Aluminum, Calcium and Zinc Complexes Supported by Potentially Tridentate Imino-Phenolate Ligands: Synthesis and Use in the Ring-Opening Polymerization of Lactide

International audienceThe coordination chemistry of the potentially tridentate phenoxyethyl- and benzylaminoethyl-iminophenol pro-ligands {ONO}H and {ONN}H on to calcium, zinc and aluminum centers has been studied. {ONO}Ca(N(SiMe3)2)(THF) (1) was prepared by a one-pot salt metathesis procedure but the analogous reaction with {ONN}H led to intractable mixtures. Reaction of {ONO}H and {ONN}H with ZnEt2 (0.5 or 1 equiv.) systematically led to isolation of the corresponding homoleptic complexes {ONO}2Zn (2) and {ONN}2Zn (3). The dimethylaluminum complexes {ONO}AlMe2 (4) and {ONN}AlMe2 (5) were readily prepared by treatment of AlMe3 with 1 equiv. of the corresponding pro-ligands. Compounds 2 and 4 both feature monomeric structures in the solid state, with chelating iminophenolate ligands and free-hanging phenoxyethyl arms. The amido complex 1 was shown to be a moderately active initiator for the controlled ring-opening polymerization (ROP) of racemic lactide at room temperature, yielding polylactides with high initiation efficiencies, relatively narrow polydispersities and a slight heterotactic bias. Immortal polymerizations were achieved by combining excess isopropanol to 1, offering up to 50 macromolecules per metal center, with well-controlled molecular features. The dimethylaluminum compounds 4 and 5 initiated the controlled ROP of lactide in the presence of 1 equiv. of benzyl alcohol as a co-initiator but required higher temperatures. Copyright © 2012 John Wiley & Sons, Ltd

Erratum: ‘Aluminum, calcium and zinc complexes supported by potentially tridentate iminophenolate ligands: synthesis and use in the ring-opening polymerization of lactide’, Applied Organometallic Chemistry, v. 26, issue 12, December 2012, pages 681-688

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Synthesis and solid-state structural characterization of di-μ-azido-bis[{azido(N, N-diethylethylenediamine)}copper(II)]

The 1:1 mixed-ligand [{Cu(N3)2(diEten)}2] (diEten=N,N-diethylethylenediamine) complex has been synthesized and characterized by i.r. spectroscopy and X-ray diffraction. The compound crystallizes in the triclinic space group P1. Its structure consists of a centrosymmetric Cu2N2 unit whose N atoms belong to end-on azido bridges. Each copper atom is also surrounded by three nitrogen atoms; two from one N, N-diethylethylenediamine, and one from the remaining azide. The five nitrogen atoms altogether occupy the vertices of a slightly distorted trigonal bipyramid, and the azidobridges produced a rather short Cu...Cu distance of 3.37 Å. © 1989 Chapman and Hall Ltd

Synthesis, Characterization and Ethylene Oligomerization Studies of Chromium Complexes Bearing Imino-Furfural Ligands

International audienceA series of chromium(III) complexes bearing imino-furfural ligands (Cr1-Cr4) were synthesized and characterized by high-resolution mass spectrometry (HRMS). All chromium precatalysts, activated with methylaluminoxane (MAO), exhibited moderate to high activities for ethylene oligomerization [turnover frequency (TOF) = 11,008-23,200 mol(ethylene) mol(Cr)-1 h-1)] producing oligomers in the range C4-C12+ with good selectivity for α-olefins. The in situ chromium precatalysts formed by mixing imino-furfural ligand L1 with [CrCl3(THF)3] or [Cr(acac)3] showed low activities, producing oligomers together with varying amounts of polyethylene. The use of different chromium sources and cocatalysts influences the activity as well as the selectivities toward α-olefin production, which suggests that different active species are formed

Nickel-containing di-charged imidazolium ligand with high crystalline organization. Interception and characterization of a transient carbene/cation species

International audienceNew nickel-containing di-charged imidazolium-based molten salt (2) was prepared by treatment of nickel chloride with bis-(2-(3-methylimidazolium-1-yl)ethyl)ether dichloride (1) in good yield. This compound has been fully characterized by elemental analysis, polarized optical microscopy (POM), differential scanning calorimetry (DSC), powder and single-crystal X-ray diffraction, and electrospray mass spectrometry. X-ray diffraction studies of 2 revealed a quite interesting 3D organization whereas cations and anions each arrange in individual chains, which are themselves connected in an extended, columnar-type network. Furthermore the presence of [NiCl4]2− unit in compound 2 induces a 3D crystalline arrangement much higher than that observed for compound 1. The ESI(+)-MS studies show the same set of fragments detected for both compound 1 and 2 displaying similar losses including the presence of a di-charged molecule. The fragmentation of nickel-containing compound 2 gave a very high intense cation-carbene ion of m/z 235, suggesting an additional stabilization by the presence of [NiCl4]2− unit in the structure of 2 related to the low intensity signal found for 1 in the same m/z