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.

Hydridorhodathiaboranes: Synthesis, Characterization, and Reactivity

“…8 These polyhedral cations show a remarkable stereochemical non-rigidity that is the key to their reactivity.…”

“…4 This polyhedral compound exhibits two principal points of reactivity: the metal centre and an adjacent B-H unit on the pentagonal face (Scheme 1). Reactions with monodentate phosphines led to the formation of metal-ligand-substitution products, [8, )(PPh 3 )-nido-8,7-RhSB 9 H 10 ], as well as compounds resulting from the substitution of the PPh 3 ligands and the addition of a third phosphine at the metal centre, [8,8, ) 3 -nido-8,7-RhSB 9 H 10 ] (Scheme 1). 5 Alternatively, the treatment of 1 with pyridine affords a hydridorhodathiaborane, [8,8,8-(H)(PPh 3 ) 2 -9-(NC 5 H 5 )-nido-8,7-RhSB 9 H 9 ] (2), in which the pyridine ligand binds to boron-9 adjacent to the metal on the pentagonal face (Scheme 1).…”

“…5 Alternatively, the treatment of 1 with pyridine affords a hydridorhodathiaborane, [8,8,8-(H)(PPh 3 ) 2 -9-(NC 5 H 5 )-nido-8,7-RhSB 9 H 9 ] (2), in which the pyridine ligand binds to boron-9 adjacent to the metal on the pentagonal face (Scheme 1). 6 The bis-PPh 3 -ligated 11-vertex nido-rhodathiaborane, 1, also undergoes substitution reactions with 1,3-dimethylimidazol-2-ylidene, IMe, giving a mixture that contains the products of monosubstitution and disubstitution, [8, )(IMe)-nido-8,7-RhSB 9 H 10 ] and [8, 2 -nido-8,7-RhSB 9 H 10 ] (Scheme 1). 7 The treatment of the monosubstituted carbene-ligated nido-rhodathiaborane with pyridine affords a new isonido-cluster, [1,1-(IMe)(PPh 3 )-3-(NC 5 H 5 )-isonido , formed by pyridine-cage substitution and dihydrogen loss.…”

“…In the context of organometallic chemistry and catalysis based on metallaheteroboranes, we have focused our work on the 11-vertex rhodathiaborane, [8, ) 2 -nido-8,7-RhSB 9 H 10 ] (1). 4 This polyhedral compound exhibits two principal points of reactivity: the metal centre and an adjacent B-H unit on the pentagonal face (Scheme 1).…”

“…The reaction between pyridine and [8, (17, 18, 19). These series of  2 -C 2 H 4 -and CO-ligated 11-vertex isonido / closorhodathiaboranes result from the substitution of one PPh 3 ligand by ethylene or CO together with H 2 loss and a concomitant nido-to-closo / isonido-cluster structural transformation.…”