What Are the Products of These Organometallic Reactions?

[rmjmu507]

Homework Statement

What would be the products of the following reactions?

(a) Phenylmercuric Chloride and phenylmagnesium chloride
(b) bromo methyl bis(triethylphosphine)palladium and dimethyl aluminum bromide
(c) dimethyl thallium fluoride and difluoro methyl boron
(d) bromo methyl bis(triethylphosphine)palladium and trans-but-2-ene

2. The attempt at a solution

(a) I believe the products would be biphenyl mercury and MgCl2, as the mercury-bound phenyl is more reactive

(b) I really do not know...dimethyl bis(triphenylphosphine) palladium and methyl aluminum bromide?

(c) I believe the products would be TlF3 and BMe3...Tl is more electropositive, so it will want to bond to form halides.

(d) Again, I really do not know. I assume the alkene would coordinate to the palladium center, but after this I can't say.

 

[TeethWhitener]

To first order, this is an exercise in comparing reduction potentials of various metals in these exchange reactions.

(a) I believe the products would be biphenyl mercury and MgCl2, as the mercury-bound phenyl is more reactive

The right answer for the wrong reason. In fact, the reasoning is almost the opposite of what you have. Mg has a more negative reduction potential than Hg, so MgCl₂ will be more stable than HgCl₂.

(b) I really do not know...dimethyl bis(triphenylphosphine) palladium and methyl aluminum bromide?

Methyl aluminum dibromide, yes. Aluminum has the lower reduction potential, so the halogens prefer to be on it instead of the palladium. (EDIT: really, the aluminum side will want to go all the way to AlBr₃ if it can do so stoichiometrically. I imagine you'd see a mixture of the two compounds)

(c) I believe the products would be TlF3 and BMe3...Tl is more electropositive, so it will want to bond to form halides.

I'm pretty sure this is fine. You don't hear much about organothallium compounds. But as a general rule, transition metal organics will react with boron trihalides to give the organoboron compounds (this is, in fact, how most organoboron compounds are made commercially).

(d) Again, I really do not know. I assume the alkene would coordinate to the palladium center, but after this I can't say.

This one's a weird one. It looks a lot like the Heck reaction, but I'm not used to seeing the Heck reaction on internal alkenes. If the mechanism follows the Heck reaction, the only thing I can think is that maybe it isomerizes trans-2-butene to a mix of cis and trans. I'm just not sure about this one, and a quick internet search brings up nothing about exchange reactions in palladium methyl bromo compounds (though they are used like other Pd organometallics in cross coupling catalysis).