Neutral and cationic organoaluminum complexes utilizing a novel anilido-phosphinimine ancillary ligand

A new chelating N,N ligand family incorporating an anilido-phosphinimine donor set has been designed and an example prepared in multigram quantities in three steps using a convenient, modular synthetic approach. The ligand 1-(NHAr)-2-(PPh2=NAr')C6H4 (1(.)H; Ar = 2,6-Pr-i(2)-C6H3; Ar' = 2,4,5-Me3C6H2) was prepared in three steps in a 30-35% overall yield and was fully characterized in its protio form as well as in the form of its lithium salt, 1(.)Li. In both compounds, the donor array assumes a conformation in which the P=N moiety dips out of the plane formed by the four atoms in the rigid ortho-disubstituted aryl ring of the ligand backbone. The coordinating properties of the new ligand were demonstrated by the synthesis of some organoaluminum derivatives. The monomeric compounds LAlMe2 (2) and LAlH2 (3) were prepared by the reaction of 1(.)H with AlMe3 and AlH3(.)NMe(3), respectively, and were fully characterized by NMR spectroscopy and X-ray crystallography. Cationic derivatives were formed by activation of 2 and 3 with either B(C6F5)(3) or [Ph3C](+)[B(C6F5)(4)](-). All of the neutral and cationic compounds qualitatively exhibited high levels of stability in comparison to related organoaluminum compounds, illustrating the exemplary steric and electronic properties of the new ligand system.