Synthetic and structural investigations of monomeric dilithium boraamidinates and bidentate NBNCN ligands with bulky N-bonded groups

The dilithiated boraamidinate complexes Li(2)PhB(NDipp)(2)](THF)(3)] (7a) (Dipp = 2,6-diisopropylphenyl) and Li(2)PhB(NDipp)(N(t)Bu)](OEt(2))(2)] (7b), prepared by reaction of PhBN(H)Dipp]N(H)R'] (6a, R' = Dipp; 6b, R' = (t)Bu) with 2 equiv of (n)BuLi, are shown by X-ray crystallography to have monomeric structures with two terminal and one bridging THF ligands (7a) or two terminal OEt(2) ligands (7b). The derivative 7a is used to prepare the spirocyclic group 13 derivative Li(OEt(2))(4)]InPhB(NDipp)(2)](2)] (8a) that is shown by an X-ray structural analysis to be a solvent-separated ion pair. The monoamino derivative PhBClN(H)Dipp] (9a), obtained by the reaction of PhBCl(2) with 2 equiv of DippNH(2), serves as a precursor for the synthesis of the four-membered BNCN ring R'N(H)](Ph)B(mu-N(t)Bu)(2)C(n)Bu] (10a, R' = Dipp). The X-ray structures of 6a, 9a, and 10a have been determined. The related derivative 10b (R' = (t)Bu) was synthesized by the reaction of Cl(Ph)B(mu-N(t)Bu)(2)C(n)Bu] with LiN(H)(t)Bu] and characterized by (1)H, (11)B, and (13)C NMR spectra. In contrast to 10a and 10b, NMR spectroscopic data indicate that the derivatives DippN(H)](Ph)B(NR')(2)CR(NR')] (11a: R =( t)Bu, R' = Cy; 11b: R = (n)Bu, R' = Dipp) adopt acyclic structures with three-coordinate boron atoms. Monolithiation of 10a produces the novel hybrid boraamidinate/amidinate (bamam) ligand LiDippN]PhB(N(t)Bu)C(n)Bu(N(t)Bu)] (12a).