Novel bidentate N-coordinated alkylaluminum complexes: synthesis, characterization, and efficient catalysis for hydrophosphonylation

Abstract

Five new alkylaluminum complexes with different pyridinyl-substituted imines or cyclohexyl-substituted imines were synthesized and characterized successfully. The aluminum complex [FlCHNCH(CH₃)Py]AlMe₂(Py = 2-pyridyl) (1) was obtained by reacting 9-[2-pyridyl-CH(CH₃)-NCH]Fl (Fl = fluorenyl) (L¹) and equimolar AlMe₃. The reactions of 9-(2-pyridyl-NCH)Fl (L²) and 9-[2-N(CH₃)₂-cyclohexyl-NCH]Fl (L³) with equimolar AlMe₃ or AlEt₃ afforded other alkylaluminum complexes [FlCHNPy]AlMe₂(Py = 2-pyridyl) (2), [FlCHNPy]AlEt₂ (Py = 2-pyridyl) (3), [FlCHNCyN(CH₃)₂]AlMe₂ (Cy = 2-cyclohexyl) (4) and [FlCHNCyN(CH₃)₂]AlEt₂ (Cy = 2-cyclohexyl) (5). All these complexes (1–5) were characterized using NMR spectroscopy, elemental analysis, and X-ray crystal structure analysis. The catalytic properties of these new alkylaluminum complexes for the hydrophosphonylation of aldimines were examined. Complex 5 showed the best catalytic performance under mild reaction conditions with a low catalyst loading (1 mol%), and 20 different substituents of aldimines were isolated with more than 90% yields.