[Sonntag]

Hi all,

I want to work on my metalorganic skills and started reading the book "The organometallic chemistry of the transition metals" of Crabtree, which we got recommened. I've tried to get through the problems (at the moment chapter 1), too. The (often quite general) solution is in the book, but often I am not sure if my thinking is really right or why the book says it's right.
So I want to write some of my ideas here and I would be glad if someone can tell me if I go into the right direction.
Thank you.

Sonntag


1. Consider the 2 complexes MeTiCl₃ and (CO)₅W(thf). Predict the order of reactivity in each case toward the following sets of ligands: NMe₃, PMe₃, CO.

For MeTiCl₃: NMe₃ >  PMe₃ > CO
Ti is in this case d₀. So the electron density at the metal atom is low.
NMe₃ is a good electron (sigma) donor, because of its electronegativity (EN). Because its EN higher it's better than PMe₃. CO gives very stable complexes through pi backbonding. Because we have Ti(IV) this does not work effectively.

For (CO)₅W(thf): CO > PMe₃ >  NMe₃
W is d₆. So the electron density is high and (pi) back bonding can be well established. So most stable complex will be with CO. The binding atom of PMe₃ is more polarizable than the N of NMe₃. Because W(0) is more soft the combination with PMe₃ will result to the more stable complex.


2. What oxidation state, of the ones commonly availabe to copper, do you think would form the strongest CO complexes?

Cu(0), because here the metal has the highest electron density that is good for a strong backbonding.


3. How would you design a synthesis of the complex trans-[PtCl₂(NH₃)(tu)] (the trans descriptor refers to a pair of identical ligands, Cl in this case, is mutually trans), given that the trans effect order is tu > Cl > NH₃.

I've started with [Pt(NH₃)₄], because NH₃ has the least trans-effect. Then, I've added 1 equivalent Cl^-, afterwards 1 equivalent tu. (tu I'd added last, because it has the greatest trans-effect.).

The solution says: Start with [PtCl₄]^2-, then add tu and then NH₃. I don't understand why to use that way.



PS: Does someone know a good book about that topic with worked problems?

[Schrödinger]

3. Your method dictates a totally different strategy. Once you add 1 equiv of Cl^-, you add 1 equiv of tu. This will invariably replace the NH₃ trans to Cl, not one of the NH₃'s cis to the Cl^-.