63 research outputs found
Salt additives as activity boosters: a simple strategy to access heterometallic cooperativity in lactide polymerisation
Incorporating Sodium to Boost the Activity of Aluminium TrenSal Complexes towards <i>rac</i>âLactide Polymerisation
Lithium HalfâSalen Complexes: Synthesis, Structural Characterization and Studies as Catalysts for <i>rac</i>âLactide RingâOpening Polymerization
Heterometallic cooperativity in divalent metal ProPhenol catalysts: combining zinc with magnesium or calcium for cyclic ester ring-opening polymerisation
In Situ Versus Isolated Zinc Catalysts in the Selective Synthesis of Homo and Multi-block Polyesters
To Be or Not To Be⊠Cooperative? Trimetallic Catalysts for the RingâOpening Polymerisation of Cyclic Esters
Multimetallic catalysts have emerged as a promising route to enhance catalyst performance in cyclic ester ring-opening polymerisation (ROP), as these complexes can outperform the monometallic analogues in terms of reactivity and/or polymerisation control. Such enhancements are often attributed to âmultimetallic cooperativityâ, yet the origins of this cooperativity often remain unclear. Here, we report the synthesis and characterisation of two trimetallic Al-salen complexes (L1(AlMe)3 and L1(AlEt)3), containing three Al-salen subunits in close proximity, and their monometallic analogues (L2(AlMe) and L2(AlEt)). These complexes have been applied as catalysts for cyclic ester ROP under a range of conditions, to probe their potential for cooperative behaviour. Trimetallic L1(AlMe)3 and L1(AlEt)3 both display high activities in rac-lactide ROP, giving kobs values of up to 11 x 10-3 min-1. Yet careful benchmarking against the monometallic complexes reveals that whether these systems display multimetallic cooperativity or not depends upon the reaction conditions. Detailed kinetic and spectroscopic studies into the origins of cooperativity revealed that the neighbouring metals play a key role in the initiation step, rather than propagation. Overall, these studies highlight the importance of understanding the reaction conditions in order to accurately define whether a catalyst displays multimetallic cooperativity
Electron rich salen-AlCl catalysts as efficient initiators for the ring-opening polymerisation of rac-lactide
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