Homo-and copolymerization of propylene and ethylene in the presence of titanium dichloride complexes with dioxolane dicarboxylate and bis(difurylmethanephenoxyimine) ligands

The polymerization of propylene and ethylene and the copolymerization of these olefins with postmetallocene catalysts [(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra(perfluorophenyl)-1,3-dioxolane-4,5-dimethanol] titanium(IV) dichloride and bis{N-(3,5-ditert-butylsalicylidene)-4-[bis(5-methyl-2-furyl)methyl]aniline}titanium( IV) dichloride have been studied. The polymerization of propylene and its copolymerization with ethylene have been carried out in a liquid monomer, while the polymerization of ethylene has been performed in toluene at the constant concentration of the monomer. Polymethylaluminoxane has been used as a cocatalyst. The activity of the catalysts in the polymerization of propylene and ethylene at 50°C is ～ 10 and ～45 kg PP/mol Ti h mol C₃H₆/l and 178.5 and 2700 kg PE/mol Ti h mol C₂H₄/l, respectively. It has been established that, in the copolymerization of propylene with ethylene, the active sites of both catalysts selectively polymerize ethylene. The resulting copolymers have a block structure (r ₁ r ₂= 4.6); as a result, the crystalline phase of polyethylene is formed in them. Polypropylene and propylene-ethylene copolymers are elastomeric materials. Polypropylene samples synthesized with [(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra(perfluorophenyl)-1,3-dioxolane-4,5-dimethanol]titanium(IV) dichloride demonstrate a high melting point (150–157°C) in combination with good elastic properties. Polyethylene is a linear polymer with the degree of crystallinity varying from 37 to 45% and a melting point of 133–134°C. The mechanical properties of the polymers and copolymers have been investigated.     

New bidentate chiral phosphoramidites in copper-catalyzed asymmetric 1,4-addition of diethylzinc to cyclic α,β-enones: enantioselective tandem 1,4-addition-aldol reactions with 2-cyclopentenone

New bidentate phosphoramidites were prepared starting from α,α,α′,α′-tetraphenyl-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) or 1,1′-bi-2-naphthol (BINOL) and either 1,2-ethylene- or 1,3-propylenediamine N,N′-disubstituted with achiral or chiral groups. The use of these ligands in the copper-catalyzed enantioselective conjugate addition of diethylzinc to 2-cyclohexenone and 2-cyclopentenone afforded products with e.e.s of up to 89 and 83%, respectively.     

Asymmetric PTC C-alkylation mediated by TADDOL—novel route to enantiomerically enriched α-alkyl-α-amino acids

Compound (4R,5R)- or (4S,5S)-2,2-dimethyl-α,α,α′,α′-tetraphenyl-1,3-dioxolane-4,5-dimethanol (TADDOL) was shown to catalyze C-alkylation of aldimine Schiff's bases of alanine esters under phase-transfer catalysis conditions (solid NaOH, toluene, ambient temperature, 10% TADDOL) with the e.e. of the final α-methylphenylalanine or α-allylalanine reaching 82%.     

Unexpected enhancement of enantioselectivity in copper(II) catalyzed conjugate addition of diethylzinc to cyclic enones with novel TADDOL phosphorus amidite ligands

The copper(II) catalyzed enantioselective 1,4-addition reactions of diethylzinc to cyclic enones in the presence of novel phosphorus amidite ligands, easily prepared from α,α,α′,α′-tetraphenyl-2,2′-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) derivatives, resulted in e.e.s up to 71% for cyclohexenone and up to 62% for cyclopentenone. A remarkable enhancement of enantioselectivity was observed upon the addition of powdered molecular sieves to the reaction mixture.     

Control of regio-, diastereo-, and enantioselectivity in the [Ti(OTs)2(TADDOLato)]-catalyzed 1,3-dipolar cycloaddition reaction between 3-acryloyloxazolidin-2-one and nitrones

Catalytic control of regio-, diastereo-, and enantioselectivity in the 1,3-dipolar cycloaddition of 3-acryl-oyloxazolidin-2-one ( 4 ) with different nitrones 2 by the application of a [TiX₂(TADDOLato)] complex as the catalyst was developed (TADDOL = α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol). In the absence of a catalyst, the 1,3-dipolar cycloaddition of 4 with 2 proceeded to give a mixture of regioisomers, whereas, in the presence of a catalyst, the regioselectivity of the reaction could be controlled. Three asymmetric [TiX₂(TADDOLato)] catalysts were tested, and it was found that use of the [Ti(OTs)₂(TADDOLato)] complex gave complete regioselectivity, high ‘endo’-selectivities (> 90% d.e.), and enantioselectivities corresponding to 48–70% e.e.     

Enantioselective 1,4-Addition of Aliphatic Grignard Reagents to Enones Catalyzed by Readily Available Copper(I) thiolates derived from TADDOL. Preliminary communication

Two simple thiols derived from the parent TADDOL, α,α,α′,α′ tetraphenyl-2,2-dimethyl-1,3-clioxolan-4,5-dimethanol, are used to prepare Cu¹ complexes C and D to catalyze (0.05 equiv.) 1,4-additions of Grignard reagents RMgCl to cyclic enones with enantioselectivities which are comparable to or better than previously reported (enantiomer ratios up to 92:8).     

Synthesis,NMR conformational studies and host–guest behaviour of new (+)-tartaric acid derivatives

A series of dimeric α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol TADDOLs has been prepared and host–guest interactions of these structures have been characterized using a series of ¹H NMR studies. Enantioselective recognition of the chiral alcohols glycidol and menthol was observed for phenyl and 2-naphthyl derivatives. The influence of steric bulk on the dynamic fluxional behaviour of the TADDOL structures was demonstrated by dynamic NMR.     

Preparation of the PdCl2 Complex of TADDOP,the Bis(diphenylphosphinite) of TADDOL: Use in enantioselective 1,3-diphenylallylations of nucleophiles and discussion of the mechanism

Reaction of the tartrate-derived diol (R,R)-α,α,α′,α′-tetraphenyl-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) with chlorodiphenylphosphane gives a new bis(diphenylphosphanyl) ligand (TADDOP). The complex 4 formed with PdCl₂ has been crystallized and its structure determined by X-ray diffraction (Fig.1). The complex is used for Pd-catalyzed enantioselective 1,3-diphenylallylations of various nucleophiles which give products with enantiomer ratios of up to 88:12 (Scheme 2). Crystallization procedures lead to the enantiomerically pure (> 99:1) product 11 derived from dimethyl malonate. The structure of the TADDOP complex 4 is compared with those of other transition-metal complexes containing chelating bis(diphenylphosphanyl) ligands (Fig.2). A crystallographic data base search reveals that the structures of transition-metal complexes containing two Ph₂P groups (superpositions in Fig.3) fall into one of two categories: one with approximate C₂ symmetry and the other with C₁ symmetry (20 and 19 examples, resp.). A mechanistic model is proposed which correlates the conformational chirality (δ or λ) of the four Ph groups' arrangement in such complexes with the topicity of nucleophile approach on Pd-bound trans,trans-1,3-diphenylallyl groups (Scheme 3 and Table).     

Single-center vs. multi-center post-metallocene catalysts for propylene polymerization

The structural characteristics of polypropylene samples prepared with two post-metallocene catalysts based on complexes bis-{M-(3,5-di-tert-butyl-salicylidene)-4-[bis-(5-methyl-2-furyl)methyl]aniline}titanium dichloride and [(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra(pentafluorophenyl)-1,3-dioxalan-4,4-dimethanol)titanium dichloride are investigated by GPC, ¹³C NMR, IR, DSC, and XRD methods. A combination of the first complex and MAO forms a single-center catalyst which polymerizes propylene to a nearly perfectly atactic polymer. A combination of the second complex and MAO forms a multi-center catalyst system producing polymer mixtures with broad molecular weight distributions containing five to six Flory components with different average molecular weights. Relative contents of the Flory components strongly depend on the type of solvent in the polymerization reactions. Some of the active centers produce high molecular weight, highly isotactic crystalline material with the melting point over 154 °C. The nature of steric errors in these polymer fractions (determined by ¹³C NMR) can be explained by a variant of stereocontrol similar to that exerted by metallocene catalysts of the C₁ symmetry.     

X-Ray, Molecular Diffusion, and NOESY NMR Studies of Chiral, Tetranuclear Cu(I) Catalysts Based on Monodentate Thiol Analogues of TADDOL

The new, stable, chiral thiol-TADDOL Cu(I) catalysts 1 (X=OH, OMe, NMe(2)) reveal an unexpected monodentate complexation mode, both in solution and in the solid state. For the first time, the aggregation state of organocopper complexes has been determined by NMR diffusion measurements. NOESY NMR data on model isocyanide Cu complexes reveal a different conformation of the TADDOL moiety as a function of the second potential donor group. TADDOL=alpha,alpha,alpha',alpha'-tetraaryl-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol.     

New Chiral Diamines of the Dioxolane Series: (+)-(4S,5S)-2,2-Dimethyl-4,5-bis(diphenylaminomethyl)- 1,3-dioxolane and (+)-(4S,5S)-2,2-Dimethyl-4,5-bis(methyl- aminomethyl)-1,3-dioxolane

The reaction of sodium diphenylamide with 2,2-dimethyl-4,5-bis(tosyloxymethyl)-1,3-dioxolane gave (+)-(4S,5S)-2,2-dimethyl-4,5-bis(diphenylaminomethyl)-1,3-dioxolane, which was brought into complex formation with cobalt chloride. Treatment of 2,2-dimethyl-4,5-bis(tosyloxymethyl)-1,3-dioxolane with sodium N-methylanilide resulted in cleavage of the SÄO bond in the p-toluenesulfonate moiety with formation of N-methyl-N-phenyl-p-toluenesulfonamide and 4,5-bis(hydroxymethyl)-2,2-dimethyl-1,3-dioxolane disodium salt. Diethyl (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarboxylate reacted with methylamine to give the corresponding dicarboxamide which was reduced with lithium aluminum hydride to (4S,5S)-2,2-dimethyl-4,5-bis(methylaminomethyl)-1,3-dioxolane having chiral carbon and nitrogen atoms.     

On the Regioselectivity Control in the Palladium-Catalyzed Hydro-alkoxycarbonylation of α,β-Unsaturated Esters

The regioselectivity of the hydro-alkoxycarbonylation of methyl acrylate, methacrylate, and crotonate catalyzed by [PdCl₂L₂] complexes (L = phosphine ligands) can be largely controlled by variation of the ligands. PPh₃, promotes preferential carbonylation at the α-position, whereas with [(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis-(methylene)]bis[diphenylphosphine] as ligand, the β-position is overwhelmingly carbonylated.     

Synthesis of spirocyclic derivatives of azaphenanthrene containing a hydroxy-m-terphenyl fragment

The reaction of 5′-[(2-naphthylamino)methyl]-2′-hydroxy[1,1′:3′,1″]terphenyl with paraformaldehyde and 1,3-cyclohexanedione, methyl 2,2-dimethyl-4,6-dioxocyclohexanecarboxylate, dimedone, furan-2,4(3H,5H)-dione, indan-1,3-dione led to the formation of spiro derivatives of azaphenanthrene.     

Comparative investigation of the inclusion preferences of optically pure versus racemic TADDOL hosts for pyridine and isomeric methylpyridine guests

Here we consider the effect of the optical purity of TADDOL (α,α,α′,α’-tetraphenyl-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol) on its discriminatory behaviour. We synthesized optically pure and racemic TADDOL, which form complexes with pyridine and the methylpyridines, and recrystallized them from various equimolar mixtures of these guests, and showed that both TADDOLs, surprisingly, discriminate similarly between them. The selectivity of optically active TADDOL was in the order 3-methylpyridine > 4-methylpyridine > pyridine > 2-methylpyridine, while this order was 3-methylpyridine > 4-methylpyridine > 2-methylpyridine > pyridine for the racemate. For many of the experiments, the extent of selectivity displayed by the two hosts was comparable. Single crystal X-ray diffraction experiments showed that preferred guests experienced stronger π-π and, even more so, H-bonding interactions with the host. Thermal analyses confirmed reports that suggested that guests that reside in channels in the host structure form less thermally stable complexes than those where the guests are accommodated in discrete cavities.     

Electron impact mass spectral fragmentation of chiral bisbenzoxazole,bisbenzothiazole and biscarbamide derivatives of 2,2-dimethyl-1,3-dioxolane

The mass spectrometric fragmentation behaviour of five pairs of (R,R)- and (S,S)-4,5-bis(benzoxazol-2-yl)-2,2-dimethyl-1,3-dioxolane derivatives, one pair of (R,R)- and (S,S)-4,5-bis(benzothiazol-2-yl)-2,2-dimethyl-1,3-dioxolanes, and three pairs of (R,R)- and (S,S)-N,N'-bis(2-hydroxyaryl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamides, all important compounds for asymmetric catalysis (P. Jiao et al., Tetrahedron Asymmetry 2001; 12: 3081), has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization conditions. The spectral observations have been rationalized in terms of fragment ion structures and fragmentation mechanisms that will provide an aid to spectral interpretation for new compounds of this type.     

Preliminary studies on a novel synthesis of β-amino acids: stereocontrolled transformation of d- and l-glyceraldehyde into 3-amino-2-(2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)propanoic acids

A stereocontrolled synthesis of the methyl ester of (2S)-3-amino-2-((4′S)-2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)propanoic acid from d-glyceraldehyde is described for the first time. This method involves the stereoselective Michael addition of the lithium salt of tris(phenylthio)methane to (S)-2,2-dimethyl-4-((E)-2-nitrovinyl)-1,3-dioxolane followed by hydrolysis of the resulting (4S)-2,2-dimethyl-4-((2′S)-3′-nitro-1′,1′,1′-tris(phenylthio)propan-2′-yl)-1,3-dioxolane to (2S)-methyl 2-((4′S)-2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)-3-nitropropanoate, which was finally reduced to the target compound. A similarly stereocontrolled transformation of l-glyceraldehyde into (2R)-methyl 3-amino-2-((4′R)-2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)propanoate is also described.     

Catalytic Enantioselective Hydrosilylation of Aromatic Ketones Using Rhodium Complexes of TADDOL-Derived Cyclic Phosphonites and Phosphites

Cyclic phosphonites and phosphites 2–4 are readily available from Cl₂PR and (R,R)- or (S,S)-α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanols (= TADDOLs 1 , which, in turn, are only two steps away from tartrate); the X-ray crystal structure of one representative, the phenyl phosphonite 2b , was determined. Five previously described and six new ones of the chiral P derivatives were tested as ligands for Rh^I- and Pd^O-catalyzed reactions such as hydrocarbonylations, hydroborations, and hydrosilylations of C?C bonds; while the resulting catalysts were highly active and regioselective, they did not lead to useful enantiomer enrichment in the products (Scheme 1). In contrast, hydrosilylation of phenyl and 2-naphthyl methyl or ethyl ketone by Ph₂SiH₂ (1.2 equiv.) gave, after desilylation, the corresponding secondary alcohols of (R)-configuration with up to 87% ee in the presence of 0.1 equiv. of the penta(2-naphthyl)-substituted phosphonite 3d and 0.02 mol-equiv. of Rh (Table 1).     

Synthesis of racemic and enantiomerically pure 2′-thia-2′,3′-dideoxycytidine as potential anti-hepatitis B virus agents

A novel class of nucleosides with the C₁, atom bonded to three hetero atoms was synthesized. 2′-Thia-2′,3′-dideoxycytidine was the pilot compound of this series. (±)-β-2′-Thia-1′,3′-dideoxycytidine ( 6 ) and (±)-α-2′-thia-2′,3′-dideoxycytidine ( 7 ) were synthesized from (±)-3-mercapto-1,2-propanediol. The synthesis of the enantiomerically pure 2′-thia-2′,3′-dideoxycytidines (α-D-form, β-D-form, α-1-form and β-L-form) from optically pure (S)-(2,2-dimethyl-1,3-dioxalan-yl)methyl p-toluenesulfonate ( 8 ) and its (R)-isomer 18 was also described. The preliminary biological results showed that (+)-β-D-2′-thia-2′,3′-dideoxycytidine ( 26 ) was the most active against human hepatitis B virus with an ED₅₀ of 3 μM.     

Polymerization of higher α-olefins with the catalytic system (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-bis(perfluorophenyldimethanolate) titanium(IV) dichloride-organoaluminum compound

The catalytic activity of the titanium(IV) dichloride complex with the (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-bis(perfluorophenyldimethanol) ligand in the presence of a cocatalyst (polymethylaluminoxane, triethylaluminum, or triisobutylaluminum) in the polymerization of higher α-olefins (1-hexene, 1-octene, 1-decene) is investigated. It is shown that, depending on the types of cocatalyst and monomer and the molar ratio of components of the catalytic system, high- or ultrahigh-molecular-mass poly(α-olefins) with M _w = (4 × 10⁵)?(3 × 10⁶) can be prepared. The chain microstructure of polyhexene is examined.     

Synthesis of (−)-(4R,5R)-4,5-bis[di-3′-(2′,6′-dimethoxypyridyl)phosphinomethyl]-2,2-dimethyl-1,3-dioxolane and its application in the Rh-catalyzed asymmetric hydrogenation reactions

The chiral ligand (−)-(4R,5R)-4,5-bis[di-3′-(2′,6′-dimethoxypyridyl)phosphinomethyl]-2,2-dimethyl-1,3-dioxolane 3 [(R,R)-Py*-DIOP] was synthesized via a key intermediate bis[3-(2,6-dimethoxypyridyl)]phosphine-borane 9. The asymmetric hydrogenation of prochiral olefins was investigated using a rhodium catalyst containing 3. For the hydrogenation of amidoacrylic acids, enols and itaconic acid, while the enantioselectivity of [Rh-(R,R)-Py*-DIOP] was similar to that of [Rh-(R,R)-DIOP] the absolute configurations of the products from the two catalyst systems were found to be opposite.