Cobalt-Catalyzed Reductive Coupling Research Articles

Cobalt-Catalyzed Reductive Coupling of Nitroarenes and Formaldehyde to N,N'-Diarylethane-1,2-diamines

Cobalt-Catalyzed Reductive Coupling of Nitroarenes and Formaldehyde to N,N'-Diarylethane-1,2-diamines

Cobalt-Catalyzed Reductive Coupling of Nitroarenes with Alcohols

Key words reductive imination - reductive amination - cobalt catalysis - carbon nanotubes - nitroarenes - alcohols

Effect of phosphine and phosphine sulfide ligands on the cobalt-catalyzed reductive coupling of 2-iodobutane with n-butyl acrylate

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(diphenylphosphino)ethane (p2) gave rise to partial oxidation of p2 to give the dicationic octahedral [Co(p2O2)2(CH3CN)2]2+ (p2O2=p2 dioxide) and dianionic p2O-bridged tetrahedral dinuclear [CoI3(p2O)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.

Synthesis of trans‐Disubstituted Alkenes by Cobalt‐Catalyzed Reductive Coupling of Terminal Alkynes with Activated Alkenes

A cobalt-catalyzed reductive coupling of terminal alkynes, RC≡CH, with activated alkenes, R'CH=CH(2), in the presence of zinc and water to give functionalized trans-disubstituted alkenes, RCH=CHCH(2)CH(2)R', is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl(2)/P(OMe)(3)/Zn catalyst system to afford 1,2-trans-disubstituted alkenes with high regio- and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl(2)/P(OPh)(3)/Zn system providing a mixture of 1,2-trans- and 1,1-disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3-enynes and acetylene gas with alkenes. Furthermore, a phosphine-free cobalt-catalyzed reductive coupling of terminal alkynes with enones, affording 1,2-trans-disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air-stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.

Cobalt-Catalyzed Regioselective Synthesis of Pyrrolidinone Derivatives by Reductive Coupling of Nitriles and Acrylamides

A convenient and highly regioselective method for the synthesis of 5-methylenepyrrolidinone derivatives from various nitriles and acrylamides via a cobalt-catalyzed reductive coupling reaction is described. A possible mechanism that involves the formation of a cobaltaazacyclopentene intermediate from nitrile and acrylamide, protonation, keto-amide cyclization, and dehydration is proposed.

Cobalt-Catalyzed Reductive Coupling of Activated Alkenes with Alkynes

Cobalt complex/Zn systems effectively catalyze the reductive coupling of activated alkenes with alkynes in the presence of water to give substituted alkenes with very high regio- and stereoselectivity in excellent yields. While the intermolecular reaction of acrylates, acrylonitriles, and vinyl sulfones with alkynes takes place in the presence of CoI2(PPh3)2/Zn, the reaction of enones and enals with alkynes requires the use of the CoI2(dppe)/Zn/ZnI2 system. The intramolecular reductive coupling of activated alkenes (enones, enals, acrylates, and acrylonitriles) with alkynes also works efficiently. Further a variety of cyclic lactones and lactams were prepared using this methodology. Possible mechanistic pathways are proposed based on a deuterium-labeling experiment carried out in the presence of D2O.

Cobalt-Catalyzed Reductive Coupling of Activated Alkenes with Alkynes

Cobalt complex/Zn systems effectively catalyze the reductive coupling of activated alkenes with alkynes in the presence of water to give substituted alkenes with very high regio- and stereoselectivity in excellent yields. While the intermolecular reaction of acrylates, acrylonitriles, and vinyl sulfones with alkynes takes place in the presence of CoI2(PPh3)2/Zn, the reaction of enones and enals with alkynes requires the use of the CoI2(dppe)/Zn/ZnI2 system. The intramolecular reductive coupling of activated alkenes (enones, enals, acrylates, and acrylonitriles) with alkynes also works efficiently. Further a variety of cyclic lactones and lactams were prepared using this methodology. Possible mechanistic pathways are proposed based on a deuterium-labeling experiment carried out in the presence of D2O.

Cobalt-Catalyzed Reductive Coupling of Saturated Alkyl Halides with Activated Alkenes

[reaction: see text] An efficient cobalt-catalyzed reductive coupling reaction of alkyl halides with electron-withdrawing alkenes (CH(2)=CR(1)EWG, EWG = electron-withdrawing group) in the presence of water and zinc powder in acetonitrile to give the corresponding Michael-type addition product (RCH(2)CR(1)EWG) 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 better yields compared to those of the corresponding bromides. It is a unique method employing CoI(2)dppe, 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.