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RT @EngleLab: The mechanism, termed asynchronous amine-assisted metalation/deprotonation is distinct from the various forms and flavors of….

Who needs aryl halides anyways? Direct C-H activation at Ni assisted by the small but mighty triethylamine 💪 then C-C coupling, where hydrazides take the lead ‼️ check out the mechanism figure and SI ! 👀.

Any other mechanism questions? Also check out our Supporting Information for more analysis and data! (14/14).

All that being said-- no mechanism can be proven definitively. We tried to systematically rule out alternatives, and the radical pathway emerged as the most consistent explanation based on all the experimental and computational data. (13/n).

What if the aryl coupling partner is already present before oxidative addition? Then the pathway would require (bpy)Ni(IV)(R)(Ar) from (bpy)Ni(II)(NNR)(Ar), but Ni(IV) is prohibitively high in energy. This raises further questions about a two-electron pathway. (12/n).

. A three-coordinate Ni(III)–alkyl from (bpy)Ni(I)NNR? Unlikely to be stable. A (bpy)Ni(II)–alkyl from Ni(0)? Then how does the ArI get activated/transferred? Past studies used Grignard reagents to ionically transfer the coupling partner, but here we do not. (11/n).

. but even if such a geometry were possible, we still face issues about ring-opening from the point above. Also, it’s unclear what that oxidative addition would lead to. (10/n).

What if Ni-mediated oxidative addition occurred via a tethered Ni–N(1)N(2)C intermediate, allowing an intramolecular organometallic pathway? The required bond lengths/angles for this process likely prevent N(2)–C from approaching Ni while maintaining Ni–N(1) coordination. (9/n).

What if an ionic dissociation mechanism started the process? Such as N–C heterolysis to form a carbanion? If that were the case, the results would likely not improve in protic solvents. But protic solvents are best! And we still have the bimolecular vs. unimolecular issue (8/n).

One might argue the ring opening results from side reactivity with Ni. But if that were the case, it should still vary with Ni loading. We tested an order of magnitude in Ni concentration and saw no such effect. (7/n).