TY - JOUR
T1 - Electrochemical and Chemical Oxidation of [Pt 2(μ- pyrophosphite) 4] 4 Revisited
T2 - Characterization of a Nitrosyl Derivative, [Pt 2(/K-pyrophosphite) 4(NO)] 3"
AU - Bennett, Martin A.
AU - Bhargava, Suresh K.
AU - Bond, Alan M.
AU - Bansal, Vipul
AU - Forsyth, Craig M.
AU - Guo, Si Xuan
AU - Privér, Steven H.
PY - 2009/3/16
Y1 - 2009/3/16
N2 - Electrochemical studies of the salts [cat] 4[Pt 2(μ-pop) 4] (cat + = Bu 4N + or PPN + [Ph 3P=N=PPh 3] +; pop = pyrophosphite, [P 2O 5H 2] 2-) have been carried out in dichloromethane. In agreement with published studies of K 4[Pt 2(μ-pop) 4] in water and [Ph 4As] 4[Pt 2(μ-pop) 4] in acetonitrile, the [Pt 2(μ-pop) 4] 4- anion is found to undergo an initial one-electron oxidation under conditions of cyclic voltammetry to a short-lived trianion, [Pt 2(μ-pop) 4] 3-. However, in the more weakly coordinating solvent dichloromethane, [Pt 2(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[Pt 2(μ-pop) 4] with [NO][BF 4] or AgBF 4 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][BF 4], a second reaction product, an orange solid, has been identified as a nitrosyl complex, [cat] 3[Pt 2(μ-pop) 4(NO)]. The X-ray structure of the PPN + salt shows the anion to consist of the usual lantern-shaped Pt 2(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 [Pt 2(μ-pop) 4X 2] 4- (X = Cl, Br, I) in dichloromethane corresponds to a chemically reversible, electrochemically irreversible two-electron process involving loss of halide and formation of [Pt 2(μ-pop) 4] 4-, as is the case in more strongly coordinating solvents.
AB - Electrochemical studies of the salts [cat] 4[Pt 2(μ-pop) 4] (cat + = Bu 4N + or PPN + [Ph 3P=N=PPh 3] +; pop = pyrophosphite, [P 2O 5H 2] 2-) have been carried out in dichloromethane. In agreement with published studies of K 4[Pt 2(μ-pop) 4] in water and [Ph 4As] 4[Pt 2(μ-pop) 4] in acetonitrile, the [Pt 2(μ-pop) 4] 4- anion is found to undergo an initial one-electron oxidation under conditions of cyclic voltammetry to a short-lived trianion, [Pt 2(μ-pop) 4] 3-. However, in the more weakly coordinating solvent dichloromethane, [Pt 2(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[Pt 2(μ-pop) 4] with [NO][BF 4] or AgBF 4 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][BF 4], a second reaction product, an orange solid, has been identified as a nitrosyl complex, [cat] 3[Pt 2(μ-pop) 4(NO)]. The X-ray structure of the PPN + salt shows the anion to consist of the usual lantern-shaped Pt 2(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 [Pt 2(μ-pop) 4X 2] 4- (X = Cl, Br, I) in dichloromethane corresponds to a chemically reversible, electrochemically irreversible two-electron process involving loss of halide and formation of [Pt 2(μ-pop) 4] 4-, as is the case in more strongly coordinating solvents.
UR - http://www.scopus.com/inward/record.url?scp=64349099333&partnerID=8YFLogxK
U2 - 10.1021/ic802213v
DO - 10.1021/ic802213v
M3 - Article
SN - 0020-1669
VL - 48
SP - 2593
EP - 2604
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 6
ER -