Catalytic Synthesis, Characterization, and Properties of Polyaminoborane Homopolymers and Random Copolymers

Abstract

Polyaminoboranes, [RNH–BH2] n , are boron–nitrogen analogues of polyolefins: however, to date, few soluble, well-characterized examples have been described. Herein, we show that metal-catalyzed dehydrocoupling of N-alkylamine–boranes Ph­(CH2) x NH2·BH3 (x = 2–4) with pendant aryl groups yields soluble polyaminoboranes [Ph­(CH2) x NH–BH2] n , using skeletal nickel, [Rh­(μ-Cl)­(1,5-COD)]2 (COD = cyclooctadiene), and [IrH2(POCOP)] (POCOP = κ3-1,3-(OPtBu2)2C6H3) as precatalysts in THF. Application of the most efficient catalytic system (1 mol %, [IrH2(POCOP)], THF, −40 °C) enabled the isolation of high molar mass, soluble polyaminoborane [Ph­(CH2)4NH–BH2] n in moderate (ca. 40%) yield. Structural characterization was achieved by multinuclear nuclear magnetic resonance, infrared, and elemental analysis; and the molar mass was determined to be high (M n > 10 000 g mol–1) by gel permeation chromatography, dynamic light scattering, and, for comparison, also 1H diffusion-ordered spectroscopy methods. The optimized dehydropolymerization conditions for the Ir catalyst were also used to prepare copolymers from mixtures of Ph­(CH2)4NH2·BH3 with either MeNH2·BH3, Ph­(CH2)2NH2·BH3, or NH3·BH3. Significantly, soluble copolymers containing ca. 67% of [NH2–BH2] repeat units were prepared. The thermal stability of the polyaminoborane homopolymers and copolymers was studied by thermogravimetric analysis. The use of a cross-linker, H3B·NH2(CH2)8NH2·BH3, in the dehydropolymerization reactions led to improved ceramic yields after pyrolysis indicating that, with appropriate structural design, polyaminoboranes may be of potential future interest as precursors of boron-based ceramics.

Uncatalyzed Formation of Polyaminoboranes from Diisopropylaminoborane and Primary Amines: a Kinetically Controlled Polymerization Reaction

“…Well‐resolved spectra were obtained and PABs I‐R (R=Et, Pr, Bu, Et/Bu (1/1), Et/Pr (1/2), Allyl) were fully characterized. In the 1 H NMR, they all exhibit a broad singlet at δ 2.5–3.0 ppm for the NH group (SI‐Figure S1, S6, S10, S14, S17 and S18) in agreement with the NMR data reported so far for this family of polymer [2k] …”

“…To date, this family of BN polymers remains relatively underdeveloped. While catalytic routes should offer interesting prospects for the efficient and tailored synthesis of polyaminoboranes (Scheme 1A), the polymerization process predominantly depends on the catalyst system [2a–l] . In terms of functionality, limitations are imposed by the compatibility between the catalyst, mostly based on late transition metals, and the nitrogen functional group of the amine‐borane substrate.…”

Thermal Dehydrogenation and Hydrolysis of BH3NH3 Catalyzed by Cyclic (Alkyl)(amino)carbene Iridium Complexes under Mild Conditions

“…The products of AB thermal dehydrogenation were characterized by 11 B NMR (Figure ) and FT-IR (Figure S39). On comparison with the literature, ,, the thermal dehydrogenation products were confirmed to be cyclotriborazane (CTB), borazine, and polyborazylene (PB), and no polyaminoborane was observed. , …”

High Molar Mass Poly(alkylphosphinoboranes) via Iron-Catalyzed Dehydropolymerization

“…Because only the low molar mass fraction of the oligomeric material ([RPH–BH 2 ] x , where x ≤ 34) could be detected by ESI-MS, the DP n obtained using this method is significantly lower than that obtained by GPC, which reveals the entire molar mass distribution. ESI-MS is known to underestimate the molecular weight of polyphosphinoboranes and polyaminoboranes when compared to GPC measurements. ,,,, It is worth noting that matrix-assisted laser desorption/ionization time-of-flight MS was unsuccessful for the analysis of polyphosphinoborane samples even after attempts with a range of different matrices (see Supporting Information for details).…”

“…ESI-MS is known to underestimate the molecular weight of polyphosphinoboranes and polyaminoboranes when compared to GPC measurements. 23,37,50,61,62 It is worth noting that matrix-assisted laser desorption/ionization time-of-flight MS was unsuccessful for the analysis of polyphosphinoborane samples even after attempts with a range of different matrices (see Supporting Information for details).…”