Closo-to-arachno redox flexibility in metallaheteroboranes may be viewed as a metal-to-ligand cooperative action with application in catalysis. The treatment of [PSH][arachno-4-SB(8)H(11)] with [RhCl(PPh(3))(3)] affords, after chromatography, three new 10-vertex rhodathiaboranes, [2,2,2-(H)(PPh(3))(2)-closo-2,1-RhSB(8)H(8)] (3), [6,6,9-(PPh(3))(3)-arachno-6,5-RhSB(8)H(9)] (4) and [2,2,2-(Cl)(H)(PPh(3))-6-(PPh(3))-closo-2,1-RhSB(8)H(7)] (5). 3 reacts quantitatively with PPh(3) to form 4, which, in turn, reacts with chlorinated solvents to give the chloro-ligated cluster 5. Kinetic studies demonstrate that the reaction of 3 with PPh(3) obeys a second-order rate law, with an associative mechanism. The Lewis acidity of 3 is quite remarkable, and, given its closo-to-arachno structural and electronic response, this cluster is expected to exhibit a rich chemistry.

New 10-vertex rhodathiaboranes are reported to exhibit reversible reaction chemistry leading to the formation of stoichiometric cycles driven by oxidation/reduction chemistry of the polyhedral boron-based clusters with ethelyne and dihydrogen.

Dedicated to Professor Thomas P. Fehlner on his 75th birthday. He has been a superb mentor of many scientists around the world working on "inorganometallic chemistry". Keywords:The reaction between [arachno-6-SB 9 H 12 ] À and [IrCl(CO)(PMe 3 ) 2 ] affords the previously reported 11-vertex cluster, [8,8,(PMe 3 ) 2 -arachno-8,7-IrSB 9 H 10 ] (4), and small amounts of the new 10-vertex iridathiaborane [9,9,9,(H)(PMe 3 ) 2 -arachno-9,6-IrSB 8 H 10 ] (5). Alternatively, a rational synthesis of iridathiadecaboranes is effected from the reaction of the 9-vertex anion [arachno-4-SB 8 H 11 ] À with [MCl(CO)(PPh 3 ) 2 ], to afford new CO-ligated 10-vertex metallathiaboranes of formulation, [9,9,9,(H)(PPh 3 ) 2 -arachno-9,6-MSB 8 H 10 ], where M ¼ Rh (6) and Ir (7), in useful yields of 61% and 60% respectively. Treatment of the 11-vertex rhodathiaborane, [8,8-(PPh 3 ) 2 -8,7-nido-RhSB 9 H 10 ] (1) with nBuLi, followed by addition of [IrCl(CO)(PMe 3 ) 2 ] affords the 12-vertex iridarhodathiaborane, [1,2-(m-CO)-1,1,2-(PMe 3 ) 3 -2-(PPh 3 )-closo-1,2-IrRhSB 9 H 9 ] (8) in low yield (0.7%). The 10-vertex metallathiaboranes, 5, 6 and 7, and the bimetallic 12-vertex cluster, 8, have been characterized by multinuclear NMR spectroscopy. In addition, the molecular structures of compounds 5, 6, and 8 have been studied by X-ray diffraction.

It has been demonstrated that the reaction of [2,2,2-(H)(PPh3)2-closo-2,1-RhSB8H8] () with PPh3 affords the boron substituted rhodathiaborane-PPh3 adduct, [6,6-(PPh3)2-9-(PPh3)-arachno-6,5-RhSB8H9] (). Building upon this reaction, we report herein that the 10-vertex hydridorhodathiaborane reacts with the Lewis bases, PCy3, py, 2-Mepy, 2-Etpy, 3-Mepy and 4-Mepy to form the rhodathiaborane-ligand adducts, [6,6-(PPh3)2-9-(L)-arachno-6,5-RhSB8H9], where L = PCy3 (), 2-Mepy (), 2-Etpy (), py (), 3-Mepy () or 4-Mepy (), and [8,9-μ-(H)-9-(PPh3)2-8-(L)-arachno-9,6-RhSB8H8], where L = py (), 3-Mepy () or 4-Mepy (). The selectivity of the reactions depended on the nature of the entering Lewis bases, affording the 6,5-isomers, , , and as single products for PPh3, PCy3, 2-Mepy and 2-Etpy; and mixtures of the 6,5-/9,6-regioisomers, /, / and / for py, 3-Mepy and 4-Mepy, respectively. The molecular structures of both regioisomers were characterized by X-ray diffraction analysis for the 6,5-isomers, and , and for the 9,6-isomers, and . Variable temperature NMR studies of the reaction between and PPh3 or 2-Mepy demonstrated that at low temperatures there is formation of the 9,6-species that subsequently isomerizes to the 6,5-regioisomer, indicating that for the more sterically hindered Lewis bases, PPh3, 2-Mepy and PCy3, the latter isomer is more stable and accessible through an intramolecular {Rh(PPh3)2} vertex flip. The formation of both isomers with py, 3-Mepy and 4-Mepy indicates that the kinetic and thermodynamic energies of the 6,5 and 9,6 rhodathiaborane-ligand adducts are similar for these Lewis bases. Lewis base bonding to exo-polyhedral boron vertices results in a change of the metal coordination from pseudo-octahedral Rh(iii) in to pseudo-square planar Rh(i) in the adducts. The chemistry described here highlights the remarkable structural flexibility of these polyhedral boron-containing compounds, their modular architecture and their easy postsynthetic modification.