Reaction mechanisms
Why gold carbenes hit phenol para-C–H
Open access · cc by · source: Europe PMC
DFT plus deuterium controls show (PhO)3PAu carbenes add at phenol para-C, then two waters shuttle the proton, beating O–H insertion.
How this study connects
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DFT plus deuterium controls show (PhO)3PAu carbenes add at phenol para-C, then two waters shuttle the proton, beating O–H insertion.
Evidence for the claim as stated.
Study at a glance
- Design
- Computational / modelling — DFT free-energy profiles for gold-carbene phenol functionalization with deuterium-control reactions
- N
- Computed (PhO)3PAu versus Ph3P pathways plus deuterated-phenol controls
- Population
- Gold-carbene C–H versus O–H insertion into phenols
- Outcome
- Para C–H addition plus a two-water proton shuttle outcompetes O–H insertion with (PhO)3PAu carbenes
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Inspect source passages
Why gold carbenes hit phenol para-C–H
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Au-carbene formation barriers are 6.5 and 11.4 kcal mol–1 for the two ligands
The calculated free energy profiles indicate that the generation of Au-carbene species is quite facile and drastically exothermic, with the low barriers of 6.5 and 11.4 kcal mol –1 , respectively.
Para addition of the gold carbene has a 15.6 kcal mol–1 barrier
In our DFT calculations, a transition state TS-c1 with a barrier of 15.6 kcal mol –1 is located for the addition of the gold carbene at the para -position of phenol.
Key findings
Au-carbene formation is cheap (6.5 and 11.4 kcal mol–1). Para addition (15.6 kcal mol–1) beats ortho (19.3) and meta (23.6). Direct [1,2]-H shift is 30.1 kcal mol–1, while a two-water shuttle is favored. The C–H product is 10.8 kcal mol–1 more stable than the O–H insertion product. Switching to Ph3P raises the C–H addition barrier and lowers the O–H barrier.
Methodology
They computed free-energy profiles for gold-carbene addition to phenol with (PhO)3P versus Ph3P ligands, compared C–H versus O–H insertion, and tested water-assisted proton transfer against a direct [1,2]-H shift. Control reactions with deuterated phenol supported the water-shuttle pathway.
Limitations
The computed barriers are IEFPCM solution free energies at 298 K, not measured rates. Only phenol/α-diazoester systems are mapped, so the water-shuttle model is not proven for other arenes or metals. Isolated product yields for a broad substrate table are not the focus.
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