Boron-Nitrogen Analogues of Cyclobutadiene, Benzene and Cyclooctatetraene

Abstract

Abstract Iminoboranes RB [tbnd] NR′, isoelectronic with alkynes, cyclooligomerize to give B-N rings (RBNR′)n that are either analogues of cyclobutadienes (n = 2) or benzenes or Dewar benzenes (n = 3) or cyclooctatetraenes (n = 4), depending on the ligand set R/R′ and on conducting the oligomerization either thermally or catalytically. Cyclodimers and cyclotetramers may either undergo reversible interconversions or cyclotetramers are formed irreversibly from cyclodimers. The (4+2) cycloaddition of cyclodimers and iminoboranes yields cyclotrimers. Cyclotrimers may thermally be converted into cyclodimers, and poly(iminoboranes), isoelectronic with polyalkynes, can thermally be depolymerized into cyclotrimers. nido-Cluster derivatives of N2B4H6, arachno-cluster derivatives of N2B3H7, four-membered rings N2B2R3R′, or five-membered rings N2B3R4R′ are isolated, when three-membered rings NB2R3, isoelectronic with cyclopropenyl cations, either dimerize or add aminoboranes H2B=NR′2 or insert nitrenes R′N (from R′N3) or insert iminoboranes R′B [tbnd] NR into the B-B bond, respectively.