Katsumi Tanaka

Stereoselectivity in olefin metathesis over molybdenum oxide supported on titanium oxide

Abstract Molybdenum oxide, MoOx (2.9 >x > 2.3), supported on β-TiO2 is a unique catalyst [6] on which olefins undergo metathesis without hydrogen scrambling at room temperature. A 1:1 mixture of cis-but-2-ene-d0 and cis-but-2-ene-d8 gave mainly trans-but-2-ene-d0, -d4, -d8, and cis-but-2-ene-d4. The initial ratio of cis-d4/trans-d4 was 3 2 . In contrast to this, the metathesis of trans-but-2-ene-d0 and trans-but-2-ene-dg yielded only trans-but-2-ene-d4 in the initial stage of reaction. That is, the metathesis of cis-olefin prefers to yield cis-olefin with some trans-olefin, and the metathesis of trans-olefin gives entirely trans-olefin. If trans-but-2-ene-d0 and -d8 are formed by metathesis of cis-but-2-ene-d0 and cis-but-2-ene-d8, the ratio of (d0 + d8)/d4 should statistically be unity. Contrary to this expectation, the ratio at the initial stage was nearly zero, which suggests that trans-but-2-ene-d0 and -d8 are formed in the initiation steps of metathesis. Besides the structure-retaining selectivity such as cis-olefin giving cis and trans-olefin trans, the metathesis of α-olefins such as propene undergoes trans stereoselectivity. It was found that ethylene can participate in the initiation steps of metathesis forming Moue5fbCH2 intermediates. These react little with ethylene in the presence of cis-2-butene although Moue5fbCHue5f8CH3 can react with ethylene in the presence of cis-2-butene. Stereoselective metathesis of propene as well as structure-retaining metathesis of cis- and trans-2-butene are well explained by the structures of metallacyclobutane intermediates.

Ethylene homologation reaction in the presence of metathesis on MoOx/SiO2 catalyst: selectively promoted by adding copper

Abstract The active MoOx species in MoO3/SiO2 catalysts for the ethylene homologation reaction (3C2H4θ2C3H6) was examined in comparison with those for the ethylene metathesis reaction (12C2C2H4+13C2C2H4θ213C1C2H4). It was concluded that ethylene homologation proceeds on reduced MoO3/SiO2 with reduced octahedral MoOx, whereas ethylene metathesis is less affected than ethylene homologation by the oxidation state and the coordination of MoOx. A preliminary attempt was made to enhance ethylene homologation by adding a co-catalyst expected to promote the reduction of MoO3. When copper was added, the homologation rate was selectively enhanced 3-fold.

THE SYNTHESIS AND POSSIBLE TRANSPORT PROPERTIES OF CALIX[4]ARENES MODIFIED WITH SIDECHAINS CONTAINING GERMANIUM

A calix[4]arene modified at upper-rim with side-chains containing germanium was prepared with an expectation that the Lewis-acidic germanium may capture the anions so that the transport property of the calixarene may be improved. It was shown that the calixarene thus modified with germanium-containing sidc-chains as well as its precursor without germanium failed to transport cations probably because of bulky tosylate moieties in the lower rim. INTRODUCTION Calixarenes, especially calix[4]arencs. are some of the most thoroughly investigated hosts and their complexing capacity for cations under certain conditions has been well investigated. During the course of our investigation on the synthesis, structure and properties of cyclic organogermanium compounds, we found that macrocyclic species such as 1,8-dimethyll,8-dihalo-l,8-digermacyclotetradecanes possess anion transport capability. Anion capturing capability is not necessarily restricted to organogermanium compounds. Previously organosilicon or organotin compounds with a similar capability have been reported. Thus, Jung and Xia reported the anion transport property of 1,1,5,5,9,9-hexamethyll ,5 ,9trisilacyclododecans, and Newcomb el al. reported a bicyelic tin compound with the same property. If the two properties mentioned above, that is, the cation-capturing capability of calixarenes and anion-capturing capability of germanium moieties, are combined, we can expect that a host with a novel property may be created: i.e., (i ) it is expected that the cation-transport capability of new hosts, modified calixarenes, may be improved as compared with that of unmodified ones because not only cations but also the counteranions are captured by the transporting host; (iij amphoteric substances such as amino acids may conveniently be captured and transported by modified calixarenes. In this paper we describe the synthesis of a calix[4]arene modified with side-chains

Discrimination of active sites for ethylene homologation and ethylene metathesis on molybdena silica catalyst

Active sites for ethylene homologation (3C2H4→2C3H6) and ethylene metathesis (C2H4−12C2+C2H4−13C2→→2C2H4−13C1) were discriminated by adding platinum to a reduced molybdena silica catalyst, and the former was presumed to be composed of several molybdenum species, while the latter was presumed to be composed of one molybdenum species.AbstractАктивные центры гомологизации этилена (3C2H4р2C3H6) и перестановки этилена (C2H4−12C2+C2H4−13C2→2C2H4−13C1) различали добавлением платины к восстановленному алюмомолибденовому катализатору. Так полагали, что первоначальный катализатор состоит из нескольких типов частиц молибдена, а последний из одного типа частиц молибдена.

Reactive intermediates for the ethene homologation reaction on molybdena–silica catalysts

Ethene has been selectively homologated to propene (3CC → 2CC—C) on reduced molybdena–silica at room temperature. The initial homologation activity was enhanced by grafting the methylene species on the surface with SnMe4. Deuterated methane and cyclopropane were formed by reacting 2H2 with the surface on which the ethene homologation had been carried out. These results clearly suggest that the ethene homologation proceeds through metal methylidene and metallocycle intermediates. The homologation accompanied the hydrogen exchange of ethene, which was considered to be a similar function to β-elimination of hydrogen from the metallocycle. [13C2]propene was dominantly formed by the reaction of [13C2]ethene on the CH2 furnished surface. Taking account of the fact that the ethene metathesis proceeds 103 times faster than the homologation, it was concluded that the propagating species for the homologation is different from that for the metathesis.

Novel catalyst, MoOx–β-TiO2, for the olefin metathesis reaction with No hydrogen scrambling

A novel catalyst is reported on which the metathesis reaction of olefins proceeds without hydrogen scrambling of isomerization through alkyl or carbonium ion intermediates: the catalyst was prepared by treating reduced MoOx–β-TiO2 with a mixture of N2O and H2 at 200 °C.

1,8-DIMETHYL-1,8-DIHALO-1,8-DIGERMACYCLOTETRADECANES. THE FIRST GERMAMACROCYCLES WITH ANION TRANSPORT CAPABILITY

It has been shown that 1,8-dichloro-1,8-dimethyl-1,8-digermacyclotetradecane transports chloride anion more effectively than bromide anion in a U-tube test. The dibromo analogue also can transport anions. The efficiency of transport of open chain analogues with a similar environment around germanium is inferior to that of cyclic systems which confirms the essential role of the ring structure for anion transport. The anion transport capability was examined for other germanium-containing 14-membered rings. A possible mechanism for anion transport is proposed.

Enhancement of ethylene metathesis rate by adsorbate interaction between ethylene and carbon monoxide

Catalyse sur MoO x /SiO 2 de la reaction de metathese entre C 2 H 4 - 12 C 2 et C 2 H 4 - 13 C 2

A study of ethene homologation over supported MoO3 catalysts: Effect of catalyst support and pretreatment

The catalytic transformation of short-chain hydrocarbons to higher homologs is an important reaction. In general, the yield of the homologated product was found to be sensitive to the structure and chain length of parent hydrocarbon and partial pressure of hydrogen used in the reaction. The yield was found to increase with the CH/sub 2//CH/sub 3/ ratio in the n-alkanes, starting from ethane and propane, which showed little or no activity, and tending to an upper limit with C/sub 7/ to C/sub 9/ alkanes. In a previous study, the authors found that various impregnated reduced MoO/sub 3/ catalysts are active for ethane homologation, which presumably occurs via insertion of active surface species (CH/sub x/) into adsorbed ethene. This note reports the results of ethene homologation over the various supported MoO/sub 3/ catalysts. The catalyst supports used in this work were TiO/sub 2/, ZrO/sub 2/, SiO/sub 2/, SiO/sub 2/-Al/sub 2/O/sub 3/ (13.75% Al/sub 2/O/sub 3/), SiO/sub 2/-Al/sub 2/O/sub 3/ (28.61% Al/sub 2/O/sub 3/), and ..gamma..-Al/sub 2/O/sub 3/. 14 references.

Homologation, hydrogenolysis, and dehydrogenation of ethane on SiO2- and SiO2Al2O3-supported reduced molybdenum oxide catalysts

Abstract Kinetics and reaction mechanisms of homologation, hydrogenolysis, and dehydrogenation of ethane were studied on reduced molybdenum oxides supported on SiO 2 and SiO 2 ue5f8Al 2 O 3 . It was found that homologation of ethane to propane occurs via (1) dehydrogenation of ethane to ethylene, (2) homologation of ethylene to propylene, and (3) hydrogenation of propylene to propane. The rate-determining step was found to be hydrogenation of adsorbed propylene or that of adsorbed C 2 H 5 species with an activation energy of 10.7 kcal/mole. In addition to homologation products, significant amounts of hydrogenolysis and dehydrogenation reaction products were also found. Dehydrogenation of ethane to ethylene had an activation energy of 25 kcal/mole, and it was quite similar to that for desorption of ethylene. Consequently, the dehydrogenation rate was assumed to be controlled by desorption of ethylene formed.