Synthesis of amino- and amido-aluminium derivatives and investigation of their dynamics in solution

Abstract

The salts Li[Al(C₄H₈N)₄]·nC₄H₈NH (n = 1, 2; C₄H₈NH = pyrrolidine) have been prepared and characterised in solution by ¹H-, ¹³C-, ⁷Li- and ²⁷Al-NMR spectroscopy. Their reaction with AlCl₃ (Cl/Li molar ratio = 3) affords the binary amido derivative [Al(C₄H₈N)₃]₂, which, on turn, is reactive towards AlX₃, yielding [AlX₂(C₄H₈N)]₂ (X = Cl, CH₃). The binuclear derivatives [AlY₂(C₄H₈N)]₂ (Y = Cl, CH₃, C₄H₈N) react with [NH₂Et₂]Cl affording the amine complexes AlY₂Cl(C₄H₈NH)_n (Y = CH₃, n = 1; Y = Cl, n = 1, 2). Alternatively, the monochloro species Al(CH₃)₂Cl(C₄H₈NH) results from the reaction of Al(CH₃)₃(C₄H₈NH) and AlCl₃(C₄H₈NH) (CH₃/Cl molar ratio = 2). The dichloro-methyl derivative Al(CH₃)Cl₂(C₄H₈NH) is obtained by reacting Al(CH₃)₃(C₄H₈NH) and AlCl₃(C₄H₈NH) (Cl/CH₃ molar ratio = 2). The Lewis adducts AlCl₃(amine)_n (amine = pyrrolidine, n = 1, 2; amine = N,N,N′-trimethylpropanediamine, n = 1) have been isolated when AlCl₃ was contacted with the stoichiometric amount of the amine. At variance with N,N,N′-trimethylpropanediamine, N,N,N′-trimethylethylenediamine and N,N,N′,N′-tetramethylethylenediamine react with AlCl₃ yielding the salt derivatives [AlCl₂(amine)₂][AlCl₄].

The dynamic processes of the coordinated amine ligands of AlCl₃(amine)_n (amine = pyrrolidine, n = 1, 2; amine = N,N,N′-trimethylpropanediamine, n = 1) and [AlCl₂(amine)₂][AlCl₄] (amine = N,N,N′,N′-tetramethylethylenediamine) have been investigated in solution by NMR spectroscopy.