Geminal arsa(in)amide and trisubstituted antimony and bismuth amides from the sterically hindered, yV-functionalised amido ligand {2-(6-Me)C₅H₃N}NSiMe₃r

The reaction of the dimeric diethyl ether solvated lithium amide, bis[{2-(6-methyl)pyridyl}trimethylsilylamidolithium dietherate], with two equivalents of arsenic(ni) trichloride in diethyl ether affords the amido arsenic dichloride compound [{2-(6-Me)C5H3N}NSiMe3(AsCi2)] (1), while four equivalents of arsenic(m) 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 AsQ2 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 MC13 (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.