Polylactide and polycaprolactone are both biodegradable polymers produced through metal-catalyzed ringopening polymerization. Foratruly sustainable lifecycle of these polymers it is essential to replace the industrially used cytotoxic catalyst tin(II) bis(2-ethylhexanoate) [Sn(Oct) 2 ]with non-toxic alternatives.Here,wereport the fastest knownrobust catalyst in the polymerization of lactide and e-caprolactone. This zinc guanidine catalyst can polymerize non-purified technical rac-lactide and e-caprolactone in the melt at different [M]/[I] ratios with fast rate constants,high molar masses,and high yields in as hort time,l eading to colorless,t ransparent polymer.Moreover,wereport that polylactide and polycaprolactone produced by zinc-guanidine complexes have favorably high crystallinities.I nf act, the obtained polylactide shows am ore robust degradation profile than its Sn(Oct) 2-catalysed equivalent due to ah igher degree of crystallinity.

The synthesis of the new hybrid guanidine ligands DMEGdmap, DMEGdeae, TMGdmab, DMEGdmab, TMGdeab and DMEGdeab is reported. These ligands were combined with zinc chloride, and the six obtained new complexes were structurally characterised by X-ray crystallography and NMR spectroscopy. Further six new zinc chloride complexes were obtained from the hybrid guanidine ligands TMGdmae, DMEGdmae, TMGdeae, TMGdmap, TMGdeap and TEGdeap. Each of the twelve com- [a]

No abstract

Eight new zinc complexes of bisguanidine ligands have been structurally characterised and tested for the polymerisation of lactide. Initially this necessitated the preparation of the new six bisguanidine ligands [TMG 2 thf, DMEG 2 thf, trans-TMG 2 (1,2)ch, trans-DMEG 2 (1,2)ch, R,R-TMG 2 (1,2)ch, R,R-DMEG 2 (1,2)ch]. With these ligands in hand, zinc chlorido complexes could be obtained, which were characterized by X-ray crystallography and NMR spectroscopy. Furthermore, two new zinc chlorido complexes are reported, based on previous bisguanidine ligands [TMG 2 (1,3)ch, DMEG 2 (1,3)ch]. All complexes show a distorted tetrahedral coordination geometry. These eight complexes are utilised as catalysts in melt polymerization

Guanidines are highly useful ligands which have conquered coordination chemistry within the last 20 years. Their CN 3 moiety allows multiple substitution patterns which enables tailoring them to a large variety of applications, ranging from bioinorganic coordination chemistry via medicinal chemistry to polymerisation catalysis. In bioinorganic chemistry, guanidines gave important stimuli in the modelling of copper type 1, 2 and 3 enzymes. This review provides with a comprehensive overview on complexes which have been reported with neutral guanidine ligands. Peralkylated guanidines as well as bicyclic or more complex guanidine-comprising entities are described in their coordination chemistry with transition and main-group metals. The structural features of the complexes as well as their most prominent features in bioinorganic chemistry or polymerisation catalysis are highlighted. Hereby, the role of the delocalisation of the positive charge within the guanidine unit gained during coordination is discussed in its importance for efficient and robust coordination. The delocalisation within the CN 3 unit can be measured by the structural value ρ which is discussed for numerous systems. The charge delocalisation makes neutral guanidines versatile and efficient for the stabilisation of highly different coordination modes and a large variety of oxidation states.