Allylic Oxidation of Cyclohexene and Indene by cis-[Ru^IV(bpy)₂(py)(O)]²⁺

Abstract

The kinetics of oxidation of cyclohexene, cyclohexen-1-ol, and indene by cis-[Ru IV (bpy) 2 (py)(O)] 2+ (bpy ) 2,2′-bipyridine and py ) pyridine) have been studied in CH 3 CN. The reactions are first-order in both Ru IV )O 2+ and substrate in an initial, rapid stage in which Ru(IV) is reduced to Ru(III). The rate constants are 0.16 ( 0.01, 1.10 ( 0.02, and 5.74 ( 0.74 M -1 s -1 for cyclohexene, cyclohexen-1-ol, and indene, respectively. A k(R,R′-H 4 )/k(R,R′-D 4 ) kinetic isotope effect of 21 ( 1 is observed for the oxidation of cyclohexene. At a 2:1 ratio of Ru IV dO 2+ to olefin, the reactions of Ru IV dO 2+ with either cyclohexene or indene give Ru II -NCCH 3 2+ and the 4-electron ketone products, 2-cyclohexen-1-one and indenone, respectively, as identified by GC-MS. As the ratio of cyclohexene to Ru IV dO 2+ is increased, cyclohexen-1-ol becomes an increasingly competitive product. The mechanisms of these reactions are highly complex. They involve two distinct stages and the formation and subsequent reactions of Ru III -substrate bound intermediates.

Synthesis, Structure and Spectral, and Electrochemical Properties of New Mononuclear Ruthenium(III) Complexes of Tris[(benzimidazol‐2‐yl)methyl]amine: Role of Steric Hindrance in Tuning the Catalytic Oxidation Activity

“…The oxidation of all the organic substrates was carried out in methanol as the solvent at room temperature under both aerobic and anaerobic conditions over 12 h. In the presence of TBHP complex 1 effects the allylic oxidation of cyclohexene to provide 2-cyclohexene-1-ol (A, 26.4 %) and 2-cyclohexene-1-one (A, 0.8 %), which is the further oxidized product of the former involving a dehydrogenation pathway [16,46] catalyzed by 1. In addition, the epoxidation product 1,2-epoxycyclohexene (E), obtained in yields lower than the allylic oxidation products, undergoes nucleophilic attack by hydroxide and methoxide ions in methanol solution to give the cleavage compounds cyclohexane-1,2-diol (E, traces) and 2-methoxy-1-cyclohexanol (E, 11.3 %), respectively.…”

“…Masuda et al have suggested that the epoxidation activity of Ru(tpa-based) complexes involves the abstraction of the allylic proton by the high-valent Ru V =O species generated by PhIO, [16,41] followed by a rapid in-caged one-electron transfer before the alkenyl radical intermediate R and Ru V -OH diffuse into solution. [46][47][48] Meyer et al have argued that the Ru IV =O species prefers an attack on the allylic C-H rather than on the olefin double Scheme 3. Proposed mechanism for allylic oxidation using TBHP.…”

“…Proposed mechanism for epoxidation using TBHP. bond, [46] [46] to yield a carbo cation, which collapses to a Ru III species upon attack of the chloride ion (or solvent molecule) to yield the epoxide and regenerate the original complex (Scheme 4). Further, the strong σ-bonding and weakly π-accepting nature of bulky benzimidazole moieties in 1 and 2 facilitate the heterolysis of the O-O bond in the reaction intermediate [Cl(ntb)Ru-O-O-tBu] + .…”

Electrocatalytic oxidation of alcohols by a [Ru(tpy)(phen)(OH2)]2+-modified electrode

“…The oxo ruthenium(IV) complexes have received a lot of attention in view of their potential as catalysts for the homogeneous oxidation of alcohols and C-H bonds adjacent to unsaturated bonds, and for DNA cleavage [1][2][3][4][5][6][7][8][9][10]. One of the most studied is [Ru IV (tpy)(bpy)(O)] 2+ , where bpy is 2,2 0 -bipyridine and tpy is 2,2 0 :6 0 ,2 00 -terpyridine.…”

Hydrocarbon Oxidation by β‐Halogenated Dioxoruthenium(VI) Porphyrin Complexes: Effect of Reduction Potential (RuVI/V) and CH Bond‐Dissociation Energy on Rate Constants

“…Meyer and co-workers proposed a hydrogen-atom abstraction mechanism for oxidation of CÀH bonds by cis-[(bpy) 2 (py)-Ru IV O] 2 + ; [50] We suggested a hydrogen-atom abstraction mechanism for CÀH bond oxidation by [Ru…”