STABILIZATION OF TRIS(TRIFLUOROMETHYL)BORANE IN COMPLEXES WITH PRIMARY, SECONDARY AND TERTIARY-AMINES - CRYSTAL AND MOLECULAR-STRUCTURE OF (CF3)3B.NHET2 AND (CF3)3B.NH2ET

Various adducts (CF3)3B·NHR1R2 of the unknown free Lewis acid tris(trifluoromethyl)borane with secondary amines have been prepared from Cl2BNR1R3 by nucleophilic trifluoromethylation with CF3Br P(NEt2)3 and subsequent protonation: R1R2Me (I), R1R2Et (II), R1 + R2C5H10 (III), R1R2cyclo-C6H11 (IV), R1Me, R2CH2Ph (V), R1Me, R2t-Bu (VI). The primary amine derivatives (CF3)3B·NH2R1, R1Et (VII) and Me (VIII), have been isolated as by-products in the preparations of II and VI, respectively. Reactions of I, II and VII with KOH yield the corresponding salts K[(CF3)3B·NMe2] (IX), K[(CF3)3B·NEt2] (X) and K[(CF3)3B·NHEt] (XI). IX and X react with CH3I, CH3OSO2CF3 and allyl bromide to yield the tertiary amine adducts (CF3)3B·NR1R2R3, R1R2R3Me (XII), R1R2Me, R3C3H5 (XIII), R1R2Et, R3Me (XIV), R1R2Et, R3C3H5 (XV). The structure of II and VII were determined by an X-ray diffraction study. The strength of the BN bonds in these compounds is reflected in their comparatively short average length (1.592(5) Å). The BC bond lengths average 1.614(4) Å, and variations of the bond angles are consistent with considerable F strain in the adducts. © 1990.