A kinetic and thermodynamic study of the unexpected comproportionation reaction between cis-[OsVIIIO4(OH)2]2− and trans-[OsVIO2(OH)4]2− to form a postulated [OsVIIO3(OH)3]2− complex anion

Abstract

A kinetic study of [OsO(4)] reduction by aliphatic alcohols (MeOH and EtOH) was performed in a 2.0 M NaOH matrix at 298.1 K. The rate model that best fitted the UV-VIS data supports a one-step, two electron reduction of Os(VIII) (present as both the [Os(VIII)O(4)(OH)](-) and cis-[Os(VIII)O(4)(OH)(2)](2-) species in a ratio of 0.34:0.66) to form the trans-[Os(VI)O(2)(OH)(4)](2-) species. The formed trans-[Os(VI)O(2)(OH)(4)](2-) species subsequently reacts relatively rapidly with the cis-[Os(VIII)O(4)(OH)(2)](2-) complex anion to form a postulated [Os(VII)O(3)(OH)(3)](2-) species according to: cis-[Os(VIII)O(4)(OH)(2)](2-) + trans-[Os(VI)O(2)(OH)(4)](2-) (k+2) <−> (k-2) 2[Os(VII)O(3)(OH)(3)](2-). The calculated forward, k(+2), and reverse, k(-2), reaction rate constants of this comproportionation reaction are 620.9 ± 14.6 M(-1) s(-1) and 65.7 ± 1.2 M(-1) s(-1) respectively. Interestingly, it was found that the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion does not oxidize MeOH or EtOH. Furthermore, the reduction of Os(VIII) with MeOH or EtOH is first order with respect to the aliphatic alcohol concentration. In order to corroborate the formation of the [Os(VII)O(3)(OH)(3)](2-) species predicted with the rate model simulations, several Os(VIII)/Os(VI) mole fraction and mole ratio titrations were conducted in a 2.0 M NaOH matrix at 298.1 K under equilibrium conditions. These titrations confirmed that the cis-[Os(VIII)O(4)(OH)(2)](2-) and trans-[Os(VI)O(2)(OH)(4)](2-) species react in a 1:1 ratio with a calculated equilibrium constant, K(COM), of 9.3 ± 0.4. The ratio of rate constants k(+2) and k(-2) agrees quantitatively with K(COM), satisfying the principle of detailed balance. In addition, for the first time, the molar extinction coefficient spectrum of the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion is reported.

Methode der kontinuierlichen Variation: Verwendung von Job‐Plots zur Untersuchung molekularer Assoziationen in der metallorganischen Chemie

“…(15)] durch Gerber und Mitarbeiter [38] Schwefeldioxid diente zur Modellierung der CO-Komplexierung an Rhodium-und Iridium-Hydroformylierungskatalysatoren. (15)] durch Gerber und Mitarbeiter [38] Schwefeldioxid diente zur Modellierung der CO-Komplexierung an Rhodium-und Iridium-Hydroformylierungskatalysatoren.…”

“…Eine Untersuchung der Oxidation von Alkoholen mit OsO 4 in Gegenwart von Natriumhydroxid [Gl. (15)] durch Gerber und Mitarbeiter [38] Schwefeldioxid diente zur Modellierung der CO-Komplexierung an Rhodium-und Iridium-Hydroformylierungskatalysatoren. [41] Salaita et al [42] verwendeten die MCV, um zu zeigen, dass Schwefeldioxid und ein Rhodium(I)-Carbonyl-Komplex in kurzen Reaktionszeiten einen beobachtbaren 1:1-Komplex ergaben [Gl.…”

“…In einer der frühesten und sorgfältigsten Untersuchungen von Ensembles mittels MCV beobachteten Weingarten und Van Wazer [51] gemischte Alkoxidamidkomplexe [Ti(OR) m -(NR' 2 ) n ] mittels 1 H-NMR-Spektroskopie [Gl. (38)]. [52] entwickelten mathematischen Verfahrens eine wegweisende Vorgehensweise dar.…”

Kinetic detection of osmium(VI) ester intermediates during the OsO4‐mediated aqueous dihydroxylation of chloroethylenes

“…A full kinetic analysis showed that this highly reactive intermediate is indeed present in low concentrations, which precludes structural characterization, but it is definitely the species that is in the center of the catalytic activity. A formal kinetic scheme is proposed to interpret the kinetic findings with the full consideration of the various labile equilibria of osmium(VIII) species in aqueous solution …”

“…A formal kinetic scheme is proposed to interpret the kinetic findings with the full consideration of the various labile equilibria of osmium(VIII) species in aqueous solution. [29][30][31][32] 2 | EXPERIMENTAL…”