For the following $CO$ insertion reaction, on using ${?}^{13}CO,$ the cis$(C{H}_{3}CO){(}^{13}CO)Mn(CO{)}_4$ is obtained exclusively. What can you conclude from this?

$(CO{)}_{5}Mn-C{H}_3+CO={?}_{\text{D}\text{e}\text{c}\text{a}\text{r}\text{b}\text{o}\text{n}\text{y}\text{l}\text{i}\text{e}\text{r}\text{u}\text{n}\text{g}}^{CO-\text{I}\text{n}\text{s}\text{e}\text{r}\text{t}\text{i}\text{o}\text{n}}$

To figure out whether this reaction is actually a $CO$ insertion $($A$),$ or a $C{H}_3$ migration

$($B$)$ information from the thermal back reaction was used $($decarbonylation$).$ The result was the following: $50\%$ cis$-(C{H}_3){(}^{13}CO)Mn(CO)4,25\%$ trans$-$

$(C{H}_3){(}^{13}CO)Mn(CO{)}_4$ and $25\%{?}^{13}CO$ free $(C{H}_3)Mn(CO{)}_5.$ What does this result mean in terms of $CO-$insertion, or $C{H}_3-$migration?