question about cisplatin

[Nan_Guan_1L]

In class, Dr. Lavelle gave an example of cisplatin. I was just wondering why does Guanine replaces the Cl on cisplatin and not the NH3?

[MinjooPark_3I]

So I searched it up and it says the chlorines leave to create a reactive space for the guanine to attach.

[rhettfarmer-3H]

I think it is key to note that the NH3 on the cisplatin has already filled its self and doesn't have any lone pairs or space for it binds. Therefore, when we look at the Cl- we have 3 pairs of lone pairs on both and its is also has a dipole movement. Hence, it is more likely that we bind at this site than the Nh3 that has 4 bonds on it and has no 3d to enter for an extended octate. Of course, I'm just thinking and using what I learned in 14a so open to other thoughts. Also, I know that cis has cl on the same side to bind to make adjacent a GG bond. I think it just can't bind to NH3 since it has filled 4 bonds.