Since the disclosure that manganese complexes of certain azamacrocyclic ligands were potent low-temperature bleaching catalysts, considerable effort has focussed on their development towards the efficient catalytic oxidation of other substrates, principally with the environmentally benign oxidant H(2)O(2). These efforts have resulted in a broad substrate scope for the system, including alkenes (to give both epoxides and cis-diols as potential products), alcohols, sulfides and C-H oxidation. Additional developments include the heterogenisation of catalytic systems as well as the first generation of enantiomerically pure ligand systems for application in asymmetric epoxidation catalysis. To date there has only been modest success in this regard, but as our understanding of the nature of the active oxidant(s) continues to develop it is likely that there will be viable applications for these systems in the near future.

Investigations have been undertaken into the synthesis of chiral derivatives of 1,4,7-triazacyclononane and 1,7-diaza-4-oxacyclononane that incorporate the C 2 -symmetric (R,R)-1,2-diaminocyclohexane backbone. The target ligands 17a and 17b have been prepared as their hydrochloride salts, the latter of which has been characterized by single crystal X-ray diffraction revealing an extensively hydrogen bonded polymeric network in the solid state. These investigations have shown that the formation of the fused bicyclic system in these ligands via standard Richman-Atkins macrocyclisation conditions is extremely difficult, particularly for the intermediate 16a, when three tosyl amide nitrogen atoms must be accommodated in the macrocyclic ring. In addition to these target ligands the unexpected piperazine 15 as well as the novel binucleating ligand 19 have also been prepared. Preliminary investigation into the coordination chemistry of 17b resulted in the formation of the copper() complex [Cu(17b)Cl 2 ] in which the copper centre exists in the expected square-pyramidal geometry with the two chloride ions and the nitrogen donors occupying the equatorial positions and with the oxygen donor apically situated. The complex has been screened for activity and found to be a potent catalyst for two hetero-Diels-Alder reactions. The first aza-Diels-Alder reaction of imine 20 with Danishefsky's diene 21 proceeds to yield the cycloadduct 22 in 94% yield. The second nitroso-Diels-Alder reaction relies on the in situ oxidation of hydroxylamine 23 to dienophile 24, catalysed by the complex in the presence of tert-butyl hydroperoxide, which is then trapped as cycloadduct 25 by cyclohexadiene in 69% yield. † Based on the presentation given at Dalton Discussion No.

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