Preparation, reactions, and nuclear magnetic resonance spectra of disubstituted derivatives of the octahydrotriborate(1–) ion, [B3H6XX′]–(X = Cl, X′= Cl, NCS, NCBH3, or NCBH2Cl); molecular structure of [B3H6Cl2]– and partial structure of [B3H6Cl(NCS)]–

Abstract

The preparation of disubstituted derivatives of [B₃H₈]^– with halogen or pseudo-halogen is reported. Ions studied include [B₃H₆Cl₂]^–(1), [B₃H₆Cl(NCS)]^–(2), [B₃H₆Cl(NCBH₃)]^–, and [B₃H₆Cl(NCBH₂Cl)]^–. N.m.r. parameters show that the ions are fluxional in solution, and ¹¹B^–11B coupling is poorly resolved. The thermal stabilities, and chemical and electrochemical behaviour of representative compounds are described. The molecular structures, illustrated by [B₃H₆Cl₂]^– and [B₃H₆Cl(NCS)]^– relate to that of [B₃H₈]^– with trans substituents. Four molecules of [N(PPh₃)₂][B₃H₆Cl₂] crystallise in space group P2₁/c with a= 10.9552(14), b= 12.840(9), c= 24.236(5)Å, and β= 92.298(13)°. R= 0.0728 for 3 267 data measured at room temperature. The [B₃H₆Cl₂]^– ion has effective C₂ symmetry and markedly asymmetric H bridges. [N(PPh₃)₂][B₃H₆Cl(NCS)] crystallises from CH₂Cl₂ as a 1 :1 solvate with Z= 2 in space group P, with a= 11.2855(22), b= 14.4000(21), c= 15.708(4)Å, α= 120.680(17), β= 109.760(18), and γ= 65.971 (14)° at 185 ± 1 K. An approximate structure solution affords R= 0.1922 for 5 706 diffraction data.