Synthesis, solution behavior and molecular structure of the new sandwich-type cobaltacarborane cluster closo,nido-[CoH(2,4-C2B8H10) (7,8-C2B8H11)]1−

•New anionic cobaltacarborane commo clusters based on {C2B8}-carborane are prepared.•Structure of [Ph3PMe][closo,nido-CoH(2,4-C2B8H10) (7,8-C2B8H11)] was studied by XRD.•Complexes are fluxional in solution and show exchange between M-H and B–H–B units.

Treatment of an anhydrous CoCl2 with the [Na][C2B8H11] (1) generated in situ from the neutral ten-vertex dicarbon carborane [5,6-nido-C2B8H12] (2) with NaH in THF at ambient temperature affords the new cobaltacarborane commo cluster closo,nido-[CoH(2,4-C2B8H10)(7,8-C2B8H11)]1− isolated as its air-stable [Ph4P]+ (3) and [Ph3PMe]+ (4) salts. As was found from the crystallographically determined structure of 4 and based on the 1H NMR spectroscopic data for both 3 and 4, these anionic salts are composed of the Co–H unit that is sandwiched between two {C2B8} cages; one of these cages, the formally doubly charged [C2B8H10]2− ligand, is involved in the η6-coordination to the metal center, but another singly charged [7,8-C2B8H11]1− ligand, which retains one bridged B–H–B hydrogen atom, is involved through its CB3-open face in the η4-coordination to the cobalt atom. At room temperature, complexes 3 and 4 exhibited fluxional behavior in solution where the exchange between terminal Co–H and bridging B–H–B hydrogen atoms occurs. This is discussed in detail based on the comparable room- and low-temperature 1H NMR spectra of 3.

Graphical abstractThe first representative of anionic cobaltacarborane commo cluster closo,nido-[CoH(2,4-C2B8H10) (7,8-C2B8H11)]1− was prepared and fully characterized as its [Ph4P]+ and [Ph3PMe]+ salts. The crystal structure of [Ph3PMe][CoH(2,4-C2B8H10) (7,8-C2B8H11)] provides a unique example of commo-metallacarborane containing two asymmetric cage ligands based on the carborane [5,6-nido-C2B8H12].Figure optionsDownload full-size imageDownload as PowerPoint slide