title: On the mechanism of Re(I)-carboxylate bond cleavage by perchloric acid: a kinetic and spectroscopic study.
abstract: We have studied the reaction between pz-CO(2)-Re(CO)(3)(bpy) and perchloric acid in acetonitrile by following the UV-vis and IR spectral changes in the reaction mixture. A fast equilibrium was found to be established between solvated protons, pz-CO(2)-Re(CO)(3)(bpy), and the protonated intermediate [pz-C(OH)O-Re(CO)(3)(bpy)](+) which finally yields pz-COOH and Re(CO)(3)(bpy)(CH(3)CN)(+) as reaction products. This intermediate has been characterized by UV-vis and IR spectroscopies and by DFT calculations. The fully optimized DFT/CPCM structures for pz-CO(2)-Re(CO)(3)(bpy) and [pz-C(OH)O-Re(CO)(3)(bpy)](+) were compared with the X-ray structure of pz-CO(2)-Re(CO)(3)(bpy). The structural parameters associated with the carboxyl group in the protonated intermediate are between those of pz-CO(2)-Re(CO)(3)(bpy) and pz-COOH. Multivariate curve resolution methods were employed to obtain the spectrum of the protonated intermediate and the concentration profiles from the full matrix of time-resolved UV-vis spectra. The proposed mechanism was numerically simulated by using Runge-Kutta methods. Model parameters were estimated by nonlinear regression fitting of the concentration profiles, yielding values of log(K) = 4.9 ± 0.3 and k = 0.16 ± 0.03 min(-1) for the formation equilibrium constant and the decay rate constant of the protonated intermediate, respectively.
authors.affiliation: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Casilla de Correo 16, Sucursal 4, (1900) La Plata, Argentina.
authors.forename: Ulises N
authors.initials: UN
authors.lastname: Fagioli
authors.forename: Fernando S
authors.initials: FS
authors.lastname: García Einschlag
authors.forename: Carlos J
authors.initials: CJ
authors.lastname: Cobos
authors.forename: Gustavo T
authors.initials: GT
authors.lastname: Ruiz
authors.forename: Mario R
authors.initials: MR
authors.lastname: Féliz
authors.forename: Ezequiel
authors.initials: E
authors.lastname: Wolcan
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D007700:Kinetics; D009942:Organometallic Compounds / Q000737:chemistry; D010472:Perchlorates / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002264:Carboxylic Acids; D009942:Organometallic Compounds; D010472:Perchlorates; D012211:Rhenium