- Effect of phosphine and phosphine sulfide ligands on the cobalt-catalyzed reductive coupling of 2-iodobutane with n-butyl acrylate
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Tris[2-(diphenylphosphino)ethyl]phosphine disulfide (pp3S2), in which two terminal phosphino groups are selectively sulfidated, was prepared by utilizing the selective sulfidation reaction of [PdI(pp3)]I. Co(II) complexes with bidentate, tridentate and tetradentate phosphines and pp3S2 were prepared from anhydrous CoI2. X-ray crystal analyses revealed that the reaction of CoI2 with 1 equivalent of 1,2-bis(diphen-ylphosphino) ethane (p2) gave rise to partial oxidation of p2 to give the dicationic octahedral [Co(p2O2)2(CH 3CN)2]2+ (p2O2 = p 2 dioxide) and dianionic p2O-bridged tetrahedral dinuclear [CoI3(p2-O)CoI3]2 (p2O = p2 monooxide) complexes, while the reaction with 2 equivalents of p2 gave the square-pyramidal [CoI(p2)2] + complex. The catalytic activity for the Co-catalyzed coupling reaction of 2-iodobutane with n-butyl acrylate was compared using multidentate phosphines and phosphine sulfides as ligands, and the efficiency of the phosphine sulfides was shown. The tendency for multidentate phosphine to deactivate the Co-catalysis can substantiate an oxidative addition driven mechanism in which the multidentate ligand should interfere with the formation of the alkyl halide Co(III) adduct and subsequent coordination of an alkene.
- Aizawa, Sen-Ichi,Fukumoto, Koichi,Kawamoto, Tatsuya
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- Cobalt-catalyzed reductive coupling of saturated alkyl halides with activated alkenes
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An efficient cobalt-catalyzed reductive coupling reaction of alkyl halides with electron-withdrawing alkenes (CH2=CR1EWG, EWG = electron-withdrawing group) in the presence of water and zinc powder in acetonitrile to give the corresponding Michael-type addition product (RCH 2CR1EWG) was described. The methodology is versatile such that unactivated primary, secondary, and tertiary alkyl bromides and iodides and various conjugated alkenes including acrylates, acrylonitrile, methyl vinyl ketone, and vinyl sulfone all successfully participate in this coupling reaction. For the alkyl halides used in the reaction, the iodides generally gave heller yields compared to those of the corresponding bromides. It is a unique method employing CoI2dppe, zinc, and alkyl halides, affording conjugate addition products in high yields. Mechanistically, the reaction appears to follow an oxidative addition driven route rather than the previously reported radical route.
- Shukla, Paritosh,Hsu, Yun-Chu,Cheng, Chien-Hong
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p. 655 - 658
(2007/10/03)
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