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Issue 38, 2010
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The Pd3(dppm)3(CO)n clusters (n = 1−,2−); rare cases of anionic palladium species

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Abstract

Two novel anionic palladium clusters, Pd3(dppm)3(CO)n (Pd3n; n = 1−,2−) were electrochemically generated from the dicationic cluster Pd32+ in 0.2M THF/Bu4NPF6via two first consecutive reversible 1-electron reductions (Pd32+ + 1 ePd3+, −0.210, and Pd3+ + 1 ePd30, −0.470 V vs. SCE) followed by two others at −2.350 (Pd30 + 1 ePd31, reversible) and at −2.690 V vs. SCE (Pd31 + 1 ePd32, irreversible). The chemical stability and instability, respectively, of the Pd3(dppm)3(CO)n clusters (Pd3n; n = 1−,2−) at the time scale of the electrochemical experiments were addressed by DFT computations. Indeed, geometry optimisations (B3LYP) indicate expected Pd–Pd, Pd–P, Pd–C bond length variations, but severe structure distortions are noted for the anions Pd31 and Pd32, including large deviations from the planarity of the Pd3P6 core and for the triangular frame of the Pd3 center. Space filling models indicate that this skeleton distortion places the phenyl-dppm groups above the unsaturated site of the M3 frame hence protecting it from any interactions with substrates, and hence explaining the stability of the Pd31 species. The computed gas phase total energy shows a decrease going from Pd32+ to Pd31+ to Pd30 and to Pd31, but increases going to Pd32 hence corroborating the relative stability of these species and the observed chemical reversibility of the CV waves. Large steps in energy stabilisation going from Pd32+ to Pd31+ to Pd30 is totally consistent with the low reduction potentials associated with these species, but the much smaller steps going from Pd30 to Pd31 and to Pd32 corroborates their much larger reduction potentials. The host–guest behaviour of Pd31 and Pd32 in the presence of the neutral substrate EtO2C–CC–CO2Et (L) and CF3CO2 (X) was examined by CV. From the shifts of the reduction waves, it was possible to demonstrate that Pd32+ and Pd3+ act as host for X but not Pd30, Pd31 and Pd32, whereas Pd32+, Pd3+, Pd30, bind L but Pd31 and Pd32 do not, corroborating evidence for stability but non-reactivity at the same time, particularly for the Pd31 cluster. All in all, these anionic clusters exhibit the lowest oxidation state for palladium species ever investigated.

Graphical abstract: The Pd3(dppm)3(CO)n clusters (n = 1−,2−); rare cases of anionic palladium species

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Publication details

The article was received on 07 Jun 2010, accepted on 07 Aug 2010 and first published on 31 Aug 2010


Article type: Paper
DOI: 10.1039/C0DT00616E
Citation: Dalton Trans., 2010,39, 8976-8981
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    The Pd3(dppm)3(CO)n clusters (n = 1−,2−); rare cases of anionic palladium species

    S. D. Molin, Y. Mugnier, D. Fortin and P. D. Harvey, Dalton Trans., 2010, 39, 8976
    DOI: 10.1039/C0DT00616E

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