musings on music and life

February 25, 2013

Ca-grignard reagents

Filed under: Chemistry — Tags: — sankirnam @ 9:58 am

There was an article in Angewandte Chemie a few weeks ago on the isolation of the phenylcalcium cation. This is the calcium analogue of the popular Grignard reagent phenylmagnesium halide. Grignard reagents are well known in organic chemistry, and organomagnesium chemistry has been very well developed for the past 100 years or so. On the other hand, the organic chemistry of calcium has hardly been explored. This is surprising given the relative abundance of calcium on the planet. On the other hand, the reactivity of “calcium grignards” is much greater than their magnesium counterparts. As this 2010 review states,

“Only very recently, have the first well-defined arylcalcium “Grignard’s” been prepared. The synthetic route is so far limited to aryl groups, which are much less sensitive to Wurtz-coupling than alkyl halide substrates. Highly reactive arylcalcium “Grignard’s” cleave ethers at -35 °C. This demonstrates the enormous difference in reactivity with the closely related organomagnesium complexes, which are often prepared in refluxing ether solvents.”

Given this information, it is impressive that the authors in the first paper have managed to isolate crystals of phenylcalcium iodide at all! They even crystallized the compound in an ethereal solvent (DME). These kinds of studies are nice since they push the boundaries of fundamental science, rather than finding the 3249876382796th way to transform A to B or make an amide bond. If it turns out that the calcium reagents have complementary or orthogonal reactivity to the traditional Grignard reagents, then these studies could usher in a new field of chemistry.


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