Miriam B. Gomes de Lima

Bio: Miriam B. Gomes de Lima is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Crystal structure & Denticity. The author has an hindex of 3, co-authored 3 publications receiving 66 citations.

Theoretical Study of the Acetylene Trimerization with CpCo

Abstract: A theoretical investigation of the mechanism of the CpCoL2 (L = CO, PR3, olefin) catalyzed acetylene cyclotrimerization reaction has been carried out at the ab initio and density functional theory (DFT) levels. The mechanism begins with a stepwise pair of ligand substitution reactions in which precatalyst CpCo(PH3)2 (1) is converted, via CpCo(PH3)(η2-C2H2) (2), to CpCo(η2-C2H2)2 (3) with the liberation of 11.3 kcal/mol at the B3LYP level. Oxidative coupling of the alkyne ligands in 3 to give a cobaltacyclopentadiene complex (4) is exothermic by 13.1 kcal/mol and is predicted to occur in a facile manner (ΔH⧧ = 12.8 kcal/mol). Reductive cyclization of the bidentate C4H4 ligand in 4 to generate CpCo(η4-cyclobutadiene) (8) is considerably exothermic (ΔH = −34.0 kcal/mol). However, the least motion pathway that transforms 4 directly into 8 which conserves a mirror plane is found to be symmetry forbidden, implying the presence of a large barrier. Coordination of a third acetylene to 4 results in the formation o...

Dimerization of Alkynes Promoted by a Pincer-Ligated Iridium Complex. C−C Reductive Elimination Inhibited by Steric Crowding

Abstract: The pincer-ligated species (PCP)Ir (PCP = κ3-C6H3-2,6-(CH2PtBu2)2) is found to promote dimerization of phenylacetylene to give the enyne complex (PCP)Ir(trans-1,4-phenyl-but-3-ene-1-yne). The mechanism of this reaction is found to proceed through three steps: (i) addition of the alkynyl C−H bond to iridium, (ii) insertion of a second phenylacetylene molecule into the resulting Ir−H bond, and (iii) vinyl−acetylide reductive elimination. Each of these steps has been investigated, by both experimental and computational (DFT) methods, to yield unexpected conclusions of general interest. (i) The product of alkynyl C−H addition, (PCP)Ir(CCPh)(H) (3), has been isolated and, in accord with experimental observations, is calculated to be 29 kcal/mol more stable than the analogous product of benzene C−H addition. (ii) Insertion of a second PhCCH molecule into the Ir−H bond of 3 proceeds rapidly, but with a 1,2-orientation. This orientation gives (PCP)Ir(CCPh)(CPhCH2) (4) which would yield the 1,3-diphenyl-enyne if ...

Mild Covalent Functionalization of Transition Metal Dichalcogenides with Maleimides: A “Click” Reaction for 2H-MoS2 and WS2

Abstract: The physical properties of ultrathin transition metal dichalcogenides (2D-TMDCs) make them promising candidates as active nanomaterials for catalysis, optoelectronics, and biomedical applications. Chemical modification of TMDCs is expected to be key in modifying/adding new functions that will help make such promise a reality. We present a mild method for the modification of the basal planes of 2H-MoS2 and WS2. We exploit the soft nucleophilicity of sulfur to react it with maleimide derivatives, achieving covalent functionalization of 2H-TMDCs under very mild conditions. Extensive characterization proves that the reaction occurs through Michael addition. The orthogonality and versatility of the thiol–ene “click” chemistry is expected to allow the a la carte chemical manipulation of TMDCs.

Hochreaktive Zwischenverbindungen aus Cokondensationsreaktionen von Eisen‐, Cobalt‐ und Nickeldämpfen mit Arenen

Abstract: 1969 berichtete Timms erstmals uber praparative Cokondensationsreaktionen von Metalldampfen mit organischen und anorganischen Substraten. Diese Arbeitstechnik breitete sich anschliesend in kurzer Zeit aus, doch ist es in den letzten Jahren etwas ruhiger um die Methode geworden. Setzt man Metallatomreaktionen nicht primar zur Herstellung neuer Produkte ein, sondern zur Gewinnung hochreaktiver Zwischenverbindungen, so ergibt sich ein Ansatzpunkt fur eine neue Synthesestrategie. Unser Ziel sind Reaktionsfolgen, die aufbauend auf einer moglichst effektiven Cokondensationsreaktion schrittweise und selektiv zu neuen Substanzklassen fuhren. Diese Vorgehensweise wird am Beispiel der Cokondensationsprodukte von Arenen mit Eisen-, Cobalt- und Nickeldampfen vorgestellt. Die dabei erhaltenen Zwischenverbindungen, die im Temperaturbereich von – 70 bis – 50°C zerfallen, lassen sich zu vielen Produktklassen umsetzen. Sie reichen von Clustern uber π-Komplexe sowie Kafigverbindungen mit Phosphor und Bor als Gerustatomen zu rein organischen Cycloadditionsprodukten.