Organometallic chemistry on a metallathiaborane cluster: Reactions of [8,8-(PPh3)(2)-nido-8,7-RhSB9H10] with bidentate phosphine ligands

Reactions of the unsaturated cluster [8,8-(PPh3)(2)-nido-8,7-RhSB9H10] (1) with the bidentate 1,n-bis(diphenylphospkino)alkanes (CH2)(n)(PPh2)(2), whe re n = 1-3 (abbreviated as dppm, dppe, and dppp, respectively), have been s tudied. When a 1:1 molar ratio of phosphine to rhodathiaborane is used, for dppe and dppp, simple substitution to form [8,8-(eta(2)-dppe)-nido-8,7-RhS B9H10] (2) or [8,8-(eta(2)-dppp)-nido-8,7-RhSBSH10] (3) is observed. Howeve r, in the presence of an excess of dppe or dppp, mixtures of the species 2 and [8,8-(eta(2)-dppe)-9-(eta(1)dppe)-nido-8,7-RhSB9H10] (4) or of 3 and [8 ,8-(eta(2)-dppp)-9-(eta(1)-dppp)-nido-8,7-RhSB9H10] (5) are formed, respect ively. Under both sets of conditions, when dppm is used, only one product, [8,8-(eta(2)-dppm)-8-(eta(1)-dppm)-nido-8,7-RhSB9H10 (6), is observed. This latter species has two dppm ligands coordinating to the metal, one in a un identate mode and the other bidentate. Species 2 and 3 are formally unsatur ated, two electrons short of the number required for the observed 11-vertex nido structure. In contrast, 4 and 5 are saturated with the cage-bonded un identate ligand providing an additional skeletal electron pair to the clust er. The species 4 and 5 are unstable in solution; depending on the conditio ns, they dissociate to give free phosphine and the chelate 2 or 3 or they u ndergo nide to close transformation with loss of dihydrogen, affording the corresponding 11-vertex close compounds [1,1-(eta(2)-dppe)-3-(eta(1)-dppe)- closo- 1,2-RhSB9H8] (17) and the dppp analogue [1,1-(eta(2)-dppp)-3-(eta(1) -dppp)closo-1,2-RhSB9H8] (18). Further reaction in the case of 5 allows iso lation of the linked cluster system [{1,1-(eta(2)-dppp)-closo-1,2-RhSB9H8]( 2)-3,3'-(mu-dppp)] (19). The species have bees characterized by NMR and mas s spectrometry, and crystal structure determinations are described for 3, t he OEt derivative of 3, [8,8-(eta(2)-dppp)-9-(OEt)-nido-RhSB9H9] (14), 6, a nd the phosphine oxide of 17, [1,1-(eta(2)-dppe)-3-(eta(1)-dppeO)-closo-1,2 -RhSB9H8] (20).