Zhang, Yuetao; Schmitt, Meghan L.; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene You Xian(Journal of the American Chemical Society, American Chemical Society (ACS), 2013-11-27)[Article]
Pluta, Roman; Krach, Patricia E.; Cavallo, Luigi; Falivene, Laura; Rueping, Magnus(ACS Catalysis, American Chemical Society (ACS), 2018-02-09)[Article]
A chiral iodoarene organocatalyst for the catalytic asymmetric fluorination has been developed. The catalyst was used in the asymmetric fluorination of carbonyl compounds, providing the products with a quaternary stereocenter with high enantioselectivities. Chiral hypervalent iodine difluoride intermediates were generated in situ by treatment of the catalyst with an oxidant and hydrogen fluoride as fluoride source. As such, the α-fluorination of a carbonyl compound was achieved with a nucleophilic fluorine source. A combined computational and experimental approach provided insight into the reaction mechanism and the origin of enantioselectivity.
He, Jianghua; Zhang, Yuetao; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene You Xian(Macromolecules, American Chemical Society (ACS), 2014-11-25)[Article]
A combined experimental and theoretical study on mechanistic aspects of polymerization of conjugated polar alkenes by frustrated Lewis pairs (FLPs) based on N-heterocyclic carbene (NHC) and Al(C6F5)3 pairs is reported. This study consists of three key parts: structural characterization of active propagating intermediates, propagation kinetics, and chain-termination pathways. Zwitterionic intermediates that simulate the active propagating species in such polymerization have been generated or isolated from the FLP activation of monomers such as 2-vinylpyridine and 2-isopropenyl-2-oxazoline-one of which, IMes+-CH2C(Me)=(C3H2NO)Al(C6F5)3 - (2), has been structurally characterized. Kinetics performed on the polymerization of 2-vinylpyridine by ItBu/Al(C6F5)3 revealed that the polymerization follows a zero-order dependence on monomer concentration and a first-order dependence on initiator (ItBu) and activator [Al(C6F5)3] concentrations, indicating a bimolecular, activated monomer propagation mechanism. The Lewis pair polymerization of conjugate polar alkenes such as methacrylates is accompanied by competing chain-termination side reactions; between the two possible chain-termination pathways, the one that proceeds via intramolecular backbiting cyclization involving nucleophilic attack of the activated ester group of the growing polymer chain by the O-ester enolate active chain end to generate a six-membered lactone (δ-valerolactone)-terminated polymer chain is kinetically favored, but thermodynamically disfavored, over the pathway leading to the -ketoester-terminated chain, as revealed by computational studies.
Roiaz, Matteo; Falivene, Laura; Rameshan, Christoph; Cavallo, Luigi; Kozlov, Sergey M.; Rupprechter, Guenther(The Journal of Physical Chemistry C, American Chemical Society (ACS), 2018-10-24)[Article]
Carbon monoxide participates in many copper-catalyzed reactions, which makes CO-induced structural changes of Cu catalysts key for important industrial processes. We have studied the interaction of carbon monoxide with the Cu(100) single crystal termination at 120, 200, and 300 K by means of low energy electron diffraction (LEED), temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS), and density functional theory (DFT) calculations. The absorption band of CO (2082 to 2112 cm-1) at elevated gas pressure (up to 5 mbar) and at 200/300 K was found at higher wavenumber than the characteristic band of the c(2×2)CO structure, and was consistent with CO adsorbed on low-coordinated Cu atoms. The combined PM-IRAS/DFT analysis revealed that exposure to CO induces surface roughening through the formation of Cu adatoms and clusters on the (100) terraces. The roughened surface seemed surprisingly active for CO dissociation, which indicates its unique catalytic properties.
Falivene, Laura; Credendino, Raffaele; Poater, Albert; Petta, Andrea; Serra, Luigi; Oliva, Romina; Scarano, Vittorio; Cavallo, Luigi(Organometallics, American Chemical Society (ACS), 2016-06-27)[Article]
Developing more efficient catalysts remains one of the primary targets of organometallic chemists. To accelerate reaching this goal, effective molecular descriptors and visualization tools can represent a remarkable aid. Here, we present a Web application for analyzing the catalytic pocket of metal complexes using topographic steric maps as a general and unbiased descriptor that is suitable for every class of catalysts. To show the broad applicability of our approach, we first compared the steric map of a series of transition metal complexes presenting popular mono-, di-, and tetracoordinated ligands and three classic zirconocenes. This comparative analysis highlighted similarities and differences between totally unrelated ligands. Then, we focused on a recently developed Fe(II) catalyst that is active in the asymmetric transfer hydrogenation of ketones and imines. Finally, we expand the scope of these tools to rationalize the inversion of enantioselectivity in enzymatic catalysis, achieved by point mutation of three amino acids of mononuclear p-hydroxymandelate synthase.
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