Direct and Transfer Hydrogenation of Ketones and Imines with a Ruthenium N-Heterocyclic Carbene Complex

Burling, Suzanne; Whittlesey, Michael K.; Williams, Jonathan M. J.

doi:10.1002/adsc.200404308

Cited by 113 publications

(37 citation statements)

References 29 publications

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“…A number of transition metal catalysts have been used for this transformation. The main focus has been on ruthenium(II) complexes [23][24][25][26][27][28][29]. However, in most of the cases, the reactions are effective only in the cases of ketones.…”

Section: Resultsmentioning

confidence: 99%

Ruthenium cationic species for transfer hydrogenation of aldehydes: Synthesis and catalytic properties of [(PPh3)2Ru(CH3CN)3Cl]+[A]− {A=BPh4 or ClO4} and structure of [(PPh3)2Ru(CH3CN)3Cl]+[BPh4]−

Naskar

Bhattacharjee

2005

Journal of Organometallic Chemistry

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Section: Resultsmentioning

confidence: 99%

Ruthenium cationic species for transfer hydrogenation of aldehydes: Synthesis and catalytic properties of [(PPh3)2Ru(CH3CN)3Cl]+[A]− {A=BPh4 or ClO4} and structure of [(PPh3)2Ru(CH3CN)3Cl]+[BPh4]−

Naskar

Bhattacharjee

2005

Journal of Organometallic Chemistry

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“…Since the [Ru 3 (CO) 12 ]-catalyzed reaction was reported first by Jones' group,11 several ruthenium complexes have been tested for transfer hydrogenation of imines with 2-propanol. [12][13][14][15][16][17][18] Wang and Bäckvall reported that a Ru-PPh 3 complex, [RuCl 2 (PPh 3 ) 3 ], catalyzes transfer hydrogenation of imines with 2-propanol and that addition of K 2 CO 3 dramatically enhances the catalytic activity of the ruthenium complex. 12 The role of the base was ascribed to formation of an alkoxoruthenium species that undergoes further -H elimination to produce a cationic ruthenium hydride species.…”

Section: Resultsmentioning

confidence: 99%

Catalytic Behavior of Cationic Hydridoruthenium(II) Complex, [RuH(NH3)(PMe3)4]+, in H2-Hydrogenation and Transfer Hydrogenation of Imines

Kayaki¹,

Ikeda²,

Tsurumaki³

et al. 2008

Bulletin of the Chemical Society of Japan

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Catalytic hydrogenation under H 2 and transfer hydrogenation of imines by secondary alcohols with hydridoruthenium complexes bearing PMe 3 and PPh 3 ligands have been examined. A cationic hydridoruthenium complex, cis-[RuH-(NH 3 )(PMe 3 ) 4 ]PF 6 (2), derived from cis-[RuH 2 (PMe 3 ) 4 ] (1) and NH 4 PF 6 , showed higher catalytic activity for H 2 -hydrogenation of N-benzylideneaniline than neutral complexes such as 1 and cis-[RuClH(PMe 3 ) 4 ] (6). The effectiveness of cationic hydridoruthenium species for the catalytic H 2 -hydrogenation of benzylideneaniline was also demonstrated by a marked increase in the yield of N-benzylaniline on treatment of 6 with AgPF 6 . The cationic complex 2 was applicable to catalytic transfer hydrogenation of imines with secondary alcohols even in the absence of a base. Isotope labeling experiments using deuterated alcohols revealed that the hydrogen atom bound to the -carbon of the donor alcohol was transferred exclusively to the imine carbon and alcoholic OD was transferred to the imine nitrogen. A rapid exchange between the alcoholic proton and the hydrido ligand of 2 was also confirmed by NMR investigation using (CH 3 ) 2 CHOD. On the basis of the experimental results the mechanisms of the H 2 -hydrogenation and transfer hydrogenation are discussed.The reduction of imines to amines is a convenient transformation for synthesizing amines as useful building blocks in pharmaceuticals and agrochemicals. A large body of work has been devoted over the past decades to designing effective transition-metal complexes for catalytic hydrogenation and transfer hydrogenation of imines.1 In these processes, catalytic cycles involving formation of metal hydrides and the subsequent hydrogen transfer to activated imines have been widely assumed.2 We have previously reported the synthesis and some catalytic activities of cationic monohydridoruthenium complexes bearing trimethylphosphine.3 While a cationic complex, cis-[RuH(NH 3 )(PMe 3 ) 4 ]PF 6 (2), can be easily prepared by treatment of a neutral dihydrido complex, cis-[RuH 2 (PMe 3 ) 4 ] (1), with an equimolar amount of NH 4 PF 6 in the presence of NH 3 in diethyl ether, use of acetone yielded an isopropylideneamine-coordinated hydridoruthenium complex cis-[RuH(HN= CMe 2 )(PMe 3 ) 4 ]PF 6 (3) (eqs 1 and 2). When the protonolysis of 1 with NH 4 PF 6 was performed in a hydrogen atmosphere at À60 C under otherwise identical conditions to the formation of 3, an amine-coordinated hydridoruthenium complex cis-[RuH(H 2 NCHMe 2 )(PMe 3 ) 4 ]PF 6 (4) was obtained via hydrogenation of isopropylideneamine (eq 3). These cationic hydrido complexes 3 and 4 can be regarded as models of the intermediates active in the catalytic hydrogenation of imines to amines.

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“…use of hydrogen gas) and transfer hydrogenation of imines and ketones [33] . Isopropanol is used as the hydrogen source, with a catalyst loading of 2 mol%.…”

Section: Carbene -Based Catalystsmentioning

confidence: 99%

Imino Reductions by Transfer Hydrogenation

Wills

2008

Modern Reduction Methods

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11 History and BackgroundIn contrast to ketones, and in particular with respect to asymmetric reductions, the reduction of compounds containing C = N bonds has remained relatively underdeveloped. Some signifi cant breakthroughs have, however, been reported in the last ten years. This chapter will review reductions through metal hydride complexes, " Meerwein -Ponndorf -Verley ( MPV ) type " reductions, and other methods including transfer hydrogenation with organocatalysts and asymmetric LeuckartWallach aminations of ketones. Although there will be discussion of mechanistic aspects, the main focus of this review will be on more recent synthetic applications. The reader ' s attention is also directed to a number of recent useful reviews of this area [1] . Mechanisms of C= N Bond Reduction by Transfer HydrogenationUsing either organic or organometallic catalysts, transfer hydrogenation of imines and other C = N bond -containing substrates, is most commonly carried out using isopropanol, formic acid or a formate salt as the hydrogen source. The most commonly, but not exclusively, used metals are ruthenium, rhodium and iridium.The mechanism of the transfer hydrogenation of imines has been the subject of some extended synthetic, computational and mechanistic studies. The tutorial review by B ä ckvall [1f] provides a very good summary of this. An excellent review by Morris [1c] also contains an incisive overview of hydrogenation and transfer hydrogenation and provides a very logical nomenclature for the possible reduction reaction pathway.The mechanisms that may be considered for imine reduction are the same as for ketone reductions and may be divided into two broad classes (Figure 11.1 ). In the fi rst of these, the MPV reduction or its reverse (Oppenauer oxidation), a metal

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Direct and Transfer Hydrogenation of Ketones and Imines with a Ruthenium N-Heterocyclic Carbene Complex

Abstract: Abstract:The dihydride ruthenium N-heterocyclic carbene complex Ru(IMes)(PPh 3 ) 2 CO(H) 2 (1) (IMes ¼ 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) is an efficient catalyst for both direct hydrogenation and transfer hydrogenation of ketones and imines, in the absence of base.

Cited by 113 publications

References 29 publications

Ruthenium cationic species for transfer hydrogenation of aldehydes: Synthesis and catalytic properties of [(PPh3)2Ru(CH3CN)3Cl]+[A]− {A=BPh4 or ClO4} and structure of [(PPh3)2Ru(CH3CN)3Cl]+[BPh4]−

Ruthenium cationic species for transfer hydrogenation of aldehydes: Synthesis and catalytic properties of [(PPh3)2Ru(CH3CN)3Cl]+[A]− {A=BPh4 or ClO4} and structure of [(PPh3)2Ru(CH3CN)3Cl]+[BPh4]−

Catalytic Behavior of Cationic Hydridoruthenium(II) Complex, [RuH(NH3)(PMe3)4]+, in H2-Hydrogenation and Transfer Hydrogenation of Imines

Imino Reductions by Transfer Hydrogenation

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