Low-Valent Tantalum/Gold Clusters: Oxidation, Protonation, and C–H Activation

Abstract

Gold-based catalysts are topical heterogeneous and molecular species, the chemical diversity of which can be expanded through heterometal doping. Herein, we leverage a carbonyl-free metal-metal salt metathesis protocol to access rare examples of low-valent tantalum/gold multimetallics. The initial reaction between [Ta(naphthalene)₃]^– and gold(I) synthons affords a trimetallic monohydride cluster (2). Whereas dihydrogen addition to 2 results in deauration en route to a Ta-µH₂-Au complex (1), oxidative transformations—either addition of chemical oxidants or cluster protonation—conserve the trimetallic core, even in the absence of a polynucleating ligand. The resultant series of compounds provide experimental anchors for computational interrogation of polarized metal-metal interactions as a function of metal identity, formal oxidation state, and ligand sphere. The electronic structure of these clusters showcases significant Ta-arene covalency, even at higher oxidation states, rationalizing a recalcitrance to undergo ligand substitution. Furthermore, the addition of in situ generated Au⁺ to2 results in an arene C–H activation process, highlighting that the naphthalene ligands in these complexes are simultaneously substitutionally inert and prone to functionalization.