Stability and C–H Bond Activation Reactions of Palladium(I) and Platinum(I) Metalloradicals: Carbon-to-Metal H‑Atom Transfer and an Organometallic Radical Rebound Mechanism

One-electron oxidation of palladium(0) and platinum(0) bis­(phosphine) complexes enables isolation of a homologous series of linear d9 metalloradicals of the form [M­(PR3)2]+ (M = Pd, Pt; R = tBu, Ad), which are stable in 1,2-difluorobenzene (DFB) solution for >1 day at room temperature when part...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2023-06, Vol.145 (25), p.14087-14100
Main Authors: Krämer, Tobias, Gyton, Matthew R., Bustos, Itxaso, Sinclair, Matthew J. G., Tan, Sze-yin, Wedge, Christopher J., Macgregor, Stuart A., Chaplin, Adrian B.
Format: Article
Language:English
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Summary:One-electron oxidation of palladium(0) and platinum(0) bis­(phosphine) complexes enables isolation of a homologous series of linear d9 metalloradicals of the form [M­(PR3)2]+ (M = Pd, Pt; R = tBu, Ad), which are stable in 1,2-difluorobenzene (DFB) solution for >1 day at room temperature when partnered with the weakly coordinating [BArF 4]− (ArF = 3,5-(CF3)2C6H3) counterion. The metalloradicals exhibit reduced stability in THF, decreasing in the order palladium­(I) > platinum­(I) and PAd3 > PtBu3, especially in the case of [Pt­(PtBu3)2]+, which is converted into a 1:1 mixture of the platinum­(II) complexes [Pt­(PtBu2CMe2CH2)­(PtBu3)]+ and [Pt­(PtBu3)2H]+ upon dissolution at room temperature. Cyclometalation of [Pt­(PtBu3)2]+ can also be induced by reaction with the 2,4,6-tri-tert-butylphenoxyl radical in DFB, and a common radical rebound mechanism involving carbon-to-metal H-atom transfer and formation of an intermediate platinum­(III) hydride complex, [Pt(PtBu2CMe2CH2)H(PtBu3)]+, has been substantiated by computational analysis. Radical C–H bond oxidative addition is correlated with the resulting MII–H bond dissociation energy (M = Pt > Pd), and reactions of the metalloradicals with 9,10-dihydroanthracene in DFB at room temperature provide experimental evidence for the proposed C–H bond activation manifold in the case of platinum, although conversion into platinum­(II) hydride derivatives is considerably faster for [Pt­(PtBu3)2]+ (t 1/2 = 1.2 h) than [Pt­(PAd3)2]+ (t 1/2 ∼ 40 days).
ISSN:0002-7863
1520-5126
DOI:10.1021/jacs.3c04167