Doubly pyridazine-bridged macrocyclic complexes of copper in+1,+2 and mixed valent oxidation states

Transmetallation of the dilead(II) complex [Pb-2(L1 ')](ClO4), [L1 ' is the (4 + 4) Schiff-base macrocycle derived from 3,6-diformylpyridazine and 1,3-diaminopropane] with copper(II) perchlorate results in the formation of a dicopper(II) complex of the (2 + 2) Schiff-base macrocycle L1, Cu-2(11)(L1)(ClO4)(4) (1), Copper(II) is unable to template the formation of 1 from the organic precursors. A series of six dicopper(II) complexes of L1 has been prepared from 1, including: [Cu-2(11)(L1)X-2](ClO4)(2) (where X = Cl- 2, Br- 3, I- 4, NCS- 5), Cu-2(11)(L1)(H2O)(2)(NO3)(2)(CLO4)(2) (6) and Cu-2(11)(L1)(H2O)(2)(ClO4)(4) (7). Three of these dicopper(II) complexes, 1(.)2MeCN, 2(.)H10 and 7, have been characterised by X-ray crystaflography. In all three cases the (2 + 2) macrocycle provides a double pyridazine bridge between the two copper(II) ions. Magnetic studies show that the double pyridazine bridge mediates strong antiferromagnetic exchange between the copper(II) ions in all of these complexes (- 2J= 412 to 532 cm (-1)), Electrochemical and spectroelectrochemical studies reveal that reduction of the dicopper(II) complexes occurs in two one electron steps. via stable mixed valent intermediates (K-c = 3.8 x 10(5) to 8.6 x 10(6) in acetonitrile, MeCN), in marked contrast to all previously studied pyridazine-bridged dicopper complexes. The thiocyanate salt of the mixed valent complex, [(CuCu1)-Cu-11(L1)(NCS)(4)Cul]MeCN (9), has been isolated, by transmetallation of [Pb-2(L1 ')](ClO4)(4) with copper(I) followed by the addition of NaNCS, and structurally characterised. Finally, the previously reported grid complex, [Cu-4(1)(L1)(2)](PF6)(4) (10) [formed by templating L1 formation on copper(I) ions], is shown by NMR spectroscopy to exist in equilibrium with another species, presumed to be a dicopper(I) complex, [Cu-2(1)(L1)(MeCN)(2)](PF6)(2) (11), in acetonitrile solution. In support of this assignment, the structure of the dicopper(I) complex, [Cu-2(1)(L1)(PPh3)(2)](PF6)(2) (12), isolated from reaction of 10 with two equivalents of PPh3, is reported. (C) 2001 Elsevier Science B.V. All rights reserved.