Whereas harnessing non-covalent interactions (NCIs) have largely been applied to late-transition metal complexes and to the corresponding catalytic reactions, there are very few examples showing the importance of NCIs in early-transition metal and main group metal catalysis. Here, we report on the effects of hydrogen bond donors in the catalytic pocket to explain the high activity and stereoselectivity of a series of aluminium catam complexes in rac-lactide ring-opening polymerisation (ROP). Four original aluminium catam catalysts have been synthetized and fully characterized. Structure-activity relationships and isotope effect show the importance of the NH moieties of the ligand in rac-lactide ROP. Computational studies highlight beneficial hydrogen bonds between the ligand and the monomer. Overall, structural characterization of the catalysts, mechanistic, kinetic and computational studies support the benefits of non-covalent interactions in the catalytic pocket.

A new series of aluminium complexes bearing 'catam' ligands has been synthesised and fully characterised. They were found to exhibit high activity at room temperature for rac-lactide ring-opening polymerisation, a rather rare feature for aluminium-based catalysts.

A series of chiral-at-metal aluminum complexes have been synthesized using chiral catam ligands. Reactivity studies demonstrate the importance of alkoxide bulkiness and complex chirality in inducing catalyst aggregation. This has been exploited in cyclic ester ring-opening polymerization (ROP). For ε-Cl ROP, enantiopure catalysts were found to outperform a racemic mixture of catalysts, as the racemic mixture resulted in lower activity heterodimeric catalytic species and reduced polymerization rates. In the case of L-LA, one catalyst enantiomer was found to be the most active of the series and outperformed both the other enantiomer and the corresponding achiral catalyst. Very high activities were observed and up to 9,200 equivalents of L-LA were polymerized in 4.5 min at 150 °C with TOF > 100,000 h–1 under industrially relevant conditions. Analysis of the catalyst orders for these reactions provided a meaningful catalyst speciation-activity relationship enabling improved understanding of both catalyst speciation and the activity of each catalytic species involved in cyclic ester ROP using chiral aluminum catalysts.

Several PNP-type diphosphine ligands have been synthesised and characterised, featuring a single or a double N-bridge between the P-donor atoms. PNP ligands 1 and 2 containing diazaphospholane donors have been...