The reactivity of NbX5 (X = F, Cl) with lactons, lactams, and the synthesis of the first nucleobase-containing niobium complex

NbX₅ (X = F, 1a; X = Cl, 1b) reacted with γ-butyrolactone (but), ε-caprolactam (cap), δ-valerolactam (val) in 1:1 M ratio in chlorinated solvent, affording either the neutral coordination adducts NbCl₅L (L = but, 2a; L = val, 2b) or the ionic ones [NbX₄L₂][NbX₆] (X = F, L = but, 3a; X = F, L = val, 3b; X = F, L = cap, 3c; X = Cl, L = cap, 3d). The reaction of 1a with equimolar amount of guanine (gua) in CH₃CN resulted in the formation of the complex [NbF₄(gua)₂][NbF₆], 3e. The addition of two equivalents of organic substrate to 1 gave selectively the compounds NbCl₅L₂ (L = but, 4a; L = val, 4b) or [NbF₄L₄][NbF₆] (L = but, 5a; L = val, 5b; L = cap, 5c). The 1:2 M reaction of 1b with ε-caprolactam proceeded with C-N bond activation and afforded the derivative , 6, in high yield.