A theoretical study of the cyclopropane ring opening by palladium

Ruthenium-Catalyzed Oxidative Cross-Coupling Reaction of Activated Olefins with Vinyl Boronates for the Synthesis of (E,E)-1,3-Dienes

An oxidative cross-coupling reaction between activated olefins and vinyl boronate derivatives has been developed for the highly stereoselective construction of synthetically useful (E,E)-1,3-dienes. The highlight of this reaction is that exclusive stereoselectivity (only E,E-isomer) was achieved from a base-free, ligand-free, and mild catalytic condition with a less expensive [RuCl₂(p-cymene)]₂ catalyst.

Pyrolysis of Polyethylene Terephthalate over Carbon-Supported Pd Catalyst

Pyrolysis of polyethylene terephthalate (PET) produces polycyclic hydrocarbons and biphenyl derivatives that are harmful to human health and the environment. Therefore, a palladium metal catalyst (5 wt.% Pd loaded on activated carbon) was used to prevent the formation of harmful materials. When a Pd catalyst/PET ratio of 0.01 was applied in pyrolysis of PET, it did not show a meaningful difference in the generation of polycyclic hydrocarbons and biphenyl derivatives. However, when a Pd catalyst/PET ratio of 0.05 was used during pyrolysis, it prevented their formation and generation at experimental temperature ranges (400–700 °C). For example, the concentration of 2-naphthalenecarboxylic acid produced, which is a typical polycyclic hydrocarbon material, was reduced by 44%. In addition, the concentration of biphenyl-4-carboxylic acid, which is contained in biphenyl derivatives, was reduced by 79% compared to non-catalytic pyrolysis at 800 °C. This was because the ring-opening reaction and free radical mechanism caused by the Pd catalyst and thermal cracking were dominant during the pyrolysis of PET. Apart from these materials, amine compounds were generated as products of the pyrolysis of PET. Amine concentration showed a similar trend with polycyclic hydrocarbons and benzene derivatives. Based on these results, the total concentration of polycyclic hydrocarbons and biphenyl derivatives was compared; the results confirmed that the concentrations of all substances were reduced. This research suggests that a metal-supported catalyst will help create a more environmentally friendly and reliable method of industrial plastic waste disposal.

Reactions of ruthenium-allenylidene complexes tethering a cyclopropyl group

Two cyclopropyl allenylidene complexes [Ru]=C=C=C(R)(C(3)H(5)) ([Ru]=[RuCp(PPh(3))(2)], Cp=Cyclopentadienyl; R=thiophene (2a) and R=Ph (2b)) are prepared from the reactions of [Ru]Cl with the corresponding 1-cyclopropyl-2-propyn-1-ol in the presence of KPF(6). Thermal treatment, halide-anion addition, and palladium-catalyzed reactions of 2a and 2b all lead to a ring expansion of the cyclopropyl group, giving the vinylidene complexes 4a and 4b, respectively, each with a five-membered ring. This ring expansion proceeds by C-C bond formation between Cβ of the cumulative double bond and a methylene group of the cyclopropyl ring. In the reaction of 2a with pyrrole, consecutive formation of two C-C bonds, one between C-2 of pyrrole and Cγ of 2a and the other between C-3 of pyrrole and Cα, results in the formation of 6a. The reaction proceeds by addition of pyrrole and 1,3-proton shifts. The hydrogenation of 2a by NaBH(4) is carried out in different solvents. The cumulative double bonds are reduced regioselectively to give a mixture of 7a and 8a. Interestingly, use of different solvents leads to different ratios of 7a and 8a. Presence of a protic solvent like methanol in dichloromethane or chloroform solution increases the yield of 8a, thus revealing that both the rates of hydroboration and deboronation increase. The structures of two new complexes 4a and 6a have been firmly established by X-ray diffraction analysis.

Theoretical study of the mechanisms of palladation of methylenecyclopropane and [3 + 2] cycloadditions

Palladation of methylenecyclopropane and [3 + 2] cycloaddition with alkenes have been studied theoretically. In palladium complexes of methylenecyclopropane or trimethylenemethane, the eta 2 forms have been shown to be more stable than the palladacyclobutane forms. However, the barrier heights to yield palladacyclobutanes are not very high and the methylene-bridged carbon can be converted to the metal-attached carbon on palladium via a ring-opened transition state, allowing the scrambling of hydrogens in methylenecyclopropane. With respect to the palladium-catalyzed [3 + 2] cycloaddition reaction of methylenecyclopropane with alkenes, the path via palladacyclobutanes has been demonstrated to be more favorable than the path via an eta 2 complex. These results are discussed by using the paired interaction orbital scheme.