Dehydropolymerisation of Methylamine Borane and an N‐Substituted Primary Amine Borane Using a PNP Fe Catalyst

Abstract

Dehydropolymerisation of methylamine borane (H 3 B⋅NMeH 2 ) using the well‐known iron amido complex [(PNP)Fe(H)(CO)] (PNP=N(CH 2 CH 2 P i Pr 2 ) 2 ) ( 1 ) gives poly(aminoborane)s by a chain‐growth mechanism. In toluene, rapid dehydrogenation of H 3 B⋅NMeH 2 following first‐order behaviour as a limiting case of a more general underlying Michaelis–Menten kinetics is observed, forming aminoborane H 2 B=NMeH, which selectively couples to give high‐molecular‐weight poly(aminoborane)s (H 2 BNMeH) n and only traces of borazine (HBNMe) 3 by depolymerisation after full conversion. Based on a series of comparative experiments using structurally related Fe catalysts and dimethylamine borane (H 3 B⋅NMe 2 H) polymer formation is proposed to occur by nucleophilic chain growth as reported earlier computationally and experimentally. A silyl functionalised primary borane H 3 B⋅N(CH 2 SiMe 3 )H 2 was studied in homo‐ and co‐dehydropolymerisation reactions to give the first examples for Si containing poly(aminoborane)s.

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).…”

“…Inorganic macromolecules containing p-block elements are of increasing interest as new materials with properties that can show key differences from those of hydrocarbon-based polymers. − For example, polymers that feature boron in the main chain have attracted attention as precursors to high-performance ceramic materials and as optoelectronic and sensory materials. − Catalytic dehydrocoupling of primary amine–borane adducts RNH 2 ·BH 3 , where environmentally benign molecular dihydrogen is the only byproduct, − has been developed as a route to high molar mass polyaminoboranes [RNH–BH 2 ] n , which are isoelectronic inorganic analogues of polyolefins. These materials possess interesting potential applications as piezoelectrics , and as precursors to BN ceramics. − Analogous high molar mass aryl P-substituted polyphosphinoboranes [RPH–BH 2 ] n (R = Ph or para-substituted aryl) were initially prepared through catalytic P–B bond formation via dehydropolymerization reaction involving primary phosphine–boranes RPH 2 ·BH 3 assisted by Rh-based precatalysts at 90–130 °C under melt conditions. − The temperature of dehydropolymerization can be lowered to 60 °C when activated adducts substituted with electron-withdrawing perfluorinated aryl groups are used .…”

Calix[4]pyrrolato Aluminate Catalyzes the Dehydrocoupling of Phenylphosphine Borane to High Molar Weight Polymers

“…In the dehydropolymerization of amine boranes, a series of Fe, Ru, Co, and Rh complexes bearing PNP‐pincer ligands were found to operate by metal–ligand cooperative bond activation [15] . Indeed, high catalytic activity and the high molar mass of the polymers could be traced back to MLC [16] . Despite these promising results, the MLC concept has never been transferred to the more challenging dehydropolymerization of phosphine boranes.…”

“…[15] Indeed, high catalytic activity and the high molar mass of the polymers could be traced back to MLC. [16] Despite these promising results, the MLC concept has never been transferred to the more challenging dehydropolymerization of phosphine boranes.…”