Facile two-electron reduction of a closo-rhodathiadecaborane

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.