Abstract
The reaction of Aryl–N=CH–CH=N–Aryl (3a: Aryl = 2,6‐Me~2~C~6~H~3~; 3b: Aryl = 2,4,6‐Me~3~C~6~H~2~) with 2 equiv. BCl~3~ in a toluene/hexane mixture at –50 °C led to an inseparable mixture of borolium salts [Aryl–N^a^=CH–CH=N(Aryl)BCl~2~(N^a^–B)]^+^BCl~4~^–^ (4a: Aryl = 2,6‐Me~2~C~6~H~3~; 9a: Aryl = 2,4,6‐Me~3~C~6~H~2~) and [Aryl–N^a^=CH–C(Cl)=N(Aryl)BCl~2~(N^a^–B)]^+^BCl~4~^–^ (4b: Aryl = 2,6‐Me~2~C~6~H~3~; 9b: Aryl = 2,4,6‐Me~3~C~6~H~2~) and the bicyclic species [HC^a^=N(Aryl)BCl~2~N(Aryl)–C^b^=(C^a^–C^b^)]~2~ (5: Aryl = 2,6‐Me~2~C~6~H~3~; 10: Aryl = 2,4,6‐Me~3~C~6~H~2~). Sodium amalgam reduction of borolium salts 4a,b and 9a,b afforded inseparable mixtures of the diazaboroles 2,6‐Me~2~C~6~H~3~N^a^CH=CR–N^b^(2,6‐Me~2~C~6~H~3~)BCl(N^a^–B) (1: R = H; 6: R = Cl) and 2,4,6‐Me~3~C~6~H~2~N^a^CH=CR–N^b^(2,4,6‐Me~3~C~6~H~2~)BCl(N^a^–B) (2: R = H; 11: R = Cl). In order to obtain pure 1 and 2, diazabutadienes 3a and 3b were slowly combined with 2 equiv. BCl~3~ in the same solvents at –78 °C. The acyclic adducts Cl~3~BN(Aryl)=CH–CH=N(Aryl)BCl~3~ (7a: Aryl = 2,6‐Me~2~C~6~H~3~; 7b: Aryl = 2,4,6‐Me~3~C~6~H~2~) were reduced with sodium amalgam to furnish the aminoboranes Cl~2~BN(Aryl)CH=CH–N(Aryl)BCl~2~ (8: Aryl = 2,6‐Me~2~C~6~H~3~; 12: Aryl = 2,4,6‐Me~3~C~6~H~2~). Stirring solutions of 8 and 12 in the presence of CaH~2~ cleanly gave the diazaboroles 1 and 2, respectively. The novel compounds were characterized by elemental analyses and ^1^H‐, ^11^B‐, ^13^C NMR and mass spectra. The molecular structures of 1, 4a, 5 and 8 were elucidated by single X‐ray diffraction analyses. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)