Dynamics of a cis-Dihydrogen/Hydride Complex of Iridium

Insertion of $CS_2$ into one of the Ir-H bonds of $[Ir(H)_5(PCy_3)_2]$ takes place to afford the dihydrido dithioformate complex $cis-[Ir(H)_2(\eta^2-S_2CH)(PCy_3)_2]$ accompanied by the elimination of $H_2$. Protonation of the dithioformate complexv using $HBF_4$‚ $Et_2O$ gives $cis-[Ir(H)(/eta_2-H_2)(\eta_2-S_2CH)(PCy_3)_2][BF_4]$ 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 J(H,D) of 6.5 and 7.7 Hz for the $H_2D$ and the $HD_2$ isotopomers of cis-$[Ir(H)(\eta_2-H_2)(\eta_2-S_2CH)(PCy_3)_2]-[BF_4]$, respectively. The H-H distance $(d_H_H)$ for this complex has been calculated to be 1.05 $\AA$, which can be categorized under the class of elongateddihydrogen complexes. The $cis-[Ir(H)(\eta{_2}-H_2)(\eta{_2}-S_2CH)(PCy-3)_2][BF_4]$ complex undergoes substitution of the bound $H_2$ moiety with $CH_3CN$ and CO resulting in new hydride derivatives, $cis-[Ir(H)-(L)(\eta{_2}-S_2CH)(PCy_3)_2][BF_4] (L ) CH_3CN, CO)$. Reaction of $cis-[Ir(H)_2(\eta{_2}-S_2CH)(PCy_3)_2]$ with electrophilic reagents such as MeOTf and Me3SiOTf afforded a new hydride aquo complex $cis-[Ir(H)(H_2O)(\ets{_2}-S_2CH)(PCy_3)_2][OTf]$ via the elimination of $CH_4$ and $Me_3SiH$, 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 $cis-[Ir(H)_2(\eta{_2}-S_2CH)(PCy_3)_2]$ and $cis-[Ir(H)-(H_2O)(\eta{_2}-S_2CH)(PCy_3)_2][OTf]$ have been determined