Cation-π interactions enabling hard/soft Ti/Ag heterobimetallic cooperativity in lactide ring-opening polymerisation.

The combination of a Ti-salen complex with AgBArF reveals unique hard/soft heterobimetallic cooperativity in lactide ring-opening polymerisation (ROP), enabling significant activity at room temperature. Reactivity, mechanistic and computational studies highlight the role of cation-π interactions in the formation of heterobimetallic species and provide key insights into the role of both metals in ROP.

Workflows Allowing Creation of Journal Article Supporting Information and Findable, Accessible, Interoperable, and Reusable (FAIR)-Enabled Publication of Spectroscopic Data.

There is an increasing focus on the part of academic institutions, funding agencies, and publishers, if not researchers themselves, on preservation and sharing of research data. Motivations for sharing include research integrity, replicability, and reuse. One of the barriers to publishing data is the extra work involved in preparing data for publication once a journal article and its supporting information have been completed. In this work, a method is described to generate both human and machine-readable supporting information directly from the primary instrumental data files and to generate the metadata to ensure it is published in accordance with findable, accessible, interoperable, and reusable (FAIR) guidelines. Using this approach, both the human readable supporting information and the primary (raw) data can be submitted simultaneously with little extra effort. Although traditionally the data package would be sent to a journal publisher for publication alongside the article, the data package could also be published independently in an institutional FAIR data repository. Workflows are described that store the data packages and generate metadata appropriate for such a repository. The methods both to generate and to publish the data packages have been implemented for NMR data, but the concept is extensible to other types of spectroscopic data as well.

Design, Synthesis, and Conformational Analysis of Oligobenzanilides as Multifacial α-Helix Mimetics.

The design, synthesis, and conformational analysis of an oligobenzanilide helix mimetic scaffold capable of simultaneous mimicry of two faces of an α-helix is reported. The synthetic methodology provides access to diverse monomer building blocks amenable to solid-phase assembly in just four synthetic steps. The conformational flexibility of model dimers was investigated using a combination of solid and solution state methodologies supplemented with DFT calculations. The lack of noncovalent constraints allows for significant conformational plasticity in the scaffold, thus permitting it to successfully mimic residues i, i+2, i+4, i+6, i+7, and i+9 of a canonical α-helix.

Di-Zinc-Aryl Complexes: CO2 Insertions and Applications in Polymerisation Catalysis.

Two new di-zinc-aryl complexes, [LZn2 Ph2 ] and [LZn2 (C6 F5 )2 ], coordinated by a diphenol tetraamine macrocyclic ligand have been prepared and fully characterised, including by single-crystal X-ray diffraction experiments. The complexes' reactivities with monomers including carbon dioxide, cyclohexene oxide, phthalic anhydride, isopropanol and phenol were investigated using both experimental studies and density functional theory calculations. In particular, [LZn2 Ph2 ] readily inserts carbon dioxide to form a carboxylate, at 1 bar pressure, whereas [LZn2 (C6 F5 )2 ] does not react. Under these conditions [LZn2 Ph2 ] shows moderate activity in the ring-opening copolymerisation of cyclohexene oxide/carbon dioxide (TOF=20 h-1 ), cyclohexene oxide/phthalic anhydride (TOF=33 h-1 ) and the ring-opening polymerisations of rac-lactide (TOF=99 h-1 ) and ϵ-caprolactone (TOF=5280 h-1 ).

Sustainable polymers from renewable resources.

Renewable resources are used increasingly in the production of polymers. In particular, monomers such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manufacture of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymerizations and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.

Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity.

Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di- and monozinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the dizinc catalysts significantly out-perform the monozinc analogs. Further, for the best dizinc catalyst, the ligand conformation controls activity: the catalyst with "folded" ligand conformation shows turnover frequency (TOF) values up to 60 000 h(-1) (0.1 mol % loading, 298 K, [LA]=1 m), whilst that with a "planar" conformation is much slower, under similar conditions (TOF=30 h(-1) ). Dizinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol % whilst conserving high activity (TOF=12 500 h(-1) ).

Chemoselective Polymerizations from Mixtures of Epoxide, Lactone, Anhydride, and Carbon Dioxide.

Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymerization (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides, and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers-ε-caprolactone, cyclohexene oxide, phthalic anhydride, and carbon dioxide-are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity, resulting in block sequence control and predictable compositions (esters and carbonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically controlled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.

Macrocyclic Dizinc(II) Alkyl and Alkoxide Complexes: Reversible CO2 Uptake and Polymerization Catalysis Testing.

The synthesis of three new dizinc(II) complexes bearing a macrocyclic [2 + 2] Schiff base ligand is reported. The bis(anilido)tetraimine macrocycle reacts with diethylzinc to form a bis(ethyl)dizinc(II) complex, [L(Et)Zn2Et2] (1). The reaction of complex 1 with isopropyl alcohol is reported, forming a bis(isopropyl alkoxide)dizinc complex, [L(Et)Zn2((i)PrO)2] (2). Furthermore, complex 1, with 2 equiv of alcohol, is applied as an initiator for racemic lactide ring-opening polymerization. It shows moderately high activity, resulting in a pseudo-first-order rate coefficient of 9.8 × 10(-3) min(-1), with [LA] = 1 M and [initiator] = 5 mM at 25 °C and in a tetrahydrofuran solvent. Polymerization occurs with good control, as evidenced by the linear fit to a plot of molecular weight versus conversion, the narrow dispersities, and the limited transesterification. The same initiating system is inactive for the ring-opening copolymerization of carbon dioxide (CO2) and cyclohexene oxide at 80 °C and 1 bar of CO2 pressure. However, stoichiometric reactions between complex 2 and CO2, at 1 bar pressure, result in the reversible formation of new dizinc carbonate species, [L(Et)Zn2((i)PrO)((i)PrOCO2)] (3a) and [L(Et)Zn2((i)PrOCO2)2] (3b), and the reaction was studied using density functional theory calculations. All of the new complexes, 1-3b, are fully characterized, including NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

Selective polymerization catalysis: controlling the metal chain end group to prepare block copolyesters.

Selective catalysis is used to prepare block copolyesters by combining ring-opening polymerization of lactones and ring-opening copolymerization of epoxides/anhydrides. By using a dizinc complex with mixtures of up to three different monomers and controlling the chemistry of the Zn-O(polymer chain) it is possible to select for a particular polymerization route and thereby control the composition of block copolyesters.

Ring-opening copolymerization (ROCOP): synthesis and properties of polyesters and polycarbonates.

Controlled routes to prepare polyesters and polycarbonates are of interest due to the widespread application of these materials and the opportunities provided to prepare new copolymers. Furthermore, ring-opening copolymerization may enable new poly(ester-carbonate) materials to be prepared which are inaccessible using alternative polymerizations. This review highlights recent advances in the ring-opening copolymerization catalysis, using epoxides coupled with anhydrides or CO2, to produce polyesters and polycarbonates. In particular, the structures and performances of various homogeneous catalysts are presented for the epoxide-anhydride copolymerization. The properties of the resultant polyesters and polycarbonates are presented and future opportunities highlighted for developments of both the materials and catalysts.

Redox and luminescent properties of robust and air-stable N-heterocyclic carbene group 4 metal complexes.

Robust and air-stable homoleptic group 4 complexes of the type M(L)2 [1-3; M = Ti, Zr, Hf; L = dianionic bis(aryloxide) N-heterocyclic carbene (NHC) ligand] were readily synthesized from the NHC proligand 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride (H3L,Cl) and appropriate group 4 precursors. As deduced from cyclic voltammetry studies, the homoleptic bis-adduct zirconium and hafnium complexes 2 and 3 can also be oxidized, with up to four one-electron-oxidation signals for the zirconium derivative 2 (three reversible signals). Electron paramagnetic resonance data for the one-electron oxidation of complexes 1-3 agree with the formation of ligand-centered species. Compounds 2 and 3 are luminescent upon excitation in the absorption band at 362 nm with emissions at 485 and 534 nm with good quantum yields (ϕ = 0.08 and 0.12) for 2 and 3, respectively. In contrast, the titanium complex 1 does not exhibit luminescent properties upon excitation in the absorption band at 310 and 395 nm. Complexes 2 and 3 constitute the first examples of emissive nonmetallocene group 4 metal complexes.

Highly active zinc alkyl cations for the controlled and immortal ring-opening polymerization of ε-caprolactone.

Zinc alkyl cations supported by N,N-BIAN-type bidentate ligands were found to be highly active in the immortal ROP of ε-caprolactone to yield narrowly disperse and chain length-controlled poly(ε-caprolactone), whether in solution or bulk polymerization conditions.

A robust zirconium N-heterocyclic carbene complex for the living and highly stereoselective ring-opening polymerization of rac-lactide.

A readily accessible and robust Zr-NHC complex was found to polymerize rac-lactide in a highly controlled, living and stereoselective manner to afford heterotactic PLA.