Arenes Ruthenium chloride

Several other versions of these catalysts have been developed. Arene complexes of monotosyl-l,2-diphenylethylenediamine ruthenium chloride give good results with a,(3-ynones.55 The active catalysts are generated by KOH. These catalysts also function by hydrogen transfer, with isopropanol serving as the hydrogen source. Entries 6 to 8 in Scheme 5.3 are examples. 

Ruthenium complexes are capable of catalyzing halogen atom transfer reactions to olefins. This has been illustrated in the enantioselective atom transfer reactions of alkane and arene-sulfonyl chlorides and bro-motrichloromethanes to olefins using chiral ruthenium complexes. Moderate ee s up to 40% can be achieved for these transformations [74-77]. These specific reactions are believed to follow a radical redox transfer chain process. 

One of the most general and useful methods of access to (tj6-arene)ruthenium(H) complexes is based on the dehydrogenation of cyclo-hexadiene derivatives by ethanolic solutions of RuC13 xH20 (6). This method has been developed for the synthesis of binuclear complexes 1 by Zelonka and Baird (7) for benzene (la) and by Bennett and co-workers (8-10) for para-cymene (lb), a useful starting material (10), and substituted benzene derivatives, such as xylene, mesitylene (9), or 1,3,5-triphenylbenzene (11) [Eq. (1)]. The chloride ligands of complexes 1 can... 

This ready access to 77 -arene ruthenium(O) complexes has allowed the entry to other functionalized derivatives. Thus, electrophilic substitution reactions have been performed starting from [Ru(77" -GOD)(r7 -haloarene)] via sequential addition of LiBu and a suitable electrophile at low temperature. A wide range of electrophiles such as acyl chlorides, chloroformates, chlorophosphines, epoxides, ketones, 7-lactones, etc., have been involved in this transformation. As an example, lithiation of [Ru(77" -GOD)(77 -l,2-MeG6H4Br)] and further reaction with... 

Tin - A crystallographic study on [Rh(COD)(Ti -dppp)(SnCl3)] reveals two molecules in the asymmetric unit with trigonal bipyramidal and square-based pyramidal geometry about rhodium, while addition of tin dichloride to arene complexes [(T -arene)RuCI(ri -S2CPR3)] results in insertion into the ruthenium-chloride bond giving further tin trichloride complexes. A number of seven-coordinate molybdenum complexes [Mo(CX))2(PR3)Cl(r -phen)(SnRCl2)] ,... 

A convenient and easily accessible way to quantify hydrophobicity is the determination of the octanolAvater partition coefficient (log P) and we have determined the hydrophobicity of 13 selected ruthenium-arene complexes (71). As expected, hydrophobicity increases with an increase of the size of the coordinated arene ring, but decreases significantly when the chloride is replaced by neutral ligands such as pyridine and 4-cyanopyridine. The latter observation is somewhat counter intuitive at first inspection, but correlates with replacement of anionic chloride to yield a dicationic complex. The hydrophobicity... 

The bifunctional amine-tethered ruthenium(II) arene complexes [Ru(r6 ti1-C6H5CH2(CH2)i1NH2)C12] (n = 1,2) (13a,b) show two consecutive hydrolysis steps to yield the mono- and bis-aqua complexes (64). At extracellular chloride concentrations, the majority of the complexes could be expected to be present as the mono-aqua adduct. Equilibrium constants were determined for both steps (for 13b, Ki = 145 mM K2 = 5.4 mM) and found to be considerably higher than those of cisplatin, which also has two reactive sites available. 

Denmark pursued intramolecular alkyne hydrosilylation in the context of generating stereodefined vinylsilanes for cross-coupling chemistry (Scheme 21). Cyclic siloxanes from platinum-catalyzed hydrosilylation were used in a coupling reaction, affording good yields with a variety of aryl iodides.84 The three steps are mutually compatible and can be carried out as a one-pot hydro-arylation of propargylic alcohols. The isomeric trans-exo-dig addition was also achieved. Despite the fact that many catalysts for terminal alkyne hydrosilylation react poorly with internal alkynes, the group found that ruthenium(n) chloride arene complexes—which provide complete selectivity for trans-... 

Mixed metal ruthenium/group 9 clusters also show rich chemistry. Synthetically, such clusters are generally synthesized by the addition of a metal chloride to an anionic boridocluster in a cluster expansion reaction. For example, [Ru3(CO)9BH4]- undergoes cluster expansion with [Ru(776-arene)Cl2]2 (arene = CgHsMe, MeCgH4-... 

Classical Friedel-Crafts catalysts such as BF3 etherate or Bronstedt acids, which are applied in stoichiometric amounts or even in excess, still have their value, because they are relatively inexpensive yet powerful catalysts for C-H transformation at arenes and, most importantly, they are often successful when modern catalysts fail. Gold(III) chloride, at less than 1 %, has impressive reactivity under very moderate reaction conditions and its selectivity is exceptionally good. Friedel-Crafts type reactions with this catalyst are, however, restricted to very electron-rich arenes. Further studies should concentrate on increasing the electrophilicity of gold catalysts. New catalysts have emerged, for instance based on ruthenium and rhenium, which promise broad applicability based on alternative mechanisms. Catalysts based on rare earth metals are discussed in the next chapter. 

A more general route to make bis(cyclophane)ruthenium(II) complexes involves a reduction of 263 (arene = benzene) with Red-Al to afford the [ 174-1,3-cyclohexadiene)(tf-cyclophane)]ruthenium(O) derivatives 271 (Scheme 28, p. 224). Treatment of 271 with hydrochloric acid gives the dimeric chloride complexes 272, which lead the desired bis(r)6-[2 ]cyclo-phane)ruthenium(II) complexes 274 via Bennett s procedure (145). Synthesis of the oligomer 275a is also achieved in quantitative yield by heating 274 with the solvated complex 7 (arene = C6Me6) in neat trifluoroacetic acid. 

Catalytic tandem isomerization/Claisen reaction of bis allyl ether was reported by Dixneuf et al. [23]. A cationic bis-oxazoline-ruthenium-arene complex S3 in the presence of both l,3-bis(2,6-diisopylphenyl)imidazolinium chloride and CS2CO3 catalyzes the selective transformation of bis-allyl ether 51 into ) c5-unsaturated aldehyde 52 via successive alkene isomerization and Claisen rearrangement (Eq. 12.21). 

The remarkable stability of ruthenium complexes could, further, be exploited for direct arylations between simple arenes as pronucleophiles and inexpensive, broadly available phenols as proelectrophiles. Notably, this operationally simple dehydrative direct arylation was achieved with a highly chemo- and regioselective ruthenium catalyst, along with a sulfonyl chloride, and proceeded overall through the functionalizations of both C-H as well as C-OH bonds (Scheme 29) [85],... 

Ruthenium-catalyzed direct arylations of the arene 58 with the secondary phosphine oxide (l-Ad)2P(0)H (54) as preligand allowed for the use of inexpensive aryl chlorides as electrophiles (Scheme 9.22) [55], Importantly, the protocol proved applicable to both electron-deficient and electron-rich aryl chlorides. 

Other ruthenium catalysts that have been used for the hydrogenation of arenes include the water-soluble and IL soluble complex Ru(ri - CioHi4)(pta)Cl2(pta = 1,3,5-triaza-7-phosphaadamantane) [37]. Comparisons were made between the catalytic activity in water and tetrafluoroborate ILs including ones contaminated with chloride, and again, in the chloride-free ILs catalytic activity is highest The related ruthenium catalyst, [Ru(q -p-cymene)(ri -triphos)Cl][PF 5] [triphos = l,l,l-tris(di-phenylphosphinomethyl)ethane] has also been shown to hydrogenate arene substrates [39]. The activity of the catalyst was compared in [BMIM][BF4] and di-chloromethane and was foimd to be considerably more active in the IL For example, in the hydrogenation of benzene to cyclohexane the TOF is 477 mol mol h when... 

Fig. 9 a ruthenium(Il)-arene complexes b rhodium and ruthenium carbene complexes c rhodium, iridium and ruthenium tripodal phosphine complexes d gold [1,3-(dimesitylmeth)dimidazolinium)] chloride complexes e metal carboxamide derivatives... 

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