Schiff bases as added chiral ligands for the [Ru(η6-C6H6)Cl2]2 catalysed hydrogen-transfer reduction of ketones with 2-propanol

Krasik, Pavel; Alper, Howard

doi:10.1016/s0040-4020(01)89371-6

Cited by 63 publications

(12 citation statements)

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“…The rhodium aquo complexes are fluxional on the NMR time scale. At room temperature, in acetone- d , the 1 H NMR spectra of the aquo complexes prepared from compounds 1 and 2 consists of a set of broad signals, whereas at −80 °C two sets of peaks are observed in 70:30 intensity ratio. For the ruthenium compounds, the mixtures contain comparable amounts of at least three components whose structures were not further investigated.…”

Section: Resultsmentioning

confidence: 99%

“…Although chiral transition metal half-sandwich compounds have been extensively used as catalysts or catalyst precursors in various organic processes, the catalytic use of imino compounds of this type has been very scarce. As far as we know, only the asymmetric hydrogen transfer reduction of alkyl−aryl ketones with 2-propanol, catalyzed by ruthenium complexes generated in situ from [{(η 6 -C 6 H 6 )RuCl} 2 (μ-Cl) 2 ] and chiral Schiff bases derived from ( 1R,2R )-diaminocyclohexane and aromatic aldehydes, has previously been reported …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Imino−Rhodium(III) and −Ruthenium(II) Compounds with Stereogenic Metal Centers

Carmona¹,

Vega²,

Lahoz³

et al. 1999

Organometallics

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The synthesis and characterization of optically active imino complexes (R M or S M)-[(η5-C5Me5)RhCl(imine)][SbF6] (imine = L n = N-(2-pyridylmethylene)-(R)-1-phenylethylamine (L1) (1a,a‘), N-(2-pyridylmethylene)-(R)-1-naphthylethylamine (L2) (2a,a‘), N-(2-pyridylmethylene)-(R)-1-cyclohexylethylamine (L3) (3a,a‘)) or [(η6-p-MeC6H4 iPr)RuCl(imine)]A (A = SbF6, imine = L1 (4a,a‘), L2 (5a,a‘), L3 (6a,a‘), N-(2-pyridylmethylene)-(1R,2S,4R)-1-bornylamine) (L4) (7a,a‘); (A = BF4, imine = L1 (4b,b‘), L2 (5b,b‘), L3 (6b,b‘), L4 (7b,b‘)) is reported. The absolute crystal structures of the (R Rh)-1a and (R Ru)-7b epimers were determined by X-ray analysis. Both complexes possess a chiral metal center in a pseudo-octahedral environment, being bonded to an η5-C5Me5 group (1a) or to an (η6-p-MeC6H4 iPr) ring (7b), a terminal chloride, and, in a chelating fashion, to the two nitrogen atoms of the imine ligand. At room temperature, in acetone or chloroform, the complexes are configurationally stable but in refluxing methanol epimerize at the metal center. Dichloromethane/acetone solutions of the solvate complexes [(η n -ring)M(imine)S]2+ are active catalysts for the Diels−Alder reaction between methacrolein or acrolein and cyclopentadiene. The reaction occurs rapidly at room temperature and, in general, good exo/endo selectivities and moderate enantioselectivities are achieved.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Imino−Rhodium(III) and −Ruthenium(II) Compounds with Stereogenic Metal Centers

Carmona¹,

Vega²,

Lahoz³

et al. 1999

Organometallics

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“…Although C 2 chiral ligands have been widely used in a series of catalytic processes because of their ability to generate high chiral inductions, [8] only a few ruthenium complexes containing C 2 polydentate N ligands have been reported in transfer hydrogenations. As far as we know, only examples bearing diaminoferrocenyl derivatives [6e, 9] (C), bis(oxazolines) [10] (D, E), aromatic substituted diimines [11] (F) and diamines [12] (G) have been described. [13] In particular, only one ruthenium complex, containing the tridentate N,N,N ligand bis(oxazolinylmethyl)amine (D), has been reported (prepared in situ from [RuCl 2 (PPh 3 )] and D).…”

Section: Introductionmentioning

confidence: 99%

New Chiral Ruthenium(II) Catalysts Containing 2,6‐Bis(4′‐(R)‐phenyloxazolin‐2′‐yl)pyridine (Ph‐pybox) Ligands for Highly Enantioselective Transfer Hydrogenation of Ketones

Cuervo

Gamasa

Gimeno

2004

Chemistry A European J

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Treatment of complex trans-[RuCl(2)(eta(2)-C(2)H(4))[kappa(3)-N,N,N-(R,R)-Ph-pybox]] [(R,R)-Ph-pybox = 2,6-bis[4'-(R)-phenyloxazolin-2'-yl]pyridine] with phosphines or phosphites in dichloromethane at 50 degrees C leads to the formation of novel ruthenium(II)-pybox complexes trans-[RuCl(2)(L)[kappa(3)-N,N,N-(R,R)-Ph-pybox]] [L = PPh(3) (1 a), PPh(2)Me (2 a), PPh(2)(C(3)H(5)) (3 a), PPh(2)(C(4)H(7)) (4 a), PMe(3) (5 a), PiPr(3) (6 a), P(OMe)(3) (7 a) and P(OPh)(3) (8 a)]. Likewise, reaction of trans-[RuCl(2)(eta(2)-C(2)H(4))[kappa(3)-N,N,N-(R,R)-Ph-pybox]] with PPh(3) or PiPr(3) in refluxing methanol leads to the complexes cis-[RuCl(2)(L)(kappa(3)-N,N,N-(R,R)-Ph-pybox] [L = PPh(3) (1 b), PiPr(3) (6 b)]. No trans-cis isomerisation of complexes 1 a-8 a has been observed. Complexes 1 a-8 a, 1 b, 6 b together with the analogous trans-[RuCl(2)[P(OMe)(3)][kappa(3)-N,N,N-(S,S)-iPr-pybox]] (10 a) and the previously reported trans- and cis-[RuCl(2)(PPh(3))[kappa(3)-N,N,N-(S,S)-iPr-pybox]] (9 a and 9 b, respectively) are active catalysts for the transfer hydrogenation of acetophenone in 2-propanol in the presence of NaOH (ketone/cat/NaOH 500:1:6). cis-Ph-pybox derivatives are the most active catalysts. In particular, cis complexes 1 b and 6 b led to almost quantitative conversions in less than 5 min with a high enantioselectivity (up to 95 %). A variety of aromatic ketones have also been reduced to the corresponding secondary alcohols with very high TOF and ee up to 94 %. The overall catalytic performance seems to be a subtle combination of the steric and/or electronic properties both the phosphines and the ketones. A high TOF (27 300 h(-1)) and excellent ee (94 %) have been found for the reduction of 3-bromoacetophenone with catalyst 6 b. Reductions of alkyl ketones also proceed with high and rapid conversions but low enantioselectivities are achieved.

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“…Transfer hydrogenation of ketones, aldehydes, and alkenes using homogenous catalysts was successfully realized by Henbest et al One of the earliest reports of enantioselective transfer hydrogenation was by Alper et al, who used chiral Schiff bases and a dichlororuthenium(II)benzene complex employing the IPA system [5]. In another report, Lemaire et al utilized chiral diamines complexed with rhodium [6].…”

Section: Early Studiesmentioning

confidence: 99%

Enantioselective Transfer Hydrogenation

Blacker¹

2006

The Handbook of Homogeneous Hydrogenation

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Transfer hydrogenation is the movement of a hydride ion and proton (or two protons and two electrons) from a hydrogen donor to a substrate acceptor, effectively a disproportionation. In the case of hydrogenation, molecular hydrogen is the donor, and this topic is considered elsewhere in this Handbook. The substrate acceptor is unsaturated and can be, for example, a ketone, imine or alkene. The hydrogen donor is a good reductant and is often an alcohol, alkane or formate. The reaction is mediated by a catalyst that helps in the hydride transfer. When applied to ketones using isopropanol as the hydrogen donor and a Lewis acid to catalyze the reaction, the non-asymmetric transformation is known as the Meerwein-Pondorf-Verley reaction. Transfer dehydrogenation is the movement of a hydride ion and proton in the opposite direction. For alcohol substrates yielding ketone products, it is also known as the Oppenauer oxidation.If the catalyst is chiral, it can transfer hydride selectively to one prochiral face of an acceptor to provide an optically active product ( Fig. 35.1).A number of excellent reviews have recently been published [1]; consequently, this chapter will consider mainly the practical aspects of asymmetric transfer hydrogenation by reviewing each of the components of the reaction, namely catalyst, hydrogen donor, substrate, product and other elements such as solvent, reaction conditions and scale-up.In broad terms there are three types of catalyst for transfer hydrogenation: dehydrogenases; heterogeneous; and homogenous metal catalysts. Here, the first two are mentioned for completeness, and the main focus of this chapter will be asymmetric transfer hydrogenation with homogenous metal catalysts.Nature uses enantioselective transfer hydrogenation to reduce metabolites, for example pyruvate to give (S)-lactic acid and 2-ketoglutarate to give (S)-2-hydroxyglutarate. The reaction is reversible and the equilibrium position depends on the concentration of the species. The enzyme catalysts are named dehydrogenases, and they employ a soluble cofactor or hydride acceptor called NAD(P) in its oxi- 1215The Handbook of Homogeneous Hydrogenation. Edited by J. G. de Vries and C. J. Elsevier

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Schiff bases as added chiral ligands for the [Ru(η6-C6H6)Cl2]2 catalysed hydrogen-transfer reduction of ketones with 2-propanol

Cited by 63 publications

References 9 publications

Imino−Rhodium(III) and −Ruthenium(II) Compounds with Stereogenic Metal Centers

Imino−Rhodium(III) and −Ruthenium(II) Compounds with Stereogenic Metal Centers

New Chiral Ruthenium(II) Catalysts Containing 2,6‐Bis(4′‐(R)‐phenyloxazolin‐2′‐yl)pyridine (Ph‐pybox) Ligands for Highly Enantioselective Transfer Hydrogenation of Ketones

Enantioselective Transfer Hydrogenation

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