Multiphase heterogeneous catalytic enantioselective hydrogenation of acetophenone over cinchona-modified Pt/C

The multiphase heterogeneous enantioselective hydrogenation of acetophenone in the presence of cinchona-modified Pt/C was investigated. The system demonstrated the feasibility of this reaction on non-activated ketones. The reaction proceeded selectively, at room temperature and atmospheric pressure, towards the formation of 1-phenylethanol, with up to 20% ee (enantiomeric excess) of either enantiomer depending on the modifier used. A mode of action of the modifier is proposed to account for the mechanism. A comparison with other systems indicates that the investigated system likely acts by a different mechanism, and that it is quite specific for acetophenone.     

Rhodium phosphine complexes immobilized on silica as active catalysts for 1-hexene hydroformylation and arene hydrogenation

In immobilizing the rhodium complexes [Rh(acac)(CO)(P)] (1) and [Rh(acac)(P)₂] (2) (P = Ph₂PCH₂CH₂Si(OMe)₃) onto SiO₂, acetylacetone is found to be released through protonation of the acac ligand by the acidic silica-OH groups. The resulting complexes [Rh(O-{SiO₂}(HO-{SiO₂})(CO)(P-{SiO₂})] (1a) and [Rh(O-{SiO₂})(HO-{SiO₂})(P-{SiO₂})₂] (2a) were successfully tested with respect to their catalytic action on 1-hexene hydroformylation as well as benzene and toluene hydrogenation. The reaction outcome, viz. the formation of aldehydes versus isomerization, depends strongly on the presence and concentration of a phosphine co-catalyst. Thus, while 1a gave only a 17% yield of aldehyde in the absence of phosphines, the yield is increased to 54% in the presence of phosphinated silica P-{SiO₂} or even 94% if PPh₃ is added to the solution. Without extra added phosphine, both 1a and 2a effect mainly the isomerization of 1-hexene to 2-hexene. Pre-catalyst 1a catalyzes also the hydrogenation of benzene at 10.5 atm H₂ and 90 °C to give cyclohexane with a TOF of 608 h⁻¹.     

Synthesis of new boron complexes: application to transfer hydrogenation of acetophenone derivatives

Two new boron complexes were synthesized from N‐[3‐(methylmercapto)aniline]‐3,5‐di‐tert‐butylsalicylaldimine ( LH ) with boron reagent BPh₃ or BF₃.Et₂O. These boron complexes are stable and easily soluble in protic solvents such as ethanol (C₂H₅OH) but hardly soluble in nonprotic solvents such as chloroform (CHCl₃), dichloromethane (CH₂Cl₂) and tetrahydrofuran (THF). All new boron complexes have been fully characterized by both analytical and spectroscopic methods. The catalytic activities of complexes [LBPh₂], 2 , and [LBF₂], 3 , in the transfer hydrogenation of acetophenone derivatives were tested. Stable boron complexes were found to be efficient catalysts in the transfer hydrogenation of aromatic ketones in good conversions up to 99% in the presence of iso‐PrOH/KOH. Copyright © 2011 John Wiley & Sons, Ltd.     

Chiral bisphospholane ligands (Me-ketalphos): synthesis of their Rh(I) complexes and applications in asymmetric hydrogenation

Rhodium complexes of functionalized bisphospholane ligands (S,S,S,S-Me-ketalphos) 1 and (R,S,S,R-Me-ketalphos) 2 have been used as catalyst precursors for the asymmetric hydrogenation of several different types of functionalized olefins and have achieved high enantioselectivities.     

Catalysis of hydrosilylation by well-defined rhodium siloxide complexes immobilized on silica

Rhodium surface siloxide complexes were prepared directly by condensation of the molecular precursors ([{Rh(μ-OSiMe₃)(cod)}₂], [{Rh(μ-OSiMe₃)(tfb)}₂], [{Rh(μ-OSiMe₃)(nbd)}₂]) with silanol groups on silica surface (Aerosil 200 and SBA-15) and their structures were characterized by ¹³C and ²⁹Si CP/MAS NMR spectroscopy. Such single-site complexes were tested for their activity in hydrosilylation of carbon–carbon double bonds with triethoxysilane, heptamethyltrisiloxane and poly(hydro,methyl)(dimethyl)siloxane. The best catalyst appeared to be cyclooctadiene ligand-containing rhodium siloxide complex immobilized on Aerosil which was recycled as many as 20 times without loss of activity and selectivity in hydrosilylation of vinylheptamethyltrisiloxane with heptamethyltrisiloxane. On the ground of CP/MAS NMR measurements it was established that the mechanism of hydrosilylation catalyzed by silica-supported rhodium siloxide complexes is different from that for the complexes in the homogeneous system.     

Synthesis of Rh(I) diamine complexes and their exploitation for asymmetric hydrogen transfer processes

In this paper, we report the synthesis and characterisation of two novel chiral diamine ligands and three new Rh(I) complexes. The diamine ligands were prepared by reducing the Schiff base precursors using NaBH₄. Unusually, when ligand 2 was recrystallised in a methanol:acetone solution (10:1) a five membered imidazolidine ring was formed, as confirmed by X-ray crystallography, multinuclear NMR spectroscopy and mass spectrometry. The Rh(I) cationic complexes were prepared in high yields and purities and these have been exploited for the asymmetric reduction of acetophenone to 1-phenylethanol. Modest conversions (up to 88%) and enantioselectivities (up to 50%) have been achieved.     

Low-valent ene-amido iron complexes for the asymmetric transfer hydrogenation of acetophenone without base

Examination of the role of base in the activation of our previously reported iron(II) complexes having the general formula [Fe(CO)(Br)(PNNP)][BPh(4)] revealed a five-coordinate iron(II) complex in which the tetradentate PNNP ligand had been doubly deprotonated. The new iron(II) complexes were used in the transfer hydrogenation of acetophenone in isopropanol in the absence of added base, and certain analogues showed catalytic activity.     

Heterogeneous asymmetric reactions: Part 21. Amino acid derived modifiers in the enantioselective hydrogenation of ethyl pyruvate over supported platinum catalyst

New modifiers were prepared from -tryptophane and tested in the enantioselective hydrogenation of ethyl pyruvate over commercial alumina supported platinum catalyst. Most of these molecules induced only low enantiomeric excesses (ee). (S)-3-(1-methyl-indol-3-yl)-2-methylamino-propan-1-ol was found to be the most effective. Using this modifier under mild reaction conditions (1 bar hydrogen pressure, 273 K), enantiomeric excess up to 43% was obtained. Due to the transformation of the modifier evidenced by ESI-MS, a slight increase in hydrogen pressure led to a dramatic drop of enantioselectivity. An interesting inversion of the sense of enantioselectivity was observed in the case of this modifier when the reaction was carried out in acetic acid instead of toluene. A possible explanation for this phenomenon is proposed.     

Rhodium complexes with dioximes as catalysts of hydroformylation and hydrogenation of 1-hexene

Rhodium(II) complexes with dioximes [Rh(Hdmg)₂(PPh₃)]₂ [I] (Hdmg=monoanion of dimethylglyoxime) and [Rh(Hdmg)(ClZndmg)(PPh₃)]₂ [II] catalyse hydroformylation and hydrogenation reactions of 1-hexene at 1 MPa CO/H₂ and 0.5 MPa H₂ at 353 K, respectively. Hydroformylation with complex [I] produces 94% of aldehydes (n/iso=2.2) and 6% 2-hexene whereas the second catalyst [II] gives ca. 40% of aldehydes (n/iso=2.1) and 60% of 2-hexene. Corresponding Rh(III) complexes are inactive in hydroformylation except of RhH(Hdmg)₂(PPh₃) [III], which shows activity similar to [I]. Complexes [Rh(Hdmg)₂(PPh₃)]₂ [I], [Rh(Hdmg)(ClZndmg)(PPh₃)]₂ [II], RhH(Hdmg)₂(PPh₃) [III] and [Rh(Hdmg)₂(PPh₃)₂]ClO₄ [V] catalyse 1-hexene hydrogenation with an average TON ca. 18 cycles/mol [Rh]×min. Complex [II] has also been found to catalyse hydrogenation of cyclohexene, 1,3-cyclohexadiene and styrene.     

Application of [BoPhoz Rh] catalysts in the asymmetric hydrogenation of a pyridyl benzothiophene alkene

The asymmetric hydrogenation of a pyridyl benzothiophene alkene has been successfully accomplished using [BoPhoz Rh] catalysts. By tailoring the steric properties of the BoPhoz ligand, the ee of the product could be increased from just 12% to 90%. This research further expands the substrate scope of the conventional class of functionalized alkenes amenable to catalytic asymmetric hydrogenation.     

Os络合物催化烯烃加氢和异构化反应

综述了近年来锇络合物用于催化烯烃加氢和异构化反应的研究进展。 Os催化剂在H2分子和转移加氢二个方面用于烯烃加氢反应均表现出较高的活性和选择性。因此它有望成为有机合成中的一个强有力的工具。     

Immobilization of chiral Rh catalyst on glass and application to asymmetric transfer hydrogenation of aryl ketones in aqueous media

A chiral catalyst, Cp＊RhTsDPEN （Cp＊ = pentamethyl cyclopentadiene, TsDPEN = substitutive phenylsulfonyl-l,2-diphenylethylenediamine）, was synthesized and immobilized at the surface of glass. The immobilized catalyst exhibited good catalytic efficiency for asymmetric transfer hydrogenation of aromatic ketones in water with HCOONa as hydrogen source.     

Kinetics of liquid-phase benzene hydrogenation on Rh/C

Liquid-phase hydrogenation of benzene was studied over Rh catalyst supported on a carbon carrier sibunit between 13 and 100°C and in a hydrogen pressure range of 20–100 bar. Kinetic data were obtained under mass transfer-free conditions. Similar to gas-phase hydrogenation activity, a maximum with temperature was observed. A kinetic model consistent with thermodynamics was applied for numerical parameter estimation. Good correspondence between the experimental and calculated data was achieved.     

Enantioselective hydrogenation of ethyl pyruvate catalyzed by PVP-stabilized rhodium nanoclusters

The enantioselective hydrogenation of ethyl pyruvate catalyzed by polyvinylpyrrolidone-stabilized rhodium nanocluster (Rh/PVP) modified by cinchonidine and quinine was studied. The results show that cinchonidine and quinine not only can induce the enantioselectivity in the hydrogenation of ethyl pyruvate, but also can greatly accelerate the reaction. Under the optimum conditions, 298 K, 5 MPa of hydrogen pressure and 4.3×10⁻³ mol/l of cinchonidine in tetrahydrofuran, the enantiomeric excess of R-(+)-ethyl lactate and turnover frequency (TOF) of ethyl pyruvate reach up to 42.2% e.e. and 941 h⁻¹, respectively. The rate of hydrogenation is faster by a factor of about 50 in the presence of cinchonidine than that without it. Quinine exhibits the similar effect.     

（1S，2S）－DPEN修饰的负载型钌膦配合物催化苯乙酮及其衍生物不对称加氢反应研究

对不含官能团的简单芳香酮来说,由于除酮羰基外不具有与催化剂中心金属进行配位的辅助功能基团,因此导致钌-膦配合物催化剂对这类酮加氢的对映选择性不高[1-2].     

Chiral ferrocenyl diphosphines for asymmetric transfer hydrogenation of acetophenone

The synthesis of new optically pure ferrocenyl diphosphines have been realized from (R)-(+)-N,N-dimethylaminoethylferrocene. Particularly, dissymmetric ferrocenyl diphosphines have been synthesized. The diphosphines have been used as ligands in asymmetric transfer hydrogenation of acetophenone in the presence of Ru catalysts.     

Crystal structure of chiral binaphthol lanthanide complexes and their catalysis in asymmetric transfer hydrogenation of acetophenone

Heterometallic [(THF)₂Na]₃[Ln(R‐Binolate)₃(H₂O)] [Ln = Sm ( 1 ) and Gd ( 2 )] has been synthesized by the reactions of either LnCl₃ or LnBr₃ with 3 equiv. Na(R‐HBinolate) and characterized by X‐ray crystallographic analysis. Structural analyses proposed that 1 and 2 are isomorphous complexes, crystallizing in the hexagonal space group P6₃ with C₃ symmetry. The coordination geometry of the lanthanide ions in 1 and 2 can be best approximated as a mono‐capped triangle antiprism. When complexes 1 and 2 were employed as catalysts in the Meerwein–Ponndorf–Verley (MPV) reactions of acetophenone, the S‐phenylethanol was separated in 94 and 85% enantiomeric excess (e.e.) for 1 and 2 , respectively. Copyright © 2005 John Wiley & Sons, Ltd.     

Ruthenium hydride complexes of chiral and achiral diphosphazane ligands and asymmetric transfer hydrogenation reactions

The half-sandwhich ruthenium chloro complexes bearing chelated diphosphazane ligands, [(η⁵-Cp)RuCl{κ²-P,P-(RO)₂PN(Me)P(OR)₂}] [R = C₆H₃Me₂-2,6] (1) and [(η⁵-Cp^∗)RuCl{κ²-P,P-X₂PN(R)PYY′}] [R = Me, X = Y = Y′ = OC₆H₅ (2); R = CHMe₂, X₂ = C₂₀H₁₂O₂, Y = Y′ = OC₆H₅ (3) or OC₆H₄^tBu-4 (4)] have been prepared by the reaction of CpRu(PPh₃)₂Cl with (RO)₂PN(Me)P(OR)₂ [R = C₆H₃Me₂-2,6 (L¹)] or by the reaction of [Cp^∗RuCl₂]_n with X₂PN(R)PYY′ in the presence of zinc dust. Among the four diastereomers (two enantiomeric pairs) possible for the “chiral at metal” complexes 3 and 4, only two diastereomers (one enantiomeric pair) are formed in these reactions. The complexes 1, 2, 4 and [(η⁵-Cp)RuCl{κ²-P,P-Ph₂PN((S)-^∗CHMePh)PPhY}] [Y = Ph (5) or N₂C₃HMe₂-3,5 (S_CS_PR_Ru)-(6)] react with NaOMe to give the corresponding hydride complexes [(η⁵-Cp)RuH{κ²-P,P-(RO)₂PN(Me)P(OR)₂}] (7), [(η⁵-Cp^∗)RuH{κ²-P,P′-X₂PN(R)PY₂}] [R = Me, X = Y = OC₆H₅ (8); R = CHMe₂, X₂ = C₂₀H₁₂O₂, Y = OC₆H₄^tBu-4 (9)] and [(η⁵-Cp)RuH{κ²-P,P-Ph₂PN((S)-^∗CHMePh)PPhY}][Y = Ph (10) or N₂C₃HMe₂-3,5 (S_CS_PR_Ru)-(11a) and (S_CS_PS_Ru)-(11b)]. Only one enantiomeric pair of the hydride 9 is obtained from the chloro precursor 4 that bears sterically bulky substituents at the phosphorus centers. On the other hand, the optically pure trichiral complex 6 that bears sterically less bulky substituents at the phosphorus gives a mixture of two diastereomers (11a and 11b). Protonation of complex 7 using different acids (HX) gives a mixture of [(η⁵-Cp)Ru(η²-H₂){κ²-P,P-(RO)₂PN(Me)P(OR)₂}]X (12a) and [(η⁵-Cp)Ru(H)₂{κ²-P,P-(RO)₂PN(Me)P(OR)₂}]X (12b) of which 12a is the major product independent of the acid used; the dihydrogen nature of 12a is established by T₁ measurements and also by synthesizing the deuteride analogue 7-D followed by protonation to obtain the D-H isotopomer. Preliminary investigations on asymmetric transfer hydrogenation of 2-acetonaphthone in the presence of a series of chiral diphosphazane ligands show that diphosphazanes in which the phosphorus centers are strong π-acceptor in character and bear sterically bulky substituents impart moderate levels of enantioselectivity. Attempts to identify the hydride intermediate involved in the asymmetric transfer hydrogenation by a model reaction suggests that a complex of the type, [Ru(H)(Cl){κ²-P,P-X₂PN(R)PY₂}(solvent)₂] could be the active species in this transformation.     

Efficient asymmetric transfer hydrogenation of activated olefins catalyzed by ruthenium amido complexes

The asymmetric transfer hydrogenation of activated olefins with chiral ruthenium amido complexes (Noyori catalyst) using formic acid-triethylamine azeotrope as hydrogen source resulted in excellent yields and high enantioselectivities (up to 88.5%).     

铱(I)联萘胺Schiff碱(BPMBNDI)配合物催化苯乙酮的不对称氢转移反应

用旋光活性2, 2'-(1, 1'-联萘)二胺和2-吡啶基甲醛缩合得到的Schiff碱BPMBNDI[N, N'-二(2-吡啶基亚甲基)-(1, 1'-联萘)-2, 2'-二亚胺]为配体与[Ir(COD)Cl]2(COD=1, 5-环辛二烯)反应, 生成了10个光学活性铱配合物。研究它们在异丙醇对苯乙酮不对称氢转移反应中的光学诱导活性时, 发现10个催化剂均具有较高的立体选择性,其中[Ir(COD)(BPMBNDI)I]催化的光学产率高达84%。