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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]

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]

The series of alkali-metal (Li, Na, K) complexes of the substituted benzyl anion 3,5-dimethylbenzyl (Me2C6H3CH2-) derived from 1,3,5-trimethylbenzene (mesitylene) have been coerced into monomeric forms by supporting them with the tripodal tetradentate Lewis donor tris(N,N-dimethyl-2-aminoethyl)amine, [N(CH2CH2NMe2)3, Me6TREN]. Molecular structure analysis by X-ray crystallography establishes that the cation-anion interaction varies as a function of the alkali-metal, with the carbanion binding to lithium mainly in a σ fashion, to potassium mainly in a π fashion, with the interaction toward sodium being intermediate between these two extremes. This distinction is due to the heavier alkali-metal forcing and using the delocalization of negative charge into the aromatic ring to gain a higher coordination number in accordance with its size. Me6TREN binds the metal in a η4 mode at all times. This coordination isomerism is shown by multinuclear NMR spectroscopy to also extend to the structures in solution and is further supported by density functional theory (DFT) calculations on model systems. A Me6TREN stabilized benzyl potassium complex has been used to prepare a mixed-metal ate complex by a cocomplexation reaction with tBu2Zn, with the benzyl ligand acting as an unusual ditopic σ/π bridging ligand between the two metals, and with the small zinc atom relocalizing the negative charge back on to the lateral CH2 arm to give a complex best described as a contacted ion pair potassium zincate. [ABSTRACT FROM AUTHOR]

Metalation of 2,4,6-tri(methyl)phenol (MeArOH) and 2,6-di(tert-butyl)-4-methylphenol (BuArOH) with NaN(SiMe3)2 in toluene and in the presence of stoichiometric amounts of the polydentate amines N,N,N′,N′-tetramethylethylenediamine (TMEDA) and N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) affords three new sodium aryloxide complexes [Na(μ-OArBu)(TMEDA)]2 (3), [Na(μ-OArMe)(PMDETA)]2 (4), and [Na(OArBu)(PMDETA)] (5). Complexes 3 to 5 have been isolated as crystalline materials in reasonable yields and characterized in the solid state by X-ray crystallography and in solution by NMR spectroscopy. Complexes 3 to 5 and the related [tris(2-dimethylaminoethyl)amine] (Me6TREN) derivatives [Na(OArMe)(HOArMe)(Me6TREN)] (1) and [Na(OArBu)(Me6TREN)] (2), recently prepared in our group, are shown to be active as initiators for the ring-opening polymerization (ROP) of rac-lactide with benzyl alcohol as a co-initiator. However, during the course of the polymerization reactions intrachain and stereorandom transesterification side-reactions were observed under some of the experimental conditions tested. [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]