title: Coordinated aqua vs methanol substitution kinetics in fac-Re(I) tricarbonyl tropolonato complexes.
abstract: Water-soluble fac-[Re(CO)(3)(L,L'-Bid)(X)] (L,L'-Bid = tropolonato, X = H(2)O, methanol) complexes have been synthesized, and the aqua and methanol substitution reactions were investigated in water (pH range 6.3-10.0) and methanol, respectively, and compared. Thiocyanate ions were used as monodentate entering ligand. The complexes were characterized by UV-vis, IR, and NMR spectroscopy. The crystal structures of the complexes [NEt(4)] fac-[Re(Trop)(CO)(3)(H(2)O)].NO(3).H(2)O (reactant) and fac-[Re(CO)(3)(Trop)(Py)], a substitution product, are reported. Overall it was found that the aqua substitution of fac-[Re(CO)(3)(Trop)(H(2)O)] is about 10 times faster than the methanol substitution reaction for fac-[Re(CO)(3)(Trop)(MeOH)], with forward and reverse rate and stability constants [k(1) (M(-1) s(-1)), k(-1) (s(-1)), K(1), (M(-1))] for thiocyanate as monodentate entering ligand as follows: fac-[Re(CO)(3)(Trop)(H(2)O)] = 2.54 ± 0.03, 0.0077 ± 0.0005, 330 ± 22/207 ± 14 and fac-[Re(CO)(3)(Trop)(MeOH)] = 0.268 ± 0.002, 0.0044 ± 0.0002, (61 ± 3)/(52 ± 4). The activation parameters [ΔH(‡)(k1) (kJ mol(-1)), ΔS(‡)(k1) (J K(-1) mol(-1))] for the aqua and methanol complex respectively are 56.1 ± 0.7, -49 ± 2 and 64 ± 1, -43 ± 5.
authors.affiliation: Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein, 9300, South Africa.
authors.forename: Marietjie
authors.initials: M
authors.lastname: Schutte
authors.forename: Andreas
authors.initials: A
authors.lastname: Roodt
authors.forename: Hendrik G
authors.initials: HG
authors.lastname: Visser
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol / Q000737:chemistry*; D008958:Models, Molecular; D012211:Rhenium / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D008024:Ligands; D014867:Water; D012211:Rhenium; D000432:Methanol