Ringerweiterungs- und -verengungsreaktionen bei BN-Vier- und -Sechsringen / Expansion and Contraction Reactions with BN Four- and Six-Membered Rings

Abstract

By the addition of iminoboranes RB≡NR′ (1a—d) to the corresponding diazadiboretidines (RBNR′)2 (2a—d), a ring expansion is observed, borazines (RBNR′)3 (3a—d) being formed. The particular iminoborane iPrB≡NiPr (la) can be added to the diazadiboretidines 2c—g to give borazines B3N3R2R′2iPr2 with an unsymmetrical set of ligands. From PhB=NtBu (1j) and (PhBNtBu)2 (2j), the Dewar borazine 3j′ is formed, which crystallizes in the space group P2,/c. The diazadiboretidines 2b—i, the borazines 3b—d,f, and the Dewar borazine 3e′ are split into the corresponding iminoboranes RB≡NtBu at 500-600 °C in the gas phase. The molten borazines 3b—d,f and Dewar borazines 3e′, j′ are contracted to the corresponding diazadiboretidines 2b—f, j at 160-320 °C. [Ligands R/R′: iPr/iPr (a), Me/tBu (b), Et/tBu (c), Pr/tBu (d), ¡Pr/ tBu (e), Bu/tBu (f), iBu/tBu (g), tBu/tBu (h), tBu(Me3Si)N/tBu (i), Ph/tBu (j).]