Reversible Room-Temperature Heterolytic Activation of Vinylic sp² C-H Bonds at a Gallium Center

The identification of molecular design principles that enable the activation of strong nonpolar bonds remains an open challenge, particularly for main-group elements. Inspired by reports of metal-framework cooperativity in gallium-containing zeolites, we demonstrate the reversible room-temperature activation of the sp² C-H bonds of olefins by the gallium aminoxy complex Ga(TEMPO)₃·THF (1) (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), facilitated by metal-ligand cooperativity (MLC). Treatment of 1 with ethylene results in reversible alkene activation, either through addition of the carbon double bond across the Ga-O-N unit forming a 3 + 2 cycloadduct or heterolysis of the C-H bond of ethylene to form a Ga-vinyl species analogous to a putative intermediate required for silica-supported single-site gallium catalysts to enter a Cossee-Arlman oligomerization cycle. Complex 1 reversibly activates a variety of alkenes through C-H bond heterolysis, and treatment of 1 with biologically derived olefins and a deuteron source (TEMPOD) resulted in deuterium incorporation at terminal alkene positions. Our work highlights the blurred lines between MLC and metal-framework cooperativity and elucidates how a main-group element can be coaxed to perform a transformation traditionally ascribed to more noble members of the periodic table.