Monosubstituted Borane Ruthenium Complexes RuH<sub>2</sub>(η<sup>2</sup>:η<sup>2</sup>‑H<sub>2</sub>BR)(PR′<sub>3</sub>)<sub>2</sub>: A General Approach to the Geminal Bis(σ-B–H)
Coordination Mode
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Abstract
A series
of borane bis(σ-B–H) ruthenium complexes RuH<sub>2</sub>(η<sup>2</sup>:η<sup>2</sup>-H<sub>2</sub>BR)(PR′<sub>3</sub>)<sub>2</sub> (R = alkyl, aryl; R′ = Cy, Cyp, <sup><i>i</i></sup>Pr) has been prepared by using two synthetic
strategies. The first one is based on a simple substitution reaction
by adding the corresponding monosubstituted H<sub>2</sub>BR borane
to the bis(dihydrogen) ruthenium complex RuH<sub>2</sub>(η<sup>2</sup>-H<sub>2</sub>)<sub>2</sub>(PCy<sub>3</sub>)<sub>2</sub>.
The second one, more general, results from the reaction of the chloro
complex RuHCl(H<sub>2</sub>)(PR′<sub>3</sub>)<sub>2</sub> (R′
= Cy, Cyp, <sup><i>i</i></sup>Pr) with the corresponding
lithium monosubstituted borohydrides RBH<sub>3</sub>Li (R = Mes, <sup><i>t</i></sup>Bu, Me, C<sub>4</sub>H<sub>3</sub>S, 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 <sup><i>t</i></sup>Bu 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
