Mesitylborane as a Bis(σ-B−H) Ligand: An Unprecedented Bonding Mode to a Metal Center
journal contribution
posted on 2007-07-18, 00:00 authored by Gilles Alcaraz, Eric Clot, Ulrike Helmstedt, Laure Vendier, Sylviane Sabo-EtienneThe new borane complex RuH<sub>2</sub>(η<sup>2</sup>:η<sup>2</sup>-H<sub>2</sub>BMes)(PCy<sub>3</sub>)<sub>2</sub> (<b>2</b>) can be isolated in good yield by reaction of H<sub>2</sub>BMes with RuH<sub>2</sub>(η<sup>2</sup>-H<sub>2</sub>)<sub>2</sub>(PCy<sub>3</sub>)<sub>2</sub> (<b>1</b>) or alternatively, by reacting the chloro dihydrogen complex RuHCl(η<sup>2</sup>-H<sub>2</sub>)(PCy<sub>3</sub>)<sub>2</sub> (<b>3</b>) with lithium mesitylborohydride. <b>2</b> has been fully characterized by NMR and X-ray diffraction crystallography. A DFT/B3PW91 analysis shows that in <b>2</b>, the H<sub>2</sub>BMes group is coordinated to the {RuH<sub>2</sub>(PCy<sub>3</sub>)<sub>2</sub>} fragment through two geminal σ-B−H bonds. This coordination involves σ-donation to the ruthenium and π back-bonding from the ruthenium to the vacant p orbital of the boron. These two geminal σ-B−H bonds are responsible for the short Ru−B distance (1.938 (4) Å by X-ray, 1.957 Å by DFT).
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