Dehydropolymerization of Amine−Boranes using Bis(imino)pyridine Rhodium Pre‐Catalysis: σ‐Amine−Borane Complexes, Nanoparticles, and Low Residual‐Metal BN−Polymers that can be Chemically Repurposed

Abstract

The sigma amine‐borane complexes [Rh(L1)(h2:h2H3B·NRH2)][OTf] (L1 = 2,6‐bis‐[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine, R = Me, Et, nPr) are described, alongside [Rh(L1)(NMeH2)][OTf]. Using R = Me as the pre‐catalyst (1 mol%) the dehydropolymerization of H3B·NMeH2 gives [H2BNMeH]n selectively. Added NMeH2, or the direct use of [Rh(L1)(NMeH2)][OTf], is required for initiation of catalysis, which is suggested to operate through formation of a neutral hydride complex, Rh(L1)H. The formation of small (1‐5 nm) nanoparticles is observed during catalysis, but studies are ambiguous as to whether the catalysis is solely nanoparticle promoted or if there is a molecular homogeneous component. [Rh(L1)(NMeH2)][OTf] is shown to operate at 0.025 mol% loadings on a 2 g scale to give polyaminoborane [H2BNMeH]n [Mn = 30,900 g/mol, Ð = 1.8] that can be purified to a low residual [Rh] (6 µg/g). Addition of Na[N(SiMe3)2] to [H2BNMeH]n results in selective depolymerization to form the eee‐isomer of N,N,N‐trimethylborazane [H2BNMeH]3: the chemical repurposing of a main‐group polymer.

Tetramerization of BEB-Doped Phenalenyls to Obtain (BE)8-[16]Annulenes (E = N, O)

“…Another powerful tool is doping the carbonaceous skeleton with other p-block elements, in particular, the replacement of C­(sp 2 )­C­(sp 2 ) pairs with their B­(sp 2 )­N­(sp 2 ) isosters . While CC/BN isosterism has been exploited for decades to create (polycyclic) aromatic hydrocarbons with novel chemical and optoelectronic properties, the respective structurally defined, soluble BN analogs of polyacetylenes, poly­(iminoborane)­s [B(R)N(R’)] n ( C , Figure ), have only become available since 2016 through the pioneering work of Helten and co-workers . Even rarer are (BN) n /2 -[ n ]­annulenes, of which Bettinger’s (BN) 4 -cycle D is arguably the most prominent representative (Figure ).…”