Reactivity of Pd3(dppm)3(CO) n+ and Pd3(dppm)3(CO)(RCCR) n+ (n = 0, +1, +2) Towards F−. Evidence of Reactive Intermediates and X-Ray Structure of [Pd3(dppm)3(MeO2CC≡CCO2Me)(F)]PF6
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The reactivity of the trinuclear palladium cluster [Pd3(dppm)3(CO)] n+ (dppm = bis(diphenylphosphinomethane); n = 2, 1) towards F− was investigated by electrochemical and spectroscopic methods. The reaction depends on the charge of the cluster. The chemical reduction of the cluster dication is observed in the presence of F− generating the paramagnetic monocationic cluster. Spin-trapping experiments with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) provided evidence for the radical F• as an intermediate. In a similar manner to the dication, the monocationic cluster [Pd3(dppm)3(CO)]+ is also reduced, but in a slower process, by the F− ion to produce [Pd3(dppm)3(CO)]0. Additionally, the alkyne cluster adducts [Pd3(dppm)3(CO)(RCCR)] n+ (n = 2, 1; R = CO2Me) are also reactive towards F−. Particularly, the dication adduct leads to a metastable fluoride adduct [Pd3(dppm)3(CO)(RCCR)(F)]+. The electroreductive behavior of this adduct involves electron-transfer steps and F− exchange equilibriums, for which digital simulation enables the extraction of the thermodynamic parameters (standard potentials and equilibrium constants). Concurrently, the monocation adduct [Pd3(dppm)3(CO)(RCCR)]+ with F−, leads to a disproponation generating 0.5 equiv. of [Pd3(dppm)3(CO)(RCCR)(F)]+ and 0.5 equiv. of [Pd3(dppm)3(CO)(RCCR)]0. The former slowly evolves to [Pd3(dppm)3(RCCR)(F)]+, which was described by X-ray diffraction method.
KeywordsCluster Palladium Fluoride Alkyne Molecular electrochemistry
Financial support by the Natural Sciences and Engineering Research Council (Canada), Centre National de Recherche Scientifique (CNRS, UMR 5260) and Université de Bourgogne (France) is gratefully acknowledged.
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