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Organometallic Chemistry on a Metallathiaborane Cluster:  Reactions of [8,8-(PPh3)2-nido-8,7-RhSB9H10] with Bidentate Phosphine Ligands

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journal contribution
posted on 08.08.1999, 00:00 by Ramón Macías, Nigam P. Rath, Lawrence Barton
Reactions of the unsaturated cluster [8,8-(PPh3)2-nido-8,7-RhSB9H10] (1) with the bidentate 1,n-bis(diphenylphosphino)alkanes (CH2)n(PPh2)2, where n = 1−3 (abbreviated as dppm, dppe, and dppp, respectively), have been studied. When a 1:1 molar ratio of phosphine to rhodathiaborane is used, for dppe and dppp, simple substitution to form [8,8-(η2-dppe)-nido-8,7-RhSB9H10] (2) or [8,8-(η2-dppp)-nido-8,7-RhSB9H10] (3) is observed. However, in the presence of an excess of dppe or dppp, mixtures of the species 2 and [8,8-(η2-dppe)-9-(η1-dppe)-nido-8,7-RhSB9H10] (4) or of 3 and [8,8-(η2-dppp)-9-(η1-dppp)-nido-8,7-RhSB9H10] (5) are formed, respectively. Under both sets of conditions, when dppm is used, only one product, [8,8-(η2-dppm)-8-(η1-dppm)-nido-8,7-RhSB9H10] (6), is observed. This latter species has two dppm ligands coordinating to the metal, one in a unidentate mode and the other bidentate. Species 2 and 3 are formally unsaturated, 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 unidentate ligand providing an additional skeletal electron pair to the cluster. The species 4 and 5 are unstable in solution; depending on the conditions, they dissociate to give free phosphine and the chelate 2 or 3 or they undergo nido to closo transformation with loss of dihydrogen, affording the corresponding 11-vertex closo compounds [1,1-(η2-dppe)-3-(η1-dppe)-closo-1,2-RhSB9H8] (17) and the dppp analogue [1,1-(η2-dppp)-3-(η1-dppp)-closo-1,2-RhSB9H8] (18). Further reaction in the case of 5 allows isolation of the linked cluster system [{1,1-(η2-dppp)-closo-1,2-RhSB9H8}2-3,3‘-(μ-dppp)] (19). The species have been characterized by NMR and mass spectrometry, and crystal structure determinations are described for 3, the OEt derivative of 3, [8,8-(η2-dppp)-9-(OEt)-nido-RhSB9H9] (14), 6, and the phosphine oxide of 17, [1,1-(η2-dppe)-3-(η1-dppeO)-closo-1,2-RhSB9H8] (20).