Copper(II) Complexes of a Series of Polypyridine Ligands Possessing a 1,2-Bis(2-pyridyl)ethane Common Moiety: Incorporation and Hydrolysis of Phosphate Esters

Two tetradentate ligands 1,2-bis[2-((dimethylamino)methyl)-6-pyridyl]ethane (L1) and 1,2-bis[2-(N-piperidinomethyl)-6-pyridyl]ethane (L2) and a hexadentate ligand 1,2-bis(2-((methyl(pyridylmethyl)amino)methyl)-6-pyridyl)ethane (L3)
were prepared as part of a series of new polypyridine ligands possessing a 1,2-bis(2-pyridyl)ethane common moiety.
L1 and L2 form mononuclear Cu(II) complexes [Cu(L)(Cl)](ClO4) [L = L1 (1) and L2 (2)], respectively. L3 forms a
dinuclear Cu(II) complex [Cu2(L3)((PhO)2PO2)2](ClO4)2 (3) or a hexanuclear Cu(II) complex [Cu6(L3)3((PhO)PO3)4](ClO4)4 (4) in the presence of (PhO)2PO2- monoanion or (PhO)PO32- dianion, respectively. The structures of 1−4
were determined by X-ray analysis. The structures in solution were investigated by means of FAB and CSI MS
spectrometers. The structural flexibility of the common 1,2-bis(2-pyridyl)ethane moiety and of the pendant groups
allows complexes 1−4 to adapt to the various structures. Each Cu ion in 1 and 2 adopts a square pyramidal
geometry with one Cl ion and two pendant groups (L1 and L2) binding in a bis-bidentate chelate mode. There is
no steric repulsion between the pendant groups, so that the ligands specifically stabilize the mononuclear structures.
L3 binds two Cu(II) ions with two pendant groups in tridentate chelate modes and, with the incorporation of phosphate
esters, various dinuclear units are formed in 3 and 4. In 4, a dinuclear unit of [Cu2(L3)]4+ links two dinuclear units
of [Cu2(L3)(PhOPO3)2] with four μ3-1,3-PhOPO32- bridges. The hydrolytic activity of 2 and a dicopper(II) complex
of L3 was examined with tris(p-nitrophenyl) phosphate (TNP) as a substrate.