Syntheses and X-ray structures of boraamidinate complexes of lithium, phosphorus, and tellurium

Abstract

The dilithiated boraamidinate complexes {Li₂[RB(N-t-Bu)₂]}₂ (1a, R = Ph; 1b, R = t-Bu), prepared by the reaction of B[N(H)-t-Bu]₃ with three equivalents of LiR, are shown by X-ray crystallography to have dimeric structures consisting of a distorted Li₄N₄ cube capped on two opposite faces by RB units. Reactions of 1a with TeCl₄ or PX₃ (X = Cl, Br) yielded complexes PhB(μ-N-t-Bu)₂TeCl₂ (2) and PhB(μ-N-t-Bu)₂PX (4a, X = Cl; 4b, X = Br), respectively. The structures of 2 and 4b were determined by X-ray crystallography. In the solid state, complex 2 forms a dimer with weak Te···Cl contacts (3.2411(6) Å). Complex 4b is monomeric with a P—Br bond length of 2.3047(11) Å. The reactions of 2 and 4a with the appropriate amounts of Li[N(H)-t-Bu] produce the monomeric tellurium imide PhB(μ-N-t-Bu)₂Te=N-t-Bu and the amido derivative PhB(μ-N-t-Bu)₂PN(H)-t-Bu (4c), respectively. The X-ray structure of 4c was determined. Deprotonation of 4c with n-BuLi produces the dimeric monolithium derivative {Li[PhB(μ-N-t-Bu)₂PN-t-Bu]}₂ (5), which was shown by X-ray crystallography to have a centrosymmetric structure with a central transoid Li₂N₂ ring.Key words: boraamidinates, lithium, tellurium, phosphorus, X-ray structures.