om060892x_si_008.cif (30.34 kB)
pH-Dependent Selective Transfer Hydrogenation of α,β-Unsaturated Carbonyls in Aqueous Media Utilizing Half-Sandwich Ruthenium(II) Complexes
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posted on 2007-01-15, 00:00 authored by Charles A. Mebi, Radhika P. Nair, Brian J. FrostHalf-sandwich ruthenium(II) PTA complexes bearing the 1,2-dihydropentalenyl (C8H9-, Dp) and indenyl
(C9H7-, Ind) ancillary ligands have been synthesized and characterized using multinuclear NMR
spectroscopy and X-ray crystallography. The complexes DpRu(PTA)(PPh3)Cl, DpRu(PTA)2Cl, IndRu(PTA)(PPh3)Cl, and [IndRu(PTA)2(PPh3)]Cl were obtained in good to excellent yields. The solid-state
structures of these compounds exhibit piano stool geometries with η5-coordination of the indenyl and
dihydropentalenyl moieties. DpRu(PTA)2Cl is water-soluble (S25°C = 43 mg/mL), while the mixed
phosphine compounds are slightly soluble in acidic solutions. The Ru−H complexes, Cp‘Ru(PTA)(PPh3)H
(Cp‘ = Ind, Cp), have been synthesized in good yield and spectroscopically and structurally characterized.
The ruthenium hydrides undergo an H/D exchange reaction with CD3OD with relative rates CpRu(PTA)(PPh3)H ≫ IndRu(PTA)(PPh3)H > CpRu(PTA)2H. The air-stable Cp‘Ru(PTA)(PR3)Cl complexes (Cp‘
= Cp, Dp, Ind; PR3 = PPh3 or PTA) exhibit activity in the regioselective transfer hydrogenation of
α,β-unsaturated carbonyls in aqueous media with HCOONa, HCOOH, or isopropanol/Na2CO3 serving
as the hydrogen source. They were found to be effective in the selective reduction of the carbonyl
functionality of cinnamaldehyde and the CC bond of benzylidene acetone and chalcone. IndRu(PTA)(PPh3)Cl was less active than Cp‘Ru(PTA)(PPh3)Cl (Cp‘ = Cp or Dp). Results of the transfer hydrogenation
of unsaturated substrates using CpRu(PTA)(PPh3)H are also reported.
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PPh 3multinuclear NMR spectroscopycarbonyl functionalityregioselective transfer hydrogenationPR 3HCOOHtransfer hydrogenationIndRubenzylidene acetonePTAphosphine compoundscompounds exhibit piano stool geometriesCD 3ODruthenium hydridesTransfer Hydrogenationhydrogen sourceC 9H IndCpcomplexacidic solutionsexhibit activityC 8H Dpdihydropentalenyl moieties
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