Intramolecular hydroamination catalysed by gold nanoparticles deposited on fibrillated cellulose

Gold nanoparticles stabilised by fibrillated citric acid-modified cellulose (Au:F-CAC) catalyse the intramolecular cycloamination of amines to unactivated alkenes under an aerobic atmosphere to afford pyrrolidine derivatives. Only 0.2 mol% of Au loading is required to complete the reaction. The high sensitivity of the Au:F-CAC catalyst to the substitution pattern of alkenes allows a unique chemoselective cycloamination, affording new compounds.

Copper-Catalyzed Enantioselective Hydroalkoxylation of Alkenols for the Synthesis of Cyclic Ethers

The copper-catalyzed enantioselective intramolecular hydroalkoxylation of unactivated alkenes for the synthesis of tetrahydrofurans, phthalans, isochromans, and morpholines from 4- and 5-alkenols is reported. The substrate scope is complementary to existing enantioselective alkene hydroalkoxylations and is broad with respect to substrate backbone and alkene substitution. The asymmetric induction and isotopic labeling studies support a polar/radical mechanism involving enantioselective oxycupration followed by C-[Cu] homolysis and hydrogen atom transfer. Synthesis of the antifungal insecticide furametpyr was accomplished.

Theoretical study of correlations between the coordination structures and catalytic activities in polymer-stabilized au nanocluster catalysts

Au nanoclusters (Au NCs) stabilized by poly(N-vinyl-2-pyrrolidone) and poly(allylamine), abbreviated to Au:PVP and Au:PAA, catalyze the aerobic oxidation of p-hydroxybenzyl alcohols, but the catalytic activity of Au:PVP is much higher than that of Au:PAA. To elucidate the correlations between the catalytic activities and coordination structures of the stabilizing polymer, the substrate accessibility on Au NCs was estimated by density functional theory (DFT) and molecular dynamics (MD) calculations. For MD simulations, we applied a systematic method to optimize the temperature parameters in temperature replica exchange molecular dynamics (T-REMD), and the coordination structures were comprehensively classified by multivariate analysis. The results show that the number of open active sites on the Au NCs is a good index for predicting the catalytic activities. © 2018 Wiley Periodicals, Inc.

The Impact of the Polymer Chain Length on the Catalytic Activity of Poly(N-vinyl-2-pyrrolidone)-supported Gold Nanoclusters

Poly(N-vinyl-2-pyrrolidone) (PVP) of varying molecular weight (M_w = 40-360 kDa) were employed to stabilize gold nanoclusters of varying size. The resulting Au:PVP clusters were subsequently used as catalysts for a kinetic study on the sized-dependent aerobic oxidation of 1-indanol, which was monitored by time-resolved in situ infrared spectroscopy. The obtained results suggest that the catalytic behaviour is intimately correlated to the size of the clusters, which in turn depends on the molecular weight of the PVPs. The highest catalytic activity was observed for clusters with a core size of ~7 nm, and the size of the cluster should increase with the molecular weight of the polymer in order to maintain optimal catalytic activity. Studies on the electronic and colloid structure of these clusters revealed that the negative charge density on the cluster surface also strongly depends on the molecular weight of the stabilizing polymers.

Dichotomous mechanistic behavior in Narasaka-Heck cyclizations: electron rich Pd-catalysts generate iminyl radicals

Pd-catalyzed cyclizations of oxime esters with pendant alkenes are subject to an unusual ligand controlled mechanistic divergence. Pd-systems modified with electron deficient phosphines (e.g. P(3,5-(CF3)2C6H3)3) promote efficient aza-Heck cyclization, wherein C-N bond formation occurs via alkene imino-palladation. Conversely, electron rich ligands, such as P(t-Bu)3, cause deviation to a SET pathway and, in these cases, C-N bond formation occurs via cyclization of an iminyl radical. A series of mechanistic experiments differentiate the two pathways and the scope of the hybrid organometallic radical cyclization is outlined. This study represents a rare example in Pd-catalysis where selection between dichotomous mechanistic manifolds is facilitated solely by choice of phosphine ligand.

Simple salts of abundant metals (Fe, Bi, and Ti) supported on montmorillonite as efficient and recyclable catalysts for regioselective intramolecular and intermolecular hydroalkoxylation reactions of double bonds and tandem processes

Montmorillonites doped with metal cations are efficient and recyclable catalysts for hydroalkoxylation reactions and amenable to flow chemistry.

Catalytic Olefin Hydroalkoxylation by Nano Particles of Pollucite

The catalytic hydroalkoxylation of α,β-unsaturated esters, nitriles, and ethers with aliphatic and aromatic alcohols over pollucite using thermal and microwave-assisted methods was investigated. To study the effect of the alcohol structures on the mechanism of the hydroalkoxylation reaction, different alcohols, such as methanol to butanol, cyclohexanol, phenol, and 2-ethylhexanol were used. The activities of pollucite, in contrast to other basic solids, were scarcely affected by the presence of air and moisture. The correlation between alcohol acidity and reaction activity is discussed. The prepared pollucite was characterized by X‐ray diffraction, volumetric nitrogen adsorption surface area analysis, and CO2 temperature‐programmed desorption. Scanning electron microscopy analysis revealed that the size of the modified nano catalyst particles was under 40 nm.

A spectroscopic study of the cis/trans-isomers of penta-2,4-dienoic acid attached to gold nanoclusters

We simulate how one can spectroscopically discriminate between cis/trans isomers of a molecular switch attached to gold nanoclusters.

Highly efficient etherification of silanes by using a gold nanoparticle catalyst: remarkable effect of O(2)

O2 is acting! A nanosized hydroxylapatite-supported Au nanoparticle (NP) catalyst exhibited high activity under aerobic conditions, and various silyl ethers could be obtained from diverse combinations of silanes with alcohols. Moreover, O2 was found to act not as a stoichiometric oxidizing reagent, but as a non-consumed promoter, significantly boosting the catalytic activity of AuNPs.

Hydroalkoxylation of unactivated olefins with carbon radicals and carbocation species as key intermediates

A unique Markovnikov hydroalkoxylation of unactivated olefins with a cobalt complex, silane, and N-fluoropyridinium salt is reported. Further optimization of reaction conditions yielded high functional group tolerance and versatility of alcoholic solvent employed, including methanol, i-propanol, and t-butanol. Use of trifluorotoluene as a solvent made the use of alcohol in stoichiometric amount possible. Mechanistic insight into this novel catalytic system is also discussed. Experimental results suggest that catalysis involves both carbon radical and carbocation intermediates.

Anti-addition mechanism in the intramolecular hydroalkoxylation of alkenes catalyzed by PVP-stabilized nanogold

(1R*,4S*,4aR*,9aS*,10S*)-10-Hydroxy-10-phenyl-1,4a,9a,10-tetrahydro-1,4-methanoanthracen-9(4H)-one (1c) was prepared for the elucidation of the reaction mechanism of intramolecular hydroalkoxylation of alkenes catalyzed by gold nanoclusters stabilized by a hydrophilic polymer, poly(N-vinyl-2-pyrrolidone) (Au:PVP). It was found that the reaction proceeded via anti-addition of alcohol to the alkene assisted by p-activation of the gold clusters, which is the same mechanism as the hydroamination by toluenesulfonamides.

Magnetically recoverable magnetite/gold catalyst stabilized by poly(N-vinyl-2-pyrrolidone) for aerobic oxidation of alcohols

Fe₃O₄:PVP/Au nanocomposite synthesized via a two-step procedure was tested as a quasi-homogenous alcohol oxidation catalyst. It was found that the nanocomposite was able to carry out aerobic oxidation of alcohols in water at room temperature. Studies show rapid magnetic recoverability and reusability characteristics.

Monomeric and dimeric nickel complexes derived from a pincer ligand featuring a secondary amine donor moiety

Reaction of NiBr(2)(CH(3)CN)(x) with the unsymmetrical pincer ligand m-(i-Pr(2)PO)(CH(2)NHBn)C(6)H(4) (Bn = CH(2)Ph) gives the complex (R,S)-kappa(P),kappa(C),kappa(N)-{2-(i-Pr(2)PO),6-(CH(2)NHBn)-C(6)H(3)}Ni(II)Br, 1, featuring an asymmetric secondary amine donor moiety. Deprotonation of the latter with methyl lithium gave a dark brown compound that could not be characterized directly, but fully characterized derivatives prepared from this compound indicate that it is the LiBr adduct of the 14-electron amido species [kappa(P),kappa(C),kappa(N)-{2-(i-Pr(2)PO),6-(CH(2)NBn)-C(6)H(3)}Ni], 2. Thus, 2.LiBr reacts with water to regenerate 1, while reaction with excess benzyl or allyl bromide gave the POCN-type pincer complexes 3 and 4, respectively, featuring tertiary amine donor moieties. On the other hand, heating 2.LiBr at 60 degrees C led to loss of LiBr and dimerization to generate the orange crystalline compound [mu(N);kappa(P),kappa(C),kappa(N)-{2-(i-Pr(2)PO),6-(CH(2)NBn)-C(6)H(3)}Ni](2), 5. Solid state structural studies show that 1, 3, and 4 are monomeric, square planar complexes involving one Ni-N interaction, whereas complex 5 is a C(2)-symmetric dimer involving four Ni-N interactions and a Ni(2)N(2) core featuring a short Ni-Ni distance (2.51 A). Preliminary reactivity tests have shown that 5 is stable toward weak nucleophiles such as acetonitrile but reacts with strong nucleophiles such as CO or 2,6-Me(2)(C(6)H(3))NC. Reactions with protic reagents showed that phthalimide appears to break the dimer to generate a monomeric species, whereas alcohols appear to leave the dimer intact, giving rise instead to adducts through N...H...O interactions. These ROH adducts of 5 were found to be active precatalysts for the alchoholysis of acrylonitrile with up to 2000 catalytic turnover numbers.