Search NASA⌕ Search

Engineering topics

Jazzar, Rodolphe

Publications and source records attributed to Jazzar, Rodolphe.

28 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The Influence of C(sp 3 )H–Selenium Interactions on the 77 Se NMR Quantification of the π-Accepting Properties of Carbenes

Selenium NMR has become a standard tool for scaling the p-accepting character of carbenes. Herein, we highlight that non-classical hydrogen bonding (NCHB), likely resulting from hyperconjugation, can play a significant role in the carbene–selenium 77 Se NMR chemical shift, thus triggering a non-linear behavior of the Se-Scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Cyclic (Alkyl)- and (Aryl)-(amino)carbene Coinage Metal Complexes and Their Applications

Cyclic (alkyl)- and (aryl)-(amino)carbenes (CAACs and CAArCs) are stronger σ-donors and π-acceptors than imidazol-2-ylidenes and imidazolidin-2-ylidenes, the well-known N-heterocyclic carbenes (NHCs). Consequently, they form strong bonds with coinage metals and stabilize both low and high oxidation states. This Review shows that CAACs and CAArCs have allowed for the isolation of copper and gold complexes that were believed to be only transient intermediates. Here, this has not only allowed for a better understanding of the mechanism of known processes but has also led to the development of novel coinage metal-catalyzed reactions. In addition to their role in homogeneous catalysis, CAAC and CAArC coinage metal complexes have recently found applications in medicinal chemistry, as well as in materials science. When possible, the performance of CAAC and CAArC ligands are compared with those of classical NHCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Influence of Carbene and Phosphine Ligands on the Catalytic Activity of Gold Complexes in the Hydroamination and Hydrohydrazination of Alkynes

Through kinetic measurements, catalytic and stoichiometric experiments, and DFT calculations, we compare the catalytic activity of gold complexes supported by a variety of ligands (R 3 P, NHC, CAAC-5, CAAC-6, and BiCAAC) in the hydroamination and hydrohydrazination of alkynes. This study provides a rationale for the superior efficiency of a gold complex bearing a bicyclic (alkyl)(amino) carbene (BiCAAC). We demonstrate that this ligand motif, which is readily available, provides a durable gold catalyst that is able to compete with sophisticated state-of-the-art phosphine and NHC ligands, which feature secondary interaction capabilities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Understanding the Activity and Enantioselectivity of Acetyl-Protected Aminoethyl Quinoline Ligands in Palladium-Catalyzed β-C(sp 3 )–H Bond Arylation Reactions

Chiral acetyl-protected aminoalkyl quinoline (APAQ) ligands were recently discovered to afford highly active and enantiose-lective palladium catalysts for the arylation of methylene C(sp 3 )-H bonds, and herein, we investigate the origins of these heightened properties. Unprecedented amide-bridged APAQ-Pd dimers were predicted by DFT calculations and were con-firmed by single crystal X-ray diffraction studies. Comparison of structural features between APAQ-Pd complexes and an acetyl-protected aminoethyl pyridine APAPy-Pd complex strongly suggests that the high activity of the former originates from the presence of the quinoline ring which slows the formation of the off-cycle palladium dimer. Furthermore, steric topographic maps for a representative subset of monomeric, monoligated palladium complexes allowed us to draw a unique parallel between the 3-dimensional structures of these catalysts and their reported asymmetric induction in β-C(sp 3 )-H bond arylation reactions. Lastly, cooperative non-covalent interactions present between the APAQ ligand and the substrate were identified as a crucial factor for imparting selectivity between chemically equivalent methylenic C(sp 3 )-H bonds prior to con-certed metalation deprotonation activation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Readily Available Primary Aminoboranes as Powerful Reagents for Aldimine Synthesis

Abstract Primary aminoboranes (RNHBR 2 ), which are readily available by spontaneous dehydrocoupling of amines and boranes cleanly react at room temperature with aldehydes to give aldimines. The overall transformation from amines to aldimines can be conveniently performed by a sequential one‐pot reaction. This synthetic strategy is especially useful for electron poor and bulky amines which are reluctant to react with aldehydes under dehydration conditions. Using a Glorius robustness screen, we show that this methodology is chemoselective, and functional group tolerant. Computational and experimental data support the irreversible formation of the aldimine product in marked contrast with traditional methods.

Junor, Glen P.↗
DOE OSTI2019

Readily Available Primary Aminoboranes as Powerful Reagents for Aldimine Synthesis

Primary aminoboranes (RNHBR 2 ), which are readily available by spontaneous dehydrocoupling of amines and boranes cleanly react at room temperature with aldehydes to give aldimines. The overall transformation from amines to aldimines can be conveniently performed by a sequential one-pot reaction. This synthetic strategy is especially useful for electron poor and bulky amines which are reluctant to react with aldehydes under dehydration conditions. Using a Glorius robustness screen, we show that this methodology is chemoselective, and functional group tolerant. Finally, computational and experimental data support the irreversible formation of the aldimine product in marked contrast with traditional methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Tandem copper hydride–Lewis pair catalysed reduction of carbon dioxide into formate with dihydrogen

The reduction of CO 2 into formic acid or its conjugate base, using dihydrogen, is an attractive process. While catalysts based on noble metals have shown high turnover numbers, the use of abundant first-row metals is underdeveloped. The key steps of the reaction are CO 2 insertion into a metal hydride and regeneration of the metal hydride with H 2 , along with the concomitant production of formate. For the first step, copper is known as one of the most efficient metals, as shown by the numerous copper-catalysed carboxylation reactions, but this metal has difficulties activating H 2 to achieve the second step. In this work, we report a catalytic system involving a stable copper hydride that activates CO 2 , working in tandem with a Lewis pair that heterolytically splits H 2 . In this system, unprecedented turnover numbers for copper are obtained. Surprisingly, through a combination of stoichiometric and catalytic reactions, we show that classical Lewis pairs outperform frustrated Lewis pairs in this process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗