In this case, there is a concerted process without intermediate of reaction. Very often,the breaking and bond formation is not simultaneous. If the dissociation is somewhat ahead of the formation of new bonds we describe it as a dissociative exchange mechanism, Id, and if conversely we have an associative exchange mechanism, Ia. The animation shows that the transition between the substrates and products is continuous, without reaction intermediate.
In the trnasition state the incorporation of the incoming group has advanced more than the dissociation of the leaving group.
The V-CO dissociation occurs in a concerted manner with the V-PPh3 bond formation, but this one going ahead. This is an associative exchange.
In this case, the dissociation of the leaving group has advanced more in the transition state than the incorporation of incoming group.
In this case, the incorporation of the incoming group in the transition state has advanced less than the dissociation of the leaving group.