ɛ‐caprolactone and lactide polymerization promoted by an ionic titanium(IV)/iron(III) polynuclear halo‐alkoxide

The ionic [Ti₃(µ₃‐OPrⁱ)₂(µ‐OPrⁱ)₃(OPrⁱ)₆][FeCl₄] halo‐alkoxide ( A ) was investigated for its activity towards the bulk polymerization of rac‐lactide (rac‐LA) and ?‐caprolactone (?‐CL) in various temperatures, monomer/ A molar proportions, and reaction times. The reactivity of A in the ring‐opening polymerization (ROP) of both monomers is mainly due to the cationic [Ti₃(OPrⁱ)₁₁]⁺ unity and proceeds through the coordination–insertion mechanism. Molecular weights ranging from 6,379 to 13,950 g mol^?1 and PDI values varying from 1.22 to 1.52 were obtained. Results of ROP kinetic studies for both ?‐CL and rac‐LA confirm that the reaction rates are first‐order with respect to monomers. The production of poly(?‐caprolactone) shows a higher sensitivity of the reaction rate to temperature, while the polymerization of rac‐LA is slower and more dependent on the thermal stability of the active species during the propagation step. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2509–2517     

Constraints on two-dimensional conformal field theories from knot invariants

The connection between Witten's topological three-dimensional gauge theory and RCFTs provides a natural setting to study the interplay between surface diffeomorphisms and intertwining of Wilson loops. These considerations lead directly to constraints on RFCTs including those previously derived by Vafa.     

Synthesis and spectroscopy of nickel(II) complexes with 5-methyl-3-formylpyrazole N(4)-methyl-N(4)-cyclohexyl thiosemicarbazone (HMPz4MCy): X-ray crystal structure of [Ni(HMPz4MCy)2]Cl2·2.5H2O

The coordination behaviour of a new pyrazolyl thiosemicarbazone, HMPz4MCy, synthesized and characterized (elemental analyses, mass spectrum, i.r. and ¹H-n.m.r) for the first time, is reported via solid state isolation of Ni^II complexes, [Ni(HMPz4MCy)₂]X₂·nH₂O (X = Cl, Br, NO₃, ClO₄ and BF₄; n = 2–3). The complex species were spectroscopically and structurally characterized. I.r. data for the free ligand and its Ni^II complexes indicate that the ligand, HMPz4MCy, exhibits a neutral NNS tridentate function via the pyrazolyl nitrogen (tertiary), azomethine nitrogen and thione sulphur. Electronic spectral data are suggestive of a distorted octahedral environment for the six-coordinate Ni^II species. X-ray crystallography of a representative species, [Ni(HMPz4MCy)₂]Cl₂·2.5H₂O (P2₁/c, monoclinic) has shown unambiguously that the crystallographic asymmetric unit consists of a [Ni(HMPz4MCy)₂]²⁺ cation and two Cl^– anions with the solvent of crystallization consisting of two H₂O molecules with full occupancy and a third H₂O molecule with half occupancy. The two NNS ligands orthogonally coordinate to the central nickel(II) ion with two azomethine nitrogen atoms in trans and the pyrazolyl nitrogen and the thione sulphur atoms in cis-positions. The crystal structure is stabilized by an extensive network of hydrogen bonds and is also additionally stabilized by C—HS contacts restricting free rotation about the N—C single bonds.     

Synthesis, spectroscopy and cyclic voltammetry of new iron(III) complexes with 5-methyl-3-formyl pyrazole 3-hexamethyleneiminyl thiosemicarbazone (HMPz3Hex): X-ray crystallographic identification of [Fe(MPz3Hex)2]ClO4 · 2H2O with an indication for unusual rotation about the azomethine double bond on complexation with iron(III)

New iron(III) complexes of 5-methyl-3-formylpyrazole 3-hexamethyleneiminylthiosemicarbazone (HMPz3Hex), [Fe(MPz3Hex)₂]X · nH₂O (where X = Cl, NO₃or ClO₄ and n = 1–2) have been synthesized and physico-chemically characterized by magnetic data (polycrystalline state), electronic, i.r. and e.p.r. spectral studies. The reported complexes are all cationic electrolytes (1:1) containing two moles of monodeprotonated title ligand and an anionic counterpart. I.r. spectra (4000–200 cm^?1) indicate coordination to the central iron(III) ion via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atoms of the primary ligand molecule. E.p.r. data (r.t. and l.n.t.) show the presence of a low-spin iron(III) cation with d _xz ² d _xz ² d _xz ¹ configuration. Cyclic voltammograms of iron(III) complexes indicate a reversible Fe⁺³/Fe⁺² couple. X-ray data of [Fe(MPz3Hex)₂]ClO₄ · 2H₂O (P₁, triclinic) authenticate a FeN₄S₂ distorted octahedral coordination with the two azomethine nitrogens trans to each other; the pyrazolyl nitrogens and thiolato sulphurs are in cis-positions, indicating an unusual rotation about the azomethine (C=N) double bond of the free HMPz3Hex during complexation with iron(III).