Copper clusters as novel photocatalysts for aerobic oxidation of arylboronic acids and esters under ecofriendly conditions.

CASTRO GODOY, WILBER D.; GIORDANO, LAUREANO; SCHMIDT, LUCIANA C; ARGÜELLO, JUAN E.

Encuentro; XIII ELAFOT; 2017

Metal clusters can be defined as metal atom aggregates with sizes between 1 to 2 nm.[1] For thesenovel materials high chemical stability and novel properties including surprising high catalyticperformances have been described.[2] Up to now, copper clusters (CuCLs) have attracted lessattention than gold and silver clusters. However, due to their low cost and unique optical andcatalytic properties different publications have recently reported the synthesis andcharacterization of CuCLs.[3] Besides, previous reports have demonstrated that photocatalyticbehavior of CuCLs would be similar to the accepted one for photoactive semiconductors (SCs),[4]which involves the generation of reactive oxygen species, such as O2?-, HOO? or HO?, produced by thereaction between adsorbed water, molecular oxygen and photoelectrons when they migrate to thesemiconductor´s surface.Recently, we have described the use of water soluble quantum dots for the oxidation of arylboronicacids and esters to obtain their corresponding phenols. In this investigation, the visible lightphotogenerated superoxide anion promotes the ipso hydroxylation of different arylboronic acidsand esters.[5]Herein, we report for the first time the photocatalytic oxidation of different arylboronic acids andarylboronic esters using CuCLs under UV-A irradiation (Scheme 1). The CuCLs were synthesizedand characterized for López-Quintela group (Nanomag Laboratory, Research TechnologicalInstitute, University of Santiago de Compostela, Spain). Under optimized conditions; we furtherstudied the reactivity scope of the reaction. This methodology proved to be compatible withelectron donors and electron withdrawing substituents and the corresponding phenols fromarylboronic esters were also obtained in good yields (48?87 %). On the other hand, arylboronicacids rendered phenols in very good to excellent yields (92?100%).