Structure and reactivity of alkoxy-zinc compounds as initiators/catalysts in the polymerization of cyclic esters

This review focuses on advances in the synthesis and structural chemistry of zinc alkoxide compounds for use in the catalytic ring-opening polymerization (ROP) of lactides (LAs). This route was used for the preparation of lactic acid based polymers - referred to as polylactides (PLAs). These polyesters have ecofriendly properties such as renewability, biocompatibility, and biodegradability, and are therefore among the most promising green polymers. PLAs have found numerous specialty applications in the biomedical industry, such as biodegradable screws and sutures, scaffolds for tissue engineering, matrices for controlled drug delivery systems, and environmentally friendly food-packaging materials. In industry, PLAs were synthesized by bulk polymerization of LA using tin(II) alkoxides synthesized in situ from tin(II) 2-ethylhexanoate. The toxicity associated with most tin compounds is a considerable drawback in the case of biomedical applications. There has therefore been much research devoted to finding well- defined complexes of high activity containing biologically benign metals. In this context, zinc alkoxides are very attractive non-toxic initiators for the synthesis of polymers that could be used in medical and environmental fields. The most broadly applied representations of zinc initiators for ROP of LA are zinc carboxylates, ß-diketonates, ß-diketiminates, phenolates and bisphenolates, trispyrazolyl- and trisindazolyl-borates, heteroscorpionates, aminophenolates, Schiff base, and iminealkoxylates. The mentioned above initiators were classified and analyzed in the context of their coordination chemistry and revealed catalytic activity in the ROP of LA. The review contains only pioneering/groundbreaking works that allowed for setting new research paths for each of the described groups of initiators, showing how this theme has changed over the last several decades

Crystal structure of a mixed-ligand dinuclear Ba—Zn complex with 2-methoxyethanol having triphenylacetate and chloride bridges

The dinuclear barium–zinc complex, μ-chlorido-1:2κ2Cl:Cl-chlorido-2κCl-bis(2-methoxyethanol-1κO)bis(2-methoxyethanol-1κ2O,O′)bis(μ-triphenylacetato-1:2κ2O:O′)bariumzinc, [BaZn(C20H15O2)2Cl2(C3H8O2)4], has been synthesized by the reaction of barium triphenylacetate, anhydrous zinc chloride and 2-methoxyethanol in the presence of toluene. The barium and zinc metal cations in the dinuclear complex are linked via one chloride anion and carboxylate O atoms of the triphenylacetate ligands, giving a Ba...Zn separation of 3.9335 (11) Å. The irregular nine-coordinate BaO8Cl coordination centres comprise eight O-atom donors, six of them from 2-methoxyethanol ligands (four from two bidentate O,O′-chelate interactions and two from monodentate interactions), two from bridging triphenylacetate ligands and one from a bridging Cl donor. The distorted tetrahedral coordination sphere of zinc comprises two O-atom donors from the triphenylacetate ligands and two Cl donors (one bridging and one terminal). In the crystal, O—H...Cl, O—H...O and C—H...Cl intermolecular interactions form a layered structure, lying parallel to (001)

New members in the [Mn10] supertetrahedron family

Two manganese complexes, [MnII4MnIII6Cl4(CH3OCH2CH2O)12 O4][MnII3TiIVCl6(CH3OCH2CH2O)6] (1) and [MnII4MnIII6Cl4(CH3OCH2CH2O)12O4] [Mn4II Cl10(CH3OCH2CH2OH)4]∙0.5CH3OCH2CH2OH, (2) have been obtained and characterized by single-crystal X-ray diffraction. Both structures consist of the decametallic dicationic [MnII4MnIII6Cl4(CH3OCH2CH2O)12O4]2 + core constructed by four vertex-sharing [MnIII3MnIIO]9 + tetrahedra. Also, these compounds contain the different tetrametallic dianions: [MnII3TiIVCl6(CH3OCH2CH2O)6]2 − (in complex 1) and [Mn4IICl10(CH3OCH2CH2OH)4]2 − (in complex 2). Magnetic dc and ac susceptibility measurements for compound (1) show that the dicationic decanuclear magnetic cluster possesses an S = 12 ± 1 spin ground-state

Constructing anhydrous halide bridged manganese(II) clusters: Synthesis, structures and magnetic properties

The reaction of Mn0 and HgCl2 with triphenylacetic acid in a mixture of 2-methoxyethanol and toluene afforded complex [Mn2IICl2(O2CCPh3)2(2-methoxyethanol)3] (1) in very good yield. Repeating the same reaction and replacing 2-methoxyethanol with THF forms the complex [Mn3IICl3.04(O2CCPh3)1.96(2-methoxyethanol)(THF)4] (2) in good yield. Furthermore the reaction between Mn0 and triphenylacetic acid in a mixture of THF and toluene after heating produces the complex [Mn4Cl5Na(O2CCPh3)4(THF)6] (3). Finally, the reaction between MnCl2 and potassium triphenylacetate or lithium triphenylacetate in THF and toluene gave complexes [Mn4Cl5K(O2CCPh3)4(THF)6] (4) and [Mn4Cl5Li(O2CCPh3)4(THF)5]·0.75(THF) (5·0.75THF), respectively, in good yields. The crystal structures of 1–5 have been determined by single-crystal X-ray crystallography. Complex 1 is a chloride bridged [MnII2] dimer in which the two metal ions are found in an O5Cl and an O3Cl2 coordination environment. Complex 2 is a trinuclear [MnII3] triangle-like cluster in which the “central” MnII ion is bridged via two chloride ions to the peripheral Mn2+ ions, additionally all manganese ions are connected by oxygen ion in a μ3 mode. Complexes 3–5 are all tetranuclear [MnII4Cl5]3+ metallic clusters displaying similar geometries, in which the tetrametallic core unit possesses a planar square arrangement. DC magnetic susceptibility studies indicate the presence of dominant antiferromagnetic exchange for all 1–4 clusters