Bipyridine-type Ligands Research Articles

Electrochemistry and spectroelectrochemistry (EPR, UV-visible-near-IR) of platinum(II) 2,2'-bipyridine and ring-metalated bipyridine complexes: PtII(L-) and PtI(L-) but not PtI(L)

The Pt(II) complexes [Pt(bpy)(py)[sub 2]][sup 2+] (I), [Pt(bpy)(Me[sub 2]N-py)[sub 2]][sup 2+] (II), [Pt(Me[sub 2]-bpy)(py)[sub 2]][sup 2+] (III), [Pt(bpy)(en)][sup 2+] (IV), [Pt(Mebpy-H)(py)[sub 2]][sup 2+] (V), [Pt(Mebpy-H)(bpy)][sup 2+] (VI), [Pt(phen)(py)[sub 2]][sup 2+] (VII), and [Pt(py)[sub 4]][sup 2+] (VIII) (bpy, 2,2[prime]-bipyridine; py, pyridine; Mebpy-H, N-methyl-2,2[prime]-bipyridinyl-C(3),N[prime]; Me[sub 2]-bpy, 4,4[prime]-dimethyl-2,2[prime]-bipyridine; Me[sub 2]N-py, 4-(dimethylamino)pyridine; en, 1,2-diaminoethane; phen, 1,10-phenanthroline) have been investigated by cyclic voltammetry and where possible by EPR spectroelectrochemistry and by UV-vis-near-IR spectroelectrochemistry. All complexes except VIII show at least two reversible reductive one-electron processes; VI shows three, and VIII shows one chemically irreversible process. In all cases, the doubly reduced species showed the characteristic [pi][sup *] [yields] [pi][sup *] UV-vis-near-IR absorptions of the ligand anion radicals. For the singly reduced species, EPR spectra show the added electron to be localized on the bipyridine-type ligand. However, the UV-vis-near-IR spectra of these species are not typical of ligand-based reduction products, and the potentials are less negative than expected for such a process. The authors conclude that the singly reduced species are best formulated as containing Pt(II), with the semioccupied and/or the lowest unoccupied ligand orbitals (corresponding to the LUMO and SLUMO of the unreduced parent species) being perturbed by the presence of metal orbitals. The doublymore » reduced species, however, are straightforward anion radical complexes of Pt(I).« less