Effect of adjacent chiral tertiary and quaternary centers on the metal-catalyzed allylic substitution reaction

The metal-catalyzed allylic substitution reaction of 5a,b and 6a was examined. Reaction with stabilized nucleophiles led to exclusive attack at the less-hindered allylic terminus, and the stereoselectivity varied with the bidentate ligand used but favored retention. The yields and reaction times were improved with the use of microwaves. Alkylation via transmetalation was only observed with phenyl- and vinylstannatranes and gave regio- and stereoselectivity opposite those observed with the stabilized anions. The epimeric carbonates 5a and 5b displayed very different reactivities. Catalysts containing metals other than palladium were completely unreactive and led to recovered starting material.     

Polymerization of asymmetric polyfunctional monomers. III. Ionic polymerization of acrylic and methacrylic esters of 2-allylphenol

The polymerization of acrylic and methacrylic esters of 2-allyphenol with different anionic, cationic and coordination catalysts was studied. The polymerization occurs exclusively or predominantly through (meth)acrylic C?C double bonds in all the studied cases. With anionic catalysts the allylic groups are not polymerizable and the polymers have linear structure. Polymerization with catalysts based on dialkylaluminum chloride (alone or associated with some metal salts) yields soluble or partially crosslinked polymers, depending on the reaction conditions. The crosslinking is due to the participation of allylic groups in the polymerization reactions. Copolymers of acrylic and methacrylic esters of 2-allylphenol with styrene, acrylonitrile, methyl methacrylate, N-vinylcarbazole and 1,3-pentadiene were synthesized by copolymerization in the presence of anionic catalysts and of systems based on dialkylaluminum chloride.     

Mixing regular convex polytopes

The mixing operation for abstract polytopes gives a natural way to construct a minimal common cover of two polytopes. In this paper, we apply this construction to the regular convex polytopes, determining when the mix is again a polytope, and completely determining the structure of the mix in each case.     

Chromium Electroplating Solutions as Two-Phase Fluids: The Influence on Solution Conductivity

The contribution of N.T. Kudryavtsev (and later his son V.N. Kudryavtsev) to the development of electrodeposition science and technology, and especially to that of chromium, is inestimable. It is a privilege on this occasion to present some considerations of the two-phase nature of chromium electroplating solutions, caused by the generation of hydrogen gas and the use of vigorous air agitation, and to discuss its influence on fluid conductivity and consequent power consumption during electrodeposition.     

Synthesis and complexation of "back-to-back" capped bis-dioxocyclams

Pyridine-capped 5,12-dioxocyclams were coupled "back-to-back" directly, with one or two intervening phenyl groups, an ethynyl group, or a diazo group via Suzuki, Sonogashira, or reductive coupling of the 4-nitropyridine monocyclam. These bis-dioxocyclams linked through extended pi-conjugated systems were complexed to copper(II) and cobalt(III), producing bis-metal complexes which were characterized spectroscopically and electrochemically. These studies gave little evidence for electronic communication between metal centers across the pi-conjugated linkers.     

Low temperature CO oxidation over iron-containing MCM-41 catalysts

Different MCM-41 samples containing framework iron were prepared and tested in CO oxidation showing unprecedented high activities after reduction in hydrogen above 773 K.     

Structure of Solvable Rational Groups

R. Gow proved that the order of a solvable rational group isdivisible only by the primes 2, 3 and 5. In this paper it isproved that in a solvable rational group the Sylow 5-subgroupis always normal and elementary Abelian. Moreover, the structureof rational {2, 5}-groups is described in detail. 2000 MathematicsSubject Classification 20C15, 20C20, 20E34, 20E45.     

Synthesis,complexation, and coordination oligomerization of 1,8-pyrazine-capped 5,12-dioxocyclams

(Methyl)(methoxy)-5,12-dioxocyclam 1 was alkylated on the secondary amines (capped) with 2,6-bis(bromomethyl)pyrazine. The resulting macrocycle was complexed to copper(II) to produce a five-coordinate complex 5a which was fully characterized by a range of spectroscopic methods (IR, UV-vis, ESR) as well as by X-ray crystallography. The structure of this complex is similar to the previously reported pyridine complex, with the five-coordinate copper having distorted square pyramidal geometry and a Cu-Pz bond length of 2.125 A. Attempts to prepare this same complex under microwave irradiation instead produced a trinuclear complex 6a having an octahedral copper(II) center complexed to two pyrazine-cyclam copper units through the amide carbonyl oxygen and the methoxyl group oxygen of the cyclam unit. The X-ray crystal structure of the trinuclear complex showed extensive distortion in the cyclam rings. The remote nitrogen of pyrazine-cyclam complex 5a was capable of coordinating an additional metal. Treatment with RuCl(2)(DMSO)(4) or Rh(2)(OAc)(4), respectively, produced trimetallic Cu-Ru-Cu complex 7 or tetrametallic Cu-Rh-Rh-Cu complex 8. The latter was fully characterized, including an X-ray crystal structure, and had two pyrazine-cyclam complexes bridged by a Rh(2)(OAc)(4) unit through the remote pyrazine nitrogens. There was little distortion in the pyrazine-cyclam copper units as compared to complex 5a: the four metals were collinear, and the two cyclam units were eclipsed. All of the copper complexes were subjected to cyclic voltametry measurements, and no reversible redox changes were observed. Magnetic measurements of 6a and 8 showed the copper atoms to be weakly antiferromagnetically coupled.     

Synthesis of aminocyclopentitols from chromium carbene complex derived aminocyclobutanones

Functionalized cyclopentenones were synthesized by the diazomethane ring expansion of cyclobutanones, produced by the photochemical reaction of vinyl oxazolidinones with chromium carbene complexes.