Facile two-electron reduction of a closo-rhodathiadecaborane

Abstract

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-SB₈H₁₁] with [RhCl(PPh₃)₃] affords, after chromatography, three new 10-vertex rhodathiaboranes, [2,2,2-(H)(PPh₃)₂-closo-2,1-RhSB₈H₈] (3), [6,6,9-(PPh₃)₃-arachno-6,5-RhSB₈H₉] (4) and [2,2,2-(Cl)(H)(PPh₃)-6-(PPh₃)-closo-2,1-RhSB₈H₇] (5). 3 reacts quantitatively with PPh₃ 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 PPh₃ 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.