Oxydative Aryl-Aryl-Verknüpfung von 6,6′,7,7′-Tetramethoxy-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-biisochinolin-Derivaten

Oxidative Aryl-Aryl-Coupling of 6,6′,7,7′-Tetramethoxy-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-biisoquinoline Derivatives We describe the synthesis of 2 by intramolecular oxidative coupling of 1, 1′-biisoquinoline derivatives 1 (Scheme 1). This heterocyclic system can be considered as a union of two apomorphine molecules and may thus exhibit dopaminergic activity. - The readily available tetrahydrobiisoquinoline 6 was methylated to 11 (Scheme 4) and reduced (with NaBH₃CN) to rac- 7 and (catalytically) to meso- 7 (Scheme 3). Reduction of 11 with NaBH₄ and of the biurethane rac- 9 with LiAlH₄/AlCl₃ afforded meso- and rac- 10 , respectively (Scheme 4). Demethylation of 6 , meso- 10 , meso- and rac- 7 led to 12 , meso- 14 , meso- and rac- 13 , respectively (Scheme 5). The latter two phenols were converted with chloroformic ester to the hexaethoxycarbonyl derivatives meso- and rac- 15 and subsequently saponified to the biurethanes meso- and rac- 16 , respectively (Scheme 5). - In order to assure proximity of the two aromatic rings, the ethano-bridged derivatives meso- and rac- 18 were prepared by condensing meso- and rac- 7 with oxalic ester and reducing the oxalyl derivatives meso- and rac- 17 with LiAlH₄/AlCl₃, respectively (Scheme 6). The ¹H-NMR, spectra at different temperatures showed that rac- 18 populated two conformers but rac- 17 only one, all with C₂-symmetry, and that meso- 17 as well as meso- 18 populated two enantiomeric conformers with C₁-symmetry. Whereas both oxalyl derivatives 17 were fairly rigid due to the two amide groupings, the ethano derivatives 18 exhibited coalescence temperatures of -20 and 30°. - The intramolecular coupling of the two aromatic rings was successful under ‘non-phenolic oxidative’ conditions with the tetramethoxy derivatives 7, 10 and 18 , the rac-isomers leading to the desired dibenzophenanthrolines, the meso-isomers, however, mostly to dienones (Scheme 9): With VOF₃ and FSO₃H in CF₃COOH/CH₂Cl₂ rac- 7 was converted to rac- 19 , rac- 18 to rac- 21 and rac- 10 to a mixture of rac- 20 and the dienone 23b of the morphinane type. Under the same conditions meso- 10 was transformed to the dienone 23a of the morphinane type, whereas meso- 18 yielded the dienone 24 of the neospirine type, both in lower yields. The analysis of the spectral data of the six coupling products offers evidence for their structures. With the demethylation of rac- 20 and rac- 21 to rac- 25 and rac- 26 , respectively, the synthetic goal of the work was reached, but only in the rac-series (Scheme 10). - In the course of this work two cleavages of octahydro-1,1′-biisoquinolines at the C(1), C(1′)-bond were observed: (1) The biurethanes 9 and 16 in both the meso- and rac-series reacted with oxygen in CF₃COOH solution to give the 3,4-dihydroisoquinolinium salts 27 and 28 ; the latter was deprotonated to the quinomethide 30 (Scheme 11). (2) Under the Clarke-Eschweiler reductive-methylation conditions meso- and rac- 7 were cleaved to the tetrahydroisoquinoline derivative 32 .     

Platinum(II) Complexes of P‐Chiral 1, 8‐Bis(diorganophosphino)naphthalenes; Crystal Structures of dmfppn,rac‐[PtCl2(dmfppn)], and rac‐[PtCl2(dtbppn)] (dmfppn = 1, 8‐di(methyl‐pentafluorophenylphosphino)naphthalene and dtbppn = 1, 8‐di(tert‐butylphenylphosphino)naphthalene)

The reaction of 1, 8‐dilithionaphthalene 2 , with 2 equivalents of rac‐Me(C₆F₅)PCl, gave a 6 : 1 mixture of rac‐ and meso‐1, 8‐di(methyl‐pentafluorophenylphosphino)naphthalene (dmfppn, rac‐ 3h and meso‐ 3h ), but no reaction was observed when the sterically crowded rac‐tBu(C₆F₅)PCl was used. In ³¹P NMR experiments, rac‐ 3h and mmeso‐ 3h exhibited characteristic signals (virtual quintets), which indicate that there is significant coupling through space (³J_PF + ⁷ J_PF ≈ 15 Hz). Compound rac‐ 3h was isolated by fractional crystallisation and treated with aqueous H₂O₂ to yield the corresponding bis‐phosphine dioxide, rac‐ 7h . In contrast to rac‐ 3h , there was no sign of through‐space coupling in rac‐ 7h , which again illustrates that the latter operates via the lone pairs at phosphorus. Platinum(II) complexes were prepared from the new, P‐chiral chelate rac‐ 3h , and the related ligand 1, 8‐di(tert‐butylphenylphosphino) naphthalene (rac‐dtbppn, rac‐ 3e ). All isolated new compounds were characterised by multinuclear NMR and IR spectroscopy, mass spectrometry, and elemental analysis. Single‐crystal X‐ray structure determinations were performed for rac‐dmfppn (rac‐ 3h ), rac‐[PtCl₂(dtbppn)] (rac‐ 17e ), and rac‐[PtCl₂(dmfppn)] (rac‐ 17h ). rac‐ 3h displays crystallographic twofold symmetry. In rac‐ 17h , the electron‐withdrawing effect of the C₆F₅ groups causes a shortening of the P_t—P bond to ca. 220 pm (cf. 223 pm in rac‐ 17e ).     

Polymerization of olefins with a novel dinuclear ansa-zirconocene catalyst having a biphenyl bridge

Both the rac- and meso-dinuclear ansa-zirconocene catalysts (μ-C₁₂H₈{[SiPh(Ind)₂]ZrCl₂}₂) were prepared by a coupling reaction between 2 equiv of diindenylphenylchlorosilane (rac- and meso-isomers) and 1 equiv of p-dilithiobiphenyl in diethyl ether at −80°C, followed by a successive reaction with ZrCl₄ · 2THF in THF at −78°C. Polymerizations of ethene and propene were conducted in a 1 dm³ high-pressure glass reactor equipped with a mechanical stirrer at 60, 80, 100, 120, and 150°C using methylalumoxane (MAO) as cocatalyst and toluene or decahydronaphthalene as the solvent. Copolymerization of ethene and 1-octene was also checked in brief. For ethene polymerization, the meso-catalyst was found to be more active, which displayed an extremely high activity to give linear polyethene with a high molecular weight and a narrow molar mass distribution (MMD). The apparent activity increased monotonously with rising polymerization temperature from 60°C up to 150°C, indicating that the active species are stable even at a high temperature. On the other hand, both the rac- and meso-catalysts showed very poor activities for propene polymerization. However, copolymerization of ethene and 1-octene proceeded at a high speed. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2269–2274, 1998     

Synthesis of symmetrical 2,2′,4,4′-tetrasubstituted[4,4′-bioxazole]-5,5′(4H,4′H)-diones and their reactions with some nucleophiles

Several symmetrical 2,2′,4,4′-tetrasubstituted[4,4′-bioxazole]-5,5′(4H,4′H)-diones 1a-f were obtained by dehydrodimerization of 5(4H)-oxazolones 2a-f . The configurations of four were established; one by X-ray crystallography rac- 1c , and three rac- 1a , meso- 1a and rac- 1b by ¹H nmr spectroscopy of their derivatives. Upon being heated, the bioxazolones isomerized, presumably by breakage of the 4,4′-carbon? carbon bond to form free radicals followed by their recombination. The results of a crossover experiment were consistent with a radical nature for this isomerization reaction. Treatment of three of the bioxazolones rac- 1a , meso- 1a and rac- 1c with methanol and amine nucleophiles led to ester and amide derivatives 7–11 of α,α'-dehydrodimeric amino acids.     

Energy-Minimized Structures and Calculated and Experimental Isomer Distributions in the Hexaaminecobalt(III) system [Co(trap)2]3+ (trap = 1,2,3-propanetriamine)

The two isomers of [Co(trap)₂]³⁺ (meso-[Co(trap)₂]³⁺ and rac-[Co(trap)₂]³⁺; trap = 1,2,3-propanetriamine) have been studied by strain-energy minimization. The two isomers have been separated preparatively by fractional crystallization, and fully characterized by ¹³C-NMR and electronic spectroscopy, and microanalyses. The calculated isomer distribution (rac/meso = 60%: 40%) is in good agreement with HPLC analysis of thermodynamic equilibrium mixtures at 298 K and 353 K (rac/meso = 55% : 45%). These results are discussed in relation to the approach of calculating isomer distributions of hexaaminecobalt(III) systems by strain-energy minimization neglecting the differences in environmental effects.     

Ring‐opening polymerization of rac‐ and meso‐lactide initiated by indium bis(phenolate) isopropoxy complexes

Ring‐opening polymerization of rac‐ and meso‐lactide initiated by indium bis(phenolate) isopropoxides {1,4‐dithiabutanediylbis(4,6‐di‐tert‐butylphenolate)}(isopropoxy)indium ( 1 ) and {1,4‐dithiabutanediylbis(4,6‐di(2‐phenyl‐2‐propyl)phenolate)}(isopropoxy)indium ( 2 ) is found to follow first‐order kinetics for monomer conversion. Activation parameters ΔH^? and ΔS^? suggest an ordered transition state. Initiators 1 and 2 polymerize meso‐lactide faster than rac‐lactide. In general, compound 2 with the more bulky cumyl ortho‐substituents in the phenolate moiety shows higher polymerization activity than 1 with tert‐butyl substituents. meso‐Lactide is polymerized to syndiotactic poly(meso‐lactides) in THF, while polymerization of rac‐lactide in THF gives atactic poly(rac‐lactides) with solvent‐dependent preferences for heterotactic (THF) or isotactic (CH₂Cl₂) sequences. Indium bis(phenolate) compound rac‐(1,2‐cyclohexanedithio‐2,2′‐bis{4,6‐di(2‐phenyl‐2‐propyl)phenolato}(isopropoxy)indium ( 3 ) polymerizes meso‐lactide to give syndiotactic poly(meso‐lactide) with narrow molecular weight distributions and rac‐lactide in THF to give heterotactically enriched poly(rac‐lactides). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4983–4991     

Directly Linked and Fused Oligoporphyrin Arrays from Oxidation of Metalloporphyrins

The Ag^I-promoted oxidative meso-meso coupling reaction of 5,15-diaryl Zn^II-porphyrins is advantageous in light of its high regioselectivity as well as its easy extension to large porphyrin arrays. Linear meso-meso linked porphyrin 128-mer and three-dimensionally arranged grid porphyrin 48-mer were isolated in a discrete form by repetitive oxidation reaction and subsequent gel-permeation chromatography (GPC)-HPLC. 5,15-Diaryl Cu^II-, Ni^II-, and Pd^II-porphyrins were converted to meso- doubly-linked diporphyrins by oxidation with(p-BrC₆H₄)₃NSbCl₆. End-aryl-capped meso-meso linked Cu^II-, Ni^II-, and Pd^II- diporphyrins were converted to completely fused meso-meso - -triply-linked diporphyrins through the oxidative ring closure (ODRC) reaction with (p-BrC₆H₄)₃NSbCl₆. Finally, we found that Sc^III-catalyzed oxidation with DDQ gave a very efficient ODRC reaction and hence allowed the synthesis of triply-linked oligoporphyrins up to 12-mer.     

Syntheses of rac/meso-{PhP(3-t-Bu-C5H3)2}-Zr{RN(CH2)3NR}, structural analyses of rac-{PhP(3-t-Bu-C5H3)2}Zr{RN(CH2)3NR} (where R is SiMe3 or Ph), and meso to rac isomerization

Syntheses of rac/meso-{PhP(3-t-Bu-C₅H₃)₂}Zr{Me₃SiN(CH₂)₃NSiMe₃} (rac-3/meso-3) and rac/meso-{PhP(3-t-Bu-C₅H₃)₂}Zr{PhN(CH₂)₃NPh} (rac-4/meso-4) were achieved by metallation of K₂[PhP(3-t-Bu-C₅H₃)₂] · 1.3 THF (2) with Zr{RN(CH₂)₃NR}Cl₂(THF)₂ (where R = SiMe₃ or Ph, respectively) using ethereal solvent. These isomeric pairs were characterized by ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy; rac-3 and rac-4 were also examined via single crystal X-ray crystallography. The structures of rac-3 and rac-4 are notable in the tendency of the cyclopentadienyl rings towards η³ coordination. While isolated samples of rac-3/meso-3 and rac-4/meso-4 slowly isomerize in tetrahydrofuran-d₈ to equilibrium ratios, the isomerization rate for 3 is more than 15-fold greater than that for 4. In addition, equilibrium ratios are rapidly reached when isolated samples of rac-3/meso-3 and rac-4/meso-4 are exposed to tetrabutylammonium chloride in tetrahydrofuran-d₈ solvent. We propose that a nucleophile (either chloride or the phosphine interannular linker) brings about dissociation of one cyclopentadienyl ring, thus promoting the rac/meso isomerization mechanism.     

Effect of co-catalyst system on α-olefin polymerization with rac- and meso-[dimethylsilylenebis(2,3,5-trimethyl-cyclopentadienyl)]zirconium dichloride

Propene, 1-butene and 1-hexene polymerization was conducted with a mixture of rac- and meso-[dimethylsilylenebis((2,3,5-tetramethyl-cyclopentadienyl))]zirconium dichloride (Me₂Si(2,3,5-Me₃Cp)₂ZrCl₂) ( 1 ) combined with methylaluminoxane (MAO), triethylaluminium (AlEt₃)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph₃CB(C₆F₅)₄) ( 2 ) and triisobutylaluminium (AliBu₃)/Ph₃CB(C₆F₅)₄, respectively, as co-catalyst systems. The ratios of polymerization rates R_p(rac)/R_p(meso) were changed with the combined cocatalysts. It was found that in the case of using trialkylaluminium/ 2 as co-catalyst R_p(rac)/R_p(meso) is lower than when using MAO in any kind of α-olefin polymerization.     

Isospecific Polymerization of Propylene By ansa-Zirconocene Diamide Compound Cocatalyzed by Mao

Abstract

The kinetics of propylene polymerization initiated by racemic ethylene-1,2-bis(1-indenyl) zirconium bis(dimethylamide) [rac-(EBI) Zr(NMe₂)₂(rac-1)] cocatalyzed by methylaluminoxane (MAO) were studied. The polymerization behaviors of rac-1/MAO catalyst investigated by changing various experimental parameters are quite different from those of rac-(EBI) ZrCl₂ (rac-2)/MAO catalyst, due to the differences in the generation procedure of cationic actives species of each metallocene by the reaction with MAO. The activity of rac-1/MAO catalyst showed maximum when [Al]/[Zr] is around 2000, when [Zr] is 137.1 μM, and when polymerization temperature is 30°C. The negligible activity of rac-1/MAO catalyst at a very low MAO concentration seems to be caused by the instability of the cationic active species. The meso pentad values of polymers produced by rac-1/MAO catalyst at 30°C are in the range of 82.8% to 89.7%. The rac-1/MAO catalyst lost stereorigid character at the polymerization temperature above 60°C. The molecular weight of polymer decreased as [Al]/[Zr] ratio, polymerization temperature, and [Zr] increased. The molecular weight distributions of all polymers are in the range of 1.8–2.3, demonstrating uniform active species present in the polymerization system.     

Ethylene/1‐hexene copolymerization with tetramethyldisiloxane‐bridged bis(indenyl) metallocenes

Ethylene/1‐hexene copolymerizations with disiloxane‐bridged metallocenes, rac‐ and meso‐1,1,3,3‐tetramethyldisiloxanediyl‐bis(1‐indenyl)zirconium dichloride (rac‐ 1 , meso‐ 1 ) activated by modified methylaluminoxane were performed to investigate the influence of conformational dynamics on comonomer selectivity. Although ¹H NOESY (nuclear Overhauser and exchange spectroscopy) analysis indicated that the most stable conformation for the meso isomer in solution was that in which both indenes project over the metal coordination site, this isomer showed higher 1‐hexene selectivity in copolymerization (r_e = 140 ± 30, r_h = 0.024 ± 0.004) than the rac isomer with only one indene over the coordination site (r_e = 240 ± 20, r_h = 0.005 ± 0.001). The meso isomer showed high 1‐hexene selectivity, a high product of reactivity ratios (r_er_h = 3.3 ± 0.5) and produced copolymers that could be separated into fractions with different ethylene content suggesting that the active species exhibited multisite behavior and populated conformations with different comonomer selectivities during the copolymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3323–3331, 2004     

Aminierende reduktive Kupplung aromatischer Aldehyde mit niervalenten Titan-Reagenzien zu 1,2-Diarylethylendiaminen

Preparation of 1,2-Diarylethylenediamines by Aminative Reductive Coupling of Aromatic Aldehydes with Low-Valent Titanium Reagents In a novel McMurry- Type one-pot reaction, aromatic aldehydes and secondary amines are poupled of give the N, N, N′, N′-tetraalkyl-1,2-diarylethylendiamines 1–22 (Table 3). To this end, a lithium dialkylamide is added to an aromatic aldehyde to give the adduct B which is then treated with 1 equiv. of TiC1₄ to yield a coloured suspension of a reagent synthetically equivalent to a iminium salt ( C/D in Scheme 4). After treatment with a low-valent Ti reagent which is prepared by reduction of TiC1₄ with either K or, preferably, Mg, the coupling products are isolated in 23 to 81% yield as a 1:1 mixture of the diastereoisomers (meso- and rac-form). These are separated either by chromatography or by crystallization and characterized.     

Strongly Luminous Tetranuclear Gold(I) Complexes Supported by Tetraphosphine Ligands,meso‐ or rac‐Bis[(diphenylphosphinomethyl)phenylphosphino]methane

A series of tetragold(I) complexes supported by tetraphosphine ligands, meso‐ and rac‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (meso‐ and rac‐dpmppm) were synthesized and characterized to show that the tetranuclear Au^I alignment varies depending on syn‐ and anti‐arrangements of the two dpmppm ligands with respect to the metal chain. The structures of syn‐[Au₄(meso‐dpmppm)₂X]X′₃ (X=Cl; X′=Cl ( 4 a ), PF₆ ( 4 b ), BF₄ ( 4 c )) and syn‐[Au₄(meso‐dpmppm)₂]X₄ (X=PF₆ ( 4 d ), BF₄ ( 4 e ), TfO ( 4 f ); TfO=triflate) involved a bent tetragold(I) core with a counter anion X incorporated into the bent pocket. Complexes anti‐[Au₄(meso‐dpmppm)₂]X₄ (X=PF₆ ( 5 d ), BF₄ ( 5 e ), TfO ( 5 f )) contain a linearly ordered Au₄ string and complexes syn‐[Au₄(rac‐dpmppm)₂X₂]X′₂ (X=Cl, X′=Cl ( 6 a ), PF₆ ( 6 b ), BF₄ ( 6 c )) and syn‐[Au₄(rac‐dpmppm)₂]X₄ (X=PF₆ ( 6 d ), BF₄ ( 6 e ), TfO ( 6 f )) consist of a zigzag tetragold(I) chain supported by the two syn‐arranged rac‐dpmppm ligands. Complexes 4 d–f , 5 d–f , and 6 d–f with non‐coordinative large anions are strongly luminescent in the solid state (λ_max=475–515 nm, Φ=0.67–0.85) and in acetonitrile (λ_max=491–520 nm, Φ=0.33–0.97); the emission was assigned to phosphorescence from ³[d_σ*σ*σ*p_σσσ] excited state of the Au₄ centers on the basis of DFT calculations as well as the long lifetime (a few μs). The emission energy is predominantly determined by the HOMO and LUMO characters of the Au₄ centers, which depend on the bent ( 4 ), linear ( 5 ), and zigzag ( 6 ) alignments. The strong emissions in acetonitrile were quenched by chloride anions through simultaneous dynamic and static quenching processes, in which static binding of chloride ions to the Au₄ excited species should be the most effective. The present study demonstrates that the structures of linear tetranuclear gold(I) chains can be modified by utilizing the stereoisomeric tetraphosphines, meso‐ and rac‐dpmppm, which may lead to fine tuning of the strongly luminescent properties intrinsic to the Au^I₄ cluster centers.     

Acetale von 1,2,3,4-Tetraoxobutan: Herstellung und Struktur von rac- und meso-2,3,3,4,4,5-Hexamethoxy-tetrahydrofuran

Acetals of 1,2,3,4-tetraoxobutane: preparation and structure determination of rac- and meso-2,3,3,4,4,5-hexamethoxy-tetrahydrofuran Oxidation of 3,4-dimethoxyfuran with 2 equiv. of bromine at ?75° in the presence of triethylamine and methanol leads to a mixture of rac- and meso-2,3,3,4,4,5-hexamethoxy-tetrahydrofuran (cf. Scheme 1, 4 and 5 ). The structure of the crystalline rac-compound has been determined by X-ray analysis.     

A Phosphanyl-Phosphagallene that Functions as a Frustrated Lewis Pair

Phosphagallenes ( 1 a / 1 b ) featuring double bonds between phosphorus and gallium were synthesized by reaction of (phosphanyl)phosphaketenes with the gallium carbenoid Ga(Nacnac) (Nacnac=HC[C(Me)N(2,6-i-Pr₂C₆H₃)]₂). The stability of these species is dependent on the saturation of the phosphanyl moiety. 1 a , which bears an unsaturated phosphanyl ring, rearranges in solution to yield a spirocyclic compound ( 2 ) which contains a P=P bond. The saturated variant 1 b is stable even at elevated temperatures. 1 b behaves as a frustrated Lewis pair capable of activation of H₂ and forms a 1:1 adduct with CO₂.     

Reaction of stereoisomeric bis(cyclohexyl)-2,2′-diones with hydrogen peroxide: structure of the formed adducts

The reaction ofmeso- andD,L-forms of bis(cyclohexyl)-2,2-dione with a methanol solution of hydrogen peroxide in a neutral medium has been studied. It has been established that in the case of theD,L-formrac-(1R,4R,9S,10S)-1,4-dihydroxy-2,3-dioxatricyclo-[8.4.0.0^4,9] tetradecane is formed, while themeso-form affordsrac-(1R,4R,9S,10R)-1-methoxy-4-hydroxy-2, 3-dioxatricyclo[8.4.0.0^4,9]tetradecane. The structures of the compounds have been established by X-ray structural analysis and by¹H and¹³C NMR spectroscopy.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 934–939, May, 1995.This work was financially supported by the International Science Foundation (Grant M04 000), the American Crystallographic Association, and the Russian Foundation for Basic Research (Project No. 94-03-09189).     

Evidence of the Quasi‐Living Character of the ansa‐Zirconocene/MAO‐Catalyzed Copolymerization of Ethylene and Norbornene

The kinetics of the ethylene‐norbornene copolymerization, catalyzed by rac‐Et(Ind)₂ZrCl₂/MAO, 90%rac/10%meso‐Et(4,7‐Me₂Ind)₂ZrCl₂/MAO and rac‐H₂C(3‐tert‐BuInd)₂ZrCl₂/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi‐living polymerization.     

Reaction of Internal Fluoroolefin Oxides with Camphor Thiosemicarbazone

Epoxy derivatives of internal fluoroolefins (both cis and trans isomers) react in a stereospecific manner with (1S)- or rac-camphor thiosemicarbazone in a polar aprotic medium to give the corresponding 5-fluoro-4-hydroxy-4,5-bis(polyfluoroalkyl)thiazol-2-ylhydrazones. From unsymmetrical 2,3-epoxydodecafluorohexane a mixture of regioisomeric hydrazones is formed. According to the ¹H and ^{1 9}F NMR data, the resulting trans-hydrazones in (CD₃)₂SO and CDCl₃ exist as mixtures of diastereoisomers occurring in a dynamic equilibrium.     

MAO‐free polymerization of propylene by rac‐ Me2Si(1‐C5H2‐2‐Me‐4‐tBu)2Zr(NMe2)2 compound

Ansa‐zirconocene diamide complex rac‐Me₂Si(CMB)₂Zr(NMe₂)₂ (rac‐1, CMB = 1‐C₅H₂‐2‐Me‐4‐^tBu) reacts with AlR₃ (R = Me, Et, i‐Bu) and then with [CPh₃]⁺[B(C₆F₅)₄]⁻ (2) in toluene in order to in situ generate cationic alkylzirconium species. In the sequential NMR‐scale reactions of rac‐1 with various amount of AlMe₃ and 2, rac‐1 transforms first to rac‐Me₂Si(CMB)₂Zr(Me)(NMe₂) (rac‐3) and rac‐Me₂Si(CMB)₂ZrMe₂ (rac‐4) by the reaction with AlMe₃, and then to [rac‐Me₂Si(CMB)₂ZrMe]⁺ (5⁺) cation by the reaction of the resulting mixtures with 2. The activities of propylene polymerizations by rac‐1/Al(i‐Bu)₃/2 system are dependent on the type and concentration of AlR₃, resulting in the order of activity: rac‐1/Al(i‐Bu)₃/2 > rac‐1/AlEt₃/2 > rac‐1/MAO ≫ rac‐1/AlMe₃/2 system. The bulkier isobutyl substituents make inactive catalytic species sterically unfavorable and give rise to more separated ion pairs so that the monomers can easily access to the active sites. The dependence of the maximum rate (R_{p, max}) on polymerization temperature (T_p) obtained by rac‐1/Al(i‐Bu)₃/2 system follows Arrhenius relation, and the overall activation energy corresponds to 0.34 kcal/mol. The molecular weight (MW) of the resulting isotactic polypropylene (iPP) is not sensitive to Al(i‐Bu)₃ concentration. The analysis of regiochemical errors of iPP shows that the chain transfer to Al(i‐Bu)₃ is a minor chain termination. The 1,3‐addition of propylene monomer is the main source of regiochemical sequence and the [mr] sequence is negligible, as a result the meso pentad ([mmmm]) values of iPPs are very high ([mmmm] > 94%). These results can explain the fact that rac‐1/Al(i‐Bu)₃/2 system keeps high activity over a wide range of [Al(i‐Bu)₃]/[Zr] ratio between 32 and 3,260. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1071–1082, 1999     

Stereoselective Effects in Reactions of Metal Complexes III. Asymmetric hydrogenation of 5, 7, 7, 12, 14, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradeca-4, 11-diene-nickel (II)

The catalytic hydrogenation in acidic solution (pH ～ 2) of the title compound

1 In order to represent this and the related compounds by meaningful abbreviations, we shall adopt the numerotation system proposed in the literature [8] [12]. The complete abbreviation of the title compound is [Ni(5, 7, 7, 12, 14, 14-Me₆-[14]-4, 11-diene-1, 4, 8, 11-N₄)]²⁺. As in the present work the 14-membered ring system with six methyl groups remains unchanged, we shall use [Ni(4, 11-dieneN₄)]²⁺ and [Ni(4, 11-aneN₄)]²⁺ and [Ni(4, 11-aneN₄)]²⁺ for the complex with the unsaturated and saturated ligand, respectively.

[Ni(4, 11-dieneN₄)]²⁺ (I) has been studied. The reaction yields only C-meso- 5, 7, 7, 12, 14, 14-hexa-methyl-1, 4, 8, 11-tetraaza-cyclotetradecane-nickel (II) (C-meso-[Ni(4, 11-aneN₄)]²⁺), when meso-[Ni(4, 11-dieneN₄)]²⁺ is the starting material. Rac-[Ni(4, 11-dieneN₄)]²⁺ yields the unstable α-C-rac-[Ni(4, 11-aneN₄)]²⁺. When optically active [Ni(4, 11-dieneN₄)]²⁺ is reduced, optically active α-[Ni(4, 11-aneN₄)]²⁺ is obtained, which in neutral or basic solution shows mutarotation due to conversion into optically active β-[Ni(4, 11-aneN₄)]²⁺ no racemization is observed. Reaction with cyanide ions yields the optically active free tetramine ligand. The reaction mechanism of this asymmetric synthesis is discussed.