Phosphine–boranes incorporating the carborane cluster

The high stability of the closo-carboranylmonophosphines and the low basicity and nucleophilicity are attributed to the electron-withdrawing character of the closo cluster. On the contrary, the nido cluster has an electron-donor character, which induces high electronic density on the phosphorus atom, then increasing the basicity and nucleophilicity of these ligands. In this way, the nido-carboranylmonophosphines react with ethanol to give the tertiary phosphonium salts and are readily oxidized by air in solution. They readily react with transition metals to form the corresponding metallacarboranes. To learn more of the distinct behavior of the closo-and nido-carboranylmonophosphines, the reaction of some of them with the BH3·THF Lewis acid has been carried out. In this communication, we report the reaction of closo- and nido-carboranylmonophosphines with BH3·THF leading to the formation of new phosphine–borane adducts. In the case of the nido-carboranylmonophosphines, all of them have shown a similar behavior irrespective of the nature of the R and R′ groups. However, the closo-carboranylmonophosphines have demonstrated to be less basic and only one of them has been able to form the corresponding phosphine–borane adduct. The crystal structure of [NBu4]+[7-PiPr2·BH3-8-Me-7,8-C2B9H10]− has also been described. The coordination chemical shift (ccs) has been calculated and a relation established between the coupling constants (11B1H and 31P11B) obtained by the 11B{1H}- and 31P{1H}-NMR and the Lewis basicity of the phosphines.