Ruthenium tris(σ-B-H) borate complexes: synthesis, structure, and reactivity

The coordination of the B-H bond to a transition metal is fundamentally intriguing due to its connection with the transition metal-mediated B-H bond activation mechanism and catalysis. Most of the reported examples are sigma-borane/borate complexes containing one or two sigma-B-H bonds. However, examples of compounds containing three sigma-B-H bonds are still much rarer. Herein, we report a facile approach for the synthesis of rare transition metal tris(sigma-B-H) borate complexes by the salt elimination protocol using [Cp*RuCl](4) and lithium trihydroborates Li[ArBH3] containing 2,6-disubstituted aryl groups. These complexes have remarkable thermal stability in solution. In addition, this novel class of compounds has the unusual sigma-complex that features three labile sigma-B-H bonds. Our studies on these new species demonstrate that the coordination sigma-B-H bond can undergo H/D exchange with D-2 and ligand substitution reactions with PPh3, PCy3 and IPr2Me2. These results provide new approaches for the synthesis of both tris(sigma-B-H) borates and bis(sigma-B-H) borates.

Automated summary

The coordination of the B-H bond to a transition metal is of fundamental interest due to its relevance to the transition metal-mediated B-H bond activation mechanism and catalysis. While most reported examples involve sigma-borane/borate complexes with one or two sigma-B-H bonds, compounds with three such bonds are much less common. This study presents a facile synthesis approach for rare transition metal tris(sigma-B-H) borate complexes by salt elimination using [Cp*RuCl](4) and lithium trihydroborates Li[ArBH3] with 2,6-disubstituted aryl groups. These complexes exhibit remarkable thermal stability in solution and feature the unusual sigma-complex with three labile sigma-B-H bonds.