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

The reaction of the dimeric diethyl ether solvated lithium amide, bis[{2-(6 -methyl)pyridyl}trimethylsilylamidolithium dietherate], with two equivalent s of arsenic(III) trichloride in diethyl ether affords the amido arsenic di chloride compound [{2-(6-Me)C5H3N}NSiMe3(AsCl2)] (1), while four equivalent s 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 report ed 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 gem inal AsCl2 groups. One arsenic centre has pyramidal geometry with the other four-coordinate arsenic centre having distorted trigonal bipyramidal geome try with the putative lone pair of electrons occupying an equatorial positi on. Homoleptic triamido-antimony and -bismuth complexes are prepared from t he 2 : 3 stoichiometric reaction of MCl3 (M = Sb, Bi) and dimeric lithium a mide. The amide nitrogen centres are coordinated fac to the metal centre wi th 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 g ives the molecule a distorted octahedral shape with a non-crystallographic C-3 axis.