Dynamics of a cis-Dihydrogen/Hydride Complex of Iridium
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Abstract
Insertion of CS2 into one of the Ir−H bonds of [Ir(H)5(PCy3)2] takes place to afford the dihydrido dithioformate complex cis-[Ir(H)2(η2-S2CH)(PCy3)2] accompanied by the elimination of H2. Protonation of the dithioformate complex using HBF4·Et2O gives cis-[Ir(H)(η2-H2)(η2-S2CH)(PCy3)2][BF4] 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 H2D and the HD2 isotopomers of cis-[Ir(H)(η2-H2)(η2-S2CH)(PCy3)2][BF4], respectively. The H−H distance (dHH) for this complex has been calculated to be 1.05 Å, which can be categorized under the class of elongated dihydrogen complexes. The cis-[Ir(H)(η2-H2)(η2-S2CH)(PCy3)2][BF4] complex undergoes substitution of the bound H2 moiety with CH3CN and CO resulting in new hydride derivatives, cis-[Ir(H)(L)(η2-S2CH)(PCy3)2][BF4] (L = CH3CN, CO). Reaction of cis-[Ir(H)2(η2-S2CH)(PCy3)2] with electrophilic reagents such as MeOTf and Me3SiOTf afforded a new hydride aquo complex cis-[Ir(H)(H2O)(η2-S2CH)(PCy3)2][OTf] via the elimination of CH4 and Me3SiH, 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(η2-S2CH)(PCy3)2] and cis-[Ir(H)(H2O)(η2-S2CH)(PCy3)2][OTf] have been determined.
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