PerspectiveChemistry

Tin Takes Ethylene On—and Off

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Science  25 Sep 2009:
Vol. 325, Issue 5948, pp. 1631-1632
DOI: 10.1126/science.1179881

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Summary

Unexpected results can force the reevaluation, refinement, or rejection of scientific theories that seemed firmly supported. In organic chemistry, a well-established set of rules based on the symmetry of molecular orbitals can predict whether reactants with double or triple bonds will form cyclic products. On page 1668 of this issue, Peng et al. (1) now report the highly efficient, simultaneous addition of two molecules of ethylene (H2C=CH2) to a tin analog of acetylene: a distannyne, RSn≡SnR, where the R groups are bulky hydrocarbons. This reaction occurs despite what on the surface appears to be the breaking of simple symmetry rules. More remarkably, the reaction can be reversed with only small changes in pressure and temperature. In organic synthesis, similar reactions create very stable cyclic products.