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

Abstract

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).

Reactions of Boranes and Metallaboranes with Phosphines

“…The species formed, [9,9-(η 2 -dppm)-9-(η 1 -dppm)-nido-9,7,8-RhC 2 B 8 H 11 ] (VIII), was completely characterized by multinuclear NMR spectroscopy, HR-MS, elemental analysis and a crystal structure determination. The structure of VIII, shown here, is similar to that we previously reported for {8,8-[η-(η 2 -dppm)-8-(η 1 -dppm)]-nido-8,7-RhSB 9 H 10 } (IX), [11] also shown, but the orientation of the ligands in the two species is different. We have developed the chemistry of VIII and discovered that it and its derivatives are not as easy to work with as IX.…”

“…Degradation and rearrangement reactions Species IX is yellow, but on standing for several days in solution, a red compound is formed which initially eluded characterization [11]. A key to the identity of this species was obtained when IX was allowed to react with II.…”

Chemistry of 11-vertex rhodathiaboranes: reactions with monodentate phosphines

“…In contrast, the use of two equivalents of PMe 2 Ph or PMe 3 gives mixtures that contain both the monosubstituted bis-(phosphine) species, [8,8-(PPh 3 )(L)-nido-8,7-RhSB 9 H 10 ], where L = PPhMe 2 (5) or PMe 3 (6), together with the products of addition of a third phosphine at the metal, viz. the tris-(phosphine) species [8,8,8-(L) 3 -nido-8,7-RhSB 9 H 10 ], where L = PPhMe 2 (7) or PMe 3 (8).…”

“…3,4 This consideration prompted us to examine how we might modify the exo-polyhedral phosphine-ligand sphere in order to explore the reactivity of new phosphine-ligated derivatives of 2, the overall target being the optimization of the catalytic activity of these cluster species. In this regard, it has previously been demonstrated that the rhodathiaborane 1 undergoes facile substituion of PPh 3 by other monodentate, and also bidentate, phosphines, 5,6 and we have examined reactions of 1 and 2 with the monodentate phosphines PMePh 2 , PMe 2 Ph and PMe 3 .…”

Organometallic chemistry on rhodaheteroborane clusters: reactions with bidentate phosphines and organotransition metal reagents

“…This suggests that the BH 3 group is fluxional in solution, probably undergoing rotation about the B-P bond, rendering the two bridging and the terminal hydrogen atoms equivalent on the NMR time scale ( G ‡ ≈ 37 kJ mol −1 2 ], where n = 3 or 2 respectively) proceed quite differently from reactions with dppm. 16 When a 1 : 1 molar ratio of phosphine to rhodathiaborane is used, simple substitution to form [8,8- but compound 7 was new, and complete characterization, including a crystal structure determination, identified the material. The properties of compounds 7 and 10 are quite similar to those of the starting material 1.…”