title: Mechanism of reaction of alkyl radicals with (Ni(II)L)2+ complexes in aqueous solutions.
abstract: The reactions of methyl radicals, *CH3, with the macrocyclic complexes Ni(II)L(1-5) (L(1-5) = cyclam derivatives, vide infra) and Ni(II)edta in aqueous solutions were studied. Methyl radicals react with all these nickel complexes, forming intermediates with Ni(III)-C sigma-bonds. The L(m)Ni(III)-CH3 complexes are formed in equilibria processes with relatively fast forward rate constants of k(f) > 1 x 10(8) M(-1) s(-1) (except in the case of NiL2-trans I cyclam, where the reaction is slower). In all cases the decomposition of the transient complexes occurs via the homolytic cleavage of the metal-carbon sigma-bond. When the homolysis is relatively slow, an isomerisation process of the transient is also observed with the exception of NiL2, where no isomerisation was observed. The results suggest that the strength of the Ni(III)-CH3sigma-bond is mainly affected by steric hindrance.
authors: Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors: Tamar
authors: T
authors: Kurzion-Zilbermann
authors: Alexandra
authors: A
authors: Masarwa
authors: Eric
authors: E
authors: Maimon
authors: Haim
authors: H
authors: Cohen
authors: Dan
authors: D
authors: Meyerstein
mesh_terms: D000106:Acetate-CoA Ligase / Q000737:chemistry; D000588:Amines / Q000737:chemistry; D006571:Heterocyclic Compounds / Q000737:chemistry*; D007700:Kinetics; D047028:Macrocyclic Compounds / Q000737:chemistry; D008697:Methane / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010088:Oxidoreductases / Q000737:chemistry; D012996:Solutions; D014867:Water / Q000737:chemistry*
chemical_list: D000588:Amines; D006571:Heterocyclic Compounds; D047028:Macrocyclic Compounds; D009942:Organometallic Compounds; D012996:Solutions; D014867:Water; C024560:cyclam; D009532:Nickel; D010088:Oxidoreductases; C021572:methyl coenzyme M reductase; D000106:Acetate-CoA Ligase; D008697:Methane