Synthesis and characterization of lithium, aluminium and zinc complexes supported by pyrazolyl-based N,N′-chelate ligands

Abstract

A series of lithium, aluminium and zinc complexes bearing [3,5-R₂C₃HN₂CHC(R¹)N(R²)]⁻ ligands were synthesized and characterized. Treatment of 1-(Me₃SiCH₂)-3,5-R₂C₃HN₂ (R = Me, Bu^t) with LiBuⁿ and then Bu^tCN afforded [Li{N(SiMe₃)C(Bu^t)CHN₂C₃HR₂-3,5}]₂ (R = Me, 2a; R = Bu^t, 2b). Reaction of both 2a and 2b with ZnCl₂ gave zinc complexes [Zn(Cl){N(SiMe₃)C(Bu^t)CHN₂C₃HR₂-3,5}]₂ (R = Me, 3a; R = Bu^t, 3b). Treatment of o-RC₆H₄NHC(Ph)CHN₂C₃HMe₂-3,5 (R = OPrⁱ, 5a; R = Me, 5b) with LiBuⁿ yielded lithium complexes similar to 2a or 2b, [Li{N(o-RC₆H₄)C(Ph)CHN₂C₃HMe₂-3,5}] (R = OPrⁱ, 6a; R = Me, 6b). Reaction of 6b with ZnCl₂ generated zinc complexes [Zn(Cl){N(o-MeC₆H₄)C(Ph)CHN₂C₃HMe₂-3,5}] (7), and with AlCl₃ gave [Al(Cl₂){N(o-MeC₆H₄)C(Ph)CHN₂C₃HMe₂-3,5}] (8). Reaction of 5a with ZnEt₂ produced [Zn{N(o-PrⁱC₆H₄)C(Ph)CHN₂C₃HMe₂-3,5}₂] (9). Reaction of 5a and 5b with AlR′₃ (R′ = Me, Et) afforded aluminium complexes [Al(R′₂){N(o-RC₆H₄)C(Ph)CHN₂C₃HMe₂-3,5}] (R = OPrⁱ, R′ = Me, 10a; R=Me, R′ = Me, 10b; R = OPrⁱ, R′ = Et, 10c; R = Me, R′ = Et, 10d). A trace of species [Al(Et₂){N(o-MeC₆H₄)C(Ph)(Et)CH₂N₂C₃HMe₂-3,5}] (11) was also isolated from the reaction products of 5b and AlEt₃. All of new compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analyses. Structures of complexes 2a, 8, 10a, 10d and 11 were additionally characterized by single-crystal X-ray diffraction techniques.