Chiral N,N‘- and N,O-Bidentate Anionic Ligands. Preparation, Metal Complexation, and Evaluation in the Asymmetric Aziridination of Olefins

Bertilsson, Sophie K.; Tedenborg, Lars; Alonso, Diego A.; Andersson, Pher G.

doi:10.1021/om981016p

Cited by 35 publications

(17 citation statements)

References 32 publications

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“…As with the neutral ligands, the anionic ligands can be divided into several families according to their potential coordination behavior. An important additional feature which allows differentiation is whether the anionic charge is carried by an external atom as in systems such as 27 ,125, 160, 162, 165, 199, 200 28 ,143 29 ,137, 138 30 ,131, 169, 172 31 ,191 or on the pyrrole nitrogen of pyrrole oxazolines,201 or largely localized on the oxazoline nitrogen atom as in 32 . 128, 129, 136, 147, 161, 168, 202 A further example will be shown below with 40 210.…”

Section: Oxazoline‐based Ligandsmentioning

confidence: 99%

Hemilability of Hybrid Ligands and the Coordination Chemistry of Oxazoline-Based Systems

Braunstein

Naud

2001

Angew. Chem. Int. Ed.

951

618

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Ligand design is becoming an increasingly important part of the synthetic activity in chemistry. This is of course because of the subtle control that ligands exert on the metal center to which they are coordinated. Ligands which contain significantly different chemical functionalities, such as hard and soft donors, are often called hybrid ligands and find increasing use in molecular chemistry. Although the interplay between electronic and steric properties has long been recognized as essential in determining the chemical or physical properties of a complex, predictions remain very difficult, not only because of the considerable diversity encountered within the Periodic Table—different metal centers will behave differently towards the same ligand and different ligands can completely modify the chemistry of a given metal—but also because of the small energy differences involved. New systems may—even through serendipity—allow the emergence of useful concepts that can gain general acceptance and help design molecular structures orientated towards a given property. The concept of ligand hemilability, which finds numerous illustrations with hybrid ligands, has gained increased acceptance and been found to be very useful in explaining the properties of metal complexes and in designing new systems for molecular activation, homogeneous catalysis, functional materials, or small‐molecule sensing. In the field of homogeneous enantioselective catalysis, in which steric and/or electronic control of a metal‐mediated process must occur in such a way that one stereoisomer is preferentially formed, ligands containing one or more chiral oxazoline units have been found to be very valuable for a wide range of metal‐catalyzed reactions. The incorporation of oxazoline moieties in multifunctional ligands of increasing complexity makes such ligands good candidates to display hemilabile properties, which until recently, had not been documented in oxazoline chemistry. Herein, we briefly recall the definition and scope of hemilabile ligands, present the main classes of ligands containing one or more oxazoline moieties, with an emphasis on hybrid ligands, and finally explain why the combination of these two facets of ligand design appears particularly promising.

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Section: Oxazoline‐based Ligandsmentioning

confidence: 99%

Hemilability of Hybrid Ligands and the Coordination Chemistry of Oxazoline-Based Systems

Braunstein

Naud

2001

Angew. Chem. Int. Ed.

951

618

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“…[RuCl 2 A C H T U N G T R E N N U N G (dmso) 4 ], [13] the chiral auxiliaries, [12] and complex L-(S)-2 d [14] were prepared according to literature procedures and other reagents were purchased from Acros, Aldrich, or Alfa and used without further purification. Solvents were distilled under an argon atmosphere from calcium hydride (MeCN, CH 2 Cl 2 , DMF) or sodium/benzophenone (THF).…”

Section: Materials and General Methodsmentioning

confidence: 99%

“…; from L-(S)-2 c: 77 % yield, 22:1 e.r. [12] We became intrigued by this class of bidentate ligands with respect to asymmetric coordination chemistry because 1) the oxazoline moiety should be able to control the metal-centered stereochemistry during the course of the coordination chemistry and 2) the basic enolate oxygen atom or the alkene C=C double bond should allow for the labilization of this ligand through protonation by weak acids or oxidative cleavage of the double bond, respectively. ; from L-(S)-2 c: 85% yield, 25:1 e.r.…”

Section: Introductionmentioning

confidence: 99%

Chiral Enol Oxazolines and Thiazolines as Auxiliary Ligands for the Asymmetric Synthesis of Ruthenium‐Polypyridyl Complexes

Huang¹,

Wang²,

Gong³

et al. 2013

Chemistry An Asian Journal

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Various ligands, such as (Z)-1-phenyl-2-[(4S)-4-phenyl-4,5-dihydro-1,3-oxazol-2-yl]ethen-1-ol ((S)-1a) and (Z)-1-phenyl-2-[(4S)-4-phenyl-4,5-dihydro-1,3-thiazol-2-yl]ethen-1-ol ((S)-1c), were investigated as auxiliaries for the asymmetric synthesis of chiral ruthenium(II) complexes. The reaction of these chiral auxiliary ligands with [RuCl2(dmso)4], 2,2′-bipyridine (bpy, 2.2 equiv), and triethylamine (10 equiv) in DMF/PhCl (1:8) at 140 °C for several hours diastereoselectively provided the complexes Λ-[Ru(bpy)2{(S)-1a-H}] (Λ-(S)-2a, 52 % yield, 56:1 d.r.) and Λ-[Ru(bpy)2{(S)-1c-H}] (Λ-(S)-2c, 48 % yield, >100:1 d.r.) in a single step after purification. Both Λ-(S)-2a and Λ-(S)-2c could be converted into Λ-[Ru(bpy)3](PF6)2 by replacing the bidentate enolato ligands with bpy, under retention of configuration, induced by either NH4PF6 as a weak acid (from Λ-(S)-2a: 73 % yield, 22:1 e.r.; from Λ-(S)-2c: 77 % yield, 22:1 e.r.), TFA as a strong acid (from Λ-(S)-2a: 72 % yield, 52:1 e.r.; from Λ-(S)-2c: 85 % yield, 25:1 e.r.), methylation with Meerwein′s salt (from Λ-(S)-2a: 59 % yield, 46:1 e.r.; from Λ-(S)-2c: 86 % yield, 37:1 e.r.), ozonolysis (from Λ-(S)-2a: 56 % yield, 22:1 e.r.; from Λ-(S)-2c: 43 % yield, 6.3:1 e.r.), or oxidation with a peroxy acid (from Λ-(S)-2a: 72 % yield, 45:1 e.r.; from Λ-(S)-2c: 79 % yield, 8.5:1 e.r.). This study shows that, except for the reaction with NH4PF6, oxazoline-enolato complex Λ-(S)-2a provides Λ-[Ru(bpy)3](PF6)2 with higher enantioselectivities than analogous thiazoline-enolato complex Λ-(S)-2c, which might be due to the higher coordinative stability of the thiazoline-enolato complex, thus requiring more prolonged reaction times. Thus, this study provides attractive new avenues for the asymmetric synthesis of non-racemic ruthenium(II)-polypyridyl complexes without the need for using a strong acid or a strong methylating reagent, as has been the case in all previously reported auxiliary methods from our group.

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“…The solvent was removed under reduced pressure, and the residue was washed with aqueous NaOH (5 mL, 2 m) and CH 2 Cl 2 (3 Â 20 mL 3, 25.5, 29.3, 46.0, 51.4, 59.0, 60.1, 64.1, 75.8, 80.6, 110.1, 124.7, 127.4, 127.8, 127.97, 128.0, 141.4, 143.8, 174 5, 28.9, 44.5, 52.5, 57.3, 57.4, 80.8, 81.8, 110.7, 124.7, 128.1, 141.6, 174.1. Reduction of the ester according to the given procedure for 2 a afforded ligand 2 c in 67 % yield. [ 3.47 (dd,J 10.8,5.6 Hz,1 H) 4.15 (d,J 5.2 Hz,1 H),4.31 (d,J 5.2 Hz,1 H),7.25 ± 7.60 (m,5 H); 13 C NMR (100 MHz,CDCl 3 ): d 25.4,28.0,41.8,56.0,56.9,64.9,80.9,82.1,110.0,124.7,125.2,127.9,128.1,141.5;MS (EI): m/z (%): 262 (14) [M] , 220 (48), 205 (27), 152 (14), 1124 (21), 105 (100), 80 (55); elemental analysis calcd (%) for C 15 H 19 NO 3 : C 68.94,H 7.33,N 5.36;found C 69.06,H 39,N 5.28.…”

Section: Methodsmentioning

confidence: 99%

Remote Dipole Effects as a Means to Accelerate [Ru(amino alcohol)]-Catalyzed Transfer Hydrogenation of Ketones

Nordin¹,

Roth²,

Tarnai³

et al. 2001

Chem. Eur. J.

Self Cite

111

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A new generation of 2-aza-norbornyl amino alcohol ligands for the catalytic transfer hydrogenation reaction of aromatic ketones was synthesized. Extremely active catalysts were formed by introducing a ketal functionality at the rear end of the ligand. Acetophenone was reduced in 96% ee at low catalyst loading, substrate to catalyst ratio, S/C 5000, within 90 minutes with isopropyl alcohol as the hydrogen donor. It was found that the dioxolane substituent in the ligand increased the turnover frequency, TOF50, from 1050 h(-1) to 3000 h(-1) at an S/C ratio of 1000. Introduction of a methyl group at the carbinol carbon resulted in TOF50 as high as 8500 h(-1). Transfer hydrogenation of a range of aromatic ketones was evaluated and found to reach completion within 30 minutes at room temperature, and excellent enantioselectivity, up to 99 % ee, was obtained. A possible explanation for the enhanced activity was provided by density functional calculations, which showed that the presence of a remote dipole in the ligand lowered the transition state energy.

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Chiral N,N‘- and N,O-Bidentate Anionic Ligands. Preparation, Metal Complexation, and Evaluation in the Asymmetric Aziridination of Olefins

Cited by 35 publications

References 32 publications

Hemilability of Hybrid Ligands and the Coordination Chemistry of Oxazoline-Based Systems

Hemilability of Hybrid Ligands and the Coordination Chemistry of Oxazoline-Based Systems

Chiral Enol Oxazolines and Thiazolines as Auxiliary Ligands for the Asymmetric Synthesis of Ruthenium‐Polypyridyl Complexes

Remote Dipole Effects as a Means to Accelerate [Ru(amino alcohol)]-Catalyzed Transfer Hydrogenation of Ketones

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