Synthetic and Structural Investigations of Monomeric Dilithium Boraamidinates and Bidentate NBNCN Ligands with Bulky N-Bonded Groups

Article abstract of DOI:10.1021/ic0352755

The dilithiated boraamidinate complexes [Li₂{PhB(NDipp) ₂}(THF)₃] (7a) (Dipp = 2,6-diisopropylphenyl) and [Li ₂{PhB(NDipp)(N^tBu)}(OEt₂)₂] (7b), prepared by reaction of PhB[N(H)Dipp][N(H)R′] (6a, R′ = Dipp; 6b, R′ = ^tBu) with 2 equiv of ⁿBuLi, are shown by X-ray crystallography to have monomeric structures with two terminal and one bridging THF ligands (7a) or two terminal OEt₂ ligands (7b). The derivative 7a is used to prepare the spirocyclic group 13 derivative [Li(OEt ₂)₄][In{PhB(NDipp)₂}₂] (8a) that is shown by an X-ray structural analysis to be a solvent-separated ion pair. The monoamino derivative PhBCl[N(H)Dipp] (9a), obtained by the reaction of PhBCl₂ with 2 equiv of DippNH₂, serves as a precursor for the synthesis of the four-membered BNCN ring {[R?N(H)](Ph)-B(μ-N ^tBu)₂CⁿBu} (10a, R? = Dipp). The X-ray structures of 6a, 9a, and 10a have been determined. The related derivative 10b (R? = ^tBu) was synthesized by the reaction of {Cl(Ph)B(u-N^tBu)₂CⁿBu} with Li[N(H) ^tBu] and characterized by ¹H, ¹¹B, and ¹³C NMR spectra. In contrast to 10a and 10b, NMR spectroscopic data indicate that the derivatives {[DippN(H)](Ph)B(NR′) ₂CR(NR′)} (11a: R = ^tBu, R′ = Cy; 11b: R = ⁿBu, R′ = Dipp) adopt acyclic structures with three-coordinate boron atoms. Monolithiation of 10a produces the novel hybrid boraamidinate/ amidinate (bamam) ligand {Li[DippN]PhB(N^tBu)CⁿBu(N ^tBu)} (12a).