Synthesis of linked carbon monolayers: films, balloons, tubes, and pleated sheets.

Because of their potential for use in advanced electronic, nanomechanical, and other applications, large two-dimensional, carbon-rich networks have become an important target to the scientific community. Current methods for the synthesis of these materials have many limitations including lack of molecular-level control and poor diversity. Here, we present a method for the synthesis of two-dimensional carbon nanomaterials synthesized by Mo- and Cu-catalyzed cross-linking of alkyne-containing self-assembled monolayers on SiO(2) and Si(3)N(4). When deposited and cross-linked on flat surfaces, spheres, cylinders, or textured substrates, monolayers take the form of these templates and retain their structure on template removal. These nanomaterials can also be transferred from surface to surface and suspended over cavities without tearing. This approach to the synthesis of monolayer carbon networks greatly expands the chemistry, morphology, and size of carbon films accessible for analysis and device applications.

Pd(II)-catalyzed conversion of styrene derivatives to acetals: impact of (-)-sparteine on regioselectivity.

[reaction: see text] Pd[(-)-sparteine]Cl(2) catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride.

A convenient palladium-catalyzed aerobic oxidation of alcohols at room temperature.

A simple Pd-catalyzed aerobic oxidation of benzylic and aliphatic alcohols to the corresponding aldehydes and ketones at room temperature is described.

Solvent-free synthesis of Janus colloidal particles.

Taking advantage of the quick and efficient access of vapor to surfaces, a simple, solvent-free method is demonstrated to synthesize Janus colloidal particles in large quantity and with high efficiency. First, at the liquid-liquid interface of emulsified molten wax and water, untreated silica particles adsorb and are frozen in place when the wax solidifies. The exposed surfaces of the immobilized particles are modified chemically by exposure to silane vapor and, in principle, subsequent dissolution of the wax opens up the inner particle surface for further chemical modification. Applying this scheme, this paper describes the production of amphiphilic Janus particles (hydrophobic on one side, hydrophilic on the other) and dipolar Janus particles (positively charged on one side, negatively charged on the other). Janus geometry is confirmed by fluorescence microscopy and flow cytometry. Amphiphilic Janus particles are found to adsorb strongly to the water-oil interface, whereas dipolar particles assemble into chains in the aqueous phase.

Palladium(II)-catalyzed aerobic dialkoxylation of styrenes: a profound influence of an o-phenol.

We report a Pd(II)-catalyzed aerobic dialkoxylation of styrene derivatives that requires an o-phenol. Initial scope and preliminary mechanistic studies are presented in which the o-phenol is proposed to facilitate the formation of a quinone methide intermediate.

Palladium(II)-catalyzed aerobic hydroalkoxylation of styrenes containing a phenol.

An intermolecular Pd-catalyzed hydroalkoxylation of styrenes that contain a phenol is presented. The reaction can be performed on terminal, disubstituted, and trisubstituted olefins in a variety of alcoholic solvents. Initial mechanistic data suggest a mechanism that involves oxidation of the alcoholic solvent to provide a Pd-hydride that inserts into an olefin. This is followed by formation of a quinone methide and subsequent addition of an alcohol to yield the hydroalkoxylated product.

Development and comparison of the substrate scope of Pd-catalysts for the aerobic oxidation of alcohols.

[reaction: see text] Three catalysts for aerobic oxidation of alcohols are discussed and the effectiveness of each is evaluated for allylic, benzylic, aliphatic, and functionalized alcohols. Additionally, chiral nonracemic substrates as well as chemoselective and diastereoselective oxidations are investigated. In this study, the most convenient system for the Pd-catalyzed aerobic oxidation of alcohols is Pd(OAc)(2) in combination with triethylamine. This system functions effectively for the majority of alcohols tested and uses mild conditions (3 to 5 mol % of catalyst, room temperature). Pd(IiPr)(OAc)(2)(H(2)O) (1) also successfully oxidizes the majority of alcohols evaluated. This system has the advantage of significantly lowering catalyst loadings but requires higher temperatures (0.1 to 1 mol % of catalyst, 60 degrees C). A new catalyst is also disclosed, Pd(IiPr)(OPiv)(2) (2). This catalyst operates under very mild conditions (1 mol %, room temperature, and air as the O(2) source) but with a more limited substrate scope.

Using mechanistic and computational studies to explain ligand effects in the palladium-catalyzed aerobic oxidation of alcohols.

The experimental and computational mechanistic details of the Pd(OAc)(2)/TEA-catalyzed aerobic alcohol oxidation system are disclosed. Measurement of various kinetic isotope effects and the activation parameters as well as rate law derivation support rate-limiting deprotonation of the palladium-coordinated alcohol. Rate-limiting deprotonation of the alcohol is contrary to the majority of related kinetic studies for Pd-catalyzed aerobic oxidation of alcohols, which propose rate-limiting beta-hydride elimination. This difference in the rate-limiting step is supported by the computational model, which predicts the activation energy for deprotonation is 3 kcal/mol higher than the activation energy for beta-hydride elimination. The computational features of the similar Pd(OAc)(2)/pyridine system were also elucidated. Details of the study illustrate that the use of TEA results in an active catalyst that has only one ligand bound to the Pd, resulting in a significant lowering of the activation energy for beta-hydride elimination and, therefore, a catalyst that is active at room temperature.

The renaissance of palladium(II)-catalyzed oxidation chemistry.

Palladium(II)-catalyzed oxidations constitute a paramount reaction class but have remained immature over the past few decades. Recently, this field has reappeared at the forefront of organometallic catalysis. This emerging area article outlines recent developments in palladium(II)-catalyzed oxidation chemistry with discussion of potential future growth.