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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.more » « less
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We report a combined experimental and computational study of Pd/Senphos-catalyzed carboboration of 1,3-enynes utilizing DFT calculations, 31 P NMR study, kinetic study, Hammett analysis and Arrhenius/Eyring analysis. Our mechanistic study provides evidence against the conventional inner-sphere β-migratory insertion mechanism. Instead, a syn outer-sphere oxidative addition mechanism featuring a Pd-π-allyl intermediate followed by coordination-assisted rearrangements is consistent with all the experimental observations.more » « less
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The first aromatic Claisen rearrangement of a 1,2-azaborine is described along with a quantitative kinetic comparison of the reaction of the azaborine with its direct all-carbon analogue. The azaborine A rearranged in a clean, regioselective fashion and reacted faster than the all-carbon substrate B at all temperatures from 140–180 °C. Activation free energies were extracted from observed first-order rate constants (A: Δ G ‡298K = 32.7 kcal mol −1 ; B: Δ G ‡298K = 34.8 kcal mol −1 ) corresponding to a twenty fold faster rate for A at observed reaction temperatures. DFT calculations show that the rearrangement proceeds via a concerted six-membered transition state and that the electronic structure of the BN and CC rings is mostly responsible for the observed regioselectivity and relative reactivity.more » « less
