually the stabilized concentration can result kinetically inefficient for the catalysis. These results suggest that, in cases of gold catalysis requiring the use of a significant quantity of gold catalyst, the turnover numbers can be increased, or the concentration of gold catalyst widely reduced, using substoichiometric protection properly tuned to the case.2017-12-30Ministerio de Economía, Industria y Competitividad (CTQ2014-52796-P)Ministerio de Economía, Industria y Competitividad (CTQ2013-48406-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – GR 169 and project VA256U13

New Insights in the Synthesis of High-Molecular-Weight Aromatic Polyamides-Improved Synthesis of Rod-like PPTA

Producción CientíficaBy employing a variation of the polyamidation method using in situ silylated diamines and acid chlorides, it was possible to obtain a rod-type polyamide: poly(p-phenylene terephthalamide) (PPTA, a polymer used in the high-value-added material Kevlar), with a molecular weight much higher than that obtained with the classical and industrial polyamidation method. The optimization of the method has consisted of using, together with the silylating agent, a mixture of pyridine and a high-pKa tertiary amine. The research was complemented by a combination of nuclear magnetic resonance and molecular simulation studies, which determined that the improvements in molecular weight derive mainly from the formation of silylamide groups in the growing polymer

Microporous Polymer Networks for Carbon Capture Applications

Producción CientíficaA new generation of porous polymer networks has been obtained in quantitative yield by reacting two rigid trifunctional aromatic monomers (1,3,5-triphenylbenzene and triptycene) with two ketones having electron-withdrawing groups (trifluoroacetophenone and isatin) in superacidic media. The resulting amorphous networks are microporous materials, with moderate Brunauer–Emmett–Teller surface areas (from 580 to 790 m2 g–1), and have high thermal stability. In particular, isatin yields networks with a very high narrow microporosity contribution, 82% for triptycene and 64% for 1,3,5-triphenylbenzene. The existence of favorable interactions between lactams and CO2 molecules has been stated. The materials show excellent CO2 uptakes (up to 207 mg g–1 at 0 °C/1 bar) and can be regenerated by vacuum, without heating. Under postcombustion conditions, their CO2/N2 selectivities are comparable to those of other organic porous networks. Because of the easily scalable synthetic method and their favorable characteristics, these materials are very promising as industrial adsorbents.Ministerio de Economía, Industria y Competitividad (grants MAT2013-45071-R / MAT2016-76413-C2-R1 / MAT2016-76413-C2-R2 / MAT2015-69844-R / CTQ2016-80913-P / CTQ2014-52796-P)Junta de Castilla y León (projects VA248U13 / VA051P17

Protection of the gold (I) Catalyst by AsPh3 in Reactions of Enynes

Producción CientíficaHBHC (Hydrogen Bond supported Heterocyclic Carbene) and NAC (Nitrogen Acyclic Carbene) neutral gold complexes have been synthesized by reaction of isocyanogold derivatives ([AuCl(CNR)] with amines. Cationic complexes [Au(carbene)(AsPh3)](SbF6) have been also prepared. The catalytic activity of both types of complex (for the former AgSbF6 is used to extract the halide) in skeletal rearrangement and methoxycyclization of enynes has been studied. The cationic complexes with AsPh3 are active but slower; as an advantage they do not decompose during the catalysis. In contrast, the catalysts formed in situ from the halide neutral complexes are very fast but undergo decomposition. An interesting trade-off was found by adding sub-stoichiometric amounts of AsPh3 (e.g. 10 mol%) relative to the gold catalyst ([Au(carbene)Cl] + AgSbF6), which prevents or dramatically reduces the decomposition observed. This protecting ligand promises to prevent or minimize undesired decomposition of gold catalysts.Ministerio de Economía, Industria y Competitividad (CTQ2013-48406-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA256U13

Expanding the Concepts Trans Influence and Back-Donation: Hybrid and Side Donations in [Cp*MIII(L)XY] (M = Rh, Ir) Complexes with CO, CN–, and CNR Ligands. A Window to Cis Influence

Producción CientíficaAnalysis of the bonding contributions in molecules [MIIICp*(L)XY] (M = Rh, Ir; Cp* = C5Me5; L = CO, CN–, CNR) has uncovered a rich variety of types of interaction that seem to have escaped detection so far, in spite of the continuous popularity of cyclopentadienyl transition-metal complexes since the 1970s. At variance with the M—C≡O bond in square-planar systems, which shows typical metal-to-CO π-back-donation, the nonorthogonal arrangement of the Cp* plane and Rh—C≡O fragment and the pseudooctahedral geometry lead to the observation of many direct lateral donations from other ligands that do not involve the metal orbitals, and we name side donations, for instance, Cp* → π*(CO), Cl → π*(CO), and F → π*(CO). Hybrid donations partially involving the metal, M–Caryl → π*(CO), are also observed. The summation of multiple contributions other than back-donation can easily account for about 20% of the electron donation to the π*(C≡O) orbitals.Junta de Castilla y León (project VA224P20)Ministerio de Economía, Industria y Competitividad (project CTQ2017-89217- P)Ministerio de Ciencia, Innovación y Universidades (project PID2020-118547GB-I00)Irish Research Council (postdoctoral fellowship GOIPD/2020/701

Striking ligand-disproportionative Cl/aryl scrambling in a simple Au(iii) system. Solvent role, driving forces and mechanisms

Producción CientíficaAryl rearrangements triggered by Cl− extraction from trans-[AuIII(Rf)2Cl2]− (Rf = C6F3Cl2-3,5), led quickly to a mixture of [Au(Rf)3(solv)], cis-[Au(Rf)2Cl(solv)] and [Au(Rf)Cl2(solv)] (solv = OEt2, OH2). 19F NMR and X-ray diffraction studies led us to identify the species present in solution and the role of the solvent in their formation, while DFT calculations confirm the thermodynamic basis of their evolution. Very different Rf–Rf coupling rates are found from (μ-Cl)2[cis-Au(Rf)2]2 or cis-[Au(Rf)2ClL] species (L = OEt2, NCMe, Cl−) depending on the coordination strength of the ligand or solvent in the fourth position.Ministerio de Economía, Industria y Competitividad (Projects CTQ2017-89217-Pand CTQ2016-80913-P

RhIAr/AuIAr′ Transmetalation: A Case of Group Exchange Pivoting on the Formation of M−M′ Bonds through Oxidative Insertion

Producción CientíficaBy combining kinetic experiments, theoretical calculations and microkinetic modelling, we show that the Pf/Rf (C6F5/C6Cl2F3) exchange between [AuPf(AsPh3)] and trans-[RhRf(CO)(AsPh3)2] does not occur through the typical concerted Pf/Rf transmetalation via electron deficient double bridges. Instead, it involves asymmetric oxidative insertion of the RhI complex into the (Ph3As)Au–Pf bond producing a [(Ph3As)Au–RhPfRf(CO)(AsPh3)2] intermediate, followed by isomerization and reductive elimination of [AuRf(AsPh3)]. Interesting differences are found between the LAu–Ar asymmetric oxidative insertion and the classical oxidative addition process of H2 to Vaska's complexes.Ministerio de Economía, Industria y Competitividad (grants CTQ2016‐80913‐P / CTQ2017‐89217‐P)Junta de Castilla y León (projects VA051P17 / VA062G18 / UIC176