[(IPent)PdCl2(morpholine)]: A Readily Activated Precatalyst for Room‐Temperature,Additive‐Free Carbon–Sulfur Coupling

A series of new, easily activated NHC–Pd^II precatalysts featuring a trans‐oriented morpholine ligand were prepared and evaluated for activity in carbon‐sulfur cross‐coupling chemistry. [(IPent)PdCl₂(morpholine)] (IPent=1,3‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene) was identified as the most active precatalyst and was shown to effectively couple a wide variety of deactivated aryl halides with both aryl and alkyl thiols at or near ambient temperature, without the need for additives, external activators, or pre‐activation steps. Mechanistic studies revealed that, in contrast to other common NHC–Pd^II precatalysts, these complexes are rapidly reduced to the active NHC–Pd⁰ species at ambient temperature in the presence of KOtBu, thus avoiding the formation of deleterious off‐cycle Pd^II–thiolate resting states.     

A Scalable Process for Production of Single-walled Carbon Nanotubes (SWNTs) by Catalytic Disproportionation of CO on a Solid Catalyst

Existing single-walled carbon nanotube synthesis methods are not easily scalable, operate under severe conditions, and involve high capital and operating costs. The current cost of SWNT is exceedingly high. A catalytic method of synthesis has been developed that has shown potential advantages over the existing methods. This method is based on a catalyst formulation that inhibits the formation of undesired forms of carbon; it can be scaled-up and may result in lower production costs.     

On Small Blocking Sets

Received: August 5, 1997     

Narrow (n,m)-distribution of single-walled carbon nanotubes grown using a solid supported catalyst

Unusually structure-selective growth of single-walled carbon nanotubes (SWNTs) has been attained using a CVD method with a solid supported catalyst. In this method, CO feedstock disproportionates on silica-supported catalytic nanoclusters of Co that are formed in situ from mixed salts of Co and Mo. The nanotube products are analyzed by spectrofluorimetry to reveal distributions resolved at the level of individual (n,m) structures. Two structures, (6,5) and (7,5), together dominate the semiconducting nanotube distribution and comprise more than one-half of that population. The average diameter of produced SWNTs is only 0.81 nm, and a strong propensity is found favoring chiral angles near the armchair limit.     

Room‐Temperature Amination of Deactivated Aniline and Aryl Halide Partners with Carbonate Base Using a Pd‐PEPPSI‐IPentCl‐ o‐Picoline Catalyst

Current state‐of‐the‐art protocols for the coupling of unreactive amines (e.g., electron‐poor anilines) with deactivated oxidative‐addition partners (e.g., electron‐rich and/or hindered aryl chlorides) involve strong heating (usually >100 °C) and/or tert‐butoxide base, and even then not all couplings are successful. The aggressive base tert‐butoxide reacts with and in many instances destroys the typical functional groups that are necessary for the function of most organic molecules, such as carbonyl groups, esters, nitriles, amides, alcohols, and amines. The new catalyst described herein, Pd‐PEPPSI‐IPent^Cl‐o‐picoline, is able to aminate profoundly deactivated coupling partners when using only carbonate base at room temperature.     

Thermally-induced morphological transition in WOx deposited on a ZrO2(1 0 0) substrate

A combined atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) study of tungsten oxide model catalysts is presented. The model catalysts were prepared by applying the real preparation method to a ZrO₂(1 0 0) single crystal support. AFM imaged several granular structures of scattered dimensions on the surface of ZrO₂(1 0 0) in the as prepared samples. After heating, at low loading the tungsten species rearranged into small WO_x particles strongly interacting with the substrate. At high tungsten content large WO₃ aggregates also formed. XPS analysis confirmed these changes. The estimated surface density of the interacting W-containing species closely matched that of real catalysts.     

Reversible formation of an intramolecular agostic CH interaction in a dimanganese complex

Agostic interactions of CH bonds with metal atoms are currently of great interest. UV irradiation of Mn₂(CO)₈ (PMe₂Ph)₂ in the presence of the HCCOEt yielded the new compound Mn₂(CO)₆(PMe₂Ph)₂ [-C(OEt)=C(H)C=C(H)C=O(OEt)],1 that contains a strong agostic interaction of an olefinic CH bond to one of the managanese atoms, Mn...C=2.349(5), Mn...H=2.01(4). This interaction can be removed (reversibly) by CO addition (25°C/1000 psi) to1 to yield the new complex Mn₂(CO)₇(PMe₂Ph)₂[-C(OEt)=C(H)C=C(H)C=O(OEt)],2.     

Blocking Sets in André Planes

We construct new examples of blocking sets in some non-Desarguesian translation planes.