Pyrene-Functionalized o -COSAN Noncovalently Anchored onto Graphene Oxide for Advanced Photocatalytic Alcohol Oxidation

Abstract We report the synthesis and characterization of new pyrene-functionalized cobaltabis(dicarbollide) anions [o-COSAN]- and their first successful immobilization onto graphene oxide (GO). The complex Na[3,3′-Co(8-O(CH2CH2O)2C(O)-(CH2–pyrene)(1,2-C2B9H10)(1′,2′-C2B9H11], denoted as Na[3], was obtained via a ring-opening reaction of a cyclic oxonium derivative with pyreneacetic acid. Subsequent cation exchange yielded the tetramethylammonium salt, [N(CH3)4][3,3′-Co(8-O(CH2CH2O)2C(O)(CH2–pyrene-1,2-C2B9H10)(1,2-C2B9H11)], [N(CH3)4][3]. Electrochemical analysis revealed irreversible oxidation peaks for the pyrene moiety alongside well-defined Co(IV)/Co(III) and Co(III)/Co(II) redox couples. Noncovalent anchoring of [Na][3] onto GO produced the hybrid material GO@3, which was thoroughly characterized by TEM, SEM, XPS, UV–vis, and DPV. GO@3 exhibited the narrowest optical and electrochemical bandgaps among the studied species. All complexes demonstrated exceptional catalytic efficiency and selectivity for the UVA-driven photooxidation of alcohols in water. Notably, homogeneous Na[3] achieved high conversions at a remarkably low loading of 0.01 mol %. While the insoluble [N(CH3)4][3], acted as a robust heterogeneous catalyst, the hybrid GO@3 surpassed the activity of the homogeneous system, showing enhanced performance in shorter reaction times. This enhancement is attributed to the synergistic role of GO in facilitating electron transfer and suppressing charge recombination. GO@3 was easily recovered by filtration and reused over six cycles without loss of activity, reaching turnover numbers (TON) exceeding 45,000.