Synthesis of aluminum alkoxide and bis-alkoxide compounds containing bidentate pyrrolyl ligands

A series of aluminum alkoxide and bis-alkoxides compounds were synthesized and characterized. Reacting 1 with 1 and 2 equiv. of t-butanol in methylene chloride generates [C4H3N(CH2NMe2)-2]2Al(O-t-Bu) (2) and [C4H3N(CH2NMe2)-2-H-C4H3N(CH2NMe2)-2]Al(O-t-Bu)2 (3) in 47% and 54% yield, respectively. The 1H NMR spectrum of 2 exhibits two singlets for NMe2 and CH2N at δ 2.52 and 3.84, respectively, representing the symmetrical manner of molecular structure 2 in a solution. Compound 3 is not thermal stable in solution which decompose into substituted pyrrole ligand C4H4N(CH2NMe2)-2 and unknown aluminum alkoxides. Reacting 1 with 2 equiv. of triphenylsilanol in methylene chloride generates a tetra-coordinated aluminum “ate” compound [C4H3N(CH2NMe2)-2-H- C4H3N(CH2NMe2)-2]Al(OSiPh3)2 (4) in 49% yield. The 1H NMR spectra of 4 at room temperature show a broad signal at δ 1.57 for NMe2 fragments and the signals for CH2N were not observed. VT 1H NMR spectra of 4 show the NMe2 fragments became two singlets (δ 1.27 and 2.12) and the CH2N exhibited two doublets (δ 2.44 and 3.56) at 240 K. The fluxional energy barrier (ΔG‡) is estimated at ca. 50 kJ/mol. The molecular structures of compounds 3 and 4 are determined by single-crystal X-ray diffractometer.

Graphical abstractReacting [C4H3N(CH2NMe2)-2]2AlH with 1 and 2 equiv. of t-butanol in methylene chloride generates [C4H3N(CH2NMe2)-2]2Al(OtBu) (2) and [C4H3N(CH2NMe2)-2-H- C4H3N(CH2NMe2)-2]Al(O-t-Bu)2 (3). [C4H3N(CH2NMe2)-2]2AlH reacts with 2 equiv. of triphenylsilanol in methylene chloride generates a tetra-coordinated aluminum “ate” compound [C4H3N(CH2NMe2)-2-H- C4H3N(CH2NMe2)-2]Al(OSiPh3)2 (4) where the NMe2 fragments became two singlets and the CH2N exhibited two doublets at 240 K. The fluxional energy barrier (ΔG‡) is estimated at ca. 50 kJ/mol.Figure optionsDownload full-size imageDownload as PowerPoint slide