scholarly journals Polymetallic Group 4 Complexes: Catalysts for the Ring Opening Polymerisation of rac-Lactide

Catalysts ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 551
Author(s):  
David T. Jenkins ◽  
Eszter Fazekas ◽  
Samuel B. H. Patterson ◽  
Georgina M. Rosair ◽  
Filipe Vilela ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Amino Acid ◽  
Weight Distribution ◽  
Ring Opening ◽  
Critical Role ◽  
X Ray ◽  
Group 4 ◽  
Pendant Arm ◽  
Carboxylate Groups ◽  
Moderate Rate

Five novel air- and moisture-stable polymetallic Ti and Zr amino acid-derived amine bis(phenolate) (ABP) complexes were synthesised and fully characterised, including X-ray crystallographic studies. The reaction of the ABP proligands with Ti or Zr alkoxides has resulted in the formation of polymetallic aggregates of different nuclearity. The steric bulk on the pendant arm of the ligand was found to play a critical role in establishing the nuclearity of the aggregated complex. Sterically, less-demanding groups, such as H or Me, facilitated the formation of tetrametallic Ti clusters, bridged by carboxylate groups, while increased steric bulk (tBu) led to the formation of binuclear μ-oxo-bridged species. The isolated complexes were employed as catalysts for the ring opening polymerisation (ROP) of rac-lactide. Overall, the Ti catalysts were all active with the smaller, bimetallic Ti aggregates exhibiting relatively faster rates. A monometallic, bis(ABP) Zr complex was found to exert remarkable ROP activity, albeit with limited control over the tacticity and molecular weight distribution of the polymer. A further oxo-bridged Zr cluster was shown to display a previously unprecedented trimetallic structure and achieved a moderate rate in the ROP of rac-lactide.

The synthesis and polymerization behaviour of silicon-bridged [1]- and [2]ferrocenophanes with sterically demanding trimethylsilyl substituents attached to the cyclopentadienyl rings

1995 ◽  
Vol 73 (11) ◽  
pp. 2069-2078 ◽  
Author(s):  
Timothy J. Peckham ◽  
Daniel A. Foucher ◽  
Alan J. Lough ◽  
Ian Manners
Keyword(s):  
Molecular Weight ◽  
Ring Opening ◽  
Ring Opening Polymerization ◽  
Monoclinic Space Group ◽  
Organometallic Polymers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cyclopentadienyl Ligands ◽  
Sterically Demanding ◽  
High Molecular Weight Poly

The silicon-bridged [1]ferrocenophane Fe(η-C5H3SiMe3)2(SiMe2) (5) was synthesized via the reaction of Li2[Fe(η-C5H3SiMe3)2]•tmeda (tmeda = tetramethylethylenediamine) with Me2SiCl2 in hexanes. The disilane-bridged [2]ferrocenophane Fe(η-C5H3SiMe3)2(Si2Me4) (7) was prepared using a similar route from the disilane ClMe2SiSiMe2Cl. Despite the presence of sterically demanding SiMe3 substituents on the cyclopentadienyl rings, compound 5 was found to undergo thermal ring-opening polymerization at 170 °C to produce very soluble, high molecular weight poly(ferrocenylsilane) 6 with Mw = 1.4 × 105, Mn = 8.4 × 104. However, the [2]ferrocenophane 7 was found to be resistant to thermal ring-opening polymerization even at 350 °C and decomposed above 380 °C. A single-crystal X-ray diffraction study of 7 revealed that the steric interactions between the bulky SiMe3 groups are relieved by a significant twisting of the disilane bridge with respect to the plane defined by the centroids of the cyclopentadienyl ligands and the metal atom. The angle between the planes of the cyclopentadienyl rings in 7 was found to be 5.4(6)°, slightly greater than that in the non-silylated analogue Fe(η-C5H4)2(Si2Me4) (4a) (4.19(2)°), and dramatically less than the corresponding tilt angle of the strained, polymerizable, silicon-bridged [1]ferrocenophane Fe(η-C5H4)2(SiMe2) (1) (20.8(5)°). The length of the Si—Si bond in 7 (2.342(3) Å) was found to be close to the sum of the covalent radii (2.34 Å). Crystals of 7 are monoclinic, space group C2/c, with a = 23.689(3) Å, b = 11.174(1) Å, c = 31.027(3) Å, β = 109.16(1)°, V = 7758(2) Å3, and Z = 12. Keywords: ring-opening polymerization, ferrocenophane, organometallic polymers.

scholarly journals Syntheses, Solid-state Structures and Catalytic Activity of Zinc Carboxylate Complexes in Lactide Polymerization

2014 ◽  
Vol 69 (11-12) ◽  
pp. 1365-1374 ◽  
Author(s):  
Christoph Scheiper ◽  
Christoph Wölper ◽  
Dieter Bläser ◽  
Joachim Roll ◽  
Stephan Schulz
Keyword(s):  
Ring Opening ◽  
Zinc Complex ◽  
X Ray Diffraction ◽  
Polymerization Catalysts ◽  
Co Catalyst ◽  
Carboxylate Complexes ◽  
X Ray ◽  
Carboxylate Groups ◽  
Solid State Structures ◽  
Lactide Polymerization

Abstract Three dinuclear zinc carboxylate complexes [L1-3Zn(μ,η2-O2CPh)]2 (1, 2, 4) containing either the bidentate N,N′-chelating β-diketiminate ligand RNC(Me)C(H)C(Me)NR (R = 2,6-iPr2-C6H3, L1, complex 1), the tridentate O,N,N-chelating ligand OC(Me)C(H)C(Me)NCH2CH2NMe2 (L2, complex 2) or the bis-N,N′-chelating bis-β-diketiminate ligand RNC(Me)C(H)C(Me)NNC(Me)- C(H)C(Me)NR (R = 2,6-iPr2-C6H3, L3, complex 4) were synthesized and characterized including single-crystal X-ray diffraction. Reaction of the neutral bis-β-diketimine (L3(H)2) with two equivalents of ZnMe2 leads to the expected heteroleptic dinuclear zinc complex L3(ZnMe)2 3 in 93% yield. Further reaction with benzoic acid PhCO2H leads to complex 4. Complex 2 forms a rather strong carboxylate-bridged dimer, whereas the carboxylate groups in complexes 1 and 4 act as asymmetrical bridges between both Zn atoms, pointing to the formation of a weakly bonded dimer. The zinc atoms in 1 and 4 are tetrahedrally coordinated, whereas in 2 the coordination number is increased to five due to the coordination of the pendant donor arm. The ring opening polymerization (ROP) of rac-lactide was investigated with the zinc complexes 1-4 and diazabicycloundec-7-ene (DBU) as a co-catalyst. Complexes 2 and 3 are active polymerization catalysts, which in the presence of DBU converted 200 equiv. of rac-lactide into polylactide within 10 min at ambient temperature. The analysis of the crude polymer showed that the lactide polymerization with catalyst 2 occurs via a slightly modified activated-monomer mechanism.

scholarly journals The composition of peptidochitodextrins from sarcophagid puparial cases

1971 ◽  
Vol 125 (3) ◽  
pp. 703-716 ◽  
Author(s):  
H. Lipke ◽  
T. Geoghegan
Keyword(s):  
Molecular Weight ◽  
Amino Acid ◽  
Protein Complex ◽  
Covalent Bonds ◽  
Aromatic Residues ◽  
Similar Molecular Weight ◽  
X Ray ◽  
Molecular Weights ◽  
Physical Interactions ◽  
The Stability

1. N-Bromosuccinimide cleaved proteins and pigments from fly puparia, increasing the chitin:protein ratio from 0.5 to 1.5. The product afforded subfractions (ratio 5:1) of molecular weights of 1200 and 1600 devoid of aromatic residues and N-terminal β-alanine, direct aryl links between polysaccharide chains being discounted. 2. The chitin–protein complex decreased in molecular weight when treated with Pronase, which suggested polypeptide bridges within the native chitin micelle. The limit dextrins generated by chitinase were mixtures of unsubstituted dextrins and peptidylated oligosaccharides, with the former predominating. 3. Peptidochitodextrins of similar molecular weight but markedly different solubility were prepared, which were indistinguishable with respect to amino acid, glucosamine, acetyl, X-ray or infrared characteristics. It is suggested that physical interactions contribute to the stability of the integument in addition to the covalent bonds that form during sclerotization.

Changes to amino acid composition of bloodmeal after chemical oxidation

RSC Advances ◽  
2015 ◽  
Vol 5 (81) ◽  
pp. 66451-66463 ◽  
Author(s):  
T. M. Hicks ◽  
C. J. R. Verbeek ◽  
M. C. Lay ◽  
M. Manley-Harris
Keyword(s):  
Molecular Weight ◽  
Amino Acid ◽  
Amino Acid Composition ◽  
Acid Composition ◽  
Weight Distribution ◽  
Peracetic Acid ◽  
Protein Solubility ◽  
Chemical Oxidation ◽  
Chemical Characteristics ◽  
Physical And Chemical

The effect of oxidative decolouring with peracetic acid on the physical and chemical characteristics of bloodmeal proteins was investigated by assessing protein solubility, molecular weight distribution and final amino acid composition.

Synthesis of functionalized pyrazole derivatives by regioselective [3+2] cycloadditions of N-Boc-α-amino acid-derived ynones

2018 ◽  
Vol 73 (7) ◽  
pp. 467-480 ◽  
Author(s):  
Eva Pušavec Kirar ◽  
Uroš Grošelj ◽  
Amalija Golobič ◽  
Franc Požgan ◽  
Sebastijan Ričko ◽  
...  
Keyword(s):  
Amino Acids ◽  
Nuclear Magnetic Resonance ◽  
Amino Acid ◽  
Ring Opening ◽  
Pyrazole Derivatives ◽  
X Ray Diffraction ◽  
X Ray ◽  
Acid Catalyzed ◽  
Azomethine Imines

Abstract [3+2] cycloadditions of ynones derived from glycine and (S)-alanine and some other dipolarophiles with azomethine imines, nitrile oxides, diazoacetate, and azidoacetate were studied. The dipolarophiles were obtained from α-amino acids, either by the reduction of the carboxy function with ethynylmagnesium bromide or by propiolation of the amino function. Cu-catalyzed cycloadditions of ynones to azomethine imines were regioselective and gave the expected cycloadducts as inseparable mixtures of diastereomers. In some instances, further oxidative hydrolytic ring-opening took place to afford 3,3-dimethyl-3-(1H-pyrazol-1-yl)propanoic acids. Acid-catalyzed cycloadditions of 3-butenone were also regioselective and provided mixtures of diastereomeric cycloadducts, which were separated by chromatography. In the reactions of title ynones with alkyl diazoacetates, in situ-formed benzonitrile oxides, and tert-butyl azidoacetate, all cycloadducts were obtained as single regioisomers. The structures of all novel compounds were established by nuclear magnetic resonance and X-ray diffraction.

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