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-C 2 B 10 H 12, with sodium naphthalide in THF (THF = tetrahydrofuran), followed by addition of [Rh 2 ( μ -Cl) 2 (cod) 2 ] (cod = 1,2:5,6- η -cyclooctadiene) and [N(PPh 3 ) 2 ]Cl, affords the monoanionic 13-vertex rhodacarborane [N(PPh 3 ) 2 ][4-(cod)- closo -4,1,6-RhC 2 B 10 H 12 ] ( 2 ). Treatment of compound 2 with sources of the cations {Cu(PPh 3 )} +, {Rh(PPh 3 ) 2 } +, {Rh(cod)} +, and {RuCl(PPh 3 ) 2 } + yields, respectively, the neutral bimetallic species [4-(cod)-3,4,7-{Cu(PPh 3 )}-3,7-( μ -H) 2 - closo -4,1,6-RhC 2 B 10 H 10 ], [4-(cod)-3,8-{Rh(PPh 3 ) 2 }-3,8-( μ -H) 2 - closo -4,1,6-RhC 2 B 10 H 10 ], [4-(cod)-3,8-{Rh(cod)}-3,8-( μ -H) 2 - closo -4,1,6-RhC 2 B 10 H 10 ], and [4-(cod)-3,7,8-{RuCl(PPh 3 ) 2 }-3,7,8-( μ -H) 3 - closo -4,1,6-RhC 2 B 10 H 9 ], of which only the copper derivative has a metal−metal bond. In addition, the reaction of 2 with CF 3 SO 3 H 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- η 3 -C 8 H 13 )- closo -4,1,6-RhC 2 B 10 H 12 ], which is stabilized by a C−H···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(CH 2 ) 4 }- closo -4,1,6-RhC 2 B 10 H 11 ].