Catalytic ipso-Nitration of Organosilanes Enabled by Electrophilic N-Nitrosaccharin Reagent.

Nitroaromatic compounds represent one of the essential classes of molecules that are widely used as feedstock for the synthesis of intermediates, the preparation of nitro-derived pharmaceuticals, agrochemicals, and materials on both laboratory and industrial scales. We herein disclose the efficient, mild, and catalytic ipso-nitration of organotrimethylsilanes, enabled by an electrophilic N-nitrosaccharin reagent and allows chemoselective nitration under mild reaction conditions, while exhibiting remarkable substrate generality and functional group compatibility. Additionally, the reaction conditions proved to be orthogonal to other common functionalities, allowing programming of molecular complexity via successive transformations or late-stage nitration. Detailed mechanistic investigation by experimental and computational approaches strongly supported a classical electrophilic aromatic substitution (SE Ar) mechanism, which was found to proceed through a highly ordered transition state.

Coordination, reactivity, and structural properties of electron-rich ethoxy- and dimethylamino-substituted 1,3-diketiminate ligands and their complexes.

In this paper we describe the synthesis, characterization, and X-ray crystal structures of two ligands, diethyl-N,N'-bis(p-tolyl)malonimidate and 1,3-bis(dimethylamino)-N,N'-bis(p-tolyl)propanediimidate. Their corresponding rhodium(i) dicarbonyl, dimethylaluminium, and bis-ligated zinc complexes have also been prepared and characterized. The donor properties of the ligands have been studied and have been compared to those of the traditional anionic N,N'-chelating ligand nacnac.

Crystal structure of (S)-sec-butyl-ammonium l-tartrate monohydrate.

The title hydrated mol-ecular salt, C4H12N+·C4H5O6-·H2O, was prepared by deprotonation of enanti-opure l-tartaric acid with racemic sec-butyl-amine in water. Only one enanti-omer was observed crystallographically, resulting from the combination of (S)-sec-butyl-amine with l-tartaric acid. The sec-butyl-ammonium moiety is disordered over two conformations related by rotation around the CH-CH2 bond; the refined occupancy ratio is 0.68 (1):0.32 (1). In the crystal, mol-ecules are linked through a network of O-H⋯O and N-H⋯O hydrogen-bonding inter-actions, between the ammonium H atoms, the tartrate hy-droxy H atoms, and the inter-stitial water, forming a three-dimensional supra-molecular structure.

Crystal structure of bis-(η2-ethyl-ene)(η5-penta-methyl-cyclo-penta-dien-yl)cobalt.

The title compound, [Co(C10H15)(C2H4)2], was prepared by Na/Hg reduction of [Co2(C10H15)2(µ-Cl)2] in THF under an ethyl-ene atmosphere and crystallized from pentane at 193 K. The Co-C(olefin) bonds have an average length of 2.022 (2) Å, while the Co-C(penta-dien-yl) bonds average 2.103 (19) Å. The olefin C=C bonds are 1.410 (1) Å. The dihedral angle between the planes defined by the cyclo-penta-dienyl ligand and the two olefin ligands is 0.25 (12)°. In the crystal, mol-ecules are linked into chains by C-H⋯π inter-actions.

Computational Study of the Palladium-Catalyzed Carbonylative Synthesis of Aromatic Acid Chlorides: The Synergistic Effect of PtBu3 and CO on Reductive Elimination.

We describe herein computational studies on the unusual ability of Pd(PtBu3 )2 to catalyze formation of highly reactive acid chlorides from aryl halides and carbon monoxide. These show a synergistic role of carbon monoxide in concert with the large cone angle PtBu3 that dramatically lowers the barrier to reductive elimination. The tertiary structure of the phosphine is found to be critical in allowing CO association and the generation of a high energy, four coordinate (CO)(PR3 )Pd(COAr)Cl intermediate. The stability of this complex, and the barrier to elimination, is highly dependent upon phosphine structure, with the tertiary steric bulk of PtBu3 favoring product formation over other ligands. These data suggest that even difficult reductive eliminations can be rapid with CO association and ligand manipulation. This study also represents the first detailed exploration of all the steps involved in palladium-catalyzed carbonylation reactions with simple phosphine ligands, including the key rate-determining steps and palladium(0) catalyst resting state in carbonylations.

Aza-oxindole synthesis via base promoted Truce-Smiles rearrangement.

A novel efficient NaOtBu-mediated protocol for the synthesis of 3,3-disubstituted aza-oxindoles proceeds via a Truce-Smiles rearrangement-cyclisation pathway.

A density functional theory investigation of the cobalt-mediated η5-pentadienyl/alkyne [5+2] cycloaddition reaction: mechanistic insight and substituent effects.

Alkyl-substituted η(5)-pentadienyl half-sandwich complexes of cobalt have been reported to undergo [5+2] cycloaddition reactions with alkynes to provide η(2),η(3)-cycloheptadienyl complexes under kinetic control. DFT studies have been used to elucidate the mechanism of the cyclization reaction as well as that of the subsequent isomerization to the final η(5)-cycloheptadienyl product. The initial cyclization is a stepwise process of olefin decoordination/alkyne capture, C-C bond formation, olefin arm capture, and a second C-C bond formation; the initial decoordination/capture step is rate-limiting. Once the η(2),η(3)-cycloheptadienyl complex has been formed, isomerization to η(5)-cycloheptadienyl again involves several steps: olefin decoordination, ß-hydride elimination, reinsertion, and olefin coordination; also here the initial decoordination step is rate limiting. Substituents strongly affect the ease of reaction. Pentadienyl substituents in the 1- and 5-positions assist pentadienyl opening and hence accelerate the reaction, while substituents at the 3-position have a strongly retarding effect on the same step. Substituents at the alkyne (2-butyne vs. ethyne) result in much faster isomerization due to easier olefin decoordination. Paths involving triplet states do not appear to be competitive.

The preparation of 2H-1,4-benzoxazin-3-(4H)-ones via palladium-catalyzed intramolecular C-O bond formation.

Pd/PtBu(3)-catalyzed intramolecular C-O bond formation has been used to access aryl- and alkyl-substituted benzoxazinones.