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Science  03 Dec 2004:
Vol. 306, Issue 5702, pp. 1651
DOI: 10.1126/science.306.5702.1651d

Alkene binding to low-valent transition metals is common. The strong interaction involves electron donation from olefin to metal, as well as back-bonding from metal d-orbitals to the olefin. For s-block metals such as the alkaline earths, however, there are no d electrons to give back, and examples of alkene coordination have been elusive. Beyond fundamental interest, such compounds would model intermediates involved in metal-catalyzed alkene polymerization. By tethering a butenyl chain to a cyclopentadienyl (Cp) ligand, Schumann et al. have succeeded in preparing compounds of the three heavy alkaline earth metals (Ca, Sr, and Ba) that show evidence of alkene interaction. The metal is sandwiched between two Cp rings, and x-ray diffraction reveals close contact in the solid state between the metal center and the C=C bonds dangling from each ring, whereas in the Mg compound, the butenyl chains face away from the metal and do not interact with it. — JSY

Angew. Chem. Int. Ed. 43, 6208 (2004).

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