Chemistry of 11-vertex rhodathiaboranes: reactions with monodentate phosphines

Abstract

The reaction of [8,8-(PPh₃)₂-nido-8,7-RhSB₉H₁₀] (1) with PR₃ in a 1 : 2 ratio affords mixtures that contain the mono-substituted bis-PR₃-ligated rhodathiaboranes [8,8-(PPh₃)(L)-nido-8,7-RhSB₉H₁₀] [L = PMe₂Ph (5), PMe₃ (6)] and the corresponding tris-PR₃-ligated compounds [8,8,8-(L)₃-nido-8,7-RhSB₉H₁₀] [L = PMe₂Ph (7), PMe₃ (8)]. These latter species are more conveniently prepared from the reaction of 1 with three equivalents of the monodentate phosphines, PMe₂Ph and PMe₃. Reaction between 1 and PMePh₂ in a 1 : 2 ratio yields the disubstituted rhodathiaborane [8,8-(PMePh₂)₂-nido-8,7-RhSB₉H₁₀] (4), whereas the use of three equivalents of phosphine leads to the formation of B-ligated eleven-vertex [8,8,8-(PMePh₂)₂(H)-nido-8,7-RhSB₉H₉-9-(PMePh₂)] (9). Compounds 4–9 have been characterized by NMR spectroscopy, and the structures of 8 and 9 confirmed by X-ray diffraction analyses. The characterization of the cluster compounds has been aided by the use of DFT calculations on some of the species. Variable-temperature NMR studies have demonstrated a lability of the PMePh₂ ligands in compounds 4 and 9, providing mechanistic insights about the ligand substitutional chemistry in these eleven-vertex rhodathiaboranes.