Transition Metal Complexes of Phosphinous Acids Featuring a Quasichelating Unit: Synthesis, Characterization, and Hetero-bimetallic Complexes

Diorganophosphane oxides were employed as preligands for the synthesis of catalytically active transition metal complexes of the phosphinous acids (CF₃)₂POH and (C₂F₅)₂POH. Their reactions with solid PtCl₂ and PdCl₂ led to the formation of mononuclear phosphinous acid complexes [Cl₂M­{P­(R^f)₂OH}₂] (M = Pd, Pt; R^f = C₂F₅, CF₃), which can be crystallized, for example, as its pyridinium salts, 2­[HPy]⁺[Cl₂Pd­{P­(CF₃)₂O}₂]^2–. In vacuo HCl is liberated from the neutral palladium complexes affording mixtures of di- and polynuclear complexes. Moreover, (C₂F₅)₂POH was reacted with several β-diketonato complexes of palladium, platinum, and nickel yielding air- and moisture-stable complexes [(acac)­M­{[P­(R^f)₂O]₂H}], featuring a quasichelating phosphinous acid phosphinito unit {P­(R^f)₂O···H···O­(R^f)₂P}⁻. Treatment of [Ni­(Cp)₂] (Cp = cyclopentadienyl) and [(cod)­RhCl]₂ (cod = 1,5-cyclooctadiene) with (C₂F₅)₂POH leads to the substitution of one Cp or chloro ligand by a quasichelating unit. The novel coordination compounds were characterized by NMR and IR spectroscopies, mass spectrometry, and X-ray diffraction analysis. The platinum complex [(acac)­Pt­{[P­(C₂F₅)₂O]₂H}] (acac = acetylacetonato) was used for the construction of hetero-bimetallic complexes by the treatment with [(cod)­RhCl]₂ and [Ni­(Cp)₂]. The trinuclear bimetallic complex [{(acac)­Pt­[P­(C₂F₅)₂O]₂}₂Ni] is the first structurally characterized hetero-bimetallic species containing a bis­(perfluoroalkyl)­phosphinito bridge.