Polymerization of Lactide Using Achiral Bis(pyrrolidene) Schiff Base Aluminum Complexes

A series of aluminum ethyls and isopropoxides based on a bis(pyrrolidene) Schiff base ligand framework has been prepared and characterized. NMR studies of the dissolved complexes indicate that they adopt a symmetric structure with a monomeric, five-coordinated aluminum center core. The aluminum ethyls used as catalysts in the presence of 2-propanol as initiator and the aluminum isopropoxides were applied for lactide polymerization in toluene to test their activities and stereoselectivities. All polymerizations are living, as evidenced by the narrow polydispersities and the good fit between calculated and found number-average molecular weights of the isolated polymers. All of these aluminum complexes polymerized (S,S)-lactide to highly isotactic PLA without epimerization of the monomer, furnished isotactic-biased polymer from rac-lactide, and gave atactic polymer from meso-lactide.

Europium complexes immobilization on titania via chemical modification of titanium alkoxide

We report a facile strategy to tether lanthanide complexes to organic-inorganic hybrid titania materials via sol-gel processing by employing chemically modified titanium alkoxide as the precursor where the organic ligand sensitizing the luminescence of lanthanide ions is bonded to titanium.

Polymerization of 2,2 '-Dimethyltrimethylene Carbonate by Lutetium Complexes Bearing Amino-Phosphine Ligands

A series of lutetium alkyl, amino, and guanidinato complexes based upon an amino-phosphine ligand framework had been prepared. These complexes were applied to initiate ring-opening polymerization of 2,2'-dimethyltrimethylene carbonate (DTC). The type of the initiator significantly influenced the catalytic activity of these complexes in a trend as follows: alkyl approximate to guanidinate > amide, whereas the complexes with flexible backbone between P and N atoms within the ligand exhibited higher activity than those with rigid backbone. The isolated PDTC had bimodal-mode molecular weight distribution. The molecular weights of each fraction increased linearly with the conversion, indicating that there might be two active species. This had been confirmed by analyses of oligomeric DTC living species and oligomer with NMR technique as the metal-alkoxide and the four-membered metallocyclic lactate. Kinetic investigation displayed that the polymerization rate was the first order with the monomer concentration.

Melanoma cell growth inhibition by beta gamma-CAT, which is a novel non-lens betagamma-crystallin and trefoil factor complex from frog Bombina maxima skin

In vertebrates, non-lens beta gamma-crystallins are widely expressed in various tissues but their functions are unknown. The molecular mechanisms of trefoil factors, initiators of mucosal healing and being greatly involved in tumorigenesis, have remained

Acute toxicity of beta gamma-CAT, a naturally existing non-lens beta gamma-crystallin and trefoil factor complex from frog Bombina maxima skin secretions

In vertebrates, non-lens beta gamma-crystallins are widely expressed in various tissues, but their functions are unknown. The molecular mechanisms of trefoil factors, initiators of mucosal healing and being greatly involved in tumorigenesis, have remained

Effects of gamma-aminobutyric acid, progesterone and ionophore A23187 on acrosome reaction of tree shrew sperm in vitro: examination of acrosome reaction with an improved fluorescence microscopy

A number of acrosome reaction (AR) initiators have been found to be effective in inducing AR of human, laboratory and domestic animal sperm. Using an improved simple fluorescence microscopy, effects of gamma-aminobutyric acid (GABA), progesterone and ionophore A23187 on sperm AR of tree shrew, a useful animal model in biomedical research, have been investigated. Spontaneous AR in 4.92-7.53% of viable sperm was observed. Complete AR in 10.31-18.25% of viable tree shrew sperm was obviously induced by 5 mu M and 10 mu M calcium ionophore A23187, 1 mM GABA, and 5 mu M progesterone, and there were no significant differences between their abilities to initiate complete AR. No significant differences of AR percentages between 1- and 2-h treatments with A23187, progesterone and/or GABA were observed. These results suggested that the responses of tree shrew sperm to these AR initiators are similar to that of human and other mammalian sperm. (C) 1997 Elsevier Science B.V.

O-2 activation and hydrolysis of Salan rare-earth metal alkyl complexes

Salan ligated yttrium alkyl complex 1, (LY)-Y-1(CH2SiMe3)(THF) (Salan = L-1: [2-O-3,5-tBu(2)-C6H2CH2N(CH3) CH2](2)), was exposed to an oxygen/ nitrogen atmosphere to give a bimetallic alkoxide complex 4, [(LY)-Y-1(mu-OCH2SiMe3)](2). Whilst the lutetium counterparts 2 ((LLu)-Lu-1(CH2SiMe3)(THF)) and 3 ((LLu)-Lu-2(CH2SiMe3)(THF); L-2: [2-O-3-tBu-C6H2CH2N(CH3) CH2](2)) were hydrolysed with moist nitrogen to afford mixed hydroxy/silyloxy complexes 5 and 6 ([(LLu)-Lu-1,2(mu-OSiMe3)(mu-OH) LuL1,2]), respectively.

Grown-like macrocycle zinc complex derived from beta-diketone ligand for the polymerization of rac-lactide

Enolic Schiff base zinc (II) complex 1 was synthesized. XRD revealed 1 was a novel crown-like macrocycle structure consisted of hexanuclear units of (LZnEt)(6) via the coordination chelation between the Zn atom and adjacent amine nitrogen atom. Further reaction of 1 with one equivalent 2-propanol at RT produced Zn-alkoxide 2 by in situ alcoholysis. Complex 2 was used as an initiator to polymerize rac-lactide in a controlled manner to give heterotactic enriched polylactide. Factors that influenced the polymerization such as the polymerization time and the temperature as well as the monomer concentration were discussed in detail in this paper.

Pyrrolide-supported lanthanide alkyl complexes. Influence of ligands on molecular structure and catalytic activity toward isoprene polymerization

The N,N- bidentate ligands 2- {( N- 2,6- R) iminomethyl)} pyrrole ( HL1, R) dimethylphenyl; HL2, R) diisopropylphenyl) have been prepared. HL1 reacted readily with 1 equiv of lanthanide tris( alkyl)s, Ln(CH2SiMe3)(3)(THF)(2), affording lanthanide bis(alkyl) complexes L(1)Ln(CH2SiMe3)(2)(THF)(n) (1a, Ln= Lu, n = 2; 1b, Ln = Sc, n = 1) via alkane elimination. Reaction of the bulky ligand HL2 with 1 equiv of Ln(CH2SiMe3)(3)( THF)(2) gave the bis(pyrrolylaldiminato) lanthanide mono(alkyl) complexes L(2)(2)Ln- (CH2SiMe3)(THF) (2a, Ln) Lu; 2b, Ln = Sc), selectively. The N,N- bidentate ligand HL3, 2- dimethylaminomethylpyrrole, reacted with Ln( CH2SiMe3) 3( THF) 2, generating bimetallic bis( alkyl) complexes of central symmetry ( 3a, Ln = Y; 3b, Ln = Lu; 3c, Ln = Sc). Treatment of the N,N,N,N- tetradentate ligand H2L4, 2,2'-bis(2,2-dimethylpropyldiimino) methylpyrrole, with equimolar Lu(CH2SiMe3)(3)(THF)(2) afforded a C-2- symmetric binuclear complex ( 4). Complexes 3a, 3b, 3c, and 4 represent rare examples of THF- free binuclear lanthanide bis( alkyl) complexes supported by non- cyclopentadienyl ligands. All complexes have been tested as initiators for the polymerization of isoprene in the presence of AlEt3 and [ Ph3C][B(C6F5)(4)]. Complexes 1a, 1b, and 3a show activity, and 1b is the most active initiator, whereas 2a, 2b, 3b, 3c, and 4 are inert.

Mixed ligands supported yttrium alkyl complexes: Synthesis, characterization and catalysis toward lactide polymerization

Treatment of yttrium tris(alkyl)s, Y(CH2SiMe3)(3)(THF)(2), by equimolar H(C5Me4)SiMe3(HCp') and indene (Ind-H) afforded (eta(5)-Cp')Y(CH2SiMe3)(2)(THF) (1) and (eta(5)-Ind)Y(CH2SiMe3)(2)(THF) (2) via alkane elimination, respectively. Complex 1 reacted with methoxyamino phenols, 4,6-(CH3)(2)-2-[(MeOCH2CH2)(2)-NCH2]-C6H2-OH (HL1) and 4,6-(CMe3)(2)-2-[(MeOCH2CH2)(2)-NCH2]-C6H2OH (HL2) gave mixed ligands supported alkyl complexes [(eta(5)-Cp')(L)]Y(CH2SiMe3) (3: L = L-1; 4: L = L-2). Whilst, complex 2 was treated with HL2 to yield [(eta(5)-Ind)(L-2)]Y(CH2SiMe3) (5). The molecular structures of 3 and 5 were confirmed by X-ray diffraction to be mono(alkyl)s of THF-free, adopting pyramidal and tetragonal-bipyramidal geometry, respectively. Complexes 3 and 5 were high active initiators for the ring-opening polymerization Of L-lactide to give isotactic polylactide with high molecular weight and narrow to moderate polydispersity.

Yttrium bis(alkyl) and bis(amido) complexes bearing N,O multidentate ligands. Synthesis and catalytic activity towards ring-opening polymerization of L-lactide

Methoxy-modified beta-diimines HL1 and HL2 reacted with Y(CH2SiMe3)(3)(THF)(2) to afford the corresponding bis(alkyl)s [(LY)-Y-1(CH2SiMe3)(2)] (1) and [(LY)-Y-2(CH2SiMe3)(2)] (2), respectively. Amination of 1 with 2,6-diisopropyl aniline gave the bis(amido) counterpart [(LY)-Y-1{N(H)(2,6-iPr(2)-C6H3)}(2)] (3), selectively. Treatment of Y(CH2SiMe3)(3)(THF)(2) with methoxy-modified anilido imine HL3 yielded bis(alkyl) complex [(LY)-Y-3(CH2SiMe3)(2)(THF)] (4) that sequentially reacted with 2,6-diisopropyl aniline to give the bis(amido) analogue [(LY)-Y-3{N(H)(2,6-iPr(2)-C6H3)}(2)] (5). Complex 2 was "base-free" monomer, in which the tetradentate beta-diiminato ligand was meridional with the two alkyl species locating above and below it, generating tetragonal bipyramidal core about the metal center. Complex 3 was asymmetric monomer containing trigonal bipyramidal core with trans-arrangement of the amido ligands. In contrast, the two cis-located alkyl species in complex 4 were endo and exo towards the 0,N,N tridentate anilido-imido moiety. The bis(amido) complex 5 was confirmed to be structural analogue to 4 albeit without THF coordination. All these yttrium complexes are highly active initiators for the ring-opening polymerization Of L-LA at room temperature.

Atom transfer radical polymerization of butadiene using MoO2Cl2/PPh3 as the catalyst

Atom transfer radical polymerization has been used to successfully synthesize polybutadiene. This was achieved by using MoO2Cl2/triphenyl phosphine as the catalyst and the various organic halide compounds such as methyl-2-chloropropionate, CCl4, 1,4-dichloromethyl benzene, I-phenylethyl chloride, and benzyl chloride as initiators. The monomer conversion increased up to 50% with polymerization time. The polydispersity indices of the polymers were as high as above 1.5. However, the polymerizations were controlled and the polydispersity indices of the polymers were less than 1.5 throughout the polymerization in reverse atom transfer radical polymerization. The chemical structure of the polymer obtained was characterized by (HNMR)-H-1 and FTIR. The valency states of molybdenum in this reactive system were detected by UV-vis spectra.

Polymerization of rac-lactide using schiff base aluminum catalysts: Structure, activity, and stereoselectivity

A series of aluminum ethyls and isopropoxides based upon N,N,O,O-tetradentate Schiff base ligand framework have been prepared. X-ray diffraction analysis and H-1 NMR confirmed that these Schiff base aluminum ethyls and isopropoxides were all monomeric species with a five-coordinated central aluminum in their solid structures. Compared to the aluminum ethyls which all retain their monomeric structure in the solution, the dinucleating phenomenons of aluminum isopropoxides with less steric hindered substituents in the solution have also been observed. The activities and stereoselectivities of these complexes toward the ring-opening polymerization of rac-lactide have been investigated. Polymerization experiments indicated that (SB-2d)(AlOPr)-Pr-i [(SB-2d) = 2,2-dimethyl-1,3-propylenebis(3,5-di-tert-butylsalicylideneiminato)] exhibited the highest stereoselectivity and (SB-3b)(AlOPr)-Pr-i [(SB-3b) = 2,2-dimethyl-1,3-propylenebis(3,5-dichlorinesalicylideneiminato)] possessed the highest activity among these aluminum isopropoxides. The substituents and the mode of the bridging part between the two nitrogen atoms both exerted significant influences upon the progress of the polymerizations, influencing either the tacticity of isolated polymers or the rate of polymerization.

The study of synthesis of poly(ethylene oxide)-b-poly(N,N-dimethylacrylamide) by atom transfer radical polymerization and self-assembly in selective solvents

Poly( ethylene oxide)-b-poly(N, N-dimethylacrylamide) (PEO-b-PDMA) was synthesized by successive atom transfer radical polymerization (ATRP) of N, N-dimethylacrylamide (DMA) monomer using PEO-Br macro initiators as initiator, CuBr and 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazamacrocyclotetra decane (Me-6[14] aneN(4)) as catalyst and ligand. PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide. GPC and H-1 NMR studies show that the plot of ln([DMA](0)/[ DMA]) against the reaction time is linear, and the molecular weight of the resulting PDMA increased linearly with the conversion. Within 3 h, the polymerization can reach almost 60% of conversion. PEO-b-PDMA copolymer with low polydispersity index (M-w/M-n approximate to 1.1) is obtained. Self-assembly of PEO-b-PDMA in selective solvents is also studied. It could self-assemble into micelles in methanol/acetone (1/10, v/v) solution. TEM analyses of the PEO-b-PDMA micelles with narrow size distribution revealed that their size and shape depend much on the copolymer composition.

Enolic Schiff-base aluminum complexes and their application in lactide polymerization

A series of NNOO-tetradentate enolic Schiff-base ligands were prepared where ligand L-1 = bis(benzoylacetone)propane-1,2-diimine, L-2 = bis(acetylacetone)-propane-1,2-diimine, L-3 = bis-(acetylacetone)cyclohexane-1,2-diimine. Their further reaction with aluminum tris(ethyl) formed complexes LAlEt (1a, 2a and 3a). The solid structure of complexes la, 2a and 3a confirmed by X-ray single crystal analysis manifested that these complexes were all monomeric and five-coordinated with an aluminum atom in the center. The configurations of these complexes varied from trigonal bipyramidal geometry (tbp) to square pyramidal geometry (sqp) due to their different auxiliary ligand architectures. H-1 NMR spectra indicated that all these complexes retained their configuration in solution states. Their catalytic properties to polymerize racemic-lacticle (rac-LA) in the presence of 2-propanol were also studied. The diimine bridging parts as well as the diketone segment substituents had very close relationship with their performance upon the polymerization process. All these complexes gave moderately isotactic polylactides with controlled molecular weight and very narrow molecular weight distributions.