Boosting Low-Valent Aluminum(I) Reactivity with a Potassium Reagent

The reagent RK [R=CH(SiMe3)(2)or N(SiMe3)(2)] was expected to react with the low-valent ((BDI)-B-DIPP)Al ((BDI)-B-DIPP=HC[C(Me)N(DIPP)](2), DIPP=2,6-iPr-phenyl) to give [((BDI)-B-DIPP)AlR]K--(+). However, deprotonation of the Me group in the ligand backbone was observed and [H2C=C(N-DIPP)-C(H)=C(Me)-N-DIPP]Al-K+(1) crystallized as a bright-yellow product (73 %). Like most anionic Al(I)complexes,1forms a dimer in which formally negatively charged Al centers are bridged by K(+)ions, showing strong K+..DIPP interactions. The rather short Al-K bonds [3.499(1)-3.588(1) angstrom] indicate tight bonding of the dimer. According to DOSY NMR analysis,1is dimeric in C(6)H(6)and monomeric in THF, but slowly reacts with both solvents. In reaction with C6H6, two C-H bond activations are observed and a product with apara-phenylene moiety was exclusively isolated. DFT calculations confirm that the Al center in1is more reactive than that in ((BDI)-B-DIPP)Al. Calculations show that both Al(I)and K(+)work in concert and determines the reactivity of1.