Highly selective coupling of alkenes and aldehydes catalyzed by [Ni(NHC){P(OPh)3}]: synergy between a strong sigma donor and a strong pi acceptor.
Ontology highlight
ABSTRACT:
SUBMITTER: Ho CY
PROVIDER: S-EPMC3148196 | biostudies-literature | 2007
REPOSITORIES: biostudies-literature
Publications
Highly selective coupling of alkenes and aldehydes catalyzed by [Ni(NHC){P(OPh)3}]: synergy between a strong sigma donor and a strong pi acceptor.
Ho Chun-Yu CY Jamison Timothy F TF
Angewandte Chemie (International ed. in English) 20070101 5
Similar Datasets
Project description:Stacking interactions have been evaluated, employing computational methods, in dimers formed by analogous aliphatic and aromatic species of increasing size. Changes in stability as the systems become larger are mostly controlled by the balance of increasing repulsion and dispersion contributions, while electrostatics plays a secondary but relevant role. The interaction energy increases as the size of the system grows, but it does much faster in π-π dimers than in σ-π complexes and more remarkably than in σ-σ dimers. The main factor behind the larger stability of aromatic dimers compared to complexes containing aliphatic molecules is related to changes in the properties of the aromatic systems due to electron delocalization leading to larger dispersion contributions. Besides, an extra stabilization in π-π complexes is due to the softening of the repulsive wall in aromatic species that allows the molecules to come closer.
| S-EPMC6645327 | biostudies-literature
Project description: Not available
| S-EPMC8241832 | biostudies-literature
Project description:In this paper, a novel recurrent sigma‒sigma neural network (RSPSNN) that contains the same advantages as the higher-order and recurrent neural networks is proposed. The batch gradient algorithm is used to train the RSPSNN to search for the optimal weights based on the minimal mean squared error (MSE). To substantiate the unique equilibrium state of the RSPSNN, the characteristic of stability convergence is proven, which is one of the most significant indices for reflecting the effectiveness and overcoming the instability problem in the training of this network. Finally, to establish a more precise evaluation of its validity, five empirical experiments are used. The RSPSNN is successfully applied to the function approximation problem, prediction problem, parity problem, classification problem, and image simulation, which verifies its effectiveness and practicability.
| S-EPMC11696508 | biostudies-literature
Project description:The π-accepting character of a terminal carbide complex acting as a ligand is demonstrated experimentally and corroborates earlier theoretical predictions. As a result, coordination of a terminal ruthenium carbide complex to electron-rich metal centres is shown to provide a facile and versatile route to carbide-bridged heterometallic complexes. Synthesis, reactivity, spectroscopic and structural characterization are reported for heterobimetallic systems with auxiliary metals from groups 9-11: Rh(i), Ir(i), Pd(ii), Pt(ii), Ag(i), and Au(i) coordinated by [Ru(C)Cl2(PCy3)2] (RuC). This encompasses the first example of a homoleptic carbide-ligated transition metal complex: [{(Cy3P)2Cl2RuC}2Au]+. Kinetics of substitution on Pt(ii) by RuC ranks the carbide complex as having intermediate nucleophilicity. The 13C-NMR signals from the carbide ligands are significantly more shielded in the bridged heterobimetallic complexes than in the parent terminal carbide complex. Structurally, RuC forms very shorts bonds to the heterometals, which supports the notion of the multiple bonded complex acting as a π-backbonding ligand. Reactions are reported where RuC displaces CO coordinated to Rh(i) and Ir(i). A strong trans influence exerted by RuC indicates it to be a stronger σ-donor than CO. The geometries around the carbide bridges resemble those in complexes of electron-rich metals with carbonyl or bridging nitride-complex-derived ligands, which establishes a link to other strong π-acceptor ligands.
| S-EPMC5950194 | biostudies-literature
Project description:Isocyanoazulenes (CNAz) constitute a relatively new class of isocyanoarenes that offers rich structural and electronic diversification of the organic isocyanide ligand platform. This article considers a series of 2-isocyano-1,3-X2-azulene ligands (X = H, Me, CO2Et, Br, and CN) and the corresponding zero-valent complexes thereof, [(OC)5Cr(2-isocyano-1,3-X2-azulene)]. Air- and thermally stable, X-ray structurally characterized 2-isocyano-1,3-dimethylazulene may be viewed as a non-benzenoid aromatic congener of 2,6-dimethyphenyl isocyanide (2,6-xylyl isocyanide), a longtime "workhorse" aryl isocyanide ligand in coordination chemistry. Single crystal X-ray crystallographic {Cr-CNAz bond distances}, cyclic voltametric {E1/2(Cr0/1+)}, 13C NMR {δ(13CN), δ(13CO)}, UV-vis {dπ(Cr) → pπ*(CNAz) Metal-to-Ligand Charge Transfer}, and FTIR {νN≡C, νC≡O, kC≡O} analyses of the [(OC)5Cr(2-isocyano-1,3-X2-azulene)] complexes provided a multifaceted, quantitative assessment of the π-acceptor/σ-donor characteristics of the above five 2-isocyanoazulenes. In particular, the following inverse linear relationships were documented: δ(13COtrans) vs. δ(13CN), δ(13COcis) vs. δ(13CN), and δ(13COtrans) vs. kC≡O,trans force constant. Remarkably, the net electron withdrawing capability of the 2-isocyano-1,3-dicyanoazulene ligand rivals those of perfluorinated isocyanides CNC6F5 and CNC2F3.
| S-EPMC7918097 | biostudies-literature
Project description:A full account of two recently developed nickel-catalyzed coupling reactions of alkenes, aldehydes, and silyl triflates is presented. These reactions provide either allylic alcohol or homoallylic alcohol derivatives selectively, depending on the ligand employed. These processes are believed to be mechanistically distinct from Lewis acid-catalyzed carbonyl-ene reactions, and several lines of evidence supporting this hypothesis are discussed.
| S-EPMC3148200 | biostudies-literature
Project description:NHC-catalyzed oxidations using carbon dioxide as the stoichiometric oxidant have been carefully investigated. These studies support a secondary role of CO(2) in suppressing side reactions and exogenous oxygen as the actual oxidant.
| S-EPMC3100891 | biostudies-literature
Project description:The recent surge in applications of deuterated pharmaceutical agents has created an urgent demand for synthetic methods that efficiently generate deuterated building blocks. Here we show that N-heterocyclic carbenes (NHC) promote a reversible hydrogen-deuterium exchange (HDE) reaction with simple aldehydes, which leads to a practical approach to synthetically valuable C-1 deuterated aldehydes. The reactivity of the well-established NHC catalysed formation of Breslow intermediates from aldehydes is reengineered to overcome the overwhelmingly kinetically favorable, irreversible benzoin condensation reaction and achieve the critical reversibility to drive the formation of desired deuterated products when an excess of D2O is employed. Notably, this operationally simple and cost-effective protocol serves as a general and truly practical approach to all types of 1-D-aldehydes including aryl, -alkyl and -alkenyl aldehydes and enables chemoselective late-stage deuterium incorporation into complex, native therapeutic agents and natural products with uniformly high levels (>95%) of deuterium incorporation for a total of 104 substrates tested.
| S-EPMC8008838 | biostudies-literature
Project description:In 1996, we reported that silyl groups of 9,10-disilylanthracenes significantly affect the UV/Vis and fluorescence spectra. Although the results indicate that the silyl groups have strong electronic effects on anthracene, the details of the mechanisms responsible for this have not yet been clarified. This article describes the analysis of the UV/Vis and fluorescence spectra of 9,10-bis(diisopropylsilyl)anthracene by theoretical calculations. This study reveals that π conjugation of anthracene is extended by cooperation of σ-π and σ*-π* conjugation between the silyl groups and anthracene. This effect increases the transition moment of the π-π* transition of anthracene. As a result, the molecular extinction coefficient of the 1La band and the fluorescence quantum yield are increased.
| S-EPMC9000373 | biostudies-literature
Project description:A Ni-catalyzed silylacylation of alkenes is presented. The reaction combines alkenes, ClZnSiR3, and acid chlorides to provide rapid access to β-silyl ketones. Importantly, the method involves a [Ni]-SiR3 complex as a catalytic intermediate, which is rarely described for three-component alkene functionalization. Finally, the synthetic utility of the products is demonstrated, and the mechanistic details are described.
| S-EPMC9031101 | biostudies-literature