Ruthenium oxidative addition

The three steps 32-34 have been suggested77 to be equilibria, and the overall equilibrium must lie far to the left because no adduct 23 is found in the reaction mixture when the reaction of sulfonyl chloride with olefin is carried out in the absence of a tertiary amine. A second possible mechanism involving oxidative addition of the arenesulfonyl halide to form a ruthenium(IV) complex and subsequent reductive elimination of the ruthenium complex hydrochloride, [HRulvCl], was considered to be much less likely. 

As a final example in this section, a contribution by Grubbs et al. is discussed. The chloride-free ruthenium hydride complex [RuH2(H2)2(PCy3)2] (37) is believed to react, in the presence of alkenes, to form an unidentified ruthenium(O) species which undergoes oxidative additions with dihalo compounds, e.g., 38, to give the corresponding ruthenium carbene complex 9 (Eq. 4) [20]. 

Chlorination of the Cp Ru(amidinate) complexes is readily achieved by treatment with CHCI3, while oxidative addition of allylic halides results in formation of cationic Ti-allyl ruthenium(IV) species (Scheme 243). °... 

Since Chatt and Davidson13 observed the first clear example of simple oxidative addition of a C—H bond of naphthalene to a ruthenium metal center, Ru(dmpe)2 (dmpe = Me2PCH2CH2PMe2), hydrocarbon activation has been the subject of many transition metal studies.11 c Sometimes, the efforts in this field have ended in findings different from the initial objectives, which have been the starting point for the development of novel organometallic chemistry. 

Successive hydrogen transfers within 60, followed by coordination of olefin and then H2 (an unsaturate route), constitute the catalytic cycle, while isomerization is effected through HFe(CO)3(7r-allyl) formed from 59. Loss of H2 from 60 was also considered to be photoinduced, and several hydrides, including neutral and cationic dihydrides of iridium(III) (385, 450, 451), ruthenium(II) (452) and a bis(7j-cyclopentadienyltungsten) dihydride (453), have been shown to undergo such reductive elimination of hydrogen. Photoassisted oxidative addition of H2 has also been dem-... 

The most plausible mechanism proceeds through oxidative addition of the aldehyde to an active Ru(0) species to form (acyl)(hydrido)ruthenium(ll) complex 155. Insertion of the less-substituted double bond of the 1,3-diene into the Ru-H bond occurs to generate an (acyl)( 73-allyl)ruthenmm(ll) intermediate of type 156. Successive regioselective reductive eliminations between the acyl and the 73-allyl ligands provide the desired product with regeneration of the... 

A mechanistic pathway is proposed based upon the observed regioselectivities and other results that were obtained during the exploration of the scope and limitations of the Alder-ene reaction.38 Initially, coordination of the alkene and alkyne to the ruthenium catalyst takes place (Scheme 5). Next, oxidative addition affords the metallocycles 42 and 43. It is postulated that /3-hydride elimination is slow and that the oxidative addition step is reversible. Thus, the product ratio is determined by the rate at which 42 and 43 undergo /3-hydride elimination. 

Cationic ruthenium complexes of the type [Cp Ru(MeCN)3]PF6 have been shown to provide unique selectivities for inter- and intramolecular reactions that are difficult to reconcile with previously proposed mechanistic routes.29-31 These observations led to a computational study and a new mechanistic proposal based on concerted oxidative addition and alkyne insertion to a stable ruthenacyclopropene intermediate.32 This proposal seems to best explain the unique selectivities. A similar mechanism in the context of C-H activation has recently been proposed from a computational study of a related ruthenium(ll) catalyst.33... 

This concerted process may operate in the case of d° early metal complexes where the oxidative addition is forbidden [194]. Nevertheless, it was postulated also in the interaction of a dihalo-ruthenium(II) intermediate and a hydrosilane... 

Ruthenium has a sufficient number of d-electrons to undergo oxidative addition of dihydrogen, which could then be quickly followed by reductive... 

In order to get a catalytic cycle it is necessary that the metal sulfide intermediate can react with hydrogen to form the reduced metal complex (or compound) and H2S. For highly electropositive metals (non-noble metals) this is not possible for thermodynamic reasons. The co-ordination chemistry and the oxidative addition reactions that were reported mainly involved metals such as ruthenium, iridium, platinum, and rhodium. 

CO Subsequently a migratory insertion will take place. Oxidative addition of H2 will be faster at the electron rich metal centre and thus the aldehyde will form. Hydrogenation takes place at ruthenium (added as Ru3(CO)i2) as indeed catalyst systems containing cobalt only are known to give 3-hydroxypropanal as the product. 

Later in 1965, Chart and Davidson [2] reported the first example of cyclometal-lation of an sp C—H bond in [Ru(dmpe)2] (3) dmpe = dimethyl phosphinoethane. These authors found not only that this complex spontaneously cyclometaUates at the phosphorus methyl groups to produce complex [Ru(H)(CH2P(Me)CH2CH2PM 62)(dmpe)] (4 see Scheme 13.4) (a later examination by Cotton and coworkers [9] of this compound provided crystallographic evidence that the cyclometalated form of [Ru(dmpe)2] is in fact a dimer (5) of the type shown in Scheme 13.3), but also that the system reacts with free naphthalene via the oxidative addition of a C—H bond to the zero-valent rathenium center to produce complex [cis-Ru(H)(2-naphthyl)(dmpe)2] (6). This species was in equilibrium with the r-coordinated naphthalene ruthenium complex [Ru(naphthalene)(dmpe)2] (7) (Scheme 13.4). 

Terminal alkynes can undergo several types of interaction with ruthenium centers. In addition to the formation of ruthenium vinylidene species, a second type of activation provides alkynyl ruthenium complexes via oxidative addition. 

This then was the first report of a compound in which alkyl C—H bond activation by a transition metal had occurred. In the solid state, this equilibrium is also in favor of the hydrido complex (V), and its crystal structure has recently been determined (15). It shows compound V to be a dimer (VI), the oxidative addition of the methyl group of a ligand on each ruthenium atom being to a second ruthenium atom. Presumably one reason why this occurs is because the product of intramolecular ring closure would contain a highly strained three-membered Ru—P—C ring (i.e., in monomer V). 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

---