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A simple and efficient synthetic approach to dihydropyrazines via YbCl 3 -catalyzed reaction of α-hydroxyketones with diamines under mild conditions was developed. The corresponding 2,3-subsitituted piperazines and pyrazines were obtained through tandem conversion of dihydropyrazines with good yields.

Reaction of chiral imines with Danishefsky's diene in the presence of a catalytic amount (20 mol%) of ytterbium triflate afforded the corresponding hetero Diels-Alder adducts with a moderate to good diastereoselectivity.

Two novel tridentate ligands of 2,6-bis-[l-(2,6-dibromophenylimino) ethyl] pyridine (L1) and2-acetyl-6-[1-(2,6-dibromophenylimino) ethyl] pyridine (L2) have been synthesized. The iron(II) complex of L1 and L2 has been characterized with the crystal structure of [Fe(L1)(L2)]2+ [FeCl4]2 CH2Cl2 [monoclinic, P21 (#11), a = 1.0562(4), b = 2.0928(4), c = 1.2914(2) nm, β = 100.12°, V = 2.810(1) nm3Dc = 1.879 g/cm3 and Z = 2].

1,3-Dipolar cycloaddition of nitrones with ethyl vinyl ether or 2,3-dihydrofuran proceeds smoothly in the presence of a catalytic amount (10 mol%) of ytterbium triflate to afford isoxazolidines and dicyclic isoxazolidine respectively with good yields and high stereoselectivity.

A variety of lanthanocene complexes, e. g. chlorides, hydrocarbyls, amides, hydrides and divalent derivatives, were synthesized by using a series of designed cyclopentadienyl, indenyl and fluorenyl ligands with ring bridges or donor-functionalized sidearms. X-Ray crystallographic analyses reveal the formation of intramolecular coordination bonds between central metals and heteroatoms (O, N) in sidearms or bridging chains. Some applications of these complexes are also discussed in this account.

Asymmetric epoxidation of chalcone catalyzed by chiral (S)-6,6'-diphenyl-BINOL-lanthanum complex affords the corresponding epoxychalcone with excellent yields as well as the good enantioselective excesses of 93%. The influences of solvent, the temperature, the structure of the chiral ligand, as well as the substrate on the stereochemistry were discussed.

Four titanium complexes having β-ketoiminate chelate ligands with fluorine or alkyl groups [(Ar)NC(CH3)C(H)C(CH3)O]2TiCl2 (3a: Ar = 2.6-F2C6H3; 3b: Ar = C6F5; 3c: Ar = 2.6-Me2C6H3; 3d: Ar = 2.6-iPr2C6H3) have been synthesized and characterized by 1H NMR and EA. Complexes 3a, 3c and 3d were further characterized by X-ray diffraction analysis and demonstrated distorted octahedral coordination structure around the titanium center. The substituents in ligands greatly affect the coordination mode, resulting in three different isomeric structures. These complexes are active catalysts for polymerization of ethylene with MMAO as cocatalyst. The substituents in ligands have also great influences on catalytic activity. The complexes with alkyl groups have lower activity, while the complexes with fluorine atoms have middle or high catalytic activity.

A series of titanium complexes of the general formula [N-(3,5-di-tert-butylsalicylidene)-2-alkyl-sulfanylanilinato]Ti(IV)Cl3 (5a, b, e and f) exhibited very high catalytic activities in ethylene homo- and copolymerization with various α-olefins in the presence of modified methylaluminoxane (MMAO). The results showed that steric hindrance of the alkylthio groups in 5a–f strongly influenced the polymerization behavior. An increase in the steric hindrance of these alkyl units led to the decrease in both catalytic activity and comonomer incorporation ratio. On the other hand, the amount of α-olefin incorporated into the copolymer chain depended on the molar ratio of the monomers in the polymerization reaction and was slightly influenced by the chain length of α-olefin. Comparisons between alkylthio and arylthio substituents on catalyst performance were also discussed in this article.

A family of titanium complexes of the general formula [N-(3,5-di-tertbutylsalicylidene)-2-alkylsulfanylanilinato]Ti(IV)Cl-3 5a-f was prepared from the reaction of TiCl4 with the potassium salts of the corresponding ligands. These complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 5b and 5e were further confirmed by single-crystal X-ray analyses. Complexes 5a-f (except for 5c) exhibited good to high catalytic activities in ethylene copolymerization with cycloolefins such as norbornene, cyclopentene, dicyclopentadiene in the presence of modified methylaluminoxane. The reaction conditions and the steric hindrance of the alkyl substituents on sulfur atom in the precatalysts influenced strongly the copolymerization behaviors and the structures of the resultant copolymers. Complex 5c with bulky tert-butylthio sidearm showed both low catalytic activity and comonomer incorporation ratio. The n-alkylthio complexes 5a, 5d-f all exhibited good ethylene copolymerization capabilities with cycloolefins, which is superior to the corresponding phenylthio complex 5g. (c) 2008 Wiley Periodicals, Inc.

The Ti complexes containing tridentate [O-NS R ] (R = Me, i Pr) ligands with alkylthio sidearms were prepared. The methylthio ether complex (R=Me shown in the Scheme) exhibits an excellent activity for copolymerization of ethylene with norbornene upon activation with MMAO, which is 10 times more active than the corresponding phenylthio one (R = Ph).

A series of new mono β-diiminato titanium complexes [(N(Ar)C(CH3))2 CH]TiCl3 (3a: Ar = 2.6-F2C6H3; 3b: Ar = C6F5; 3c: Ar = 2.6-Me2C6H3) have been synthesized and characterized. The crystal structure of 3a revealed that the β-diiminato ligand in our complex is more close to the η2-coordination mode with little delocalization of the double bonds, which is different from the strong delocalization in the ligands of η5-coordinated (Tolnacnac)TiCl3 and η2-coordinated (Dipnacnac)ZrCl3. The significant electronic effects of fluoro-substituents on the olefin polymerization activity of mono β-diiminato titanium complexes were found. Titanium complexes with fluorine-containing β-diiminato ligands, on activation with MMAO, are extremely active catalysts for polymerization of ethylene. The activity of copolymerization of ethylene and 1-hexene is higher than homopolymerization of ethylene and increases with the increase of 1-hexene concentrations, which show the positive “comonomer effect.” The molar percentage of 1-hexene incorporation and polymer microstructures can also be modulated by the initial comonomer concentrations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 211–217, 2008

New imido-carboranes 1-(CHNC6H3R2-2,6)-1,2-C2B10H11 (R = iPr (3a), Me (3b)) were successfully prepared by Schiff base condensation of 1-CHO-1,2-C2B10H11 with R2C6H3NH2. They were readily converted into the corresponding imido-dicarbollyl ligands 7-(CHNHC6H3R2-2,6)-7,8-C2B9H11 (R = iPr (4a), Me (4b)) by refluxing in dry MeOH. Treatment of 3a with Ti(NMe2)4 in hot toluene gave a constrained-geometry complex, [η1:η5-(iPr2C6H3NCH)C2B9H10]Ti(NMe2)2 (5a). Under the same reaction conditions, interaction of 3b with Ti(NMe2)4 produced a mixture of [η1:η5-(Me2C6H3NCH)C2B9H10]Ti(NMe2)2 (5b) and [η1:η5-(Me2N)CH(NMe2)(C2B9H10)Ti(NMe2)2 (8). Reaction of 4a with M(NMe2)4 in toluene/DME at room temperature afforded 5a and [η1:η5-(iPr2C6H3NCH)C2B9H10]M(NMe2)2(NHMe2) (M = Zr (6a), Hf (7a)), respectively. Complexes 5a, 6a, and 7a were active catalysts for the polymerization of ethylene in the presence of MMAO with activities of 3−16 kg/mol·h·atm. These new complexes were fully characterized by various spectroscopic techniqu...

Bis(imino)pyridyl complexes of Fe and Co in combination with methyl- alumoxane form very active homogeneous catalytic systems for polymerization of eth- ylene. GPC analysis of the polymers prepared with the complexes indicates that the Co complexes produce single-center catalysts whereas the Fe complexes produce cata- lysts with numerous types of active centers. Different centers in the latter catalyst systems respond differently to reaction conditions such as the reaction duration, the (MAO):(Fe) ratio, the ethylene concentration, etc. The article examines the effects of reaction variables on the performance of both types of catalysts and proposes an ex- planation for the complex behavior of the catalysts derived from the Fe complexes.

An efficient stereoselective aza-Henry reaction of N-tosyl imine, catalyzed by the coordination of diethylzinc with a chiral semi-aza-crown ligand, with moderate to high ee (up to 83%) is reported.

A series of new organolanthanide(II) complexes with furfuryl- and tetrahydrofurfuryl-functionalized indenyl ligands were synthesized via one-electron reductive elimination reaction. Treatments of [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3 (Ln = Yb, Eu) with 2 equiv. of C4H7OCH2C9H7 (1) or C4H3OCH2C9H7 (2), respectively in toluene at moderate high temperatures produced, after workup, the corresponding organolanthanide(II) complexes with formula [η5:η1-(C4H7OCH2C9H6)]2LnII (Ln = Yb (5), Ln = Eu (6)) and [η5:η1-(C4H3OCH2C9H6)]2LnII (Ln = Yb (7), Ln = Eu (8)) in reasonable to good yields. Treatments of [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3 (Ln = Yb, Eu) with 2 equiv. of C4H7OCH2C9H6SiMe3 (3) or C4H3OCH2C9H6SiMe3 (4), respectively, in toluene at moderate high temperatures afforded, after workup, the corresponding organolanthanide(II) complexes with formula [η5:η1-(C4H7OCH2C9H5SiMe3)]2LnII (Ln = Yb (9), Ln = Eu (10)) and[η5:η1-(C4H3OCH2C9H5SiMe3)]2LnII (Ln = Yb (11), Ln = Eu (12)) in good to high yields. All the compounds were fully characterized by spectroscopic methods and elemental analyses. The structure of complex 9 was additionally determined by single-crystal X-ray analyses. Studies on the catalytic activities of complexes showed that the complexes having silyl group functionalized indenyl ligands have high catalytic activities on e-caprolactone polymerization. The temperatures, substituted groups on the indenyl ligands of the complexes, and solvents effects on the catalytic activities of the complexes were examined.

Ytterbium(III) triflate efficiently catalyzes the one-pot reaction of homophthalic anhydride with aldehydes and amines at ambient temperature to afford the corresponding cis-isoquinolonic acid derivatives in good to excellent yields with high diastereoselectivity. This method provides a novel and much improved modification of the three-component reaction in terms of mild reaction conditions, short reaction times, clean reaction profiles, small quantity of catalyst, and simple work-up procedure. Another important feature of this method is that the catalyst can be easily recovered from the aqueous layer after the reaction and can be reused with no loss of activity.

o‐Diaminobenzene derivatives react smoothly with ortho‐esters in the presence of 0.5 mol% of Yb(OTf)3 under solvent‐free conditions to afford the corresponding benzimidazole derivatives in good to excellent yields. In addition, Yb(OTf)3 can be easily recovered almost quantitatively from the aqueous layer after the reaction was completed, and it could be reused with no loss of activity.

Mesomeric divalent 1,1‘-(3-oxapentamethylene)-bridged bis(indenyl)lanthanidocenes, meso-[O(CH2CH2C9H6)2]Ln·(DME) (Ln = Sm (2),Yb (3)), have been synthesized by reduction of a mixture of rac/meso-[O(CH2CH2C9H6)2]LnCl·THF (Ln = Sm, Yb) with Na or reaction of LnI2 (Ln = Sm, Yb) with [O(CH2CH2C9H6K)2] in THF followed by recrystallization in DME. The structures of these meso, ansa-lanthanidocenes were determined by X-ray diffraction analysis. The factors that dictated the rac/meso selectivity are discussed. Nonbridged divalent lanthanide complexes (CH3OCH2CH2C9H6)2LnII (Ln = Sm (4), Yb (5)) were also synthesized for comparison by the reaction of LnI2 (Ln = Sm, Yb) with (CH3OCH2CH2C9H6)2K in THF. Stereoselective polymerization of methyl methacrylate with these divalent lanthanide complexes as single-component catalysts was preliminarily investigated.

An array of aromatic aldehydes undergoes crossed aldol condensation with ketones in the presence of a catalytic amount of Yb(OTf) 3 under solvent-free conditions to afford the corresponding α,α'-bis(substituted benzylidene)cycloalkanones in excellent yields without occurrence of any side reactions. This method is very general, simple and environmental friendly in contrast with the existing methods, which use many classical Lewis acids. Furthermore, the catalyst can be recovered conveniently and reused efficiently without the loss of activity.

Zusammenfassung Die Absorptionsspektren von pseudo-trigonal-bipyramidal koordiniertem Nd(η 5 -C 5 H 4 CH 2 CH 2 OMe) 3 ( 1 ) und Nd(η 5 -C 5 H 4 CH 2 CH 2 PMe 2 ) 3 ( 2 ) wurden sowohl bei Raumtemperatur als auch bei tiefen Temperaturen gemessen. Den erhaltenen Spektren wurden die zugrundeliegenden partiellen Kristallfeld(KF)-Aufspaltungsmuster entnommen und durch Anpassung der Parameter eines phanomenologischen Hamilton-Operators simuliert. Bei 55 bzw. 53 Zuordnungen wurden fur die Komplexe 1 und 2 reduzierte r.m.s.-Abweichungen von 31 cm −1 bzw. 23 cm −1 erzielt. Die verwendeten Parameter gestatten die Bestimmung der jeweils von den Nd 3+ -Ionen wahrgenommenen Ligandenfeldstarken der Verbindungen 1 und 2 , die Einordnung dieser Komplexe in verkurzte empirische nephelauxetische und relativistische nephelauxetische Serien und die Aufstellung ihrer experimentorientierten nichtrelativistischen und relativistischen Molekulorbitalschemata im f-Bereich.

Six five-coordinate difluoro-substituted 2,6-bis(imino)pyridyl iron and cobalt complexes, [{2,6-(2,X-F2C6H3NCCH3)2C5H3N}MCl2] (X = 6, M = Fe (1), Co (2); X = 5, M = Fe (3), Co (4)); X = 4, M = Fe (5), Co (6)), were synthesized by reactions of the corresponding bis(imino)pyridyl ligands with FeCl2·4H2O or CoCl2 in tetrahydrofuran (THF). However, a reaction between 2,6-diacetylpyridinebis(2,6-difluoroanil) and FeCl2·4H2O in CH3CN provided the ion-pair complex [Fe{2,6-(2,6-F2C6H3NCCH3)2C5H3N}2]2+[FeCl4]2- (7) instead of a five-coordinate complex. The molecular structures of complexes 3 and 6 were determined by X-ray diffraction. The catalytic activities of complexes 1−7 for ethylene oligomerization were studied using modified methylaluminoxane (MMAO) as cocatalyst. At 60 °C and 10 atm of ethylene pressure, the iron complexes 1, 3, and 5 show very high activities: 4.07 × 107, 9.33 × 107, and 11.1 × 107 g/((mol of cat.) h), respectively. The oligomers formed consist mainly of dimer, trimer, and tetramer, with...

Novel one-pot Biginelli-type reaction has been developed. Aromatic and aliphatic aldehydes with β-dicarbonyl compounds and thiourea in the presence of catalytic amount 5 mol% of Yb(OTf)3 at 100° C for 60–90 min under solvent-free conditions proceeded smoothly to afford corresponding dihydropyrimidin-thiones. The yields of the classical Biginelli reaction can be increased from 20–50% to 81–91% while the reaction time was shortened from 18–48 h to 60–90 min. In addition the catalyst can be easily recovered and reused.

An efficient synthesis of an array of quinazolin-4(3 H)- ones from anthranilic acid, ortho esters (or formic acid) and amines using Yb(OTf)3 in one-pot under solvent-free conditions is de- scribed. Compared with the classical reaction conditions, this new synthetic method has the advantage of excellent yields (75-99%), shorter reaction time (few minutes) and reusability of the catalyst.

A series of silylene- and methylene-bridged fluorenyl cyclopentadienyl ansa -lanthanocene chlorides, hydrocarbyls, amides and tetrahydroborates with C s - or C 1 -symmetry have been synthesized successfully. X-ray structural studies have been carried out for these complexes. The hydrocarbyls and amides were applied for catalyzing the polymerization of methyl methacrylate and lactones.

The one-carbon atom bridged amide complex [Ph2C(Flu)(Cp)]LuN(TMS)2 (2) (Flu=C13H8, Cp=C5H4, TMS=SiMe3) has been synthesized by reaction of its chloride precursor with LiN(TMS)2 in toluene. An X-ray structure of the amide complex 2 exhibits apparently intramolecular βSiC agostic interaction with Lu. Polymerization of methyl methacrylate (MMA) and lactones with this complex has also been investigated.

In the presence of 10 mol% of La(O-i-Pr)3, a three-component condensation reaction of aldehyde, secondary amine and trimethylsilylcyanide proceeded smoothly to afford N,N-dialkyl-α-cyanoamine in good yield.

Various 4-substituted-1-methyltetrahydroquinolines are easily accessible from the one-pot condensation reaction of N-methylaniline with commercial formaldehyde solution and electron-rich alkenes in the presence of Dy(OTf)3 (1 mol %) under mild conditions at ambient temperature and in the absence of any organic solvents.

Reaction of the dimethylsilyl-bridged flourene cyclopentadiene ligand with 1 equiv of n-butyllithium or sodium hydride smoothly afforded the corresponding monoalkali-metal salts [(FluMe2Si)Cp]M·(THF)n (Cp = C5H4, Flu = C13H9) (M = Li (1), n = 0; M = Na (2), n = 1). Complexes 1 and 2 were characterized by single-crystal X-ray structural analyses. These revealed that both of them have similar linear polymeric structural aggregate types in the solid state. In complexes 1 and 2, the fluorenyldimethylsilyl groups attached to the cyclopentadienyl rings are arranged in gaps and oriented on the same side of the multideck chain.

A series of chiral 1,1‘-(3-oxapentamethylene)-bridged bis(indenyl) ansa-lanthanidocenes have been high stereoselectively synthesized. The reaction of YbCl3 with O(CH2CH2C9H6K)2 in THF provided a rac/meso mixture of [O(CH2CH2C9H6)2]YbCl(THF); the major diastereomer formed is racemic. The rac-[O(CH2CH2C9H6)2]YbCl(THF) (1) was isolated after recrystallization of a rac/meso mixture of [O(CH2CH2C9H6)2]YbCl(THF) in THF. Direct amidation (or alkylation) of the rac/meso lanthanidocene chloride mixtures in toluene provided solely pure racemic ansa-lanthanidocene amides [O(CH2CH2C9H6)2]LnN(SiMe3)2 (Ln = Y (2), Pr (3), Nd (4), Yb (5), Lu (6)) and pure racemic ansa-lanthanidocene hydrocarbyls [O(CH2CH2C9H6)2]LnCH2SiMe3 (Ln = Dy (7), Yb (8)). The structures of 1 and 5 were determined by X-ray diffraction. The amide and hydrocarbyl complexes are efficient single-component catalysts for methyl methacrylate polymerization. The effects of solvent and reaction temperature on the polymerization were studied. Very high molec...

A series of new Cs-symmetric organolanthanocene chlorides, [R2Si(Flu)(R‘Cp)Ln(μ-Cl)]2 (Flu = C13H8, fluorenyl; Cp = C5H3) (R = Me, R‘ = H, Ln = Y (1), Lu (2), Dy (3), Er (4); R = Ph, R‘ = tBu, Ln = Y (5), Dy (6)), has been synthesized by the reaction of anhydrous lanthanide chloride with the dilithium salt of the ligand Me2Si(FluH)(CpH). Treatment of the resulting chlorides with ME(TMS)2 (M = Li or K, E = N, CH) gave the amide and hydrocarbyl derivatives Me2Si(Flu)(Cp)LnE(TMS)2 (E = N, Ln = Dy (7), Er (9); E = CH, Ln = Dy (8), Er (10)). X-ray structures of chloride compounds reveal unusual Cp−SiMe2−Cp bridging dimeric coordination. All of the amide and hydrocarbyl complexes show normal chelating structure and exhibit apparently intramolecular γ-agostic Ln−Me−Si interaction. These complexes are active for the polymerization of methyl methacrylate.

Racemic planar chiral metallocenes bis(2-methoxyethylindenyl) yttrium and lanthanum tetrahydroborates (MeOCH^2CH^2C^9H^6)^2Lnμ2-H)nBH^4-n (Lu = Y, n = 2(1); Ln = La, n = 3, (2)) have been stereoselectively isolated in high yield by reaction of the corresponding lanthanoeene chlorides with sodium borohydride in THF at room temperature. The two complexes have been fully characterized by elemental analyses, MS. ~1H NMR and IR spectra. The tetrahydroborate ion has been identified as slipped bidentate (μ^2-H)^2BH^2 and tridentate (μ^2H)^3BH ligands in I and 2, respectively. 2000 Elsevier Science Ltd. All rights reserved.

α-Aryl-N-phenyl nitrones reacted with silyl ketene acetals mediated by lanthanum trifloromethanesulfonate (triflate) to afford the addition product in excellent yield under mild conditions. α-Aryl-N-tert-butyl nitrone reacted with ethyl trimethylsilylacetate to yield the unexpected α,β-unsaturated ester in a 100% E-form. A possible mechanism for the process is discussed.

First examples of racemic bis(2-dimethylaminoethylindenyl) divalent unsolvated organolanthanide complexes (Me 2 NCH 2 CH 2 C 9 H 6 ) 2 Sm ( 1 ) and (Me 2 NCH 2 CH 2 C 9 H 6 ) 2 Yb ( 2 ) have been synthesized by the reaction of (Me 2 NCH 2 CH 2 C 9 H 6 )K with LnI 2 (Ln=Sm, Yb). The two compounds have been characterized by elemental analysis and 1 H-NMR spectrometry. The X-ray crystal structure of 2 has been determined by diffraction study. The crystals are prismatic, space group P 2 1 / a (≠14), with a =17.342(6) A, b =8.542(7) A, c =17.353(2) A, β =118.70°, V =2254(1) A 3 , Z =4, D =1.607 g cm −3 .

The tris-alkylborohydride Cp Q 2 NdHBEt 3 (Cp Q =C 5 H 4 CH 2 CH 2 OCH 3 ) obtained by reaction of NaHBEt 3 with Cp Q 2 NdCl is fairly stable in solution whereas the hydride Cp Q 2 NdH formed from Cp Q 2 NdCl and NaH or by hydrogenolysis of Cp Q 2 NdR (R=CH 2 SiMe 3 or CH(SiMe 3 ) 2 ) is a species of very short life, undergoing rearrangement to Cp Q 3 Nd. This transient hydride is not observed but can be trapped with ketones—propanone or pivalone, leading to the alkoxides Cp Q 2 NdOCHR′ 2 (R′=Me or CMe 3 ). The same alkoxides are obtained from Cp Q 2 NdHBEt 3 .

The reaction of anhydrous lanthanide chlorides LnCl3 with the dilithium salt of (C13H9)CPh2(C5H5) in thf at ambient temperature led to the formation of the ‘ate’ complexes [Li(thf)4][LnCl2{(C13H8)CPh2(C5H4)}] (Ln = Lu 1 or Y 2). Treatment of [Ln(BH4)3(thf)3] with 3 equivalents of (C13H8)CPh2(C5H4)Li2 in thf solution gave the anionic complexes [Li(thf)4][Ln(BH4)2{(C13H8)CPh2(C5H4)}] (Ln = La 3 or Nd 4). The crystal structures of complexes 1, 3, 4 were determined and indicated that they existed as discrete cation and anion pairs, which showed two crystallographically independent molecules in the unit cell.

Chiral lanthanocene chlorides (CH3OCH2CH2C9H6)2LnCl (Ln=Y 1, La 2, Nd 3, Gd 4, Ho 5 and Lu 6) with an ether-functionalized indenyl ligand were synthesized by the reaction of 1-(2-methoxyethylindenyl) potassium (in situ) with corresponding anhydrous lanthanide chlorides in THF. The X-ray crystal structures of four such complexes were determined and these indicated that they were unsolvated monomeric complexes with a trans arrangement of both the sidearms and indenyl rings in the solid state. This configuration also predominated in THF solution, as evidenced by NMR spectra of the diamagnetic complexes 1, 2 and 6, although some minor species of 1 and 2 did form upon dissolution.

Several representative chiral ansa-lanthanocene chlorides have been synthesized and characterised with a rac∶meso ratio of 6∶1 using an ether-bridged bis(indenyl) ligand. The structure of these complexes was identified by X-ray crystallography in the solid state or 1H NMR spectroscopy in solution. The ligand proved to be rather rigid leading to the favoured unsymmetric rac isomer. The 1H NMR spectra indicated that the configuration of the rac isomer in solution agrees well with that in the solid state and, interestingly, the two bridged indenyl rings of the rac isomers slowly oscillated.

By using a direct ortho-lithiation strategy and/or Ni-catalysed coupling reaction, we have conveniently synthesized three new chiral polysubstituted BINOLs of vast synthetic potential from (S)-BINOL 1 in reasonable yields. Moreover, we have examined closely their influence on the enantioselectivity of the asymmetric Pudovik reaction catalyzed by chiral binaphthol-modified lanthanum alkoxides. The results show that the steric bulk of 3,3′-substituents of BINOL is responsible for a lowering of the enantioselectivity of the reaction, while coordination between the oxygens of the ortho-substituents and the lanthanum ion is beneficial in improving the asymmetric induction. 6,6′-Diphenyl-BINOL has the advantage over simple BINOL in giving the best asymmetric results. Further studies on this aspect are in progress.

Organolanthanum reagents[RLaCl 2 ] generated in situ from LaCl 3 and alkyl lithium or allyl magnesium could undergo a highly regioselective 1,2-addition to N -alkyl α,β -unsaturated imines, which provided a new and useful approach to synthesize allyl amines with good yields and high regioselectivity. Furthermore, for N -chiral alkyl α,β -unsaturated imine, in the case of n -butyl lithium, the diastereoselectivity achieved highly 90%.

Yb(OTf) 3 can catalyze the glyoxylate-ene reaction effectively as a water-stable and reusable catalyst. Moreover, the selectivity of DA product or ene product can be adjusted by solvents in the reaction of glyoxylates with a diene (isoprene). In the presence of chiral ytterbium complexes generated in situ from Yb(OTf) 3 and optical 6,6′-disubstituted binaphthols, methyl glyoxylate smoothly reacts with α-methyl styrene to afford α-hydroxyl esters in modest optical yields. © 1997 Elsevier Science Ltd.

A simple and efficient synthetic approach to dihydropyrazines via YbCl 3 -catalyzed reaction of α-hydroxyketones with diamines under mild conditions was developed. The corresponding 2,3-subsitituted piperazines and pyrazines were obtained through tandem conversion of dihydropyrazines with good yields.

The FT-Raman and selected IR spectra of 14 heterobimetallic complexes of (CO) 3 CrC 6 H 5 -C 5 H 4 M(CO) n (NO) m X (M = transition metal, X = other ligands) are reported. FT-Raman exhibits distinct strong characteristic bands of coordinated C 6 H 5 -C 5 H 4 ligand ring deformation near 1540, 1490 and 1280 cm −1 and the coordinated phenyl ring deformation mode near 1000 cm −1 , which are negligible in IR spectra. It is also easy to find the M-CO stretching and M-C-O bending as well as phenyl-M stretching bands in the FT-Raman spectra. The v(CO) IR absorptions in THF solution were reasonably assigned according to the local symmetry of the complexes.

Several complexes [O(CH2CH2C5H3R)2LnCl] (R  1Bu, Ln  Y, Nd, Sm, Yb; R  SiMe3, Ln  La, Y, Nd, Yb) were synthesized using chelating ligands and characterized by mass-, IR-, 1H NMR-spectroscopies and elemental analyses. The spectra indicate that these complexes are unsolvated ansa-metallocene chlorides and the two bridged cyclopentadiene rings coordinate to the same metal ion with an intramolecular coordination bond between the oxygen atom of the bridge and the metal ion. These complexes are still sensitive to air and moisture, but they all have good thermal stability under inert gas and excellent solubility in hydrocarbon solvents. The reactivities of the systems of these metallocene chlorides and sodium hydride were investigated. Compared with the solubility of these complexes in a range of solvents, the influence of steric factors arising from the bulky substituents on the cyclopentadiene rings or the radial size of the metal ions are relatively slight.

Zusammenfassung Durch Dotierung einer Cp 3 La(NCCH 3 ) 2 -Matrix mit unterschiedlichen Mengen von Pr 3+ konnten relativ stabile Cp 3 La 1 − x Pr x (NCCH 3 ) 2 ( 1 ) ( x = 0,6; 0,3; 0,1)-Einkristalle gezuchtet werden. Auf der Grundlage absorptions- und lumineszenzspektroskopischer Untersuchungen sowie teilweise von Messungen des magnetischen Zirkulardichroismus wurden die Kristallfeld (KF)-Aufspaltungsmuster von 1 und (CH 3 OCH 2 CH 2 C 5 H 4 ) 3 Pr ( 2 ) abgeleitet. Die Parameter eines empirischen Hamilton-Operators wurden den KF-Aufspaltungsmustern von 1 und 2 angepaβt, wobei r.m.s.-Abweichungen von 27 cm −1 bzw. 24 cm −1 bei 25 bzw. 24 Zuordnungen erzielt wurden. Bei Verwendung der berechneten Wellenfunktionen und Eigenwerte konnte die Temperaturabhangigkeit der mittleren paramagnetischen Suszeptibilitat von Cp 3 Pr(NCCH 3 ) 2 sowie von 2 in ausgezeichneter Weise reproduziert werden.

The compounds O(CH2CH2C5H4)(2)Ln(THF)(2) [Ln = Sm(1), Yb(2)] were synthesized by the reduction of O(CH2CH2C5H4)(2)LnCl with sodium metal in tetrahydrofuran (THF) at room temperature. Recrystallization of 2 from dimethoxyethane (DME) produced the single-crystal O(CH2CH2C5H4)(2)Yb(DME) (3) whose structure has been determined by an X-ray diffraction study. The crystals are orthorhombic, space group Pcab, with a = 14.168(4), b = 13.541(6), c = 19.314(8) Angstrom, Z = 8, D-calc. = 1.66 g cm(-3).

Organic halides can be ubiquitous long-lived contaminants to the environment. Dehalogenation of organic halides with sodium hydride (NaH) as reductant catalyzed by two varieties of lanthanides was reported in respect of environmental remediation. The first catalyst is a dicyclopentadienyl yttrium halide, and organoyttrium hydride was thought to be the reactive species. The second catalyst is a lanthanide isopropoxide which showed higher catalytic reactivity, and an aggregate is involved in the suggested mechanism.

The use of Cp2YCl and YCl3 as effective catalysts for the regioselective acylative cleavage of epoxides, especially for the conversion of α, β-epoxyketones to α-chloroenones is described.

Chemical preparation and X-ray diffraction determined crystal structures of (CH{sub 3}OCH{sub 2}CH{sub 2}C{sub 5}H{sub 4}){sub 2}LnCl [Ln = La (1), Pr (2), Nd (3), Sm (4), Gd (5), Dy (6), Ho (7), Er (8), Tm (9), Yb (10), Lu (11), Y (12)] are reported. Further characterization by elemental analysis, MS, NMR, and IR spectroscopy was performed for these complexes. From these data, the molecular structures are described.