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FlowNMR spectroscopy has become a popular and powerful technique for online reaction monitoring. DOSY NMR is an established technique for obtaining information about diffusion rates and molecular size on static samples. This work extends the FlowNMR toolbox to include FlowDOSY based on convection compensation and use of a low-pulsation pump or flow effect correction, allowing accurate and precise diffusion coefficients to be obtained at flow rates up to 4.0 mL min−1 in less than 5 minutes. [ABSTRACT FROM AUTHOR]

The chemical industry is increasingly looking to develop bio-based alternatives to petroleum-based platform chemicals, in order to reduce dependence on diminishing fossil resources and to decrease GHG emissions. 5-Hydroxymethylfurfural (HMF) and 2,5-furandicarboxylic acid (FDCA) are two examples of bio-based chemicals which could allow for the synthesis of a wide range of chemicals and materials, particularly polymers, from renewable feedstocks. This review paper summarises and critically evaluates results from existing life cycle assessment (LCA) and technoeconomic analysis (TEA) studies of HMF and FDCA synthesis and, by doing this, provides several points of advice for future investigations and assessments of synthetic routes towards these bio-based products. Chemical considerations such as choice of solvent system, catalyst and energy production are reviewed; and methodological issues in LCA, such as treatment of biogenic carbon and allocation methods, are discussed. Overall, results suggest that the production of HMF and FDCA-based products may offer lower impacts from CO2 emissions than their fossil-based counterparts, but this often comes with an increase in environmental impacts in other impact categories. Higher operating costs from expensive fructose feedstocks and high energy demands also make HMF and FDCA less economically viable than current chemicals. Moving forwards, further investigation into different lignocellulosic feedstocks, energy production units and the development of new catalytic systems may help in making HMF and FDCA production more favourable than the production of fossil-based counterparts. [ABSTRACT FROM AUTHOR]

The use of a simple, cheap and effective organocatalyst, tetramethylammonium methyl carbonate, has been exploited for the transesterification of a range of commercial polymer samples. PLA, PCL, PC and PET have been successfully broken down into useful products, with the repolymerisation of DMT to PET demonstrated, highlighting a truly circular economy approach. [ABSTRACT FROM AUTHOR]

A stereoselective, solvent-free ring-opening polymerisation (ROP) of lactide (LA) in supercritical carbon dioxide (scCO2) is reported for the first time. The key aim is to exploit scCO2 to lower the temperature of traditional melt polymerisations, lowering the energy requirement and leading to cleaner polymeric materials. We have utilised a zirconium amine-trisphenolate initiator-stereoselective catalyst [(iPrO)Zr(OPh(tBu)2-CH2)3N] to yield highly heterotactic poly(lactide) (PLA) homopolymer (Pr = 0.74–0.84) from rac-LA, demonstrating control of the PLA microstructure in scCO2. In addition, high monomer conversion (86–93%) was achieved in short reaction time (1 h), affording poly(lactide) with a very low degree of transesterification and narrow molecular weight distribution. Most importantly, all the reactions were performed at only 80 °C, almost 100 °C lower than the conventional melt process (typically performed at 130–180 °C), representing a very significant potential energy saving. [ABSTRACT FROM AUTHOR]

A tungsten-based polyoxometalate catalyst employing aqueous H2O2 as a benign oxidant has been used for the solvent free catalytic epoxidation of the trisubstituted alkene bonds of a wide range of biorenewable terpene substrates. This epoxidation protocol has been scaled up to produce limonene oxide, 3-carene oxide and α-pinene oxide on a multigram scale, with the catalyst being recycled three times to produce 3-carene oxide. Epoxidation of the less reactive disubstituted alkene bonds of terpene substrates could be achieved by carrying out catalytic epoxidation reactions at 50 °C. Methods have been developed that enable direct epoxidation of untreated crude sulfate turpentine to afford 3-carene oxide, α-pinene oxide and β-pinene oxide. Treatment of crude epoxide products (no work-up) with a heterogeneous acid catalyst (Amberlyst-15) results in clean epoxide hydrolysis to afford their corresponding terpene-anti-diols in good yields. [ABSTRACT FROM AUTHOR]

A new way to combine two different polymerisation reactions, using a single catalyst, results in efficient block polymer synthesis. The selective polymerisation of mixtures of l-lactide-O-carboxyanhydride and cyclohexene oxide, using a di-zinc catalyst in a one-pot procedure, allows the preparation of poly(l-lactide-b-cyclohexene carbonate). The catalysis near quantitatively recycles the carbon dioxide released during polyester formation into the subsequent polycarbonate block, with an atom economy of up to of 91%. [ABSTRACT FROM AUTHOR]

A range of ligands based upon 2-(aminomethyl)piperidine have been successfully complexed to Mg(ii), Zn(ii) and group IV metal centres. These complexes have been characterised both in solution and solid state with different coordination geometries realised dependant on the nature of the ligand. For the Mg(ii) and Zn(ii) complexes, M(1–2)2, were isolated and analysed by DOSY NMR spectroscopy. These ligands also furnished diastereomeric group IV complexes, M(1–2)2(OiPr)2. Group IV salalen and salan complexes, M(4–5)(OR)2 were also found to be diastereomeric in nature, with either β-cis or α-cis geometriesrespectively. The tridentate ligand, 6H2, yielded five coordinate complexes with both Ti(iv) and Zr(iv). All complexes were screened for the ring opening polymerisation of rac-lactide under both solvent and melt conditions. For the Mg(ii) and Zn(ii) complexes, good activity was observed with Zn(1–2)2 demonstrating immortal polymerisation characteristics. [ABSTRACT FROM AUTHOR]

We report the rationalised design of aluminium initiators and their application for ROP of rac-lactide (rac-LA). A very minor change to the ligand backbone (imine reduction) to give secondary amines was found to have a dramatic effect on activity and selectivity with isotactic PLA being realised. [ABSTRACT FROM AUTHOR]

The copper phosphinimide complexes [Cu{μ-N=PR3}]4 (1, R = NMe2 and 2, R = Ph) were obtained in good yields from the reactions of Cu[Mes] (Mes = mesityl, C6H2Me3-2,4,6) with the corresponding iminophosphoranes, HNPR3. The molecular structures of 1 and 2 reveal the presence of planar eight-membered {Cu4N4} rings which contrasts with the saddle-shaped {M4N4} rings found in related metal phosphinimide complexes. According to computations, there is negligible aromaticity in the planar {Cu4N4} rings in 1 and 2 and the saddle shape observed in related {M4N4} rings is due to steric factors. [ABSTRACT FROM AUTHOR]

Unsymmetrical amine tris(phenolate) ligands have been prepared and complexed to Zr(IV). In the solidstate dimeric species are observed, which persist in solution. The complexes show interesting coordination chemistry and the nature of which is discussed. These complexes are analogues of a highly stereoselective C3-symmetric Zr(IV) amine tris(phenolate) alkoxide and have been prepared, characterised and trialled for the ring-opening of rac-lactide providing insight into the effect of symmetry and ligand steric bulk on selectivity. The polymerisations have been investigated in solution and under the industrially preferred melt conditions (130 °C). The rate law for the ROP has been determined - with Zr2(1)2(OiPr)2, a pseudo first order dependency was seen, however for Zr2(2)2(OiPr)2 this changed to a half order dependency in initiator. [ABSTRACT FROM AUTHOR]

Five new lithium aryloxide complexes stabilised by polyamine ligands have been synthesised by simple deprotonation reactions of the parent aryl alcohols H–OAr [OAr = OC6H5, OC6H2-2,4,6-(Me)3and OC6H2-2,6-(tBu)2-4-(Me)] with LiN(SiMe3)2in the presence of the Lewis bases N,N,N′,N′-tetramethylethylenediamine (TMEDA) and N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA). All the compounds have been characterised by multinuclear NMR and X-ray crystallographic studies. The PMDETA derivative of the phenol adopts a tetrameric ladder-like structural motif in the solid state, exhibiting an unusual bridging coordination mode of the N-donor ligand. The 2,4,6-trimethylphenol derivatives exhibit dimeric (TMEDA), and tetrameric (PMDETA) structural motifs in the solid state. Meanwhile, the TMEDA and PMDETA derivatives of the sterically hindered 2,6-di-tert-butyl-4-methylphenol exhibit a rare monomeric structural motifs, which appears to remain unaltered in C6D6solution. [ABSTRACT FROM AUTHOR]

The toluene solution structure of an N-lithio(triphenyl)phosphazene (Ph3PNLi) mixed aggregate with lithium bromide (LiBr), 5, has been elucidated for the first time based on multinuclear magnetic resonance measurements (1H, 6Li, 7Li, 13C and 31P). The structure consist of two dimers [Li(μ-Z)]2 (Z= Br, NPR3) linked through LiX (X= N, Br) bridges. This arrangement is a cubane-like structure analogous to that found in the solid-state. [ABSTRACT FROM AUTHOR]

Metalation of an ammonium tris(phenol) ligand affords new lithium/sodium derivatives having central pseudocubane motifs in which one of the metallic positions is replaced by a four-coordinate hydrogen atom. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate the utility of Group 4 metals for the well-controlled and stereoselective (syndiotactic) ring opening polymerization (ROP) of rac-β-butyrolactone (BBL) and their ability to form copolymers. [ABSTRACT FROM AUTHOR]

In this communication we report the preparation of highly active catalysts for the production of polylactide and the subsequent conversion of polylactide to methyl lactate. The use of these catalysts for potential recycling applications is discussed. [ABSTRACT FROM AUTHOR]

The first examples of Group 1 metal complexes of tris(2-dimethylaminoethyl)amine (Me6TREN) are reported including monomeric sodium complexes containing η4-bound ligands, suggesting their potential use in alkali-metal-mediated synthetic applications. [ABSTRACT FROM AUTHOR]

Correction for 'Waste not, want not: CO 2 (re)cycling into block polymers' by Sumesh K. Raman et al., Chem. Commun., 2019, 55, 7315-7318.

A new way to combine two different polymerisation reactions, using a single catalyst, results in efficient block polymer synthesis. The selective polymerisation of mixtures of l-lactide-O-carboxyanhydride and cyclohexene oxide, using a di-zinc catalyst in a one-pot procedure, allows the preparation of poly(l-lactide-b-cyclohexene carbonate). The catalysis near quantitatively recycles the carbon dioxide released during polyester formation into the subsequent polycarbonate block, with an atom economy of up to of 91%.

A range of ligands based upon 2-(aminomethyl)piperidine have been successfully complexed to Mg(ii), Zn(ii) and group IV metal centres. These complexes have been characterised both in solution and solid state with different coordination geometries realised dependant on the nature of the ligand. For the Mg(ii) and Zn(ii) complexes, M(1-2) 2 , were isolated and analysed by DOSY NMR spectroscopy. These ligands also furnished diastereomeric group IV complexes, M(1-2) 2 (O i Pr) 2 . Group IV salalen and salan complexes, M(4-5)(OR) 2 were also found to be diastereomeric in nature, with either β-cis or α-cis geometriesrespectively. The tridentate ligand, 6H 2 , yielded five coordinate complexes with both Ti(iv) and Zr(iv). All complexes were screened for the ring opening polymerisation of rac-lactide under both solvent and melt conditions. For the Mg(ii) and Zn(ii) complexes, good activity was observed with Zn(1-2) 2 demonstrating immortal polymerisation characteristics.

The copper phosphinimide complexes [Cu{μ-N[double bond, length as m-dash]PR3}]4 (1, R = NMe2 and 2, R = Ph) were obtained in good yields from the reactions of Cu[Mes] (Mes = mesityl, C6H2Me3-2,4,6) with the corresponding iminophosphoranes, HNPR3. The molecular structures of 1 and 2 reveal the presence of planar eight-membered {Cu4N4} rings which contrasts with the saddle-shaped {M4N4} rings found in related metal phosphinimide complexes. According to computations, there is negligible aromaticity in the planar {Cu4N4} rings in 1 and 2 and the saddle shape observed in related {M4N4} rings is due to steric factors.

Unsymmetrical amine tris(phenolate) ligands have been prepared and complexed to Zr(iv). In the solid-state dimeric species are observed, which persist in solution. The complexes show interesting coordination chemistry and the nature of which is discussed. These complexes are analogues of a highly stereoselective C3-symmetric Zr(iv) amine tris(phenolate) alkoxide and have been prepared, characterised and trialled for the ring-opening of rac-lactide providing insight into the effect of symmetry and ligand steric bulk on selectivity. The polymerisations have been investigated in solution and under the industrially preferred melt conditions (130 °C). The rate law for the ROP has been determined - with Zr2()2(O(i)Pr)2, a pseudo first order dependency was seen, however for Zr2()2(O(i)Pr)2 this changed to a half order dependency in initiator.

A chiral pseudo-C(3)-symmetric titanium triflate that employs the point chirality of a single stereogenic centre to control the propeller chirality of its aryl rings has been used to catalyse an asymmetric sulfoxidation reaction.

Reaction of Al(OiPr)3 with the tris-phenol amine ligand L1H3 in toluene at ambient temperature results in the formation of the iso-propanol adduct [HOiPr.Al(L1)]. Single crystal X-ray diffraction analysis reveals the structure to be a hydrogen bonded dimer. Reaction of Al(OiPr)3 (or AlMe3) with L1H3 in THF affords the related, and structurally characterised THF adduct, [THF.Al(L1)]. Similar reaction of Al(OiPr)3 (or AlMe3) with the bis-phenol amine and tetra-phenol diamine ligands, L2H3 and L3H4, results in the formation and isolation of the complexes [Al(L2)]2 and [Al(L3)H] respectively, both of which have been structurally characterised via single crystal X-ray diffraction studies. Reaction of the alkoxide bridged dimer [Al(L2)]2 with the strong Lewis base HMPA results in the formation of the monomeric HMPA adduct [HMPA.Al(L2)] which was also structurally characterised. The adduct [HOiPr.Al(L1)] and the dimer [Al(L2)]2 were tested for their activity in the ring-opening polymerisation (ROP) of rac-lactide under solvent-free conditions (130 degrees C). Under the conditions employed [Al(L2)]2 failed to produce polymer after 48 h, in stark contrast to [HOiPr.Al(L1)] which after 24 h and 48 h produced narrow molecular weight polymer (24 h: yield=25%, Mn=14500 and PDI=1.05; 48 h: yield=65%, Mn=47700 and PDI=1.06).

In this communication we report, for the first time, the ring-opening polymerisation in the melt of rac-lactide with heterogeneous catalysts. Homogeneous model systems based on silsesquioxanes have been prepared for comparison.

Chiral Schiff bases (1H to 4H) and a series of their Group 4 metal alkoxide complexes [(R-1)2Ti(O(i)Pr)2, (R-2)2Ti(O(i)Pr)2, (R-1)(2)Zr(O(i)Pr)2, (R-2)2Zr(O(i)Pr)2, (R-3)2Zr(O(i)Pr)2, (R-4)2Zr(O(i)Pr)2, (S-1)2Zr(O(i)Pr)2 and (rac-1)2Zr(O(i)Pr)2] have been prepared and characterised by 1H, and 13C NMR spectroscopy. In solution, both Lambda and Delta isomers were observed, suggesting a low degree of chiral induction from the ligand. One ligand (R-4H) and three complexes [Delta-(R,R-2)2Ti(O(i)Pr)2, Lambda-(R,R-1)2Zr(O(i)Pr)2 and Delta-(R,R-3)2Zr(O(i)Pr)2] have also been characterised by single crystal X-ray diffraction. All complexes were found to have a pseudo-octahedral alpha-cis geometry. The complexes were tested as initiators for the ring-opening polymerisation of rac-lactide in solution and in the melt. The titanium complexes are inactive in solution and afford atactic polylactide in the melt. Zr(iv) complexes afford heterotactically enriched polylactide both in toluene solution (at 20 degrees C and 80 degrees C) and in the melt. Polymerisations were generally found to be well-controlled, giving predictable molecular weights and low molecular weight distributions. Ligand variation (substituents and/or chirality) has little effect on either the activity or selectivity of initiators. Zirconium initiators were found to be unusually robust as they were able to maintain well-controlled polymerisation following addition of water to reactions in solution and when using unpurified monomer for reactions in the melt.

Under solvent-free conditions (at 130 degrees C), zirconium and hafnium amine tris(phenolate) alkoxides are extremely active, well-controlled, single-site initiators for the ring-opening polymerization of rac-lactide, yielding highly heterotactic polylactide.