Switching between Hydrogenation and Olefin Transposition Catalysis via Silencing NH Cooperativity in Mn(I) Pincer Complexes

While Mn-catalyzed (de)hydrogenation of carbonyl derivatives has been well established, the reactivity of Mn hydrides with olefins remains very rare. Herein, we report a Mn(I) pincer complex that effectively promotes site-controlled transposition of olefins. This reactivity is shown to emerge once the N-H functionality within the Mn/NH bifunctional complex is suppressed by alkylation. While detrimental for carbonyl (de)hydrogenation, such masking of the cooperative N-H functionality allows for the highly efficient conversion of a wide range of allylarenes to higher-value 1-propenybenzenes in near-quantitative yield with excellent stereoselectivities. The reactivity toward a single positional isomerization was also retained for long-chain alkenes, resulting in the highly regioselective formation of 2-alkenes, which are less thermodynamically stable compared to other possible isomerization products. The detailed mechanistic analysis of the reaction between the activated Mn catalyst and olefins points to catalysis operating via a metal-alkyl mechanism-one of the three conventional transposition mechanisms previously unknown in Mn complexes.

Automated summary

In this study, a Mn(I) pincer complex that promotes site-controlled transposition of olefins was reported. By suppressing the N-H functionality within the complex through alkylation, a wide range of allylarenes can be efficiently converted to higher-value 1-propenybenzenes with excellent stereoselectivities. The complex also retains the reactivity towards a single positional isomerization for long-chain alkenes.