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 phosphineborane adduct (R2PHBH3)-B-. (R = p-CF3C6H4) at 60 degrees C is catalyzed by the rhodium complex [{Rh(g-Cl)(1,5-cod)}(2)] to give the four-membered chain R2PH-BH2-R(2)p-BH3. A mixture of the cyclic trimer [R(2)p-BH2], and tetramer [R2P-BH2](4) was obtained from the same reaction at a more elevated temperature of 100 degrees C. The analogous rhodium-catalyzed dehydrocoupling of the primary phosphine-borane adduct (RPH2BH3)-B-. at 60 degrees C gave the high molecular weight polyphosphinoborane polymer [RPH-BH2](n) (M-W = 56170, 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).