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Topic: hydrosilylation reaction rate comparison  (Read 2003 times)

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Offline craken66

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hydrosilylation reaction rate comparison
« on: June 09, 2017, 07:37:46 AM »
Hello,
I am writing to inquire reaction rate b/w speier's and karstedt's catalyst for hydrosilylation which is for coupling of Si-H and vinyl group. Which catalyst is better in terms of rxn rate? I'll appreiciated for anwering of it. Thank you.

Offline wildfyr

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Re: hydrosilylation reaction rate comparison
« Reply #1 on: June 09, 2017, 07:50:20 AM »
Hmm... I frankly never noticed a big difference in speed, reactions were done in around 8 hours. However karsteadt's is more stable and less hygroscopic. Something important which BLEW MY MIND is that hydrosilation needs OXYGEN to work.

http://pubs.acs.org/doi/abs/10.1021/ja9825377

"The oxygen effect was first noted by Chalk and Harrod who reported that triethoxysilane and 1-alkenes did not react in the absence of air but reacted vigorously upon exposure to air using chloroplatinic acid as the catalyst."

Offline Enthalpy

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Re: hydrosilylation reaction rate comparison
« Reply #2 on: June 09, 2017, 09:16:38 AM »
Wiki claims that the addition is most often anti-Markovnikov
https://en.wikipedia.org/wiki/Hydrosilylation
Did I read properly? How easy is it to obtain the anti-Markovnikov product?

And by the way, what do you think of wiki's reaction
Et3SiH + PhC≡CPh  :rarrow: Et3Si(Ph)C=CH(Ph)
I had expected :rarrow: Et3SiC(Ph)=CH(Ph)

Offline wildfyr

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Re: hydrosilylation reaction rate comparison
« Reply #3 on: June 09, 2017, 10:36:38 AM »
It is something like 99%+ anti markovnikov under typical conditions. I have never seen a markovnikov product in the NMR of my reactions.

I'm confused by your example, could you draw the lewis stuctures? My brain is telling me those are the same thing... is it E vs Z?

Offline Enthalpy

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Re: hydrosilylation reaction rate comparison
« Reply #4 on: June 09, 2017, 03:11:10 PM »
Thank you!

About the example at Wiki, maybe I interpret it wrongly, like this:
Et3Si(Ph)C=CH(Ph) here Ph is on Si, which is impossible with tetravalent Si
Et3SiC(Ph)=CH(Ph) here Ph is on C, the product I expect after Si-H adds on C≡C
CC[Si](CC)(CC)C(c1ccccc1)=Cc2ccccc2
What is the convention? (Branches) written always after the carrying atom, like in Smiles, would be unambiguous but bring here the drawback of separating the C from the =.

Offline wildfyr

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Re: hydrosilylation reaction rate comparison
« Reply #5 on: June 11, 2017, 04:02:52 AM »
Now that I know what you're getting at, I agree with your notation but this is one of those I might give a shot at IUPAC naming for more clarity

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