title: Second-sphere interaction of anions with a weakly binding metal complex host: probing the effect of counteranions.
abstract: The reaction of [Re(OTf)(CO)5] with N-methylimidazole (MeIm) afforded [Re(CO)3(MeIm)3]OTf (1). The reactions of 1 with KPF6, NaBPh4 and NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl) afforded [Re(CO)3(MeIm)3]PF6 (2) [Re(CO)3(MeIm)3]BPh4 (3) and [Re(CO)3(MeIm)3]BAr'4 (4) respectively. An analogous reaction using N-phenylimidazole (PhIm) yielded [Re(CO)3(PhIm)3]BAr'4 (7). These new compounds were characterized by IR and NMR, and the structures of 1 and 2 were determined by X-ray diffraction. Compounds [Re(CO)3(MeIm)3]2[PtCl6] (5), [Re(CO)3(MeIm)3][HSO4] (6), [Re(CO)3(PhIm)3][Br] (8) and [Re(CO)3(PhIm)3][NO3] (9) were crystallized from equimolar mixtures of either 4 or 7 and the tetrabutylammonium salt of the corresponding anion, and their structures were determined by X-ray diffraction. The solution behavior of 1-4, 7 toward several anions was studied spectroscopically, including the quantitative determination of binding constants by 1H NMR. The cationic tris(imidazole)complexes are stable against imidazole-by-anion substitution, and the main hydrogen bonding interactions involve the imidazole NC(H)N groups. The binding constants for compounds 1-4 with several external anions follow the order 1<2<3<4, indicating that the strength of the cationic complex-counteranion interaction follows the order OTf(-) > PF6(-) > BPh4(-) > BAr'4(-).
authors.affiliation: Departamento de Química Orgánica e Inorgánica -IUQOEM, Facultad de Química, Universidad de Oviedo-CSIC, 33006 Oviedo, Spain. japm@uniovi.es
authors.forename: Julio
authors.initials: J
authors.lastname: Pérez
authors.forename: Lucía
authors.initials: L
authors.lastname: Riera
authors.forename: Laura
authors.initials: L
authors.lastname: Ion
authors.forename: Víctor
authors.initials: V
authors.lastname: Riera
authors.forename: Kirsty M
authors.initials: KM
authors.lastname: Anderson
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Steed
authors.forename: Daniel
authors.initials: D
authors.lastname: Miguel