Proton-Assisted Hydrogen Activation on Polyhedral Cations

作者：Calvo Beatriz; Macias Ramon^*; Jose Artigas Maria; Lahoz Fernando J; Oro Luis A

来源：Chemistry - A European Journal, 2013, 19(12): 3905-3912.

DOI：10.1002/chem.201203925

• activation
• cations
• hydrogen
• metallathiaboranes
• rhodium

The treatment of [1,1-(PR3)2-3-(Py)-closo-1,2-RhSB9H8] (PR3=PMe3 (2) or PPh3 and PMe3 (3); Py=pyridine) with triflic acid (TfOH) affords [1,3--(H)-1,1-(PR3)2-3-(Py)-1,2-RhSB9H8]+ (PR3=PMe3 (4) or PMe3 and PPh3 (5)). These products result from the protonation of the 11-vertex closo-cages along the Rh(1)B(3) edge. These unusual cationic rhodathiaboranes are stable in solution and in the solid state and they have been fully characterized by multinuclear NMR spectroscopy. In addition, compound 5 was characterized by single-crystal X-ray diffraction. One remarkable feature in these structures is the presence of three {Rh(PPh3)(PMe3)}-to-{n-SB9H8(Py)} (n=4 or 5) conformers in the unit cell, thus giving an uncommon case of conformational isomerism. [1,1-(PPh3)2-3-(Py)-closo-1,2-RhSB9H8] (1), that is, the bis-PPh3-ligated analogue of compounds 2 and 3, is also protonated by TfOH, but, in marked contrast, the resulting cation, [1,3--(H)-1,1-(PPh3)2-3-(Py)-1,2-RhSB9H8]+ (6), is attacked by a triflate anion with the release of a PPh3 ligand and the formation of [8,8-(OTf)(PPh3)-9-(Py)-nido-8,7-RhSB9H9] (9). The result is an equilibrium that involves cationic species 6, neutral OTf-ligated compound 9, and [HPPh3]+, which is formed upon protonation of the released PPh3 ligand. The resulting ionic system reacts readily with H2 to give cationic species [8,8,8-(H)(PPh3)2-9-(Py)-nido-8,7-RhSB9H9]+ (7). This reactivity is markedly higher than that previously found for compound 1 and it introduces a new example of proton-assisted H2 activation that occurs on a polyhedral boron-containing compound.

• 出版日期2013-3