Construction of Two Discrete Molecular High-Nuclearity Copper(II) Complexes as Heterogeneous Catalysts for Oxidative Coupling Polymerisation of 2,6-Dimethylphenol

Reaction of a rigid conjugated clamp-like multi-pyridine ligand N,N'-bis(pyridin-3-yl)-2,6-pyridinedicarboxamide (H2L) with CuSO4 center dot 5H(2)O or Cu(OAc)(2) resulted in the formation of two high-nuclearity, discrete molecular copper(II) complexes, namely [Cu-10(H2L)(5)(SO4)(8)(mu(3)-OH)(4)(H2O)(2)]center dot 4CH(3)-CH2OH center dot 7H(2)O (1) and [Cu-6(L)(4)(CH3COO)(4)]center dot 2DMF center dot 6H(2)O (2). In 1, ten copper atoms are engaged by five H2L ligands, eight SO42- and four mu(3)-OH groups to form a novel decanuclear copper complex which sits on a crystallographic twofold axis passing through the centre of the complex. The structure of 2 features a hexanuclear copper cage and a crystallographic centre of inversion is at the mid-point of the compound. The rigid conjugated clamp-like H2L ligands, polydentate in nature, form a "coordination pocket" arising from their "arms" to entrap the copper atoms and play an important role in the assembly of discrete molecular high-nuclearity complexes 1 and 2. Applications of 1 and 2 as heterogeneous catalysts for the oxidative polymerisation of 2,6-dimethylphenol showed very promising results at ambient temperature and these novel catalytic systems are very mild, efficient, regioselective and easily recyclable. The interesting catalytic properties of 1 and 2 can be attributed to their particular structural characteristics and their unusual reactivities based on cooperativity or electron transfer between multicopper centres. Magnetic studies of these copper(II) cages indicate antiferromagnetic behaviour. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)