Square-planar Rhodium(I) complexes partnered with [arachno-6-SB9H12]-:: A route toward the synthesis of new rhodathiaboranes and organometallic/thiaborane salts

Treatment of [RhCl(eta(4)-diene)](2) (diene = nbd, cod) with the N-heterocyclic ligands 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bpy), 1,10-phenanthroline (phen), and pyridine (py) followed by addition of Cs[arachno-6-SB9H12] affords the corresponding salts, [Rh(eta(4)-diene)(L-2)][SB9H12] [diene = cod, L-2 = bpy (1), Me(2)bpy (3), phen (5), (py)(2) (7); diene = nbd, L-2 = bpy (2), Me(2)bpy (4), phen (6), (py)(2) (8)]. These compounds are characterized by NMR spectroscopy and mass spectrometry, and in addition, the cod-Rh species 1 and 3 are studied by X-ray diffraction analysis. These saltlike reagents are stable in the solid state, but in solution the rhodium(I) cations, [Rh(eta(4)-diene)(L-2)](+), react with the polyhedral anion [SB9H12](-) leading to a chemistry that is controlled by the d(8) transition element chelates. The nbd-Rh(I) complexes react faster than the cod-Rh(I) counterparts, leading, depending on the conditions, to the synthesis of new rhodathiaboranes of general formulas [8,8-(L-2)-nido-8,7-RhSB9H10] [L-2 = bpy (9), Me(2)bpy (10), phen (11), (py)(2) (12)] and [8,8-(L-2)-8-(L')-nido-8,7-RhSB9H10] [L' = PPh3, L-2 = bpy (13), Me(2)bpy (14), phen (15); L' = NCCH3, L-2 = bpy (16), Me(2)bpy (17), phen (18)]. Compound 13 is characterized by X-ray diffraction analysis confirming the 11-vertex nido-structure of the rhodathiaborane analogues 14-18. In dichloromethane, 1 and 3 yield mixtures that contain the 11-vertex rhodathiaboranes 9 and 10 together with new species. In contrast, the cod-Rh(I) reagent 5 affords a single compound, which is proposed to be an organometallic rhodium complex bound exo-polyhedrally to the thiaborane cage. In the presence of H-2(g) and stoichiometric amounts of PPh3, the cod-Rh(I) reagents, 1, 3, and 5, afford the salts [Rh(H)(2)(L-2)(PPh3)(2)][SB9H12] [L-2 = bpy (19), Me(2)bpy (20), phen (21)]. Similarly, in an atmosphere of CO(g) and in the presence of PPh3, compounds 1-6 afford [Rh(L-2)(PPh3)(2)(CO)][SB9H12] (L-2 = bpy (22), Me(2)bpy (23), phen (24)]. The structures of 19 and 24 are studied by X-ray diffraction analysis. The five-coordinate complexes [Rh(L-2)(PPh3)(2)(CO)](+) undergo PPh3 exchange in a process that is characterized as dissociative. The observed differences in the reactivity of the nbd-Rh(I) salts versus the cod-Rh(I) analogues are rationalized on the basis of the higher kinetic lability of the nbd ligand and its faster hydrogenation relative to the cod diene.