Synthesis and Characterization of Primary Aluminum Parent Amides and Phosphides

The synthesis and characterization of the sterically crowded primary alanes (AriPr4AlH2)2 (AriPr4 = C6H3-2,6­(C6H3-2,6-iPr2)2) and (AriPr8AlH2)2 (AriPr8 = C6H-2,6­(C6H2-2,4,6-iPr6)2-3,5-iPr2) are described. They, along with their previously reported less-hindered analogue (ArMe6AlH2)2 (ArMe6 = C6H3-2,6­(C6H2-2,4,6-Me3)2), were reacted with ammonia to give the parent amido alanes {ArxAl­(H)­NH2}2 (Arx = ArMe6, 1; AriPr4, 2; AriPr8, 3), which are the first well-characterized hydride amido derivatives of aluminum and are relatively rare examples of parent aluminum amides. In contrast, the reaction of (ArMe6AlH2)2 with phosphine yielded the structurally unique Al/P cage species {(ArMe6Al)3(μ-PH2)3(μ-PH)­PH2} (4) as the major product and a smaller amount of {(ArMe6Al)4(μ-PH2)4(μ-PH)} (5) as a minor product. All compounds were characterized by NMR and IR spectroscopy, while compounds 2–5 were also characterized by X-ray crystallography.