Die Cyclodimerisierung der Alkyl(tert-butylimino)borane / The Cyclodimerisation of Alkyl(tert-butylimino)boranes

Abstract

Iminoboranes RB = NtBu (R = Me, Et, Pr; 1a-c) undergo a catalytic cyclodimerisation to 2a-c at -10 to -20 °C, but a thermal cyclotrimerisation to 3a-c at 50 °C. The cyclodimer 2a and the cyclotetramer 4a (R = Me) are reversibly transformed into each other at 20 to 70 °C. The cyclodimer 2d (R = Bu), kinetically stable with respect to the cyclotrimer 3d, yields 3d when reacted with the monomer 1d . The ethyloboration of the new monomer 1a , its cycloaddition with PhN3, and its azidosilation by Me3SiN3 are described. The coordination compounds (OC)4Cr[(RBNtBu)2] (9a-c) are formed from Cr(CO)5(THF) or from Cr(CO)4(COD) either with 1a-c or with 2a-c.