Cycloruthenation

Very recently, Parkhomenko et al. used cycloruthenated complexes 155a and 155b to catalyze the Kharasch addition of Cl3CBr to styrene, methyl methacrylate, acrylate, and 1-hexene in high yields [226]. The reaction with CC14, on the other hand, required microwave irradiation for all complexes and substrates to achieve moderate to good yields. 

The cycloruthenation of substituted A, A -dimethylbenzylamines by [77°-C6H6)RuCl( t-Cl)]2 in acetonitrile in the presence of NaOH and KPp6, which led to the formation of corresponding cycloruthenated complexes in good to moderate yields, has also been studied <1999OM2390>. For example, the work of Le Lagadec and co-workers is illustrated in Equation (17) <2004JOM4820>. As shown in Equation (17), the cycloruthenation of the 3-substituted A, A -dimethylbenzylamine 69 afforded two positional isomers as a result of the Ru(li) attack at the G-2 or C-6 aromatic carbons. 

Abstract Stoichiometric cycloruthenation reactions of substrates containing Lewis-basic functionalities set the stage for efficient ruthenium-catalyzed C-H bond functionalization reactions. Thereby, selective addition reactions of C-H bonds across alkenes or alkynes enabled atom-economical synthesis of substituted arenes. More recently, ruthenium-catalyzed direct arylation reactions were examined, which display an unparalleled scope and, hence, represent economically and environmentally benign alternatives to traditional cross-coupling chemistry. 

Stoichiometric cycloruthenation reactions, as well as the early example of catalytic deuteration of phenol (see above) [38] served for the development of efficient catalytic strategies for C-C bond formations through C-H bond functionalizations. Indeed, ruthenium-catalyzed atom-economical [51] addition reactions of arenes onto C-C multiple bonds, hydroarylations [52-57], were found to be very useful. In an early example, Lewis and Smith disclosed a regioselective alkylation of phenol through in situ formation of its phosphite, and subsequent directed C-H bond functionalization (Scheme 8) [58],... 

Several cycloruthenated complexes have been prepared and characterized, but no comparison can be made with the development of Ru(II)-polypyridine chemistry. This is even more true as far as luminescence is concerned hundreds of luminescent Ru(II) polypyridine complexes have been investigated [15], whereas only a few luminescent cycloruthenated complexes have been reported. 

Synthesis of cycloruthenated pyrido[2,3-fl]pyrrolo[3,4-c]carbazole-5,7(6H)-diones and ruthenium complexes as protein kinase inhibitors 07SU177. 

The cyclometalated Ru species generated electrochemically are very reactive in oxidation of reduced flavin adenine dinucleotide of GO. The excellent coupling between GO reduced by D-glucose and the Ru species is illustrated by the rate constant for the complex [Ru(phpy)(Me2phen)2]PF6, which equals 1.8x10 M s at pH 6.7 and 25 °C. There are no complexes of higher reactivity in Table VII Other cycloruthenated complexes are very reactive as well (Table IX). Variation of the nature of cycloruthenated and diimine... 

When the C-H activation process is inefficient or difficult to carry out, one can often resort to alternative methods such as transmetallation reactions, as in the synthesis of the interesting cycloruthenated complex 13. The corresponding C-H activation process for 2 gives only a 38% yield." A similar method was employed for the synthetically useful cyclopalladated ketone derivative 15 and for the organomolybdenum complex 17.Oxidative additions of suitably substituted iodo derivatives on Pd(0) were employed to synthesize the primary 8-napthylamine complex 19 and the complexes 21 with a variety of substitution patterns on the thioether group. 

The cycloruthenated complex 13 reacts with disubstituted alkynes to afford the novel Ti -aiene Ru(0) complexes 49 which were isolated, characterized by X-ray methods, and oxidatively demetallated by treatment with Cu(II) salts to afford metal-free(7i0"isoquinolium salts 43 (with PF as counterion). Kinetic studies have revealed that the reaction proceeds via insertion of the alkyne into the Ru-C bond and that for this process the rate-limiting step is very similar to that found for the analogous palladium compound. Irradiation or thermal treatment of the cycloruthenated complex 50 with diphenylacetylene yields diphenylindole 51 as product. A similar reaction is observed with the corresponding iron or molybdenum complexes. ... 

A cycloruthenated amine complex, depicted in Scheme 4.26, was successfully applied by Arends s group to promote the DKR of phenylethanol." The reaction was performed with CAL-B in the presence of isopropyl acetate and t-BuOK, providing the corresponding enantiopure acetate in good yield. 

C-H activation process. The first attempt to explain the mechanism of the cycloruthenation was earned out by Maseras, Dixneuf and co-workers through DFT calculations on the system [Ru(IMe)(Cl)2(2-pyridylbenzene)] using bicarbonate as the base. In this study two different pathways were considered for the cyclometallation of phenylpyridine oxidative addition and the concerted metallation-demetallation mechanism (Scheme 1). 

The syntheses of other diene derivatives have also been reported, ineluding (i) the reduetion of the bis(arene) [Os rf -G6H6)(77 -[22]-l,4-cyclophane)][BF4]2 with Red-Al (Red-Al = sodium bis(2-methoxyethoxy)dihydroaluminate) whieh produces [Os( 7 -G6H8)(77 -[22]-l,4-cyclophane)] in good yield," " and (ii) the formation of r/" -coordinated isoquinoline heterocycles by reaction of the G,A-cycloruthenated compounds 352 with 3-hexyne and 3-phenyl-2-propyne in methanol (Equation (36)). " Two regioisomers, 353a and 353b, are obtained in the case of the unsymmetrieal alkyne PhG=GMe. 

A range of azo and imine derivatives has also been shown to be suitable for cyclometallation reactions. Thus, cycloruthenated (phenylazo)phenyl and 4,4 -dimethyl(phenylazo)phenyl derivatives 279 (Figure 39) have been obtained by reactions of the corresponding mercurated azo derivatives with [ RuGl(p-Gl)(r/ -/>-cymene) 2] in refluxing GHGI3 or MeOH. Transmetallation methodology has also proved to be efficient for the cycloruthenation of... 

Insertion reactions of unsaturated organic substrates into the Ru-G bond of aryl-cycloruthenated complexes have been reported. Thus, alkenyl-type derivatives 285 (Figure 40) have been synthesized by reacting ruthenacycles... 

A novel route to synthesize phthahmide derivatives through ruthenium-catalyzed C-H bond functionalization of aromatic amides was developed by Ackermann and coworkers (Eq. (7.57)) [66]. This method is applicable to generate a potent COX-2 enzyme inhibitor in step-economical way. The reaction features by the insertion of a cycloruthenated species into a C—Het multiple bond of isocyanate and cleavage of pyrrolidinyl group. Electron-rich amides were found to favor the reaction, and an initial reversible C-H bond metalation step was also observed. 

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