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

Abstract

The dehydrocoupling of the fluorinated secondary phosphine-borane adduct R2PH.BH3 (R = p-CF3C6H4) at 60 degrees C is catalyzed by the rhodium complex [{Rh(mu-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 degrees C. The analogous rhodium-catalyzed dehydrocoupling of the primary phosphine-borane adduct RPH2.BH3 at 60 degrees 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).

Transition‐Metal‐Catalyzed Dehydrocoupling: A Convenient Route to Bonds between Main‐Group Elements

“…[40] Significantly, the catalytic dehydrocoupling temperature of 60 8C for the conversion of 6 to 9 is much lower than that previously reported for the conversions of 3 a to 4 a (90-130 8C for 6 h) and 3 b to 4 b (120 8C for 15 h). [33] This demonstrates the significant influence of changing the substituent at phosphorus in the phosphane-borane adduct on the reaction conditions.…”

“…With this in mind, the catalytic dehydrocoupling of fluoroaryl-substituted phosphane-borane adducts (p-CF 3 C 6 H 4 ) 2 PH·BH 3 (5) and (p-CF 3 C 6 H 4 )PH 2 ·BH 3 (6) was studied with the aim of accessing milder reaction temperatures. [40] This approach was successful, as the Rhcatalyzed dehydrocoupling of 5 at 60 8C in the absence of solvent afforded the linear dimer R 2 PH-BH 2 -PR 2 -BH 3 (R = p-CF 3 C 6 H 4 ) 7, while at 100 8C the cyclic species [{R 2 P-BH 2 } 3 ] 8 a and [{R 2 P-BH 2 } 4 ] (R = p-CF 3 C 6 H 4 ) 8 b (Figure 4) were obtained. [40] The temperatures required for all of these transformations are 20-30 8C lower than that of the corresponding dehydrocoupling of Ph 2 PH·BH 3 .…”

Electronic and bite angle effects in catalytic C–O bond cleavage of a lignin model compound using ruthenium Xantphos complexes

“…2-Phenoxy-1-phenylethanol, 1 6,7-bis(diphenyl- proceedures. [4][5][6][7][8] All reagents were purchased from commercial suppliers and used as received, unless otherwise noted. NMR spectra were obtained on a Bruker AVANCE III 500 spectrometer.…”

Reactions of Amine– and Phosphane–Borane Adducts with Frustrated Lewis Pair Combinations of Group 14 Triflates and Sterically Hindered Nitrogen Bases

“…[33,34] Other Group 13-15 Lewis acid-Lewis base adducts such as phosphane-borane adducts have also been shown to undergo metal-catalyzed dehydrogenation to yield linear or cyclic oligomers or highmolecular-weight polymers. [35][36][37][38] Led by key discoveries by Stephan and co-workers, much recent interest has focused on the metal-free activation of small molecules by exploiting the reactivity of mixtures containing sterically encumbered Lewis acids and bases. [39] tions for which dehydrogenation reaction times are longer, detectable quantities of [H 2 B(µ-H)(µ-NMe 2 )BH 2 ] (14) are observed.…”