title: Mechanistic behaviour of alkylcobaloximes and imino-oxime complexes related to vitamin B(12).
abstract: The ligand substitution reactions of complexes of the type trans-[(R)Co(Chel)S](+/0) with L, where chel = (DO)(DOH)pn = 2,2'-(1,3-diaminopropanebis(2-methyl-3-butanone)oxime), R = CH(3), L = imidazole, pyrazole, 1,2,4-triazole and 1-methylimidazole, and S = water and MeOH, and chel = (Hdmg)(2) = bis(dimethylglyoximate), R = CH(2)Cl, CH(2)Br, and CH(2)I, L = thiourea and pyridine, and S = water, were studied in detail as a function of temperature and pressure. The reported activation parameters (DeltaH, DeltaS and DeltaV) support the operation of a dissociative interchange (I(d)) mechanism. Complexes of the type trans-[RCo(Hdmg)(2)L] (R = CH(2)Cl, CH(2)Br, and CH(2)I; L = H(2)O and Py) were fully optimized at the B3LYP/LANL2DZp level, and the structural data support the mechanistic assignment based on the reported activation parameters. For the reaction of trans-[(CH(3))(2)Co((DO)(DOH)pn)] with acid, the activation parameters (DeltaH, DeltaS and DeltaV) were found to be 37 +/- 1 kJ mol(-1), -86 +/- 3 J mol(-1) K(-1) and -18.9 +/- 0.7 cm(3) mol(-1), respectively, and support a protonation mechanism.
authors.affiliation: Inorganic Chemistry, Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstr. 1, 91058 Erlangen, Germany.
authors.forename: Basam M
authors.initials: BM
authors.lastname: Alzoubi
authors.forename: Fanny
authors.initials: F
authors.lastname: Vidali
authors.forename: Ralph
authors.initials: R
authors.lastname: Puchta
authors.forename: Carlos
authors.initials: C
authors.lastname: Dücker-Benfer
authors.forename: Alessandro
authors.initials: A
authors.lastname: Felluga
authors.forename: Lucio
authors.initials: L
authors.lastname: Randaccio
authors.forename: Giovanni
authors.initials: G
authors.lastname: Tauzher
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D003198:Computer Simulation; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry*; D010091:Oximes / Q000737:chemistry*; D011789:Quantum Theory; D014805:Vitamin B 12 / Q000737:chemistry*
chemical_list: D007093:Imidazoles; D008024:Ligands; D009942:Organometallic Compounds; D010091:Oximes; D003035:Cobalt; D014805:Vitamin B 12