Mononuclear, dinuclear and hydroxo-bridged tetranuclear complexes from reactions of CuII ions, mandelic acid and diimine ligands

The reaction of copper(II) hydroxocarbonate, mandelic acid (H(2)MANO) and 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) in water affords [Cu(bpy)(mu(2)-MANO)](2) center dot 8H(2)O (1), [Cu(bpy)(MANO)] center dot 4H(2)O (2) and the opened tetranuclear hydroxo-bridged copper(II) complexes of formulae [CU4(mu(3)-OH)(2)(mu(2)-MAN-O)(2)(bpy)(4)](phglyo)(2) center dot 8H(2)O (3) (phglyo=phenylglyoxylate) or [CU4(mu(3)-OH)(2)(mu(2)-OH)(2)(OH2)(2)(phen)(4)] (Bza)(2)(OH)(2) center dot 5H(2)O (4) (Bza = benzoate), respectively. The compounds have been characterized by spectroscopic techniques and studied by single-crystal X-ray diffractometry. The formation of 3 and 4 takes place in basic media through dehydrogenation or oxidative dehydrogenation followed by in situ oxidative decarboxylation of mandelic acid to phenylglyoxylate or benzoate, respectively. These results indicate that cooperative catalysis of diimine ancillary ligands and copper(H) is essential. (c) 2008 Elsevier Ltd. All rights reserved.