Structure of copper 4-(n,n- dimethylamino)pyridine complexes and their catalytic activity in the oxidative coupling of 2,6-dimethylphenol |
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| Institution: | 1. Division of Translational Alzheimer Neurobiology, Department of Neurobiology Care Sciences and Society, Center for Alzheimer Research, Karolinska Institutet, Stockholm, Sweden;2. Division of Clinical Geriatrics, Department of Neurobiology Care Sciences and Society, Center for Alzheimer Research, Karolinska Institutet, Stockholm, Sweden;3. Department of Geriatric Medicine, University of Oslo, Oslo, Norway;4. Department of Geriatric Medicine, Karolinska University Hospital Huddinge, Stockholm, Sweden;5. Department of Pathology, University of Helsinki, Helsinki, Finland;6. Division of Pathology, Department of Laboratory Medicine, Karolinska University Hospital Huddinge, Stockholm, Sweden;7. Department of Chemistry, Uppsala University, Uppsala, Sweden;1. Guangzhou University of Chinese Medicine, Guangzhou, 510405, China;2. Department of Spinal Surgery, The First Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, 510405, China;3. The First Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, 510405, China;4. Laboratory Affiliated to National Key Discipline of Orthopaedic and Traumatology of Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou, 510405, China |
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| Abstract: | The oxidative coupling of 2,6-dimethylphenol (DMP) by copper complexes of 4-(N,N)-dimethylamino)pyridine (DMAP) has been studied. Catalytic experiments were carried out in which the DMAP-to-copper ratio and the amount and nature of the copper counter ions were varied. Supporting UV and EPR experiments were performed, and it was concluded that both dinuclear and mononuclear complexes are catalytically active, the mononuclear species being the more active. In solution both species are in equilibrium with one another. The mono/di ratio can be increased by addition of extra DMAP ligands. An excess of coordinating counter-ions increases the amount of dinuclear species. However, a few coordinating counterions are inevitable, and the catalytically most active species was found to be ‘Cu(DMAP)4Cl(OH)’, the role of Cl− probably being that of a bridging counter-ion promoting the formation of dinuclear Cu(I) complexes for the reoxidation step. The DMAP ligands are coordinated to Cu(II) through the pyridine N-atoms, as was determined by X-ray analysis. The Cu(II)DMAP complexes are catalytically active even without initial hydroxide addition. It is believed that the strongly basic DMAP ligands produce some hydroxide from traces of water present in the reaction medium. The species ‘Cu(DMAP)4Cl(OH)’ proved to be able to produce relatively high molecular weight polyphenylene oxide (PPO) in short time and with good specificity ( >95%). |
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