title: Reactivity of the organometallic fac-[(CO)3ReI(H2O)3]+ aquaion. Kinetic and thermodynamic properties of H2O substitution.
abstract: The water exchange process on [(CO)(3)Re(H(2)O)(3)](+) (1) was kinetically investigated by (17)O NMR. The acidity dependence of the observed rate constant k(obs) was analyzed with a two pathways model in which k(ex) (k(ex)(298) = (6.3 +/- 0.1) x 10(-3) s(-1)) and k(OH) (k(OH)(298)= 27 +/- 1 s(-1)) denote the water exchange rate constants on 1 and on the monohydroxo species [(CO)(3)Re(I)(H(2)O)(2)(OH)], respectively. The kinetic contribution of the basic form was proved to be significant only at [H(+)] < 3 x 10(-3) M. Above this limiting [H(+)] concentration, kinetic investigations can be unambiguously conducted on the triaqua cation (1). The variable temperature study has led to the determination of the activation parameters Delta H(++)(ex) = 90 +/- 3 kJ mol(-1), Delta S(++)(ex) = +14 +/- 10 J K(-1) mol(-1), the latter being indicative of a dissociative activation mode for the water exchange process. To support this assumption, water substitution reaction on 1 has been followed by (17)O/(1)H/(13)C/(19)F NMR with ligands of various nucleophilicities (TFA, Br(-), CH(3)CN, Hbipy(+), Hphen(+), DMS, TU). With unidentate ligands, except Br(-), the mono-, bi-, and tricomplexes were formed by water substitution. With bidentate ligands, bipy and phen, the chelate complexes [(CO)(3)Re(H(2)O)(bipy)]CF(3)SO(3) (2) and [(CO)(3)Re(H(2)O)(phen)](NO(3))(0.5)(CF(3)SO(3))(0.5).H(2)O (3) were isolated and X-ray characterized. For each ligand, the calculated interchange rate constants k'(i) (2.9 x 10(-3) (TFA) < k'(I) < 41.5 x 10(-3) (TU) s(-1)) were found in the same order as the water exchange rate constant k(ex), the S-donor ligands being slightly more reactive. This result is indicative of I(d) mechanism for water exchange and complex formation, since larger variations of k'(i) are expected for an associatively activated mechanism.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Institut de Chimie Moléculaire et Biologique, BCH, CH-1015 Lausanne, Switzerland.
authors.forename: Bernadette
authors.initials: B
authors.lastname: Salignac
authors.forename: Pascal V
authors.initials: PV
authors.lastname: Grundler
authors.forename: Sonia
authors.initials: S
authors.lastname: Cayemittes
authors.forename: Urban
authors.initials: U
authors.lastname: Frey
authors.forename: Rosario
authors.initials: R
authors.lastname: Scopelliti
authors.forename: André E
authors.initials: AE
authors.lastname: Merbach
authors.forename: Roman
authors.initials: R
authors.lastname: Hedinger
authors.forename: Kaspar
authors.initials: K
authors.lastname: Hegetschweiler
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
authors.forename: Ulrich
authors.initials: U
authors.lastname: Prinz
authors.forename: Gerhard
authors.initials: G
authors.lastname: Raabe
authors.forename: Ulrich
authors.initials: U
authors.lastname: Kölle
authors.forename: Syd
authors.initials: S
authors.lastname: Hall