The Oxidation Potentials of Aldehydes and Ketones

Adkins, Homer; Elofson, R. M.; Rossow, Alfred G.; Robinson, Cowin C.

doi:10.1021/ja01179a012

Cited by 173 publications

(91 citation statements)

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“…These high values of rate and productivity of Os in hydrogenation are unprecedented [5, 6, 9a,b] and rely on a combination of the accelerating NÀH effect [1] with the robust metal frame. In the absence of H 2 in ethanol, these osmium complexes led to poor conversion of 10 a (less than 30 % after 2 h), in accordance with the unfavorable redox potential of ethanol for ketone reduction, [14] which indicates that transfer hydrogenation is a less important pathway when H 2 is used. Complex 3 has been proven to efficiently catalyze the hydrogenation of linear and cyclic aliphatic ketones 10 b and 10 c (S/ C = 50 000) and the diaryl ketone 10 d (S/C = 10 000) in less than 1 h. Also, the aromatic and aliphatic aldehydes 10 e and 10 f were easily and quantitatively reduced to primary alcohols within 10 min at 60 8C by using 0.5 mol % NaOEt.…”

mentioning

confidence: 79%

Chiral and Nonchiral [OsX₂(diphosphane)(diamine)] (X: Cl, OCH₂CF₃) Complexes for Fast Hydrogenation of Carbonyl Compounds

Baratta

Barbato

Magnolia

et al. 2010

Chemistry A European J

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The osmium complexes trans-[OsCl(2)(dppf)(diamine)] (dppf: 1,1'-bis(diphenylphosphino)ferrocene; diamine: ethylenediamine in 3, propylenediamine in 4) were prepared by the reaction of [OsCl(2)(PPh(3))(3)] (1) with the ferrocenyl diphosphane, dppf and the corresponding diamine in dichloromethane. The reaction of derivative 3 with NaOCH(2)CF(3) in toluene afforded the alkoxide cis-[Os(OCH(2)CF(3))(2)(dppf)(ethylenediamine)] (5). The novel precursor [Os(2)Cl(4)(P(m-tolyl)(3))(5)] (2) allows the synthesis of the chiral complexes trans-[OsCl(2)(diphosphane)(1,2-diamine)] (6-9; diphosphane: (R)-[6,6'-dimethoxy(1,1'-biphenyl)-2,2'-diyl]bis[1,1-bis(3,5-dimethylphenyl)phosphane] (xylMeObiphep) or (R)-(1,1'-binaphthalene)-2,2'-diylbis[1,1-bis(3,5-dimethylphenyl)phosphane] (xylbinap); diamine=(R,R)-1,2-diphenylethylenediamine (dpen) or (R,R)-1,2-diaminocyclohexane (dach)), obtained by the treatment of 2 with the diphosphane and the 1,2-diamine in toluene at reflux temperature. Compounds 3-5 in ethanol and in the presence of NaOEt catalyze the reduction of methyl aryl, dialkyl, and diaryl ketones and aldehydes with H(2) at low pressure (5 atm), with substrate/catalyst (S/C) ratios of 10,000-200,000 and achieving turnover frequencies (TOFs) of up to 3.0 x 10(5) h(-1) at 70 degrees C. By employment of the chiral compounds 6-9, different ketones, including alkyl aryl, bulky tert-butyl, and cyclic ketones, have successfully been hydrogenated with enantioselectivities up to 99% and with S/C ratios of 5000-100,000 and TOFs of up to 4.1 x 10(4) h(-1) at 60 degrees C.

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mentioning

confidence: 79%

Chiral and Nonchiral [OsX₂(diphosphane)(diamine)] (X: Cl, OCH₂CF₃) Complexes for Fast Hydrogenation of Carbonyl Compounds

Baratta

Barbato

Magnolia

et al. 2010

Chemistry A European J

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“…The 31 P NMR spectrum of 10 in the presence of this alcohol shows two doublets at d = 2.5 and 0.6 ppm ( 2 J P,P = 9.0 Hz) in addition to those of 10, which is consistent with the formation of the alcohol adduct 10·(ROH). It should be pointed out that the synthesis of 10 is accomplished without isolation of the hydride and by exploiting the higher redox potential of the diaryl ketone compared to Me 2 CO. [14] Since our investigations show that chloride 3 forms an equilibrium mixture of hydride and alkoxide complexes in basic alcohol, it is probable that these species are involved in both TH [7b, 15] and HY. Thus, [OsH(CNN)P 2 ] is likely to be a key species in both catalytic reactions and leads to the alkoxide [Os(OR)(CNN)P 2 ] upon reaction with the ketone substrate.…”

Section: Methodsmentioning

confidence: 99%

Osmium(II) CNN Pincer Complexes as Efficient Catalysts for Both Asymmetric Transfer and H₂ Hydrogenation of Ketones

et al. 2008

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Catalytic asymmetric hydrogenation (HY) and transfer hydrogenation (TH) of carbonyl compounds are usually performed with Ru, Rh, and Ir complexes, [1] and much less attention has been devoted to other transition-metal basedsystems. Although osmium complexes have occasionally been employed in the HY [2] and TH [3] of carbonyl compounds, we have recently shown that [OsCl 2 P 2 (Pyme)][4a] [P 2 = diphosphane; Pyme = 1-(pyridin-2-yl)methanamine)] complexes are extremely active catalysts in the TH of ketones, with reaction rates comparable to those of their Ru analogues.[4b] Owing to the stronger bonding of Os compared to Ru, robust and thermally stable chiral complexes can be obtained using a suitable set of ligands, which is a crucial breakthrough in achieving catalysts that display high productivity.[5] Since the CNN pincer complexes [RuCl(CNN)P 2 ][6] obtained from 1-(6-arylpyridin-2-yl)methanamines (HCNN) are among the most active catalysts for the TH of carbonyl compounds, we decided to investigate the chemistry of osmium complexes with CNN ligands and report herein the isolation of the first CNN pincer osmium derivatives [OsCl(CNN)P 2 ]. These complexes are extremely active and productive catalysts for both the TH and HY of ketones (turnover frequency (TOF) of up to 1.3 10 6 h À1 ). Moreover, asymmetric TH [7] and HY [1] have been achieved (ee values of up to 98 %) with a remarkably low loading (0.005-0.002 mol %) of the chiral version of these pincer complexes. Finally, the reversible nature of the ketone insertion into the Os À H bond suggests that Os-hydride and Os-alkoxide species are involved in TH and HY. Treatment of [OsCl 2 (PPh 3 ) 3 ] with 1 a (1.2 equiv) in 2-propanol in the presence of the weak base NEt 3 at reflux for 2 h affords the CNN pincer complex 2 [8] in 94 % yield (Scheme 1). The 31 P NMR spectrum of 2 shows two doublets at d = 7.1 and À1.6 ppm with a 2 J P,P coupling constant of 15.7 Hz, which is typical for a cis OsP 2 arrangement. The singlet at d = 7.95 ppm in the 1 H NMR spectrum is due to the CH proton close to the orthometalated carbon. Complex 3[8] is easily obtained in high yield upon treatment of [OsCl 2 (PPh 3 ) 3 ] with Ph 2 P(CH 2 ) 4 PPh 2 (dppb) and then with 1 a in the presence of NEt 3 (Scheme 1). The NCH 2 group gives a 13 C NMR signal at d = 54.8 ppm ( 3 J C,P = 2.6 Hz), whereas the orthometalated carbon appears at d = 161.5 ppm ( 2 J C,P = 9.0 and 3.9 Hz). The chiral pincer complex 4 was prepared in a similar manner to 3 but with dppb in combination with 1 b (85 % yield), whereas 5 and 6 (55 and 47 % yield, respectively) were obtained from (S,R)-Josiphos with 1 a and 1 c, respectively (Scheme 1).[8] 31 P NMR spectroscopic control experiments revealed the formation of different isomers in the reaction mixtures; the predominant stereoisomer was isolated from the reaction mixtures.The osmium derivatives 2-6 were found to be highly active catalysts for the TH of different ketones 7 (0.1m) in basic 2-propanol (Scheme 2). Thus, fast reduction of acetophenone (7 a) into 1-pheny...

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“…[11] It is worth noting that because of the higher redox potentials of aldehydes/primary alcohols relative to those of ketones/secondary alcohols, the dehydrogenation of secondary alcohols is thermodynamically easier. [12] In addition, the catalytic alcohol dehydrogenation represents a key step for broadening the alcohol reactivity, thus giving access to CÀC and CÀN bond-forming reactions through a hydrogen borrowing process. [1e] Recently, the Ru and Os phosphane complexes cis-[MCl 2 (PP)A C H T U N G T R E N N U N G (ampy)] (M = Ru, [13] Os; [14] PP = diphosphane, ampy = 2-(aminomethyl)pyridine) were found to be highly efficient catalysts for the (asymmetric) transfer hydrogenation and hydrogenation of ketones.…”

Section: A C H T U N G T R E N N U N G (=Chph)a C H T U N G T R E N Nmentioning

confidence: 99%

Pincer and Diamine Ru and Os Diphosphane Complexes as Efficient Catalysts for the Dehydrogenation of Alcohols to Ketones

Baratta

Bossi

Putignano

et al. 2011

Chemistry A European J

146

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The ruthenium and osmium complexes [MCl(2)(diphosphane)(L)] (M=Ru, Os; L=bidentate amino ligand) and [MCl(CNN)(dppb)] (CNN=pincer ligand; dppb=1,4-bis-(diphenylphosphino)butane), containing the N−H moiety, have been found to catalyze the acceptorless dehydrogenation of alcohols in tBuOH and in the presence of KOtBu. The compounds trans-[MCl(2)(dppf)(en)] (M=Ru 7, Os 13; dppf=1,1'-bisdiphenylphosphino)ferrocene; en=ethylenediamine) display very high activity and different substrates, including cyclic and linear alcohols, are efficiently oxidized to ketones by using 0.8-0.04 mol % of catalyst. The effect of the base and the comparison of the catalytic activity of the Ru versus Os complexes are reported. The ruthenium complex 7 generally leads to a faster conversion into ketones with respect to the osmium complex 13, which displays better activity in the dehydrogenation of 5-en-3β-hydroxy steroids. The synthesis of new Ru and Os complexes [MCl(2)(PP)(L)] (PP=dppb, dppf; L=(±)-trans-1,2-diaminocyclohexane,2-(aminomethyl)pyridine, and 2-aminoethanol) of trans and cis configuration is also reported.

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The Oxidation Potentials of Aldehydes and Ketones

Cited by 173 publications

References 3 publications

Chiral and Nonchiral [OsX₂(diphosphane)(diamine)] (X: Cl, OCH₂CF₃) Complexes for Fast Hydrogenation of Carbonyl Compounds

Chiral and Nonchiral [OsX₂(diphosphane)(diamine)] (X: Cl, OCH₂CF₃) Complexes for Fast Hydrogenation of Carbonyl Compounds

Osmium(II) CNN Pincer Complexes as Efficient Catalysts for Both Asymmetric Transfer and H₂ Hydrogenation of Ketones

Pincer and Diamine Ru and Os Diphosphane Complexes as Efficient Catalysts for the Dehydrogenation of Alcohols to Ketones

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The Oxidation Potentials of Aldehydes and Ketones

Cited by 173 publications

References 3 publications

Chiral and Nonchiral [OsX2(diphosphane)(diamine)] (X: Cl, OCH2CF3) Complexes for Fast Hydrogenation of Carbonyl Compounds

Chiral and Nonchiral [OsX2(diphosphane)(diamine)] (X: Cl, OCH2CF3) Complexes for Fast Hydrogenation of Carbonyl Compounds

Osmium(II) CNN Pincer Complexes as Efficient Catalysts for Both Asymmetric Transfer and H2 Hydrogenation of Ketones

Pincer and Diamine Ru and Os Diphosphane Complexes as Efficient Catalysts for the Dehydrogenation of Alcohols to Ketones

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Chiral and Nonchiral [OsX₂(diphosphane)(diamine)] (X: Cl, OCH₂CF₃) Complexes for Fast Hydrogenation of Carbonyl Compounds

Chiral and Nonchiral [OsX₂(diphosphane)(diamine)] (X: Cl, OCH₂CF₃) Complexes for Fast Hydrogenation of Carbonyl Compounds

Osmium(II) CNN Pincer Complexes as Efficient Catalysts for Both Asymmetric Transfer and H₂ Hydrogenation of Ketones