Sandmeyer's reaction cannot be used in the preparation of

$$\begin{gathered} {\mathrm{C}}_6{\mathrm{H}}_5-{\mathrm{N}}_2^{+}{\mathrm{Cl}}^{-}\stackrel{{\mathrm{Cu}}_2{\mathrm{Cl}}_2/\mathrm{HCl}}{\to }{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{Cl} ; \\ {\mathrm{C}}_6{\mathrm{H}}_5-{\mathrm{N}}_2^{+}{\mathrm{Cl}}^{-}\stackrel{{\mathrm{Cu}}_2{\mathrm{Br}}_2/\mathrm{HBr}}{\to }{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{Br} ; \\ {\mathrm{C}}_6{\mathrm{H}}_5-{\mathrm{N}}_2^{+}{\mathrm{Cl}}^{-}\stackrel{{\mathrm{Cu}}_2{\left(\mathrm{CN}\right)}_2/\mathrm{KCN}}{\to }{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{CN}; \\ \mathrm{The} \mathrm{above} \mathrm{reactions} \mathrm{are} \mathrm{examples} \mathrm{of} \mathrm{sandmeyer}\text{'}\mathrm{s} \mathrm{reaction} \\ \mathrm{but} \mathrm{the} \mathrm{reaction} \mathrm{below} \mathrm{is} \mathrm{not}. \\ {\mathrm{C}}_6{\mathrm{H}}_5-{\mathrm{N}}_2^{+}{\mathrm{Cl}}^{-}\stackrel{\mathrm{KI}}{\to }{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{I} ; \end{gathered}$$