Homobimetallic gold(I) compounds exhibit unique properties in photocatalysis. Au2(μ-dppm)2(OTf)2 (denoted as Au–Au(OTf)2) demonstrates excellent catalytic activity in the carbocyclization/gem-diborylation cascade of aryl iodides, but the photocatalytic mechanism and electronic structure of the active catalyst remain elusive. This study investigates the detailed catalytic mechanism of photoinduced energy transfer reactions, using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Computational results reveal that the coordination of the carbonate ion (CO32–) ligand to Au2(μ-dppm)22+ (Au–Au2+) not only shortens the Au–Au bond length, which enhances aurophilic interactions, but also distinctly influences the dinuclear gold architecture. The two structures formed between Au–Au(OTf)2 and Na2CO3, Au–AuCO3-I (axis coordination) and Au–AuCO3-II (bond coordination), induce a bathochromic shift in the absorption spectrum. This shift matches the emission spectrum of blue LEDs, enabling the efficient sensitization of triplet-state aryl iodides. Sensitization of the aryl iodide substrate by Au–AuCO3-I and Au–AuCO3-II via an energy transfer (EnT) process from their high triplet-state energies leads to homolytic C–I bond cleavage, which enables the radical carbocyclization/gem-diborylation cascade. This study unveils the crucial role of carbonate in modulating the photophysical properties and reactivity of dinuclear gold catalysts, providing important insight into the design of efficient gold-based photocatalysts.
Li et al. (Thu,) studied this question.