Contributions to the chemistry of boron. Part 194. Synthesis and characterization of mono, bi-, and tri-cyclic boron–nitrogen–sulphur ring systems. Crystal structure of 2,7,9,14-tetrakis(diethylamino)-3,5,6,10,12,13-hexathia-1,8-diaza-2,4,7,9,11,14-hexaboratricyclo[9.3.0.04,8]tetradecane

Abstract

Reactions of the triborylamines N(BX₂)₃(X = Cl or Br) with bis(dimethylboryl)disulphane (2) proceed via 4-dihalogenoboryl-3,5-dihalogeno-1,2,4,3,5-dithiazadiborolidines (3) to 2,8-dihalogeno-3,4,6,7-tetrathia-1-aza-2,5,8-triborabicyclo[3.3.0^1,5]octanes (4a) and (4b). The bromo derivative (4b) reacts with additional (2)(1 : 1 molar ratio) to produce impure NB₃S₆, but with an excess of (2) to yield a tricyclic system NB₄S₆(CH₃). The halogen atoms in (4a) and (4b) can be substituted by methyl groups from Sn(CH₃)₄ as the methylating agent. Amination of compound (4a) with Sn(CH₃)₃[N(C₂H₅)₂] seems to proceed via the bis(diethylamino) derivative, but a new tricyclic system (8) is the final product the structure of which has been determined by X-ray crystallography. U.v. and He I photoelectron spectra support n.m.r. evidence that the bicyclic rings (4) are planar 10π-electron systems. This conclusion is supported by MNDO and PPP calculations.