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)

Abstract

The Pt(I1) complexes [Pt(bpy)(py)2I2+ ( 0 , [Pt(bpy)(Me2N-py)2I2+ (IIL [Pt(Me2-bpy)(py)2I2+ (III), [Pt(bpy)-(en)12+ (W, [PtWebpy-H)(py)2I2+ (V), [ P W e b p y -H)(bpy)I2+ (VI), [Pt(phen)(py)2I2+ (VW, and [Pt(pyhl2+ (VIII) (bpy, 2,2'-bipyridine; py, pyridine; Mebpy -H, N-methyl-2,2'-bipyridinyl-C(3),N'; Me*-bpy, 4,4'-dimethyl-2,2'-bipyridine; Me2N-py, 4-(dimethylamino)pyridine; en, 1 ,Zdiaminoethane; phen, 1,lO-phenanthroline) have been investigated by cyclic voltammetry and where possible by EPR spectroelectrochemistry and by UV-vis-near-IR spectroelectrochemistry. All complexes except VI11 show at least two reversible reductive one-electron processes;VI shows three, and VI11 shows one chemically irreversible process. In all cases, the doubly reduced species showed the characteristic u* -A* 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. We 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 SLUM0 of the unreduced parent species) being perturbed by the presence of metal orbitals. The doubly reduced species, however, are straightforward anion radical complexes of Pt(1).

Luminescent PtII Complexes of Tridentate Cyclometalating 2,5‐Bis(aryl)‐pyridine Ligands

“…Importantly, the initial spectrum cannot be recovered upon re‐reduction, in line with the irreversible character of the CV waves. During the first reduction of 4 and 4a , new long‐wavelength bands, with maxima at 816 and 870 nm, arise that are typical for a pyridine‐based reduction, and the corresponding species are best described as [Pt II (L · 3– )(DMSO)] · – . These absorptions are only slightly redshifted upon a second reduction from 4 · – to 4 2– (Figure ).…”

“…These absorptions are only slightly redshifted upon a second reduction from 4 ·-to 4 2- (Figure 6). In analogy to the complex [Pt(bpy)(Py) 2 ] 2+ and its related derivatives, [37] the rather similar spectra of 4 ·-and 4 2-point to Pt-based second reduction, with the products best described as [Pt…”

“…During the first reduction of 4 and 4a, new long-wavelength bands, with maxima at 816 and 870 nm, arise that are typical for a pyridine-based reduction [37,38] and the corresponding species are best described as [Pt…”

Diruthenium Complexes of p‐Benzoquinone–Imidazole Hybrid Ligands: Innocent or Noninnocent Behavior of the Quinone Moiety

“…[19] Reductiont om onocations should also produce aw eak NIR absorption that was, however, detectedo nly for 2 + ,w hich involves bpy radical anions. [20] Bands in the visible region are assigned differently,d ue to the different electronic structures (Figure 7): 1 + exhibits IL and ligand-to-ligand charget ransfer (LLCT) absorptions between semiquinone and the unreduced bipyridineg roups,w hereas 2 + shows IL and MLCT transitions. [18] Further reduction to neutral 1 was possible, and showed diminishing MLCT absorptions in the visible region, whereas weak IL and LLCT features emerged in the NIR region.…”

Oxidation State Assignments in the Organoplatinum One‐Electron Redox Series [(N^N)PtMes2]n, n = +,0, –,2‐

“…In the historically significant organoplatinum research area the typically common platinum(II) compounds with 5d 8 configuration are of continued interest because of their synthetically useful two‐electron processes, leading to Pt 0 or Pt IV systems . In contrast, one‐electron reactivity to produce genuine mononuclear Pt I or Pt III compounds is rare,, most reversible reductions of Pt II compounds have been shown to lead to Pt II complexes of radical anions exhibiting “noninnocent ligand behavior“ . One‐electron oxidation of Pt II compounds was generally observed to proceed irreversibly, except when axially shielding ligands such as Mes = mesityl = 2,4,6‐trimethylphenyl were employed .…”