Protonation of Dppbz- and Binap-Ligated Rhodathiaboranes Yielding Hydron, Hydride, and Hydrogen Exchange

The reaction of the 11-vertex rhodathiaborane [8,8,8-(H)(PPh₃)₂-3-(NC₅H₅)-nido-7,8-RhSB₉H₁₀] (1) with 1,2-bis(diphenylphosphine)benzene (dppbz) and (S)-(-)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (binap) affords [1,1-(η²-dppbz)-3-(NC₅H₅)-closo-1,2-RhSB₉H₈] (2) and [1,1-(η²-binap)-3-(NC₅H₅)-closo-1,2-RhSB₉H₈] (3). These 11-vertex closo-rhodathiaborane chelates result from PPh₃ ligand substitution at the rhodium center and a nido-to-closo structural cluster transformation driven by H₂ loss. Treating compounds 2 and 3 with triflic acid (TfOH) leads to the formation of cationic clusters 4 and 5. The hydrons bind to the polyhedral clusters, acquiring hydride character and providing chemical nonrigidity that manifests through metal vertex-to-thiaborane pseudo-rotations and concomitant hydron tautomerisms. The resulting cations react with hydrogen to form mixtures of hydrons, hydrogen, and hydridorhodathiaboranes in equilibrium. The reaction products are the result of heterolytic cleavage of the H-H bond, with full participation of the clusters and the addition of hydrogen atoms to the cages. In these reactions, there is a conversion of electrons and hydrons into hydrogen, and hydrogen into hydride ligands, demonstrating that these boron-based metal compounds act as electron reservoirs, capable of promoting multielectron processes.