Highly selective induction of metal-centered chirality in the ligand exchange reaction of planar-chiral cyclopentadienyl–ruthenium complex bearing an anchor phosphine ligand

Onitsuka, Kiyotaka; Dodo, Noriko; Matsushima, Yuji; Takahashi, Shigetoshi

doi:10.1039/b009412i

Cited by 24 publications

(19 citation statements)

References 13 publications

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“…[8] We have been investigating the syntheses and stereoselective reactions of planar-chiral cyclopentadienyl (Cp'; see Eq.(1) for ligand) ruthenium complexes. [9] Previously, we reported the first example of Ru-catalyzed asymmetric allylic amination and alkylation of symmetrically substituted allyl carbonates using planar-chiral Cp'Ru complexes 1. [10] We describe herein the Ru-catalyzed reaction of unsymmetrically substituted allyl halides with phenol and alcohol to give ethers with high regio-and enantioselectivities.To optimize the conditions, we chose the reaction of cinnamyl chloride (2 a, LG = Cl) with o-cresol (3 a) [Eq.…”

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confidence: 99%

“…(1) for ligand) ruthenium complexes. [9] Previously, we reported the first example of Ru-catalyzed asymmetric allylic amination and alkylation of symmetrically substituted allyl carbonates using planar-chiral Cp'Ru complexes 1. [10] We describe herein the Ru-catalyzed reaction of unsymmetrically substituted allyl halides with phenol and alcohol to give ethers with high regio-and enantioselectivities.…”

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confidence: 99%

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Regio‐ and Enantioselective O‐Allylation of Phenol and Alcohol Catalyzed by a Planar‐Chiral Cyclopentadienyl Ruthenium Complex

2008

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Optically active allylic aryl ethers have high potential for use as precursors of biologically active organic molecules. [1, 2] Whereas stereospecific allylation of phenol derivatives has been demonstrated with transition-metal catalysts, [3] the enantioselective version catalyzed by chiral palladium complexes has been successfully applied to the synthesis of natural products.[4] However, compared to the myriad reports on enantioselective allylic alkylation and amination, there has been little research on enantioselective allylic substitutions with alcohol and phenol. [5] Recently, an efficient Ir-catalyzed system has been reported to give allyl aryl ethers as well as allyl silyl ethers with high regio-and enantioselectivities. [6,7] Although Ru complexes with chiral bisoxazoline ligands also show catalytic activity towards asymmetric allylic substitution with oxygen nucleophiles, the regio-and enantioselectivities are not very high. [8] We have been investigating the syntheses and stereoselective reactions of planar-chiral cyclopentadienyl (Cp'; see Eq. (1) for ligand) ruthenium complexes.[9] Previously, we reported the first example of Ru-catalyzed asymmetric allylic amination and alkylation of symmetrically substituted allyl carbonates using planar-chiral Cp'Ru complexes 1.[10] We describe herein the Ru-catalyzed reaction of unsymmetrically substituted allyl halides with phenol and alcohol to give ethers with high regio-and enantioselectivities.To optimize the conditions, we chose the reaction of cinnamyl chloride (2 a, LG = Cl) with o-cresol (3 a) [Eq. (1)]. After careful examination, we found that the reaction of 2 a (2.0 equiv) with 3 a was effectively catalyzed by 3 mol % (S)-1 a in THF at 3 8C in the presence of K 2 CO 3 (3.0 equiv) to give the branched ether 4 a with R configuration in 92 % yield and 95 % ee, along with a trace amount of the linear ether 5 a. The proper selection of cinnamyl derivatives and Ru catalyst was essential to achieve high selectivity (Table 1). Although methyl-and phenyl-substituted planar-chiral Cp'Ru complexes (S)-1 b and (S)-1 c also catalyzed the reaction with high regioselectivity, the enantioselectivities were lower than that obtained with (S)-1 a (Table 1, entries 1-3). The substituent at the 4-position on the Cp' ring has a similarly large effect on the enantioselectivity in the allylic aminations and alkylations.[10] The reaction of cinnamyl bromide (2 b) also produced 4 a in good yield, albeit with slightly lower enantioselectivity than the reaction of 2 a (Table 1, entry 4). When cinnamyl phosphate (2 c) or cinnamyl carbonate (2 d) was used as a substrate, a mixture of 4 a with low enantioselectivities and 5 a was obtained in good yield (Table 1, entries 5 and 6). Cinnamyl acetate (2 e) was not suitable for the present reaction owing to its low reactivity (Table 1, entry 7).The scope of the present O-allylation catalyzed by (S)-1 a under the optimized conditions was examined [Eq. (2)], and the results are summarized in Table 2. The reactions of 2 a with various p...

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Regio‐ and Enantioselective O‐Allylation of Phenol and Alcohol Catalyzed by a Planar‐Chiral Cyclopentadienyl Ruthenium Complex

2008

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“…Indeed, complex 9 shows the shortestR u-P distance for any analogousc omplex with n = 1o r2 .T he shortest RuÀPd istance previouslyr eported was 2.231(2) . [28] The RuÀNd istances are, in most cases, relativelyi nsensitive to the other ligands at Ru.…”

Section: Coordination Chemistrymentioning

confidence: 98%

Filling a Niche in “Ligand Space” with Bulky, Electron‐Poor Phosphorus(III) Alkoxides

Hussein

Priester

Beet

et al. 2019

Chemistry A European J

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The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron‐rich species. Many of the electron‐poor PIII ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron‐poor PIII ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of PIII ligands bearing highly fluorinated alkoxide groups of the general form PRn(ORF)3−n, where R=Ph, RF=C(H)(CF3)2 and C(CF3)3; n=1–3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron‐poor ligands.

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“…For example, DFT calculations revealed that coordinatively unsaturated 16 electron fragments like [CpW(NO)(L)] may adopt singlet or triplet structures, which are separated by barriers of only 2-6 kcal mol 21 , depending on the nature of L. While the singlet state will adopt a pyramidal structure, a planar arrangement is predicted to be energetically preferable for the triplet species and this opens the possibility for a low-energy inversion pathway at the central metal atom via an intermediate spin-state change. 10 Techniques used to determine experimentally the ratios of enantiomeric complexes and their evolution with time include polarimetry and CD spectroscopy, although these methods are not that straightforward as NMR spectroscopy is in the analysis of mixtures of diastereomeric complexes that differ in the configuration at the metal atom, where isomer ratios can be directly obtained from the integration of suitable signals in the 1 H or especially 31 P NMR spectra in the case of phosphine complexes.…”

Section: (Vide Infra)mentioning

confidence: 99%

“…19] Whereas for the Cp based system 42 the two diastereomers 42a and 42b are formed in a 90+10 ratio, only one isomer is observed in the case of the sterically more demanding Cp* substituted derivative 43. The complex syntheses are carried out in refluxing toluene and the diastereomer ratios were determined by 31 P NMR spectroscopy from the crude reaction mixtures, so that they are not affected by workup manipulations and truly reflect the degree of stereodifferentiation in the complexation reactions. The reactions are under thermodynamic control, as a 4+1-mixture of 42a, b, obtained in another manner, equilibrates in hot toluene to approach the 90+10 value already observed in the original preparation.…”

Section: Cp-ligands With Tethered Chiral Donor Groupsmentioning

confidence: 99%

Chiral organometallic half-sandwich complexes with defined metal configuration

Ganter

2003

Chem. Soc. Rev.

150

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Chiral organometallic half-sandwich complexes with stereogenic metal atoms are close relatives of chiral organic compounds with stereogenic carbon atoms. Similarities and differences between these two classes of compounds are outlined. Some representative metal complexes are discussed in an introductory section followed by a more detailed treatment of the available strategies to control the metal configuration by means of chiral auxiliaries. Special sections are devoted to the discussion of the configurational stability of chiral-at-metal complexes and their applications in stoichiometric and catalytic stereoselective reactions.

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Highly selective induction of metal-centered chirality in the ligand exchange reaction of planar-chiral cyclopentadienyl–ruthenium complex bearing an anchor phosphine ligand

Cited by 24 publications

References 13 publications

Regio‐ and Enantioselective O‐Allylation of Phenol and Alcohol Catalyzed by a Planar‐Chiral Cyclopentadienyl Ruthenium Complex

Regio‐ and Enantioselective O‐Allylation of Phenol and Alcohol Catalyzed by a Planar‐Chiral Cyclopentadienyl Ruthenium Complex

Filling a Niche in “Ligand Space” with Bulky, Electron‐Poor Phosphorus(III) Alkoxides

Chiral organometallic half-sandwich complexes with defined metal configuration

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