文摘

Electrochemical studies of the salts [cat]₄[Pt₂(μ-pop)₄] (cat⁺ = Bu₄N⁺ or PPN⁺ [Ph₃PNPPh₃]⁺; pop = pyrophosphite, [P₂O₅H₂]²⁻) have been carried out in dichloromethane. In agreement with published studies of K₄[Pt₂(μ-pop)₄] in water and [Ph₄As]₄[Pt₂(μ-pop)₄] in acetonitrile, the [Pt₂(μ-pop)₄]⁴⁻ anion is found to undergo an initial one-electron oxidation under conditions of cyclic voltammetry to a short-lived trianion, [Pt₂(μ-pop)₄]³⁻. However, in the more weakly coordinating solvent dichloromethane, [Pt₂(μ-pop)₄]³⁻ appears to undergo oligomerization instead of solvent-induced disproportionation; thus the overall process remains a one-electron reaction rather than an overall two-electron oxidative addition process, even under long time-scale, bulk electrolysis conditions. Chemical oxidation of [cat]₄[Pt₂(μ-pop)₄] with [NO][BF₄] or AgBF₄ gives mainly a dark, insoluble, ill-defined solid that appears to contain Pt(III) according to X-ray photoelectron spectroscopy (XPS). In the case of [NO][BF₄], a second reaction product, an orange solid, has been identified as a nitrosyl complex, [cat]₃[Pt₂(μ-pop)₄(NO)]. The X-ray structure of the PPN⁺ salt shows the anion to consist of the usual lantern-shaped Pt₂(μ-pop)₄ framework with an unusually large Pt−Pt separation [2.8375(6) Å]; one of the platinum atoms carries a bent nitrosyl group [r(N−O) = 1.111(15) Å; (Pt−N−O) = 118.1(12)°] occupying an axial position. The nitrosyl group migrates rapidly on the ³¹P NMR time-scale between the metal atoms at room temperature but the motion is slow enough at 183 K that the expected two pairs of inequivalent phosphorus nuclei can be observed. The X-ray photoelectron (XP) spectrum of the nitrosyl-containing anion confirms the presence of two inequivalent platinum atoms whose 4f_7/2 binding energies are in the ranges expected for Pt(II) and Pt(III); an alternative interpretation is that the second platinum atom has a formal oxidation number of +4 and that its binding energy is modified by the strongly σ-donating NO⁻ ligand. Reduction of [Pt₂(μ-pop)₄X₂]⁴⁻ (X = Cl, Br, I) in dichloromethane corresponds to a chemically reversible, electrochemically irreversible two-electron process involving loss of halide and formation of [Pt₂(μ-pop)₄]⁴⁻, as is the case in more strongly coordinating solvents.