Hidetaka Takahashi

Organic syntheses by means of noble metal compounds : XXXIII. Carbonylation of azobenzene-palladium chloride complexes☆

Abstract Palladium chloride complexes of symmetrically and asymmetrically substituted azobenzenes have been prepared. The carbonylation of the complexes in protic solvents affords 2-aryl-3-indazolinones in a high yield. It was found by degradative work of the carbonylated products that when the asymmetrically substituted azobenzene was treated with palladium chloride, a palladiumcarbon σ-bond is formed preferentially with the benzene ring having an electron donating group.

Carbonylation of aryl- and vinyl-tellurium compounds with carbon monoxide in the presence of palladium(II) salts

Abstract Aryl- and vinyl-tellurium(II or IV) compounds react with carbon monoxide (CO) in suitable organic solvents to give the corresponding carboylic acids in moderate to quantitative yields in the presence of a stoichiometric amount of a palladium(II) salt. Treatment of ( Z )-styrylphenyl telluride with atmospheric pressure of CO at room temperature in the presence of palladium(II) chloride or lithium chloropalladate(II) affords predominantly ( E )-cinnamic acid, while in the presence of palladium(II) acetate similar reaction gives the ( Z )-acid highly selectively. Under higher CO pressures (5–50 atm), however, the ( Z )-acid becomes the major product, even when palladium(II) chloride is used. The following pathways are proposed for this carbonylation: (1) in the first step organotellurium compounds form the monomeric and/or dimeric palladium complexes such as [(R 2 Te)PdCl 2 ] 2 and/or (R 2 Te) 2 PdCl 2 (R = aryl, vinyl), then (2) the migration of R moiety from tellurium to palladium (transmetallation) occurs to afford the reactive aryl- or alkenyl-palladium compounds, and (3) the compounds react with CO to give the corresponding acylpalladium compounds, after alkaline hydrolysis, the carboxylic acids are formed. The presence of an ionic carbene-like organopalladium complex is proposed for the formation of the ( Z )-acid from ( Z )-telluride.

A new route to seleno and telluro esters by Co2(CO)8-mediated and -catalyzed carbonylation of diaryl diselenides and ditellurides with carbon monoxide

Abstract Diaryl Diselenides react with CO(5–100 atm) at 100-200°C during 1–4 h in the presence of Co2(CO)8 to give the corresponding aryl selenocarboxylic acid esters in 21–96% yields. Similar treatment of diphenyl ditelluride gives the telluro analogues in lower yields. Didodecyl diselenide also gives the corresponding seleno ester, while esters were not produced from dibenzyl diselenide and didodecyl ditelluride. Under milder conditions (10 atm CO/125°C/1 h) the reactivity of (PhM)2 (M  S, Se, Te) for the corresponding esters was found to be in the order Te > Se > S. The carbonylation of diaryl diselenides proceeds catalytically in Co2(CO)8 in the presence of triphenylphosphine. It was shown unambiguously that benzoylcobalt tetracarbonyl, which is one of the possible intermediates when aryl is phenyl, reacts smoothly with diphenyl diselenide or ditellutide to give the corresponding ester, phenyl selenobenzoate or tellurobenzoate, respectively, in a good yield.

Co2(CO)8-mediated and -catalyzed carbonylation of diaryl diselenides and ditellurides to seleno and telluro esters

Abstract Diaryl diselenides and ditellurides react with CO (5–100 atm) at 100–200°C in the presence of Co2(CO)8 to give the corresponding seleno and telluro esters in 21–96% yield. The carbonylation proceeds catalytically in CO2(CO)8 in the presence of triphenylphosphine. It was shown unambiguously that benzoylcobalt tetracarbonyl, which is one of possible intermediates, reacts with diphenyl diselenide or ditelluride to give phenyl selenobenzoate or tellurobenzoate, respectively.

Styryl coupling vs. styryl acetate formation in reactions of styryl tellurides with palladium(II) salts

Abstract In sharp contrast to the expected formation of a telluride-palladium complex, the treatment of either ( E , E )- and ( Z , Z )-distyryl tellurides ( 1 and 2 ) or ( E )- and ( Z )-styryl phenyl tellurides ( 5 and 6 ) with Li 2 PdCl 4 in acetonitrile at 25°C results in the formation of stereoisomeric 1,4-diphenylbuta-1,3-dienes, whereas the treatment of 1 and 2 with Pd(OAc) 2 produces styryl acetates solely or mainly.

The palladium(II)/carbon monoxide-mediated biaryl formation from aryltellurium trihalides

Abstract Treatment of aryltellurium trihalides (ArTeX 3 : Ar = Ph, 4-BrC 6 H 4 , 4-MeC 6 H 4 , 4-MeOC 6 H 4 , 4-BuOC 6 H 4 , 4-PhOC 6 H 4 , 2-naphthyl; X = Cl, Br) with a palladium(II) salt in acetonitrile at 25°C affords, in good yields (29–78%), the corresponding biaryls (ArAr) either in the atmosphere or under 1 atm CO. The presence of CO accelerates this aromatic coupling significantly to produce some active palladium carbonyl species, the formation of which was confirmed by IR spectroscopy of Li 2 PdCl 4 in acetonitrile solution under CO; a strong sharp absorption and a weaker sharp one appeared at 2140 and 1908 cm −1 , respectively, attributable to the ν(CO) of the (PdCO) species. Treatment with alkali after reaction was essential to producing the biaryls.

Sodium benzenetellurolate-catalysed selective reduction of aromatic nitro compounds to azoxy compounds

Treatment of aromatic nitro compounds with sodium borohydride in alkaline ethanol in the presence of a catalytic amount of diphenyl ditelluride at 25 °C affords the corresponding azoxy compounds selectively in high yields, in situ generated sodium benzenetellurolate being the active species which produces the intermediate aromatic nitroso compounds.