The majority of ligands in modern chemistry utilize carbon-rich (alkyl or aryl) substituents to tune the steric and electronic properties of the ligand heteroatom moiety that binds to the metal. Yet, carbon-based substituents possess fundamental limitations in terms of their electron-donating and electron-withdrawing abilities. This ultimately sets a finite window for electronic modulation that these species can provide. Furthermore, given the chemical nature of these substituents, it is nearly impossible to design ligands where steric bulk remains invariant while electronic effects can be tuned over a wide range. Recently, it has been shown that icosahedral carborane moieties possess unique electronic features, which allow tuning electronic properties of ligands without affecting their steric profiles. While this work highlights such a unique possibility using thio- and selenoether ligands as examples, the generality and applicability of this new approach remains to be further understood. As such, the ongoing work has been focused on the development of new methods for the functionalization of carborane species to yield phosphine ligands. This presentation will describe a recently discovered metal-catalyzed coupling process producing a new class of B-functionalized carborane-based phosphinoborane ligands. These B-functionalized phosphinoboranes exhibit extreme electron-rich character and thus display coordination properties that are drastically different from their previously known C-functionalized carborane-based congeners.

Icosahedral carborane-based phosphinoboranes

245th National Meeting (2013)

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