Tetsu Yamakawa

Cp2Ni-KOt-Bu-BEt3 (or PPh3) Catalyst System for Direct C−H Arylation of Benzene, Naphthalene, and Pyridine

Ni-catalyzed direct C-H arylation of benzene and naphthalene using aryl halides was investigated. For the first time, the arylation was successfully catalyzed by Cp(2)Ni (5 mol %) in the presence of KOt-Bu and BEt(3). This Ni catalyst system was also applied to direct C-H arylation of pyridine, an electron-deficient heteroarene; PPh(3) was used instead of BEt(3) in this case.

Mechanistic study on dehydrogenation of methanol with [RuCl2(PR3)3]-type catalyst in homogeneous solutions

Abstract Catalytic dehydrogenation of methanol has been investigated in homogeneous solutions with a series of Ru(II) complexes, [RuCl2(P(p-C6H4X)3)3] (X = H (1), Me (2), F (3), OMe (4)) and [RuCl2(PMePh2)3] (5). In the gas phase, hydrogen was formed selectively (> 99.5%), and formaldehyde, methylal (formaldehyde dimethyl acetal) and methyl formate were found in the liquid phase with satisfactory stoichiometry to the formed hydrogen. The reaction was retarded by the extra addition of free phosphine, suggesting the presence of pre-equilibrium dissociation of phosphine ligand. Kinetic analyses from this viewpoint explained well the dependence of rate on the concentration of catalyst (saturation curve). The order of evaluated pre-equilibrium constant (1 ≈ 2 > 5) is in accord with the general idea that the dissociation of phosphine ligand is controlled principally by steric bulk of ligands. The order of rate (3 > 1 > 2 > 4) for 1–4, possessing the same cone angle of phosphine ligand, correlated clearly with basicity of phosphines. The results are interpreted in terms of the mechanism of rate-determining β-hydrogen abstraction in the Ru-OCH3 intermediate.

One-step formation of methyl acetate with methanol used as the sole source and catalysis by RuII–SnII cluster complexes

RuII–SnII cluster complexes [Ru(SnCl3)5L]3–(L = MeCN, PPh3) have been found to be effective for the catalytic conversion of methanol to methyl acetate in a single step.

Synthesis of acetic acid from methanol alone by homogeneous metal complex catalyst. Part II1. Mechanistic study on methyl acetate formation from methanol alone by [(η5-C5H5)(PPh3)2RuX] (X=Cl, SnF3) complex catalyst

Abstract Catalytic activity of [( η 5 -C 5 H 5 ) (PPh 3 ) 2 RuX] (X=Cl ( 1 ), SnF 3 ( 2 )) was investigated for the highly selective formation of methyl acetate with methanol used as the sole source. Complex 2 was found to be more catalytically active than the singlemetallic complex 1 . For both complexes, the initial reaction rate was first order with respect to the catalyst concentration, and a saturation curve was obtained for dependence on the reactant concentration. Extra addition of Cl − ion considerably slowed the reaction with 1 taken as catalyst, and an almost linear relationship was obtained between the reciprocal of initial rate and the concentration of added Cl − ion. This fact indicates the presence of pre-equilibrium to form catalyst-reactant complex through the substitution of Cl − ligand. In the case of 2 , extra addition of PPh 3 gave a similar effect on the rate, allowing the same type of kinetic analysis. The role of Sn(II) ligand is considered in line with the mechanism that satisfies the rate equations derived from these kinetic results.

Photocatalysis of trans-[RhCl(CO)(PPh3)2] under MLCT irradiation for 2-propanol dehydrogenation

Abstract Exclusive evolution of hydrogen without carbon monoxide was observed for the liquid-phase dehydrogenation of 2-propanol with trans -[RhCl(CO)(PPh 3 ) 2 ] under MLCT irradiation, suggesting the catalytic role of the photogenerated [RhCl(PPh 3 ) 2 ] species before its rapid replenishment with CO ligand. A quantum efficiency exceeding unity (1.6) was obtained at 364 nm and 108 °C in refluxing solution mixed with diglyme. Homogeneous photocatalysis in the visible region was discussed from the standpoint of energy storing.

COMMUNICATION: CATALYSIS OF METHYL ACETATE FORMATION FROM METHANOL ALONE BY (η5-C5H5)(PPh3)2RuX (X = Cl, SnCl3, SnF3): HIGH ACTIVITY FOR THE SnF3 COMPLEX

The authors have recently shown that the Ru(II)-Sn(II) bimetallic complex can catalyze the unprecedented one-step formation of acetic acid (or methyl acetate) with methanol used as the sole source. It was suggested that the reaction consists of sequential processes of methanol {r_arrow} formaldehyde (methyl){r_arrow}methyl formate {r_arrow} acetic acid (methyl acetate). While the Ru(II) complexes capable of catalyzing the dehydrogenation of methanol into methyl formate are known, this catalyst system is unique because of its extra ability to isomerize methyl formate to acetic acid without a CO atmosphere (usually high pressure) or an iodide promoter (often corrosive to reaction apparatus). In this communication, the authors examine the cyclopentadienyl bis(triphenylphosphine) ruthenium(II) auxilliary in view of its well defined geometry and configurational stability, and demonstrate that combination with the SnF{sub 3} ligand gives quite high catalytic ability compared to the conventional SnCl{sub 3} ligand. 12 refs., 1 fig.Abstract We have recently shown1,2 that the Ru(II)-Sn(II) bimetallic complex can catalyze the unprecedented one-step formation of acetic acid (or methyl acetate) with methanol used as the sole source. It was suggested that the reaction consists of sequential processes of methanol → formaldehyde (methylal) → methyl formate → acetic acid (methyl acetate). While the Ru(II) complexes capable of catalyzing the dehydrogenation of methanol into methyl formate are known,3–5 this catalyst system is unique because of its extra ability to isomerize methyl formate to acetic acid without a CO atmosphere (usually high pressure) or an iodide promoter (often corrosive to reaction apparatus).6 In this communication, we examine the cyclopentadienyl bis(triphenylphosphine) ruthenium(II) auxilliary in view of its well-defined geometry and configurational stability,7 and demonstrate that combination with the SnF3 − ligand8 gives quite high catalytic ability compared to the conventional9 SnCl3 − ligand.

Isomerization of methyl formate to acetic acid catalysed by the Ru(II)-Sn(II) heteronuclear cluster complex [Ru(SnCl3)5(PPh3)]3−

Abstract The RuII-SnII heteronuclear cluster complex [Ru(SnCl3)5(PPh3)]3− has been found to be catalytically active for the isomerization of methyl formate to acetic acid. The initial reaction rate showed a first order dependence on the catalyst concentration, and showed a saturation curve for the reactant concentration in its high-concentration region. Extra addition of PPh3 and Cl− ion considerably retarded the reaction with almost linear relationships between the reciprocal of initial rates and the concentration of additives. A rate equation derived from these kinetic data indicates the presence of a pre-equilibrium of dual ligand dissociation from the catalyst (PPh3 from RuII and Cl− from SnII) to form the catalyst-reactant complex, where the relatively soft RuII and the hard SnII interact simultaneously with the soft CO group and hard OCH3 group of methyl formate, respectively. It is postulated that such a multi-center interaction in this cluster system facilitates the overall rearrangement of CH3 group (from O atom to C atom) to realize the isomerization of methyl formate to acetic acid without CO atmosphere or iodide promoter, but with an activation energy comparable to that for Rh or Ni catalyst which requires both of them.

Synthesis of acetic acid from methanol alone by homogeneous metal complex catalyst. Part 41. In-situ formation of catalyst species and halogen effect in the RuCl3·3H2O–SnX2 (X=F, Cl, Br, I) composite system

Abstract Highly selective formation of methyl acetate has been found possible from methanol alone using the catalyst generated in situ from RuCl 3 ·3H 2 O and SnCl 2 as well as SnX 2 (X=F, Br, I). The reaction did not occur in the absence of SnCl 2 added and the optimum [Sn]/[Ru] ratio appeared at about 16. The halogen effect showed the order of SnF 2 >SnCl 2 >SnBr 2 >SnI 2 , which indicates the importance of cationic character of Ru(II) center to facilitate its electrophilic interaction with β -hydrogen of Ru–OCH 3 intermediate in the rate-limiting dehydrogenation step.

Thermo- and photocatalytic dehydrogenation of 2-propanol with [RuL(SnCl3)5]4− (LCl− or SnCl3−) complexes

Abstract Photocatalytic dehydrogenation rates of 2-propanol with [RuCl(SnCl 3 ) 5 ] 4− were 48-fold those in the dark. The quantum yield at 254 nm exceeded unity (2.0), under boiling and refluxing conditions, in spite of its endothermic nature. A thermally inert complex [Ru(SnCl 3 ) 6 ] 4− acquired the catalytic activity of dehydrogenation by its photo-transformation into [RuCl(SnCl 3 ) 5 ] 4− , suggesting tin (II) -Iigand dissociation under photoirradiation. The observed isotope effects of 2.53 (photoreaction) and 2.10 (dark reaction) for 2-propanol-2-d, at 82.4°C indicate that the step involving CH bond splitting at the methine group is usually rate-determining.

Acetic acid and methyl acetate formation from methanol alone over ruthenium (II)-tin (II) cluster complex catalysts supported on copper-containing oxides

Acetic acid is a very important chemical, and the carbonylation of methanol (the Monsanto process) is now one of the main processes involved in its production. Recently, we found that homogeneous Run-Sn” cluster complexes { [Ru(SnC13)5L]3-, L=CH3CN and PPh 3 are effective for the formation of } methyl acetate in a single step with methanol used as the sole source [ 11. This reaction is to be preferred over the Monsanto process because neither carbon monoxide as a carbonylation source nor iodide promoter (often corrosive to reaction apparatus) is required. However, these cluster complexes show low solubilities in methanol and conventional solvents and hence the yields of methyl acetate are rather low. In the present study, we tried to improve this advantageous characteristic by making a heterogeneous catalyst where the Run-Sn” cluster complex is supported on various inorganic supports; by performing the reaction in the gas phase, the relative amount of cluster complex in contact with methanol will be increased. Notably it was found that when copper-containing oxides (wellknown heterogeneous catalysts for methyl formate formation from methanol) were used as supports, activity and selectivity to acetic acid ( + methyl acetate) formation were remarkably enhanced.