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.
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.
How this study connects
Role on claims
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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.
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