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

Abstract

The reagent RK [R=CH(SiMe₃ )₂ or N(SiMe₃ )₂ ] was expected to react with the low-valent (^DIPP BDI)Al (^DIPP BDI=HC[C(Me)N(DIPP)]₂ , DIPP=2,6-iPr-phenyl) to give [(^DIPP BDI)AlR]^- K⁺ . However, deprotonation of the Me group in the ligand backbone was observed and [H₂ C=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, 1 forms 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) Å] indicate tight bonding of the dimer. According to DOSY NMR analysis, 1 is dimeric in C₆ H₆ and monomeric in THF, but slowly reacts with both solvents. In reaction with C₆ H₆ , two C-H bond activations are observed and a product with a para-phenylene moiety was exclusively isolated. DFT calculations confirm that the Al center in 1 is more reactive than that in (^DIPP BDI)Al. Calculations show that both Al^I and K⁺ work in concert and determines the reactivity of 1.