Reversible 1,2-Methyl Migration to an N-Heterocyclic Carbene in a PCNHCP Cobalt(I) Complex Enables Stereoselective (E and Z) Allyl Ether Isomerization

With growing efforts pushing towards sustainable catalysis, using earth-abundant metals has become increasingly important. Here we present the first examples of cobalt PCNHCP pincer complexes that demonstrate dual stereoselectivity for allyl ether isomerization. While the cationic cobalt complex [((PCNHCP)Co)2-μ-N2][BAr4F]2 (3) affords the Z-isomer of the enol ether predominantly, the corresponding methyl complex [(PCNHCP)CoMe)] (4) mostly gives the E-isomer. The dichotomy in selectivity is investigated computationally, revealing important contributions from the steric profile of the substituents on the metal (Me or N2), including an unprecedented migration of the methyl substituent from cobalt to the N-heterocyclic carbene carbon, which is further explored in this report.