Teiji Chihara

Catalytic Dehydration of Alcohol to Olefin and Ether by Halide Clusters of Nb, Mo, Ta and W Possessing an Octahedral Metal Core

Molecular halide clusters, [(M6Cl12)Cl2(H2O)4]⋅4H2O (M = Nb, Ta) and (H3O)2[(M6Cl8)Cl6]⋅6H2O (M = Mo, W), develop catalytic activity for the dehydration of alcohols to yield olefins and ethers when they are treated at 300 °C. The activity of the W cluster appears at 250 °C at which temperature it changes to the poorly crystallized three-dimensional linked cluster [W6Cli8]Cla4Cla-a4/2, and decreases at 400 °C at which temperature the crystallinity improves.

Syntheses and structures of methyl-, acetyl- and allyl-ruthenium carbidocarbonyl clusters

Abstract Reaction of the dianionic ruthenium carbidocarbonyl cluster [PPN]2[Ru6C(CO)16] (PPN = (PPh3)2N) (1) with methyl iodide at 120 ° C proceeds with retention of the octahedral metal framework and gives the methyl cluster [PPN][Ru6C(CO)16(CH3)] (3). Treatment of 3 with CO (50 atm) at room temperature gives the acetyl cluster [PPN][Ru6C(CO)16(COCH3)] (6). Reaction of 1 with allyl bromide at 85 ° C gives the allyl cluster [PPN][Ru6C(CO)15(C3H5)] (7) in which the allyl ligand coordiantes to one of the edges of the metal octahedron in μ,η3-manner. The structures of these clusters were unequivocally determined by X-ray diffraction. 3: monoclinic, space group P21/n, a 18.785(4), b 17.762(5), c 17.085(4) A, β 94.42(2)°, Z = 4; R = 0.059, Rw = 0.050 for 5937 unique observed reflections. 6: monoclinic, P21/n (isomorphous with 3), a 18.965(5), b 17.646(7), c 17.366(5) A, β 94.79(3)°, Z = 4; R = 0.069, Rw = 0.040 for 7156 unique observed reflections. 7: monoclinic, P21/a, a 19.343(3), b 19.099(3), c 15.802(3) A, β 98.50(2)°, Z = 4; R = 0.054, Rw = 0.031 for 6304 unique observed reflections.

Chemistry of hexaruthenium carbidocarbonyl cluster complexes. Syntheses and X-ray crystal structures of Ru6C(CO)15(μ-SePh)(μ-AuPPh3), Ru6C(CO)14(μ-SePh)2, and Ru6C(CO)14(μ-SePh)(μ,η3-C3H5)

Abstract Treatment of [PPN] 2 [Ru 6 C(CO) 16 ] (PPN=(PPh 3 ) 2 N) ( 1 ) with phenylselenenyl chloride at room temperature yields [PPN][Ru 6 C(CO) 15 (SePh)] ( 2a ). Reaction of 2a with AuClPPh 3 in the presence of silver tetrafluoroborate affords Ru 6 C(CO) 15 (SePh)(AuPPh 3 ) ( 3 ), which has edge bridging SePh and AuPPh 3 ligands. Heating of 2a under reflux in bis(2-methoxyethyl) ether yields Ru 6 C(CO) 14 (SePh) 2 ( 4 ) with two edge bridging SePh ligands. Reaction of 2a with allyl bromide at 110°C gives an allyl cluster Ru 6 C(CO) 14 (SePh)(C 3 H 5 ) ( 5 ) in which the allyl ligand coordinates to a metal-metal edge in a μ,η 3 -manner and the SePh ligand bridges another edge. The structures of 3 , 4 , and 5 have been determined by single crystal X-ray diffraction studies.

Crystal Structures of a Bond Alternating Chain Compound [{Ni 2(Medpt) 2( µ-ox)( µ-N 3)} n] {(ClO 4)·0.5H 2O} n and a Dimer Compound [Ni 2(dpt) 2( µ-ox)(H 2O) 2](NO 3)(PF 6)

We have studied crystal structures of a Ni bond alternating chain compound [{Ni 2 (Medpt) 2 (µ-ox)(µ-N 3 )} n ] {(ClO 4 )·0.5H 2 O} n (Medpt=methyl-bis(3-aminopropyl)amine, ox=C 2 O 4 ) ( 1 ) and a Ni dimer compound [Ni 2 (dpt) 2 (µ-ox)(H 2 O) 2 ] (NO 3 )(PF 6 ) (dpt=bis(3-aminopropyl)amine) ( 2 ) by x-ray diffraction. Both title compounds crystallize in the triclinic system, space group P \bar1 with f w =646.41, a =8.032(1)A, b =13.436(1)A, c =13.968(2)A, α=63.84(1)°, β=80.54(1)°, γ=81.29(1)°, V =1329.3(2)A 3 , Z =2, R =0.067 and R w =0.075 for 1 and with f w =710.88, a =8.814(1)A, b =12.255(1)A, c =13.487(1)A, α=81.16(1)°, β=89.57(1)°, γ=88.53(1)°, V =1439.0(1)A 3 , Z =2, R =0.059 and R w =0.068 for 2 . The difference of chain structures between 1 and a similar bond alternating compound [{Ni 2 (dpt) 2 (µ-ox)(µ-N 3 )} n ](PF 6 ) n is discussed.

Structural characterization of ansa-zirconocene dichloride bearing a vicinal di-tert-butylcyclopentadienyl ligand and high pressure polymerization of 1-hexene catalyzed by sterically hindered zirconocene complexes

Abstract An ansa -zirconocene complex having a vicinally di- tert -butyl-substituted cyclopentadienyl ligand, Me 2 Si(C 5 H 4 )(C 5 H 2 -3,4- t -Bu 2 )ZrCl 2 ( 1 ), has been synthesized and characterized by X-ray diffraction (orthorhombic, space group: Pbca , a =18.3690(8), b =18.0749(12), c =13.2039(9) A, V =4383.9(4) A 3 , Z =8, R =0.0283, R w =0.0291). Complex 1 has a very much twisted structure due to its steric repulsion. In solution, however, the two tert -butyl groups are magnetically equivalent even at −80°C, indicating very fast oscillation of the bridged cyclopentadienyl unit with respect to the metal center. Complex 1 and nonbridged zirconocene dichlorides with tert -butyl-substituted cyclopentadienyl ligands, (C 5 H 4 - t -Bu) 2 ZrCl 2 ( 2 ), (C 5 H 3 -1,2- t -Bu 2 ) 2 ZrCl 2 ( 3 ) and (C 5 H 3 -1,3- t -Bu 2 ) 2 ZrCl 2 ( 4 ), have been employed as methylaluminoxane (MAO)-activated catalysts for polymerization of 1-hexene under high pressure conditions (100–750 MPa=ca. 1000–7500 atm). Comparison with some non and methyl-substituted metallocenes are also discussed.

Hydration of cyclohexene by alkyl‐immobilized H‐ZSM‐5 catalyst in decalin–water system

In the hydration of cyclohexene, alkylchlorosilane‐treated ZSM‐5s, which floated at the interface of the two liquids, were observed to be solid interface catalysts in a decalin–water system. The catalysts, especially cyclohexyl‐immobilized H‐ZSM‐5, show their capacity of accelerating the hydration with suppression of the formation of by‐products such as dicyclohexyl ether.

Selective synthesis of oxygenates in the CO–H2 reaction on supported ruthenium carbido-cluster catalysts

Supported ruthenium carbido-cluster catalysts ([Ru6C(CO)16Me]–/oxide) selectively produced methanol, dimethyl ether, and formaldehyde in CO–H2, in contrast to the preferential formation of methane and hydrocarbons on supported ruthenium cluster catlysts {[Ru6(CO)18]2–/oxide} without the interstitial carbon and conventional metallic Ru catalysts.

Different behavior between Pt and Pd catalysts in the hydrogenolysis of cyclohexanediones and hydroxycyclohexanones

Abstract Hydrogenolysis reactions of cyclohexanediones, hydroxycyclohexanones, and some related alicyclic ketones were studied over Pt, Pd, Ir, and Rh catalysts at atmospheric hydrogen pressure in t -butyl alcohol as a solvent. Pt and Pd had high catalytic activities for the hydrogenolysis of carbon-oxygen bonds. However, Ir and Rh scarcely had any activity unless 1,3-cyclohexanedione and 3-hydroxycyclohexanone were involved. The mechanisms of the hydrogenolysis differed with Pt and Pd. In the hydrogenation of 4-methoxycyclohexanone, Pt afforded cyclohexyl methyl ether as the hydrogenolysis product; while Pd afforded cyclohexanone, which was then hydrogenated to cyclohexanol. Thus Pt cleaved the carbon-oxygen double bond, and Pd cleaved the carbon-oxygen single bond. Deuterolysis of cyclohexanone and 4-methoxycyclohexanone on Pt gave mainly d 2 species of cyclohexane and cyclohexyl methyl ether as the hydrogenolysis products. This indicated that the carbon-oxygen double bonds were directly cleaved to yield methylene groups on Pt. Almost of all 3-hydroxycyclohexanone was hydrogenolyzed to cyclohexanone on Pd; whereas cyclohexanone as well as cyclohexanol was not hydrogenolyzed at all. In the case of Pd, the carbon-oxygen single bond was cleaved when it was activated by formation of π-oxoallyl adsorbed species on the catalyst at the carbon-oxygen double bond.

Attractive interactions of alkyl substituents with palladium catalyst in the hydrogenation of cyclohexanones

Abstract Cyclohexanone and its 4-alkyl-substituted derivatives were hydrogenated over Pd catalyst in cyclohexane solvent both individually and competitively in pairs (cyclohexanone and one of the derivatives). Most of the derivatives were less reactive than cyclohexanone individually, but more reactive competitively. These findings were explained in terms of attractive interactions between Pd and the alkyl substituents. Similar results were obtained on 2- and 3-alkyl-substituted cyclohexanones. The rate of cyclohexanone hydrogenation was different in five different hexane isomers used individually as solvents. This solvent effect was also explicably based on the concept of Pd-alkyl interactions.

Substituent effects in heterogeneous catalysis: IX. Adsorption strength and reactivity of 4-substituted cyclohexanones in platinum-metal-catalyzed hydrogenation

Abstract Substituent effects in platinum-metal-catalyzed hydrogenation were studied using 4-substituted cyclohexanones (substituent = OH, OMe, Cl, COOEt, Ph, C 6 H 11 , COOH, NMe 2 ) as reaction substrates. The hydrogenation rates of these derivatives were compared with that of cyclohexanone in both individual and competitive reactions. Despite the employment of several different metals and a variety of substituents, including acidic COOH and basic NMe 2 , all of the relative rates fell within a rather limited range: 0.05–6.3 for competitive reactions and 0.10–2.1 for individual reactions. An analysis of these relative rate data indicates that in most cases the adsorption strength of the substituent-bearing cyclohexanones is greater than that of cyclohexanone, thus suggesting an attractive substituent-metal surface interaction. Palladium was distinguished from other platinum-group metals in its unusual weakness of carbonyl adsorption. In order to better understand the substituent effects of COOH and NMe 2 , the effects of acid and base addition were also examined.