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The question is:

Reaction of $\ce{Et2P(CH2)3PEt2}\text{ with }\ce{PCl3}$ ($1:1$) in the presence of $\ce{SnCl2}$ gives a ring system A, which exhibits two phosporus NMR resonances, a doublet and a triplet. Predict the structure of A and rationalise its NMR spectrum. Explain the role of $\ce{SnCl2}$ in the reaction and predict the result of reacting A with $\ce{CF3SO2Me}$ (hint: treat $\ce{CF3SO2Me}$ as a source of $\ce{Me+}$ and think carefully about the structures of the $\ce{P}$ atoms).

My working is as follows:

notes

I'm confused about the part that asks for electronic structures of $\ce{P}$ atoms. Do the $\ce{P}$ atoms have any $\pi$ character bonding?

To be specific, does the $\ce{P}$ cation center react with the $\ce{Me+}$ even though the formal charges tend to repel each other?

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  • $\begingroup$ You have two positively charged species coming together to form a neutral species at the end. $\endgroup$ – SendersReagent Mar 20 '16 at 0:21
  • $\begingroup$ Yeah i know that doesnt make sense, but i dont know how else to explain the reaction @DGS $\endgroup$ – justbehappy Mar 20 '16 at 0:29
  • $\begingroup$ @DGS but there is a lone pair on the P cation, i thought maybe that balances out the +ve charge? $\endgroup$ – justbehappy Mar 20 '16 at 0:30
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    $\begingroup$ Well, $+2 \ne 0$, so you can't balance charges that way, you would have to have a two electron reduction happen to cause that. $\ce{SnCl2}$ could just be acting as a lewis acid catalyst, and then you would have your phosphorus in the correct oxidation state to have that take place. How to get there, though, is kind of a tricky question. I'm trying to figure it out currently. $\endgroup$ – SendersReagent Mar 20 '16 at 0:35
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    $\begingroup$ I gotta get back to work. I would stare at this all night, otherwise, but for reference, here is this reference. $\endgroup$ – SendersReagent Mar 20 '16 at 0:54

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