Synthesis of the 13-vertex rhodacarborane anion [4-(1,2:5,6-η-cod)-closo-4,1,6-RhC2B10H12]- and its reactions with electrophiles

Reduction of closo-1,2-C2B10H12, with sodium naphthalide in THF (THF = tetrahydrofuran), followed by addition of [Rh-2(mu-Cl)(2)(cod)(2)] (cod = 1,2:5,6-eta-cyclooctadiene) and [N(PPh3)(2)]Cl, affords the monoanionic 13-vertex rhodacarborane [N(PPh3)(2)][4-(cod)-closo-4,1,6-RhC2B10OH12] (2). Treatment of compound 2 with sources of the cations {Cu(PPh3)}(+), {Rh(PPh3)(2)}(+), {Rh(cod)}(+), and {RuCl(PPh3)(2)}(+) yields, respectively, the neutral bimetallic species [4-(cod)-3,4,7-{Cu(PPh3)}-3,7-(mu-H)(2)-closo-4,1,6-RhC2B10H10], [4-(cod)-3,8-{Rh(PPh3)(2)}-3,8-(mu-H)(2)-closo-4,1,6-RhC2B10H10], [4-(cod)-3,8-{Rh(cod)-3,8-(mu-H)(2)-closo-4,1,6-RhC2B10H10], and [4-(cod)-3,7,8-{RuCl(PPh3)(2)}-3,7,8-(mu-H)3-ClOSO-4,1,6-RhC2B(10)H(9)], of which only the copper derivative has a metal-metal bond. In addition, the reaction of 2 with CF3SO3H results in protonation of the cyclooctadiene ligand with concomitant oxidation of the rhodium center, yielding the ostensibly 16-electron Rh-III compound [4-(1-3-eta(3)-C8H13)-closo-4,1,6-RhC2B10H12], which is stabilized by a C-H center dot center dot center dot Rh agostic interaction. Alternatively, treatment of 2 with hydride-abstracting reagents in the presence of THF results in substitution at a cage BH vertex, forming the zwitterionic complex [4-(cod)-7-{O(CH2)(4)}-closo-4,1,6-RhC2B10H11].