+ Site Statistics
+ Search Articles
+ PDF Full Text Service
How our service works
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ Translate
+ Recently Requested

Chiral enol oxazolines and thiazolines as auxiliary ligands for the asymmetric synthesis of ruthenium-polypyridyl complexes

Chiral enol oxazolines and thiazolines as auxiliary ligands for the asymmetric synthesis of ruthenium-polypyridyl complexes

Chemistry, An Asian Journal 8(9): 2274-2280

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.

Please choose payment method:

(PDF emailed within 0-6 h: $19.90)

Accession: 052063643

Download citation: RISBibTeXText

PMID: 23818279

DOI: 10.1002/asia.201300598

Related references

Chiral-auxiliary-mediated asymmetric synthesis of ruthenium polypyridyl complexes. Accounts of Chemical Research 46(11): 2635-2644, 2014

Proline as chiral auxiliary for the economical asymmetric synthesis of ruthenium(II) polypyridyl complexes. Inorganic Chemistry 51(18): 10004-10011, 2013

Chiral-auxiliary-mediated asymmetric synthesis of tris-heteroleptic ruthenium polypyridyl complexes. Journal of the American Chemical Society 131(28): 9602-9603, 2009

Chiral salicyloxazolines as auxiliaries for the asymmetric synthesis of ruthenium polypyridyl complexes. Inorganic Chemistry 49(17): 7692-7699, 2010

Ruthenium-catalyzed asymmetric epoxidation of olefins using H2O2, part I: synthesis of new chiral N,N,N-tridentate pybox and pyboxazine ligands and their ruthenium complexes. Chemistry 12(7): 1855-1874, 2006

Influence of auxiliary ligands on the photophysical characteristics of a series of ruthenium(II)-polypyridyl complexes. Journal of Physical Chemistry. a 116(44): 10728-10735, 2013

Diamines as auxiliary ligands for tuning photophysical and electrochemical properties of Ruthenium(II) polypyridyl complexes. Journal of Molecular Structure 1158: 197-204, 2018

Trans ruthenium(II) complexes with NH-bridged tetradentate symmetric and asymmetric polypyridyl ligands. Inorganic Chemistry 41(23): 5937-5939, 2002

Synthesis and antioxidant activity of pyrazolyl-oxazolines/thiazolines and isoxazolyl-oxazolines/thiazolines. Medicinal Chemistry Research 23(3): 1084-1098, 2014

Reactivity studies of 6-arene ruthenium (II) dimers with polypyridyl ligands: isolation of mono, binuclear p-cymene ruthenium (II) complexes and bisterpyridine ruthenium (II) complexes. Polyhedron 22(23): 3155-3160, 2003

Ruthenium(Ii) complexes derived from C 2 -symmetric ferrocene-based chiral bis(phosphinite) ligands: synthesis and catalytic activity towards the asymmetric reduction of acetophenones. Applied Organometallic Chemistry 29(11): 764-770, 2015

Polypyridyl ruthenium(II) complexes with tetrazolate-based chelating ligands. Synthesis, reactivity, and electrochemical and photophysical properties. Inorganic Chemistry 46(22): 9126-9138, 2007

Synthesis, crystal structure and DNA-binding properties of ruthenium(II) polypyridyl complexes with dicationic 2,2-dipyridyl derivatives as ligands. Polyhedron 27(13): 2845-2850, 2008

Synthesis of ruthenium complexes with carbonyl and polypyridyl ligands derived from dipyrido(3,2-a:2',3'-c)phenazine: Application to the water gas shift reaction. Applied Organometallic Chemistry 17(1): 36-41, 2003

Asymmetric transfer hydrogenation of prochiral ketones catalyzed by chiral ruthenium complexes with aminophosphine ligands. Journal of Molecular Catalysis A: Chemical 147(1-2): 105-111, 1999