Dynamics of a <i>cis</i>-Dihydrogen/Hydride Complex of Iridium

Insertion of CS<sub>2</sub> into one of the Ir−H bonds of [Ir(H)<sub>5</sub>(PCy<sub>3</sub>)<sub>2</sub>] takes place to afford the dihydrido dithioformate complex <i>cis</i>-[Ir(H)<sub>2</sub>(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>] accompanied by the elimination of H<sub>2</sub>. Protonation of the dithioformate complex using HBF<sub>4</sub>·Et<sub>2</sub>O gives <i>cis</i>-[Ir(H)(η<sup>2</sup>-H<sub>2</sub>)(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>][BF<sub>4</sub>] wherein the H atom undergoes site exchange between the dihydrogen and the hydride ligands. The dynamics was found to be so extremely rapid with respect to the NMR time scale that the barrier to exchange could not be measured. Partial deuteration of the hydride ligands resulted in a <i>J</i>(H,D) of 6.5 and 7.7 Hz for the H<sub>2</sub>D and the HD<sub>2</sub> isotopomers of <i>cis</i>-[Ir(H)(η<sup>2</sup>-H<sub>2</sub>)(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>][BF<sub>4</sub>], respectively. The H−H distance (<i>d</i><sub>HH</sub>) for this complex has been calculated to be 1.05 Å, which can be categorized under the class of <i>elongated</i> dihydrogen complexes. The <i>cis</i>-[Ir(H)(η<sup>2</sup>-H<sub>2</sub>)(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>][BF<sub>4</sub>] complex undergoes substitution of the bound H<sub>2</sub> moiety with CH<sub>3</sub>CN and CO resulting in new hydride derivatives, <i>cis</i>-[Ir(H)(L)(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>][BF<sub>4</sub>] (L = CH<sub>3</sub>CN, CO). Reaction of <i>cis</i>-[Ir(H)<sub>2</sub>(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>] with electrophilic reagents such as MeOTf and Me<sub>3</sub>SiOTf afforded a new hydride aquo complex <i>cis</i>-[Ir(H)(H<sub>2</sub>O)(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>][OTf] via the elimination of CH<sub>4</sub> and Me<sub>3</sub>SiH, respectively, followed by the binding of a water molecule (present in trace quantities in the solvent) to the iridium center. The X-ray crystal structures of <i>cis</i>-[Ir(H)<sub>2</sub>(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>] and <i>cis</i>-[Ir(H)(H<sub>2</sub>O)(η<sup>2</sup>-S<sub>2</sub>CH)(PCy<sub>3</sub>)<sub>2</sub>][OTf] have been determined.