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)-NCH]Fl (Fl = fluorenyl) (L1) and equimolar AlMe3. The reactions of 9-(2-pyridyl-NCH)Fl (L2) and 9-[2-N(CH3)2-cyclohexyl-NCH]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.