Shape-selective oxidation of benzylic alcohols by a receptor functionalized with a dicopper(II) pyrazole complex

Article abstract of DOI:10.1021/ja00092a017

A novel metallohost containing a substrate-binding site and two copper ions held by two bis-pyrazole ligand sets is described. The cavity of this molecule can bind dihydroxybenzene guests (association constants in chloroform are in the range K_a = 2000-3000 M^-1). In the presence of benzylic alcohols the Cu(II) centers of the metallohost are reduced to Cu(I). During this process the alcohols are oxidized to aldehydes. Benzylic alcohols possessing phenolic hydroxyl functions are extremely effective in the reduction reaction. It is believed that they are bound in the cavity of the metallohost and are oriented in the correct position with respect to the copper centers. This results in a rate enhancement of at least 4 orders of magnitude for the oxidation reaction.