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
Résumé
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. © 2010 Springer Science+Business Media, LLC.