Dicopper(II) complexes of a phenolate-hinged ditopic ligand with solvent-derived ancillary ligands bound at the potentially dimetallic exogenous site

Copper complexes based on the [Cu-2(bpbp)](3+) core (bpbp(-) = 2,6-bis((N,N '-bis-(2-picolyl)amino)methyl)-4-tertbutylphenolate) containing methoxide o r water ancillary ligands, [Cu-2(bpbp)(OCH3)](ClO4)(2) (1), [Cu-2(bpbp)(OH2 )(2)](ClO4)(3) (2) and Cu-2(bpbpH)(OH2)(4)(ClO4)(4) (3), were isolated from methanol-water solutions above pH 3, between pH 2-3, and below pH 2; respe ctively. ESR and magnetochemistry reveal that the copper ions are antiferro magnetically (J = - 156 cm(-1)) and weakly ferromagnetically (J = + 5.3 cm( -1)) coupled in the doubly-bridged 1 and its singly-bridged pseudo acid con gener 2, respectively. They are uncoupled in 3, consistent with each copper atom being bound only by an amine and two pyridine donors of bpbpH and oxy gen donors of water and/or perchlorate. Thus the phenol residue of the dinu cleating ligand is protonated and uncoordinated. Further, the ESR spectra s how that complexes 1, 2 and 3 retain their integrity in solution. ESI mass spectra demonstrate that, as expected, the cations are labile in solution. However, the patterns that emerge support the formulations; numerous ions c ontaining the [Cu-2(bbpp)](3+) core plus water, hydroxide and methoxide lig ands are observed. The intensities of the more protonated species increase in the spectra going from complex 1 to 3. The only complex to give a molecu lar ion for the intact cation was 1, and only from methanol solutions. Howe ver, the dominant ion observed in the mass spectra of 1 is [Cu-2(bpbp)(OH)] (2+) from all solvents tried. Thus in solution, the methoxide complex, 1, i s in equilibrium with the isoelectronic hydroxide complex, [Cu-2(bpbp)(OH)] (ClO4)(2), with the latter favored. Complex 1 was used to provide a labile preformed core for bridge replacement reactions, and the acetate and pyrazo late complexes, [Cu-2(bpbp)(CH3CO2)](ClO4)(2) (4) and [Cu-2(bpbp)(C3H3N2)]( ClO4)(2) (5), were prepared in this manner. (C) 2000 Elsevier Science Ltd. All rights reserved.