Contribution to the Reactivity of N,N'-Diaryl-1,4-diazabutadienes Aryl–N=CH–CH=N–Aryl (Aryl = 2,6-Dimethylphenyl; 2,4,6-Trimethylphenyl) Towards Boron Trichloride

Weber L, Förster J, Stammler H-G, Neumann B. Contribution to the Reactivity of N,N'-Diaryl-1,4-diazabutadienes Aryl–N=CH–CH=N–Aryl (Aryl = 2,6-Dimethylphenyl; 2,4,6-Trimethylphenyl) Towards Boron Trichloride. European Journal of Inorganic Chemistry. 2006;2006(24):5048-5056.The reaction of Aryl-N=CH-CH=N-Aryl (3a: Aryl = 2,6-Me2C6H3; 3b: Aryl=2,4,6-Me3C6H2) with 2 equiv. BCl3 in a toluene/hexane mixture at -50 degrees C led to an inseparable mixture of borolium salts [Aryl-N-a=CH-CH=N(Aryl)BCl2(N-a-B)]+BCl4- (4a: Aryl = 2,6-Me2C6H3; 9a: Aryl = 2,4,6-Me3C6H2) and (Aryl-N-a=CH-C(Cl)=N(Aryl)BCl2(N-a-B)+BCl4- (4b: Aryl = 2,6-Me2C6H3; 9b: Aryl = 2,4,6-Me3C6H2) and the bicyclic species [HCa=N(Aryl)BCl2N(Aryl)-C-b=(C-a-C-b)](2) (5: Aryl = 2,6-Me2C6H3; 10: Aryl = 2,4,6-Me3C6H2). Sodium amalgam reduction of borolium. salts 4a,b and 9a,b afforded inseparable mixtures of the diazaboroles 2,6-(Me2C6H3NCH)-C-a=CR-N-b(2,6-Me2C6H3)BCl(N-a-B) (1: R = H; 6: R = Cl) and 2,4,6-(Me3C6H2NCH)-C-a=CR-N-b (2,4,6-Me3C6H2)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. BCl3 in the same solvents at -78 degrees C. The acyclic adducts Cl3BN(Aryl)= CH-CH=N(Aryl)BCl3 (7a: Aryl=2,6-Me2C6H3; 7b: Aryl = 2,4,6-Me3C6H2) were reduced with sodium amalgam to furnish the aminoboranes Cl2BN(Aryl)CH=CH-N(Aryl)BCl2 (8: Aryl = 2,6-Me2C6H3; 12: Aryl = 2,4,6-Me3C6H2). Stirring solutions of 8 and 12 in the presence of CaH2 cleanly gave the diazaboroles I and 2, respectively. The novel compounds were characterized by elemental analyses and H-1-, B-11-, C-13 NMR and mass spectra. The molecular structures of 1, 4a, 5 and 8 were elucidated by single X-ray diffraction analyses. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006