Synthesis, Characterization, and Properties of the Polyphosphinoboranes [RPH−BH₂]_n(R = Ph,iBu,p-nBuC₆H₄,p-dodecylC₆H₄):  Inorganic Polymers with a Phosphorus−Boron Backbone

Abstract

The polyphosphinoboranes [PhPH−BH2] n (1), [iBuPH−BH2] n (2), [(p-nBuC6H4)PH−BH2] n (3), and [(p-dodecylC6H4)PH−BH2] n (4) were prepared from the corresponding phosphine−borane adducts RPH2·BH3 (R = Ph, iBu, p-nBuC6H4, p-dodecylC6H4) via a rhodium-catalyzed dehydrocoupling procedure at elevated temperatures (ca. 90−130 °C). Samples of polymers 1 and 2 and the new materials 3 and 4 were characterized by multinuclear NMR spectroscopy, and the molecular weights were determined by light scattering methods in THF or CH2Cl2 solutions. The absolute weight-average molecular weight of 2 was determined by static light scattering and found to be M w = 13 100, and values of M w of ca. 20 000 were estimated for the sample of polymers 1 and the new material 3 using dynamic light scattering (DLS). The molecular weights of polymers 3 and 4 were also analyzed by gel permeation chromatography using polystyrene standards, and values up to M w = ca. 80 000, M n = ca. 10 000 were determined for 3 and M w = ca. 168 000, M n = ca. 12 000 for 4. The chemical stability of 1 in THF toward HNEt2 or nBu3P was demonstrated using NMR spectroscopy and DLS analysis, which indicated that no significant polymer degradation occurred. WAXS analysis of 1 and 3 showed that the polymers are amorphous. The glass transition temperatures (T g) of polymers 2, 3, and 4 were analyzed by DSC and were detected at ca. 5, 8, and −1 °C, respectively. TGA analysis on 1−3 revealed T 5% values (temperature for which 5% or the weight is lost) of 240 °C for 1 and ca. 150−160 °C for 2 and 3. After heating to 1000 °C, ceramic yields in the range of 35−80% were obtained. The high ceramic yield for 1 (75−80%) indicates that this material is of interest as a pyrolytic precursor to boron phosphide-based solid-state materials.

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

“…[26] The 19 F NMR resonance for 5 at d À62.5 ppm differs slightly from that of monomer 2 (d À63.7 ppm). As previously reported for other polyphosphinoboranes, [15,16] polymer 5 is also air-and moisture-stable in the solid state.…”

“…[15,16] The synthesis of these polymers was most effectively achieved using rhodium (pre)catalysts [{Rh(m-Cl) ( B NMR spectroscopy that in the absence of Rh catalyst, the reactions are very slow and yield poorly defined oligomeric materials that appear to have branched structures. [15] To investigate whether aryl-substituted monomers bearing electronegative groups are indeed more reactive than those previously studied, we synthesized and investigated the para-substituted phosphine-borane adducts (p-CF 3 C 6 H 4 ) 2 PH·BH 3 1 and (p-CF 3 C 6 H 4 )PH 2 ·BH 3 2.…”

“…[18] The electronic nature of the substituents at phosphorus in phosphine-borane adducts might be expected to significantly influence both the rate of dehydrocoupling and the polymer properties. The observation that the catalytic dehydrocoupling of PhPH 2 ·BH 3 and Ph 2 PH·BH 3 is more facile compared with that of iBuPH 2 ·BH 3 and iBu 2 PH·BH 3 [16] as well as tBu 2 PH·BH 3 [19] is likely associated with differences in the polarity of the PÀH bonds. The strong (+)-inductive effect of the alkyl group attached to phosphorus is expected to decrease the polarity of the P-H functionality, which in turn, would be anticipated to render the bond less reactive for catalytic dehydrocoupling with B d + ÀH dÀ bonds.…”

“…The strong (+)-inductive effect of the alkyl group attached to phosphorus is expected to decrease the polarity of the P-H functionality, which in turn, would be anticipated to render the bond less reactive for catalytic dehydrocoupling with B d + ÀH dÀ bonds. [16] Conversely, the presence of electron withdrawing substituents on phosphorus would be expected to make metal-catalyzed dehydrocoupling reactions more favourable. Furthermore, the presence of the fluorinated substituents would represent a significant new structural variation for polyphosphinoboranes as this would be expected to introduce additional useful properties.…”

Coordination of Boron‐centered Lewis Acids by organo‐substituted Phosphanylboranes

“…However, due to the nearly non-polar P-H bonds, [6] the catalytic dehy-drocoupling routes depend on electron withdrawing effects from aryl groups on phosphorus, resulting in a limited substrate scope. The only examples of poly(alkylphosphinoboranes) (alkyl = electron donating group) with a moderate molar mass were prepared by dehydrocoupling of iBuPH 2 ·BH 3 [7] and FcCH 2 PH 2 ·BH 3 . [8] Our group is especially interested in the synthesis and reactivity of Lewis base stabilized phosphanylboranes of the type R 2 P-BH 2 ·NMe 3 (R = H, alkyl, aryl).…”