Kotohiro Nomura

Transition metal catalyzed hydrogenation or reduction in water

Abstract This paper summarizes recent reports on (i) hydrogenation (including transfer hydrogenation by HCO 2 Na) of olefins or aldehydes in water, and (ii) reduction of aromatic nitro compounds with carbon monoxide and water by homogeneous transition metal catalysts. The discussion will be focused on the hydrogenation of α , β -unsaturated aldehydes by ruthenium–sulfonated phosphine complexes that show remarkable chemoselectivity toward CO bonds. The author also introduces selective reduction of aromatic nitro-groups by ruthenium or rhodium catalysts under CO/H 2 O conditions. These catalytic reactions are very important from both synthetic and industrial viewpoints, not only because the after-treatment of by-products can be simplified from the conventional methods, but also because the reaction also proceeds with high selectivity affording the desired products.

Highly Efficient Dimerization of Ethylene by (Imido)vanadium Complexes Containing (2-Anilidomethyl)pyridine Ligands: Notable Ligand Effect toward Activity and Selectivity

(Imido)vanadium(V) complexes containing the (2-anilidomethyl)pyridine ligand, V(NR)Cl(2)[2-ArNCH(2)(C(5)H(4)N)] (R = 1-adamantyl (Ad), cyclohexyl (Cy), phenyl), exhibit remarkably high catalytic activities (e.g. TOF = 2 730 000 h(-1) (758 s(-1)) by V(NAd)Cl(2)[2-(2,6-Me(2)C(6)H(3))NCH(2)(C(5)H(4)N)) for ethylene dimerization in the presence of MAO, affording 1-butene exclusively (selectivity 90.4 to >99%). The steric bulk of the imido ligand plays an important role in the selectivity (polymerization vs dimerization), and the electronic nature directly affects the catalytic activity (activity: R = Ad > Cy > Ph).

Ruthenium catalyzed hydrogenation of methyl phenylacetate under low hydrogen pressure

Abstract PhCH2CO2Me has been efficiently hydrogenated to yield PhCH2CH2OH (1) and PhCH2CO2CH2CH2Ph (2) even under relatively low hydrogen pressure (

n-Alkene and dihydrogen formation from n-alkanes by photocatalysis using carbonyl(chloro)phosphine–rhodium complexes

n-Alkenes and dihydrogen were obtained from n-alkanes by photocatalysis using carbonyl(chloro)phosphine–rhodium complexes; the rate of alkane dehydrogenation was the same as that of propan-2-ol dehydrogenation under the same photocatalytic reaction conditions.

(Imido)vanadium(V)-alkyl, -alkylidene complexes exhibiting unique reactivity towards olefins and alcohols

This minireview introduces recent results in the synthesis of a series of (imido)vanadium(V)-alkyl complexes, and some reactions with alcohols (phenols) that are proposed to proceed via intermediates involving coordination of the alcohols (phenols). (Imido)vanadium(V)-alkylidene complexes, prepared by α-hydrogen elimination in the presence of a neutral donor ligand (PMe3, etc.), exhibited high activity for ring-opening metathesis polymerisation of cyclic olefins (norbornene) even at high temperature; these are promising for olefin metathesis by vanadium complex catalysts.

Direct synthesis of 2-phenylethanol by hydrogenation of methyl phenylacetate using homogeneous ruthenium-phosphine catalysis under low hydrogen pressure

Methyl phenylacetate could be efficiently hydrogenated to yield 2-phenylethanol under lower hydrogen pressure (<10 atm) by using ruthenium-phosphine catalysis composed of Ru(acac)3, P(n-C8H17)3 in the presence of Zn. Effect of both phosphine and Zn plays an crucial role in order for this hydrogenation to proceed under mild conditions.

Synthesis of (1-Adamantylimido)vanadium(V) Complexes Containing Aryloxo, Ketimide Ligands : Effect of Ligand Substituents in Olefin Insertion/Metathesis Polymerization

A series of (1-adamantylimido)vanadium(V) complexes containing anionic donor ligands of the type, V(NAd)Cl2(L) [Ad = 1-adamantyl; L = O-2,6-Me2C6H3 (2), O-2,6-(i)Pr2C6H3 (3), NC(t)Bu2 (5), NC((t)Bu)CH2SiMe3 (6), NC((t)Bu)Ph (7), NCPh2 (8)], have been prepared from V(NAd)Cl 3, which was in turn prepared from VOCl3 by treatment with 1-adamantylisocyanate in octane, by treatment with the corresponding lithium salts (lithium phenoxides, lithium ketimides) in Et2O. These complexes (2, 3, 5-8) were identified by NMR spectroscopy and elemental analysis, and the structures for 2 and 5 were determined by X-ray crystallography. The reaction of V(NAd)Cl3 with 2,6-dimethylphenol in n-hexane afforded the tris(aryloxo) analogue V(NAd)(O-2,6-Me2C6H3)3 (4), the structure of which was determined by X-ray crystallography. 8 gradually decomposed in toluene to give a dimeric species, [N(Ad)H3](+)[V2(mu2-Cl)3Cl2(NAd)2(NCPh2)2](-) (10), but 8 was stabilized as a PMe 3 coordinated species, V(NAd)Cl2(NCPh2)(PMe3)2 (9): the structures for 9 and 10 were determined by X-ray crystallography. These complexes were evaluated as catalyst precursors for ethylene polymerization in the presence of MAO. The ketimide analogues, especially 5, exhibited moderate catalytic activity, and the activity with a series of V(NAd)Cl2(L)-MAO catalyst systems increased in the order: L = NC(t)Bu2 (5, 516 kg-PE/mol x V x h) > NC((t)Bu)Ph (7, 300) > NCPh2 (8, 105) > NC((t)Bu)CH2SiMe3 (6, 70.8). These complexes (2, 3, 5, 6) were found to be effective as catalyst precursors for the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of MeMgBr and PMe3.

Polymerization of 1-hexene, 1-octene catalyzed by Cp′TiCl2(O-2,6-iPr2C6H3)–MAO system. Unexpected increase of the catalytic activity for ethylene/1-hexene copolymerization by (1,3-tBu2C5H3)TiCl2(O-2,6-iPr2C6H3)–MAO catalyst system

Abstract Although (1,3-tBu2C5H3)TiCl2(O-2,6-iPr2C6H3) (4) showed the lowest catalytic activity for polymerization of 1-hexene, 1-octene with the series of Cp′TiCl2(O-2,6-iPr2C6H3) [Cp′= Cp, tBuC5H4, 1,3-Me2C5H3, 1,3-tBu2C5H3, and C5Me5]–methylaluminoxane (MAO) catalysts, 4 exhibited the significant catalytic activity for copolymerization of ethylene with 1-hexene, resulting in obtaining a copolymer with relatively high 1-hexene content (20.2–36.5 mol%) with relatively narrow molecular weight distribution.

Efficient selective reduction of aromatic nitro compounds by ruthenium catalysis under COH2O conditions

Abstract Ruthenium-carbonyl complexes in the presence of small amounts of amines have exhibited both significant catalytic activities and remarkable selectivities of nitro group for reduction of aromatic nitro compounds under CO H 2 O conditions. Notable increases of the catalytic activities were found upon the addition of a small amount of the specified amine, such as diisopropylamine, piperidine, dibutylamine, and triethylamine; the reaction rate increased at higher reaction temperatures, under higher CO pressures. The powerful importance of the present catalysis can be emphasized, because aromatic nitro group was reduced exclusively without the other unsaturated groups such as CO, CN, CC, and CC being reduced: the desired aromatic amines were, therefore, catalytically obtained in high yields. The reduction was also found to proceed without by-producing hydrogen gas generated from the water-gas shift reaction (WGSR). The role of amines in this catalysis was thus suggested to be different from that in the WGSR. Comparing the results here with those reported previously, an original reaction pathway in this catalysis, such as intramolecular hydrogen transfer between metal-nitrene and hydride, can be considered; the mechanism has also been discussed and presented in this paper.

Effect of aryloxo ligand for ethylene polymerization by (arylimido)(aryloxo)vanadium(V) complexes–MAO catalyst systems: attempt for polymerization of styrene

Abstract Ethylene polymerization using (arylimido)(aryloxo)vanadium complexes of type, VCl 2 (N-2,6-Me 2 C 6 H 3 )(OAr) [OAr=O-2,6-Me 2 C 6 H 3 ( 1 ), O-2,6- i Pr 2 C 6 H 3 ( 2 ), O-2,6-Ph 2 C 6 H 3 ( 3 ), and O-2,6- t Bu 2 -4-MeC 6 H 2 ( 4 )], has been explored in the presence of MAO. The substituents on the aryloxo ligand were found to play an essential role for the catalytic activity, and effect of both Al/V molar ratio and temperature for the activity depended upon the substituents. High catalytic activity was observed especially at low temperature of 0 °C when 3 was used as the catalyst precursor, whereas 1 showed the highest activity at 25 °C. However, 2 –MAO catalyst showed extremely low activity for styrene polymerization.