Dimeric Rare-Earth BINOLate Complexes: Activation of 1,4-Benzoquinone through Lewis Acid Promoted Potential Shifts

Reaction of p-benzoquinone (BQ) with a series of rare-earth metal/alkali metal/1,1'-BINOLate (REMB) complexes (RE: La, Ce, Pr, Nd; M: Li) results in the largest recorded shift in reduction potential observed for BQ upon complexation. In the case of cerium, the formation of a 2: 1 Ce/BQ complex shifts the two-electron reduction of BQ by greater than or equal to 1.6 V to a more favorable potential. Reactivity investigations were extended to other REIII (RE = La, Pr, Nd) complexes where the resulting highly electron-deficient quinone ligands afforded isolation of the first lanthanide quinhydrone-type charge-transfer complexes. The large reduction-potential shift associated with the formation of 2: 1 Ce/BQ complexes illustrate the potential of Ce complexes to function both as a Lewis acid and an electron source in redox chemistry and organic-substrate activation.