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Rhodium-Catalyzed Dehydrocoupling of Fluorinated Phosphine–Borane Adducts: Synthesis, Characterization, and Properties of Cyclic and Polymeric Phosphinoboranes with Electron-Withdrawing Substituents at Phosphorus



The dehydrocoupling of the fluorinated secondary phosphine–borane adduct R2PH⋅BH3 (R = p-CF3C6H4) at 60 °C is catalyzed by the rhodium complex [{Rh(μ-Cl)(1,5-cod)}2] to give the four-membered chain R2PH-BH2-R2P-BH3. A mixture of the cyclic trimer [R2P-BH2]3 and tetramer [R2P-BH2]4 was obtained from the same reaction at a more elevated temperature of 100 °C. The analogous rhodium-catalyzed dehydrocoupling of the primary phosphine–borane adduct RPH2⋅BH3 at 60 °C gave the high molecular weight polyphosphinoborane polymer [RPH-BH2]n (Mw = 56 170, PDI = 1.67). The molecular weight was investigated by gel permeation chromatography and the compound characterized by multinuclear NMR spectroscopy. Interestingly, the electron-withdrawing fluorinated aryl substituents have an important influence on the reactivity as the dehydrocoupling process occurred efficiently at the mildest temperatures observed for phosphine–borane adducts to date. Thin films of polymeric [RPH-BH2]n (R = p-CF3C6H4) have also been shown to function as effective negative-tone resists towards electron beam (e-beam) lithography (EBL). The resultant patterned bars were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS).