Ring-Opening Metathesis Polymerization of the Dewar Isomer of 1,2-Azaborinine, a B–N Isostere of Benzene

Abstract

The successful polymerization of the Dewar isomer of an azaborinine heterocycle is reported. Controlled ring-opening metathesis polymerization was accomplished with Grubbs and Hoveya−Grubbs second generation catalysts (G2, HG2), as well as a Z-selective Ru catalyst (HGM2001). The structure of the polymers containing 4-membered B−N heterocycles was verified by GPC and multinuclear and 2D NMR. Differences in stereochemistry of polymers derived from G2/HG2 versus the Z-selective catalyst HGM2001 were substantiated by 2D NOESY, FT-IR, and Raman analyses. The incorporation of B−N heterocycles into these polymer structures is promising as a route to functional polymers that contain polar side groups.

Facile Energy Release from Substituted Dewar Isomers of 1,2‐Dihydro‐1,2‐Azaborinines Catalyzed by Coinage Metal Lewis Acids

“…[6] The Dewar isomers of 1,2-dihydro-1,2-azaborinines were employed by Liu and co-workers for the synthesis of aminoborylated cyclobutanes, [8] while Liu, Jäkle and coworkers achieved polymers containing the 1,2-azaboretidine ring from these monomers. [9] Yet, the efficient and controlled energy release, a decisive characteristic of a successful MOST system, has received limited attention. The only catalyst able to trigger the cycloreversion of BND1 was reported to be Wilkinson's catalyst.…”

A BN-Benzvalene

“…In collaboration with the Bettinger group, we discovered that 1,2-azaborine undergoes a clean photoisomerization to BN-Dewar benzene upon UV light irradiation ( hv > 280 nm) . Subsequently, the BN-Dewar benzene species has been investigated as potential molecular solar thermal fuels, , new synthetic building blocks for 1,2-aminoborylated cyclobutane derivatives, and as a monomer for ring-opening metathesis polymerization . During our investigation of the photochemistry of 1,2-azaborines, we discovered that a C5-aryl-functionalized 1,2-azaborine (with N -TBS and B -Mes substitution) produced the BN-benzvalene isomer in addition to the BN-Dewar isomer upon photolysis (Scheme ).…”