Extremely Electron-Rich, Boron-Functionalized, Icosahedral Carborane-Based Phosphinoboranes

We have prepared the first examples of B9-connected trivalent
aryl
and alkyl phosphinoborane species via Pd-catalyzed phosphination of
9-iodo-meta-carborane. Our studies highlight the
unique electronic features of the B9-connected meta-carboranyl moiety as compared to its C1-based analogue. This work
suggests that the B9-functionalized meta-carboranyl
substituent in these ligands exhibits more electron-releasing character
than any other known carbon-based substituent, ultimately laying the
foundation for a new class of phosphine ligands with extremely electron-rich
character.