Monosubstituted Borane Ruthenium Complexes RuH2(η2:η2-H2BR)(PR′3)2: A General Approach to the Geminal Bis(σ-B-H) Coordination Mode
Résumé
A series of borane bis(σ-B-H) ruthenium complexes RuH2(η2:η2-H2BR)(PR′3)2 (R = alkyl, aryl; R′ = Cy, Cyp, iPr) has been prepared by using two synthetic strategies. The first one is based on a simple substitution reaction by adding the corresponding monosubstituted H2BR borane to the bis(dihydrogen) ruthenium complex RuH2(η2-H2)2(PCy3)2. The second one, more general, results from the reaction of the chloro complex RuHCl(H2)(PR′3)2 (R′ = Cy, Cyp, iPr) with the corresponding lithium monosubstituted borohydrides RBH3Li (R = Mes, tBu, Me, C4H3S, Ph). All the complexes have been characterized by multinuclear NMR, IR, and X-ray diffraction studies. DFT calculations have been used to better define the bonding mode of the borane ligand to the metal center as well as to establish the thermodynamic cycle that delineates the coordination process. The tBu species displays a dynamic behavior evidencing an equilibrium between a borohydride and a σ-borane formulation. The thienyl case illustrates the competition between sulfur coordination and a bis(σ-B-H) coordination mode.