Takeshi Nishiguchi

Transfer hydrogenation and transfer hydrogenolysis: VIII. Hydrogen transfer from amines to olefins catalyzed by heterogeneous and homogeneous catalysts

Abstract It was found that Pd-carbon, Pd-asbestos, and Pd-black have high catalytic activity in the hydrogen transfer from indoline to cycloheptene. RuCl 2 (PPh 3 ) 3 , RhCl 3 · 2H 2 O, IrCl 3 , (NH 4 ) 2 PdCl 4 , and RhH(PPh 3 ) 4 also showed high activity. The hydrogen-donating ability of organic compounds in the hydrogen transfer reaction catalyzed by Pd-carbon decreased in the order: indoline > formic acid > tetrahydroquinoline > piperidine > pyrrolidine > cyclohexene > N -methylpyrrolidine > di- n -propylamine > d,l -limonene > 1,2-dihydronaphthalene, etc. Though monoenes were hydrogenated efficiently, 1,3- and 1,5-cyclooctadiene were reduced to cyclooctene in high selectivity. The initial rate of the hydrogen transfer from indoline to cycloheptene was proportional to the amine concentration at first and then became independent of the amine concentration. The rate showed a maximum when the olefin concentration was varied. This result indicates the poisoning effect of the olefin.

Transfer hydrogenation and transfer hydrogenolysis—21 : Dehydrogenation of alcohols by quinones

Abstract Dehydrogenation of benzyl-type alcohols and hydroaromatic compounds by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetrachloro-p-benzoquinone were examined, and the hydrogen transfer from 1-phenyl-1-propanol to DDQ was investigated in detail. The yield of the propiophenone increased when solvents which would be expected to increase the concentration of the charge transfer complex between the alcohol and DDQ were used. Initial rates of the reaction in dioxane were proportional to the concentration of the hydrogen donor and that of the hydrogen acceptor. In the dehydrogenation of several para- or meta-substituted 1-phenyl-1-propanols at 60°, −3.30 was obtained as a value of reaction constant. Relative rates of the reaction of PhCH(OH)Et, PhCH(OD)Et, PhCD(OH)Et, and PhCD(OD)Et were 8.9,9.1,1.0 and 1, respectively. This result suggests that the transfer of the H atom attached to the α-carbon of the alcohol is the rate-determining step. This and some other results support a two-step ionic mechanism for the dehydrogenation of alcohols.

Transfer hydrogenation and transfer hydrogenolysis : XXII. Hyrogenolysis of triphenylphospine coordinated to transition metals by hydrogen transfer from organic compounds

Abstract When heated with some organic compounds, the triphenylphosphine ligand of RuH 2 (PPh 3 ) 4 , RhH(PPh 3 ) 4 , RuCl 2 (PPh 3 ) 3 , and RhCl(PPh 3 ) 3 were hydrogenolyzed almost completely to benzene and those of PtCl 2 (PPh 3 ) 2 , Pt(PPh 3 ) 4 , and PdCl 2 (PPh 3 ) 2 underwent this conversion to a considerable extent. In the reaction of RuH 2 (PPh 3 ) 4 in pyrrolidine the amount of the benzene formed was about three times as much as that of the triphenylphosphine consumed. Biphenyl was detected in the reaction of the Ru 11 -species. In the hydrogen transfer from 2-propanol and 2-propanol- d 8 no primary kinetic isotope effect was observed, and the cleavage and oxidative addition of PC bonds of phosphine ligands was inferred to be the rate-determining step of the reaction.

Effect of organic additives having functional groups in olefin metathesis

Abstract The dependence of product yields on the amount of various organic additives containing heteroatom functional groups was investigated for the metathesis of 2-heptene in benzene at room temperature catalyzed by WCl 6 SnBu 4 (1:1). Without additives, heptylbenzenes were major products, and 5-decene and 2-butene were minor ones. With increasing amounts of ethers, ketones, sulfides, pyridine, amines, a cyanide, an amide, a sulfoxide, a tertiary phosphine, and alcohols, the yield of 5-decene first increased markedly and that of heptylbenzene decreased; thereafter, the yield of 5-decene was also lowered. When reaction temperatures were elevated to 80 or 120 °C, the amount of the additives needed to inhibit metathesis increased. In particular, for ether and ester addition significant metathesis was observed even at an additive/catalyst ratio of 30. This suggests that the metathesis of unsaturated ethers and esters proceeds rather efficiently. A comparison of the relative ability of these additives to inhibit metathesis and alkylation shows that the active species in the former reaction are softer acids than those of the latter. It was shown that additives raise metathesis yields mainly by protecting the active species of metathesis from decay, although the inhibition of the alkylation may also have some effect on the yields. The decay of metathesis species takes place easily in a medium where the alkylation proceeds well.

Transfer hydrogenation and transfer hydrogenolysis: XII. Selective hydrogenation of fatty acid methyl esters by various hydrogen donors

The selective hydrogenation of methyl linoleate was studied using various organic compounds as hydrogen sources in the presence of homogeneous and metallic palladium catalysts. Complete selectivity to monoenes and relatively little formation of isolatedtrans double bonds were realized by the hydrogen transfer from L-ascorbic acid at 47% conversion of starting material to hydrogenation products. The hydrogenation bytrans-1,2-cyclohexanediol catalyzed by RuH2(PPh3)4 also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH2(PPh3)4, also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH2(PPh3)4, the presence of these hydroxy compounds increased the isomerization of methyl elaidate tocis-monoenes.

Isomerization of 1,5-cyclooctadiene to cis-bicyclo[3.3.0]oct-2-ene catalyzed by transition metal complexes

Abstract The isomerization of 1,5-cyclooctadiene to cis -bicyclo[3.3.0]oct-2-ene, 1,4-cyclooctadiene and 1,3-cyclooctadiene catalyzed by transition metal complexes was studied. Nickel(II) complexes were found to have excellent catalytic activities for the isomerization to the bicyclic compound. The effect of reaction solvent, additives, reaction temperature, reaction time, catalyst concentration and 1,5-cyclooctadiene concentration were studied using NiBr 2 (PBu 3 n ) 2 as a catalyst. A modified π-allyl mechanism is proposed for the isomerization.

Homogeneous transfer-hydrogenation of olefins catalysed by FeII, CoII, and NiII complexes: o- and p-dihydroxybenzene as hydrogen donors

In the homogeneous hydrogenation of eight membered cyclo-olefins, o- and p-dihydroxybenzene were superior to alcohols as hydrogen donors, and FeCl2(PPh3)2 and FeBr2(PPh3)2 were the most active catalysts of the complexes MX2(PPh3)2, where M is FeII, CoII, and NiII, and X is Cl–, Br–, and I–.