What is it about?
Organomagnesium compounds are among the most widely used reagents in organic synthesis, but some exhibit unusual carbene-like behavior that is not fully understood. In this study, we investigated a series of 1-heteroatom-substituted alkylmagnesium chlorides containing nitrogen, oxygen, sulfur, fluorine, chlorine, or bromine substituents. These reactive intermediates were generated from sulfoxide precursors and examined through both experimental studies and density functional theory (DFT) calculations. By comparing their structures and 1,2-hydrogen-shift reactions, we established how the nature of the heteroatom influences their reactivity. The results revealed a clear spectrum ranging from carbanion-like species to highly carbene-like magnesium carbenoids.
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Why is it important?
Reactive organometallic intermediates are often classified as either carbanions or carbenoids, but the boundary between these categories is not always clear. This work provides a systematic comparison of heteroatom-substituted alkylmagnesium chlorides and identifies structural factors that determine their carbene character. We found that amino- and thio-substituted species behave predominantly as carbanions, whereas halo-substituted species exhibit strong magnesium carbenoid character. The experimentally observed reactivity closely matched the activation energies calculated for 1,2-hydrogen shifts, providing a practical way to predict carbene-like behavior. These findings improve our understanding of organomagnesium chemistry and may help guide the design of new synthetic transformations involving carbenoid intermediates.
Perspectives
This study originated from our interest in the unusual reactivity of magnesium alkylidene carbenoids and related organomagnesium species. While individual examples of heteroatom-substituted alkylmagnesium compounds had been reported, a systematic comparison of their carbene character had not been carried out. By combining experiments and computational chemistry, we were able to establish a consistent picture of how different heteroatoms influence reactivity. I particularly enjoyed seeing how simple experimental observations correlated remarkably well with the theoretical calculations. I hope that this work provides a useful framework for understanding reactive organometallic intermediates and inspires further studies on the borderland between carbanions and carbenoids.
Associate Professor Tsutomu Kimura
Read the Original
This page is a summary of: DFT and experimental characterization of 1-heteroatom-substituted alkylmagnesium chlorides, Journal of Organometallic Chemistry, October 2024, Elsevier,
DOI: 10.1016/j.jorganchem.2024.123315.
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