Synthetic and structural studies on copper 1H-[1,10]-phenanthrolin-2-one coordination complexes: Isolation of a novel intermediate during 1,10-phenanthroline hydroxylation

The synthesis and crystal structure elucidation of a novel dinuclear heteroleptic copper(II) complex has led to an alternative mechanism in the formation of covalent hydrates. During further studies on the synthesis and properties of [Cu2(ophen)2] (1), a dinuclear complex of copper(I) with 1H-[1,10]-phenanthrolin-2-one (Hophen), two intermediates/alternative products 2 and 3 were isolated. The dinuclear, antiferromagnetic com-plex [Cu2(ophen)2(phen)2]·(NO3)2·9H2O (3, phen= 1,10-phenanthroline) contains two five-coordinate copper(II) ions, both with trigonal-bipyramidal coordination, which are bridged together through deprotonated hydroxyl groups with a Cu-Cu non-bonding distance of 3.100 Å. Complex [Cu(phen)2(H2O)](NO3)2 (2) is a polymorph of a previously reported material. The occurrence of 2 and 3 has led us to propose a variation to the Gillard mechanism for the formation of covalent hydrates in bidentate N-heterocycles in which the attacking nucleophile may be the deprotonated form of 2, [Cu(phen)2(OH)]-, rather than free OH-.