Ir(III) complexes of diamine ligands for asymmetric ketone hydrogenation

The use of a combination of IrCl₃ with a series of ligands derived from the C2-symmetric diamine diphenylethanediamine (DPEN) forms a catalyst capable of the asymmetric hydrogenation of ketones in up to 85% ee.     

Ru(II) complexes of cyclohexane diamine and monodentate phosphorus ligands for asymmetric ketone hydrogenation

The incorporation of a trans-1,2-diaminocyclohexane in place of DPEN provides improvements in enantioselectivity to asymmetric ketone hydrogenation reactions using BrXuPHOS–Ru–diamine catalysts. Substrates containing halogenated aryl rings are particularly compatible with this catalyst, however, α-chlorinated ketones remain resistant to reduction under any conditions.     

Ruthenium(II) pincer complexes with oxazoline arms for efficient transfer hydrogenation reactions

Well-defined P^NN^CN pincer ruthenium complexes bearing both strong phosphine and weak oxazoline donors were developed. These easily accessible complexes exhibit significantly better catalytic activity in transfer hydrogenation of ketones compared to their PN³P analogs. These reactions proceed under mild and base-free conditions via protonation-deprotonation of the ‘NH’ group in the aromatization-dearomatization process.     

Asymmetric hydrogenation of ketones using a ruthenium(II) catalyst containing BINOL-derived monodonor phosphorus-donor ligands

[structure: see text] A series of ruthenium(II) complexes containing BINOL-based monodonor phosphorus ligands have been prepared and applied to the asymmetric catalysis of the hydrogenation of aryl/alkyl ketones. The best ligands for this application are those which contain an aromatic groups with either a methoxide or bromide on the ortho position. Using these ligands, alcohols with ee's of up to 99% are formed.     

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.     

BINAP/1,4-diamine-ruthenium(II) complexes for efficient asymmetric hydrogenation of 1-tetralones and analogues

A combined system of a RuCl(2)(binap)(1,4-diamine) complex and t-C(4)H(9)OK in i-C(3)H(7)OH catalyzes enantioselective hydrogenation of various 1-tetralone derivatives and some methylated 2-cyclohexenones. Hydrogenation of 2-methyl-1-tetralone under dynamic kinetic resolution gives the cis alcohol with high ee. [reaction: see text]     

Ruthenium (II)-sulfonated BINAP: A novel water-soluble asymmetric hydrogenation catalyst.

Ruthenium (II)-sulfonated-BINAP has been synthesized and this novel water-soluble complex is shown to be an excellent asymmetric hydrogenation catalyst for 2-acylamino acid precursors and methylenesuccinic acid in both methanolic as well as in neat water solvent systems. Enantiomeric excesses approaching 90% have been obtained in aqueous and methanolic solvents. Effects of solvent, pressure and the addition of organic base on enantioselectivity are described.     

Ruthenium(III) complexes of amine-bis(phenolate) ligands as catalysts for transfer hydrogenation of ketones

Twelve ruthenium(III) complexes bearing amine-bis(phenolate) tripodal ligands of general formula [Ru(L¹–L³)(X)(EPh₃)₂] (where L¹–L³ are dianionic tridentate chelator) have been synthesized by the reaction of ruthenium(III) precursors [RuX₃(EPh₃)₃] (where E = P, X = Cl; E = As, X = Cl or Br) and [RuBr₃(PPh₃)₂(CH₃OH)] with the tripodal tridentate ligands H₂L¹, H₂L² and H₂L³ in benzene in 1:1 molar ratio. The newly synthesized complexes have been characterized by analytical (elemental and magnetic susceptibility) and spectral methods. The complexes are one electron paramagnetic (low-spin, d⁵) in nature. The EPR spectra of the powdered samples at RT and the liquid samples at LNT shows the presence of three different ‘g’ values (g_x ≠ g_y ≠ g_z) indicate a rhombic distortion around the ruthenium ion. The redox potentials indicate that all the complexes undergo one electron transfer process. The catalytic activity of one of the complexes [Ru(pcr-chx)Br(AsPh₃)₂] was examined in the transfer hydrogenation of ketones and was found to be efficient with conversion up to 99% in the presence of isopropanol/KOH.     

Ruthenium(II) complexes with ferrocene-modified arene ligands: synthesis and electrochemistry

A series of arene-ruthenium complexes of the general formula [RuCl₂{η⁶-C₆H₅(CH₂)₂R}L] with R=OH, CH₂OH, OC(O)Fc, CH₂OC(O)Fc (Fc=ferrocenyl) and L=PPh₃, (diphenylphosphino)ferrocene, or bridging 1,1^′-bis(diphenylphosphino)ferrocene, have been synthesized. Two synthetic pathways have been used for these ferrocene-modified arene-ruthenium complexes: (a) esterification of ferrocene carboxylic acid with 2-(cyclohexa-1,4-dienyl)ethanol, followed by condensation with RuCl₃ · nH₂O to afford [RuCl₂{η⁶-C₆H₅(CH₂)₂OC(O)Fc}]₂, and (b) esterification between ferrocene carboxylic acid and [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}L] to give [RuCl₂{η⁶-C₆H₅(CH₂)₃OC(O)Fc}L]. All new compounds have been characterized by NMR and IR spectroscopy as well as by mass spectrometry. The single-crystal X-ray structure analysis of [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] shows that the presence of a CH₂CH₂CH₂OH side-arm allows [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] to form an intramolecular hydrogen bond with a chlorine atom. The electrochemical behavior of selected representative compounds has been studied. Complexes with ferrocenylated side arms display the expected cyclic voltammograms, two independent reversible one-electron waves of the Ru(II)/Ru(III) and Fe(II)/Fe(III) redox couples. Introduction of a ferrocenylphosphine onto the ruthenium is reflected by an additonal reversible, one-electron wave due to ferrocene/ferrocenium system which is, however, coupled with the Ru(II)/Ru(III) redox system.     

Ruthenium(II) complexes bearing pyridine‐based tridentate and bidentate ligands: catalytic activity for transfer hydrogenation of aryl ketones

Ru(II) complexes of the general formula [RuCl₂(′′)(L)] (1: ′N = N_b, L = MeOH; 2: ′N = N_b, L = CH₃CN; 3: ′N = N_d, L = CH₃CN; 4: ′N = N_p, L = CH₃CN), [Ru(p‐cymene)(_a–b)Cl]Cl (5a: N N_a = 2,2′‐bipyridine; 5b: N N_b = 4,4′‐dimethyl–2,2′‐bipyridine), [Ru(′′)(_a–b)Cl]Cl (6a: ′N = N_b, _a = 2,2′‐bipyridine; 6b: ′N = N_b, _b = 4,4′‐dimethyl‐2,2′‐bipyridine; 7a: ′N = N_d, _a = 2,2′‐bipyridine; 7b: ′N = N_d, _b = 4,4′‐dimethyl‐2,2′‐bipyridine; 8a: ′N = N_p, _a = 2,2′‐bipyridine; 8b: ′N = N_p, _b = 4,4′‐dimethyl‐2,2′‐bipyridine) and [Ru(′′)(_a)Cl]BF₄ (9a: ′N = N_b; _a = 2,2′‐bipyridine) were synthesized from the corresponding [RuCl₂(p‐cymene)]₂ dimer, ′′ and _a–b ligands. The compounds were characterized by elemental analysis, IR and NMR. Complex 9a was studied by X‐ray diffraction, confirming its cationic‐mononuclear [RuCl(_bb)(_a)]⁺ nature. The synthesized Ru(II) complexes (1–8) were employed as catalysts for the transfer hydrogenation of ketones to secondary alcohols in the presence of KOH using 2‐propanol as a hydrogen source at 82°C. The rates of the transfer hydrogenation reactions strongly depended on the type of and ancillary ligands. Copyright © 2012 John Wiley & Sons, Ltd.     

Ruthenium(II) complexes with triphenylphosphine or triphenylarsine and other monodentate ligands

Synthesis and studies on some five-coordinate ruthenium(II) complexes, viz. [Ru(MPh₃)(C₆H₅CHO)₂Cl₂] and [Ru(MPh₃)₂(CO)Cl₂] (where M = P or As) have been described. Reactions of [Ru(MPh3)(C₆H₅CHO)₂Cl₂] with N,N-dimethylformamide, dimethylsulphoxide and pyridine and of [Ru(MPh₃)₂(CO)Cl₂] with pyridine are described.     

Ruthenium(III) and ruthenium(II) complexes containing triphenylarsine and other ligands

The reactions of [RuCl₃(AsPh₃)₃] with ligands containing nitrogen (alkyl and aryl cyanides, pyridine, α-picoline N.N′-bipyridyl, 1,10-phenanthroline), oxygen (ketones, aldehydes, N,N-dimethylformamide, tetrahydrofuran, dimethylsulphoxide and nitroalkanes) and sulphur (CS₂ and Me₂S) donor atoms have been studied. The reactions of [RuCl₃(AsPh₃)₃] with tetra alkyl and aryl ammonium and arsonium salts have also been explored. The compounds obtained have been characterised by analyses, conductivity measurements, magnetic measurements and IR spectra. The electronic spectra of the complexes are discussed in terms of possible structures. An equilibrium between hexacoordinated and pentacoordinated species is suggested on the basis of electronic spectral studies.     

Ruthenium(II)-catalyzed transfer hydrogenation of aldehydes with new water-soluble monotosylated ethylenediamines as ligands

New water-soluble monotosylated ethylenediamines containing quaternary ammonium groups were conveniently synthesized from ethylenediamine. The ruthenium catalysts prepared in situ from ruthenium complex [RuCl₂(p-cymene)]₂ and water-soluble monotosylated ethylenediamine ligands were used in transfer hydrogenation of aldehydes, and excellent conversions and chemoselectivities were achieved with sodium formate as reductant in neat water.     

Highly efficient Rh(I)-catalyzed asymmetric hydrogenation of enamines using monodente spiro phosphonite ligands

A highly enantioselective hydrogenation of nonfunctionalized enamines has been developed by using rhodium complexes of chiral spiro phosphonite ligands, providing chiral tertiary amines in excellent enantioselectivities.     

Ruthenium(II) and ruthenium(III) complexes derived from O,O-donor ligands

The new [Ru¹¹(PPh₃)₂L₂] complexes [L=monoanion of tropolone, benzoylacetone, or 3-hydroxy-2-pyridinone (hypy)], [RuH(PPh₃)₃L′][HL′=maltol, dibenzoylmethane or 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdmhypy)] and [Ru^IIIX₂(EPh₃)₂L″] complexes (X=Cl, Br; E=As or P; L″=hypy, dmhypy) have been prepared, and characterized by spectroscopic techniques. Their redox behaviour was studied by cyclic voltammetry. Most of the complexes were found to be effective catalysts for the oxidation ofp-methoxybenzyl alcohol to the corresponding aldehyde in the presence ofN-methylmorpholine-N-oxide as co-oxidant.     

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.     

UREAphos: supramolecular bidentate ligands for asymmetric hydrogenation

Supramolecular bidentate phosphite ligands are presented as a new class of ligands for rhodium catalysed asymmetric hydrogenation.     

Chiral phosphine-phosphoramidite ligands for highly efficient Ir-catalyzed asymmetric hydrogenation of sterically hindered N-arylimines

A mild and general iridium-catalyzed, highly enantioselective hydrogenation of sterically hindered N-arylimines with a new H(8)-BINOL-derived phosphine-phosphoramidite ligand has been developed. The present catalytic system features high turnover numbers (up to 100000) and good to perfect enantioselectivities (up to 99% ee) for the hydrogenation of a variety of sterically hindered N-arylimines.