Aluminum amine-bis(phenolate) complexes for ring-opening polymerization of rac-lactide and ε-caprolactone

Five aluminum-based amine-bis(phenolate) complexes, three of them novel, with variation of the pendant donor arm were synthesized in excellent yields, and characterized by NMR spectroscopy and X-ray crystallography. The quantitative conversion of the aluminum alkyl species to the corresponding benzyl alkoxide was achieved by the addition of 1 mol eq. of benzyl alcohol, and was confirmed by 1H NMR spectroscopy. The aluminum alkoxides were excellent mediators for the ring-opening polymerization (ROP) of rac-lactide, yielding atactic poly(lactic acid), having excellent correlation between theoretical and calculated molecular weights accompanied by narrow molecular weight distributions. ROP of ε-caprolactone by the aluminum alkoxides showed modest control at 50°C in toluene, but much greater control was achieved when polymerizations were conducted at 25°C, with narrower molecular weight distributions observed in some cases. A relationship between the complex pendant donor arm and the resulting activity in the ROP of both rac-lactide and ε-caprolactone is discussed

Bis(μ-diethyl­phosphido-κ2 P:P)bis­[bis(2,4,6-trimethyl­phen­yl)indium(III)]

The title compound, [In2(C9H11)4(C4H10P)2], contains a centrosymmetric In2P2 core with short inter­molecular In—P bonds. This core has acute P—In—P and obtuse In—P—In bond angles compared with other [R 2InPR′2]2 analogues, due to the presence of the bulky aromatic substituents on the In atom and the non-sterically demanding ethyl substituents on the P atom

Ring-opening polymerization of <em>rac</em>-lactide and ε-caprolactone using zinc and calcium salicylaldiminato complexes

Tridentate Schiff base complexes of zinc and calcium were prepared and tested in the ring-opening polymerization of ε-caprolactone and rac-lactide to generate biodegradable polymeric materials from biocompatible metals. Alteration of the pendant donor arm attached to the imine backbone provides some control over catalyst composition and polymerization activity. Complexes of the formula [ONN]ZnN(SiMe3)2, where [ONN] = 2-(N-donor arm-imine)[4,6-di(tert-butyl)phenoxide], were isolated with ethyldimethylamine, ethylpiperidine, and ethylmorpholine substituents, while disproportionation led to the isolation of [ONN]2Zn complexes with methylpyridine, quinoline, and ethyldiisopropylamine derivatives, two of which were crystallographically characterized. Calcium complexes were more stable and novel [ONN]CaN(SiMe3)2 complexes with ethylpiperidine and ethyldiisopropylamine substituents were reported. Zinc and calcium catalysts coordinated to a single tridentate ligand were effective at initiating the polymerization of ε-caprolactone, but did not control the polymerizations, whereas the bis(ligand) complexes produced no polymer. These catalysts were effective at controlling the polymerization of rac-lactide. Coordinatively saturated complexes inhibit the polymerization, while initiation from either the amido or ligand alkoxide functionalities produces poly(lactic acid) with low polydispersities. </jats:p

Synthesis and characterization of tantalum(V) boronate clusters : multifunctional Lewis acid cages for binding guests

Open and shut cases: Tantalum(V) boronate clusters [(Cp*Ta)3(μ2‐η2‐RBO2)3(μ2‐O)2(μ2‐OH)(μ3‐OH)] (Cp*=η5‐C5Me5; 1: R=Ph, 2: R=iBu) with Lewis acidic cavities were prepared. Whereas the cavity of 2 is blocked by the iBu groups, that of 1 is open and can bind Lewis basic guests such as ketones (see picture) by interaction with one boronate and one μ3‐OH ligand

Ethyl 6-methyl-4-[2-(4,4,5,5-tetra­methyl-1,3,2-dioxaborolan-2-yl)thio­phen-3-yl]-2-thioxo-1,2,3,4-tetra­hydro­pyrimidine-5-carboxyl­ate

A new Biginelli compound, C18H25BN2O4S2, containing a boronate ester group was synthesized from a lithium bromide-catalysed reaction. The compound crystallizes with two independent mol­ecules in the asymmetric unit that differ mainly in the conformation of the ester functionality. The crystal structure is stabilized by inter­molecular N—H⋯O and N—H⋯S hydrogen bonds involving the 3,4-dihydro­pyrimidine-2(1H)-thione NH groups as donors and the carbonyl O and thio­phene S atoms as acceptors

catena-Poly[[bis(pyridine)­lead(II)]bis(μ-penta­fluoro­benzene­thiol­ato)]

The title compound, [Pb(C6F5S)2(C5H5N)2]n, shows the PbII atom in a ψ-trigonal bipyramidal S2N2 bonding environment. Pyridine N atoms occupy axial sites, while thiol­ate S atoms and a stereochemically active lone pair occupy equatorial sites. Very long inter­molecular Pb⋯S inter­actions [3.618 (4) and 3.614 (4) Å] yield a weakly associated one-dimensional polymeric structure extending parallel to [010]

Aluminium salophen and salen initiators in the ring-opening polymerisation of <em>rac</em>-lactide and <em>rac</em>-β-butyrolactone: Electronic effects on stereoselectivity and polymerisation rates

Three aluminium salophen and two aluminium salen complexes were synthesised, characterised and screened in the ring-opening polymerisation (ROP) of rac-lactide and rac-β-butyrolactone. The focus was on controlling the apparent polymerisation rate (k p) and stereoselectivity of poly(lactic acid) and poly(3-hydroxybutyrate) by modulating the electron density at the aluminium centre or by switching from an alkyl backbone (salen complex) to an aryl backbone (salophen complex). The salen complexes generally showed higher k p as well as isoselectivity compared to the salophen complexes. For instance, salophen and salen complexes biased the microstructure of poly(3-hydroxybutyrate) towards syndiotacticity and isotacticity, respectively. Electron-withdrawing or electron-donating backbones on a salophen complex tuned k p, with electron-donating backbones offering faster k p

Louis-Bernard Guyton de Morveau e a revolução química das Luzes

O objetivo deste artigo é investigar a concepção enciclopédica de revolução científica posta em prática pelo químico francês L.-B. Guyton de Morveau (1737-1816). Deslocando a análise do conhecimento químico das Luzes do programa traçado por Lavoisier (1743-1794), sugerimos uma concepção revolucionária republicana, proclamada como resultado do esforço de uma coletividade. Daremos destaque a três abordagens revolucionárias de Guyton de Morveau no âmbito da química. A primeira foi sua atuação no ensino dessa ciência, cuja pedagogia e métodos de ensino foram fundamentais para sua imersão social. Além disso, entre 1770 e 1790, Guyton de Morveau teve desempenhos decisivos no seio da empresa enciclopédica e no seio da escola química francesa

Metastable Se6 as a ligand for Ag+: from isolated molecular to polymeric 1D and 2D structures

Attempts to prepare the hitherto unknown Se6 2+ cation by the reaction of elemental selenium and Ag[A] ([A]- = [Sb(OTeF5)6]-, [Al(OC(CF3)3)4]-) in SO2 led to the formation of [(OSO)Ag(Se6)Ag(OSO)][Sb(OTeF5)6]2 1 and [(OSO)2Ag(Se6)Ag(OSO)2][Al(OC(CF3)3)4]2 2a. 1 could only be prepared by using bromine as co-oxidant, however, bulk 2b (2a with loss of SO2) was accessible from Ag[Al(OC(CF3)3)4] and grey Se in SO2 (chem. analysis). The reactions of Ag[MF6] (M= As, Sb) and elemental selenium led to crystals of 1/∞{[Ag(Se6)]∞[Ag2(SbF6)3]∞} 3 and {1/∞[Ag(Se6)Ag]∞}[AsF6]2 4. Pure bulk 4 was best prepared by the reaction of Se4[AsF6]2, silver metal and elemental selenium. Attempts to prepare bulk 1 and 3 were unsuccessful. 1–4 were characterized by single-crystal X-ray structure determinations, 2b and 4 additionally by chemical analysis and 4 also by X-ray powder diffraction, FT-Raman and FT-IR pectroscopy. Application of the PRESTO III sequence allowed for the first time 109Ag MAS NMR investigations of 4 as well as AgF, AgF2, AgMF6 and {1/∞[Ag(I2)]∞}[MF6] (M= As, Sb). Compounds 1 and 2a/b, with the very large counter ions, contain isolated [Ag(Se6)Ag]2+ heterocubane units consisting of a Se6 molecule bicapped by two silver cations (local D3d sym). 3 and 4, with the smaller anions, contain close packed stacked arrays of Se6 rings with Ag+ residing in octahedral holes. Each Ag+ ion coordinates to three selenium atoms of each adjacent Se6 ring. 4 contains [Ag(Se6)+]∞ stacks additionally linked by Ag(2)+ into a two dimensional network. 3 features a remarkable 3-dimensional [Ag2(SbF6)3]- anion held together by strong Sb–F … Ag contacts between the component Ag+ and [SbF6]- ions. The hexagonal channels formed by the [Ag2(SbF6)3]- anions are filled by stacks of [Ag(Se6)+]∞ cations. Overall 1–4 are new members of the rare class of metal complexes of neutral main group elemental clusters, in which the main group element is positively polarized due to coordination to a metal ion. Notably, 1 to 4 include the commonly metastable Se6 molecule as a ligand. The structure, bonding and thermodynamics of 1 to 4 were investigated with the help of quantum chemical calculations (PBE0/TZVPP and (RI-)MP2/TZVPP, in part including COSMO solvation) and Born–Fajans–Haber-cycle calculations. From an analysis of all the available data it appears that the formation of the usually metastable Se6 molecule from grey selenium is thermodynamically driven by the coordination to the Ag+ ions