Synthesis of a novel class of chiral N,N,N-tridentate pyridinebisimidazoline ligands and their application in Ru-catalyzed asymmetric epoxidations

A new class of easily tunable N,N,N-pyridinebisimidazoline (pybim) ligands have been synthesized. The synthesis and tunability of these chiral tridentate ligands are much easier and flexible compared to the popular pyboxes, making the former a suitable ligand tool box for various asymmetric transformations. Ruthenium complexes of the new ligands were synthesized and applied in the asymmetric epoxidation of olefins using hydrogen peroxide as the oxidant. Excellent yields and moderate to good enantioselectivities were achieved in the epoxidation of aromatic olefins.     

Ruthenium-catalyzed asymmetric epoxidation of olefins using H2O2, part I: synthesis of new chiral N,N,N-tridentate pybox and pyboxazine ligands and their ruthenium complexes

The synthesis of chiral tridentate N,N,N-pyridine-2,6-bisoxazolines 3 (pybox ligands) and N,N,N-pyridine-2,6-bisoxazines 4 (pyboxazine ligands) is described in detail. These novel ligands constitute a useful toolbox for the application in asymmetric catalysis. Compounds 3 and 4 are conveniently prepared by cyclization of enantiomerically pure alpha- or beta-amino alcohols with dimethyl pyridine-2,6-dicarboximidate. The corresponding ruthenium complexes are efficient asymmetric epoxidation catalysts and have been prepared in good yield and fully characterized by spectroscopic means. Four of these ruthenium complexes have been characterized by X-ray crystallography. For the first time the molecular structure of a pyboxazine complex [2,6-bis-[(4S)-4-phenyl-5,6-dihydro-4H-[1,3]oxazinyl]pyridine](pyridine-2,6-dicarboxylate)ruthenium (S)-2 aa, is presented.     

Dendrimers Functionalized with Palladium Complexes of N-, N,N-, and N,N,N-Ligands

Pyridine, pyridine imine, and bipyridine imine ligands functionalized by a phenol have been synthesized and characterized, in many cases by X-ray diffraction. Several of these N-, N,N-, and N,N,N,-ligands have been grafted onto the surface of phosphorhydrazone dendrimers, from generation 1 to generation 3. The complexation ability of these monomers and dendrimers towards palladium(II) has been assayed. The corresponding complexes have been either isolated or prepared in situ. In both cases, the monomeric and dendritic complexes have been tested as catalysts in Heck couplings and in Sonogashira couplings. In some cases, a positive dendritic effect has been observed, that is, an increase of the catalytic efficiency proportional to the dendrimer generation.     

Syntheses, structures, and luminescence of novel lanthanide complexes of tripyridylamine, N,N,N',N'-tetra(2-pyridyl)-1,4-phenylenediamine and N,N,N',N'-tetra(2-pyridyl)biphenyl-4,4'-diamine

Two novel blue luminescent bridging ligands N,N,N',N'-tetra(2-pyridyl)-1,4-phenylenediamine (tppd) and N,N,N',N'-tetra(2-pyridyl)-1,1-biphenyl-4,4'-diamine (tpbpd) have been synthesized. Several novel lanthanide complexes containing 2,2',2"-tripyridylamine (2,2',2"-tpa), 2,2',3"-tpa, tppd, or tpbpd ligands have been synthesized and characterized structurally, which include Pr(hfa)3(2,2',2"-tpa), I, Ln(tmhd)3(2,2',3"-tpa), 2 (Ln = Dy, 2a; Eu, 2b; Tb, 2c; Sm, 2d), [Eu(tmhd)3][Pr(hfa)3](2,2',3"-tpa), 3, [Pr(hfa)3]2(tppd), 4, and [Ln(hfa)3]2(tpbpd), 5, where Ln = Pr (5a), Eu (5b), tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionato, and hfa = hexafluoroacetylacetonate. The Dy(III), Eu(III), and Tb(III) complexes display a bright photoluminescence, which can be achieved by either a direct excitation process or an indirect excitation process. Compounds 2a-2d can be sublimed readily.     

N,N’-双(2’-羟基苯乙酮)缩二胺合锰(Ⅲ)的合成和催化烯烃环氧化研究

本文合成了N,N’-双(2’-羟基苯乙酮)缩乙二胺、N,N’-双(2’-羟基苯乙酮)缩1,2-丙二胺、N,N’-双(2’-羟基苯乙酮)缩1,3-丙二胺和N,N’-双(2’-羟基苯乙酮)缩邻苯二胺四种Schiff配体以及它们的锰(Ⅲ)配合物1,2,3和4。并考察了这四种锰(Ⅲ)配合物作为催化剂,催化以NaOCl为氧源环氧化苯乙烯和环己烯的反应的性能。同时考察了反应温度、助配体、NaOCl的浓度以及pH值对催化环氧化反应的影响。     

Synthesis and application of chiral N, N'-dialkylated cyclohexanedi- amine for asymmetric hydrogenation of aryl ketones

Chiral N, N'-dialkylated cyclohexanediamine derived ligands have been synthesized and used in the asymmetric hydrogenation of aryl ketones. Optically active alcohols with up to 90% enantiomeric excess were obtained in high yields.     

Synthesis of a new type of chiral N,P- and N,O-ligands

Novel chiral ligands of dihydro-QUINAP (FLiNAP) and dihydro-QUINOL (FLiNOL) have been synthesized in optically pure forms.     

Enantioselective hydrogenation of aromatic ketones catalyzed by Ru complexes of Goodwin-Lions-type sp2N/sp3N hybrid ligands R-BINAN-R'-Py

Goodwin-Lions-type sp2N/sp3N hybrid ligands R-BINAN-R'-Py possessing a C2 axis binaphthyl skeleton have been designed and synthesized. Combination of the new non-phosphine ligand with Ru(pi-CH2C(CH3)CH2)2(cod) has been revealed to catalyze the hydrogenation of aromatic ketones with high enantioselectivity of up to 99% ee. The reaction proceeds essentially without the need for any bases, but the reactivity is enhanced by the addition of KOt-C4H9 attaining an S/C ratio of up to 10 000. The success should expand the range of possibilities in designing catalysts not only for hydrogenation but also for many other reactions.     

Ligand topology effects on olefin oxidations by bio-inspired [FeII(N2Py2)] catalysts

Linear tetradentate N2Py2 ligands can coordinate to an octahedral FeII center in three possible topologies (cis-alpha, cis-beta, and trans). While for the N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane (bpmen) complex, only the cis-alpha topology has been observed, for N,N'-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (bpmcn) both cis-alpha and cis-beta isomers have been reported. To date, no facile interconversion between cis-alpha and cis-beta topologies has been observed for ironII complexes even at high temperatures. However, this work provides evidence for facile interconversion in solution of cis-alpha, cis-beta, and trans topologies for [Fe(bpmpn)X2] (bpmpn=N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane; X=triflate, CH3CN) complexes. As reported previously, the catalytic behavior of cis-alpha and cis-beta isomers of [Fe(bpmcn)(OTf)2] with respect to olefin oxidation depends dramatically on the geometry adopted by the iron complex. To establish a general pattern of the catalysis/topology dependence, this work presents an extended comparison of the catalytic behavior for oxidation of olefins of a family of [Fe(N2py2)] complexes that present different topologies. 18O labeling experiments provide evidence for a complex mechanistic landscape in which several pathways should be considered. Complexes with a trans topology catalyze only non-water-assisted epoxidation. In contrast, complexes with a cis-alpha topology, such as [Fe(bpmen)X2] and [Fe(alpha-bpmcn)(OTf)2], can catalyze both epoxidation and cis-dihydroxylation through a water-assisted mechanism. Surprisingly, [Fe(bpmpn)X2] and [Fe(beta-bpmcn)(OTf)2] catalyze epoxidation via a water-assisted pathway and cis-dihydroxylation via a non-water-assisted mechanism, a result that requires two independent and distinct oxidants.     

Asymmetric hydrogenation of aromatic ketones using an iridium(I) catalyst containing ferrocene-based P–N–N tridentate ligands

Six ferrocene-based P–N–N tridentate ligands have been synthesized and applied in the Ir-catalyzed asymmetric hydrogenation of aromatic ketones. A wide range of ketones are hydrogenated enantioselectively to afford the corresponding optically active alcohols in the enantioselectivities of up to 86.6% ee. The substituent groups on the P-phenyl and pyridine rings play an important role with regard to the enantioselectivity.     

Synthesis and metal complexes of chiral c(2)-symmetric diamino-bisoxazoline ligands

A synthetic route to tetradentate chiral N(4) ligands has been developed with the aim to study the potential of corresponding iron and manganese complexes as catalysts for enantioselective epoxidation. These ligands, which contain two oxazoline rings and two trialkylamino groups as coordinating units, are readily prepared in enantiomerically pure form by the reaction of chiral 2-chloromethyloxazolines with achiral N,N'-dimethylethane-1,2-diamine or chiral (R,R)-N,N'-dimethylcyclohexane-1,2-diamine. The ligands derived from N,N'-dimethylethane-1,2-diamine reacted with anhydrous metal halides MnCl(2) and FeCl(2) in a stereoselective manner to give octahedral mononuclear complexes that have the general formula Delta-[(L)MCl(2)]. In contrast, the ligands derived from N,N'-dimethylcyclohexane-1,2-diamine formed complexes with different coordination modes depending on the diastereomer employed: in one case the metal ion was found to be pentacoordinate, in the other case a hexacoordinated complex was observed. The structure of a series of Fe and Mn complexes was determined by X-ray analysis. The coordination chemistry of these ligands was further studied by X-ray and NMR analyses of the diamagnetic isostructural complexes [(L)ZnCl(2)]. Analogous ionic complexes, which were prepared by removing chloride with silver trifluoromethanesulfonate or hexafluoroantimonate, were tested as catalysts for the epoxidation of olefins.     

Development of pinene-derived N,P ligands and their utility in catalytic asymmetric hydrogenation

New diastereomeric N,P-ligands, derived from the natural product (+)-alpha-pinene, have been synthesized and evaluated in iridium-catalyzed asymmetric hydrogenation. The ligands are tetrahydroquinoline derivatives synthesized directly from commercially available alpha-pinene utilizing resolution or recrystallization to separate diastereomers. In reduction of a range of different trisubstituted alkenes the catalysts express very different activities ranging from no activity to high activity. One of the catalysts gives good ee values for some substrates.     

Alkene epoxidation catalysed by binuclear manganese complexes

Binuclear manganese(II) complexes with macrocyclic ligands have been synthesized by template Schiff base condensation of diethylenetriamine and pentane-2,4-dione or 1,3-diphenyl-propane-1,3-dione. Catalytic epoxidation of simple olefins with hydrogen peroxide and t-BHP were studied using the above manganese complexes in the presence of a base. The influence of reaction temperature, the additive methanol and the cocatalyst had been investigated. The major products of the oxidations were the epoxides. The new manganese complexes showed significant catalytic activities for the epoxidation of alkenes using hydrogen peroxide as oxidant and ammonium acetate as cocatalyst.     

Preparation, structure characterization, and oxidation activity of ruthenium complexes with tripodal ligands bearing noncovalent interaction sites

Ruthenium(II/III) complexes with tripodal tris(pyridylmethyl)amine ligands bearing one, two, or three pivalamide groups (MPPA, BPPA, TPPA: amide-series ligands) or neopentylamine ones (MNPA, BNPA, TNPA: amine-series ligands) at the 6-position of the pyridine ring have been synthesized and structurally characterized. The X-ray structure analyses of the single crystals of these complexes reveal that they complete an octahedral geometry with the tripodal ligand and some monodentate ligands. The amide-series ligands prefer to form a Ru(II) complex, while the amine-series ones give a Ru(III) complex. In the presence of PhIO oxidant, the catalytic activities for epoxidation of olefins, hydroxylation of alkane, and dehydrogenation of alcohol have been investigated using the six ruthenium complexes [Ru(II)(tppa)Cl(2)] (1), [Ru(III)(tnpa)Cl(2)]PF(6) (2), [Ru(II)(bppa)Cl]PF(6) (3), [Ru(III)(bnpa)Cl(2)]PF(6) (4), [Ru(II)(mppa)Cl]PF(6) (5), and [Ru(III)(mnpa)Cl(2)]PF(6) (6). Among them, the amide-series complexes, 1, 3, and 5, showed a higher epoxidation activity in comparison with the amine-series ones, 2, 4, and 6. On the other hand, the latter showed a higher reactivity for hydroxylation, allylic oxidation, and C=C bond cleavage reactions compared with the former. Such a complementary reactivity is interpreted by the character of the ruthenium-oxo species involving electronically equivalent formulas, Ru(V)=O and Ru(IV)-O.     

新的双胺双膦钌配合物的合成、表征和催化性能

Polydentate ligands, N,N'-bis[o-(diphenylphosphino)benzylidene]-1,2-propane-diamine [P2N2Me for short] and N,N'-bis[o-(diphenylphosphino)benzy1]-1,2-propanediamine [P2N2 H4Me for short] have been synthesized. The interaction of RuCl2(DMSO)4 with one equivalent of P2N2Me or P2N2H4Me in refluxing toluene gave trans-RuCl2(P2N2Me) and trans-RuCl2(P2N4H4Me) in good yield, respectively. The ligands and the complexes have been fully characterized by elemental analysis and spectroscopic methods. The complexes act as an excellent catalyst precursor in hydrogen transfer hydrogenation of acetophenone in catalyst: acetophenone :iso-PrOK of 1: 100: 15, leading to 2-phenylethanol of 89-96% yield.     

The synthesis and photophysical studies of cyclometalated Pt(II) complexes with C,N,N-ligands containing imidazolyl donors

Two new C,N,N-type ligands (HL(2) and HL(3)), containing a C(phenyl), a N(pyridyl), and a N(imidazolyl) donor, and their cycloplatinated complexes, [Pt(L(2))Cl] (1), [Pt(L(3))Cl] (2), [Pt(L(2))(PPh(3))](+) (3) and [Pt(L(3))(PPh(3))](+) (4), have been successfully synthesized and characterized. Spectroscopic and (3)MLCT luminescent properties of these Pt(II) cyclometalated complexes were found to be pH dependent. This was attributed to the protonation/deprotonation of the acidic 1-imidazolyl-NH moieties on the ligands. All the cycloplatinated complexes (both protonated and deprotonated forms) possessed two-photon excitability with two-photon absorption cross-sections ranging from 6.0 to 30.0 GM (protonated forms) and from 16.2 to 24.9 GM (deprotonated forms).     

Asymmetric Diels—Alder Reaction Catalyzed by Novel Chiral Dibenzo[a,c] cycloheptadiene Bis（oxazoline） Metal Complexes

A series of novel chiral C2-symmetric bis (oxazoline) ligands have been synthesized.The copper and magnesium complexes,prepared in situ from copper(Ⅱ)-triflate of magnesium triflate with the new enantiopure oxazoline ligands,were evaluated as chiral catalysts in the enantioselective Diels-Alder reaction of cyclopentadiene with N-crotenoyl-oxazolidin-2-one.Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands.     

Well-Defined,Versatile and Recyclable Half-Sandwich Nickelacarborane Catalyst for Selective Carbene-Transfer Reactions

Catalytic carbene-transfer reactions constitute a class of highly useful transformations in organic synthesis. Although catalysts based on a range of transition-metals have been reported, the readily accessible nickel(II)-based complexes have been rarely used. Herein, an air-stable nickel(II)-carborane complex is reported as a well-defined, versatile and recyclable catalyst for selective carbene transfer reactions with low catalyst loading under mild conditions. This catalyst is effective for several types of reactions including diastereoselective cyclopropanation, epoxidation, selective X−H insertions (X = C, N, O, S, Si), particularly for the unprotected substrates. This represents a rare example of carborane ligands in base metal catalysis.     

Cobalt(III) complexes of formyl- and acetylpyrazine N(4)-substituted thiosemicarbazones

Cobalt(III) complexes of acetyl- and formylpyrazine N(4)-substituted thiosemicarbazones have been synthesized and characterized by spectral and physical techniques. The crystal structure of the bis{formylpyrazine N(4)-methylthiosemicarbazone}cobalt(III) complex shows the two ligands coordinated in a mer-configuration, and the orientation of the thiosemicarbazone moiety's N(4)-methyl is Z with respect to the thiolato sulfur in both ligands. Included is the crystal structure of the bis- {2-acetylpyridineN(4)-propylthiosemicarbazone}cobalt(III) complex in which the two thiosemicarbazone ligands are also in the mer-configuration, but one ligand has the propyl group oriented Z with respect to the thiolato sulfur and the other E. Both complexes' bond lengths and bond angles are compared with other cobalt(III) thiosemicarbazone complexes.     

Synthesis Of N,N′-Diaralkyl 2H-1,2,6-Tetrahydrothiadiazines

Several derivatives of the 2H-1,2,6-Lctrahydrothiadiazine ring system have been synthesized by the interaction of the sulfur transfer reagent N,N-thiobisphthalimide (TBP) with appropriately substituted N,N′-bis-(benzyl)-1,3-diaminopropanes.