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

Abstract

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.