Geminal arsa(III)amide and trisubstituted antimony and bismuth amides from the sterically hindered, N-functionalised amido ligand [{2-(6-Me)C5H3N}NSiMe3]−

Abstract

The reaction of the dimeric diethyl ether solvated lithium amide, bis[{2-(6-methyl)pyridyl}trimethylsilylamidolithium dietherate], with two equivalents of arsenic(III) trichloride in diethyl ether affords the amido arsenic dichloride compound [{2-(6-Me)C₅H₃N}NSiMe₃(AsCl₂)] (1), while four equivalents of arsenic(III) trichloride in diethyl ether gives the complex [{2-(6-Me)C₅H₃N}N(AsCl₂)₂] (3) through the cleavage of the N–Si bond. This compound is also isolated from the redistribution reaction of the previously reported compound [{2-(6-Me)C₅H₃N}NAsCl]₂ (2) with two equivalents of AsCl₃ in toluene. The crystal structure of (3) shows it to be monomeric with two geminal AsCl₂ groups. One arsenic centre has pyramidal geometry with the other four-coordinate arsenic centre having distorted trigonal bipyramidal geometry with the putative lone pair of electrons occupying an equatorial position. Homoleptic triamido–antimony and –bismuth complexes are prepared from the 2∶3 stoichiometric reaction of MCl₃ (M = Sb, Bi) and dimeric lithium amide. The amide nitrogen centres are coordinated fac to the metal centre with each ligand chelating the metal giving it six-fold coordination. The M–N(amide) bonds are much shorter than the M–N(pyridyl) bonds, suggestive of a putative lone pair of electrons intersecting the [N(pyr)]₃ plane. This gives the molecule a distorted octahedral shape with a non-crystallographic C₃ axis.