Li, Na, K and Ca complexes capable of rac-lactide polymerization in both the melt and in solution were synthesized. MALDI-TOF MS showed mainly cyclic PLA was obtained even in the presence of an alcohol co-initiator.

The hitherto most realistic low-molecular-weight analogue for the 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO) is reported. The ACCOs 2-His-1-carboxylate iron(II) active site was mimicked by a TpFe moiety, to which the natural substrate ACC could be bound. The resulting complex [Tp(Me,Ph) FeACC] (1), according to X-ray diffraction analysis performed for the nickel analogue, represents an excellent structural model, featuring ACC coordinated in a bidentate fashion-as proposed for the enzymatic substrate complex-as well as a vacant coordination site that forms the basis for the first successful replication also of the ACCO function: 1 is the first known ACC complex that reacts with O2 to produce ethylene. As a FeOOH species had been suggested as intermediate in the catalytic cycle, H2 O2 was tested as the oxidant, too, and indeed evolution of ethylene proceeded even more rapidly to give 65 % yield.

The L-cysteine derived N2S2 ligand precursor H2L and its nickel(ii) complex L2Ni2 were investigated with respect to their behaviour in contact with electrophilic and nucleophilic methylation reagents (H2L = (N,N'-dimethyl-(2R,5R)-bis-(sulfanylmethyl)-piperazine). Treatment of deprotonated L(2-) with MeI led to the selective methylation of the thiolate groups thus generating a novel potential ligand, Me2L, which is neutral and contains two thioether donors. The coordinating properties of Me2L were demonstrated by the synthesis of a first nickel(ii) complex: reaction with NiBr2 led to a mononuclear complex 2 where all donor atoms coordinate to the nickel ion, which completes its octahedral coordination sphere by the two bromide ligands. If, however, the complex [LNi]2 (1) is treated with MeI only one thiolate function per ligand moiety is methylated, while the other one remains a thiolate. This leads to [MeLNi](+) complex metal fragments, which trimerize including a μ3-bridging iodide ion to give the compound 3 that was tested with regards to ACS reactivity. While it behaved inert towards CO, attempts to replace the bridging iodide ligand by methyl units in reactions with nucleophilic methylation reagents led to a product, which could not be identified but reacted with CO. Work-up showed that this protocol had converted the thiolate function of MeL(-) into a thioester function, which corresponds to an ACS-like reactivity.

Das bislang realistischste niedermolekulare Analogon für die 1-Aminocyclopropan-1-carbonsäure-Oxidase (ACCO) wird beschrieben. Das aktive Zentrum der ACCO, bestehend aus einer 2-His-1-Carboxylateisen(II)-Spezies, wurde durch eine Tp-Eisen-Einheit nachgeahmt, welche in der Lage ist, ACCz ub inden. Der resultierende Komplex [Tp Me,Ph FeACC] (1) [7] Nach wie vor bleiben also viele Fragen zur Substratwechselwirkung,z ur Rolle verschiedener Kofaktoren/Kosubstrate (Ascorbinsäure,D isauerstoff und Kohlendioxid) und zum Katalysemechanismus unbeantwortet.Bioanorganische Modellstudien kçnnen wertvolle Informationen über strukturelle Parameter sowie auch über Voraussetzungen für die enzymatische Reaktivität liefern. Dennoch sind bislang kaum Verbindungen bekannt, die manunter der Minimalvoraussetzung,dass sie ACCenthalten und eine nennenswerte ACCO-ähnliche Reaktivität besitzen -als ACCO-Modelle betrachten kçnnte. [8,9] Ein Eisen-Komplex ist bekannt, der jedoch zweikernig ist, Eisen(III)-Ionen enthält und zwei verbrückende ACC-Liganden aufweist.[