Ruthenium precursor

Synthetic routes to active ruthenium metathesis catalysts are classified according to the ruthenium precursor used. 

A mixed solution of platinum and ruthenium precursors was prepared by adding H2PtCl6 and RuClj at a certain ratio to de-ionized water. The solution was in negnated on y-alumina of size 300-... 

A kinetic study of the hydrodefluorination of C F H in the presence of EtjSiH indicated a first-order dependence on both [fluoroarene] and [ruthenium precursor] and a zero-order dependence on the concentration of alkylsilane, implying that the rate-limiting step in the catalytic cycle involves activation of the fluoroarene. The regioselectivity for hydrodefluorination of partially fluorinated substrates such as CgFjH has been accounted for by an initial C-H bond activation as shown in the... 

It was not possible to isolate defined complexes with clear bidentate coordination for the ligands MandyPhos and TaniaPhos using established ruthenium precursors such as [Ru(COD)Cl2]x, [Ru(benzene)Cl2]2, [Ru(p-cymene)Cl2]2,... 

In contrast, the use of carbonyl-derived ruthenium catalysts on different supports has been explored in ammonia synthesis [120-122], The use of K2[Ru4(CO)i3] as ruthenium precursor on MgO or carbon yields especially effective catalysts for low-temperature ammonia synthesis [120, 122],... 

The stoichiometric reaction of propyl propargylic ether with the similar ruthenium precursor XVIIIb (X OTf) led to the formation of the same isolable carbene-ruthenium complex XXb and propanal (Scheme 8.14). 

When the ruthenium precursor contains an electron-rich phosphine such as tris(p-methoxyphenyl)phosphine, and if a large excess of this ligand is used in the catalytic reaction, the formation of valerolactones by oxidation of a postulated transient alkoxycarbene ruthenium moiety is favored (Scheme 10) [20]. 

Bases such as methoxide or ferf-butoxide give adducts such as 12 which can be isolated and characterized [40] but generally afford the corresponding carbene at room temperature upon loss of methanol or tert-butanol, respectively (Eq. 19). Thus, the NHC is formed in situ and can produce the desired complexes with a ruthenium precursor. In contrast to the saturated tert-butanol adducts of the NHC (12), the corresponding adducts from unsaturated NHCs have not been isolated and afford the carbene directly, presumably due to the higher stability of the aromatic carbene 13 (Eq. 20). The methanol adducts of the triazohum-based NHCs such as 14 [41] are more stable and... 

Carboxylic acids also add to terminal alkynes to produce enol esters. A variety of ruthenium precursors such as Ru3(CO)12 [ 12], Ru(cod)2/PR3, where cod is cy-clooctadiene, [13] RuCl2(PR3)(arene) [14,15] or [Ru(02CH)(C0)2(PR3)]2 [16] are good catalysts to perform the selective addition of the carboxylate to the C2 position of alkynes to afford geminal enol esters bearing a methylene group. 

Reaction of the arene ruthenium precursor 200 with polystyrene and hydrogen leads to the loss of both cycloolefins and gives a polymeric ruthenium complex, used for catalytic hydrogenation, for which EXAFS indicated a Ru—C distance of 2.05 A. A similar reaction of derivative 200 with 1,3-diphenylpropane gives complex 203 and a compound of composition (diphenylpropane)Ru2 (204) (129,130) [Eq. (18)]. 

The abnormal carbene complex 27 (bonded through C3) is formed from the reaction between M3(CO)i2 (M = Ru, Os) and the bulky NHC ImAd2 (l,3-di(adamantyl)imidazol-2-ylidene) the reaction with the ruthenium precursor occurs readily in thf at room temperature, whereas the osmium reaction requires heating at 70 °C. Thermolysis of 27 affords 28.30... 

Abstract Ruthenium holds a prominent position among the efficient transition metals involved in catalytic processes. Molecular ruthenium catalysts are able to perform unique transformations based on a variety of reaction mechanisms. They arise from easy to make complexes with versatile catalytic properties, and are ideal precursors for the performance of successive chemical transformations and catalytic reactions. This review provides examples of catalytic cascade reactions and sequential transformations initiated by ruthenium precursors present from the outset of the reaction and involving a common mechanism, such as in alkene metathesis, or in which the compound formed during the first step is used as a substrate for the second ruthenium-catalyzed reaction. Multimetallic sequential catalytic transformations promoted by ruthenium complexes first, and then by another metal precursor will also be illustrated. 

The metathetic transformation of enynes in the presence of ruthenium precursors provide conjugated cycloalkenes, which are reactive under Diels-Alder reaction conditions with dienophiles. Many examples of such thermally activated [2 + 4] cycloadditions have been reported in the literature [51-59], and the beneficial effect of a ruthenium catalyst has been shown when the reaction was performed in one pot without isolation of the diene [60]. 

Ruthenium compounds have been extensively studied as catalysts for the aerobic oxidation of alcohols [142]. They operate under mild conditions and offer possibilities for both homogeneous and heterogeneous catalysts. The activity of common ruthenium precursors such as RuCl2PPh3, can be increased by the use of ionic liquids as solvents (Fig. 4.58). Tetramethylammoniumhydroxide and aliquat 336 (tricaprylylmethylammonium chloride) were used as solvent and rapid conversion of benzyl alcohol was observed [145]. Moreover the tetra-methylammonium hydroxide/RuCl2(PPh3)3 could be reused after extraction of the product. 

The triethoxysilane endgroup had to be introduced as the respective isocyanate and was then used to attach the polymer on the silicon support. In a final step, the NHC are formed and the ruthenium precursor loaded onto the polymer. Only 13% of the imidazolium sites are attached to ruthenium. The formation of this polymer supported Grubbs catalyst is doubtless a synthetic masterpiece, however, immobilisation of the Grubbs catalyst was achieved in a far less complicated manner only a few years later by a far simpler method by Fiirstner and coworkers [244]. 

---