title: Reductions by titanium(II) as catalyzed by titanium(IV).
abstract: The cobalt(III) complexes, [(NH3)5CoBr]2+ and [(NH3)5CoI]2+ are reduced by Ti(II) solutions containing Ti(IV), generating nearly linear (zero-order) profiles that become curved only during the last few percent of reaction. Other Co(III)-Ti(II) systems exhibit the usual exponential traces with rates proportional to [Co(III)]. Observed kinetics of the biphasic catalyzed Ti(II)-Co(III)Br and Ti(II)-Co(III)I reactions support the reaction sequence: [Ti(II)(H20)n]2+ + [Ti(IV)F5]- (k1)<==>(k -1) [Ti(II)(H2O)(n-1)]2+ + [(H2O)Ti(IV)F5]-, [Ti(II)(H2O)(n-1)]2+ + Co(III) (k2)--> Ti(III) + Co(II) with rates determined mainly by the slow Ti(IV)-Ti(II) ligand exchange (k1 = 9 x 10(-3) M(-1) s(-1) at 22 degrees C). Computer simulations of the catalyzed Ti(II)-Co(III) reaction in perchlorate-triflate media yield relative rates for reduction by the proposed active [Ti(II)(H2O)(n-1)]2+ intermediate; k(Br)/k(I) = 8.
authors.affiliation: Department of Chemistry, Kent State University, Kent, Ohio 44242, USA.
authors.forename: Ritam
authors.initials: R
authors.lastname: Mukherjee
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Yang
authors.forename: Edwin S
authors.initials: ES
authors.lastname: Gould
mesh_terms: D001966:Bromine / Q000737:chemistry*; D002384:Catalysis; D002621:Chemistry / Q000379:methods*; D003035:Cobalt / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008956:Models, Chemical; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*
chemical_list: D008024:Ligands; D003035:Cobalt; D014025:Titanium; D001966:Bromine