Takahiro Mashino

Highly selective aldol reaction of dibenzoylmethanes with formaldehyde catalyzed by cobalt schiff base complex under neutral conditions

Abstract Coordinatively saturated hydroxocobalt(III) Schiff base complexes catalyze highly selective aldol reaction of dibenzoylmethanes with formaldehyde in methanol to give 1,3-dibenzoylpropanes, resulting from retro-Claisen reaction of 1,1,3,3-tetrabenzoylpropanes, which are obtained quantitatively in dichloromethane. Coordinatively saturated cobalt(III) Schiff base complexes ligating a substrate anion as a monodentate ligand is found to be the reactive species.

Structural effect of cobalt Schiff base complex catalyst on its catalytic activity in dioxygenolysis of 3-methylindole

Abstract Dioxygenolysis of 3-methylindole catalyzed by a series of cobalt(II) Schiff base complexes electronically and sterically designed gives 2-( N -formylamino)acetophenone as the sole product, but the reaction rate depended largely on the structure of the complex: the more positive E ° (Co II / Co III ) brings about the more catalytic activity. Steric hindrance of coordination of the substrate to the catalyst retards the reaction.

Cobalt schiff base complex promoted retro-claisen reaction of 1-(2-hydroxyphenyl)-3-phenyl-1,3-propanediones and flavone formation

Abstract Co(salpr) promotes the conversion of 1-(2-hydroxyphenyl)-3-phenyl-1,3-propanediones to retro-Claisen reaction products and flavones in methanol under oxygen. Base catalysis by Co(salpr)(OH) produced in situ is responsible for the reaction.

Cobalt-Schiff Base Complex Catalyzed Epoxidation of Olefins with Naoc1

Abstract Cobalt-Schiff base complexes are found to catalyze the oxidation of olefins with NaOCl to give mainly epoxides together with vic -dichloro- and α-chlorocarbonyl compounds. The reaction rate depended on the nature of the cobalt catalyst as well as the structure of the olefin substrate. Proposed mechanism involves rate determining homolytic cleavage of the Co-O bond in Co III (L)(OCl), a hypochloritocobalt complex intermediate, under the interaction with the substrate.

Field control of regioselectivity in CoIII(salpr)(OH) promoted oxygenation of 4-aryl-2,6-di-tert-butylphenols

Abstract In the Co III (salpr)(OH) catalyzed oxygenation of 4-aryl-2,6-di- tert -butylphenols, the position of dioxygen incorporation is completely controlled by the nature of solvent; dioxygen incorporation occurs only at ortho position in an uncoordinative solvent leading to the corresponding peroxy- o -quinolatocobalt(III)(salpr), whereas dioxygen is unexpectedly incorporated into para position in coordinative amines to give p -quinols quantitatively.

On the mechanism of a model quercetinase reaction using a cobalt Schiff-base complex

Cyclic voltammetry of a substrate anion–catalyst binary complex intermediate [CoIII(salen)L1][substrate = various flavonols (HL1); H2salen =N,N′-bis(salicylidene)ethane-1,2-diamine] in a model quercetinase reaction using [CoII(salen)] as catalyst has revealed that the intermediate partly undergoes ionic dissociation in dimethylformamide (dmf) to give L1 and [CoIII(salen)(dmf)2]+. Dioxygen is then incorporated into the flavonolate anion in a non-radical manner, which is promoted by the counter cobalt cation complex, finally to give [CoIII(salen)L2(dmf)](HL2= a depside product) which then forms L2 and [CoIII(salen)(dmf)2]+. The reaction rate was affected by the nature of the cation employed: [CoIII(salen)(dmf)2]+ is more effective than K+.

Cobalt-Schiff Base Complex Promoted Oxygenation of Alkynes

Abstract Cobalt-Schiff base complexes are found to catalyze the oxygenation of alkynes in alcoholic solvents at an elevated temperature resulting in incorporation of monooxygen and the alcohol into the triple bond without any carbon-carbon bond cleavage. Thus, phenylacetylene gives acetophenone ( 2 ), and mandelic ( 3 ) and phenylglyoxylic esters ( 4 ). The formation of 2 results from the following successive reactions: addition of Co(L 1 )(H) produced in situ to the triple bond giving 1-phenyl-1-ethenylcobalt followed by dioxygen insertion into the resulting Co-C bond to form an organoperoxocobalt(III) complex that undergoes readily homolytic cleavage of the peroxy bond. The esters 3 and 4 may result from dioxygen insertion into an another phenylacetylidocobalt complex intermediate, from which phenylglyoxal as the direct precursor of 3 would be derived.