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

The dilithiated boraamidinate complexes {Li 2 [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 Li 4 N 4 cube capped on two opposite faces by RB units. Reactions of 1a with TeCl 4 or PX 3 (X = Cl, Br) yielded complexes PhB( -N-t-Bu) 2 TeCl 2 ( 2 ) and PhB( -N-t-Bu) 2 PX ( 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( -N-t-Bu) 2 Te=N-t-Bu and the amido derivative PhB( -N-t-Bu) 2 PN(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( -N-t-Bu) 2 PN-t-Bu]} 2 ( 5 ), which was shown by X-ray crystallography to have a centrosymmetric structure with a central transoid Li 2 N 2 ring.Key words: boraamidinates, lithium, tellurium, phosphorus, X-ray structures.