Ruthenium complexes chiral chelating ligands

Similarly, ra 5-cyclopropanes were obtained from alkenes, such as styrene and 2,5-dimethyl-hexa-2,4-diene, with relative yields > 90% when a diazoacetate bearing a bulky ester group was decomposed by a copper catalyst with bulky salicylaldimato ligands. Several metal complexes with bulky Cj-symmetrlc chiral chelating ligands are also suitable for this purpose, e.g. (metal/ligand type) copper/bis(4,5-dihydro-l,3-oxazol-2-yl)methane copper/ethyl-enediamine ruthenium(II)/l,6-bis(4,5-dihydro-l, 3-oxazol-2-yl)pyridine cobalt(III)/ salen. The same catalysts are also suited for enantioselective reactions vide infra). For the anti selectivity obtained with an osmium-porphyrin complex, see Section 1.2.1.2.4.2.6.3.1. 

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... 

This chapter reports principally on studies with ruthenium chiral phosphine and chiral sulfoxide complexes and their use for catalytic hydrogenation. We have used the familiar diop ligand, [2R,3R-(—)-2,3-Oisopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino) butane] (7) a related chiral chelating sulfoxide ligand dios, the bis(methyl sulfinyl)butane analog (21) (S,R S,S)-(+)-2-meth-ylbutyl methyl sulfoxide(MBMSO), chiral in the alkyl group and R-(+)-methyl para-tolyl sulfoxide(MPTSO), chiral at sulfur. Preliminary data on some corresponding Rh(I) complexes are presented also. 

The catalytic activation of allylic carbonates for the alkylation of soft car-bonucleophiles was first carried out with ruthenium hydride catalysts such as RuH2(PPh3)4 [108] and Ru(COD)(COT) [109]. The efficiency of the cyclopen-tadienyl ruthenium complexes CpRu(COD)Cl [110] and Cp Ru(amidinate) [111] was recently shown. An important catalyst, [Ru(MeCN)3Cp ]PF6, was revealed to favor the nucleophilic substitution of optically active allycarbonates at the most substituted allyl carbon atom and the reaction took place with retention of configuration [112] (Eq. 85). The introduction of an optically pure chelating cyclopentadienylphosphine ligand with planar chirality leads to the creation of the new C-C bond with very high enantioselectivity from symmetrical carbonates and sodiomalonates [113]. 

Recently van der Zeijden reported the synthesis of a chiral ligand and the formation of ruthenium complexes with it. When (lS)-neomenthanethiol (500) was treated with potassium followed by spiro[2.4]-hepta-4,6-diene (81) and chlorotrimethylsilane ligand, 501 was obtained in quantitative yield (Scheme 97). Reaction of 501 with RuCl2(PPh3)3 afforded nonch-elated complex 502 in 64% yield. Treatment with silver triflate gave chelate 503, which decomposed within a few hours. 

In this chapter, I outline our recent progress in asymmetric reductive and oxidative transformations with bifunctional molecular catalysts based on ruthenium, rhodium, and iridium complexes bearing chiral chelating amine ligands. 

The chiral ruthenium chelate complexes were tested as catalysts in the reconstitutive addition reaction of 288 and 289 to give 290. In some cases the chemical yields were good however, the ee remained rather low. It has been discussed whether this is the result of a poor enantioselectivity of the catalysis or a racemization process of the product. Van der Zeijden obtained chiral diastereomeric chelates 314 and 315 in nonracemic form (66% ee) by treatment of ligand (5)-49 (66% ee) with RuCp-... 

The past decade has witnessed extensive modifications of Af-heterocyclic carbene ligands for ruthenium olefin metathesis catalysts. This includes symmetrical and unsymmetrical NHCs, 1,3- and 4,5-substitutions, introduction of heteroatoms into the backbone, NHC ring size variation, and introduction of chirality. Most of these changes were initially targeted to improve stability and activity of the catalyst, while recent approaches are mainly focused on affording well-defined stereoselectivity. However, the activity and stability of the ruthenium-based metathesis catalysts are not solely ruled by the type of neutral NHC ligand the anionic ligands, chelation mode, substrates used, and the reaction conditions naturally also influence catalytic properties. One of the main lessons learned from ruthenium olefin metathesis development is that there is no one catalyst fits all and every type of application must be studied in detail in order to discover the most efficient catalytic complex. 

In 2002, Hoveyda and coworkers introduced an alternative concept to install chirality in ruthenium olefin metathesis complexes through a Ci-symmetric bidentate NHC ligand, bearing binaphtholate moieties (Figure 11.33). The NHCs in this type of complexes lacked backbone substitution and it was chelation that prevented free rotation of the ligand [118]. In this case, chiral information installed within the A-substituent was transferred directly to the ruthenium center. Unfortunately, these complexes were found to be less active because of the reduced Lewis acidity at the metal center, mainly due to the exchange of Cl... 

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