"Masked" Lewis-acidity of an aluminum α-phosphinoamide complex.

The reaction of PhP(DIPP)NH with AlMe cleanly gives an aluminum amide complex that crystallizes as a centrosymmetric dimer with a six-membered Al-N-P-Al-N-P ring. In aromatic solvents the dimer remains intact but the Al-P bond is readily broken upon addition of THF to form PhP(DIPP)NAlMe·THF. Efforts to use [PhP(DIPP)NAlMe] as a "masked" Lewis acidic activator for olefin polymerization catalysts were unsuccessful but the complex showed a Frustrated Lewis pair reactivity instead. The P/Al complex reacts with isocyanates to give the C[double bond, length as m-dash]O inserted product that crystallizes as a five-membered ring system Al-O-C(NR)-P-N. The reaction of [PhP(DIPP)NAlMe] with CO, however, gave an insertion in the N-Al bond and the dimeric product [PhP(DIPP)NCOAlMe] was isolated. The dimer [PhP(DIPP)NAlMe] is one of the few Al/P FLPs that can activate C[double bond, length as m-dash]C double bonds irreversibly. A reaction with allyl methyl sulfide and 1-hexene led to the clean formation of the structurally similar activated alkene products [(DIPP)N-PhP-CH(CHSMe)CH]AlMe and [(DIPP)N-PhP-CH(CH)CH]AlMe.