Monomeric boron and tin(II) heterocyclic derivatives of 1,8-diaminonaphthalenes: Synthesis, characterization and X-ray structures

The reaction of the diaminonaphthalene dilithium salt (THF) ₂Li₂[(NSiMe₃)₂C₁₀H ₆] with BX₃ (X = Cl, Br) in hexane provides the monomeric compounds BX[(NSiMe₃)₂C₁₀H₆] [3 (X = Cl), 4 (X = Br)] with a tricoordinate boron atom. Attempts to reduce 3 and 4 with lithium, sodium, potassium or sodium/potassium alloy with the intention to isolate a boranide resembling a carbene were unsuccessful. However, the diaminonaphthalene dilithium salt (THF)₂Li₂[(NSi-iPr ₃)₂C₁₀H₆] (2) reacts with SnCl ₂ in THF to provide the carbene analog 5. Compounds 2, 3 and 5 were characterized by single-crystal X-ray structure analysis. The structures of 3 and 5 show the naphthalene backbone to be nearly planar, while the heterocycles in 3 and 5 containing boron and tin atoms, respectively, have torsion angles (3: 30.06°; 5: 37.27°) with respect to the naphthalene plane. The boron atom has a trigonalplanar environment, and the stannylene tin-nitrogen bonds form a very acute N-Sn-N angle of 92.2°.