Dynamic ion-pairing behaviour of “naked” aluminyls: Facile activation of H2

This work discloses an unprecedented dynamic ion-pairing behaviour of “naked” aluminyl anions related to their stability and reactivity in solution. Rapid exchange between contacted and charge-separated species of the aluminyl anion [(BDI’)Al(I)]– (BDI’ = H2C=C(NAr)-C(H)=C(Me)-NAr; Ar = 2,6-iPr2C6H3) occurs in solution with [M(L)]+ counterions (M = Cs, K). While the two-dimensional polyether 18-crown-6 (L) favours the formation of persistent contacted species, the three-dimensional 2.2.2-cryptand ligand allows facile exchange. These aluminyl processes are probed by NMR spectroscopy, including DOSY NMR, and X-ray crystallography, which provide intimate details of the ion-pairing equilibrium and ionic separations. The labilities of these aluminyls are shown to be important in their stability and reactivity with the non-polar H2.