Ruthenium-catalyzed transfer hydrogenation of aromatic ketones with aminophosphine or bis(phosphino)amine ligands derived from isopropyl substituted anilines

A series of new highly active Ru(II) complexes with two new (N-diphenylphosphino)isopropylanilines, having an isopropyl substituent at carbon 2- (1) or 2,6- (2) and two new bis(diphenylphosphino)isopropylanilines, having an isopropyl substituent at carbon atom 2- (3) or 4- (4), were prepared starting from the dimeric complex [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂. All the compounds have been fully characterized by microanalysis, IR, ³¹P{1H} NMR, ¹H NMR and ¹³C NMR spectroscopies. Following activation by NaOH, complexes 5–8 were tested in the transfer hydrogenation of acetophenone derivatives with iso-PrOH as the hydrogen source. Catalytic studies showed that the complexes are excellent catalytic precursors for the transfer hydrogenation of acetophenone derivatives.     

Organometallic ruthenium, rhodium and iridium complexes containing a P-bound thiophene-2-(N-diphenylphosphino)methylamine ligand: Synthesis, molecular structure and catalytic activity

Reaction of Ph₂PNHCH₂-C₄H₃S with [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂, [Ru(η⁶-benzene)(μ-Cl)Cl]₂, [Rh(μ-Cl)(cod)]₂ and [Ir(η⁵-C₅Me₅)(μ-Cl)Cl]₂ yields complexes [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-p-cymene)Cl₂], 1, [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2, [Rh(Ph₂PNHCH₂-C₄H₃S)(cod)Cl], 3 and [Ir(Ph₂PNHCH₂-C₄H₃S)(η⁵-C₅Me₅)Cl₂], 4, respectively. All complexes were isolated from the reaction solution and fully characterized by analytical and spectroscopic methods. The structure of [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2 was also determined by single crystal X-ray diffraction. 1-4 are suitable precursors forming highly active catalyst in the transfer hydrogenation of a variety of simple ketones. Notably, the catalysts obtained by using the ruthenium complexes [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-p-cymene)Cl₂], 1 and [Ru(Ph₂PNHCH₂-C₄H₃S)(η⁶-benzene)Cl₂], 2 are much more active in the transfer hydrogenation converting the carbonyls to the corresponding alcohols in 98-99% yields (TOF ≤ 200 h⁻¹) in comparison to analogous rhodium and iridium complexes.     

Cationic and neutral ruthenium(II) complexes containing both arene or Cp* and functionalized aminophosphines. Application to hydrogenation of aromatic ketones

Hydrogen transfer reduction processes are attracting increasing interest from synthetic chemists in view of their operational simplicity. For this aim, a series of novel Ru(II) complexes with the P-N-P ligands were synthesized starting from the complex [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂ or [RuCp*Cl(COD)]. The complexes were fully characterized by analytical and spectroscopic methods. ³¹P-{¹H} NMR, DEPT, ¹H-¹³C HETCOR or ¹H-¹H COSY correlation experiments were used to confirm the spectral assignments. Complexes 5, 6 and 7 catalyze the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of iso-PrOH as the hydrogen source. Catalytic studies showed that all complexes are excellent catalytic precursors for the transfer hydrogenation of acetophenone derivatives in 0.1 M iso-PrOH solution. Notably 5 acts as an excellent catalyst giving the corresponding alcohols in excellent conversions up to 99% (TOF ≤ 492 h⁻¹).     

New active ruthenium(II) complexes based N3,N3′-bis(diphenylphosphino)-2,2′-bipyridine-3,3′-diamine and P,P′-diphenylphosphinous acid-P,P′-[2,2′-bipyridine]-3,3′-diyl ester ligands for transfer hydrogenation of aromatic ketones by propan-2-ol

The dimeric starting material [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂ reacts with N3,N3′-bis(diphenylphosphino)-2,2′-bipyridine-3,3′-diamine, 1 and P,P′-diphenylphosphinous acid-P,P′-[2,2′-bipyridine]-3,3′-diyl ester, 2 ligands to afford bridged dinuclear complexes [C₁₀H₆N₂{NHPPh₂-Ru(η⁶-p-cymene)Cl₂}₂], 3 and [C₁₀H₆N₂{OPPh₂-Ru(η⁶-p-cymene)Cl₂}₂], 4 in quantitative yields. These bis(aminophosphine) and bis(phosphinite) based Ru(II) complexes serve as active catalyst precursors for the transfer hydrogenation of acetophenone derivatives in 2-propanol and especially 4 acts as a good catalyst, giving the corresponding alcohols in 99% yield in 20 min (TOF ? 280 h⁻¹).     

Synthesis and characterization of tris{2-(N,N-bis(diphenylphosphino) aminoethyl} amine derivatives: Application of a palladium(II) complex as a pre-catalyst in the Heck and Suzuki cross-coupling reactions

The polydendate bis(phosphino)amine, tris{2-(N,N-bis(diphenylphosphino)aminoethyl}amine 1 has been prepared in a single step from the reaction of tris(2-aminoethyl)amine with six equivalents of PPh₂Cl in the presence of NEt₃ in THF. Oxidation of 1 with aqueous H₂O₂, elemental sulfur or grey selenium gave the corresponding oxide, sulfide or selenide derivatives. [{(P(E)Ph₂)₂NCH₂CH₂}₃N] (E: 2a O, 2b S, 2c Se), respectively. Reaction of [{(PPh₂)₂NCH₂CH₂}₃N] with 3 equiv. of PdCl₂(cod) or PtCl₂(cod) gave the corresponding chelate complexes, [Pd₃Cl₆1] or [Pt₃Cl₆1]. The new compounds were fully characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of the Pd(II) complex was tested in the Suzuki coupling and Heck reactions. The Pd(II) complex catalyzed the Suzuki coupling and Heck reaction affording biphenyls and stilbenes, respectively, in high yields.     

Novel cyclohexyl‐based aminophosphine ligands and use of their Ru(II) complexes in transfer hydrogenation of ketones

Two new aminophosphines – furfuryl‐(N‐dicyclohexylphosphino)amine, [Cy₂PNHCH₂–C₄H₃O] ( 1 ) and thiophene‐(N‐dicyclohexylphosphino)amine, [Cy₂PNHCH₂–C₄H₃S] ( 2 ) – were prepared by the reaction of chlorodicyclohexylphosphine with furfurylamine and thiophene‐2‐methylamine. Reaction of the aminophosphines with [Ru(η⁶‐p‐cymene)(μ‐Cl)Cl]₂ or [Ru(η⁶‐benzene)(μ‐Cl)Cl]₂ gave corresponding complexes [Ru(Cy₂PNHCH₂–C₄H₃O)(η⁶‐p‐cymene)Cl₂] ( 1a ), [Ru(Cy₂PNHCH₂–C₄H₃O)(η⁶‐benzene)Cl₂] ( 1b ), [Ru(Cy₂PNHCH₂–C₄H₃S)(η⁶‐p‐cymene)Cl₂] ( 2a ) and [Ru(Cy₂PNHCH₂–C₄H₃S)(η⁶‐benzene)Cl₂] ( 2b ), respectively, which are suitable catalyst precursors for the transfer hydrogenation of ketones. In particular, [Ru(Cy₂PNHCH₂–C₄H₃S)(η⁶‐benzene)Cl₂] acts as a good catalyst, giving the corresponding alcohols in 98–99% yield in 30 min at 82 °C (up to time of flight ≤ 588 h^?1). Copyright © 2014 John Wiley & Sons, Ltd.     

Novel half‐sandwich η5‐Cp *–rhodium(III) and η5‐Cp *–ruthenium(II) complexes bearing bis(phosphino)amine ligands and their use in the transfer hydrogenation of aromatic ketones

Two new half‐sandwich η⁵‐Cp*–rhodium(III) and η⁵‐Cp*–ruthenium(II) complexes have been prepared from corresponding bis(phosphino)amine ligands, thiophene‐2‐(N,N‐bis(diphenylphosphino)methylamine) or furfuryl‐2‐(N,N‐bis(diphenylphosphino)amine). Structures of the new complexes have been elucidated by multinuclear one‐ and two‐dimensional NMR spectroscopy, elemental analysis and IR spectroscopy. These Cp*–rhodium(III) and Cp*‐ruthenium(II) complexes bearing bis(phosphino)amine ligands were successfully applied to transfer hydrogenation of various ketones by 2‐propanol. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Synthesis and characterizations of N,N-bis(diphenylphosphino)ethylaniline derivatives and X-ray crystal structure of palladium (II), platinum (II) complexes

N,N-Bis(diphenylphosphino)ethylaniline compounds, [Ph₂P]₂N-C₆H₄-C₂H₅, with ethyl groups at the ortho- and para-positions have been synthesized. Oxidation of the aminophosphines with hydrogen peroxide, elemental sulfur and selenium gave the corresponding oxides, sulfides and selenides [Ph₂P(E)]₂N-C₆H₄-C₂H₅ (E = O, S, Se). Complexes [MCl₂{(Ph₂P)₂N-C₆H₄-(C₂H₅)}] (M = Pd, Pt) and [Cu{(Ph₂P)₂N-C₆H₄-C₂H₅}₂]PF₆ were obtained by the reaction of N,N-bis(diphenylphosphino)ethylaniline with [MCl₂(COD)] (M = Pd, Pt) and [Cu(MeCN)₄]PF₆. The new compounds were characterized by NMR, IR spectroscopy and microanalysis. In addition, representative solid-state structures of the palladium and platinum complexes were determined using single crystal X-ray diffraction analyses.     

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.     

Catalytic transfer hydrogenation of ketones catalyzed by orthometalated ruthenium(III) 2-(arylazo)phenolate complexes containing triphenylarsine

Air-stable, mononuclear orthometalated ruthenium(III) 2-(arylazo)phenolate complexes of the general composition [RuX(AsPh₃)₂(L)] (X = Cl or Br; L = CNO donor of the 2-(arylazo)phenolate ligands) have been synthesized and characterized by IR, UV-vis, and EPR as well as by elemental analysis. One of the complexes [RuBr(AsPh₃)₂(azo-OMe)] was structurally characterized by X-ray analysis and was found to be an efficient catalyst for the transfer hydrogenation of ketones with excellent conversion in the presence of isopropanol at 80 °C in 1 h.     

Synthesis and characterization of transition metal complexes of thiophene‐2‐methylamine: X‐ray crystal structure of palladium (II) and platinum (II) complexes and use of palladium(II) complexes as pre‐catalyst in Heck and Suzuki cross‐coupling reactions

The reactions of thiophene‐2‐(N‐diphenylphosphino)methylamine, Ph₂PNHCH₂‐C₄H₃S, 1 and thiophene‐2‐[N,N‐bis(diphenylphosphino)methylamine], (Ph₂P)₂NCH₂‐C₄H₃S, 2, with MCl₂(cod) (M = Pd, Pt; cod = 1,5‐cyclooctadiene) or [Cu(CH₃CN)₄]PF₆ yields the new complexes [M(Ph₂PNHCH₂‐C₄H₃S)₂Cl₂], M = Pd 1a, Pt 1b, [Cu(Ph₂PNHCH₂‐C₄H₃S)₄]PF₆, 1c, and [M(Ph₂P)₂NCH₂‐C₄H₃S)Cl₂], M = Pd 2a, Pt 2b, {Cu[(Ph₂P)₂NCH₂‐C₄H₃S]₂}PF₆, 2c, respectively. The new compounds were isolated as analytically pure crystalline solids and characterized by ³¹P‐, ¹³C‐, ¹H‐NMR and IR spectroscopy and elemental analysis. Furthermore, the solid‐state molecular structures of representative palladium and platinum complexes of bis(phosphine)amine, 2a and 2b, respectively, were determined using single crystal X‐ray diffraction analysis. The palladium complexes were tested as potential catalysts in the Heck and Suzuki cross‐coupling reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

Two pseudo-N3 ligands and the catalytic activity of their ruthenium(II) complexes in transfer hydrogenation and hydrogenation of ketones

Complex RuCl₂(PPh₃)(iBu-BTP) (5) was synthesized by the reaction of 2,6-bis(5,6-bis(iso-butyl)-1,2,4-triazin-3-yl)pyridine (iBu-BTP) and RuCl₂(PPh₃)₃ in refluxing toluene, and its molecular structure was confirmed by X-ray crystallographic determination. Complex 5 was applied as a catalyst for transfer hydrogenation of ketones and exhibited catalytic activity comparable to RuCl₂(PPh₃)(Me₄BPPy) (1) (Me₄BPPy = bis(3,5-dimethylpyrazol-1-yl)pyridine) in some cases. The difference between the catalytic activity of 5 and 1 is attributed to the significantly different arrangement and positions of the PPh₃ and chlorides and also to the different electron density on the N-heterocycles. Complex 1 exhibited good to excellent catalytic activity in hydrogenation of ketones under mild conditions. These results have suggested new applications of iBu-BTP and Me₄BPPy as promising planar tridentate pseudo-N₃ ligands to construct highly active transition-metal catalysts.     

Binuclear ruthenium(II) pyridazine complex catalyzed transfer hydrogenation of ketones

A convenient and general method of synthesis of binuclear ruthenium(II) pyridazine complex was reported. The synthesized complex was characterized by analytical and spectral methods. The structure of the complex was confirmed by X-ray diffraction technique and was found to be an efficient catalyst for the transfer hydrogenation of ketones with excellent conversions in the presence of isopropanol/KOH at 82 °C. The effect of solvents, bases, and different catalyst/substrate ratio for the reaction was also investigated.     

Unexpected differences in the reactivity between MPh2Cl2 (M = Pb or Sn) and benzil bis(thiosemicarbazone). X-ray crystal structure of benzil bis(thiosemicarbazonate)lead(II)

The differences in the reactivity of diphenyllead and diphenyltin dichloride with benzil bis(thiosemicarbazone) LH₆ are explored. The reaction of PbPh₂Cl₂ afforded the complex [Pb(LH₄)] 1, containing the ligand doubly deprotonated and without the phenyl groups bonded to the metal. The reaction with SnPh₂Cl₂ in the absence of solvent yielded the complex [Sn(LH₄)Cl₂] 2. The lead(II) complex, also obtained by the reaction with lead(II) nitrate, was formed by a redistribution of the organolead derivative followed by a reductive elimination reaction, while the tin one was formed by a dephenylation process. Reactions in solution of the organotin derivative are complicated and depending on the working conditions different compounds could be isolated: the organostannoxane [Sn₂Ph₄ClO(OH)]₂, which was confirmed by X-ray crystallography, or a complex containing a triazine-3-thione ligand, formed by the loss of one of the thiosemicarbazone arms with subsequent cyclisation. The compounds were characterized by IR, mass spectrometry, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy in solution and in the solid state. The structure of [Pb(LH₄)] has been studied by X-ray diffraction and the ligand acts as a N₂S₂ planar bideprotonated ligand, with the lead(II) ion localized 1.3858 Å over this plane.     

(-)-Menthol as a source of new N,N-diamine ligands for asymmetric transfer hydrogenation

The synthesis of new chiral N-monotosylated-1,2-diamines based on the (-)-menthol skeleton is presented. The elimination of HCl from neomenthyl chloride obtained from an Appel reaction led to p-menth-3-ene in excellent yield. Further functionalization of the double bond in p-menth-3-ene with chloramine-T gave the corresponding N-tosylaziridines, which upon reaction with sodium azide and subsequent reduction of the azide functional group, formed the 1,2-diamine system. The synthesized chiral ligands proved effective in the asymmetric transfer hydrogenation of aromatic ketones and an endocyclic imine.     

Rhodium(III) NCN pincer complexes catalyzed transfer hydrogenation of ketones

Air-stable monomeric rhodium(III) NCN pincer complexes were synthesized via direct C-H bond activation of 1,3-bis(2-pyridyloxy)benzene, 3,5-bis(2-pyridyloxy)toluene and 3,5-bis(2-pyridyloxy)anisole with RhCl₃·3H₂O in ethanol under reflux. The synthesized complexes were characterized by elemental analysis and ¹H NMR. One of the complexes was structurally characterized by X-ray analysis. An investigation into the catalytic activity of the complex 1a as catalyst for transfer hydrogenation of ketones to alcohols at 82 °C in the presence of iPrOH/KOH was undertaken with the conversions up to 99%.     

Synthesis and structural characterisation of cobalt(II) and iron(II) chloride complexes containing bis(2-pyridylmethyl)amine and tris(2-pyridylmethyl)amine ligands

Treatment of (2-C₅H₄N)CH_{2 3}N (TPA) with one equivalent of MCl₂ in n-BuOH at elevated temperatures affords the six-coordinate complexes [(TPA)MCl₂] (M = Co (1), Fe (2)) and, in the case of CoCl₂, the five-coordinate chloride salt [(TPA)CoCl]Cl (3). Conversely, addition of an excess of CoCl₂ in the latter reaction leads to [(TPA)CoCl]₂[CoCl₄] (4) as the only isolable product. Interaction of one equivalent of (2-C₅H₄N)CH_{2 2}NH (DPA) and MCl₂ under similar reaction conditions to that described above affords the dimeric species [(fac-DPA)MCl(μ-Cl)]₂ (M = Co (5), Fe (6)), while the bis(ligand) halide salts [(fac-DPA)₂M]Cl₂ (M = Co (7), Fe (8)) are accessible on addition of two equivalents of DPA. In the presence of air, 6 undergoes oxidation to give [ (fac-DPA)FeCl_{2 2}(μ-O)] (9). Single-crystal X-ray diffraction studies are reported for 1, 2 · MeCN, 3, , 7 · 3MeCN, 8 · 3MeCN and 9.