Reactions of 11-vertex rhodathiaboranes with HCl: synthesis and reactivity of new Cl-ligated clusters.

Reactions of [8,8,8-(H)(PPh(3))(2)-9-(Py)-nido-8,7-RhSB(9)H(9)] (1), [1,1-(PPh(3))(2)-3-(Py)-closo-1,2-RhSB(9)H(8)] (2), and [1,1-(CO)(PPh(3))-3-(Py)-closo-1,2-RhSB(9)H(8)] (4), where Py = Pyridine, with HCl to give the Cl-ligated clusters, [8,8-(Cl)(PPh(3))-9-(Py)-nido-8,7-RhSB(9)H(9)] (3) and [8,8,8-(Cl)(CO)(PPh(3))-9-(Py)-nido-8,7-RhSB(9)H(8)] (5), have recently demonstrated the remarkable nido-to-closo redox flexibility and bifunctional character of this class of 11-vertex rhodathiaboranes. To get a sense of the scope of this chemistry, we report here the reactions of PR(3)-ligated analogues, [8,8,8-(H)(PR(3))(2)-9-(Py)-nido-8,7-RhSB(9)H(9)], where PR(3) = PMePh(2) (6), or PPh(3) and PMe(3) (7); and [1,1-(PR(3))(2)-3-(Py)-closo-1,2-RhSB(9)H(8)], where PR(3) = PPh(3) and PMe(3) (8), PMe(3) (9) or PMe(2)Ph (10), with HCl to give Cl-ligated clusters. The results demonstrate that in contrast to the PPh(3)-ligated compounds, 1, 2, and 3, the reactions with 6-10 are less selective, giving rise to the formation of mixtures that contain monophosphine species, [8,8-(Cl)(PR(3))-9-(Py)-nido-8,7-RhSB(9)H(9)], where PR(3) = PMe(3) (11), PMe(2)Ph (12), or PMePh(2) (15), and bis-ligated derivatives, [8,8,8-(Cl)(PR(3))(2)-9-(Py)-nido-8,7-RhSB(9)H(9)], where PR(3) = PMe(3) (13) or PMe(2)Ph (14). The {RhCl(PR(3))}-containing compounds, 3, 11, 12, and 15, are formally unsaturated 12 skeletal electron pair (sep) clusters with nido-structures. Density functional theory (DFT) calculations demonstrate that the nido-structure is more stable than the predicted closo-isomers. In addition, studies have been carried out that involve the reactivity of 3 with Lewis bases. Thus, it is reported that 3 interacts with MeCN in solution, and it reacts with CO and pyridine to give the corresponding Rh-L adducts, [8,8,8-(Cl)(L)(PPh(3))-9-(Py)-nido-8,7-RhSB(9)H(9)], where L = CO (5) or Py (20). On the other hand, the treatment of 3 and 5 with Proton Sponge (PS) promotes the abstraction of HCl, as [PSH]Cl, from the nido-clusters, and the regeneration of the parent closo-species, completing two new stoichiometric cycles that are driven by Brønsted acid/base chemistry.