Why Are Olefins Oxidized by RuO₄under Cleavage of the Carbon−Carbon Bond whereas Oxidation by OsO₄Yieldscis-Diols?

Abstract

Quantum chemical calculations using gradient-corrected (B3LYP) density functional theory have been carried out to investigate the mechanism of the oxidative cleavage of alkenes by ruthenium tetraoxide. The initial reaction of the tetraoxide with the olefin occurs via a [3+2] cycloaddition as in the case of osmium tetraoxide. The results clearly show that the bond cleavage does not take place at the primary adduct, but much later in the reaction path. After the formation of the ruthenium(VI)dioxo-2,5-dioxolane, the reaction proceeds with the addition of a second olefin to yield ruthenium(IV)-bis(2,5-dioxolane), which in turn becomes oxidized first to rutheniumoxo(VI)-bis(2,5-dioxolane) 6(Ru) and then to ruthenium(VIII)-dioxo-bis(2,5-dioxolane) 7(Ru). Only in complexes containing the metal center in the formal oxidation state +VIII are low activation barriers for C-C bond cleavage and exothermic formation of carbonyl compounds as products calculated. The lowest activation barrier, DeltaH(++) = 2.5 kcal/mol, is calculated for the C-C bond breaking reaction of 7(Ru) which is predicted as the pivotal intermediate of the oxidation reaction. The calculations of the oxidation reaction with OsO(4) show that those reactions where the oxidation state of the metal increases have larger activation barriers for M = Ru than for M = Os, while reactions which reduce the oxidation state have a lower activation barrier for ruthenium compounds. Also, reactions which increase the oxidation state of the metal are in the case of M = Os more exothermic than for M = Ru. In this work, all important points of the potential energy surface (PES) are reported, and the complete catalytic cycle for the oxidative cleavage of olefins by ruthenium tetraoxide is presented.

A Highly Efficient Procedure for Ruthenium Tetroxide Catalyzed Oxidative Cyclizations of 1,5‐Dienes

“…In analogy to the known permanganate [7b,7d] and osmium tetroxide mediated [9c] reactions and on the basis of recent DFT (density functional theory) calculations, [25] we propose the following mechanism for the ruthenium tetroxide mediated oxidative cyclization (Scheme 5). Oxidation of the pre-catalyst is followed by an initial [3+2] cycloaddition [26] between ruthenium tetroxide and one of the olefinic double bonds, giving rise to a cyclic ruthenium() ester intermediate (A).…”

RuO4-mediated oxidation of N-benzylated tertiary amines. 2. Regioselectivity for N,N-dimethyl- and N,N-diethylbenzylamine as substrates

“…NMR Spectra. The 1 H-and 13 C-NMR features of all compounds of interest are collected in Tables 2 and 3 4 ). The previous procedure 1 was slightly modified as concerning the work-up.…”

“…For instance, 4A-B would give the corresponding secondary benzylamines 8A-B and the aliphatic aldehydes 9A-B; similarly, 5A-B could be cleaved to the secondary aliphatic amines 10A-B and benzaldehyde (11). In the case of 2B, which possesses an (N-β)C-H bond, deprotonation to the enamine 12 could also occur; oxidative cleavage of the C=C double bond in 12 would give 4 an equimolecular mixture of formamide 13 and formaldehyde (9A). As observed previously, 1 small amounts of the N-oxides 14A-B might also result from 1A-B.…”

“…No such stereoelectronic constraints exist in the similar acyclic derivatives. Consequently, we decided to study the RuO 4 …”

Facile Cycloaddition of Transition Metal Oxides Onto the Sidewall of Boron-Doped Fullerene

“…8,9 In recent years, Ru-based oxidation catalysis is finding significant applications in many respects due to the unique properties of this extremely versatile transition metal. 10 Hence, it can be envisaged that the addition of RuO 4 onto C 60 should be much more facile than that of OsO 4 ; this process may readily occur without the presence of an organic base as a catalyst.…”