Syntheses, Structural Characterizations, and Reactivity Studies of Half-Sandwich Cobalt, Rhodium, and Iridium Metallatricarbadecaboranyl Complexes

The syntheses and structural characterizations
of the first extensive
series of Group 9 (Co, Rh, and Ir) tricarbadecaboranyl half-sandwich
complexes are reported. The carbonyl complexes 1,1-(CO)2-2-Ph-closo-1,2,3,4-MC3B7H9, M = Co (1), Rh (2), and 8,8,8-(CO)3-9-Ph-nido-8,7,9,10-IrC3B7H9 (3) were obtained by the reactions
of Li+(6-Ph-nido-5,6,9-C3B7H9)− with Co­(CO)4I,
[Rh­(CO)2Cl]2, and Ir­(CO)3Cl, respectively.
Further reactions of 1, 2, and 3 with 1,2-bis­(diphenyl­phos­phino)­ethane (dppe) yielded
the 1,1-dppe-2-Ph-closo-1,2,3,4-MC3B7H9, M = Co (4), Rh (5), and 8-CO-8,8-dppe-9-Ph-nido-8,7,9,10-IrC3B7H9 (6) derivatives with
their crystallographic determinations showing that 1 and 2 contain the η6-2-Ph-2,3,4-C3B7H91– ligand with the metallatricarbadecaboranyl
cluster fragments having closo-octadecahedral geometries,
while 3 has a slipped-cage η4-9-Ph-7,9,10-C3B7H91– coordination
and a nido-cluster framework. The reaction of Li+(6-Ph-nido-5,6,9-C3B7H9)− with [Rh­(COD)­Cl]2 and
[Ir­(COD)­Cl]2 produced the COD coordinated complexes 1,1-COD-2-Ph-closo-1,2,3,4-MC3B7H9,
M = Rh (7), Ir (8), with η6-2-Ph-2,3,4-C3B7H91– ligands and closo-cluster structures. On the other
hand, slipped-cage structures with η4-9-Ph-7,9,10-C3B7H91– coordination
were achieved by the reactions of 1, 3,
or 8 with an excess of the stronger donor tert-butyl isocyanide to give 8,8,8-(CNtBu)3-9-Ph-nido-8,7,9,10-MC3B7H9, M = Co (9), Ir (10), respectively,
or by the reaction of 8 with 1 equiv of tert-butyl isocyanide to give 8,8-COD-8-CNtBu-9-Ph-nido-8,7,9,10-IrC3B7H9 (11). Upon the reaction of 1 with diphenylacetylene, both carbonyls were displaced with subsequent
alkyne cyclization to form the tetraphenylcyclobutadienyl complex
1,1-(η4-C4Ph4)-2-Ph-closo-1,2,3,4-CoC3B7H9 (12). The crystalline tetramethylcyclobutadienyl derivative
1,1-(η4-C4Me4)-2-Ph-closo-1,2,3,4-CoC3B7H9 (13) was synthesized by the reaction of Li+(6-Ph-nido-5,6,9-C3B7H9)− with (η4-C4Me4)­Co­(CO)2I, and its crystallographic determination
confirmed the formation of a complex where a formal Co3+ ion is sandwiched between η4-C4Me42– and η6-2-Ph-2,3,4-C3B7H91– ligands. In
contrast to the reactions with diphenylacetylene, the reaction of 8 with 3-hexyne resulted in cage deboronation to produce 2,2-COD-10-Ph-closo-2,1,6,10-C3B6H8 (14). Neither 7 nor 8 would undergo
oxidative-addition when treated with I2. Although 11 reacted with I2 and perfluoro-1-iodohexane,
oxidative-addition products were also not obtained, but instead, iodation
of a cage boron occurred to produce 8,8-COD-1-CNtBu-9-Ph-11-I-nido-8,7,9,10-IrC3B7H8 (15).