Ruthenium-Catalyzed Isomerization of Allylic Alcohols: Oxidation State Determines Resistance Against Diene Inhibition

Abstract

The novel complex mer-[RuCl 3 (dmso)(phen)] (1) has been prepared and characterized by X-ray diffraction. The ruthenium center is in a distorted octahedral environment with the three chloride ions coordinated in a mer-fashion and an S-bonded dmso ligand trans to one of the phen nitrogen atoms. Electrochemical experiments show two reversible waves in acetonitrile solution, corresponding to the couples Ru III/II (0.11 V) and Ru IV/III (1.73 V). The analogous Ru II complex cis,cis-[RuCl 2 (dmso) 2 (phen)] (2) shows one reversible wave at 1.08 V, corresponding to the Ru III/II couple. Both complexes exhibit high catalytic activity in the isomerization of 3-buten-2-ol to butanone. The initial turnover frequency (TOF) for 1 in diglyme/water at 130°C is 295 h −1 with a firstorder k ini of 0.6 h −1 , while 2 reaches an initial TOF of 260 h −1 and a k ini of 0.5 h −1 . A cumulative turnover number (TON) of 1025 has been obtained with 1 as a catalyst precursor. The activity of 1 and 2 has been compared to that of in situ mixtures with both Ru III and Ru II precursors. All Ru II complexes are deactivated before 100% conversion has been attained.

Scope, mechanism and diene inhibition of isomerization of allylic alcohols to saturated ketones catalyzed by ruthenium(II)-cyclopentadienyl complexes

“…Yet, the most active catalyst precursor thus far for the overall hydration-isomerization reaction, [RuCl 3 (dmso)(phen)], is only moderately active in isomerization of allylic alcohols in the absence of dienes [11]. This prompted us to investigate alternative catalyst precursors with higher intrinsic isomerization activities.…”

“…The maximum conversion was obtained with a catalytic system formed by in situ mixing of a ruthenium(III) salt and 2,2 0 -bipyridine (bpy) or 1,10-phenanthroline (phen) [9,10]. A subsequent investigation in our group of possible deactivation routes for this type of catalyst [11] led to the discovery of a significantly improved system [12].…”

“…This hinders orientation of the allylic alcohol substrate in a suitable way to undergo b-hydrogen abstraction, thereby hampering isomerization catalysis. The RuCp-complexes behave differently from ruthenium-phenanthroline complexes [11]. With the latter type of complexes, significant amounts of MVK are formed and indirect evidence exists for the formation of ruthenium-allyl species.…”

The dual role of cis-[RuCl2(dmso)4] in the synthesis of new water-soluble Ru(II)–phosphane complexes and in the catalysis of redox isomerization of allylic alcohols in aqueous–organic biphasic systems

“…Based on integrated 1 H signal intensities of free and coordinated dmso as well as those of coordinated pta we concluded that the product was [RuCl2(dmso)2(pta)2] (2). The singlet 31 P signal refers to the phosphanes being in trans position each to the other (Scheme 2). This observation is in agreement with that substitution of chloride in this solvent is not favoured.…”

“…[29 ] In addition, pta has been successfully used for synthesis of anticancer Ru(II)-arene complexes [30] . Strikingly, 1 itself was only scarcely used [31,32] as catalyst in such reactions so its study was also accomplished.…”