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 PhN 3 , and its azidosilation by Me 3 SiN 3 are described. The coordination compounds (OC) 4 Cr[(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.