June 15, 2024, 06:29:49 AM
Forum Rules: Read This Before Posting


Topic: Why no alt. Tosylates to OTf for replacement of Halide in Pd cat. cross coupling  (Read 2440 times)

0 Members and 1 Guest are viewing this topic.

Offline Cheese_Burgers

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +0/-1
In reactions such as the ullmann, sonogashira, and heck I am finding literature that shows the substitution of Halides I, Br, and Cl substituted compounds with triflates (trifluorosulfonate ester groups).

I assume that other tosylates did not work and thus are not reported in literature. Does anyone have any idea why they did not work? For example, why wouldn't a regular  paratolulene tosylate work?

How is palladium coordinating with the triflate species for any of these reactions?

Thanks

Offline clarkstill

  • Chemist
  • Full Member
  • *
  • Posts: 477
  • Mole Snacks: +77/-4
I assume it's something to do with the stability of the triflate as a leaving group (pKa of TfOH ~ -13!) being more similar to that of the halogens than the tosylate (pKa of TsOH ~ -3).  I guess by the Hammond postulate, this also means that oxidative insertion is fast because the C-X bond is weak? There is no special coordination between the triflate and palladium, it just acts as a "pseudohalogen" - and undergoes the same oxidative insertion mechanism you would draw for a normal cross coupling.

Offline Dan

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 4716
  • Mole Snacks: +469/-72
  • Gender: Male
  • Organic Chemist
    • My research
I assume that other tosylates did not work and thus are not reported in literature.

Tosylates do work and have been widely reported - this kind of tosylate reactivity has been known for around a decade.

See for starters: http://scholar.google.co.uk/scholar?q=tosylate+coupling&btnG=&hl=en&as_sdt=0%2C5&as_vis=1

Triflates are more reacive though, probably for the reasons clarkstill outlined.

My research: Google Scholar and Researchgate

Offline Cheese_Burgers

  • Regular Member
  • ***
  • Posts: 21
  • Mole Snacks: +0/-1
Thank you so much!

Sponsored Links