B. Györi, J. Emri
Oct 26, 1982
Citations
0
Influential Citations
10
Citations
Journal
Journal of Organometallic Chemistry
Abstract
Abstract Several amine-cyano(pyrrolyl)borane complexes [A · BH(NC4H4)CN] containing a chiral boron atom were prepared from the reactions of sodium cyanohydrodipyrrolylborate-tridioxane 1 [NaBH(NC4H4)2CN · 3C4H8O2] with amine hydrochlorides as well as by base exchange from the appropriate 4-cyanopyridine complex [4-CNC5H4N · BH(NC4H4)CN]. Amines with an sp2 N atom give stable complexes of a wide range of basicity (pKa = 0.8−9.7), in contrast to the anines with sp3 hybridized N where only the stronger bases (pKa ⪢ 7.3) are capable of giving stable complexes (mainly secondary and tertiary amines). These compounds undergo hydrolysis in neutral and alkaline media, while in strong acids they give stable boronium ions by protonation at the α-C atom of the pyrrolyl group. The compounds (−)-(S)-α-phenylethylamine-(−)-cyanopyrrolylborane and (+)-(R)-α-phenylethylamine-(+)-cyanopyrrolylborane have been prepared in pure form; in solution they undergo slow epimerization. Treatment of the appropriate complexes with KH has given the chiral boron-containing borates KBH(NC4H4)(CN)X (X = imidazolyl-, pyrazolyl-). Dicyanohydropyrrolylborane was obtained from 4-cyanopyridine-cyanopyrrolylborane and NaCN.