Rapid reversible borane to boryl hydride exchange by metal shuttling on the carborane cluster surface† †Electronic supplementary information (ESI) available. CCDC 1545735 and 1545736. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc01846k Click here for additional data file. Click here for additional data file.

In this work, we introduce a novel concept of a borane group vicinal to a metal boryl bond acting as a supporting hemilabile ligand in exohedrally metalated three-dimensional carborane clusters. The (POBOP)Ru(Cl)(PPh3) pincer complex (POBOP 1⁄4 1,7-OP(i-Pr)2-m-2-carboranyl) features extreme distortion of the two-center-two-electron Ru–B bond due to the presence of a strong three-centertwo-electron B–H/Ru vicinal interaction. Replacement of the chloride ligand with a hydride afforded the (POBOP)Ru(H)(PPh3) pincer complex, which possesses B–Ru, B–H/Ru, and Ru–H bonds. This complex was found to exhibit a rapid exchange between hydrogen atoms of the borane and the terminal hydride through metal center shuttling between two boron atoms of the carborane cage. This exchange process, which involves sequential cleavage and formation of strong covalent metal–boron and metal– hydrogen bonds, is unexpectedly facile at temperatures above 50 C corresponding to an activation barrier of 12.2 kcal mol . Theoretical calculations suggested two equally probable pathways for the exchange process through formally Ru(0) or Ru(IV) intermediates, respectively. The presence of this hemilabile vicinal B–H/Ru interaction in (POBOP)Ru(H)(PPh3) was found to stabilize a latent coordination site at the metal center promoting efficient catalytic transfer dehydrogenation of cyclooctane under nitrogen and air at 170 C.