Ruthenium chiral arene complexes

Fig. 14. Dynamic chiral recognition of 9-ethylguanine by chiral ruthenium-arene complex 9.

Keywords Arene chromium complexes Arene ruthenium complexes Enantioselective total synthesis Planar-chiral metal complexes Natm-al products... 

Dyson and coworkers have reported the biological effect of dichlorido and oxalato derivatives of enantiomerically pure RAPTA-type ruthenium(II) complexes [14]. The enantiomers were synthesized by using a chiral arene (R)- or (S)-2-phenyl-iV-(l-phenylethylene)acetamide) as a ligand (Figure 3.9b). The cytotoxicity of all the epimers was evaluated in human ovarian cancer cells (A2780 and A2780cisR) with the S-enantiomers being more active than the R-enantiomers in both cell lines. Additionally, the dichlorido derivatives showed in vitro selectivity toward cancer cells over healthy HEK cells. 

Chiral 1-alkyl-substituted tetrahydroisoquinolines have been obtained in excellent yield and with ee up to 95%, using A-sulfonylated diamines containing ruthenium arene complexes as catalysts (Fig. 80) (341). 

The chiral 3-substituted-l,2-benzisothiazoline 1,2-dioxides, shown in Figure 82, can be prepared from the corresponding iV-sulfonylimines by ATH reduction, using a ruthenium arene complex with the chiral ligand TsDPEN as the catalyst (342). By using a HCOOH/NET3 mixture as the hydrogen donor, 91% ( Bu) and 93% (Bu) ee were obtained in the S enantiomer. 

Noyori Asymmetric Transfer Hydrogenation Noyori s well-designed chiral Ru -arene complexes catalyze the asymmetric transfer hydrogenation of ketones and imines (not shown) with stable organic hydrogen donors such as 2-propanol [69]. The reaction is reversible, and the involved chiral ruthenium species and the proposed transition state are depicted in Scheme 2.140. 

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. 

Ruthenium complexes of formula [(ri -arene)Ru(LL )(H20)](SbF6)2 (arene = CeHg, p-MeC6H4 Pr, CeMee LL = bidentate chelate chiral ligand with PN, PP, or... 

Bis(phoshacyclopentadienyl)titanium(II) complexes, preparation and reactivity, 4, 265 Bisphosphanes on DIOP modification, 10, 7 in hydrogenations, 10, 7 in hydrogenations, P-chiral ligands, 10, 11 Bisphosphinidenes, with platinum(II), 8, 453 -54 Bisphosphinites, in hydrogenations, 10, 14 Bis(phosphinoalkyl-thioether)arenes, in ruthenium isocyanides, 7, 138... 

The moderate Lewis acidity of ruthenium complexes was used to promote catalytic Diels-Alder reaction of dienes and acrolein derivatives [21-23]. The enantioselective Diels-Alder reaction of methacrolein with dienes was catalyzed with cationic ruthenium complexes containing an arene or cyclo-pentadienyl (Cp) ligand and a chiral ligand such as phosphinooxazoline, pyridyl-oxazoline, monoxidized 2,2 -bis(diphenylphosphino)-1, T-binaphthyl (BINPO)or l,2-bis[bis(pentafluorophenyl)phosphanyloxy]-l,2-diphenylethane (BIPHOP-F). The reaction gave the cycloadduct in high yields with excellent... 

Arene)ruthenium(II) complexes 120-124, having a planar chirality, have been obtained recently (71,72). Complexes 121-123 are formed by addition of optically active amines (L1 and L2) or phosphine (L3) to the dinuclear complex 120 (Scheme 10). They exist as a mixture of two configurationally stable diastereoisomers. The absolute configuration of one of the diastereoisomers of 123 has been determined, and complex 124 containing a chelating optically active diamine has also been isolated (71,72). 

Very recently, Ikariya reported chiral amido ruthenium complex-catalyzed asymmetric Michael addition of dimethyl malonate with conjugate enones using Ru[(i ,i )-TsDPEN](>7 -arene) ((R,R)-TsDPEN = (lR,2R)-N-(p-toluenesulfonyl)-l,2-di-phenylethylenediamine) [84], The reaction of cyclopentenone with dimethyl malonate gave the corresponding /3-alkylation product in 99% yield with 97% e.e. (Eq. 9.60). For this mthenium-catalyzed asymmetric Michael addition, the Bronsted basicity of the amido ligand is responsible for the excellent catalytic activity. 

In this section, we will review the nature and chemical reactivities of several kinds of ruthenium complexes under the following headings ruthenium carbonyl complexes, dichlororuthenium complexes, chlorohydrido complexes, dihydridoruthenium complexes, ruthenium complexes with chiral ligands, ruthenium complexes with cyclopentadienyl ligands, and ruthenium arene/diene complexes. 

Abstract Planar-chiral ri -arene-Cr(CO)3 complexes represent highly valuable buUdlng blocks for the dlastereo- and enantloselectlve synthesis of complex natural products and related bloactlve compounds. Highly original and competitive overall syntheses of various classes of natural products, such as sesquiterpenes, diterpenes, alkaloids and compounds with axial chirality, have been developed. In certain cases, the whole strategy is based on arene chromium chemistry and the various chemical and stereochemical effects of the metal unit are exploited In several subsequent transformations. Cationic Cp-ruthenium complexes allow arylether formation by Sj Ar reactions and have found application in the synthesis of glyco-peptide antibiotics. 

A singular chiral adduct was formed between C70 and two RujfCOjg units which are known for the complexation of arenes. From the corresponding mono -adduct it was known that the trinuclear ruthenium moieties add preferentially to the hexagons of highest local curvature [143]. Assuming addition of two Ru3(CO)9 units at opposite poles, three constitutional isomers of [[Ru3(CO)9 2(ft-T2, /2, rf-C7o)] are possible in analogy to the addition of achiral divalent addends to a-type bonds (cf. Sect. 4.2.1) [54,131 ] One of them has symmetry and two have C2-symmetry. Of the three formed isomers, the major one afforded crystals suitable for X-ray analysis it has an inherently chiral addition pattern and corresponds to structure ( )-59 [143] (Fig. 9). 

Other chiral diamine-( -arene)ruthenium catalysts were developed by Noyori where the chirality was centred at the metal (see Figure 3.18). These complexes were effective catalysts for asymmetric transfer hydrogenation of carbonyl compounds and a mechanism involving a metal-ligand bifunctional process was proposed. 

M. Yamakawa, I. Yamada, R. Noyori, CWn Attraction the origin of enantioselectivity in transfer hydrogenation of aromatic carbonyl compounds catalyzed by chiral 77 -arene-ruthenium(II) complexes, Angew. Chem. Int. Ed., 2001, 40, 2818-2821. 

Various oxidations with [bis(acyloxy)iodo]arenes are also effectively catalyzed by transition metal salts and complexes [726]. (Diacetoxyiodo)benzene is occasionally used instead of iodosylbenzene as the terminal oxidant in biomimetic oxygenations catalyzed by metalloporphyrins and other transition metal complexes [727-729]. Primary and secondary alcohols can be selectively oxidized to the corresponding carbonyl compounds by PhI(OAc)2 in the presence of transition metal catalysts, such as RuCls [730-732], Ru(Pybox)(Pydic) complex [733], polymer-micelle incarcerated ruthenium catalysts [734], chiral-Mn(salen)-complexes [735,736], Mn(TPP)CN/Im catalytic system [737] and (salen)Cr(III) complexes [738]. The epox-idation of alkenes, such as stilbenes, indene and 1-methylcyclohexene, using (diacetoxyiodo)benzene in the presence of chiral binaphthyl ruthenium(III) catalysts (5 mol%) has also been reported however, the enantioselectivity of this reaction was low (4% ee) [739]. 

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