Syntheses of Ring-Fused B−N Heteroaromatic Compounds

3a,7a-Azaborindene (14) has been prepared by two multistep syntheses using the Grubbs ring-closing metathesis from appropriate B-vinyl,N-allyl-aminoboranes. 14 was deprotonated by KN(SiMe₃)₂ to give 3a,7a-azaborindenylpotassium (5). The reaction of 5 with Cp*ZrCl₃ afforded the corresponding Zr(IV) complex 18, which on activation with excess methylaluminoxane, forms a good catalyst for the polymerization of ethylene. The reaction of 5 with methylene chloride and BuLi gave 4a,8a-azaboranaphthalene (6), which is isoelectronic and isostructural with naphthalene. DFT calculations on 6 gave a structure that is in good agreement with X-ray diffraction data.