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 provides 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⁺ to 2 results in an arene C–H activation process, highlighting that the naphthalene ligands in these complexes are simultaneously substitutionally inert and prone to functionalization.