Silver as an Exopolyhedral Auxiliary to the Rhenacarborane Anion [Re(CO)₃(η⁵-7,8-C₂B₉H₁₁)]^-†

The rhenacarborane salt Cs[Re(CO)₃(η⁵-7,8-C₂B₉H₁₁)] (1) has been used to synthesize the tetranuclear metal complex [{ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃}₂{μ-Ph₂P(CH₂)₂PPh₂}] (3) where two [ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃] fragments have been shown by X-ray crystallography to be bridged by a single 1,2-bis(diphenylphosphino)ethane ligand. Reaction of 1 with Ag[BF₄] in the presence of the ligands bis- or tris(pyrazol-1-yl)methane yields the complexes [ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃{κ²-CH₂(C₃H₃N₂-1)₂}] (4) or [{ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃}₂{μ-κ¹,κ²-CH(C₃H₃N₂-1)₃}] (5), respectively. From X-ray studies, the former comprises a Re−Ag bond bridged by the carborane cage and with the bis(pyrazol-1-yl)methane coordinating the silver(I) center in an asymmetric κ² mode. Complex 5 was unexpectedly found to contain a tris(pyrazol-1-yl)methane bridging two [ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃] fragments in a κ¹,κ² manner. Treatment of 1 with Ag[BF₄] in the presence of 2,2‘-dipyridyl and 2,2‘:6‘,2‘ ‘−terpyridyl yields [ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃{κ²-(C₅H₄N-2)₂}] (6) and [ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃{κ³-C₅H₃N(C₅H₄N-2)₂-2,6}] (7). The X-ray structure determination of 7 revealed an unusual pentacoordinated silver(I) center, asymmetrically ligated by a κ³-2,2‘:6‘,2‘ ‘-terpyridyl molecule. The same synthetic procedure using N,N,N‘,N‘-tetramethylethylenediamine gave a tetranuclear metal complex [{ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃}₂{μ-Me₂N(CH₂)₂NMe₂}₂] (8) which is believed, in the solid state, to be bridged between the silver atoms by two of the diamine molecules. The salt 1 with Ag[BF₄] in the absence of any added ligand gave the tetrameric cluster [ReAg{μ-5,6,10-(H)₃-η⁵-7,8-C₂B₉H₈}(CO)₃]₄ (9) where, in the solid state, four [ReAg(μ-10-H-η⁵-7,8-C₂B₉H₁₀)(CO)₃] units are held together by long interunit B−H ⇀ Ag bonds.