Ruthenium complexes diastereomers

Expanding on the encapsulation of organometallic guests, half-sandwich complexes of the form CpRu(q -diene)(H2O) were encapsulated in 1 [32]. When the diene portion of the half sandwich complex is unsymmetrically substituted, the ruthenium atom becomes a chiral center. Addition of CpRu(2-ethylbutadiene) (H2O) (4) to 1 revealed the existence of two diastereomers. Encapsulation of these racemic ruthenium complexes in racemic 1 leads to diastereomeric pairs of enantiomeric host-guest complexes (A/R, A/S, A/R, A/S) (Figure 7.3). However, chiral discrimination was not observed with the diastereomeric ratio (d.r.) being 50 50. 

Internal propargylic alcohols (89) are alkylated enantioselectively in high yields to give a mixture of diastereomers (90), using a ruthenium complex and an amine... 

NMR spectra of (p-cymene)ruthenium (II) Schiff base complex, derivative of (S)-(a-methylbenzyl) and 3,5-di-ferf-butylsalicylaldimine, at room temperature in CDCI3 solution evidenced the presence of diastereomers at the ratio of 88 12.93 On the basis of a detailed analysis of 2D NMR spectra (ROESY) measured at 293 and 233 K, the (RRu,Sc) configuration of the major diastereomer in solution was suggested. 

Numerous studies aimed at the understanding of the mechanism of these processes rapidly appeared. In this context, Murai examined the behavior of acyclic linear dienyne systems in order to trap any carbenoid intermediate by a pendant olefin (Scheme 82).302 A remarkable tetracyclic assembly took place and gave the unprecedented tetracyclo[6.4.0.0]-undecane derivatives as single diastereomer, such as 321 in Scheme 82. This transformation proved to be relatively general as shown by the variation of the starting materials. The reaction can be catalyzed by different organometallic complexes of the group 8-10 elements (ruthenium, rhodium, iridium, and platinum). Formally, this reaction involves two cyclopropanations as if both carbon atoms of the alkyne moiety have acted as carbenes, which results in the formation of four carbon-carbon bonds. 

In contrast to the chelate formation with ligand 4 the reaction of the amino-methyl ligand 3 follows another path and no chelate complex is formed. Instead two molecules of ligand 3 are P-coordinated to the Ru atom while the amino-methyl side-chains remain uncoordinated. Two diastereomeric products were observed, a meso complex 12a and a Cj-symmetric diastereomer 12b, which has two molecules of 3 with identical configurations coordinated to ruthenium (Scheme 1.5.4) [11]. 

R = Ph) " have been prepared by reaction of blue ruthenium(III) chloride with the corresponding diketone under basic conditions or by ligand exchange with [Ru(acac)3]. The tris chelate complexes of (-t-)-3-acetylcamphor and (-i-)-3-trifluoroacetylcamphor [RUL3], for example, have been prepared by ligand exchange reaction with [Ru(acac)3] in ethyl benzoate at 160°C the diastereomers have been separated by tic on silica and assigned by H NMR studies. For tris complexes of... 

The allyl alcohol (2.84) could be hydrogenated with exceptionally high diastere-oselectivity using ruthenium/(J )-TolBINAP complexes. The substrate diastere-oselectivity and catalyst selectivity represent a matched pair, since, when the enantiomeric (S)-TolBINAP ligand was used, the opposite diastereomer was formed with only 56% de. 

A proposed mechanism, shown in Scheme 1, involves a six-member cyclic transition state between the aryl ketone and the active form of the catalyst, 2 [6]. The stable catalyst precursor 1 is transformed to the active catalyst, 2, through the loss of HCl. Treatment with 2-propanol forms ruthenium hydride 3 as a single diastereomer. Complexation of an aryl ketone precedes the hydride transfer step, which results in the reduced product. The mild reaction conditions make this catalyst an excellent candidate for incorporation in an imprinted network. The reported enantiometric excesses (ee s, +90%) serve as a useful benchmark to evaluate the influence of the imprinted polymer on the reduction. To the extent that the ruthenium center is situated in an imprinted cavity, the MIP can influence the approach of the ketone to the metal ion or better accommodate a specific reduction product. 

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