91Ó°ÊÓ

The cation \(\left[\mathrm{Mo}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) can be prepared by dissolving \(\mathrm{K}_{3}\left[\mathrm{MoCl}_{6}\right]\) in \(0.5 \mathrm{M} p\)-toluenesulphonic acid (which behaves similarly to the triflic acid discussed in the text) and allowing the solution to stand at room temperature in the absence of \(\mathrm{O}_{2}\), for a day. Suggest why this sequence is more successful than the action of \(\mathrm{H}_{2} \mathrm{O}\) on \(\mathrm{K}_{3}\left[\mathrm{MoCl}_{6}\right]\).

In the preparation of the complexes \(\mathrm{Cr}(\mathrm{CO})_{5} \mathrm{X}(\mathrm{X}=\) sulfur donor ligand) the recommended method is to UV- irradiate a solution of \(\mathrm{Cr}(\mathrm{CO})_{6}\) in THF (tetrahydrofuran) in an oxygenfree apparatus to give the complex \(\left[\mathrm{Cr}(\mathrm{CO})_{5}(\mathrm{THF})\right]\). This is followed by reaction with the ligand \(\mathrm{X}\). Direct reaction between \(\mathrm{Cr}(\mathrm{CO})_{6}\) and \(\mathrm{X}\) generally leads to sulfur- bridged complexes. Explain the thinking behind this route to \(\mathrm{Cr}(\mathrm{CO})_{5} \mathrm{X}\).

One procedure for the preparation of \(\mathrm{Ir}_{4}(\mathrm{CO})_{12}\) is to start with commercially available \(\mathrm{Na}_{2}\left[\operatorname{IrCl}_{6}\right]\) in ethanol and reduce it to the \(\left[\operatorname{IrCl}_{6}\right]^{3-}\) ion with \(\mathrm{I}^{-}\). Gaseous \(\mathrm{CO}\) is then passed into the solution, and together with the addition of solid \(\mathrm{K}_{2} \mathrm{CO}_{3}\), leads to the product, a black solid. Give a retrospective rationale of this sequence.