Unusual cationic rhodathiaboranes: synthesis and characterization of [8,8,8-(H)(PR3)2-9-(Py)-nido-8,7-RhSB9H10]+ and [1,3-μ-(H)-1,1-(PR3)2-3-(Py)-isonido-1,2-RhSB9H8]+

Abstract

The treatment of the hydridorhodathiaboranes, [8,8,8-(H)(PR₃)₂-9-(Py)-nido-8,7-RhSB₉H₉], where PR₃ = PPh₃ (2), PMePh₂ (3), PPh₃ and PMe₂Ph (4), or PMe₃ and PPh₃ (5), and [8,8,8-(H)(PMePh₂)₂-9-(PMePh₂)-nido-8,7-RhSB₉H₉] (6), with TfOH affords [8,8,8-(H)(PR₃)₂-9-(Py)-nido-8,7-RhSB₉H₁₀]⁺ cations, where PR₃ = PPh₃ (12), PMePh₂ (13), PPh₃ and PMe₂Ph (14), or PMe₃ and PPh₃ (15), and [8,8,8-(H)(PMePh₂)₂-9-(PMePh₂)-nido-8,7-RhSB₉H₁₀]⁺ (16). Compounds 13 and 14 lose H₂ to give [1,3-μ-(H)-1,1-(PR₃)₂-3-(Py)-isonido-1,2-RhSB₉H₈]⁺, where PR₃ = PMe₂Ph (18), PPh₃ and PMe₂Ph (21), or PMePh₂ (22). Similarly, the 11-vertex rhodathiaboranes, [1,1-(PR₃)₂-3-(Py)-1,2-RhSB₉H₈], where PR₃ = PPh₃ (7), PMe₂Ph (8), PMe₃ (9), or PPh₃ and PMe₃ (10), react with TfOH to give the corresponding cations, [1,3-μ-(H)-1,1-(PR₃)₂-3-(Py)-isonido-1,2-RhSB₉H₈]⁺, where PR₃ = PPh₃ (17), PMe₂Ph (18), PMe₃ (19), or PPh₃ and PMe₃ (20). Four conformers of 20 are studied by X-ray diffraction methods and DFT-calculations, identifying packing motifs that stabilize different metal–thiaborane linkages, and energy variations that are involved in these conformational changes. It is demonstrated that the proton induces nonrigidity on these clusters as well as an enhancement of their Lewis acidity.