Aluminum complexes incorporating symmetrical and asymmetrical tridentate pincer type pyrrolyl ligands: synthesis, characterization and reactivity study

Abstract

A series of aluminum complexes incorporating substituted symmetrical and asymmetrical tridentate pyrrolyl ligands are synthesized conveniently and the treatment of the derivatives with small organic molecules are analyzed. The reaction of lithiated [C₄H₂NH(2-CH₂NH^tBu)(5-CH₂NR₁R₂)], where for 1, R₁ = R₂ = Me; 2, R₁ = H, R₂ = ^tBu, with AlCl₃ in diethyl ether affords Al[C₄H₂N(2-CH₂NH^tBu)(5-CH₂NMe₂)]Cl₂ (3) and Al[C₄H₂N(2,5-CH₂NH^tBu)₂]Cl₂ (4), respectively, in high yields. Furthermore, subjecting 3 and 4 to reaction with one equiv. of LiNMePh in diethyl ether generates Al[C₄H₂N(2-CH₂NH^tBu)(5-CH₂NMe₂)][NMePh]Cl (5) and Al[C₄H₂N(2,5-CH₂NH^tBu)₂][NMePh]Cl (6), respectively, while eliminating one equiv. of LiCl. The reaction between compound 4 with two equiv. of LiO-Ph-4-Me in diethyl ether yields the aluminum di-phenoxide compound Al[C₄H₂N(2,5-CH₂NH^tBu)₂](O-Ph-4-Me)₂ (7) whereas the combination of 3 and two equiv. of LiNH^tBu, produces Al[C₄H₂N(2-CH₂N^tBu)(5-CH₂NMe₂)](NH^tBu)(NH₂^tBu) (8). Additionally, the mixing of 1 and one equiv. of AlMe₃ renders Al[C₄H₂N(2-CH₂NH^tBu)(5-CH₂NMe₂)]Me₂ (9). Adding one more equiv. of AlMe₃ with 9 affords {Al[C₄H₂N(2-CH₂NH^tBu)(5-CH₂NMe₂)AlMe₃]Me₂} (10), which can also be obtained by treating 1 with two equiv. of AlMe₃ directly. The treatment of 9 with one equiv. of 2,6-dimethylphenol in diethyl ether gives the aluminum alkoxide derivative, Al[C₄H₂N(2-CH₂NH^tBu)(5-CH₂NMe₂)](O-C₆H₃-2,6-Me₂)Me (11). Furthermore, the reaction between 9 and one equiv. of 1-ethyl-1-phenyl ketene, initiates the aluminum dimethyl complex Al{C₄H₂N[2-CH₂CEtPh-C(O)-NH^tBu](5-CH₂NMe₂)}Me₂ (12) with a C–N bond breakage and a C–C bond formation. All the Al-derivatives are characterized by ¹H and ¹³C NMR spectroscopy and the molecular structures are determined by single crystal X-ray diffractometry in solid state.