Reactions of 11-Vertex Rhodathiaboranes with HCl: Synthesis and Reactivity of New Cl-Ligated Clusters

Reactions of [8,8,8-(H)­(PPh3)2-9-(Py)-nido-8,7-RhSB9H9] (1), [1,1-(PPh3)2-3-(Py)-closo-1,2-RhSB9H8] (2), and [1,1-(CO)­(PPh3)-3-(Py)-closo-1,2-RhSB9H8] (4), where Py = Pyridine, with HCl to give the Cl-ligated clusters, [8,8-(Cl)­(PPh3)-9-(Py)-nido-8,7-RhSB9H9] (3) and [8,8,8-(Cl)­(CO)­(PPh3)-9-(Py)-nido-8,7-RhSB9H8] (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 PR3-ligated analogues, [8,8,8-(H)­(PR3)2-9-(Py)-nido-8,7-RhSB9H9], where PR3 = PMePh2 (6), or PPh3 and PMe3 (7); and [1,1-(PR3)2-3-(Py)-closo-1,2-RhSB9H8], where PR3 = PPh3 and PMe3 (8), PMe3 (9) or PMe2Ph (10), with HCl to give Cl-ligated clusters. The results demonstrate that in contrast to the PPh3-ligated compounds, 1, 2, and 3, the reactions with 610 are less selective, giving rise to the formation of mixtures that contain monophosphine species, [8,8-(Cl)­(PR3)-9-(Py)-nido-8,7-RhSB9H9], where PR3 = PMe3 (11), PMe2Ph (12), or PMePh2 (15), and bis-ligated derivatives, [8,8,8-(Cl)­(PR3)2-9-(Py)-nido-8,7-RhSB9H9], where PR3 = PMe3 (13) or PMe2Ph (14). The {RhCl­(PR3)}-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)­(PPh3)-9-(Py)-nido-8,7-RhSB9H9], 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.